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PUBLIC COMMENT VERSION
Assessing the Public Health Implications of the Criteria
(NAAQS) Air Pollutants and Hydrogen Sulfide
MIDLOTHIAN AREA AIR QUALITY
MIDLOTHIAN, ELLIS COUNTY, TEXAS
NOVEMBER 16, 2012
COMMENT PERIOD ENDS: JANUARY 18, 2013
U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES
Agency for Toxic Substances and Disease Registry
Division of Community Health Investigations
Atlanta, Georgia 30333
Health Consultation: A Note of Explanation
A health consultation is a verbal or written response from ATSDR or ATSDR’s
Cooperative Agreement Partners to a specific request for information about health risks
related to a specific site, a chemical release, or the presence of hazardous material. In
order to prevent or mitigate exposures, a consultation may lead to specific actions, such
as restricting use of or replacing water supplies; intensifying environmental sampling;
restricting site access; or removing the contaminated material.
In addition, consultations may recommend additional public health actions, such as
conducting health surveillance activities to evaluate exposure or trends in adverse health
outcomes; conducting biological indicators of exposure studies to assess exposure; and
providing health education for health care providers and community members. This
concludes the health consultation process for this site, unless additional information is
obtained by ATSDR or ATSDR’s Cooperative Agreement Partner which, in the
Agency’s opinion, indicates a need to revise or append the conclusions previously issued.
You May Contact ATSDR Toll Free at
1-800-CDC-INFO
or
Visit our Home Page at: http://www.atsdr.cdc.gov
HEALTH CONSULTATION
PUBLIC COMMENT RELEASE
Assessing the Public Health Implications of the Criteria
(NAAQS) Air Pollutants and Hydrogen Sulfide
MIDLOTHIAN AREA AIR QUALITY
MIDLOTHIAN, ELLIS COUNTY, TEXAS
Prepared By:
U.S. Department of Health and Human Services
Agency for Toxic Substances and Disease Registry (ATSDR)
Division of Community Health Investigations
“This information is distributed solely for the purpose of predissemination public comment
under applicable information quality guidelines. It has not been formally disseminated by the
Agency for Toxic Substances and Disease Registry. It does not represent and should not be
construed to represent any agency determination or policy.”
Midlothian Area Air Quality—Assessing the Public Health Implications of the Criteria
(NAAQS) Air Pollutants and Hydrogen Sulfide Health Consultation Public Comment Release
FOREWORD
The Agency for Toxic Substances and Disease Registry, ATSDR, was established by Congress
in 1980 under the Comprehensive Environmental Response, Compensation, and Liability Act,
also known as the Superfund law. This law set up a fund to identify and clean up our country's
hazardous waste sites. The Environmental Protection Agency, EPA, and the individual states
regulate the investigation and clean-up of the sites.
Since 1986, ATSDR has been required by law to conduct public health assessment activities at
each of the sites on the EPA National Priorities List. The aim of these evaluations is to find out
if people are being exposed to hazardous substances and, if so, whether that exposure is harmful
and should be stopped or reduced. If appropriate, ATSDR also conducts public health
assessments when petitioned by concerned individuals. Public health assessments are carried out
by environmental and health scientists from ATSDR, and from the states with which ATSDR has
cooperative agreements. The public health assessment program allows the scientists flexibility
in the format or structure of their response to the public health issues at hazardous waste sites.
For example, a public health assessment could be one document or it could be a compilation of
several health consultations - the structure may vary from site to site. Nevertheless, the public
health assessment process is not considered complete until the public health issues at the site are
addressed.
Exposure: As the first step in the evaluation, ATSDR scientists review environmental data to
see how much contamination is at a site, where it is, and how people might come into contact
with it. Generally, ATSDR does not collect its own environmental sampling data but reviews
information provided by EPA, other government agencies, businesses, and the public. When
there is not enough environmental information available, the report will indicate what further
sampling data is needed.
Health Effects: If the review of the environmental data shows that people have or could come
into contact with hazardous substances, ATSDR scientists evaluate whether or not these contacts
may result in harmful effects. ATSDR recognizes that children, because of their play activities
and their growing bodies, may be more vulnerable to these effects. As a policy, unless data are
available to suggest otherwise, ATSDR considers children to be more sensitive and vulnerable to
hazardous substances. Thus, the health impact to the children is considered first when evaluating
the health threat to a community. The health impacts to other high risk groups within the
community (such as the elderly, chronically ill, and people engaging in high risk practices) also
receive special attention during the evaluation.
ATSDR uses existing scientific information, which can include the results of medical,
toxicological and epidemiological studies and the data collected in disease registries, to
determine the health effects that may result from exposures. The science of environmental
health is still developing, and sometimes scientific information on the health effects of certain
substances is not available. When this is so, the report will suggest what further public health
actions are needed.
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Conclusions: The report presents conclusions about the public health threat, if any, posed by a
site. When health threats have been determined for high risk groups (such as children, elderly,
chronically ill, and people engaging in high risk practices), they will be summarized in the
conclusion section of the report. Ways to stop or reduce exposure will then be recommended in
the public health action plan.
ATSDR is primarily an advisory agency, so usually these reports identify what actions are
appropriate to be undertaken by EPA, other responsible parties, or the research or education
divisions of ATSDR. However, if there is an urgent health threat, ATSDR can issue a public
health advisory warning people of the danger. ATSDR can also authorize health education or
pilot studies of health effects, full-scale epidemiology studies, disease registries, surveillance
studies or research on specific hazardous substances.
Community: ATSDR also needs to learn what people in the area know about the site and what
concerns they may have about its impact on their health. Consequently, throughout the
evaluation process, ATSDR actively gathers information and comments from the people who
live or work near a site, including residents of the area, civic leaders, health professionals and
community groups. To ensure that the report responds to the community's health concerns, an
early version is also distributed to the public for their comments. All the comments received
from the public are responded to in the final version of the report.
Public Comments:
ATSDR will accept public comments on this health consultation until January 18, 2013.
Comments must be made in writing. Comments (without the names of persons who submitted
them) and ATSDR’s responses will appear in an appendix to the final health consultation. Names
of those who submit comments will be subject to release in answer to requests made under the
U.S. Freedom of Information Act (FOIA).
Send comments to [email protected], or mail to:
ATSDR Records Center
Attn: Rolanda Morrison
Re: Midlothian Area Air Quality—Assessing the Public Health Implications of the Criteria
(NAAQS) Air Pollutants and Hydrogen Sulfide
4770 Buford Highway, NE (MS F-09)
Atlanta, Georgia 30341
For more information about ATSDR’s work in Midlothian visit
http://www.atsdr.cdc.gov/sites/midlothian/ or call 1-800-CDC-INFO.
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Abbreviations
ATSDR
EPA
H2S
MRL
NAAQS
NCDC
NEI
PM
PM10
PM2.5
ppb
ppm
PSEI
TCEQ
TDSHS
TNRCC
TRI
TSP
µg/m3
UT-Arlington
WHO
Agency for Toxic Substances and Disease Registry
Environmental Protection Agency
hydrogen sulfide
Minimal Risk Level
National Ambient Air Quality Standard
National Climatic Data Center
National Emissions Inventory
particulate matter
particulate matter with aerodynamic diameter of 10 microns or less
particulate matter with aerodynamic diameter of 2.5 microns or less
parts per billion
parts per million
Point Source Emissions Inventory
Texas Commission on Environmental Quality
Texas Department of State Health Services
Texas Natural Resources Conservation Commission
Toxics Release Inventory
total suspended particulate
micrograms per cubic meter
University of Texas at Arlington
World Health Organization
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Midlothian Area Air Quality—Assessing the Public Health Implications of the Criteria
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Table of Contents
1. Purpose and Statement of Issues................................................................................................1
2. Background ................................................................................................................................3
2.1.
Air Emission Sources.......................................................................................................3
2.2.
Background on Relevant Industrial Processes.................................................................3
2.3.
Air Emissions Sources in Midlothian ..............................................................................5
2.4.
Demographics ................................................................................................................13
2.5.
Local Climatic and Meteorological Conditions.............................................................14
2.6.
General Air Quality in Ellis County ..............................................................................15
3. Measured and Estimated Air Pollution Levels ........................................................................17
3.1.
Carbon Monoxide ..........................................................................................................17
3.2.
Lead................................................................................................................................20
3.3.
Nitrogen Dioxide ...........................................................................................................24
3.4.
Ozone .............................................................................................................................25
3.5.
Sulfur Dioxide................................................................................................................31
3.6.
Hydrogen Sulfide ...........................................................................................................34
3.7.
Summary ........................................................................................................................36
4. Public Health Implications Discussion ....................................................................................39
4.1.
Sulfur Dioxide................................................................................................................39
4.2.
Fine Particulate Matter (PM2.5)......................................................................................41
4.3.
Ozone .............................................................................................................................42
4.4.
Lead................................................................................................................................43
4.5
Mixtures (including ozone)............................................................................................45
4.6 Gaps and Limitations .........................................................................................................46
5. Child Health Considerations ....................................................................................................47
6. Community Concerns Evaluation ............................................................................................49
7. Conclusions and Recommendations ........................................................................................54
8. Public Health Action Plan........................................................................................................59
9. Authors, Technical Advisors ...................................................................................................60
10. References................................................................................................................................61
11. Tables.......................................................................................................................................67
12. Figures......................................................................................................................................84
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Appendix A.
ATSDR Carbon Monoxide Modeling............................................................. A-1
Appendix B.
Sulfur Dioxide Health Evaluation....................................................................B-1
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SUMMARY
INTRODUCTION
The Agency for Toxic Substances and Disease Registry (ATSDR) and
the Texas Department of State Health Services (TDSHS) are conducting
an extensive review of environmental health concerns raised by
community members in Midlothian, Texas. The goal of this review is to
determine if chemical releases from local industrial facilities could affect
or have affected the health of people and animals in the area. The
facilities of concern are three cement manufacturing facilities and a steel
mill. ATSDR plans to achieve this goal through a series of projects.
This Health Consultation documents ATSDR’s findings from the project:
assessing the public health implications of exposures to the National
Ambient Air Quality Standard (NAAQS) pollutants (particulate matter,
ozone, sulfur dioxide, nitrogen oxides, carbon monoxide, and lead) and
hydrogen sulfide (H2S).
ATSDR has already released a Health Consultation (ATSDR, 2012a) to
address community members’ concerns about the various air pollution
measurements that have been collected in Midlothian since 1981. The
purpose of that Health Consultation was to take a careful look at the
available monitoring data and determine which measurements are—and
are not—suitable for use in ATSDR’s future health evaluations like this
one. The previous Health Consultation identified pollutants, time frames,
and locations for which the available data provide a sufficient basis for
reaching health conclusions; it also identifies important gaps in the data.
These findings are incorporated into this Health Consultation’s
evaluation of NAAQS pollutants and H2S.
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CONCLUSIONS
CONCLUSION 1—
Sulfur Dioxide (SO2
Exposures
ATSDR reached six conclusions in this Health Consultation:
In the past (1997–late 2008), breathing air contaminated with sulfur
dioxide (SO2) for short periods (5 minutes) could have harmed the
health of sensitive individuals (e.g., people with asthma), particularly
when performing an activity (such as exercising or climbing steps) that
raised their breathing rate. SO2 levels that might have harmed sensitive
individuals were infrequent and limited to areas primarily in Cement
Valley and possibly areas east, south, and southeast of the TXI
Operations, Inc (TXI) fence line. These exposures occurred primarily
from about 5 p.m. to 6 a.m. Harmful exposures also could have occurred
before 1997; however, monitoring data are not available to confirm this
conclusion. Breathing air contaminated with SO2 in the past (during
the period 1997 to late 2008) was not expected to harm the health of the
general population.
Reductions in SO2 levels in Cement Valley have occurred since late
2008 resulting in exposures to both sensitive individuals and the general
public that are not expected to be harmful. These reductions may be
caused, in part, by declining production levels at local industrial facilities.
Future harmful exposures in Cement Valley could occur if production
rises to at least previous levels and actions are not taken to reduce SO2
emissions.
No SO2 data are currently available to evaluate exposures to individuals
who live downwind of the Ash Grove Cement and Holcim facilities where
the SO2 emissions have been similar to those from TXI in the past that
produced harmful exposures in Cement Valley and possibly elsewhere.
Therefore, ATSDR cannot determine if harmful exposures to SO2 have
been occurring downwind of the Holcim and Ash Grove facilities.
BASIS FOR
DECISION
Past SO2 exposures were not above the Environmental Protection Agency
(EPA) standard in place at that time but were above the current standard.
When SO2 concentrations exceed 400 ppb (parts per billion), sensitive
individuals may experience symptoms such as coughing, wheezing, and
chest tightness. At lower SO2 concentrations (200 ppb to 400 ppb),
sensitive individuals functioning at elevated breathing rates may
experience asymptomatic effects (e.g., mild constriction of bronchial
passages). Adverse health effects from exposures to SO2 concentrations
less than 200 ppb are uncertain, but may occur in some people more
sensitive or vulnerable than people participating in clinical studies.
People with asthma, children, and older adults (>65 years) have been
identified as groups susceptible to the health problems associated with
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breathing SO2. Human scientific studies (clinical investigations and
epidemiologic studies) have provided evidence of a causal relationship
between SO2 and respiratory disease (morbidity) in people with asthma
and other more limited human studies (epidemiologic) have consistently
reported that children and older adults may be at increased risk for SO2
associated adverse respiratory effects. Groups potentially sensitive to air
pollutants include the obese, people with preexisting cardiopulmonary
disease, and people with a pro-inflammatory condition such as diabetes,
but some of these relationships have not been examined specifically in
relation to SO2.
CONCLUSION 2—
Particulate Matter
Exposures
Breathing air contaminated with PM2.5 (particulate matter with
aerodynamic diameter of 2.5 microns or less) downwind of TXI and
Gerdau Ameristeel for 1 year or more is not likely to have harmed
people’s health, except in a localized area just north of the Gerdau
Ameristeel fence line during 1996-1998. PM2.5 is both a local and
regional air quality concern. The PM2.5 levels observed in the Midlothian
area are not considerably different from levels measured in multiple
locations throughout the Dallas— Fort Worth metropolitan area. These
PM2.5 levels are caused by emissions from mobile (e.g., cars and trucks)
and industrial sources in the Midlothian area and beyond. Nevertheless,
for people, especially those with preexisting respiratory and cardiac
disease, who lived in a localized area of Cement Valley (just north of the
Gerdau Ameristeel fence line during 1996–1998), public health concern is
warranted for adverse health effects from long-term exposure to PM2.5.
Short-term potentially harmful levels of PM2.5 have been infrequent in
Midlothian. These infrequent exposures could have resulted in harmful
cardiopulmonary effects, especially in sensitive individuals, but not the
general public.
ATSDR noted several data gaps in relation to PM exposures. In general,
monitoring stations in the Midlothian area have been placed near or at
locations believed to have either high air-quality impacts from facility
operations or a high potential for exposure. However, ATSDR is
uncertain about PM2.5 exposures downwind of Ash Grove and Holcim
because of a lack of data and information. In addition, ambient air
monitoring data are more limited for the residential neighborhoods in
immediate proximity to the cement manufacturing facilities’ limestone
quarries. PM exposure is the primary concern for these localized
residential areas.
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BASIS FOR
DECISION
Most measured annual average PM2.5 levels in the Midlothian area were
not above EPA’s current or proposed standard. In the past (1996–2008),
annual average PM2.5 levels measured were just below the range of
concentration proposed by EPA for lowering the annual average standard,
except for the estimated exposure levels just north of Gerdau Ameristeel
fence line during the period 1996–1998. Although no PM2.5
measurements were collected north of Gerdau Ameristeel, other data
ATSDR has reviewed suggest that this area most likely had the highest
PM2.5 concentrations in the area, particularly in the years 1996–1998.
These estimated PM2.5 levels were at the upper end of the risk range in
several epidemiologic studies.
Infrequent, short-term PM2.5 levels in Midlothian have been in the range
considered by the EPA (based on the Air Quality Index or AQI) to be a
concern for sensitive populations, but not the general public. However, as
defined by EPA, short-term levels of PM2.5 in the Midlothian area have
not exceeded the current standard.
No PM2.5 monitoring data are available to evaluate exposures downwind
of the Ash Grove facility. Furthermore, although annual average PM2.5
levels detected at the Holcim monitor indicate possible harmful levels,
ATSDR is uncertain about what actual off-site exposures are occurring
downwind of Holcim.
CONCLUSION 3—
Ozone Exposures
Several of the levels of ozone detected in Midlothian since monitoring
began in 1997 indicate that sensitive individuals have an increased
likelihood of experiencing harmful respiratory effects (respiratory
symptoms and breathing discomfort). This likelihood is true primarily
for active children and adults and for people with respiratory diseases,
such as asthma. The general population of Midlothian is not expected
to experience harmful effects from ozone exposure except on rare
occasions when ozone levels reach approximately 100 ppb or more.
Ellis County is one of 11 counties that make up the Dallas–Fort Worth
ozone non-attainment area, which means that ozone levels in the
metropolitan area occasionally exceed EPA’s health-based standards.
Ozone levels also have exceeded the World Health Organization (WHO)
health guidelines. Emissions from industrial sources, mobile sources, and
natural sources throughout the area contribute to this problem.
BASIS FOR
DECISION
Scientific studies indicate that breathing air containing ozone at
concentrations similar to those detected in Midlothian can reduce lung
function and increase respiratory symptoms, thereby aggravating asthma
or other respiratory conditions. Ozone exposure also has been associated
with increased susceptibility to respiratory infections, medication use by
persons with asthma, doctor’s visits, and emergency department and
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hospital admissions for individuals with respiratory disease. Ozone
exposure also might contribute to premature death, especially in people
with heart and lung disease. School absenteeism and cardiac-related
effects may occur, and persons with asthma might experience greater and
more serious responses to ozone that last longer than responses among
people without asthma.
ATSDR believes that sufficient information exists to warrant concern
for multiple air pollutant exposures to sensitive individuals, especially
CONCLUSION 4—
Mixture Exposures
in the past (during the period 1997 to late 2008) when SO2 levels were
higher and when these persons were breathing at higher rates (e.g.,
while exercising). ATSDR believes the severity of health effects from a
mixture exposure is not likely to exceed those discussed for SO2, PM2.5,
or ozone exposure alone. For past SO2 exposures, however, the number
of sensitive individuals affected may have been greater because effects
may have occurred at a lower SO2 concentration when combined with
exposure to ozone, PM2.5, or both. Potential effects to a larger sensitive
population, especially in the past, may be limited to the same locations
but during the warmer months when PM2.5 and ozone levels are usually
the highest. In addition, potential effects to this larger sensitive
population may also have resulted from multiple exposures that occurred
during several consecutive days.
BASIS FOR
DECISION
The current state of the science limits our ability to make definitive
conclusions on the significance of simultaneous exposures to multiple
criteria air pollutants. ATSDR’s conclusions are based on our best
professional judgment related to our understanding of the possible
harmful effects of air pollutant exposures in Midlothian and our
interpretation of the current scientific literature; therefore, these
conclusions are presented with some uncertainty.
CONCLUSION 5—
Lead Exposures
Past lead air exposures during the period 1993 to 1998, in a localized
area just north of the Gerdau Ameristeel fence line, could have harmed
the health of children who resided or frequently played in this area.
The estimated health effect of these exposures would have been a slight
lowering of IQ (Intelligence quotient) levels (1-2 points) for some
children living in the area. Since 1998, air lead levels in this area
decreased, resulting in estimated childhood blood lead levels below the
Centers for Disease Control’s (CDC) reference level (currently 5 µg/dL).
Monitoring data do not indicate that lead levels in air have occurred
above EPA’s current standard (0.15 µg/m3) in other areas of Midlothian,
either now or in the past.
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Midlothian Area Air Quality—Assessing the Public Health Implications of the Criteria
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BASIS FOR
DECISION
Past lead air exposures were not above the EPA standard at that time but
were above the current standard. ATSDR evaluated past lead exposures
in air using a model developed by the EPA to estimate childhood blood
lead levels. Based on our current knowledge of the health effects of lead
exposures in children, ATSDR used a blood lead reference level of 5
µg/dL in the model to account for the risk of adverse health effects at
levels below below 10 µg/dL, which had been used as a level of concern.
ATSDR also ran the model using 10 µg/dL. Using a combination of
default parameters in the EPA lead model and using the highest annual
and quarterly average air lead levels from the Gerdau Ameristeel monitor
during the period 1993–1998, the model estimates that children in that
area of Cement Valley could have had, on average, approximately
an18%–21% risk of a blood lead level between 5-10 µg/dL because of
breathing outdoor air. Stated another way, if 100 children lived in the
vicinity of the Gerdau Ameristeel monitors during the period 1993–1998,
the model predicts that approximately 21 or fewer children would have
blood lead levels between 5-10 µg/dL, a level that might result in small
IQ deficits (1-2 points). The model also predicted that there was not an
appreciable risk (less than 5%) of these exposures resulting in a
childhood blood lead level of 10 µg/dL or more.
Some uncertainty exists with these findings given that we do not know
what the lead levels in air were downwind of the Gerdau monitor and we
do not know if small children were exposed at all in this sparsely
populated area of Cement Valley.
CONCLUSION 6-
Exposure to Other
Contaminants
ATSDR does not expect harmful effects in Midlothian from current or
past exposures to the air pollutants carbon monoxide, nitrogen dioxide,
or hydrogen sulfide.
BASIS FOR
Based on available monitoring data and other information (emission
reports, knowledge of what might be emitted from cement or steel
operations, and worst-case computer air modeling), the levels of carbon
monoxide, nitrogen dioxide, and hydrogen sulfide are below healthprotective comparison values developed by EPA, WHO, or ATSDR.
DECISION
NEXT STEPS—All
Conclusions
Sulfur Dioxide Specific: To reduce current or future peak exposures to
sulfur dioxide, ATSDR recommends the following:
• Reduce emissions—Texas Commission on Environmental
Quality (TCEQ) should take actions to reduce future SO2
emissions from TXI to prevent harmful exposures.
• Evaluate and reduce exposures—TCEQ should conduct ambient
air monitoring to characterize exposures to persons located
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downwind of the Ash Grove and Holcim facilities and take
actions to reduce SO2 emissions from these facilities if harmful
exposures are indicated.
PM Specific: To reduce current or future PM2.5 exposures, ATSDR
recommends the following:
• Reduce emissions—TCEQ should take actions to reduce future
PM2.5 emissions from TXI and Gerdau to prevent harmful
exposures.
• Evaluate and reduce exposures—TCEQ should conduct
appropriate ambient air monitoring to characterize exposures to
persons located downwind of the Ash Grove and Holcim
facilities and take actions to reduce PM2.5 emissions from these
facilities if harmful exposures are indicated. In addition,
particulate matter monitoring is needed in residential areas that
are in immediate proximity to the facilities’ limestone quarries.
ATSDR will issue two other Health Consultations that will further
evaluate cement kiln dust (CKD): one document will consider the
specific chemicals within CKD and whether those pose a health hazard
when inhaled; another document will consider the extent to which CKD
has contaminated soils and waterways through atmospheric deposition.
Mixtures Specific: To reduce and prevent multiple contaminant
exposures, ATSDR recommends the following:
• TCEQ should evaluate and prevent harmful PM2.5 and sulfur
dioxide exposures from local sources.
• TCEQ should continue efforts to reduce regional ozone
exposures.
All Air Pollutants:
• TCEQ should ensure that the levels of the air pollutants, carbon
monoxide and nitrogen dioxide, do not increase to levels of
concern in the future.
• ATSDR and the Texas Department of State Health Services
(TDSHS)will distribute health education material related to
exposures to SO2, PM2.5, and ozone specifically for sensitive and
potentially sensitive populations. These materials will include
information on health effects and ways to minimize harmful
exposures to air pollution.
• ATSDR and TDSHS will provide educational material
specifically for health professionals on air pollution and patient
health.
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• ATSDR will work with TCEQ to address the recommendations
of this Health Consultation and will evaluate any additional data
that might become available in relation to these
recommendations.
FOR MORE
INFORMATION
If you have questions about this document or ATSDR’s ongoing work on
the Midlothian facilities, please call ATSDR at 1-800-CDC-INFO and
ask for information about the “Midlothian, Texas evaluations.” If you
have concerns about your health, you should contact your healthcare provider.
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Midlothian Area Air Quality—Assessing the Public Health Implications of the Criteria
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1. Purpose and Statement of Issues
In July 2005, a group of residents of Midlothian,
Texas, submitted a petition to the Agency for Toxic
Substances and Disease Registry (ATSDR). The
petition expressed multiple concerns, but primarily
that nearby industrial facilities were emitting air
pollutants at levels that were affecting the health of
residents. ATSDR accepted this petition, and the
Texas Department of State Health Services (TDSHS),
under a cooperative agreement with ATSDR,
prepared a response.
Specifically, in December 2007, TDSHS, with
ATSDR concurrence, issued a public comment draft
Health Consultation that attempted to respond to
concerns outlined in the original petition. Many
comments were received on the draft Health
Consultation.
During the process of evaluating these comments,
ATSDR and National Center for Environmental
Health Director requested that the ATSDR and
TDSHS team take a more comprehensive look at the
site. This new evaluation would review the initial
petitioner’s concerns, which questioned whether data
generated by air monitors were being collected in a
manner that could provide pertinent answers to the
community health concerns. ATSDR and TDSHS are
now looking at all available data to determine if there
is a relationship between air emissions and health
concerns in the community. As outlined in its
Midlothian Public Health Response Plan (ATSDR,
2011), ATSDR will complete this reevaluation in a
series of projects.
Purpose of this Document
This Health Consultation documents
ATSDR’s findings from the project:
assessing the public health implications
of exposures to the National Ambient
Air Quality Standard (NAAQS)
pollutants (particulate matter, ozone,
sulfur dioxide, nitrogen oxides, carbon
monoxide, and lead) and hydrogen
sulfide (H2S). The findings from
ATSDR’s first Health Consultation
(ATSDR, 2012a) are incorporated into
this document’s evaluation of the public
health implications of potential
exposures to the NAAQS pollutants and
H2 S .
Readers should note that ATSDR’s role
in evaluating ambient air in Midlothian
is as a public health agency, which is
considerably different from the roles of
other agencies, particularly those
charged with addressing environmental
issues. In this document, ATSDR
evaluates the public health implications
of the levels of air pollutants in the
Midlothian area. These evaluations are
not meant to address the region’s
compliance, or lack thereof, with state
and federal standards, such as EPA’s
NAAQS, even though this Health
Consultation uses the NAAQS as a
means for the first step in evaluating
the air monitoring data collected in the
Midlothian area. State and federal
environmental agencies are responsible
for evaluating the area’s compliance
with the NAAQS and other
environmental standards.
The first ATSDR Health Consultation (ATSDR,
2012a) assessed the utility of existing ambient air
monitoring data for addressing Midlothian residents’
concerns regarding air emissions from four industrial facilities, while also considering additional
air quality impacts from other sources (e.g., motor vehicle traffic).
To evaluate these concerns, ATSDR gathered relevant information on facility emissions, local
meteorological conditions, and ambient air monitoring data. The findings in this document are
based on all validated ambient air monitoring data and related information available to ATSDR
as of late 2011 (except for some SO2 data that became available in 2012). ATSDR accessed
information from multiple parties, including the petitioner, local community groups, industry,
1
Midlothian Area Air Quality—Assessing the Public Health Implications of the Criteria
(NAAQS) Air Pollutants and Hydrogen Sulfide Health Consultation Public Comment Release
and consultants; scientists from the University of Texas at Arlington (UT-Arlington); TDSHS;
the Texas Commission on Environmental Quality (TCEQ); and the U.S. Environmental
Protection Agency (EPA).
This Health Consultation documents ATSDR’s findings from the project: assessing the public
health implications of exposures to the National Ambient Air Quality Standard (NAAQS)
pollutants (particulate matter, ozone, sulfur dioxide, nitrogen oxides, carbon monoxide, and lead)
and hydrogen sulfide (H2S). The findings from the first Health Consultation (ATSDR, 2012a)
are incorporated into this document’s evaluation of the public health implications of potential
exposures to the NAAQS pollutants and H2S.
2
Midlothian Area Air Quality—Assessing the Public Health Implications of the Criteria
(NAAQS) Air Pollutants and Hydrogen Sulfide Health Consultation Public Comment Release
2. Background
This section presents background information that ATSDR considered when evaluating the
utility of the ambient air-monitoring studies previously conducted in the Midlothian area. Refer
to Section 3 of this Health Consultation for ATSDR’s interpretations of this background
information and assessment of the ambient air monitoring conducted in the Midlothian area.
2.1. Air Emission Sources
Midlothian is located in Ellis County, Texas,
approximately 30 miles south of the Dallas-Fort
Worth metropolitan area. Figure 1 shows the location
of Midlothian and the four industrial facilities of
interest. This section provides background
information on the various emission sources that
affect air quality in Midlothian, with a focus on the
four industrial facilities shown in Figure 1.
Air Emissions in Midlothian
The air exposure pathway begins with
air emission sources—processes that
release pollutants into the air. Once
released, these pollutants move from
their sources to locations where people
may be exposed. This section presents
background information on the air
emission sources of interest in the
Midlothian area: a steel mill and three
cement manufacturing facilities that
operate multiple kilns. Other local
emission sources also are identified
and discussed.
Operations at all four facilities of interest have
changed over the years. Some changes would have
increased air emissions (e.g., increased production
levels in certain years, use of different fuels in the kilns) whereas others would have decreased
air emissions (e.g., installation of pollution control devices). In some cases, changes at the
facilities might have simultaneously decreased emissions of certain pollutants and increased
emissions of others. These changing operations are important to consider when evaluating the air
quality concerns in the Midlothian area. Emissions also can change considerably from one hour
to the next—a topic addressed later in this Health Consultation.
The four facilities of interest in Midlothian emit several pollutants at rates that have consistently
ranked among the highest for industrial facilities in Ellis County that submit data to TCEQ’s
Point Source Emissions Inventory. Accordingly, this section presents detailed summaries of
emission data for the four facilities. Other emission sources (e.g., motor vehicles) are briefly
acknowledged and characterized for completeness.
2.2. Background on Relevant Industrial Processes
This section presents general information on the relevant manufacturing processes for the
facilities of interest in Midlothian, with a focus on the types of air emissions commonly found at
cement kilns and steel mills. Please refer to the ATSDR Health Consultation Assessing the
Adequacy of the Ambient Air Monitoring Database for Evaluating Community Health Concerns
for more details (ATSDR, 2012a)
2.2.1. Air Emissions from Cement Kilns
Cement is a commercial product that is used to make concrete. Although cement manufacturing
facilities employ various production technologies, most facilities share some common design
features. A very simplified account of common elements of cement manufacturing follows.
3
Midlothian Area Air Quality—Assessing the Public Health Implications of the Criteria
(NAAQS) Air Pollutants and Hydrogen Sulfide Health Consultation Public Comment Release
Cement is typically manufactured by feeding crushed limestone, shale, and other ingredients into
kilns that operate at high temperatures, typically at least 2,700o F (EPA, 1993). Facilities burn
various fuels to sustain these kiln temperatures. Fuels used across industry include coal, oil,
natural gas, hazardous waste, and tires. When the raw materials are heated to the temperatures
achieved in the kilns, they form a material known as “clinker,” which is the solid output from the
kilns that is cooled and mixed with gypsum to form the cement product.
Many by-products also are formed and exit the kiln in air exhaust. The primary by-product is
cement kiln dust, which is a highly alkaline dust of fine particle size. Air pollution control
equipment, such as baghouses and electrostatic precipitators, are typically used to reduce
emissions of cement kiln dust in the exhaust air from the kilns. Cement kiln dust not collected in
the controls or otherwise captured for further processing is emitted by the stacks typically found
at cement kilns, along with combustion by-products, which include carbon monoxide, nitrogen
oxides, sulfur dioxide, and various volatile organic compounds (e.g., formaldehyde) and semivolatile organic compounds (e.g., dioxins and furans).
Besides their kilns, cement manufacturing facilities have other operations that process materials.
These operations might include mining for limestone at on-site quarries, crushing and blending
raw materials, and other material handling processes. Air emissions from these and various other
operations tend to occur at ground level and are not always vented through air pollution controls.
Detailed information specific to the Midlothian facilities is presented later in this section.
2.2.2. Air Emissions from Steel Mills
Most steel in the United States is manufactured in either basic oxygen furnaces or in electric arc
furnaces (EPA, 2000a). Electric arc furnaces are the manufacturing technology of choice at
facilities that manufacture steel from scrap metal, as occurs in Midlothian. With this technology,
scrap metal and, if necessary, alloys are loaded into the furnace. Electrical energy is then used to
melt the scrap metal. During the melting process, impurities in the steel react with the air in the
furnace to form various by-products that are vented to the air, typically after passing through
some form of air pollution control device. These emissions can include inorganics (i.e., metals
and elements) originally found in the scrap and volatile organic compounds (VOCs) that can
form from the impurities present in the melting process.
After each batch of scrap metal is melted, the electric arc furnace is tilted and the desired
contents are poured into a mold, in which the molten steel gradually cools and takes its final
form. The steel then usually undergoes additional finishing processes (e.g., rolling, beam
straightening) to make the final product. Slag is a solid by-product from the melting process.
Steel mills employ various strategies for managing slag, including disposal and beneficial reuse.
Pollutants typically emitted from steel mills that melt scrap in electric arc furnaces include
particulate matter (PM) or dust, VOCs, carbon monoxide, nitrogen oxides, and sulfur dioxide.
The PM emitted from these facilities contains various inorganic compounds.
4
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Overview. Information is provided on the facilities’ history, ownership, location, and
main production processes, including types and amounts of fuels used to power their
furnaces and kilns.
Annual estimated air emissions. The facilities’ self-reported estimated annual air
emissions are summarized, using data they submitted to TCEQ’s Point Source Emissions
Inventory.
These data were accessed for criteria pollutants (e.g., carbon monoxide, lead, particulate
matter [PM], sulfur dioxide, nitrogen oxides) and precursors to some criteria pollutants
(e.g., VOCs). As with the Toxics Release Inventory (TRI) data, the criteria pollutant
emission data in the Point Source Emissions Inventory are self-reported. However,
annual emission data for some criteria pollutants are based on continuous emission
monitoring data at the facilities of interest. Continuous emission monitors are devices that
continuously measure air emissions inside stacks and other process areas. In other words,
these devices directly measure emissions, so facilities do not need to estimate their
emissions. This section also identifies whether any of the facilities’ annual emissions
rank among the state’s top 25 emitters in the Point Source Emissions Inventory.
Short-term estimated air emissions. This section summarizes the frequency and
magnitude of certain short-term air contaminant releases, which annually averaged
emission data do not characterize. TCEQ regulations require industrial facilities to
disclose information associated with certain scheduled activities that lead to excess
emissions (e.g., process maintenance, planned shutdowns) and unscheduled emission
events (e.g., following process upsets or accidental releases). Whether reporting is
required depends on several factors, such as the nature of the release and the amount of
pollutants emitted.
Facility-specific information on short-term estimated air emissions is based on data that
facilities submitted to TCEQ’s “Air Emission Event Reports” database. TCEQ
subsequently makes these reports publicly available in summary form on its Web site.
ATSDR accessed the entire history of online emission event data, which dates back to
2003 (TCEQ, 2010a). All information provided by the facilities (including the pollutant
emission rates) is self-reported and typically estimated. Short-term events may have
occurred at the facilities of interest but were never reported to TCEQ; however, the
environmental impacts of these events would likely be detected by nearby offsite
monitoring devices, especially those that operate continuously.
Understanding the short-term contaminant emissions is an important consideration for at
least two reasons. First, several community members have voiced concern specific to
acute (or short-term) exposures. Second, tabulations of annual average emissions and air
pollution levels might mask important peaks in facility releases. Therefore, this document
and ATSDR’s future Health Consultations consider the implications of both short-term
and long-term air pollution levels.
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Facility Profiles
The following pages in this document
present brief profiles for the four
facilities of interest. The purpose of this
section is to document some of the most
relevant background information that
ATSDR collected. These profiles should
not be viewed as comprehensive
summaries of the individual facilities and
their histories.
Overview. Ash Grove Texas L.P. is a
business entity that operates a Portland
cement manufacturing facility located north
of Midlothian, referred to in this document
as “Ash Grove Cement.”1 The parent
company of this facility is Ash Grove
Cement Co. From 1990 until 2003, the
facility in Midlothian was owned and
Although this section, by design, focuses
operated by another entity called North
on the individual facilities separately, this
Texas Cement Company, L.P.; and before
Health Consultation considers the
1990, the facility was owned and operated
combined air quality impacts from all
by Gifford Hill Cement Company. The
four facilities and additional air emission
sources throughout the Midlothian area.
facility was constructed in 1965 and began
operating in 1966, and it currently operates
three rotary kilns to manufacture cement.
These kilns began operating in 1966, 1969, and 1972 (TNRCC, 1995). Cement is
manufactured by feeding limestone, shale, and other raw materials into the rotary kilns,
which operate at temperatures reaching 4,000 degrees Fahrenheit (oF). Most of the raw
materials used in the process are from an onsite quarry, but some materials come from
offsite sources via truck and rail. The solid product from the kilns is subsequently ground
together with gypsum to make Portland cement.
Various fuels have been used at the facility over the years to fire its kilns. For example,
only natural gas was used to fire the kilns after the facility was first built. In the 1970s,
fuel oil handling equipment was added, and other fuels (e.g., coal, coke, wood chips)
were added in subsequent years. As described further below, waste-derived fuel was
burned in the mid-1980s into the early-1990s, and whole tires were allowed as a fuel
starting in the 1990s. The facility is currently not able to use tire chips and has never used
tire chips. The facility has not used wood chips extensively or used oil in the last decade.
This facility employs a combination of coal, petroleum coke, and tires to fire its kilns;
natural gas was typically used only for startup of the kilns but usage has expanded in
recent years.
From 1986 to 1991, the facility also was authorized to burn waste-derived fuel in its kilns
as a supplemental energy source. Starting in 1989, industrial facilities managing
hazardous waste were required to submit biannual reports to EPA on the quantities of
waste that were managed. In 1989, a total of 55,000 tons of hazardous waste were
reportedly used for purposes of energy recovery; and in 1991, a total of 14,200 tons of
hazardous waste were used for this purpose (EPA, 2010b). The practice of burning
hazardous waste ceased in 1992.
1
This document primarily uses “Ash Grove Cement” to refer to the cement manufacturing facility located in
Midlothian. Ash Grove Texas L.P. is the business entity that currently operates that facility. References to “the
facility” throughout this document refer to the cement manufacturing plant, which was owned and operated by
different entities over the years.
Midlothian Area Air Quality—Assessing the Public Health Implications of the Criteria
(NAAQS) Air Pollutants and Hydrogen Sulfide Health Consultation Public Comment Release
At the time, hazardous waste combustion in cement kilns was regulated under an EPA
regulation that addressed combustion of hazardous waste in boilers and industrial
furnaces. That regulation required affected facilities to conduct compliance tests to
determine allowable waste feed rates, use of automatic waste feed cutoffs to prevent feed
rates from exceeding these limits, and other safeguards. In 1995, the facility received
authorization to burn whole tires in its cement kilns and the facility is required to report
to TCEQ its ongoing usage of tire-derived fuel (TCEQ, 2009a). Annual statistics for the
facility’s usage of tire-derived fuel follow (Ash Grove Cement, 2010):
1996
1997
1998
1999
2000
2001
2002
5,500 tons
18,400 tons
33,400 tons
37,100 tons
38,200 tons
38,200 tons
37,400 tons
2003
2004
2005
2006
2007
2008
2009
39,400 tons
43,300 tons
43,000 tons
43,400 tons
42,400 tons
44,800 tons
29,300 tons
These data show varying annual usage of tire-derived fuel, including a substantial
decrease in usage in 2009. According to Ash Grove Cement’s air permit, the facility is
currently allowed to fire its kilns with multiple fuels. The facility is reportedly in the
process of decommissioning two of its kilns and reconstructing the third. These changes have
been reflected in the air permit amended in May 2012.
Ash Grove Cement’s production processes have numerous sources of air emissions.
Exhaust air from the three kilns, for example, vents to the atmosphere through 150-foot
tall stacks, after first passing through electrostatic precipitators designed to capture PM
and other pollutants before being released to the air. Selective non-catalytic reduction
technology has recently been implemented in all three kilns to reduce air emissions of
nitrogen oxides. These air pollution controls collect a large portion of the kiln’s
emissions, including cement kiln dust, but are not 100 % efficient, and every kiln at Ash
Grove Cement emits various pollutants through its stacks. The facility is required to
continuously monitor emissions of carbon monoxide, nitrogen oxides, and sulfur dioxide
(and the facility was previously required to monitor emissions of VOCs), although many
other pollutants are released from this source. These continuous monitors are placed
directly in the kiln stacks.
Emissions also occur from the facility’s quarry activities, physical processing of raw
materials (e.g., crushing, grinding, milling), materials handling operations, stockpiles,
and other storage areas. Many of these other emission sources are also equipped with air
pollution controls to help reduce releases. For example, dust collectors capture PM from
many of the materials handling operations. Facility-wide emissions can vary considerably
with time, because Ash Grove Cement occasionally changed its fuel sources and the
design of its unit operations; new equipment has been added over the years, and some
older equipment has been taken out of service.
7
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industrial facilities of interest. An estimated 38,908 people live within 3 miles of any of
these facilities, and some people are life-long residents. The main population center of
Midlothian is located between the facilities of interest, although several residential
developments and individual properties are located throughout the area. According to the
census data, approximately 11 % of the population within 3 miles of these facilities, are
children; 6 % are elderly; and 22 % are women of childbearing age. Please refer to
ATSDR’s earlier health consultation (ATSDR 2012a) for a map and details on the
demographic characteristics of the area.
Residents closest to the facilities. All four main industrial facilities in Midlothian own
large tracts of land which helps ensure that no one lives in immediate proximity to the
facilities’ main industrial operations, where air quality impacts from some emission
sources would be greatest. Observations from site visitors and review of aerial
photographs, however, confirm that numerous residents live just beyond the four
facilities’ property lines. For instance, several dozen homes are located along the eastern
boundary of TXI Operations. Multiple homes along Ward Road, Wyatt Road, Cement
Valley Road, and other streets are located across U.S. Highway 67 from TXI Operations
and Gerdau Ameristeel. Similarly, a residential area and Jaycee Park are located along
the southeastern boundary of Ash Grove Cement, and another residential area is near the
facility’s northeastern boundary. Holcim has nearby residential receptors; the closest ones
live near the facility’s northwestern and southeastern boundaries.
Nearest areas with potential for elevated short-term exposures. In addition to the
residential neighborhoods and areas listed above, ATSDR considered short-term
exposures that residents, visitors, and passers-by might experience when they are in close
proximity to the four industrial facilities. These short-term exposures can occur at many
places, such as along U.S. Highway 67, which passes along the boundary of all four
facilities; at recreational facilities near the facility boundaries (e.g., Jaycee Park, Pecan
Trails Golf Course, Massey Lake); and at various nearby business establishments.
ʹǤͷǤ
ATSDR reviewed climatic and meteorological conditions in the Midlothian area because these
factors affect how air emissions move from their sources to downwind locations. The Midlothian
area is flat with gently rolling terrain. The National Climatic Data Center (NCDC) collects
climatic data at multiple locations in Ellis County, and the Waxahachie weather station has the
longest period of record. From 1971 to 2000, the average temperature in this area ranged from
46.0° F in January to 84.6° F in July, and the area received an average of 38.81 inches of
precipitation a year, almost entirely in the form of rain (NCDC, 2004).
To assess the prevailing wind patterns, ATSDR obtained wind speed and wind direction data for
multiple meteorological stations in the Midlothian area. ATSDR summarized data for two of
these stations in a format known as a wind rose (see ATSDR, 2012a). A wind rose displays the
statistical distribution of wind speeds and directions observed at a meteorological station. The
wind roses indicate that the prevailing wind direction in the Midlothian area is from south to
north, although pronounced contributions also are observed from north to south and from
southeast to northwest. For example, the Wyatt Road and Old Fort Worth Road monitors are
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2008 caused ammonia emissions to exceed allowable levels for 3 hours. None of these
emission events occurred on days when TCEQ received complaints about TXI
Operations’ emissions.
ǤǤͻǤ
Air quality in Midlothian is affected by emissions from all local (and some distant) sources and
not only by emissions from the four main facilities of interest. Consequently, the ambient air
monitors in the area measure air pollution levels that reflect contributions from several emission
sources.
Most industrial facilities, like the cement kilns and steel mill in Midlothian, are referred to as
point sources. Other emission sources are typically classified into two categories: area sources
and mobile sources. Area sources are small air pollution sources that individually do not emit
enough pollutants to be considered a point source, but collectively throughout an area can
account for a considerable quantity of emissions. Examples of area sources include agricultural
tilling, dry cleaners, and gasoline stations. Mobile sources refer to any vehicle or equipment with
a gasoline or diesel engine (e.g., on-road and off-road motor vehicles, construction equipment),
and aircraft and recreational watercraft. The following paragraphs briefly review information on
emissions from sources other than the four facilities of interest.
EPA’s National Emissions Inventory (NEI) estimates the relative magnitude of annual emissions
from point, area, and mobile sources for every county across the nation. According to the 2005
NEI, the most recent release available when ATSDR started this evaluation, the four industrial
facilities of interest emit approximately 85 % of the sulfur dioxide and 60 % of the nitrogen
oxides released to the air throughout all of Ellis County, and they account for approximately 20
% of the countywide emissions of carbon monoxide and fine PM (EPA, 2010b). NEI does not
present emission data for short-term emission events.
These data offer some insights on the different types of emission sources found in and near
Midlothian but must be interpreted in proper context. Although the NEI data suggest that sources
other than the facilities of interest might account for the majority of countywide emissions for
certain pollutants, that suggestion does not necessarily mean air pollution levels at a given
location are dominated by these other sources. On the contrary, emissions from the four facilities
of interest are expected to have considerably greater air quality impacts at locations nearest these
facilities, especially considering their proximity to each other.
ʹǤͶǤ
ATSDR examines demographic data to determine the number of people who are potentially
exposed to environmental contaminants and to consider the presence of sensitive populations,
such as young children, women of childbearing age ( aged 15–44 years) and the elderly (aged 65
years and older). This section considers general population trends for residents in the city of
Midlothian and also identifies residential areas closest to the facilities.
General population trends. Information compiled in the 2000 U.S. Census, provides
demographic data for areas within 3 miles of the property boundaries of the four
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Following is a summary of the total amount of hazardous waste that TXI Operations
burned for purposes of energy recovery, according to the facility’s BRS reports:2
1991
1993
1995
1997
1999
40,600 tons
56,200 tons
90,700 tons
57,700 tons
74,700 tons
2001
2003
2005
2007
62,400 tons
31,600 tons
50,000 tons
42,100 tons
On average, across the years listed, TXI Operations burned approximately 56,200 tons of
hazardous waste annually for purposes of energy recovery (EPA, 2010a)—an amount
roughly equivalent to burning more than 150 tons of hazardous waste per day, assuming
continuous operations. The quantities burned since 2001 are low in comparison with
other years because of permit restrictions that limited the number of kilns that could
operate simultaneously. This waste has come almost entirely from offsite sources.
Examples of the specific types of waste burned at TXI Operations include, but are not
limited to, organic liquids and sludge, waste oils, and solvents. During the years TXI
Operations burned hazardous waste, automatic waste feed cutoff systems were employed
to ensure that the quantities of waste-derived fuel did not exceed pre-established input
limits that were based on compliance testing. Further, continuous emissions monitoring
for total hydrocarbons provided data that could be used to assess the adequacy of fuel
combustion. Various other requirements were mandated under an EPA regulation
affecting combustion of hazardous waste in boilers and industrial furnaces.
TCEQ’s web site documents 84 complaints that residents submitted to the agency
between from 2002 to 2010 regarding TXI Operations’ air emissions (TCEQ 2010b).
More than half of these complaints were filed because of odors, when residents and
passers-by reported smelling strong chemical and chlorine-like odors. Some odor
complaints referenced odors of sulfur and burning tires, and nearly every odor complaint
occurred at night. The other complaints pertained to primarily dust and smoke coming
from the facility. In some cases, the complainants reported symptoms (e.g., cough,
burning sensation in nostrils) believed to result from facility emissions.
Annual estimated air emissions. Section 3 reviews the history of TXI Operations’
annual emissions for the pollutants considered in this Health Consultation.
Short-term estimated air emissions. From 2003 to 2011, TXI Operations submitted 36
air emission event reports to TCEQ. Thirty-five were excess opacity events and emission
events and the other one was a scheduled maintenance event. Four emission events in the
database were reported for the following: the safety valve in a storage tank ruptured in
April 2005, releasing several VOCs; a dislodged brick in a rotary kiln in August 2006
caused increased emissions reported as excess opacity; a kiln shutdown in February 2008
led to excess emissions of sulfur dioxide; and problems encountered with a pump in April
2
The BRS data are presented for all years with available information. Data shown are for the amount of hazardous
waste burned for purposes of energy recovery. TXI Operations did not report any data to BRS for 1989. All data
points are rounded to three significant figures.
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one event reportedly lasted approximately 9 hours. Opacity measurements appeared to
trigger most of these reportable events, and none were apparently triggered by an
excessive pollutant-specific emission rate.
ǤǤͺǤ
Overview. TXI Operations, the largest of the three Portland cement manufacturing
facilities in Midlothian, is located southwest of the city center, adjacent to Gerdau
Ameristeel. The facility was formerly known as Midlothian Cement Plant. TXI
Operations began operating in 1960 and operates five cement kilns that came online in
1960, 1964, 1967, 1972, and 2002. Four of these are “wet kilns,” and the newest is a “dry
kiln.” An onsite quarry provides the limestone and shale used to manufacture cement.
Other raw materials are delivered via truck. The kilns are fired at temperatures that reach
2,800 oF and produce clinker, which is ground together with gypsum to make the
Portland cement product.
TXI Operations has used multiple fuels to fire its kilns, originally natural gas. In 1974,
TXI Operations was also permitted to fire its kilns with fuel oil. In 1980, 1983, and 1987,
the facility was authorized to fire kilns using coal, petroleum coke, and waste-derived
fuel, respectively. In the past, the four wet kilns were authorized to fire natural gas, fuel
oil, coal, petroleum coke, and waste-derived fuel. The dry kiln is authorized to fire
natural gas and coal as fuel. Although TXI Operations was permitted to burn hazardous
waste since 1987, the facility has not used this fuel continuously over the years. Data
summarized later in this section indicate that the facility burned hazardous waste during
1991 to 2007. TXI no longer burns hazardous waste in its wet kilns; TXI has permanently
shut down its wet kilns and the authority to operate these kilns has been removed from its
permit.
TXI Operations has many air emission sources that are typically found at cement
manufacturing facilities. Exhaust air from the active kiln passes through a high-efficiency
fabric filter baghouse to reduce emissions of PM and a wet scrubber to reduce emissions
of sulfur dioxide, nitrogen oxides, and other pollutants. This exhaust gas then passes
through a regenerative thermal oxidizer, which reduces emissions of carbon monoxide
and VOCs. Ultimately, the exhaust from the kilns exits through 200-foot or 310-foot tall
stacks, which TXI Operations continuously monitors emissions of several pollutants,
including carbon monoxide, nitrogen oxides, and sulfur dioxide. The specific monitoring
requirements varied across the kilns, although only a single kiln operates. In addition to
pollution controls for kiln emissions, the facility has equipped several other process
operations with baghouses and other types of dust collectors to reduce PM emissions.
Every other year, TXI Operations is required to provide EPA information on the amount
of waste-derived fuel (i.e., hazardous waste) that the facility feeds to its kilns for energy
recovery purposes (EPA, 2010a). That information is loaded into EPA’s Biennial
Reporting System (BRS) database, which can be queried by the public. Currently, BRS
waste management statistics are available for every other year during 1989 through 2009.
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1994
1995
1996
1997
1998
1999
2000
2001
5,313 tons
18,722 tons
18,513 tons
11,076 tons
1,647 tons
417 tons
829 tons
1,015 tons
2002
2003
2004
2005
2006
2007
2008
2009
15,480 tons
25,629 tons
8,403 tons
13,137 tons
14,464 tons
9,918 tons
9,256 tons
10,430 tons
According to Holcim’s air permit, the facility is currently allowed to fire its kilns with
natural gas, coal, tire chips, oil, non-hazardous liquids, non-hazardous solids, and
petroleum coke.
Holcim’s cement manufacturing operations emit air pollutants from multiple sources, and
various measures are in place to reduce facility emissions. Both kilns now operate with
selective non-catalytic reduction (SNCR) technology to reduce emissions of nitrogen
oxides. Exhaust air from the two kilns (and other production areas) passes through
baghouses (to reduce PM in emissions) and wet scrubbers (to reduce sulfur dioxide
emissions). Process gases from the kilns eventually vent to the atmosphere through 250
foot and 273-foot tall stacks, in which the facility continuously monitors emissions of
sulfur dioxide, carbon monoxide, nitrogen oxides, and ammonia. Emissions also occur
from the facility’s quarry activities, physical processing of raw materials, materials
handling operations, and storage areas, and some of these emission sources are also
equipped with baghouses to remove PM from process exhaust streams.
In July 2005, following an application to increase nitrogen oxide emissions, Holcim
reached a settlement agreement with DFW Blue Skies Alliance and Downwinders at
Risk. This agreement led to Holcim funding several projects to reduce emissions and
monitor local air quality. For example, Holcim agreed to continuously measure
downwind ambient air concentrations of fine PM—a project that operated from 2006 to
early 2010.
According to queries run on TCEQ’s Web site, the agency received 11 complaints from
residents about air emissions from Holcim between 2002 and 2010 (TCEQ, 2010b). Five
of these complaints were filed during the period May 2005 to April 2006. Most of the
complaints pertained to a strong burning plastic or burning chemical odor emanating
from the facility. The odor reportedly caused headaches in some residents and forced
others to stay indoors.
Annual estimated air emissions. Section 3 below reviews the history of Holcim’s
annual emissions for the pollutants considered in this Health Consultation
Short-term estimated air emissions. From 2003 to 2010, Holcim submitted 17 air
emission event reports to TCEQ. Of these, six were scheduled maintenance or startup
activities. The remaining 11 events were excess opacity events and emission events. All
but one of these were of short duration (i.e., roughly between 5 minutes and 2.5 hours);
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2011a). Currently, Gerdau Ameristeel is not required to continuously monitor pollutant
emission rates from any of its main stacks.
According to queries run on TCEQ’s Web site, the agency received 52 complaints from
residents about air emissions from Gerdau Ameristeel during the period 2002 to 2010
(TCEQ, 2010b). These complaints were filed for various reasons: odor was cited as a
reason for 24 of these complaints. The most frequently cited odor was a burning plastic
smell (for 12 of the complaints). Residents also reported detecting diesel, metal, sulfur,
and chemical odors. Other reasons that residents filed complaints included deposition of
dust, visible smoke, and excessive industrial activity. Nearly every complaint specific to
Gerdau Ameristeel occurred during nighttime hours.
Annual estimated air emissions. Section 3 below reviews the history of Gerdau
Ameristeel’s annual emissions for the pollutants considered in this Health Consultation.
Short-term estimated air emissions. During the period 2003 to 2011, Gerdau
Ameristeel submitted 30 air contaminant emission event reports to TCEQ: 28 excess
opacity events and two emission events. One of the emission events involved
approximately 800 excess pounds of PM released to the air over a 32-hour time frame,
when dust control measures for unpaved roads were suspended related to a failed water
supply well.
ǤǤǤ
Overview. Holcim Texas Limited Partnership (LP) (referred to in this document as
“Holcim”) is a Portland cement manufacturing facility located northeast of Midlothian.
The facility began its operations as Box Crow Cement Company and subsequently
became Holnam Texas LP before being renamed to Holcim Texas LP. Holcim operates
two dry kilns; the first began operating in 1987 and the second in 2000. An onsite quarry
provides limestone and other raw materials used to feed the rotary kilns, which operate at
temperatures reaching 3,000o F. Raw materials are crushed and milled onsite before being
fed to pre-heaters that precede the kilns. The solid product from the kilns, or clinker, is
cooled and ground together with gypsum to make Portland cement.
Since 1987, Holcim has used multiple fuels to fire its kilns. The facility was originally
permitted to use coal and natural gas. In 1994, Holcim was also authorized to burn tire
chips as supplemental fuel in pre-processing operations. Data that the facility reported to
TCEQ indicate that the amount of tire scraps burned at Holcim varies from one year to
the next (TCEQ, 2009a). Annual statistics for the facility’s usage of tire-derived fuel
follow (TCEQ 2009a, 2010c):
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According to queries run on TCEQ’s Web site, the agency received no complaints from
residents about air emissions specifically from Ash Grove Cement between 2002 and
2010 (TCEQ, 2010b).
Annual estimated air emissions. Section 3 below reviews the history of Ash Grove
Cement’s annual emissions for the pollutants considered in this Health Consultation.
Short-term estimated air emissions. According to data ATSDR accessed in 2011, Ash
Grove Cement submitted 257 air emission event reports to TCEQ dating back to 2003. Of
these, 87 were scheduled maintenance, startup, or shutdown activities. The remaining 170
events were excess opacity events and emission events. Only one of these event reports
included a pollutant-specific emission rate. On February 16, 2005, Ash Grove Cement
experienced an hour-long emission event that released 106 pounds of carbon monoxide
into the air; no other pollutants were identified in the excess emission event report. Some
reports made by Ash Grove Cement were reportedly based on an expectation that there
was a chance that the type of event (i.e., startup, shutdown, or maintenance) could result
in emissions of one or more pollutants over a permit limit. However, reporting of such
information should not be inferred to indicate that emissions above permitting limits
automatically occurred.
ǤǤǤ
Overview. Gerdau Ameristeel—sometimes referred to as Chaparral Steel—operates a
secondary steel mill located southwest of Midlothian and adjacent to TXI Operations (see
Section 2.3.4). The facility began operating in 1975 (TNRCC, 1995) and currently uses
two electric arc furnaces and three rolling mills to melt and recycle scrap steel. The scrap
steel is obtained from an automobile shredder and junkyard, also located at the facility.
The two electric arc furnaces melt scrap steel, and then casting operations form the
material into structural steel beams, reinforcing bars, and other shapes and forms. The
facility does not operate coke ovens to generate energy; therefore, coke oven emissions
will not be considered in this investigation.
Gerdau Ameristeel’s production processes have multiple emission sources. Air emissions
from the two furnaces are controlled through the use of positive and negative pressure
baghouses, which collect airborne particles that would otherwise be released to the
environment. Exhaust air from these baghouses vents to the atmosphere through any of
three stacks; two are 150 feet tall and the third is 80 feet tall. Emissions also occur from
the facility’s automobile shredding operation, melt shop, and scrap and slag handling.
Many of these operations also are equipped with air pollution controls. For example, the
slag crusher and alloy processes have baghouses that capture PM from exhaust streams
that would otherwise be emitted to the air. The extent of air pollution controls changed
over time. For instance, in 1988, Gerdau Ameristeel installed a new baghouse that
considerably reduced emissions of particulate matter, and further reductions occurred in
the early 1990s when another new baghouse was installed and the facility’s “roof vents”
in certain production areas were removed. A complete list of these controls is available
from the facility’s submissions to TCEQ’s Point Source Emission Inventory (TCEQ,
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considered downwind of TXI and Gerdau Ameristeel when the winds are blowing in the
prevailing directions. However, on occasion, the Midlothian Tower might be downwind of these
facilities when the wind is blowing from the north to the south. (See ATSDR 2012a for details
on this analysis.)
ATSDR then examined the extent to which prevailing wind patterns in the Midlothian area vary
by month and time of day. At the Old Fort Worth Road and Midlothian Tower meteorological
stations, average wind speeds were highest in March and April and lowest in August and
September; wind speeds, on average, were also highest during the early afternoon (2:00 p.m. to
4:00 p.m.); wind speeds at both stations tended to be lightest around sundown (6:00 p.m. to 8:00
p.m.) and sunup (4:00 a.m. to 6:00 a.m.). In nearly every month of the year, winds blew most
frequently from south to north. Contributions from the other main directions in the area varied
slightly from month to month. Wind direction did not vary considerably with time of day.
ʹǤǤ
For more than 20 years, EPA and state environmental agencies have evaluated general air quality
in populated areas by measuring ambient air concentrations of six common air pollutants, also
known as criteria pollutants. These pollutants are carbon monoxide, lead, nitrogen dioxide,
ozone, two forms of PM, and sulfur dioxide. For every criteria pollutant, EPA has established a
health-based National Ambient Air Quality Standard. In cases where air quality does not meet
the standard, states are required to develop and implement plans to bring air pollution levels into
attainment with the health-based standards. The following paragraphs review the general air
quality near Midlothian, as gauged by measured levels of criteria pollutants:
Ozone. Currently, numerous ambient air monitoring stations measure ozone levels
throughout selected summer and fall months in the Dallas-Fort Worth metropolitan area.
Measured ozone levels at several of these stations have exceeded EPA’s health-based
standards, suggesting that the air quality in this area is at times unhealthy. As a result,
EPA currently designates the Dallas-Fort Worth area as a “non-attainment area” for
ozone. All of Ellis County is included in this non-attainment area. Air quality warnings
are typically issued when ozone levels are expected to be elevated. The Dallas-Fort
Worth area is considered one of three “serious” non-attainment areas for ozone in the
United States. This designation is lower than the two “extreme” and three “severe” nonattainment areas but higher than the numerous other “moderate” non-attainment areas
nationwide. Residents can learn more about ozone at http://www.AirNow.gov.
The ozone air quality issues in Dallas-Fort Worth are complex and result from numerous
industrial and motor vehicle emissions over a broad geographic region. The exact
contribution of any single source to elevated ozone levels is difficult to assess.
Other pollutants. For the remaining criteria pollutants (carbon monoxide, lead, nitrogen
dioxide, PM, and sulfur dioxide), the Dallas-Fort Worth area is considered to be in
attainment with EPA’s health-based air quality standards. In June 2010, EPA
strengthened its health-based standard for sulfur dioxide, but the agency recently reported
Midlothian Area Air Quality—Assessing the Public Health Implications of the Criteria
(NAAQS) Air Pollutants and Hydrogen Sulfide Health Consultation Public Comment Release
that air quality in the Dallas-Fort Worth metropolitan area currently meets the stricter
(and more health-protective) standard (EPA, 2010c).
16
Midlothian Area Air Quality—Assessing the Public Health Implications of the Criteria
(NAAQS) Air Pollutants and Hydrogen Sulfide Health Consultation Public Comment Release
3. Measured and Estimated Air Pollution Levels
This section summarizes data on air pollution levels measured in Midlothian. For each pollutant
considered in this Health Consultation, this section presents background information on the
pollutant and why it is expected to be found in the facilities’ emissions. The section also
documents reported emission rates for the pollutants of interest, including how those emissions
vary across facilities and with time. Finally, the section documents the measured air pollution
levels and how those vary from one location to the next. Modeling results are presented only for
the pollutant for which no direct measurements are available (i.e., carbon monoxide). Data
summaries and maps are used throughout this section to document the air pollution
measurements and where they were collected.
As an initial step in the health evaluation, the measured air pollution levels are compared with
health-based air quality standards and guidelines published by EPA, TCEQ, or the World Health
Organization (WHO). These values have been developed to protect the health of all individuals,
including sensitive populations (e.g., persons with asthma, children, and the elderly). Sections
3.1 through 3.6 present detailed data evaluations for the individual pollutants, and Section 3.7
summarizes these findings. Section 4 of this Health Consultation presents ATSDR’s detailed
health evaluations for each pollutant above health-based guidelines or standards.
3.1. Carbon Monoxide
Carbon monoxide is released by many sources, typically when carbon-containing fuels do not
burn completely. On a national scale, motor vehicles account for approximately 90 % of carbon
monoxide emissions from manmade sources (EPA, 2008a). However, emissions from industrial
sources can dominate in areas with extensive manufacturing activity, like Midlothian.
Environmental exposure to CO can occur while traveling in motor vehicles, working, visiting
urban locations associated with combustion sources, or cooking and heating with domestic gas,
charcoal, or wood fires, and by inhaling environmental tobacco smoke. WHO (1999)
summarized environmental concentrations as follows: CO concentrations in ambient air
monitored from fixed-site stations are usually below 9 ppm (8 h average). However, short-term
peak concentrations up to 50 ppm are reported on heavily traveled roads. The CO levels in
homes are usually lower than 9 ppm; however, the peak value in homes could be up to 18 ppm
with gas stoves, 30 ppm with wood combustion, and 7 ppm with kerosene heaters. The CO
concentrations inside motor vehicles are generally 9–25 ppm and occasionally over 35 ppm.
Similar exposure levels were reported by EPA (2000b).
Table 1 summarizes CO emissions data available from TCEQ’s Point Source Emissions
Inventory (PSEI) for the four facilities of interest. According to this inventory, these four
facilities have consistently had the highest CO emissions among the industrial facilities found in
Ellis County. The emissions also rank high among facilities statewide. For example, in 2005, the
PSEI includes carbon monoxide emissions for more than 1,600 facilities. In that year, emissions
from the Midlothian facilities ranked 13th (Holcim), 28th (Gerdau Ameristeel), 63rd (TXI
Operations), and 99th (Ash Grove Cement) when compared with the other facilities across the
state.
17
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Other emissions trends are evident from Table 1. For instance, during the last 15 years of
inventory data shown, Holcim’s annual carbon monoxide emissions were the highest of the four
facilities, followed by emissions from Gerdau Ameristeel, TXI, and Ash Grove Cement. During
this 15-year period, emissions were lowest in 2009 and 2010. Emissions in these 2 years were
particularly low for the three cement manufacturing facilities, consistent with an industry-wide
decline in production that occurred during this same time (USGS, 2011).
ATSDR has compiled all publicly available ambient air monitoring data for the Midlothian area.
However, no monitors in or near Midlothian have measured air pollution levels for carbon
monoxide. To fill this gap in the environmental data, ATSDR used models to estimate past air
quality impacts for this pollutant. Appendix A of this report documents the modeling analysis,
which was based on assumptions generally designed to assess worst-case air quality impacts. For
example, the emissions data used in the model were based on the highest years of emissions
documented in Table 1. The model included the carbon monoxide emissions data for Ash Grove
Cement from 1990, for Gerdau Ameristeel from 1994, for Holcim from 2004, and for TXI from
1990. Further, to assess the worst case scenario, ATSDR assumed that these emissions all
occurred at the same time. The model was run to predict air pollution levels from all four sources
combined, and the main results were as follows:
The highest 1-hour average carbon monoxide concentration estimated by the model was
0.85 parts per million (ppm) at a location north of the Gerdau Ameristeel property line,
near the intersection of Wyatt Road and U.S. Highway 67. In contrast, EPA’s standard
for this concentration is 35 ppm, and TCEQ has also adopted this standard. Further,
WHO’s health guideline for 1-hour levels is 26 ppm (WHO, 2000). Thus, the highest
estimated air quality impact attributed to the facilities is more than 30 times lower than
the corresponding health-based standards and guidelines.
The highest 8-hour average carbon monoxide concentration estimated by the model was
0.55 ppm, again at a location north of Gerdau Ameristeel. Both EPA’s standard (which
TCEQ has adopted) and WHO’s health guideline for this variable is 9 ppm—more than
15 times higher than the estimated air quality impacts from the facilities.
The model used in this analysis does not estimate air concentrations for averaging periods
shorter than 1 hour. Therefore, ATSDR could not compare estimated concentrations with
WHO’s health guidelines derived for 15-minute and 30-minute averaging periods. This
lack is not considered a major limitation in the health evaluation because even if we
assume that the highest 1-hour CO value increased by a factor of four to simulate what a
15-minute value might be, the levels would all be below the WHO guideline.
ATSDR has not developed a Minimal Risk Level for CO. Given the physiologic role of
endogenous carbon monoxide (i.e., natural production of CO by the human body), an
exposure threshold for carbon monoxide actions, if one exists at all, is likely at or near
the endogenous production rate. Therefore, any exogenous source of carbon monoxide
exposure would have the potential for exceeding the threshold and producing potentially
adverse effects. Although there might be an exposure level that can be tolerated with
minimal risk of adverse effects, the currently available toxicologic and epidemiologic
data do not identify such minimal risk levels. The lowest levels of effects have been
Midlothian Area Air Quality—Assessing the Public Health Implications of the Criteria
(NAAQS) Air Pollutants and Hydrogen Sulfide Health Consultation Public Comment Release
seen in epidemiologic studies. These studies indicate an increased risk of arrhythmias in
coronary artery disease patients and exacerbation of asthma when the concentration range
is about 0.5-10 ppm (ATSDR, 2012b). ATSDR estimated 1 and 8 hour CO
concentrations in Midlothian at 0.85 and 0.55, respectively. Although ATSDR cannot
rule out a harmful effect in some very sensitive persons, the estimated worst-case
exposure levels are at the low end of the range that showed these effects in epidemiologic
studies. Moreover, the estimated levels are below the background level for the DallasFort Worth metropolitan area and what might be typically found in a home or
automobile.
The modeling results are estimates of carbon monoxide air quality impacts from the four
Midlothian facilities, and do not consider contributions from other sources. To assess potential
contributions from other sources (e.g., motor vehicles), ATSDR considered carbon monoxide
monitoring data collected in two high motor vehicle traffic areas in the Dallas–Fort Worth
metropolitan area. These data are accessible from EPA’s “AirData” database, which is a
clearinghouse of air pollution measurements collected nationwide. According to that database,
the highest 1-hour average carbon monoxide concentration over the last 5 years at the two longterm monitoring stations in Dallas and Fort Worth was 3 ppm (EPA, 2012a). Therefore, carbon
monoxide levels in the Midlothian area caused by mobile sources are likely substantially less
than this amount, but no measurements are available to support this judgment.
Overall, no carbon monoxide monitoring has occurred in Midlothian, and Ellis County is not
designated as a non-attainment area for EPA’s air quality standards. ATSDR’s modeling analysis
indicates that the greatest air quality impacts from carbon monoxide are lower than EPA’s
health-based air quality standards. Even when considering reasonable estimates for contributions
from mobile sources, carbon monoxide levels throughout Midlothian likely do not exceed healthbased air quality standards.
ATSDR acknowledges that estimated air quality impacts for carbon monoxide are based entirely
on a modeling analysis, which has inherent uncertainties and limitations. The main sources of
uncertainty are the model inputs for local meteorology, the model inputs for facility emission
rates, and inherent limitations in air dispersion models. As Appendix A indicates, the
meteorologic data used in this assessment were developed specifically for modeling air quality
concerns in Ellis County, and the prevailing wind patterns in that data set are consistent with
those recently observed in the Midlothian area. Further, the modeling considers 5 years of
meteorologic data—the number of years of data that EPA recommends be included in air quality
modeling analyses to ensure that worst-case meteorologic conditions are adequately captured
(EPA, 2005). Further, ATSDR believes the model inputs do not underestimate actual annual
emissions for three reasons. First, the values entered into the model were the highest facilityspecific emissions data from 1990 to 2011. Second, the model assumed that the highest emission
rate from all four facilities occurred in the same year, even though that was not the case. Third,
the emissions data for the three cement manufacturing companies are measured directly with
continuous emissions monitors and are therefore expected to be highly accurate. Taken together,
these observations all suggest that the modeling analysis offers a reasonable account of carbon
monoxide air pollution levels attributable to the facilities’ emissions. However, the principal
limitation in the assessment is that the modeling is based on annual average emission rates, and
19
Midlothian Area Air Quality—Assessing the Public Health Implications of the Criteria
(NAAQS) Air Pollutants and Hydrogen Sulfide Health Consultation Public Comment Release
not peak hourly releases, as discussed in Appendix A. Nonetheless, given that the estimated air
quality impacts are more than 15 times lower than the corresponding air quality standards and
health guidelines, ATSDR has confidence in basing its health conclusions on the carbon
monoxide modeling results.
Based on the above analyses, ATSDR will not further evaluate carbon monoxide in the Public
Health Implications Section below.
3.2. Lead
Lead is a naturally occurring metal. Typically found at low levels in soils, lead is processed for
many industrial and manufacturing applications, and it is found in many metallic alloys. Lead
was previously found in many gasoline additives, but this use was gradually phased out starting
in the 1970s. On a national level, many different sources emit lead, including boilers, electricitygenerating facilities, and incinerators. A recent EPA assessment found that iron and steel
foundries (which includes Gerdau Ameristeel) accounted for approximately 7.7 % of the nation’s
total manmade emissions in 2002, whereas emissions from Portland cement manufacturing
facilities (which includes the other three Midlothian facilities) accounted for approximately 1.5
% of the nation’s total emissions (EPA, 2006a).
Table 2 summarizes lead emissions data available from TCEQ’s PSEI and for EPA’s Toxics
Release Inventory (TRI) for the four facilities of interest. In any given calendar year, a facility’s
emissions data reported to PSEI are not always the same as those reported to TRI because of
differences in these two programs’ reporting requirements. When compiling data for display in
Table 2, ATSDR selected the higher value for annual emissions reported in either inventory.
Table 2 reveals two important trends in the facilities’ lead emissions. First, air emissions of lead
from Gerdau Ameristeel far exceeded emissions from the other facilities over the entire period of
record. For the past 20 years, this facility’s lead emissions accounted for at least 80 % of the total
emissions from all four facilities. In fact, emissions from Gerdau Ameristeel have consistently
ranked high among other industrial facilities in Texas. For example, according to the PSEI data
for 1995, lead emissions from Gerdau Ameristeel ranked 2nd out of the 67 facilities in the state
for which emissions data are in the inventory (TCEQ, 2011a). Second, a substantial decrease in
lead emissions occurred in the late 1980s; the total emissions summed across all four facilities
decreased by more than 95 % during this time. Two improvements in capturing lead emissions
occurred at Gerdau Ameristeel in 1988 and 2003 (Personal Communication, Dale Harmon,
Gerdau Ameristeel, 2/15/12). Information about these improvements helps in interpreting the
ambient air monitoring data.
Table 3 summarizes the ambient air monitoring data collected for lead in the Midlothian area.
ATSDR’s first Health Consultation for this site concluded that these data were collected with
scientifically defensible methods and met standard data quality objectives (ATSDR, 2012a).
During the past 30 years, airborne lead levels have been measured at 16 monitoring locations in
the Midlothian area (Figure 1). Table 3 organizes the lead summary statistics by decade to
illustrate how air quality impacts have changed with time:
20
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Lead data from the 1980s. The only
monitoring station in the Midlothian area
that measured lead in the 1980s was located
on the roof of Midlothian City Hall. From
1981 to 1983, 24-hour average samples
were collected every sixth day, following
standard sampling frequencies applied
throughout Texas and the United States. The
highest 3-month rolling average lead
concentration at this site was 0.237 μg/m3.
This 3-month average occurred in OctoberNovember-December, 1981. Therefore, the
highest quarterly average lead concentration
at this station was below the health-based
NAAQS that was active at the time (1.5
μg/m3) but higher than the current version
(0.l5 μg/m3).
EPA’s Lead Air Quality Standards
EPA issued its first health-based NAAQS
for lead in 1978. That standard required
that ambient air concentrations of lead
averaged over a calendar quarter must not
3
exceed 1.5 μg/m . This standard is based
on lead in air samples for total suspended
particulate (TSP) matter.
In 2008, EPA issued a new NAAQS for
lead, based on a more current healtheffects review. The 2008 standard requires
lead concentrations for any 3-month rolling
3
average not to exceed 0.15 μg/m . The
new standard still applies to lead in TSP;
however, monitoring for lead in other
particle sizes is permitted in some
circumstances when assessing compliance
with the standard. TCEQ requires lead
levels to meet EPA’s standards.
However, the Midlothian City Hall
Note: The WHO health guideline for lead is
monitoring station is not located directly
3
0.5 μg/m based on annual average
downwind from the largest industrial lead
concentrations (WHO, 2000). This
emission source in the area (Gerdau
document uses EPA’s health-based
Ameristeel). In fact, winds in this area rarely NAAQS for evaluating lead concentrations,
because that value is more health
blow from the southwest to the northeast,
protective.
which suggests that measurements at
Midlothian City Hall likely do not reflect
the highest air quality impacts associated with the local industrial emission sources.
ATSDR compared measurements from Midlothian City Hall with other measurements
statewide, which were made in 1981 by the Texas Air Control Board and other agencies.
To do so, ATSDR accessed all lead monitoring data archived on TCEQ’s Texas Air
Monitoring Information System (TCEQ, 2012). In 1981, ambient air monitoring for lead
occurred at more than 100 sites statewide. This monitoring was conducted using
consistent methods, and 89 of these sites had a sufficient number of samples to calculate
quarterly average concentrations.3 Across these 89 sites, the highest quarterly average
lead concentration ranged from 0.04 to 1.96 μg/m3. Further, the highest quarterly average
concentration at Midlothian City Hall (0.23 μg/m3) ranked 45th of the 89 stations
considered for this analysis, which included a mix of stations in urban, suburban, and
rural locations.
Considered together, these factors suggest that the lead levels measured in 1981 and 1983
do not capture the greatest air quality impacts from nearby industrial sources, but instead
reflect contributions from sources common to populated areas. Emissions from mobile
sources likely were a major contributor to the lead levels measured at Midlothian City
Hall. Although the United States began phasing out use of lead additives in gasoline in
3
For purposes of this evaluation, ATSDR considered only those monitoring sites that had at least 10 valid 24-hour
average samples per calendar quarter.
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the late 1970s, these additives continued to be used into the 1990s, and mobile sources
accounted for most of the nation’s lead emissions up through 1990 (EPA, 2006a).
Lead data from the 1990s. As Table 3 indicates, five ambient air monitoring stations in
the Midlothian area measured airborne lead levels at some time during the 1990s. Some
of the stations measured lead in TSP, but others measured lead in particulate matter with
aerodynamic diameter of 10 microns or less (PM10). Total suspended particles are
considered inhalable—meaning there can be exposure via inhalation and by ingestion
when cilia remove lead from lung (thorax) and the lead is subsequently swallowed and
ingested. This smaller particle size fraction is often applied in air quality studies because
PM10 is commonly viewed as “respirable” particles—those that tend to pass through the
nose and mouth and enter the lungs. ATSDR reviews the two types of measurements
separately.
The Gerdau Ameristeel site that measured lead in TSP was located at 2060 South
Highway 67. As Figure 1 shows, this site is located directly north of the Gerdau
Ameristeel facility. At this site, 24-hour average samples were collected every sixth day,
and 319 valid lead sampling results are available from January 1993 to August 1998.
Data are available for 23 consecutive calendar quarters. None of the quarterly average
concentrations exceeded EPA’s health-based NAAQS at the time (1.5 μg/m3). However,
18 of the 23 quarterly average concentrations are greater than EPA’s current standard
(0.15 μg/m3). The highest average lead concentration for any calendar quarter was 0.443
μg/m3, and this was observed for the months of April, May, and June in 1995. This site
also recorded some of the highest quarterly average concentrations of lead in the state.
For example, according to the Texas Air Monitoring Information System, 35 lead
monitoring stations operated statewide in 1993. That year, the highest quarterly average
lead concentration at the Gerdau Ameristeel site was 0.239 μg/m3, and only one other
monitoring station in the state had higher quarterly average lead concentrations (TCEQ,
2012). The measurements at this site occurred during 1993 –1998, after Gerdau
Ameristeel’s emissions had decreased considerably from their highest levels on record
(see Table 2). Therefore, this monitoring station likely did not capture the facility’s
highest air quality impacts. Annual average lead concentrations detected at the Gerdau
Ameristeel monitor during this timeframe are as follows:
1993
1994
1995
1996
1997
1998
0.239 μg/m3
0.176 μg/m3
0.251 μg/m3
0.205 μg/m3
0.197 μg/m3
0.192 μg/m3 (based on samples taken from January through August)
As Table 3 shows, four other lead monitoring stations operated in the 1990s. These
stations were located throughout the Midlothian area and measured lead in PM10 in the
1991–1993 period. During this time, the highest average lead concentrations were at the
monitoring station (Cement Valley Road) closest to and downwind from the Gerdau
Ameristeel facility; lower concentrations occurred at the other three stations. The highest
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quarterly average lead concentration (0.035 μg/m3) observed across all four stations is
lower than EPA’s current and former health-based lead standards, but the measured
concentrations were in the PM10 size fraction, and the health standard is based on the TSP
size fraction. However, a recent statistical analysis conducted by EPA indicates that, on
average, lead concentrations in TSP are usually no more than twice as high as lead
concentrations in PM10.4 Applying this result to Midlothian suggests that airborne lead
levels at these four monitoring stations were not above the level of the current healthbased standard; however, we do not know what the levels were before monitoring began.
In summary, quarterly average lead concentrations immediately north of Gerdau
Ameristeel exceeded EPA’s current health-based standard, but not the standard in place
at that time, throughout much of the 1990s, but the available data suggest that this was a
highly localized effect. ATSDR’s modeling analysis (see Appendix A) also confirms that
air quality impacts from Gerdau Ameristeel would decrease rapidly with downwind
distance.
Lead data from the 2000s. Table 3 lists the ten monitoring sites that measured ambient air
concentrations of lead since 2000. The monitoring data from these sites continue to
exhibit the same spatial variations; lead levels are highest at locations immediately
downwind from Gerdau Ameristeel. TCEQ’s recent air quality study in Midlothian found
that lead levels at the Wyatt Road monitoring station were higher than at the three other
fixed stations considered in that program, a finding that was statistically significant
(TCEQ, 2010d). However, the magnitude of the lead concentrations during this period
was considerably lower than what was observed in earlier years. The highest quarterly
average lead concentration during this period was 0.026 μg/m3 in PM10. Based on the
statistical analysis previously cited, such lead levels in PM10 are almost certainly lower
than EPA’s current health-based standard for lead in TSP.
Overall, the data presented in this section highlight important spatial and temporal
variations for airborne lead levels in Midlothian. Spatially, the highest lead
concentrations were observed at the monitoring station closest to Gerdau Ameristeel—the
facility with the highest lead emissions in the Midlothian area (see Table 2). Temporally,
the highest ambient air concentrations of lead were observed in the mid- to late-1990s,
but even higher lead concentrations likely occurred during earlier years, when emissions
from Gerdau Ameristeel were higher.
Considering that lead was detected at the Gerdau Ameristeel monitoring station for the
years 1993–1998 above the current EPA standard, lead will be further evaluated in the
Public Health Implications Section below.
4
When EPA proposed the current health-based standard for lead, agency officials conducted a statistical analysis of
the relative amounts of lead in PM10 and TSP. This was done by obtaining monitoring data from all sites nationwide
that concurrently measured both lead in PM10 and lead in TSP. EPA’s statistical analysis of the data from these 23
sites found that the average concentration of lead in TSP was never more than twice the average concentration of
lead in PM10 (EPA, 2008b).
Midlothian Area Air Quality—Assessing the Public Health Implications of the Criteria
(NAAQS) Air Pollutants and Hydrogen Sulfide Health Consultation Public Comment Release
3.3. Nitrogen Dioxide
Nitrogen oxides are a group of nitrogen-containing pollutants typically found in urban air.
Nitrogen dioxide accounts for most nitrogen oxides and is the pollutant for which EPA has
developed its health-based NAAQS. Most airborne nitrogen oxides come from combustionrelated sources, including mobile sources, industrial sources, and electricity generating facilities.
Cement manufacturing facilities and steel mills are known to emit nitrogen oxides.
Table 4 presents nitrogen oxides emissions data available from TCEQ’s Point Source Emissions
Inventory (PSEI) for the four Midlothian facilities from 1990 to 2010. These four facilities have
consistently had the highest nitrogen oxides emissions among the industrial facilities in Ellis
County. The emissions also rank high among the industrial facilities statewide. For example, in
2005, the PSEI contains nitrogen oxides emissions for more than 1,600 facilities in Texas. In that
year, emissions from the Midlothian facilities ranked 14th (Holcim), 19th (TXI Operations), 38th
(Ash Grove Cement), and 195th (Gerdau Ameristeel) when compared with other facilities across
the state.
Other emissions trends are evident from Table 4. For instance, the highest nitrogen oxides
emissions in any given year in the Midlothian area were from Ash Grove Cement, Holcim, or
TXI Operations; emissions from Gerdau Ameristeel were considerably lower. Across all four
facilities, the years with the highest total emissions were 1994 to 2005. Of the 20 inventory years
shown in Table 4, 2009 and 2010 had the lowest combined nitrogen oxides emissions . The
decreased emissions in these years is consistent with the trend for carbon monoxide emissions
and again likely results from a decline in production in the cement manufacturing industry that
occurred during this same time (USGS, 2011).
Table 5 summarizes the ambient air monitoring data collected for nitrogen dioxide in the
Midlothian area, and Figure 2 shows where the monitors were located. ATSDR’s first Health
Consultation for this site concluded that these data were collected with scientifically defensible
methods and met standard data quality objectives (ATSDR, 2012a). Continuous monitors operate
at these sites and output a series of 1-hour average concentrations from which annual average
concentrations can be calculated. As Table 5 shows, the annual average nitrogen dioxide
concentrations at the three stations of interest ranged from 4.50 to 10.87 parts per billion (ppb).
These values are lower than 53 ppb, which is EPA’s health-based standard, and TCEQ has
adopted the same standard. The range of annual average concentrations measured in Midlothian
(4.50 to 10.87 ppb) is also lower than 21 ppb—the corresponding health guideline published by
WHO (WHO, 2006). Similarly, the highest 1-hour average concentration measured during this
time was 78.61 ppb. EPA’s health-based standard for 1-hour average concentrations is 100 ppb,
based on the 98th percentile concentration averaged over 3 consecutive calendar years; TCEQ has
adopted this standard. The measured 1-hour average levels are also lower than the WHO health
guideline for 1-hour concentrations (106 ppb). Therefore, all short-term and long-term nitrogen
dioxide concentrations measured in the Midlothian area were lower than current air quality
standards and within health guidelines.
These observations are notable because the monitoring data span the years 2000 to 2011, which
include many years when the combined emissions from the four facilities were highest. Further,
two of these monitoring stations were located in residential neighborhoods immediately
24
Midlothian Area Air Quality—Assessing the Public Health Implications of the Criteria
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downwind from the Gerdau Ameristeel and TXI Operations facilities. These stations are
therefore expected to provide a reasonable indication of the highest exposures that might have
occurred during 1990–2011. Inferences about air quality impacts before 1990 are difficult to
make without information on nitrogen dioxide emission rates for these years.
Based on the above analyses, ATSDR will not further evaluate nitrogen dioxide exposures in
the Public Health Implications Section below.
3.4. Ozone
Ozone is commonly found in urban air pollution. Ozone levels are typically highest during the
afternoon of the summer months, when the influence of direct sunlight is the greatest. The
Midlothian facilities do not release ozone directly into the air. Rather, ozone forms in air when
emissions of nitrogen oxides and volatile organic compounds mix together and react with
sunlight. Although the Midlothian facilities emit these pollutants (e.g., see Table 4), mobile
sources and numerous other industrial sources throughout the area also contribute to the local
ozone air quality issues.
Ellis County, where Midlothian is located, is one of 11 counties that together constitute the
Dallas–Fort Worth ozone non-attainment area. This designation means that airborne ozone levels
in these counties do not meet, or are expected not to meet, EPA’s health-based air quality
standard for this pollutant. The current version of EPA’s standard is 0.075 ppm for 8-hour
average ozone concentrations, and compliance with the standard is calculated based on statistical
analyses of three consecutive years of measurements. TCEQ has adopted the EPA health-based
standard, and WHO has established a health guideline of 0.05 ppm for 8-hour average ozone
concentrations (WHO, 2006). The measured concentrations of ozone throughout the
metropolitan area have occasionally exceeded all of these levels.
The Dallas-Fort Worth metropolitan area has not met EPA’s ozone standards for approximately
20 years, although EPA has revised the standard multiple times during this time. TCEQ monitors
ozone throughout this area and has operated two ozone monitoring stations in the vicinity of
Midlothian (see Figure 3): the Midlothian Tower site monitored ozone from 1997 to 2007, and
the Old Fort Worth Road site monitored ozone from 2006 to 2011. The Midlothian Tower site
recorded ozone concentrations above the level of the NAAQS for several years (TCEQ, 2011b),
and the Old Fort Worth Road site has been measuring ozone concentrations close to the level of
the NAAQS. Based on the data from both monitors, from August 1997 to September 2011, the
8-hour EPA ozone standard has been exceeded 236 times. The range of maximum 8-hours
values at the Midlothian Tower station during 1997–2007 was 78–120 ppb, and the range at the
Old Fort Worth Road station was 75–96 ppb. The levels above the standard tended to be highest
during May through September, although April and October have also had 8-hour periods above
the standard.
Some additional observations regarding ozone in the Midlothian area deserve mention. First, the
ozone air quality issues in the Dallas-Fort Worth area are not unique; the area is one of many
metropolitan areas nationwide that does not meet EPA’s ozone standard. EPA has recently
estimated that more than 100 million people nationwide live in areas that do not meet the
agency’s health-based ozone standard (EPA, 2010d). Second, the ozone issues near Midlothian
25
Midlothian Area Air Quality—Assessing the Public Health Implications of the Criteria
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cannot be attributed to a single emissions source. Emissions from the Midlothian facilities
certainly contribute to the ozone found throughout the metropolitan area, as do emissions from
industrial sources, motor vehicles, and natural sources over a broad geographic region. For
example, planning documents suggest that total nitrogen oxides emissions throughout the DallasFort Worth non-attainment area were 519 tons per day in 2006 (TCEQ, 2011b); however, the
combined emissions of nitrogen oxides across all four Midlothian facilities in 2006 (see Table 4)
was approximately 25 tons per day—less than 5 % of the areawide nitrogen oxides emissions.
For these and other reasons, this Health Consultation addresses ozone as a general air quality
issue that is only partly affected by emissions from the Midlothian facilities and will be further
evaluated in the Public Health Implications Section below.
3.5 Particulate Matter
Particulate matter (PM), which refers to airborne droplets and particles, comes from many
sources, including wind-blown dust, other natural sources, and manmade sources. For more than
30 years, various government agencies have regulated air concentrations of PM, and those
regulations have been based on a scientific understanding of how different sizes of PM affect
human health. The text box (see next page) explains how EPA regulations have changed over the
years and documents the current WHO PM health guidelines. The remainder of this section is
organized by the three PM size fractions most often used when evaluating outdoor air quality.
3.4.1. Total Suspended Particulates (TSP)
Ambient air monitoring for TSP occurred at one place in Midlothian. During May 1981–
December 1984, the 24-hour average TSP samples were collected once every 6 days at the
monitoring station located on the rooftop of Midlothian City Hall (see Figure 4). During this
time, the highest individual 24-hour measurement was 194 µg/m3, which is below EPA’s healthbased standard at the time. The highest annual average TSP concentration at this location (86.3
µg/m3) occurred in 1982. This concentration was higher than EPA’s health-based standard at the
time, and ranked high among annual average TSP levels observed statewide. Specifically, in
1982, nearly 150 TSP monitoring stations collected enough data to calculate annual average
concentrations, and the value observed at Midlothian City Hall ranked 22nd among these sites
(TCEQ, 2012).5 The extent to which emissions from the Midlothian facilities contributed to these
measured concentrations is unclear, especially considering that the prevailing wind direction in
the area would not have blown emissions from the facilities to this monitor. Another
complication is that TSP includes larger particles of natural origin (e.g., wind-blown dust), which
typically do not factor as much into the finer particle sizes. Since the scientific community
currently believes that PM2.5 and PM10 are better indicators of exposure to particles than TSP and
that the former TSP monitoring station was not located where facility emissions would likely
have the greatest impact, the majority of this evaluation focuses on PM10 and PM2.5—the size
fractions that currently have health-based standards. Based on the above information, TSP
exposures during 1981–1984 will not be further evaluated in the Public Health Implications
Section below.
5
This comparison was based on all sites documented in TCEQ’s TAMIS database that had at least 40 valid 24-hour
average TSP measurements during calendar year 1982.
26
Midlothian Area Air Quality—Assessing the Public Health Implications of the Criteria
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PM: Particle Size and Public Health
For more than 30 years, EPA has regulated airborne concentrations of PM. Health studies have
documented that the size of airborne particles is related to types of adverse health effect. This Health
Consultation classifies emissions and air concentrations of PM according to their size, using the following
three categories:
Total suspended particulate (TSP). EPA issued its first health-based air quality standards for PM in
1971, and the health-based standard required that annual average concentrations of TSP not exceed 75
3
3
µg/m and that 24-hour average concentrations not exceed 260 µg/m more than once per year. TSP
includes particles up to approximately 40 microns in diameter.
Particulate matter smaller than 10 microns (PM10). PM10 is the subset of TSP composed of particles
and droplets with aerodynamic diameters of 10 microns or less—a diameter much smaller than that of
human hair. Regulators began focusing on PM10 because research started to indicate that these
particles were more likely to pass through the nose and mouth and enter the lungs. In other words, these
particles were respirable. In 1987, EPA’s health-based air quality standards shifted focus from TSP to
PM10. At the time, EPA issued standards based on annual average and 24-hour average PM10
concentrations. However, the agency recently revoked the annual standard, and only the short-term
3
standard remains: 24-hour average PM10 concentrations are not to exceed 150 µg/m more than once
per year (on average) over a 3-year period. WHO’s health guidelines are much lower: the annual
3
3
average health guideline for PM10 is 20 µg/m , and the 24-hour health guideline for PM10 is 50 µg/m .
Particulate matter smaller than 2.5 microns (PM2.5). PM2.5—or “fine particulate”—is the subset of TSP
composed of particles and droplets with aerodynamic diameters of 2.5 microns or less. By definition,
PM2.5 is also a subset of PM10. EPA started regulating air concentrations of PM2.5 in 1997, after research
demonstrated that exposure to these smaller particles can be associated with a range of adverse health
effects (see Section 4). EPA’s health-based standards require that annual average concentrations of
3
th
PM2.5, averaged over three consecutive calendar years, do not exceed 15 µg/m . Further, the 98
percentile of 24-hour average PM2.5 concentrations, averaged over three consecutive calendar years,
3
must not exceed 35 µg/m . WHO’s health guidelines for PM2.5 are even lower: the annual average health
3
3
guideline is10 µg/m , and the 24-hour health guideline is 25 µg/m .
3.4.2. Particulate Matter Smaller than 10 Microns (PM10)
Table 6 presents PM10 emissions data available from TCEQ’s Point Source Emissions Inventory
(PSEI) for the four Midlothian facilities from 1990 to 2010. The PM10 emissions listed for these
facilities have consistently ranked among the highest for industrial facilities in Ellis County. The
emissions also rank high among industrial sources statewide. In 2005, the PSEI contains PM10
emissions data for more than 1,600 facilities in Texas. In that year, emissions from the
Midlothian facilities ranked 43rd (Holcim), 44th (TXI Operations), 53rd (Ash Grove Cement), and
91st (Gerdau Ameristeel) when compared with the other facilities across the state. Since 1995,
estimated annual PM10 emissions from the three cement manufacturing facilities were always
higher than those from Gerdau Ameristeel. During that time, the highest PM10 emissions across
all four facilities occurred during 1996– 2002—years when air monitoring also occurred; the
lowest PM10 emissions from the cement manufacturing facilities occurred in 2009 and 2010,
consistent with the timing of an industry-wide decline in production (USGS, 2011).
27
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As Figure 5 shows, PM10 monitoring has occurred at 13 locations in the immediate vicinity of
the Midlothian facilities. These sites operated at different periods during 1991– 2004. No PM10
monitoring data was identified for earlier years, which most likely indicates that air pollution
levels of this pollutant were not regulated at the federal level until 1987. ATSDR’s first Health
Consultation for this site concluded that these data were collected with scientifically defensible
methods and met standard data quality objectives (ATSDR, 2012a). All sites employed the same
sampling schedule: 24-hour average samples were collected every sixth day. Across all sites,
more than 2,500 valid sampling results are available for review. The following paragraphs and
Tables 7 and 8 summarize these monitoring data for annual and 24-hour averaging periods:
Annual average concentrations. As Table 7 shows, the highest annual average PM10
concentration observed across all 13 monitoring locations was 50.8 μg/ m3, which is
marginally higher than the level of EPA’s former health-based NAAQS.6 This former
standard was withdrawn by EPA because new scientific information indicated that it was
not a good indicator of long-term health effects from PM exposures (EPA, 2006a). This
highest annual average was based on data from the Gerdau Ameristeel monitor from
1996. The annual average levels for 1997 and 1998 from this same station were 48.1 and
50.2 μg/m3, respectively, which are above or close to the former EPA PM10 annual
average standard. All but one of these monitoring locations had at least one annual
average PM10 concentration higher than the WHO health guideline. However, it is not
uncommon for PM10 levels to exceed 20 μg/m3. A recent EPA study evaluated air quality
trends at more than 2,000 ambient air monitoring stations and found that more than half
of these stations had annual average concentrations greater than 20 μg/m3 (EPA, 2009).
Another important insight comes from Table 8, which indicates that, except for the
immediate vicinity north of the Gerdau Ameristeel fenceline, annual average PM10
concentrations upwind from the Midlothian facilities did not differ from PM10
concentrations downwind from Gerdau Ameristeel and TXI Operations. This observation
suggests that many sources contribute to the PM10 levels in the area. Furthermore, the
following data suggest that the highest PM10 levels were likely localized in an area just
north of the Gerdau Ameristeel fence line (which is consistent with ATSDR’s modeling
results):
Annual Average PM10 (μg/m3), 1996–1998
Station
1996
1997
1998
Gerdau Ameristeel
Old Fort Worth Road
Midlothian Tower
Tayman Drive Treament Plant
50.8
20.9
22.0
21.9
48.1
19.9
21.4
No data
50.2
24.9
26.0
No data
24-Hour average concentrations. Across all 13 monitoring stations, more than 2,500
PM10 measurements were collected during 1991–2004. The highest 24-hour average
6
The former NAAQS was based on annual arithmetic mean concentrations, averaged over 3 consecutive calendar
years. Although the highest annual average concentration for a single calendar year at the Gerdau Ameristeel site
was greater than 50 μg/m3, none of the arithmetic mean concentrations averaged over 3 consecutive calendar years
exceeded this value.
Midlothian Area Air Quality—Assessing the Public Health Implications of the Criteria
(NAAQS) Air Pollutants and Hydrogen Sulfide Health Consultation Public Comment Release
PM10 concentration recorded to date (127 µg/m3) occurred at the monitoring station
directly downwind from Gerdau Ameristeel. The highest 24-hour average levels at nearly
every station were greater than the corresponding WHO health guideline (50 µg/m3), but
this level is not uncommon for monitoring stations in Texas and other arid environments.
To determine whether PM10 concentrations were higher on days when sampling was not
conducted or to quantify how high those concentrations might have been is impossible.
Most of the data summarized in Tables 7 and 8 suggest that PM10 concentrations measured in the
Midlothian area meet EPA’s current and former health-based standards, but are greater than
WHO’s health guidelines, which are highly protective. Further, annual average PM10
concentrations did not vary considerably between locations upwind and downwind from Gerdau
Ameristeel and TXI Operations except for the immediate vicinity north of the Gerdau Ameristeel
fenceline. Although annual average PM10 levels numerically exceeded the EPA’s former healthbased standard for 2 years at the monitoring station located just north of Gerdau Ameristeel (the
standard was not exceeded as defined by EPA), the available data suggest that this was a highly
localized effect. ATSDR’s modeling analysis (see Appendix A) also confirms that air quality
impacts from Gerdau Ameristeel would decrease rapidly with downwind distance. Inferences
about PM10 levels before1990 are difficult to make because of the lack of emissions and ambient
air monitoring data for those years. Possible exposures to fine particulate matter, based on
measured and estimated levels from measured PM2.5, are discussed below.
Based on the above analysis, ATSDR will further evaluate long-term PM10 exposures (as a
proxy for PM2.5) in the immediate vicinity north of the Gerdau Ameristeel fenceline in the
Public Health Implications Section below.
3.5.3 Particulate Matter Smaller than 2.5 Microns (PM2.5)
Table 9 presents PM2.5 emissions data available from TCEQ’s Point Source Emissions Inventory
(PSEI) for the four Midlothian facilities. Unlike other pollutants, which had extensive emissions
data documented back to 1990, the available PM2.5 emissions data is complete from only 2000 to
2010. The lack of emissions data for earlier years most likely reflects that federal regulation of
PM2.5 air concentrations was not implemented until 1997. Consistent with the other pollutants
discussed earlier, the estimated annual PM2.5 emissions listed for these facilities are among the
highest for Ellis County and also rank high among industrial sources statewide. In 2005, the
PSEI contains PM2.5 emissions data for more than 1,500 facilities in Texas. In that year,
emissions from the Midlothian facilities ranked 25th (Holcim), 33rd (Ash Grove Cement), 57th
(Gerdau Ameristeel), and 58th (TXI Operations) when compared with the other facilities across
the state. During 2000–2008, the total PM2.5 emissions across the four facilities did not change
considerably. However, the total PM2.5 emissions decreased in 2009 and 2010.
As Figure 6 shows, PM2.5 monitoring has occurred at four locations in the immediate vicinity of
the Midlothian facilities. These sites operated at different periods during 2000–2011. Two
different monitoring methods are used at these sites: some collect 24-hour average samples every
sixth day, and others operate continuously with real-time measured concentrations recorded
every hour. ATSDR’s first Health Consultation for this site concluded that these data were
collected with scientifically defensible methods and met standard data quality objectives;
however, a slight negative bias was noted in the continuous PM2.5 monitoring data (ATSDR,
29
Midlothian Area Air Quality—Assessing the Public Health Implications of the Criteria
(NAAQS) Air Pollutants and Hydrogen Sulfide Health Consultation Public Comment Release
2012a). The following paragraphs and Table 10 summarize these monitoring data for two
averaging periods:
Annual average concentrations. The scientific community now believes that the current
standard (15 µg/m3) for fine PM (measured by PM2.5) is a better indicator of possible long-term
health effects from PM exposures than was the former EPA annual average standard for PM10
(EPA, 2006b). As Table 10 shows, the highest full year annual average PM2.5 concentration
observed across all four monitoring locations was 11.9 µg/m3(except for a partial-year value of
12.4 µg/m3 at Midlothian Tower in 2005), which is lower than EPA’s current standard and
proposed range of 12–13 µg/m3 for a lowered standard (EPA, 2012d). The highest annual
average concentration in Midlothian was observed at the Wyatt Road site that operated a
continuous monitor. In ATSDR’s first Health Consultation (ATSDR, 2012a), a negative bias
was identified in data from continuous monitors versus data from 24-hour monitors at the TCEQ
monitors located on Old Fort Worth Road. TCEQ had previously identified this concern and
began adjusting all its continuous monitoring data by 2 µg/m3 in 2005 (Personal Communication,
Tracie Phillips, TCEQ, 9/27/2012). To be consistent with this approach, ATSDR adjusted all
TCEQ continuous monitoring data before 2005 by this same value. ATSDR is uncertain about
the magnitude of the negative bias for the Holcim continuous monitoring data, which was not
operated by TCEQ, because these data were not adjusted (Personal Communication, Kate Gross,
Trinity Consultants, 10/5/12). If the Holcim data are adjusted in the same manner as the TCEQ
data, these would represent the highest measured annual average PM2.5 levels detected in
Midlothian and be in the range proposed by EPA for lowering the PM2.5 annual average standard.
Moreover, many of the annual average PM2.5 concentrations in Table 10 were above the more
conservative WHO health guideline (10 µg/m3). Exposures downwind of Ash Grove are
uncertain because we do not have any monitoring data. In addition, ATSDR is uncertain
whether harmful exposures actually occurred downwind of Holcim because of the potential
negative data bias (discussed above) and because the monitor is located at the fence line in a
sparsely populated area. Table 10 also documents that the highest annual average PM2.5
concentrations were nearly identical across the four monitoring stations, which included stations
south of TXI Operations and north of Holcim, indicating some regional contributions.
ATSDR evaluated concurrent PM10 and PM2.5 data from the Midlothian area and determined that
the long-term ratio of PM2.5 to PM10 ranged from about 0.47 to 0.52. Given this, we estimated
that annual average PM2.5 levels in the vicinity of the Gerdau Ameristeel monitor, from 1996 to
1998, could have ranged from about 22.6 to 26.4 µg/m3, which is above both the current and
proposed EPA standard. Using EPA’s approach, the 3-year average level might have been above
the NAAQS standard of 15 µg/m3 for these years in the vicinity of the Gerdau Ameristeel
monitor. Applying this same approach to annual average PM10 data from other monitors suggests
that PM2.5 levels could have been close to the current and proposed PM2.5 standard, especially for
the Wyatt Road, Old Fort Worth Road, Gorman Road, and Midlothian Tower monitors.
However, ATSDR is uncertain whether these estimated levels could have resulted in harmful
exposures because we do not have measured PM2.5 data and our estimates were close to the
current or proposed EPA standard.
For these reasons, long-term exposures to PM2.5, in a localized area north of the Gerdau fence
line during 1996–1998 will be further evaluated in the Public Health Implications Section
below.
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Midlothian Area Air Quality—Assessing the Public Health Implications of the Criteria
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24-hour average concentrations. Across all four monitoring stations, the highest 24-hour average
PM2.5 concentration recorded to date (52.1 µg/m3) occurred at the Wyatt Road monitoring
station, which is downwind from Gerdau Ameristeel and TXI Operations. All four monitoring
stations recorded at least one 24-hour average concentration greater than the level of EPA’s
health-based standard (35 µg/m3). Because of the possible negative bias in data from the
continuous PM2.5 monitors, a level above the standard or even higher may have occurred on
additional days; however, ATSDR cannot determine how many days or what the highest levels
could have been. Although EPA scientific staff concluded that consideration should be given to
revising the current annual average PM2.5 standard of 15 µg/m3, they also concluded that support
for revising the current 24-hour PM2.5 standard level (EPA, 2011b) is limited.
Based on the highest concentrations on record from all monitoring stations (Table 10), the EPA
24-hour average health-based standard was exceeded infrequently (about 22 times during 2000–
2011, and several of these high concentrations occurred on the same day at different monitors).
Several of these levels slightly exceeded the standard. It is important to note that although the
standard was exceeded several times on a numerical basis, it did not exceed the standard as
defined by EPA. Based on this analysis, short-term exposures to PM2.5 will be further
evaluated in the Public Health Implications Section in relation to the overall air exposures to
the community.
ATSDR’s previous health consultation noted a data gap which primarily relates to particulate
matter. The monitoring that has been conducted in Midlothian clearly does not characterize air
pollution levels at every single residential location over the entire history of facility operations.
In ATSDR’s judgment, one notable gap in monitor placement is the lack of monitoring data for
residential neighborhoods in immediate proximity to the four industrial facilities, where fugitive
emissions (those not accounted for in stack emissions) likely have the greatest air quality
impacts. Current and past monitoring locations might not adequately characterize particulate
matter levels for all residents located immediately adjacent to certain onsite operations, such as
limestone quarry activity (ATSDR 2012a). In addition, as stated above, another important data
and information gap is in our understanding of PM2.5 exposures downwind of the Ash Grove and
Holcim facilities.
3.5. Sulfur Dioxide
Sulfur dioxide is a gas formed when fuels containing sulfur (e.g., coal) are burned, and during
metal smelting and other industrial processes. On a national level, manmade sulfur dioxide
emissions are dominated by contributions from fuel combustion at electricity-generating
facilities and other industrial sources; fuel combustion in mobile sources accounts for smaller
amounts (EPA, 2008a). Cement manufacturing facilities and steel mills are both known to emit
sulfur dioxide.
Table 11 presents sulfur dioxide emissions data available from TCEQ’s Point Source Emissions
Inventory (PSEI) for the four Midlothian facilities from 1990 to 2010. The three cement
manufacturing facilities have consistently had the highest sulfur dioxide emissions among the
industrial facilities in Ellis County. Emissions from these three facilities also have ranked high
among the industrial facilities statewide. For example, in 2005, the PSEI contains sulfur dioxide
emissions data for approximately 1,400 facilities in Texas. In that year, emissions from the
31
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cement manufacturing facilities in Midlothian ranked 22nd (Ash Grove Cement), 31st (TXI
Operations), and 34th (Holcim) when compared with the other facilities across the state. In that
year, sulfur dioxide emissions from Gerdau Ameristeel did not rank among the top 100 facilities
statewide.
Other trends are evident from Table 11. For instance, in any given year, the three cement
manufacturing facilities accounted for at least 98 % of the sulfur dioxide emissions across all
four facilities combined; Gerdau Ameristeel always accounted for less than 2 %. Before 2000,
TXI Operations tended to have the highest sulfur dioxide emissions, but since that time the
highest values were reported for Ash Grove Cement. Finally, of the 20 inventory years shown in
Table 11, the years with the lowest sulfur dioxide emissions combined across all four facilities
were 2009 and 2010—a trend consistent with the emissions data reported in this section for other
pollutants.
Tables 12 and 13 summarize the ambient air monitoring data collected for sulfur dioxide in the
Midlothian area. ATSDR’s first Health Consultation for this site concluded that these data were
collected with scientifically defensible methods and met standard data quality objectives
(ATSDR, 2012a). As Figure 7 shows, sulfur dioxide monitoring has occurred at four locations.
Continuous monitors operate at these sites and provide 1-hour average concentrations, from
which concentrations can be calculated for different averaging periods. These monitors can
provide data for averaging times as short as 5-minutes. The EPA does not have a standard for
this short averaging time, but the WHO has a 10-minute guideline of 200 ppb (WHO, 2006).
This section focuses on data from the three stations with at least 1 full calendar year of data.7
ATSDR evaluated summary statistics for three different averaging periods:
Annual average concentrations. The highest annual average sulfur dioxide concentration
measured was 5.47 ppb. This occurred in 2000 at the Old Fort Worth Road monitoring
station, located downwind from the stacks at TXI Operations. From 1971 to 2010, EPA’s
health-based NAAQS for annual average sulfur dioxide concentrations was 30 ppb.
However, that standard was revoked in 2010, following EPA’s most recent health effects
review of long-term exposures to sulfur dioxide (EPA, 2008c). The purpose of including
annual average concentrations in this Health Consultation is to indicate how air quality
impacts changed over time. As Table 12 shows, annual average sulfur dioxide
concentrations were typically higher at locations downwind from TXI Operations, as
compared with the upwind monitoring location. Further, the highest annual averages
occurred during 1999–2001, when emissions from TXI Operations were high.
1-Hour average concentrations. The highest 1-hour average sulfur dioxide concentration
was 211.54 ppb in 2001 at the Old Fort Worth Road monitoring station. Before 2010,
EPA did not have a health-based air quality standard for 1-hour averages, which was then
set at 75 ppb. Specifically, for every monitoring station, the standard requires that the 99th
percentile of 1-hour daily maximum sulfur dioxide concentrations averaged over 3
consecutive years to not exceed 75 ppb. Table 13 displays these values for the Midlothian
7
In 1986, a sulfur dioxide monitoring station at Cedar Drive operated for 4 months. Sulfur dioxide was rarely
detected at the station, and the average concentrations were lower than all health-based screening levels discussed in
this section.
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data for the two stations that had at least 3 years of data. Elevated 1-hour SO2
concentrations began to increase around 5 p.m. and taper off around 6 a.m.; the highest
frequency of elevations were between 7 pm and 3 am. All months of the year have
experienced 1-hour SO2 levels above the standard; however April, May, and October
have the highest frequency, and June, August, November, and December have the lowest
frequency.
Based on EPA’s approach, Table 13 shows that the 1-hour measurements at the upwind
station (Midlothian Tower) were all lower than the 2010 EPA NAAQS value; however,
individual measurements exceeded the standard 24 times between 1997 and 2005. Shortterm average concentrations of sulfur dioxide measured at Old Fort Worth Road between
1997 and 2008 would not have met EPA’s current air quality standards, but they met the
standard at the time. The current EPA 1-hour standard was exceeded 312 times at the
Old Fort Worth Road monitor during 1997 to early 2008 and six times at the Wyatt Road
station during 2005 to early 2006. After annual sulfur dioxide emissions from TXI fell
below 2,000 tons per year, the measured concentrations were lower than EPA’s current
standard. Definitive conclusions regarding SO2 exposures north of TXI before 1997
cannot be made because of the lack of monitoring data. Exposures could have been
similar to or greater than the highest levels detected during 1997–2011 at the Old Fort
Worth Road and Wyatt Road monitors. We base this possibility on SO2 emissions from
TXI, which during 1997 to 2011were similar to or greater than the levels before 1997. In
addition, 1-hour measurements were location specific. For example, on days when the
SO2 levels exceeded the standard at the Old Fort Worth Road station, they did not exceed
it at the Midlothian Tower station (except for 1 day in March 2005). This information
suggests that elevated SO2 levels are likely from a specific source rather than a regional
effect. The number of SO2 exceedances at the Old Fort Worth Road monitor were
consistent with trends for TXI. That is, the years having the most concentrations above
the standard of 75 ppb were the same as those when TXI emissions were high.
To evaluate this trend further, we compared the hourly wind direction measurements at
the Old Forth Worth Road monitor and similar hourly SO2 measurements (see Figure 9).
The highest SO2 levels were downwind from TXI. Figure 9 also shows some minor SO2
peaks downwind from Ash Grove and Holcim. ATSDR evaluated the wind direction
during the 24 instances of exceedances of the standard at the Midlothian Tower station.
The peaks occurred almost exclusively when the wind was blowing from the main
sources at TXI (i.e., in a downwind direction from TXI). ATSDR cannot rule out a
minor contribution of SO2 from Gerdau Ameristeel to the peak levels found at the Old
Fort Worth and Midlothian Tower monitors; however, based on reported emissions data,
the main contributor is likely to be TXI.
24-Hour average concentrations. At Midlothian Tower, 24-hour average concentrations
of sulfur dioxide varied; the highest 24-hour average concentration in a given year ranged
from 11 ppb in 2007 to 25 ppb in 1997. At Old Fort Worth Road, the highest 24-hour
average levels were between 15 ppb and 49 ppb during 1997–2008, and then declined to
5 ppb and less in recent years.
Midlothian Area Air Quality—Assessing the Public Health Implications of the Criteria
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During 1971–2010, EPA’s health-based standards for sulfur dioxide included a 24-hour
average concentration of 140 ppb, not to be exceeded more than once per year. All 24
hour values in Midlothian were lower than EPA’s former standard. However, the WHO’s
health comparable guideline is 8 ppb (WHO, 2006). This value was exceeded at both the
Midlothian Tower and Old Fort Worth Road stations in most years of monitoring through
2008, but levels were below that level after 2008. The significance of this observation
will be discussed further in Section 4.
For additional context, ATSDR compared the 24-hour average concentrations of sulfur
dioxide measured in the Midlothian area with those measured elsewhere in Texas. This
comparison was done for 2 years: the year with the highest measured sulfur dioxide
concentrations (2001) and the most recent year of complete data (2010) in Midlothian. In
2001, only one of 21 other monitoring stations in Texas recorded 24-hour average sulfur
dioxide concentrations higher than those at Old Fort Worth Road (EPA, 2012a). In 2010,
28 sulfur dioxide monitoring stations in Texas were submitting data to EPA’s Air Quality
System, and 13 of those stations recorded 24-hour average concentrations higher than
those at Old Fort Worth Road. Overall, in the years 1999 to 2001, Old Fort Worth Road
ranked among the stations with the highest 24-hour average sulfur dioxide concentrations
in the state. As sulfur dioxide emissions from TXI Operations decreased in following
years, so did the measured concentrations at this station.
In summary, ambient air monitoring for sulfur dioxide in the Midlothian area has focused on
areas southwest of Midlothian, near Gerdau Ameristeel and TXI Operations. The highest
concentrations were consistently observed at the Old Fort Worth Road monitoring station, which
is located immediately downwind from TXI Operations. Sulfur dioxide levels at this station were
highest during 1997–2008 and have decreased since then—consistent with the decreasing
emissions at the TXI Operations facility. Based on the data and information above, short-term
exposures to SO2, especially downwind of the TXI operations, will be further evaluated in the
Public Health Implications Section below.
A data gap in this evaluation is the lack of sulfur dioxide monitoring data at locations north of
Midlothian. As Figure 7 shows, sulfur dioxide has never been monitored at locations
immediately downwind from the Ash Grove Cement and Holcim facilities. Of these two
facilities, Ash Grove Cement continues to have higher annual emissions and has emitted more
than 4,000 tons of sulfur dioxide in recent years (except for 2009). Another data gap is that no
inferences can be made about sulfur dioxide concentrations before 1990 because of the lack of
information on facility emissions.
3.6. Hydrogen Sulfide
Hydrogen sulfide is a gas released from many natural and manmade sources. Some industrial
sources include sewage treatment facilities, manure-handling operations, pulp and paper mills,
petroleum refineries, and food processing plants (ATSDR, 2006). Steel mills and cement
manufacturing facilities can have operations (e.g., wastewater treatment) known to release
hydrogen sulfide gases. However, these two industries are not listed among the largest emissions
sources of hydrogen sulfide documented in various recent environmental health reviews (e.g.,
ATSDR, 2006; WHO, 2003).
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Reliable estimates of hydrogen sulfide emissions from the Midlothian facilities are not available.
TCEQ’s emissions inventory has no hydrogen sulfide emissions data for the four facilities, and
TRI has only recently required industrial facilities to report releases of hydrogen sulfide. A
recent rule added hydrogen sulfide to the list of TRI chemicals, and industrial facilities that meet
the reporting thresholds will be required to disclose emissions that occurred in 2012 and
thereafter. Accordingly, the first TRI air emissions data for hydrogen sulfide will not be publicly
available until late in 2013.
Ambient air monitoring for hydrogen sulfide has occurred at four locations in the Midlothian
area (see Figure 8), at the same locations where sulfur dioxide monitoring took place. The
monitoring focused on air quality impacts southwest of Midlothian, near the Gerdau Ameristeel
and TXI Operations facilities. ATSDR’s first Health Consultation for this site concluded that the
data collected generally followed scientifically defensible methods and met data quality
objectives (ATSDR, 2012a). However, two limitations were noted: (1) monitoring results from
the Cedar Drive monitoring station are not considered because they were collected by using an
insensitive device that never detected hydrogen sulfide; and (2) monitoring results from 1997 to
1999 had a detection limit of approximately 5 to 10 ppb and therefore are not sufficient for
evaluating long-term exposures at levels comparable to EPA’s Reference Concentration of 1.4
ppb. Table 14 summarizes all remaining data, which highlight the following trends:
Annual average concentrations. The highest annual average concentration of hydrogen
sulfide was 0.60 ppb, which occurred in 2005 at the Wyatt Road monitoring station. This
value—and all other annual average concentrations shown in Table 14—is lower than
EPA’s Reference Concentration (1.4 ppb) for long-term hydrogen sulfide exposures.
ATSDR has an intermediate Minimal Risk Level (exposures from 15-364 days of 20 ppb)
but does not have a long-term or chronic MRL. Further, the data in Table 14 indicate that
annual average hydrogen sulfide concentrations were not different between upwind and
downwind monitoring stations. In some years, the monitoring station upwind from the
industrial facilities (Midlothian Tower) exhibited higher annual average concentrations
than the station downwind from these facilities. This finding is consistent with a
statement made earlier about steel mills and cement manufacturing facilities not typically
being the largest emissions sources for this pollutant.
1-Hour average concentrations. Table 14 shows that the highest 1-hour average
hydrogen sulfide concentrations were measured between 2000 and 2011. The highest
individual hourly measurement—14.4 ppb—is lower than the health-based screening
values. For short-term exposures, the most relevant screening values are ATSDR’s acute
inhalation Minimal Risk Level (70 ppb for exposure durations of less than 2 weeks),
TCEQ’s air quality standard (80 ppb averaged over a 30-minute period), and WHO’s
health guideline (106 ppb averaged over a 24-hour period).
Overall, all short-term and long-term average hydrogen sulfide concentrations recorded for the
Midlothian area have been lower than corresponding health-based air quality standards and
guidelines. Hydrogen sulfide has not been monitored in the vicinity of Ash Grove Cement or
Holcim. However, trends in the available monitoring data suggest that cement manufacturing
facilities likely have limited air quality impacts —a finding that is consistent with ATSDR’s
Midlothian Area Air Quality—Assessing the Public Health Implications of the Criteria
(NAAQS) Air Pollutants and Hydrogen Sulfide Health Consultation Public Comment Release
broad research for this pollutant. Based on the above evaluation, ATSDR will not further
evaluate hydrogen sulfide exposures in the Public Health Implications Section below.
3.7. Summary
The following paragraphs summarize the air quality data for the pollutants considered in this
Health Consultation. Refer to Section 4 for ATSDR’s public health evaluation for these
pollutants. In addition, please see Table 15 for a summary of health comparison values
considered in the above evaluation and which air pollutants are determined to be a contaminant
of concern for further evaluation in the Public Health Implications Section below.
Carbon monoxide. The estimated carbon monoxide concentrations attributed to the Midlothian
facilities are lower than EPA’s health-based standards and WHO’s health guidelines. This
finding is based on ATSDR’s modeling analysis, which considered the highest carbon monoxide
emission rates reported for the four facilities of interest during 1990–2010. No inferences can be
made about carbon monoxide levels before 1990, because of the lack of information on facility
emissions in those years. Based on the above analyses, ATSDR will not further evaluate
carbon monoxide in the Public Health Implications Section below
Lead. The highest airborne lead levels in the Midlothian area were measured downwind from
Gerdau Ameristeel—the facility that consistently had the highest lead emissions of the four
facilities of interest. Measured lead concentrations were typically greatest immediately north of
this facility. In the mid-1990s, the lead levels measured in this area ranked among the highest
lead concentrations measured statewide. This appears to be a highly localized effect, with lead
concentrations decreasing rapidly with downwind distance from the facility.
In the 1990s, measured lead concentrations immediately north of the facility were below EPA’s
health-based lead standard at the time (1.5 µg/m3), but were greater than EPA’s current standard
(0.15 µg/m3). In 18 of 23 consecutive calendar quarters with sufficient data during 1993–1998,
the quarterly average lead concentrations at the Gerdau Ameristeel monitoring station exceeded
the standard that EPA issued in 2008. The highest downwind quarterly average lead
concentration (0.443 µg/m3) was observed in 1995. No annual average measurements were
greater than WHO’s current health guideline (0.5 µg/m3). Lead emissions from Gerdau
Ameristeel were notably higher before ambient air monitoring for lead took place at locations
downwind from the facility, especially in 1987, 1988, and 1989 (see Table 2). A logical
inference is that lead concentrations downwind from the facility in those years were likely higher
than the highest level measured in the monitoring programs. Because of the lack of emissions
data available for this period, commenting on lead levels near Gerdau Ameristeel during its first
years of operation (1975-1986) is difficult.
In 1981 and 1983, quarterly average lead concentrations at Midlothian City Hall exceeded the
health-based standard that EPA issued in 2008, but did not exceed the WHO health guideline.
This most likely reflected influences from mobile sources, because numerous monitoring stations
throughout Texas exhibited comparable lead levels during the early 1980s. No inferences can be
made about lead levels before 1987, because information on facility emissions in those years is
lacking. Given that lead was detected at Gerdau Ameristeel monitoring station for the years
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1993–1998 above the current EPA standard, lead will be further evaluated in the Public
Health Implications Section below.
Nitrogen dioxide. All measured nitrogen dioxide concentrations in the Midlothian area have been
lower than EPA’s health-based standards and WHO’s health guidelines, considering both longterm (annual) and short-term (1-hour) exposure durations. The monitoring data from 2000 to
2011 and emissions data from 1990 to 2010 suggest that nitrogen dioxide levels have not
exceeded health-based standards or guidelines in residential areas dating back to 1990. No
inferences can be made about nitrogen dioxide levels before 1990, because information on
facility emissions in those years is lacking. Based on the above analyses, ATSDR will not
further evaluate nitrogen dioxide in the Public Health Implications Section below.
Ozone. Ellis County is one of 11 counties that make up the Dallas–Fort Worth ozone nonattainment area, which means that ozone levels in the metropolitan area occasionally exceed
EPA’s health-based standards. Levels in Ellis County also have been above WHO’s health
guidelines. Emissions from industrial sources, mobile sources, and natural sources throughout
the area contribute to this problem. For these and other reasons, this Health Consultation
addresses ozone as a general air quality issue that is only partly affected by emissions from the
Midlothian facilities and will be further evaluated in the Public Health Implications Section
below.
Particulate matter. Ambient air monitoring of particulate matter has occurred for many years in
Midlothian, with the particle size fraction measured—TSP, PM10, and PM2.5—changing from
one year to the next. Unlike other pollutants, which showed distinct spatial variations and peak
concentrations downwind from certain facilities, the PM concentrations were uniform across the
locations where sampling occurred except for the PM sampling that occurred at the Gerdau
Ameristeel monitor during the years 1996–1998. ATSDR’s evaluation focuses on the particle
sizes that are most likely to be inhaled (PM10 and PM2.5). The available data suggest that
measured annual average PM2.5 concentrations were all below EPA’s current health-based
standard (except for a partial year at Midlothian Tower for 2005), most were below the EPA
proposed range for lowering the standard, and many were greater than WHO’s protective health
guideline. Based on ATSDR’s estimate of PM2.5 levels from annual average PM10 data, detected
at the Gerdau Ameristeel monitor for the years 1996–1998, average PM2.5 levels could have
exceeded the current and proposed standard. None of the measured 24-hour PM10 levels were
above the EPA standard but some were above the WHO standard that is designed to protect
against harmful PM2.5 exposures.
Based on the highest concentrations on record from all monitoring stations (Table 10), the EPA
24-hour average health-based standard was exceeded infrequently (about 22 times during 2000–
2011, and several of these high concentrations occurred on the same day at different monitors).
Several of these levels slightly exceeded the standard. It is important to note that although the
standard was exceeded several times on a numerical basis, it did not exceed the standard as
defined by EPA. This finding is considerable because much of the monitoring occurred in areas
expected to have the greatest air quality impacts; therefore, the data suggest that short-term PM
exposures, especially for fine particles, were likely from a combination of regional and local
sources with an exact contribution from each uncertain. However, localized PM elevations
found north of the Gerdau Ameristeel fence line, during the years 1996–1998, were likely from
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emissions from Gerdau as a primary contributor. Additional days when the 24-hour PM2.5
standard was exceeded could have occurred, but this was not indicated from the continuous
monitors because of the negative bias found versus the 24-hour monitors (ATSDR, 2012a). As
with the other pollutants, no inferences can be made about PM concentrations for years before
1990, because available emissions and ambient air monitoring data for those times was limited.
For these reasons, ATSDR will further evaluate long-term PM10 exposures (as a proxy for
PM2.5) in the immediate vicinity north of the Gerdau Ameristeel fence line for the years 1996–
1998 and short-term exposures to PM2.5 will be further evaluated in the Public Health
Implications Section below.
Sulfur dioxide. Ambient air concentrations of sulfur dioxide were extensively measured at three
locations southwest of Midlothian during 1997–2011. The measured air quality impacts were
consistently highest at the monitoring station directly north of—and downwind from—TXI
Operations. The concentrations at this station generally tracked with the facility’s emissions: air
quality impacts were highest in years when emissions were high, and air quality impacts were
lowest after the facility’s emissions began to decrease. During 1997–2008, some 1-hour sulfur
dioxide concentrations at Old Fort Worth Road exceeded the health-based standard that EPA
implemented in 2010, but met EPA’s health-based standards that were in place at the time.
Similarly, until 2008, 24-hour average concentrations of sulfur dioxide at both the upwind and
downwind stations were above WHO’s health guideline. No inferences can be made about sulfur
dioxide levels before 1990, because of the lack of information on facility emissions in those
years. Based on the data and information above, short-term past exposures to SO2, especially
in the area downwind of the TXI and Gerdau Ameristeel operations, will be further evaluated
in the Public Health Implications Section below.
Hydrogen sulfide. All measured hydrogen sulfide concentrations in the Midlothian area have
been lower than health-based standards and guidelines published by ATSDR, EPA, TCEQ, and
WHO. This finding applies to both long-term (annual) and short-term (1-hour) exposure
durations. The concentrations measured at the monitoring station downwind from Gerdau
Ameristeel and TXI Operations were not different from those measured at the monitoring station
upwind from these facilities, suggesting that emissions from these facilities are not the primary
influence on local hydrogen sulfide levels. No quantitative data are available for assessing
hydrogen sulfide levels before 2000, because of the lack of information on facility emissions in
those years. However, the available information suggests that these facilities have minimal
impacts on local hydrogen sulfide levels—a finding that likely applies to earlier years of
operation. Based on the above analyses, ATSDR will not further evaluate hydrogen sulfide
exposures in the Public Health Implications Section below.
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4. Public Health Implications Discussion
4.1. Sulfur dioxide
EPA’s 1-hour standard of 75 ppb
is designed to protect people
from exposures to high, shortterm peaks of SO2 (from 5
minutes to 24-hour exposures).
In addition, EPA determined that
little health evidence suggests an
association between long-term
low-level exposure to SO2 and
public health effects (EPA,
2010e).
ATSDR believes that the best
data available for evaluating the
health implications of exposure
to sulfur dioxide is peak
concentrations, such as 5-minute
average measurements
(measured by TCEQ from 1997
to present). The remainder of
this section uses this averaging
period, even though EPA’s and
TCEQ’s short-term health-based
standards are based on 1-hour
average levels.
SO2 peak (5-minute)
exposure summary
Conclusions for Sulfur Dioxide
For the general population, breathing sulfur dioxide at measured
concentrations from 1997 to 2011 in the Cement Valley and in areas east
and south of the TXI facility boundary for peak (5-minute) exposures is
not expected to be harmful.
Sensitive populations (e.g., individuals with asthma) may experience
respiratory symptoms if they are exposed to peak sulfur dioxide
concentrations higher than 400 ppb, specifically during times of elevated
inhalation rates, such as while exercising. Exposures above 400 ppb
have occurred very infrequently (three times in 2005 and once in 2008
in Cement Valley and once at the Midlothian Tower monitor in 1997).
Symptoms may include coughing, wheezing, or chest tightness, and are
likely reversible. For concentrations lower than 400 ppb sulfur dioxide,
sensitive individuals at elevated inhalation rates may experience effects
such as bronchoconstriction without developing symptoms.
People with asthma, children, and older adults (65+ years) have been
identified as groups susceptible to the health problems associated with
breathing SO2. Clinical investigations and epidemiologic studies have
provided strong evidence of a causal relationship between SO2 and
respiratory diseases (morbidity) in people with asthma and more limited
epidemiologic studies have consistently reported that children and older
adults (65+ years) may be at increased risk for SO2-associated adverse
respiratory effects. Potentially susceptible groups to air pollutants
include obese individuals, those with preexisting cardiopulmonary
disease, and those with a pro-inflammatory condition such as diabetes,
but some of these relationships have not been examined specifically in
relation to SO2.
Outdoor vs. Indoor Exposures--outdoor SO2 can enter indoor settings,
primarily when residents have their windows open. No valid SO2 indoor
air monitoring data are, however, available at this site. Indoor air
concentrations likely will not exceed the peak outdoor concentrations
noted in this section, unless a resident has a substantial indoor source.
When windows are open, we expect the same conclusions presented
here for outdoor settings to apply to indoor settings.
ATSDR grouped the 5-minute peak SO2 concentrations into categories based on health endpoints
(Appendix B provides a detailed discussion and additional references). Clinical studies reported
in peer-reviewed scientific literature provided the basis for the health endpoint derivations.
ATSDR bases its public health evaluation of sulfur dioxide exposures largely on previous
clinical studies that involved recruitment of volunteers who were exposed to sulfur dioxide and
monitored for effects. These studies required informed consent and were closely monitored to
ensure they were conducted ethically. For sulfur dioxide, these clinical studies have been
conducted on healthy volunteers, including some who had mild to moderate asthma. However,
the studies did not include children or people with severe asthma or. Some people who live in
Midlothian might be more sensitive to sulfur dioxide than were the volunteers who participated
in these clinical studies. For sensitive people at increased breathing rates, effects of exposure to
SO2 concentrations below 200 ppb are uncertain because studies have not been conducted at this
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Midlothian Area Air Quality—Assessing the Public Health Implications of the Criteria
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level. In general, these clinical studies have controlled exposure conditions that include humidity
and temperature. Cold and dry air, which occurs in real-world exposure conditions, has been
reported to induce effects at lower SO2 concentrations.
People with asthma, children, and older adults (65+ years) have been identified as groups
sensitive to the health problems associated with breathing SO2 (EPA, 2010d; EPA, 2008c).
Human health studies (clinical investigations and epidemiologic studies) have provided strong
evidence of a causal relationship between SO2 and respiratory diseases (morbidity) in people
with asthma and more limited epidemiologic studies have consistently reported that children and
older adults may be at increased risk for SO2-associated adverse respiratory effects (EPA,
2010e). Potentially sensitive groups to air pollutants include obese individuals, those with
preexisting cardiopulmonary disease, and those with a pro-inflammatory condition such as
diabetes (EPA, 2008c), but some of these relationships have not been examined specifically in
relation to SO2.
Analysis of the sampling conducted during 1997–2011 resulted in the following average
exposure estimates by concentration category (see Figure 10 for a scatterplot of peak 5-minute
average SO2 data and health endpoints and Table 16 for the percentages of peak [5-minute] SO2
concentrations by monitoring station and year during 1997–2011).
Greater than (>) 400 ppb
During this period, 5-minute SO2 concentrations >400 ppb occurred only five times. Of these
five occasions, three occurred in 2005 and one in 2008 in Cement Valley and once in the area of
the Midlothian Tower in 1997. One 5-minute SO2 detections >500 ppb (Wyatt Road) and four 5
minute SO2 detections (Wyatt Road, Old Fort Worth Road, and Midlothian Tower) between 400
500 ppb also occurred. None have occurred since 2008.
Sensitive individuals, especially when at increased breathing rates, to levels above 400 ppb could
result in bronchoconstriction resulting in symptoms such as coughing, wheezing, or chest
tightness. For concentrations >500 ppb, exposure to sensitive individuals may result in more
frequent use of medication, seeking medical assistance, or cessation of physical activity. These
exposures are estimated to have occurred infrequently and were temporally and spatially limited
to the area north of TXI and Gerdau Ameristeel in the Cement Valley area.
200 ppb - 400 ppb
During this period, 129 5-minute SO2 levels between 200–400 ppb occurred at the Old Fort
Worth Road and Wyatt Road monitors; eight occurred at the Midlothian Tower.
When exposed to SO2 at this concentration range, sensitive individuals breathing at an increased
rate could have effects such as mild bronchoconstriction without experiencing symptoms such as
coughing, wheezing, or chest tightness. Affected individuals may not be aware of the
bronchoconstriction, which is estimated as mild and transient. Based on available data and
information, exposure occurred infrequently and was temporally and spatially limited primarily
to individuals living in the Cement Valley and, secondarily, those residing in the areas just east,
south, and southeast of the TXI fence line (see Figure 7).
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10 ppb - 200 ppb
Detections between 100–200 ppb SO2 were- multiple and widespread, especially in the Cement
Valley area. During this period, 2,603 5-minute SO2 measurements between 100–200 ppb
occurred at the Old Fort Worth Road and Wyatt Road monitors and 225 at the Midlothian
Tower. The 5-minute SO2 level was between ATSDR’s chronic MRL of 10 ppb and 100 ppb
was 59,820 times at Old Fort Worth Road and Wyatt Road monitors and 22,895 times at the
Midlothian Tower monitor.
In clinical studies, sensitive individuals (such as those with mild to moderate asthma) using a
mouthpiece have experienced effects when exposed to sulfur dioxide concentrations less than
200 ppb (Sheppard et al., 1981). The lowest observed adverse effect level (LOAEL) from this
study was 100 ppb. ATSDR has determined that a reasonable acute Minimal Risk Level (MRL),
based on this study, should be ten times below the LOAEL or 10 ppb. Whether exposures below
200 ppb might cause effects in sensitive individuals at increased ventilation rates under normal
environmental conditions is uncertain, given that clinical investigations have not been conducted
in free-breathing asthmatics at concentrations below 200 ppb. Individuals who lived in Cement
Valley likely experienced exposures above the LOAEL every year from 1997 to 2008 and
possibly those living east, south and southeast of the TXI facility, likely experienced exposures
above the LOAEL during 1997–2006 (except 2004). No exposures above the LOAEL were
likely during 2009–2011 in Cement Valley, and starting in 2007, not in areas south, east, and
southeast of the TXI facility boundaries (although this is somewhat uncertain because we do not
have data from the Midlothian Tower after 2007 but we base our assessment on lower TXI
emissions and the much lower levels in the Cement Valley).
4.2. Fine Particulate Matter (PM2.5)
Mortality and cardiovascular and respiratory morbidity have been associated with both short-and
long-term exposure to PM2.5 (EPA, 2009). Most measured annual average PM2.5 levels since
2000 in the Midlothian area are not above EPA’s current or proposed standard. Moreover,
ATSDR estimates that PM2.5 exposures in a localized area of Cement Valley, just north of
Gerdau Ameristeel during 1996–1998, were above the current EPA standard and might have
been about twice the proposed EPA standard. In addition, also based on ATSDR estimates of
past annual average PM2.5 levels, exposures above the EPA current or proposed standard could
have occurred occasionally for several years in the 1990s, especially among people who lived in
other areas of Cement Valley, east and south of the TXI property line, and in the Gorman Road
area. However, as stated previously, ATSDR is uncertain whether exposures above the current
or proposed EPA standard actually occurred in these areas. In addition, short-term PM2.5 levels
infrequently exceeded the current standard of 35 µg/m3 numerically during the period 2000
2011; however, as defined by EPA, short-term levels of PM2.5 in the Midlothian area have not
exceeded the current standard.
As PM health effect thresholds have not been identified, and given a substantial interpersonal
variability in exposure and subsequent harmful effects, that any standard or guideline value will
lead to complete protection for everyone against all possible adverse health effects is unlikely
(WHO, 2006). Population subgroups that may be more sensitive to the effects of PM exposure
include infants, older adults (65+ years), individuals with asthma, COPD or cardiovascular
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disease, diabetics, lower socioeconomic status, and those with certain genetic polymorphisms
(EPA 2009).
Several health studies have investigated potential health effects resulting from long-term
exposure to particulate matter. The historical mean PM2.5 concentration was 18 µg/m3 (range
11.0 - 29.6 µg/m3) in the Six-Cities Study and 20 µg/m3 (range 9.0 – 33.5 µg/m3) in the
American Cancer Society (ACS) study (Dockery et al., 1993; Pope et al., 1995, 2002; HEI, 2000;
Jerrett, 2005). Thresholds (exposure levels where health effects are first seen) are not apparent
in these studies. In the ACS study, statistical uncertainty in the risk estimates becomes apparent
at concentrations of about 13µg/m3, below which the confidence bounds significantly widen
because of the variability in the exposure concentrations. According to the results of the Dockery
et al. (1993) study, the risks are similar in the cities with the lowest long-term PM2.5
concentrations (i.e., 11 and 12.5 µg/m3). Increases in risk are apparent in the city with the nextlowest long-term PM2.5 average concentration (i.e., 14.9 µg/m3), indicating that when annual
mean concentrations are in the range of 11–15 µg/m3, health effects can be expected (WHO
2006).
Results from using the EPA AirNow AQI Calculator, indicate that the highest 24-hour PM2.5
levels recorded in Midlothian show in an increased likelihood of respiratory symptoms in
sensitive individuals, aggravation of heart or lung disease and premature mortality in individuals
with cardiopulmonary disease and the elderly but not for the general population (EPA, 2012b).
4.3. Ozone
Conclusions for Ozone:
Ellis County is one of 11 counties that make up the
Dallas–Fort Worth ozone non-attainment area, which
means that ozone levels in the metropolitan area
occasionally exceed EPA’s health-based standards and
WHO’s health guidelines. Emissions from industrial
sources, mobile sources, and natural sources throughout
the area contribute to this problem.
The general population of Midlothian is not expected to
experience harmful effects from ozone exposure except
on rare occasions when ozone levels reach around 100
ppb or more.
Many of the levels of ozone detected in Midlothian since
monitoring began in 1997 indicate that sensitive
individuals have an increased likelihood of experiencing
harmful respiratory effects (respiratory symptoms and
breathing discomfort). This is primarily true for active
children and adults and people with respiratory diseases,
such as asthma.
Breathing air containing ozone can
reduce lung function and increase
respiratory symptoms, thereby
aggravating asthma or other
respiratory conditions. Ozone
exposure also has been associated
with increased susceptibility to
respiratory infections, more
frequent medication use by people
with asthma, doctor’s visits, and
emergency department and hospital
admissions for individuals with
respiratory disease. Ozone
exposure also might contribute to
premature death, especially in
people with heart and lung disease.
More recent information indicates
that other outcomes such as school
absenteeism, cardiac-related
effects, and greater, more serious,
and more long-lasting symptoms among people with asthma may occur (EPA, 2008d).
Moreover, a controlled exposure study of healthy young volunteers to ozone at levels similar to
the EPA standard resulted in cardiovascular changes that could put a sensitive individual at risk
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for an adverse cardiovascular event. These results provide biological plausibility and support to
the previous findings in other types of human health studies (epidemiologic) of an association
between ozone exposures and increased risk of death and disease (Devlin et al., 2012).
Many of the 8-hour ozone levels reported in the Midlothian area since monitoring began in late
1997, indicate that sensitive individuals have an increased likelihood of respiratory symptoms
and breathing discomfort. These reactions are true for primarily active children and adults and
people with respiratory disease, such as asthma. On rare occasions during this period, levels
reached 100 ppb or more, indicating that even non-sensitive individuals from the general
population may have experienced harmful effects (EPA, 2012b).
4.4. Lead
4.4.1
Recent Human Studies on the Effects of Lead
Until recently, the CDC had established a level of concern for case management of 10 µg/dL.
This means that when blood lead levels in children exceed 10 µg/dL, CDC recommends that
steps be taken to lower their blood lead levels. More information about CDC’s recommendations
can be found in Preventing Lead Poisoning in Young Children (CDC, 2005). CDC also provides
tips for preventing exposure to lead. These tips can be found at this web address:
http://www.cdc.gov/nceh/lead/tips.htm.
Many people have mistakenly used this level in blood as a safe level of exposure or as a no effect
level. Recent scientific research, however, has shown that blood lead levels below 10 µg/dL can
cause serious harmful effects in children. As a result, there is no identified “safe” blood lead
level for children. Blood lead levels below 10 µg/dL have been shown to cause neurological,
behavioral, immunological, and developmental effects in young children. Specifically, lead
causes or is associated with decreases in (IQ; attention deficit hyperactivity disorder (ADHD);
deficits in reaction time; problems with visual-motor integration and fine motor skills; withdrawn
behavior; lack of concentration; issues with sociability; decreased height; and delays in puberty,
such as breast and pubic hair development, and delays in menarche (ATSDR, 1999).
On January 4, 2012, CDC’s Advisory Committee on Childhood Lead Poisoning Prevention
(ACCLPP) recommended that CDC adopt the 97.5 percentile for children aged 1–5 years as the
reference value for blood lead levels to identify children and environments associated with leadexposure hazards. The 97.5% currently is 5 ug/dL (CDC, 2012a). The full report is available at
http://www.cdc.gov/nceh/lead/ACCLPP/Final_Document_011212.pdf. On June 7, 2012, the
CDC released a statement concurring with the recommendations of the ACCLPP (CDC, 2012b).
The full statement can be found at:
http://www.cdc.gov/nceh/lead/ACCLPP/CDC_Response_Lead_Exposure_Recs.pdf. Based on
CDC’s concurrence, there is no longer a blood lead “level of concern.”
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4.4.2 Estimating children’s lead dose from air levels just north of the Gerdau
Ameristeel facility
Conclusions for Lead:
Past air lead exposures, during 1993–1998, in a
The 2008 EPA lead standard for air was
localized area just north of the Gerdau
developed to prevent the loss of 1–2 IQ
Ameristeel fence line, could have harmed the
points in young children (EPA, 2008e). In
health of children who resided or frequently
addition, the U.S. EPA developed a model to
played in these areas. The estimated health
estimate the contribution of lead in air (and
effect of these exposures would have been a
other media, including soil) to children’s
slight lowering of IQ levels (1–2 points) for
blood lead level. The model is called the
some children living in this area. There is
integrated exposure uptake biokinetic
some uncertainty with these findings given that
(IEUBK) model
we do not know what the lead levels in air were
(http://www.epa.gov/superfund/lead/products
downwind of the Gerdau monitor, and we do
.htm#guid). The model estimates the
not know if small children were exposed at all
percentage of children aged 6 months to 7
in this sparsely populated area of Cement
years that exceed a specified blood lead level
Valley.
at certain air lead concentrations. In most
situations, the EPA’s goal is to limit exposure
Since 1998, lead levels in this localized area
to lead in a child or group of similarly
have decreased sharply. Monitoring data do
exposed children that would have an
not indicate that lead exposures above EPA
estimated risk of no more than 5% chance of
standards have occurred in other areas of
exceeding a blood lead level of 10 µg/dL
Midlothian currently or in the past.
(EPA, 2002).
ATSDR has run the model using EPA’s default parameters for lead in food, in water, and from
soil ingestion. ATSDR also ran the model using the updated reference value of 5 µg/dL to
account for the risk of adverse health effects in children with levels below 10 µg/dL. Using a
combination of default parameters for the IEUBK model and using the highest annual (1995)
and quarterly average levels from the Gerdau Ameristeel monitor during 1993–1998, the model
estimates children have, on average, about a 18.5-21.4 % risk of having blood lead
concentrations between 5 and 10 µg/dL. Stated another way, if 100 children lived on properties
in the vicinity of the Gerdau Ameristeel monitors during 1993–1998, and lead in air
concentrations were 0.251-0.443 µg/m3, the IEUBK model predicts that about 21 or fewer
children out of 100 will have a blood lead level between 5-10 µg/dL, a level that might result in
small IQ deficits. Because no blood lead levels are safe in children, measures to reduce lead in
the environment will reduce the risk of health effects.
The model did not predict an increased risk of childhood blood levels to reach 10 µg/dL or more.
Although the results for the model run at 10 µg/dL may appear inconsistent with the 2008
NAAQS for lead, the NAAQS is not strictly based on the IEUBK model. In fact, the 2008
NAAQS for lead is based on air-related exposure and IQ loss that was established to prevent a
loss of 1-2 IQ points. This evidence-based framework was established by a quantitative
exposure/risk assessment process that relied on an air to blood ratio (Personal Communication,
Mark Follansbee, EPA IEUBK Contractor, March 14, 2012). Moreover, uncertainty in these
findings exist because of the following:
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1) We do not know what the air levels were downwind of the Gerdau monitor.
2) That a small population was exposed is likely, given the low-population density in
Cement Valley near the Gerdau monitor.
Evaluation of the actual childhood blood lead data in the Midlothian area will be conducted in a
future ATSDR Health Consultation.
4.5 Mixtures (including ozone)
Throughout this section, the health evaluations have focused on individual pollutants. This
analysis is consistent with the toxicological literature, which focuses on health effects following
single pollutant exposures. In the Midlothian area, however, as with many industrial sites, realworld environmental exposures occur simultaneously and involve multiple pollutants. This
section considers the public health implications of such exposures, focusing particularly on the
potential for co-exposures to ozone, PM2.5, and sulfur dioxide. Many gaps exist in our
understanding of the full range of health impacts of air pollution (i.e., the mixture of pollutants)
and scientific and regulatory communities are at least 10 years away from being able to
implement changes to address these issues (Mauderly et al., 2010).
Conclusions for Mixtures:
ATSDR believes that sufficient information exists to warrant concern for sensitive individuals
simultaneously exposed to multiple air pollutants, especially in the past (1997 to late 2008)
when SO2 levels were higher and when these persons were breathing at higher rates (e.g., while
exercising, etc.). ATSDR believes the severity of health effects from a mixture exposure is not
likely to exceed those discussed for SO2, PM2.5, or ozone exposure alone. For past SO2
exposures, it is possible that the number of sensitive individuals affected may have been greater
because effects may have occurred at a lower SO2 concentration when combined with exposure
to ozone, PM2.5, or both. Potential effects to a larger sensitive population, especially in the
past, may be limited to an exposure to those contaminants present at sufficient concentration
during the same time and at the same locations during the warmer months when PM2.5 and
ozone levels are generally the highest. In addition, potential effects to this larger sensitive
population may also have resulted from multiple exposures occurring during several
consecutive days. These conclusions are based on our best professional judgment and ATSDR
recognizes the uncertainty associated with them.
Using the available ambient air monitoring data, ATSDR first notes where and when individual
pollutants reached their peak levels:
• Ozone. Ambient air concentrations of ozone tend to peak in the summer with the highest
levels likely in the afternoons primarily during May and September with some elevations
reported in April and October.
• PM2.5. Levels in the Midlothian area tend to be highest during warm months. All of the
numerical exceedances of the 24-hour PM2.5 standard occurred between May and
September. However, as defined by EPA, the 24-hour standard has not been exceeded in
Midlothian.
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• Sulfur dioxide. Monitoring data from the Old Fort Worth Road, Wyatt Road, and
Midlothain Tower indicated elevated sulfur dioxide concentrations (i.e., above the EPA
1-hour standard of 75 ppb). Elevated concentrations begin to increase around 5 p.m. and
taper off around 6 a.m.; the highest frequency of elevations occurred between 7 p.m. and
3 a.m. In all months of the year, 1-hour SO2 levels were above the standard; however
April, May, and October had the highest frequency and June, August, November, and
December had the lowest. As noted previously, the populations exposed lived primarily
in the Cement Valley area and, secondarily, east, southeast, or south of the TXI property
boundary.
Taken together, the previous observations suggest that the timeframe of greatest concern for past
exposures to mixtures was during the late afternoon hours or early evening hours from late
spring to early fall. This concern would be greatest for the Cement Valley, where the highest
and most frequent sulfur dioxide concentrations are estimated to have occurred. In this area, co
exposures were possible between elevated levels of sulfur dioxide and ozone or sulfur dioxide
and PM2.5, or possibly all three pollutants combined. However, the effects of ozone, sulfur
dioxide, and PM2.5 may have a lag effect, and a direct relationship to co-exposures around the
same hour or on the same day is not likely to tell the whole story regarding the total effects of the
past and current mixtures exposures. For example, a sensitive person may be exposed to harmful
levels of one NAAQS constituent on one day only but may not exhibit the effect until the next
day or several days later. Meanwhile, this person could then be exposed again to harmful levels
of the same or other NAAQS constituents during subsequent days.
Some sulfur-dioxide sensitive individuals functioning at elevated ventilation rates may have
experienced enhanced effects from exposure to a mixture of sulfur dioxide and ozone or PM2.5.
The number of sensitive individuals affected in the past may have increased because effects may
have occurred at a lower sulfur dioxide concentration. Scientific information is insufficient to
allow meaningful quantitative analysis, but is sufficient to warrant concern for sensitive
populations, especially those who are at higher ventilation rates (e.g., exercising, etc.).
Nevertheless, past exposure to the mixture of all three constituents is limited temporally and
spatially by sulfur dioxide, primarily in the Cement Valley and secondarily to areas south, east,
and southeast the TXI boundary. However, other areas may have had concurrent PM2.5 and
ozone exposures without elevated SO2 exposures. Given the infrequent elevations of SO2 above
200 ppb and the spatial and temporal limitations identified here, ATSDR believes the severity of
health effects from a mixture exposure is not likely to exceed those discussed for SO2, PM2.5, or
ozone exposure alone. Because, however, effects may have occurred at a lower SO2
concentration, the number of affected individuals might have increased beyond what would be
expected from exposure to a single air pollutant.
4.6 Gaps and Limitations
In this health consultation, ATSDR considered the public health implications of the measured
and estimated air pollution levels in the Midlothian area relating to the NAAQS constituents and
hydrogen sulfide. Furthermore, ATSDR considered whether the available data form an adequate
basis for reaching conclusions. The following discussion does not focus on gaps and limitations
for those timeframes in the past where ATSDR will never be able to evaluate exposures;
however, it focuses on the gaps in our understanding of current and future exposures and the
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limitations of our evaluation. A more in-depth discussion can be found in ATSDR’s previous
health consultation (ATSDR, 2012a).
4.6.1 SO2 Limitation
ATSDR’s conclusions for sulfur dioxide were based primarily on data from a monitoring
network that indicate exposures to person living in the Cement Valley or east, south, or
southeast of the TXI facility boundary. While TXI SO2 emissions have declined in recent years,
the SO2 emissions from Ash Grove and Holcim have been comparable to TXI emissions in the
late 1990s and early 2000s that produced harmful levels of SO2 in several locations, primarily
Cement Valley. Additional monitoring data are needed to determine exposures of people who
live downwind of the Ash Grove and Holcim facilities.
4.6.2 PM Limitations
In ATSDR’s judgment, the most notable gap is the lack of monitoring data for residential
neighborhoods in immediate proximity to the four industrial facilities, where fugitive emissions
would be expected to have the greatest air quality impacts. Current and past monitoring
locations likely do not adequately characterize particulate matter levels for all residents located
immediately adjacent to certain onsite operations, such as limestone quarry activity. Particulate
matter monitoring is needed in these areas to evaluate exposures.
4.6.3 Mixtures Limitations
ATSDR notes that a limitation inherent in the public health assessment process is that scientists
do not have a complete understanding how simultaneous exposures to several environmental
contaminants may cause health effects. For the pollutants considered in this analysis—especially
sulfur dioxide, ozone and particulate matter, however, hundreds of toxicologic and
epidemiologic studies have examined how exposures are possibly related to health effects in
humans. Therefore, the evaluations of individual pollutants considered in this health consultation
are based on extensive scientific research, but the scientific understanding of the health effects of
exposures to pollutant mixtures is less advanced. ATSDR’s conclusions regarding the health
implication of exposures to a mixture of air pollutants is based on our best professional judgment
related to our understanding of the possible harmful effects of air pollutant exposures in
Midlothian and our interpretation of the current scientific literature; therefore, these conclusions
are presented with some uncertainty.
As with most site-specific environmental health evaluations ATSDR conducts, the findings and
conclusions in this health consultation have some inherent gaps and limitations. But for the
reasons cited above, ATSDR concludes that this assessment does not have major limitations that
would preclude scientifically defensible conclusions.
5.
Child Health Considerations
In communities with air pollution issues, the many physical differences between children and
adults demand special emphasis. Children could be at greater risk than adults from certain kinds
of exposure to hazardous substances. Children frequently play outdoors, especially during the
summertime or after school during the warm months, which can increase their exposure
potential. Further, a child’s lower body weight and higher intake rate results in a greater dose of
hazardous substance per unit of body weight. If toxic exposure levels are high enough during
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critical growth stages, the developing body systems of children can sustain permanent damage.
Further, children are dependent on adults for access to housing, access to medical care, and risk
identification. Thus adults need as much information as possible to make informed decisions
regarding their children’s health.
When preparing this health consultation, ATSDR considered these and other children’s health
concerns. For instance, when selecting health-based comparison values for the exposure
evaluation, ATSDR identified, when available, comparison values protective of children’s
exposure and of health conditions, such as asthma, more common in children. As one example,
ATSDR used the most recent EPA’s National Ambient Air Quality Standards to screen air
pollution levels for lead, ozone, particulate matter, and sulfur dioxide. EPA developed these
standards to protect the health of sensitive populations, including children. In addition, ATSDR
compared the environmental data to other guidelines, such as those fromWHO, and investigated
whether current NAAQS standards are protective—given our current scientific knowledge. For
example, we determined that the current annual average PM2.5 standard of15 µg/m3 might not be
protective of children and that EPA is proposing to lower the standard to 12-13 µg/m3.
It is not clear that children are more toxicologically sensitive to SO2 but might be more
vulnerable because of increased exposure. While physiologically based pharmacokinetic
modeling has suggested that children might be more vulnerable in the pulmonary region to fine
particulate matter, it also suggests that children’s airways might not be more sensitive than adults
to reactive gases such as SO2 (Ginsberg et al., 2005).
Factors that might contribute to enhanced lung deposition in children include higher ventilation
rates, less contribution from nasal breathing, less efficient uptake of particles in the nasal
airways, and greater deposition efficiency of particle and some vapor phase chemicals in the
lower respiratory tract. A child breathes faster than an adult, which might result in increased
uptake (Koenig et al., 2000). Children spend 3 times as much time outdoors as adults and engage
in 3 times as much time playing sports and other vigorous activities (EPA, 1997). Based on these
parameters, children are more likely to be exposed to more outdoor air pollution than adults.
Epidemiologic evidence suggests that air pollution effects (lung function decrements) in children
might not be fully reversible, even if the exposure stops, although SO2 was not a major
contaminant in these studies (Gauderman et al., 2004).
Recent literature suggests that exposure to air pollution during pregnancy causes adverse birth
outcomes and health problems for the mother and child. Two of the pollutants of concern for
these outcomes, particular matter and ozone, are also considered a concern in Midlothian.
Research shows that prenatal exposure to these pollutants can increase the risk of preterm
delivery and low birth weight, which contribute substantially to infant death and developmental
disabilities (EPA, 2010f).
ATSDR identified other environmental health concerns specific to children for this site: elevated
airborne levels of ozone and fine particulate matter. Many children who live in the Midlothian
area, like children who live in numerous urban and suburban areas in Dallas-Fort Worth
Metropolitan area and across the country, have a greater risk of suffering from ozone-related
adverse health effects than do adults.
ATSDR’s concern for this subject is based partly from the fact that ozone and PM2.5 levels are
generally highest during the afternoon hours on sunny summer days, when most children are not
in school and might be playing outdoors. Another reason for concern is that people with asthma
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have been identified as a sensitive population for both ozone and PM2.5 exposure, and asthma is
more prevalent among children than among adults (Mannino et al., 2002). Finally, some families
with children might not seek or understand information in air quality forecasts. These factors are
of concern because children with asthma or children who engage in moderate to strenuous
exercise (e.g., swimming and running) during poor air quality days are at risk for respiratory
problems.
Many resources are available to help prevent children from exposure to unhealthful levels of
ozone and PM2.5. On days with the most elevated air pollution levels, TCEQ issues air quality
alerts or forecasts, which are typically broadcast by the local media. Parents should encourage
their children, especially children with asthma, to play indoors on days when air pollution levels
are predicted to be unhealthful. EPA’s Web site now includes a substantial amount of
information on ozone, PM2.5, and related air quality problems. Adults are encouraged to access
this information, whether from their home computers or those at local libraries, at
www.epa.gov/airnow. Additionally, EPA recently launched a Web site that presents air pollution
information related to children’s health. The site, “Air Quality Index for Kids!”, is available in
English and Spanish at www.epa.gov/airnow/aqikids.
6. Community Concerns Evaluation
Since 2005, ATSDR and TDSHS have been
collecting and documenting community concerns
regarding the Midlothian facilities. The agencies
have learned of these concerns through various
means, including a door-to-door survey of residents,
a community survey, and multiple public meetings
and availability sessions in Midlothian. The concerns
expressed by community members have addressed
many topics, including human health, animal health,
and the adequacy and reliability of ambient air
monitoring data collected in the Midlothian area.
Concerns Addressed in This Document:
This Health Consultation addresses
community concerns regarding the
potential exposures to the NAAQS
constituents and H2S related to the
Midlothian facilities and for potential
exposures to these air pollutants from
other sources. Future ATSDR
evaluations will evaluate community
concerns related to exposures to other
air pollutants, animal concerns and
health-outcome data.
The following are responses to community concerns related to the evaluation of the NAAQS
constituents:
1. Protectiveness of the regulatory health-based screening guidelines
Response: ATSDR used several sources for health-screening guidelines (EPA, ATSDR, and
WHO) to evaluate which air pollutants to further evaluate. In addition, ATSDR evaluated how
current each health screening value is in relation to the most recent scientific information. For
example, EPA is considering lowering the annual average PM2.5 value to around 12-13 µg/m3
from its current level of 15 µg/ m3. This information was taken into account in this health
consultation.
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2. Persistence of emissions and the effects of continuous low-level exposure to
individual chemicals and/or mixtures
Response: The ability of the scientific community to fully and quantitatively evaluate the health
effects from the mixture of air pollutants people are exposed to is at least ten years away
(Mauderly et al., 2010). However, in this health consultation, in addition to evaluating the health
effects of exposure to single air pollutants, we attempted to evaluate the combined effect of the
three major air pollutants that may be harmful to the health of a person living in Midlothian
(particularly sensitive individuals). ATSDR believes that sufficient information exists to warrant
concern for multiple air pollutant exposures to sensitive individuals, especially in the past (1997
late 2008). However, current scientific knowledge does not allow for a definitive and
quantitative conclusion. See more information above in the Public Health Implications for
individual air pollutants and in the Mixtures section.
3. Impact on pregnant women, infants, children, the elderly, the immune-suppressed
Response: Infants, children, the elderly, and immune-suppressed individuals are all considered
populations sensitive to the effects of exposures to air pollutants. Recent literature suggests that
exposure to air pollution during pregnancy causes adverse birth outcomes and health problems
for the mother and child. The specific concerns of children are discussed above in the Child
Health Considerations section. In a future health consultation, ATSDR will evaluate data on
birth defects and adverse birth outcomes for the Midlothian area.
4. Confounding circumstances (i.e., Ellis Co. is an ozone non-attainment area)
Response: This health consultation evaluated the public health implications of all NAAQS
constituents whether they were primarily related to the major industries (sulfur dioxide), partially
related (PM2.5), or primarily unrelated (ozone). See the Mixtures discussion above for details.
5. Health effects of air quality. Are there air quality issues in Midlothian?
Response: ATSDR believes that current exposures to ozone and infrequent short-term levels of
PM2.5 and past exposures to these, long-term levels of PM2.5 and sulfur dioxide could harm the
health of sensitive individuals who currently and previously resided in Midlothian. In addition,
ATSDR believes that potential future exposures to sulfur dioxide and PM2.5 also could harm the
health of sensitive individuals if actions are not taken to monitor and to prevent harmful
exposures.
6. Strong smell in air. Smell of rotten eggs around sunset
Response: Hydrogen sulfide and not SO2 is usually associated with the smell of rotten eggs.
Sulfur dioxide odors have been described as having a very pungent smell. ATSDR did not
identify hydrogen sulfide levels as a concern but did determine that past sulfur dioxide levels
could have harmed the health of some community members. In addition, ATSDR did not
identify a major source of hydrogen sulfide but did determine that the local cement industries are
major sources of sulfur dioxide emissions. The timing of the concern (sunset) is consistent with
when SO2 elevations did begin to occur and it is possible that people are smelling sulfur dioxide
and not hydrogen sulfide.
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7. Transportation contribution to air quality problem
Response: Throughout the country, air pollution is affected by many sources of emissions
including large industrial facilities like the cement manufacturing operations and steel mills in
Midlothian, smaller industrial and commercial operations typically found in populated areas
(e.g., gasoline stations, dry cleaners, auto refinish shops), and mobile sources (e.g., automobiles,
trucks, locomotives, and aircraft). Some emission sources are of natural origin, such as wildfires
and wind-blown dust. All of these sources combined will affect air pollution levels at a given
location. Midlothian is no exception in this regard.
Quantifying precisely the extent to which different sources affect air pollution levels can
be difficult. However, some insights can be gleaned from EPA’s National Emissions Inventory
(NEI), which includes estimates of the relative magnitude of annual emissions from different
types of manmade emission sources for every county across the nation. To comment on the
contribution of “transportation sources” to local air quality, ATSDR compiled the 2008 NEI data
for several different pollutants (EPA, 2012a). For inventory year 2008, this analysis showed that
transportation sources accounted for an estimated: 72 % of the total carbon monoxide emissions
in Ellis County; 39 % of the total nitrogen oxides emissions in Ellis County; and less than 5 % of
the total emissions for sulfur dioxide and fine particulate matter.
Therefore, for certain pollutants (e.g., carbon monoxide, nitrogen oxides), transportation
sources account for a considerable portion of the emissions in Ellis County; but for other
pollutants (e.g., sulfur dioxide, particulate matter), transportation sources are less important.
However, focusing strictly on Midlothian—and not all of Ellis County—the emissions from the
four large industrial sources account for most emissions of most pollutants of interest in this
Health Consultation.
8. Need to address cement kiln dust
Response:
At cement manufacturing facilities, the high-temperature kilns are designed to manufacture
clinker, which is used to make cement. During this process, the kilns also generate fine-grained
particles that are carried in the cement kiln exhaust gas. These fine-grained particles are referred
to as cement kiln dust (CKD). CKD is a highly alkaline material. The primary constituent is
calcium oxide, which can account for almost half of CKD by weight; with lesser quantities of
silicon dioxide, sulfur trioxide, aluminum oxide, and potassium oxide (EPA, 1993; KDOT,
2004).
Cement kiln dust may cause dry skin, discomfort, irritation, severe burns, and dermatitis.
Exposure of sufficient duration to wet kiln dust, or dry kiln dust on moist areas of the body, can
cause serious, potentially irreversible damage to the skin, eye, respiratory and digestive tracts
because of chemical (caustic) burns, including third-degree burns. Kiln dust is also capable of
causing dermatitis by irritation and allergy. Skin affected by dermatitis may include symptoms
such as redness, itching, rash, scaling, and cracking. Breathing CKD may cause nose, throat, or
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lung irritation and choking, depending on the degree of exposure. Inhalation of high levels of
dust can cause chemical burns to the nose, throat, and lungs (Lafarge, 2011; Ash Grove, ND).
Most of the CKD generated in cement kilns is captured in air pollution control devices
(e.g., electrostatic precipitators, baghouses), but some is emitted to the air through the kiln
stacks. CKD that is collected in air pollution controls can then be used for various purposes. For
instance, this material is often recycled into the cement manufacturing process or collected and
used for commercial purposes: CKD is used to stabilize soils in construction projects, for landfill
cover, and as a filler for mine reclamation activities. However, some CKD generated is still
disposed of in landfills and other disposal units. CKD can enter ambient air through the stacks
and also as releases from handling captured CKD. Although facilities typically take measures to
reduce the amount of CKD released to the air, some of the material inevitably escapes.
In this Health Consultation, the consideration is the extent to which CKD contributes to
airborne particulate matter. CKD includes particles of many sizes, and the particle size
distribution depends on the specific production processes and air pollution controls at a given
cement manufacturing facility. Some CKD will have particles small enough that they can blow
from open surfaces into the air and that they can also be respirable—meaning, they are small
enough to be inhaled and enter the lungs. Specifically, EPA has reported that between 22 % and
95 % of CKD can be found in the respirable range (EPA, 1993). Therefore, any CKD that the
Midlothian facilities release in the respirable size fraction should be reflected in the ambient air
monitoring data collected from offsite locations.
ATSDR evaluated pictures and videos of emissions from TXI and Gerdau Ameristeel (we
do not expect CKD emissions from Gerdau) which were provided by local citizens. These
videos and pictures confirm that many fugitive dust emission events have occurred at these
facilities. Some videos also show emission events where large plumes of dust appear to be
originating from the ground level and not from the stacks. These events do not appear to be
normal. ATSDR cannot determine from these videos and pictures whether any of the releases
shown contain CKD or dust from other materials (for example, limestone).
In summary, airborne CKD needs to be evaluated from many perspectives. This Health
Consultation considers the extent to which CKD contributes to particulate matter found in
outdoor air. ATSDR will be issuing two other Health Consultations that will further evaluate
CKD: one document will consider the specific chemicals in CKD and whether those pose a
health hazard when inhaled and another document will consider the extent to which CKD has
contaminated soils and waterways through atmospheric deposition.
9. Cars are dusty all the time – thick/white dust
Response: Baghouse ruptures or operational upsets at local facilities could have resulted in dust
being deposited on area automobiles (either on the facilities or off). Moreover, releases of dust
that could blanket automobiles is not inconsistent with the operations at the three cement plants
operating in Midlothian, especially in relation to cement kiln dust (see answer to #8 above). At
least one other community near a cement processing plant also has noted that their cars
frequently have a coat of thick, white, dust covering their cars, which they believe is cement kiln
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dust (Boulder Weekly, n.d). A future ATSDR health consultation will more thoroughly evaluate
the extent to which airborne particles have deposited to, and possibly contaminated, other media.
10. Concern for specific health effects, such as:
• Respiratory diseases (e.g., respiratory infections, asthma that improves when out of
area, etc.)
• Allergies
• Sinus problems
• Cancer
• Autoimmune diseases (e.g., Graves disease and sarcoidosis involving lungs and eye
lids)
Response: Certain respiratory illnesses, including sinus problems and allergies, are consistent
with what might be expected from exposures to SO2, ozone, or PM2.5, but this statement does not
suggest that any given incident of these health outcomes is caused solely by inhalation of ozone,
PM2.5, or sulfur dioxide in the Midlothian area. Rather, causality of any given disease is usually
a result of multiple factors, such as smoking, lifestyles, eating habits, occupational exposures,
etc. In addition, the air pollutants of concern are known to aggravate conditions such as asthma
and these conditions could alleviate once individuals are outside the Midlothian area. Longterm particulate matter exposures have been associated with lung cancer. However, particulate
matter is composed of many different combinations of chemicals, depending on the sources in
any given area. Therefore, particulate matter itself might not be carcinogenic, but an individual
constituent may be. Potential cancer effects of these constituents (e.g., metals) will be evaluated
by ATSDR in a future health consultation. No studies have been conducted to assess the
relationship between air pollutants and the specific autoimmune diseases of concern to the
public. Exposures to particulate matter air pollution is a concern for sensitive populations, which
includes individuals with diabetes (type-1 diabetes is an autoimmune disease). However, no
studies have associated particulate matter exposures with cause of diabetes. ATSDR will
evaluate data for cancer, respiratory and cardiovascular disease, diabetes, and other diseases in
the Midlothian area in a future health consultation.
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7. Conclusions and Recommendations
Sulfur dioxide exposures : sensitive (e.g., individuals with asthma) and general
populations
Conclusions
In the past (1997–late 2008), breathing air contaminated with sulfur dioxide (SO2) for short
periods (5 minutes) could have harmed the health of sensitive individuals (e.g., people with
asthma), particularly when performing an activity (such as exercising or climbing steps) that
raised their breathing rate. SO2 levels that might have harmed sensitive individuals were
infrequent and limited to areas primarily in Cement Valley and possibly areas east, south, and
southeast of the TXI Operations, Inc (TXI) fence line. These exposures occurred primarily from
about 5 p.m. to 6 a.m. Harmful exposures also could have occurred before 1997; however,
monitoring data are not available to confirm this conclusion. Breathing air contaminated with
SO2 in the past (during the period 1997 to late 2008) was not expected to harm the health of
the general population.
Reductions in SO2 levels in Cement Valley have occurred since late 2008 resulting in
exposures to both sensitive individuals and the general public that are not expected to be
harmful. These reductions may be caused, in part, by declining production levels at local
industrial facilities. Future harmful exposures in Cement Valley could occur if production rises
to at least previous levels and actions are not taken to reduce SO2 emissions.
No SO2 data are currently available to evaluate exposures to individuals who live downwind of
the Ash Grove Cement and Holcim facilities where the SO2 emissions have been similar to those
from TXI in the past that produced harmful exposures in Cement Valley and possibly elsewhere.
Therefore, ATSDR cannot determine if harmful exposures to SO2 have been occurring
downwind of the Holcim and Ash Grove facilities.
When sulfur dioxide concentrations exceed 400 ppb, sensitive individuals may experience
symptoms such as coughing, wheezing, and chest tightness. At lower sulfur dioxide
concentrations (200 ppb to 400 ppb), sensitive individuals functioning at elevated breathing rates
may experience asymptomatic effects (e.g., mild constriction of bronchial passages). Adverse
health effects from exposures to sulfur dioxide concentrations less than 200 ppb are uncertain,
but may occur in some individuals more sensitive or vulnerable than those participating in
clinical investigations.
People with asthma, children, and older adults (65+ years) have been identified as groups
sensitive to the health problems associated with breathing SO2. Human scientific studies (clinical
investigations and epidemiologic studies) have provided evidence of a causal relationship
between SO2 and respiratory morbidity in people with asthma and other more limited human
studies (epidemiologic) have consistently reported that children and older adults might be at
increased risk for SO2-associated adverse respiratory effects. Potentially sensitive groups to air
pollutants include obese individuals, those with preexisting cardiopulmonary disease, and those
with a pro-inflammatory condition such as diabetes, but some of these relationships have not
been examined specifically in relation to SO2.
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Recommendations
To reduce current and potential future peak exposures to sulfur dioxide, ATSDR recommends
the following:
• Reduce emissions—TCEQ should take actions to reduce future SO2 emissions from TXI
to prevent harmful exposures.
• Evaluate and reduce exposures—TCEQ should conduct ambient air monitoring to
characterize community exposures to SO2 downwind of the Ash Grove and Holcim
facilities and take actions to reduce emissions from these facilities if harmful exposures
are indicated.
Fine particulate matter (PM2.5) exposures
Conclusions
Breathing air contaminated with PM2.5 downwind of TXI and Gerdau Ameristeel for 1 year or
more is not likely to have harmed people’s health, except in a localized area just north of the
Gerdau Ameristeel fence line during 1996-1998. PM2.5 is both a local and regional air quality
concern. The PM2.5 levels observed in the Midlothian area are not considerably different from
levels measured in multiple locations throughout the Dallas— Fort Worth metropolitan area.
These PM2.5 levels are caused by emissions from mobile (e.g., cars and trucks) and industrial
sources in the Midlothian area and beyond. Nevertheless, for people, especially those with
preexisting respiratory and cardiac disease, who lived in a localized area of Cement Valley (just
north of the Gerdau Ameristeel fence line during 1996–1998), public health concern is warranted
for adverse health effects from long-term exposure to PM2.5. Short-term potentially harmful
levels of PM2.5 have been infrequent in Midlothian. These infrequent exposures could have
resulted in harmful cardiopulmonary effects, especially in sensitive individuals, but not the
general public.
Most measured annual average PM2.5 levels in the Midlothian area were not above EPA’s current
or proposed standard. For many years in the past (1996–2008), annual average PM2.5 levels
measured were just below the range of concentration proposed by EPA for lowering the annual
average standard except for the estimated exposure levels just north of Gerdau Ameristeel fence
line during 1996–1998. Although no PM2.5 measurements were collected north of Gerdau
Ameristeel, other data ATSDR has reviewed suggest that this area most likely had the highest
PM2.5 concentrations in the area, particularly in the years 1996–1998. These estimated PM2.5
levels were at the upper end of the risk range in several important scientific (epidemiologic)
studies. Infrequent, short-term PM2.5 levels in Midlothian have been in the range considered
by the EPA (based on the Air Quality Index or AQI) to be a concern for sensitive populations,
but not the general public. However, as defined by EPA, short-term levels of PM2.5 in the
Midlothian area have not exceeded the current standard.
ATSDR noted several data gaps in relation to particulate matter exposures. In general,
monitoring stations in the Midlothian area have been placed near or at locations believed to
either have high air quality impacts from facility operations or a high potential for exposure.
However, ATSDR is uncertain about PM2.5 exposures downwind of Ash Grove and Holcim
because of a lack of data and information. In addition, ambient air monitoring data are more
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limited for the residential neighborhoods in immediate proximity to the cement manufacturing
facilities’ limestone quarries. Particulate matter exposure is the primary concern for these
localized residential areas.
Recommendations
To reduce current or future PM2.5 exposure, ATSDR recommends the following:
• Reduce emissions—TCEQ should take actions to reduce future PM2.5 exposures from
TXI and Gerdau Ameristeel to prevent harmful exposures.
• Evaluate and reduce exposures—TCEQ should conduct appropriate ambient air
monitoring to characterize exposures to persons located downwind of the Ash Grove and
Holcim facilities and take actions to reduce PM2.5 emissions from these facilities if
harmful exposures are indicated. In addition, particulate matter monitoring is needed in
residential areas that are in immediate proximity to the facilities’ limestone quarries.
Ozone Exposures
Conclusions
Several of the levels of ozone detected in Midlothian since monitoring began in 1997 indicate
that sensitive individuals have an increased likelihood of experiencing harmful respiratory
effects (respiratory symptoms and breathing discomfort). This is primarily true for active
children and adults and people with respiratory diseases, such as asthma. The general
population of Midlothian is not expected to experience harmful effects from ozone exposure
except on rare occasions when ozone levels reach approximately 100 ppb or more.
Ellis County is one of 11 counties that make up the Dallas–Fort Worth ozone non-attainment
area, which means that ozone levels in the metropolitan area occasionally exceed EPA’s healthbased standards. Levels detected also exceed the WHO’s health guidelines. Emissions from
industrial sources, mobile sources, and natural sources throughout the area contribute to this
problem. Scientific studies indicate that breathing air containing ozone can reduce lung function
and increase respiratory symptoms, thereby aggravating asthma or other respiratory conditions.
Ozone exposure also has been associated with increased susceptibility to respiratory infections,
medication use by persons with asthma, doctor’s visits, and emergency department and hospital
admissions for individuals with respiratory disease. Ozone exposure also may contribute to
premature death, especially in people with heart and lung disease. More recent information
indicates that other outcomes such as school absenteeism, cardiac-related effects, and an
indication that persons with asthma may experience larger and more serious responses to ozone
that last longer than responses for healthy individuals.
Recommendations-- See Mixtures below.
Mixtures Exposure (including ozone)
Conclusion
ATSDR believes that sufficient information exists to warrant concern for multiple air
pollutant exposures to sensitive individuals, especially in the past (1997 to late 2008) when SO2
levels were higher and when these persons were breathing at higher rates (e.g., while
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exercising, etc.). ATSDR believes the severity of health effects from a mixture exposure is not
likely to exceed those discussed for SO2, PM2.5, or ozone exposure alone. For past SO2
exposures, it is, however, possible that the number of sensitive individuals affected may have
been greater because effects may have occurred at a lower SO2 concentration when combined
with exposure to ozone, PM2.5, or both. Potential effects to a larger sensitive population,
especially in the past, may be limited to an exposure to those contaminants present at sufficient
concentration during the same time and at the same locations during the warmer months when
PM2.5 and ozone levels are generally the highest. In addition, potential effects to this larger
sensitive population also may have resulted from multiple exposures occurring during several
consecutive days.
The current state of the science limits our ability to make definitive conclusions on the
significance of simultaneous exposures to multiple criteria pollutants. ATSDR’s conclusions
are based on our best professional judgment related our understanding of the possible harmful
effects of air pollutant exposures in Midlothian and our interpretation of the current scientific
literature; therefore, these conclusion are presented with some uncertainty.
Recommendations
To reduce and prevent multiple contaminant exposures, ATSDR recommends the following:
• TCEQ should evaluate and prevent harmful sulfur dioxide and PM2.5 exposures from
local sources.
• TCEQ should continue efforts to reduce regional ozone exposures.
Lead Exposures
Conclusions
Past lead air exposures during 1993 and 1998, in a localized area just north of the Gerdau
Ameristeel fence line, could have harmed the health of children who resided or frequently
played in these areas. The estimated health effect of these exposures would have been a slight
lowering of IQ levels (1–2 points) for some children living in this area.
Since 1998, lead levels in this localized area decreased sharply, and have fallen below the
NAAQS standard. Monitoring data do not indicate elevated air lead levels have occurred or are
occurring in other areas of Midlothian currently or in the past.
ATSDR evaluated past lead exposures in air using a model developed by the EPA to estimate
childhood blood lead levels. Based on our current knowledge of the health effects of lead
exposures in children, ATSDR used an updated blood lead reference level of 5 µg/dL in the
model to account for the risk of adverse health effects below 10 µg/dL, which has traditionally
been used as a level of concern. ATSDR also ran the model using 10 µg/dL. Using a
combination of default parameters for the EPA lead model and using the highest annual and
quarterly average air lead levels from the Gerdau Ameristeel monitor from 1993 to1998, the
model estimates children in that area of Cement Valley could have had, on average, about an
18%–21% risk of a blood lead level between 5-10 µg/dL caused by breathing outdoor air. Stated
another way, if 100 children lived on properties in the vicinity of the Gerdau Ameristeel
monitors during 1993–1998 the model predicts that about 21 or fewer children of 100 would
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have blood lead levels between 5-10 µg/dL, a level, which might result in small IQ deficits. The
model also predicted that there was not an appreciable risk of these exposures resulting in a
childhood blood lead level of 10 µg/dL or more. There is some uncertainty with these findings
given that we do not know what the lead levels in air were downwind of the Gerdau monitor and
we do not know if small children were exposed at all in this sparsely populated area of Cement
Valley.
Recommendations
Because there is no known safe blood lead level for children, we emphasize the importance of
environmental assessments to identify and mitigate lead hazards before children demonstrate
BLLs above the reference value. Continue existing prevention strategies to reduce
environmental exposures from lead in soil, dust, paint and water before children are exposed.
Educate families, service providers, advocates, and public officials on primary prevention of lead
exposure in homes and other child-occupied facilities, so that lead hazards are eliminated before
children are exposed. Clinicians should monitor the health status of all children with a confirmed
BLL ≥5 µg/dL for subsequent increase or decrease in BLL until all recommended environmental
investigations and mitigation strategies are complete, and should notify the family of all affected
children of BLL test results in a timely and appropriate manner.
Exposure to Other NAAQS Air Contaminants
Conclusion
ATSDR does not expect harmful effects in Midlothian from current or past exposures to the
air pollutants carbon monoxide, nitrogen dioxide, and hydrogen sulfide. If these air pollutant
concentrations remain at these levels, future exposures should not result in adverse effects.
Based on available monitoring data and other information (emission reports, knowledge of what
might be emitted from cement or steel operations, and worst-case computer air modeling) the
levels of carbon monoxide, nitrogen dioxide, hydrogen sulfide are below health-protective
comparison values developed by the EPA, WHO, or ATSDR.
Recommendation
TCEQ should insure that levels of these air pollutants do not increase to levels of concern in the
future.
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8. Public Health Action Plan
This health consultation is one of the several evaluations being conducted by ATSDR under the
overall Public Health Response Plan developed to address community concerns. The following
are public health actions planned specifically related to the findings from this health
consultation:
ATSDR or TDSHS will:
o Distribute health education material related to exposures to SO2, PM2.5, and ozone
specifically for sensitive and potentially sensitive populations. This material will
include information on health effects and ways to minimize harmful exposures to air
pollution;
o Provide educational material specifically for health professionals on air pollution and
patient health;
o Work with TCEQ to address the recommendations of this health consultation and
evaluate any additional data that might become available in relation to these
recommendations; and
o Issue two other Health Consultations that will further evaluate cement kiln dust
(CKD): one document will consider the specific chemicals in CKD and whether they
pose a health hazard when inhaled, and another document will consider the extent to
which CKD has contaminated soils and waterways through atmospheric deposition.
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9. Authors, Technical Advisors
Primary Author:
Greg Ulirsch, MS, PhD
Environmental Health Scientist, ATSDR
Technical Advisors:
John Wilhelmi, MS, Eastern Research Group
Michelle Colledge, MPH, PhD, ATSDR
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10. References
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Ash Grove Cement. 2010. Annual tire derived fuel usage at Ash Grove Cement Company,
Midlothian, Texas plant. E-mails from Michael Harrell, Ash Grove Cement dated June 28, 2010.
ATSDR, 1998. Agency for Toxic Substances and Disease Registry. Toxicological profile for
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ATSDR, 1999. Agency for Toxic Substances and Disease Registry. Toxicological profile for
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EPA, 1993. US Environmental Protection Agency. 1993. Report to Congress on Cement Kiln
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http://www.epa.gov/ttn/ecas/regdata/EIAs/iands.pdf.
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EPA, 2002. US Environmental Protection Agency. User’s Guide of the Integrated Exposure
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EPA, 2008c. Integrated Science Assessment for Sulfur Oxides—Health Criteria. U.S.
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66
Midlothian Area Air Quality—Assessing the Public Health Implications of the Criteria
(NAAQS) Air Pollutants and Hydrogen Sulfide Health Consultation Public Comment Release
11. Tables �
67
Midlothian Area Air Quality—Assessing the Public Health Implications of the Criteria
(NAAQS) Air Pollutants and Hydrogen Sulfide Health Consultation Public Comment Release
Table 1. Estimated Annual Carbon Monoxide Emissions from Midlothian Facilitiesa,b
Year
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
Ash Grove Cement
(tons per year)
627
—c
181
506
281
364
327
506
425
466
530
587
418
382
362
505
477
497
413
175
275
Gerdau Ameristeel
(tons per year)
1,835
—c
2,063
2,046
2,139
2,136
1,736
1,873
1,781
1,602
1,719
1,582
1,608
1,578
1,642
1,590
1,736
1,700
1,503
906
1,315
Holcim
(tons per year)
—d
—c
—d
—d
433
1,502
3,091
2,798
3,399
2,332
4,383
5,375
5,052
5,100
6,088
3,536
4,173
3,354
5,365
2,520
1,776
TXI Operations
(tons per year)
1,052
—c
89
1,046
747
741
844
1,032
966
982
818
716
763
692
613
779
1,017
774
653
294
306
Notes: a All data are shown in units of tons per year (tpy).
b
Emissions data are taken from TCEQ’s Point Source Emissions Inventory (TCEQ, 2011), with all data
points rounded to the nearest ton.
c
No Point Source Emissions Inventory were available for calendar year 1991.
d
In the earliest years of the Point Source Emissions Inventory, Holcim reported data for numerous
pollutants, but has entries of zero emissions for carbon monoxide.
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Midlothian Area Air Quality—Assessing the Public Health Implications of the Criteria
(NAAQS) Air Pollutants and Hydrogen Sulfide Health Consultation Public Comment Release
Table 2. Estimated Annual Lead Emissions from Midlothian Facilitiesa,b
Year
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
Ash Grove
(tons per year)
—c
—c
—c
0.06
—c
0.10
0.02
0.02
0.02
0.02
0.02
0.02
0.02
0.02
0.02
0.02
0.02
0.02
0.02
0.01
0.01
0.01
0.01
0.01
Gerdau Ameristeel
(tons per year)
17.55
11.21
9.42
0.68
1.45
1.60
2.45
3.00
3.00
0.99
2.16
1.93
1.95
2.11
1.93
1.97
1.28
0.52
0.50
0.55
0.54
0.47
0.28
0.41
Holcim
(tons per year)
—c
—c
—c
—d
—c
—d
—d
—d
—d
—d
—d
—d
—d
0.07
0.09
0.03
0.13
0.08
0.08
0.08
0.08
0.08
0.04
0.01
TXI Operations
(tons per year)
—c
—c
—c
—d
—c
0.12
0.02
0.01
0.01
< 0.01
0.02
0.01
0.13
0.13
0.01
0.01
0.01
< 0.01
0.02
0.02
0.03
0.03
0.02
0.01
Notes: a All data are shown in units of tons per year (tpy).
b
Emissions data were accessed from both TCEQ’s Point Source Emissions Inventory (TCEQ, 2011) and
EPA’s Toxics Release Inventory (EPA, 2011). The table displays the higher annual emissions number from
these inventories. Numbers displayed in plain font are from the Point Source Emissions Inventory, and
numbers shown in bold italic font are from the Toxics Release Inventory. All data are rounded to the
second decimal place. When summarizing TRI data, emissions for both “lead” and “lead compounds” were
considered in the tallies.
c
No Point Source Emissions Inventory were available for calendar years 1987, 1988, 1989, and 1991. TRI
emissions data are shown for these calendar years.
d
In the earliest years of the Point Source Emissions Inventory, Holcim reported data for numerous
pollutants, but has entries of zero emissions for lead for several years; and TXI has an entry of zero
emissions for lead for inventory year 1990.
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Midlothian Area Air Quality—Assessing the Public Health Implications of the Criteria (NAAQS) Air Pollutants and Hydrogen
Sulfide Health Consultation Public Comment Release
Table 3. Summary of Ambient Air Monitoring Data for Lead, 1981-2011a
Name of Monitoring Station
City Hall Roof
Auger Road
Auger Road Water Treatment Plant
Cedar Drive
Cement Valley Road
Gerdau Ameristeel
CAMS 302 – Wyatt Road
J.A. Vitovsky Elementary School
Jaycee Park
Midlothian High School
Midlothian Tower
Mountain Peak Elementary School
Old Fort Worth Road
Tayman Drive Water Treatment Plant
Triangle Park
Wyatt Road
Number
of
Samples
Time Frame
Monitors operating in the 1980s
5/1981-12/1981, 1/1983-12/1983
94
Monitors operating in the 1990s
1/1991-10/1992
68
1/1991-12/1991, 2/1993-6/1993
56
1/1992-6/1993
14
1/1992-5/1992
13
1/1993-8/1998
319
Monitors operating in the 2000s
1/2001-6/2004
196
5/5/2009-5/9/2009
5
12/2008-7/2009
20
7/3/2009-7/7/2009
5
5/2002-8/2005
197
2/26/2009-3/2/2009
5
12/2008-7/2009
20
9/2005-9/2011
366
12/2008-7/2009
20
12/6/2008-12/10/2008
5
12/2008-7/2009
29
Particle
Size
Highest 24
Hour Average
Concentration
(µg/m3)
Highest Quarterly
Average
Concentration
(µg/m3)
TSP
0.46
0.233
PM10
PM10
PM10
PM10
TSP
0.034
0.034
0.009
0.068
1.51
0.006
0.009
0.004
0.035
0.443 c
PM10
PM10
PM10
PM10
PM2.5
PM10
PM10
PM2.5
PM10
PM10
PM10
0.125
0.0023
0.0077
0.0027
0.0294
0.0025
0.0117
0.0331
0.0138
0.0060
0.0741
0.026
—b
0.001
—b
0.007
—b
0.002
0.006
0.004
—b
0.015
Notes: a Lead monitoring data were either downloaded from TCEQ’s Texas Air Monitoring Information System (TCEQ, 2012) or taken from TCEQ’s recent
air quality study in Midlothian (TCEQ, 2010).
b
Quarterly average concentrations were not calculated for sites that collected 24-hour average lead samples on five consecutive days.
c
Two health-based screening values were used to evaluate these data. EPA’s current NAAQS is a 3-month rolling average concentration of 0.15 µg/m3,
and WHO’s health guideline is an annual average concentration of 0.5 µg/m3. The row shown in bold font had quarterly average lead concentrations
above EPA’s current NAAQS, though these values met EPA’s NAAQS that were in effect at the time the measurements were collected.
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Midlothian Area Air Quality—Assessing the Public Health Implications of the Criteria
(NAAQS) Air Pollutants and Hydrogen Sulfide Health Consultation Public Comment Release
Table 4. Estimated Annual Nitrogen Oxides Emissions from Midlothian Facilitiesa,b
Year
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
Ash Grove Cement
(tons per year)
2,999
—c
3,359
3,668
4,027
3,771
3,908
3,164
2,724
3,005
2,905
2,923
2,572
2,625
2,350
2,250
2,220
1,757
1,385
1,266
1,291
Gerdau Ameristeel
(tons per year)
388
—c
310
299
346
307
601
924
653
515
510
479
490
456
471
461
498
481
438
209
297
Holcim
(tons per year)
731
—c
1,341
1,353
1,680
750
1,975
2,134
1,893
1,222
3,475
3,078
4,204
3,728
4,228
4,867
3,055
2,862
3,184
951
694
TXI Operations
(tons per year)
3,022
—c
3,321
2,268
5,430
5,910
5,506
5,819
6,226
5,267
4,515
4,444
4,221
3,472
4,347
4,323
3,446
2,916
2,877
1,022
1,154
Notes: a All data are shown in units of tons per year (tpy).
b
Emissions data are taken from TCEQ’s Point Source Emissions Inventory (TCEQ, 2011), with all data
points rounded to the nearest ton.
c
No Point Source Emissions Inventory were available for calendar year 1991.
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Midlothian Area Air Quality—Assessing the Public Health Implications of the Criteria
(NAAQS) Air Pollutants and Hydrogen Sulfide Health Consultation Public Comment Release
Table 5. Summary of Ambient Air Monitoring Data for Nitrogen Dioxide, 2000–2011a
Year
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
Nitrogen Dioxide Concentrations (ppb)
Upwind Stations
Downwind Stations
Midlothian Tower
Old Fort Worth Road
Wyatt Road
Annual average concentrations, by year
EPA NAAQS = 53 ppb; WHO health guideline = 21 ppb
9.47b
—c
—c
c
4.50
—
—c
4.52
—c
—c
b
6.92
10.37
—c
7.55
10.75
9.23b
6.85
10.87
8.78
5.56
9.99
9.31b
4.75b
9.34
—c
c
—
10.02
—c
—c
7.24
—c
c
—
7.24
—c
—c
6.72b
—c
Highest 1-hour average concentrations, by year
EPA NAAQS = 100 ppb; WHO health guideline = 105 ppb
40.49b
—c
—c
c
46.53
—
—c
45.94
—c
—c
b
51.17
52.41
—c
56.23
66.93
41.79b
78.61
49.93
49.83
59.35
58.62
47.83b
56.19b
49.78
—c
c
—
72.79
—c
—c
54.96
—c
c
—
52.59
—c
—c
50.29b
—c
Notes: a Data were downloaded from TCEQ’s Texas Air Monitoring Information System (TCEQ, 2012).
b
Monitoring site did not operate during the entire calendar year; data are based on all valid measurements
from the calendar year.
c
Monitoring data were not collected at these sites during these years.
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Midlothian Area Air Quality—Assessing the Public Health Implications of the Criteria
(NAAQS) Air Pollutants and Hydrogen Sulfide Health Consultation Public Comment Release
Table 6. Estimated Annual PM10 Emissions from Midlothian Facilitiesa,b
Year
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
Ash Grove
(tons per year)
235
—c
210
228
259
282
830
541
565
549
505
445
451
271
274
276
290
277
274
169
217
Gerdau Ameristeel
(tons per year)
129
—c
135
137
123
140
114
134
119
151
166
155
157
150
155
156
167
163
148
109
129
Holcim
(tons per year)
119
—c
90
78
53
47
306
305
361
361
393
356
379
342
341
328
502
399
338
198
130
TXI Operations
(tons per year)
26
—c
371
331
332
295
270
291
296
305
310
366
301
300
309
327
273
301
291
163
141
Notes: a All data are shown in units of tons per year (tpy).
b
Emissions data are taken from TCEQ’s Point Source Emissions Inventory (TCEQ, 2011), with all data
points rounded to the nearest ton.
c
No Point Source Emissions Inventory were available for calendar year 1991.
73
Midlothian Area Air Quality—Assessing the Public Health Implications of the Criteria (NAAQS) Air Pollutants and Hydrogen
Sulfide Health Consultation Public Comment Release
Table 7. Summary of Ambient Air Monitoring Data for PM10, 1991-2004a
Name of Monitoring Station
Time Frame
Number of
Samples
Highest 24-Hour
Average
Concentration
(µg/m3)
Auger Road
Auger Road Water Treatment
Box Crow
CAMS 302 – Wyatt Road
Cedar Drive
Cement Valley Road
Gerdau Ameristeel
Gorman Road
Hidden Valley
Midlothian Tower
Mountain Creek
Old Fort Worth Road
Tayman Drive Water Treatment Plant
1/1991-1/1993
1/1991-1/1992, 1/1993-11/1994
11/1993-1/1995
1/2000-6/2004
1/1992-10/1994
1/1992-6/1992
1/1996-12/1998
3/1992-4/1993
9/1992-10/1993
11/1994-6/2004
3/1992-4/1993
11/1994-6/2004
1/1993-12/1996
118
148
66
256
168
24
181
66
68
569
62
566
279
84
70
79
73
79
30
127
99
72
94
52
126
83
Highest Annual
Average
Concentration
(µg/m3)
21.0
23.2
23.5
27.4
21.0
—b
50.8d
31.0
22.0
26.0
19.0
29.5
23.6
Notes: a PM10 monitoring data were downloaded from TCEQ’s Texas Air Monitoring Information System (TCEQ, 2012) and obtained from an air quality study
published in 1995 by the Texas Natural Resource Conservation Commission (TNRCC, 1995).
b
Annual average concentrations were only calculated for sites that recorded at least 30 valid 24-hour average PM10 measurements in a calendar year.
c
The following health-based screening values were used to evaluate these data:
For 24-hour average concentrations, EPA’s health-based NAAQS is 150 µg/m3, not to be exceeded more than once per year on average over 3
years; and WHO’s health guideline is 50 µg/m3.
For annual average concentrations, EPA’s former health-based NAAQS is 50 µg/m3; and WHO’s current health guideline is 20 µg/m3.
d
Bold font is used to indicate measured concentrations above the level of EPA’s current or former NAAQS for PM10.
74
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Table 8. Annual Average PM10 Concentrations at Selected Monitoring Stationsa,b
Year
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
Upwind Stations
Midlothian
Tower
22.5
22.0
21.4
26.0
22.7
24.8
21.7
23.2
24.7
19.6b
Annual Average PM10 Concentrations (µg/m3)
Downwind Stations
Old Fort
Gerdau Ameristeel
Wyatt Road
Worth Road
—c
—c
22.7
c
20.9
—
50.8
—c
48.1
19.9
c
—
50.2
24.9
—c
—c
24.6
26.9
27.4
—c
24.7
25.1
—c
23.7
23.6
—c
29.5
27.1
—c
b
b
20.5
26.1
—c
Notes: a Data were downloaded from TCEQ’s Texas Air Monitoring Information System (TCEQ, 2012).
b
Monitoring site did not operate during the entire calendar year; data are based on all valid measurements
from the calendar year.
c
Monitoring data were not collected at these sites during these years.
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Table 9. Estimated Annual PM2.5 Emissions from Midlothian Facilitiesa,b
Year
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
Ash Grove
(tons per year)
258
96
348
234
239
241
247
235
234
145
183
Gerdau Ameristeel
(tons per year)
136
128
130
125
135
136
145
140
128
97
119
Holcim
(tons per year)
393
355
378
300
323
309
465
356
292
167
106
TXI Operations
(tons per year)
101
143
115
114
127
131
141
155
151
76
70
Notes: a All data are shown in units of tons per year (tpy).
b
Emissions data are taken from TCEQ’s Point Source Emissions Inventory (TCEQ, 2011), with all data
points rounded to the nearest ton. The earliest year with PM2.5 data available for all four facilities is 2000.
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Sulfide Health Consultation Public Comment Release
Table10. Summary of Ambient Air Monitoring Data for PM2.5, 2000-2011ab
Name of Monitoring Station
CAMS 302—Wyatt Road
(8/2000-3/2006)
Holcim Facility Boundary
(1/2006-1/2010)
Midlothian Tower
(2/2000-12/2006)
Old Fort Worth Road
(9/2005-12/2011)
Notes:
Type of
Sampling
Year
2001
2002
2003
2004
2005
2006
2007
2008
2009
2000
2001
2002
2003
2004
2005
2006
2006
2007
2008
2009
2010
2011
Continuous
Continuous
Continuous
Continuous
24-hour
24-hour
24-hour
24-hour
24-hour
24-hour
a
10.2
11.4
11.7
10.9
11.9
11.5
10.2
11.8
10.5
10.0
10.4
11.8 (partial)
11.5
11.5
12.4(partial)
10.2
11.0
11.4
11.8
9.2
9.7
10.3
Highest 24-Hour Average
Concentration (µg/m3)c
52.1
42.2
50.2
50.6
PM2.5 monitoring data were downloaded from TCEQ’s Texas Air Monitoring Information System (TCEQ, 2012) and obtained from researchers at the University of Texas at Arlington (UTArlington, 2008-2010). ATSDR adjusted the annual average PM2.5 TCEQ data from the continuous monitors before 2005 by 2 µg/m3 to account for the negative bias from these types of
monitors. TCEQ reported all annual average continuous monitoring data from 2005 forward by including this adjustment (Personal Communication, Tracie Phillips, TCEQ, 2012); therefore,
ATSDR did not do this adjustment for TCEQ continuous monitoring data for this timeframe. ATSDR does not have side-by-side 24-hour data to determine what the magnitude of the
negative bias might have been for the Holcim continuous monitoring data; therefore, it is possible that the values presented may underestimate PM2.5 exposure downwind of Holcim. If data
were available from both continuous and 24-hour sampling, ATSDR reports the highest value. ATSDR did not report partial year data unless at least 50% of the data were available for that
year.
b
The following health-based screening values were used to evaluate these data:
For 24-hour average concentrations, EPA’s health-based NAAQS is 35 µg/m3, based on the 98th percentile concentration averaged over 3 years; and WHO’s health guideline is 25
µg/m3.
For annual average concentrations, EPA’s health-based NAAQS is 15 µg/m3 averaged over 3 years; the EPA proposed range for lowering the annual average PM2.5 is 12-13
µg/m3, and WHO’s health guideline is 10 µg/m3.
c
Bold font is used to indicate which maximum concentrations are above the level of EPA’s NAAQS for daily PM2.5; refer to Section 4.5.3 for further insights on the magnitude of the 98th
percentile concentrations, which are more relevant for comparing to the health-based standards. Bold and italicized font is used to indicate which annual average concentrations were above
the EPA proposed range for lowering the standard—none of the reported values are above the current EPA NAAQS for annual average PM2.5.
77
Annual Average
Concentration
(µg/m3)c
Midlothian Area Air Quality—Assessing the Public Health Implications of the Criteria
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Table 11. Estimated Annual Sulfur Dioxide Emissions from Midlothian Facilitiesa,b
Year
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
Ash Grove Cement
(tons per year)
2,796
—c
4,388
2,284
3,577
2,083
3,134
3,633
3,872
4,830
4,368
4,927
4,434
5,026
6,216
6,013
6,263
6,227
4,776
2,697
4,115
Gerdau Ameristeel
(tons per year)
1d
—c
1d
1d
1d
1d
144
142
129
121
131
120
122
120
125
122
133
130
115
74
108
Holcim
(tons per year)
3,053
—c
3,756
2,967
4,116
3,643
5,864
3,903
3,691
2,522
4,483
2,427
3,167
2,501
2,658
2,655
3,330
2,481
2,706
1,661
1,089
TXI Operations
(tons per year)
13,068
—c
4,398
4,357
4,983
6,111
5,109
5,317
5,490
5,129
6,303
4,339
2,099
2,333
2,324
3,356
2,551
2,497
1,721
550
493
Notes: a All data are shown in units of tons per year (tpy).
b
Emissions data are taken from TCEQ’s Point Source Emissions Inventory (TCEQ, 2011), with all data
points rounded to the nearest ton.
c
No Point Source Emissions Inventory were available for calendar year 1991.
d
In the earliest years of the Point Source Emissions Inventory, emissions data for Gerdau Ameristeel were
considerably lower than what the facility reported in subsequent years. The reason for this is not known.
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Table 12. Annual Average Sulfur Dioxide Concentrations, 1997-2011a
Year
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
Annual Average Sulfur Dioxide Concentrations (ppb)
Upwind Stations
Downwind Stations
Midlothian Tower
Old Fort Worth Road
Wyatt Road
Annual average concentrations, by year
No health-based standards available from EPA, TCEQ, or WHO
2.47b
1.82b
—c
1.41
2.61
—c
1.13
3.87
—c
1.60
5.47
—c
1.35
3.51
—c
0.92
0.88
—c
1.15
1.22
—c
1.08
1.02
0.46b
1.53
2.65
0.93
0.48b
1.11
2.11
0.82b
0.87
—c
c
—
0.87
—c
c
—
0.54
—c
—c
0.87
—c
c
b
—
0.65
—c
Notes: a Data were downloaded from TCEQ’s Texas Air Monitoring Information System (TCEQ, 2012).
b
Monitoring site did not operate during the entire calendar year; data are based on all valid measurements
from the calendar year.
c
Monitoring data were not collected at these sites during these years.
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Table 13. Additional Trends in 1-Hour Average Sulfur Dioxide Monitoring Dataa,b
Evaluation Based on EPA’s Health-Based NAAQS: 75 ppb
99th Percentile of Daily Maximum 1-Hour Sulfur Dioxide Concentrations
(ppb), Averaged over Three Consecutive Calendar Years
3-Year Period
Midlothian Tower
Old Fort Worth Road
1997-1999
54.3
122.7
1998-2000
56.7
139.7
1999-2001
62.7
158.7
2000-2002
71.7
125.3
2001-2003
65.7
92.0
2002-2004
58.3
62.3
2003-2005
51.7
81.0
2004-2006
49.3
93.3
2005-2007
52.3
101.3
—c
2006-2008
85.7
c
—
2007-2009
57.3
c
—
2008-2010
31.0
—c
2009-2011
15.3
Notes: a Data were accessed using queries on EPA’s AirData system, including exceptional events (EPA, 2012).
The 99th percentile values were downloaded for individual years, from which averages were calculated over
three consecutive years.
b
Summaries are shown for only those sites with three consecutive years of sulfur dioxide monitoring data.
c
Monitoring data were not collected at these sites for the entire 3-year periods.
d
Entries in bold font are higher than the level of EPA’s current health-based standard, which the agency
passed in 2010.
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Table 14. Summary of Ambient Air Monitoring Data for Hydrogen Sulfide, 2000-2011a
Hydrogen Sulfide Concentrations (ppb)
Year
Upwind Stations
Downwind Stations
Midlothian Tower
Old Fort Worth Road
Wyatt Road
Annual average concentrations, by year
EPA RfC = 1.4 ppb
—c
2000
0.28
0.31
2001
0.39
0.29
—c
2002
0.35
0.34
—c
2003
0.58
0.55
—c
2004
0.33
0.60b
0.59b
c
2005
0.23
—
0.60
2006
0.13
0.20b
0.48b
2007
0.01b
0.47
—c
c
2008
—
0.42
—c
2009
—c
0.35
—c
c
2010
—
0.28
—c
2011
—c
0.27
—c
Highest 1-hour average concentrations, by year
ATSDR Acute MRL = 70 ppb; TCEQ standard = 80 ppb; WHO health guideline = 106 ppb
2000
2.82
2.88
—c
2001
10.08
2.82
—c
2002
4.77
6.98
—c
2003
7.27
13.95
—c
2004
2.85
3.72b
3.16b
c
2005
2.66
—
14.36
2006
4.05
2.92b
2.15b
2007
2.13b
7.25
—c
c
2008
—
4.32
—c
2009
—c
4.16
—c
c
2010
—
3.60
—c
2011
—c
3.97
—c
Notes: a Data were downloaded from TCEQ’s Texas Air Monitoring Information System (TCEQ, 2012).
b
Monitoring site did not operate during the entire calendar year; data are based on all valid measurements
from the calendar year.
c
Monitoring data were not collected at these sites during these years.
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Table 15. Summary of Health Comparison Values Used and Selection of NAAQS/H2S Air
Pollutants as a Contaminant of Concerna
Air Pollutant
EPA HCV
WHO HCV
ATSDR HCV
Carbon
monoxide
Lead
Nitrogen
dioxide
Ozone
PM (as TSP)
35 ppm (1-hour)
9 ppm (8-hour)
0.15 µg/ m3
100 ppb (1-hour)
53 ppb (annual)
75 ppb (8-hour)
260 µg/m3 (24-hour)b
75 µg/m3 (annual)b
150 µg/ m3 (24-hour
50 µg/m3 (annual)b
35 µg/m3 (24-hour)
15 µg/m3 (annual)
12-13 µg/m3 (proposed
annual)
75 ppb (1-hour)
26 ppm (1-hour)
9 ppm (8-hour)
0.5 µg/ m3 (annual)
106 ppb (1-hour)
21 ppb (annual)
50 ppb (8-hour)
NA
NA
COC
(Y/N)
N
NA
NA
Y
N
NA
NA
Y
N
NA
Y
NA
Y
PM10
PM2.5
Sulfur dioxide
Hydrogen
sulfide
Notes:
1.4 ppb (annual)
50 µg/m3 (24-hour)
20 µg/m3 (annual)
25 µg/m3 (24-hour)
10 µg/m3(annual)
8 ppb (24-hour)
190 ppb (10-minute)
106 ppb (24-hour)
a
A Contaminant of Concern is defined as one that is selected for further evaluation in the Public Health
Implications Section because it is above a HCV.
b
Previous EPA standard which has since been revoked.
EPA-United States Environmental Protection Agency
HCV-Health Comparison Value
WHO-World Health Organization
COC-Contaminant of Concern
ppm-parts per million
NA-none available
µg/m3-micrograms per meter cubed
ppb-parts per billion
PM-particulate matter
TSP-total suspended particulates
82
10 ppb (chronic, Y
1 year or greater)
70 ppb (acute,
N
1-14 days)
Midlothian Area Air Quality—Assessing the Public Health Implications of the Criteria (NAAQS) Air Pollutants and Hydrogen
Sulfide Health Consultation Public Comment Release
Table 16: Percentage Peak (5-Minute Average) Sulfur Dioxide Concentrations by Monitoring Station (1997-2011)�
Monitoring Station (Timeframe)
Sulfur Dioxide Concentration (ppb)
% > 400
% >200-400
<<0.001
0.01
0
0
b
0.002
0.008
<<0.001
<<0.001
% >100-200
0.23
0
0.04
0.2
% >10-100
5.1
0.58
1.3
2.3
OFWR (1997-2008)
OFWR (2009-2011)
Wyatt Road (2004-2006)a
Midlothian Tower (1997-2007)
ppb-parts per billion
>-Greater than
OFWR-Old Fort Worth Road
<<-Much less than
a-The only full year of data available for the Wyatt Road monitor was 2005—data for 2004 and 2006 accounted for about 20-25% of
all possible measurements for those years.
b-Three 5-minute SO2 measurements above 400 ppb occurred at the Wyatt Road Monitor during 2005. The highest SO2 level
recorded for all monitors and timeframes (568 ppb) was one of these measurements.
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12. Figures
Figure 1. Locations of Lead Monitoring Stations
Figure 2. Locations of Nitrogen Dioxide Monitoring Stations
Figure 3. Locations of Ozone Monitoring Stations
Figure 4. Location of TSP Monitoring Station
Figure 5. Locations of PM10 Monitoring Stations
Figure 6. Locations of PM2.5 Monitoring Stations
Figure 7. Locations of Sulfur Dioxide Monitoring Stations
Figure 8. Locations of Hydrogen Sulfide Monitoring Stations
Figure 9. Frequency of Sulfur Dioxide Exceedances by Wind Direction at Old Fort Worth
Road Monitor (September 1997—May 2009)
Figure 10. Peak 5-Minute Sulfur Dioxide Levels in Midlothian Area from 1997-2011
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Midlothian Area Air Quality—Assessing the Public Health Implications of the Criteria
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Figure 1
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Figure 2
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Midlothian Area Air Quality—Assessing the Public Health Implications of the Criteria
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Figure 3
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Figure 4
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Figure 5
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Figure 6
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Figure 7
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Figure 8
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Midlothian Area Air Quality—Assessing the Public Health Implications of the Criteria (NAAQS) Air Pollutants and Hydrogen
Sulfide Health Consultation Public Comment Release
Figure 9: Frequency of Sulfur Dioxide Exceedances by Wind Direction at the
Old Fort Worth Road Monitor (September 1997- May 2009)
Frequency of 1-hour SO2 Exceedances
15
12
9
6
3
Wind Direction (degrees)
93
350-360
340-350
330-340
320-330
310-320
300-310
290-300
280-290
270-280
260-270
250-260
240-250
230-240
220-230
210-220
200-210
190-200
180-190
170-180
160-170
150-160
140-150
130-140
120-130
110-120
100-110
90-100
80-90
70-80
60-70
50-60
40-50
30-40
20-30
10-20
0-10
0
Midlothian Area Air Quality—Assessing the Public Health Implications of the Criteria
(NAAQS) Air Pollutants and Hydrogen Sulfide Health Consultation Public Comment Release
Figure 10: Peak 5-Minute Sulfur Dioxide Levels in Midlothian Area from 1997-2011
1.
ATSDR MRL – ATSDR’s acute Minimal Risk Level (10 ppb) for Sulfur Dioxide.
ATSDR 1998: Toxicological profile for sulfur dioxide.
2.
LOAEL – ATSDR acute Lowest Observed Adverse Effect Level (LOAEL)(100 ppb)
using mouthpiece exposure in human clinical study. Shepard et al. 1981: Exercise increases
sulfur dioxide-induced bronchoconstriction in asthmatic subjects. Am Rev Respir Dis 123:486
491.
3.
Lower range of reported oronasal effects (200 ppb), based on several studies. USEPA
2008c: Integrated science assessment for sulfur oxides – health criteria. Office of Research and
Development. EPA/600/R-08/047FA.
4.
Lower range of statistically significant symptom expression (400 ppb), based on several
studies. USEPA 2009c: Risk and exposure assessment to support the review of the SO2 Primary
National Ambient Air Quality Standards: second draft.
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Midlothian Area Air Quality—Assessing the Public Health Implications of the Criteria
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Appendices
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Midlothian Area Air Quality—Assessing the Public Health Implications of the Criteria
(NAAQS) Air Pollutants and Hydrogen Sulfide Health Consultation Public Comment Release
Appendix A. ATSDR Carbon Monoxide Modeling
For most of the criteria pollutants considered in this Health Consultation, ATSDR based its
conclusions on ambient air monitoring data, or direct measurements of levels of air pollution in
the Midlothian area. This basis was not the case for carbon monoxide because no ambient air
monitoring data are available for this pollutant. Therefore, ATSDR conducted air dispersion
modeling analysis for carbon monoxide. Such models can be used to estimate air pollution levels
based on facility configurations, emission rates, local meteorologic conditions, and other factors.
This appendix describes the air dispersion modeling analysis that ATSDR conducted. All model
input files used for this modeling are available in electronic format from ATSDR, upon request.
The modeling described in this appendix was designed to characterize the combined air quality
impacts from all four industrial facilities in the Midlothian areaand does not account for
influences from any other sources.
Model selection. Modeling was performed using the AERMOD model, version number 11103.
AERMOD was chosen because it is recommended in EPA’s Guideline on Air Quality Models
(EPA, 2005). AERMOD has been widely used for modeling how pollutants move from industrial
facilities through the air to offsite locations. This model can be used for evaluating different
types of emission sources, including point, area, and volume sources. AERMOD also can be
used to assess air pollution levels in all types of terrain, including flat and complex.
Pollutants. This appendix reviews the modeling that ATSDR conducted for carbon monoxide.
ATSDR also used this model to evaluate air-quality impacts for several other air pollutants.
Those results will be presented in a separate Health Consultation.
Facilities and sources modeled. The modeling focused on emissions from Ash Grove Cement,
Gerdau Ameristeel, Holcim, and TXI Operations. For carbon monoxide, the overwhelming
majority of emissions that the facilities reported to the state emission inventory come from either
kiln stacks (at the cement manufacturing facilities) or furnace stacks (at the steel mill). This
reporting is consistent with the knowledge that industrial emission sources of carbon monoxide
are dominated by fuel combustion sources and other high-temperature sources.
ATSDR’s approach was to model carbon monoxide emissions from one stack per facility, and
the stack selected was the one expected to have the least favorable dispersion (i.e., the shortest
kiln or furnace stack and the lowest exit velocity). For each facility, ATSDR allocated 100 %of
the facilitywide emissions to the one stack selected for modeling. In other words, 100 %of each
facility’s carbon monoxide emissions were considered in the model—they were just assumed to
be emitted from the stack that would lead to the highest offsite air quality impacts. Although
some facilities have ground-level emissions source of carbon monoxide (e.g., exhaust from
trucks and small engines), these account for a small fraction of the facility’s overall inventories.
The tables at the end of this protocol list the stack parameters and emission rates for the facilities
of interest. Building downwash was not considered, primarily because the stacks are higher than
the nearby buildings and structures.
Meteorologic data. AERMOD, like most refined dispersion models, requires inputs that
characterize local meteorologic conditions—typically hourly observations of wind speed, wind
A1
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1$$46 $LU 3ROOXWDQWV DQG +\GURJHQ 6XOILGH +HDOWK &RQVXOWDWLRQ 3XEOLF &RPPHQW 5HOHDVH
direction, temperature, and other parameters. For this modeling, ATSDR used the electronic
meteorologic data sets that TCEQ had already processed for modeling applications in Ellis
County, Texas. The data used were for medium surface roughness, which is appropriate for rural
and suburban areas. The specific data set processed by TCEQ and used in modeling applications
in this area includes surface meteorological data from the Dallas–Fort Worth Airport for calendar
years 1985, 1987, 1988, 1989, and 1990; these data are processed with upper air data from
Stephenville, Texas. The five individual year datasets were combined into a single file for input
to the model.
Terrain data. Elevation data for the Midlothian area were obtained from the National Elevations
Dataset available from the U.S. Geological Survey. These data were used to assign elevations to
every location where air pollution was modeled and to make realistic assessments of how local
terrain affects atmospheric dispersion.
Receptor grid. In the field of dispersion modeling, “receptors” refer to the locations where
models estimate air pollution levels. Receptors can be assigned to any geographic area of
interest. The proposed receptor grid for this modeling application was selected to help pinpoint
locations with maximum impact from the primary stack at an individual facility. It is standard
practice to have a high concentration of receptors in areas where one expects air pollution levels
to be highest and fewer receptors in other areas. This approach helps ensure the highest air
pollution levels are identified, while saving computational time. The receptor grid for this
modeling is depicted in Figures C-1, C-2, and C-3, and included three tiers of receptors:
Fine grid for near-field receptors. The most receptors were placed in the immediate
vicinity of the four facilities. Specifically, receptors were placed at 100-meter intervals
along the facility boundaries and at regular spacing to a distance 1 kilometer from the
facility boundary. Concentrations were not modeled for locations within the facility
boundaries. Figures C-1 and C-2 show the near-field receptor grid.
Intermediate grid receptors. At distances between 1 and 5 kilometers from the facility
boundaries, receptors were placed at 500-meter intervals. Figure C-3 shows these
receptors.
Coarse grid for far-field receptors. At locations between 5 and 10 kilometers from the
facilities, receptors were placed at 1,000-meter intervals. Figure C-3 shows the locations
of these receptors. Modeling was not conducted for locations more than 10 kilometers
away from the facility boundaries. The outputs from the modeling confirmed that this
modeling domain was adequate and that higher air quality impacts for carbon monoxide
did not occur at locations further downwind.
Model inputs and emission rates. Table C-1 lists all of the model inputs for the individual
facilities. For the stacks considered in the analysis, the table lists the geographic coordinates, the
stack height and diameter, and the temperature and velocity of the emissions from the stack.
These parameters are all taken from publicly available Emission Inventory Questionnaire data.
Carbon monoxide emission rates used in the modeling (and shown in Table C-1) are the highest
annual carbon monoxide emissions levels documented in the TCEQ Point Source Emission
$
Midlothian Area Air Quality—Assessing the Public Health Implications of the Criteria
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Inventory for any year during the period 1990– 2010. These annual emissions are the total
amounts of carbon monoxide released over the course of the year. For purposes of modeling,
these values were used to calculate emission rates, which were assumed to remain constant
throughout the year.
Model outputs and averaging times. The model was run with 5 years of meteorologic data, and
carbon monoxide concentrations were calculated for each receptor. These concentrations
represent the combined air quality impact from all four Midlothian facilities, not considering
contributions from other sources. The highest air quality impacts were observed at locations
immediately north of the Gerdau Ameristeel and TXI Operations facilities. Table C-2 lists the
highest predicted carbon monoxide concentrations for several averaging periods.
Uncertainties and limitations. ATSDR considered the uncertainties and limitations of these
modeling results. The model inputs for stack parameters are based on direct observations of
facility conditions, and these are believed to be highly accurate. The meteorologic data used in
the model are based on observations at the Dallas–Fort Worth Airport. Although this location is
approximately 30 miles away from Midlothian, the prevailing wind directions in the data set are
similar to those encountered in the Midlothian area.
The main source of uncertainty is likely associated with the emissions data. ATSDR took steps to
ensure that the highest annual emissions were modeled. For example, for each facility, the
highest annual carbon monoxide emissions were considered in the assessment. Further, even
though the highest emissions occurred during different years across the four facilities, the model
assumed the highest annual emissions from all four facilities occurred at the same time. ATSDR
believes the emissions data to be accurate, given that reported emissions (at least in recent years)
are largely based on continuous emissions monitoring data from the stacks; some of the facilities
are required to directly measure the amounts of carbon monoxide that they are releasing. Despite
these efforts to ensure that the modeling is based on health-protective assumptions, the main
limitation in the emissions data is that the assessment is based on annual emissions, which were
assumed to remain constant throughout the year. In reality, emissions vary from one hour to the
next, and short-term fluctuations in emissions are not captured in the modeling analysis (but
short-term fluctuations in the local meteorologicl conditions are addressed). Therefore, the
possibility remains that some short-term carbon monoxide concentrations were higher than the
worst-case levels predicted by the model, but they probably would have occurred only if elevated
short-term emissions happened during times with unfavorable meteorologic conditions.
References
[EPA] US Environmental Protection Agency. 2005. Guideline on Air Quality Models. Code of
Federal Regulations, Chapter 40, Part 51, Appendix W. November 9, 2005.
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Table A-1. Model Input Parameters
Input Parameters
Stack modeled
UTM-North (zone 14)
UTM-East (zone 14)
Stack height
Stack diameter
Exit temperature
Exit velocity
CO annual emissions
Source of emissions data
Facility
Ash Grove Cement
“Kiln #1”
3,599,875 meters
687,419 meters
150 feet
10.5 feet
350 oF
31 feet/second
1,254,600 lbs/year
1990 emission inventory
Gerdau Ameristeel
“Baghouse A”
3,592,800 meters
684,525 meters
80 feet
11.9 feet
150 oF
5.9 feet/second
4,278,660 lbs/year
1994 emission inventory
Holcim
“Kiln #1”
3,599,176 meters
690,633 meters
273 feet
13.5 feet
233 oF
56 feet/second
12,175,846 lbs/year
2004 emission inventory
TXI Operations
“Kiln #4”
3,593,584.25 meters
685,435.55 meters
200 feet
9 feet
383 oF
37.43 feet/second
2,104,000 lbs/year
1990 emission inventory
Notes: The stack parameters are all taken from data documented on the facility’s Emission Inventory Questionnaires for years 2000,
2007, 2010. Stack parameters are not expected to change from one year to the next. In each case, the stack modeled is the kiln or
furnace stack expected to have the highest air quality impacts. For purposes of the modeling, 100 % of the facility’s carbon monoxide
emissions were assumed to be emitted from these stacks.
The emissions data represent the highest annual carbon monoxide emission rates that were available from TCEQ’s Point
Source Emissions Inventory. ATSDR obtained all relevant records for the four industrial facilities, dating back to the first year of this
emission inventory (1990). The entries shown above are the highest annual emissions over the entire period of record. ATSDR’s
modeling assumed that emissions occurred at these rates over the entire period considered in the modeling analysis.
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Table A-2. Highest Estimated Carbon Monoxide Concentrations
Averaging Time
1-hour
8-hour
Annual average
5-year average
Highest Estimated Carbon Monoxide Concentration
Micrograms per cubic meter (µg/m3)
Parts per billion (ppb)
848
971
553
633
103
118
87
100
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Figure A-1. Aerial Photograph Showing Near-Field Receptor Grid near Ash Grove
Cement and Holcim
Note: Map shows placement of near-field receptors in the vicinity of the Ash Grove
Cement and Holcim facilities. The near-field receptors are placed along the property lines
and at 100-meter intervals and appear in the map as green dots. No receptors are placed
within the facility boundaries.
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Figure A-2. Aerial Photograph Showing Near-Field Receptor Grid near Gerdau
Ameristeel and TXI Operations
Note: Map shows placement of near-field receptors in the vicinity of the Gerdau
Ameristeel and TXI Operations facilities. The near-field receptors are placed along the
property lines and at 100-meter intervals and appear in the map as green dots. No
receptors are placed within the facility boundaries. Some intermediate-range receptors
(placed at 500-meter intervals)also are displayed.
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Figure A-3. Illustration Showing Entire Receptor Grid for Modeling Domain
Note: Map shows proposed placement of all receptors. The far-field receptors at 1,000
meter intervals appear around the exterior of the illustration. The intermediate range
receptors at 500-meter intervals also are visible. The near-field receptors at 100-meter
intervals also are displayed, but they appear as a shaded area rather than individual points
because of their close proximity when displaying the entire modeling domain.
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Appendix B. Sulfur Dioxide Health Evaluation
ATSDR addresses health concerns in public health assessments using both quantitative
and qualitative methods. For SO2, the qualitative strength of evidence approach will
serve a primary role in deciding the public health significance of SO2 levels. The
strength of evidence approach requires (1) a thorough review of the scientific literature
for health effects from acute and chronic exposures, (2) an evaluation of the potential for
sensitive groups to be exposed, (3) the evaluation of site-specific exposure scenarios, and
(4) the evaluation of co-exposures to other air pollutants.
Although health guidelines describe levels believed to be safe from exposure to a specific
chemical on a population basis, they do not describe the likelihood of adverse health
effects for exposures above that value. As part of ATSDR’s strength of evidence
evaluation, we evaluate the likelihood of harmful effects occurring should a health
guideline be exceeded. The site-specific evaluation will consider sensitive populations,
co-exposures to other contaminants, and the location, frequency, duration and time of day
the exposures occur.
Health Effects Assessment
ATSDR evaluated potential health effects in the health consultation by considering the
locations of concentrations of SO2 of concern, the time of day, the frequency and duration
of SO2 peaks of concern, and co-exposure to other contaminants. The following identifies
the SO2 concentration ranges and associated ATSDR level of concern.
>10 – 400 ppb SO2.
ATSDR recognizes the variability in asthmatic response and uncertainty associated with
adopting any single SO2 concentration as a level of concern.
Exposures to 10-400 ppb SO2 appears to be the range of most uncertainty as to whether
an effect will occur and whether that effect should be considered adverse. ATSDR will
use the Midlothian 5-minute data to conduct a site-specific assessment to characterize the
likelihood of health effects occurring in this range.
Exposures in this range might be considered a public health hazard depending on the
frequency and duration of exposure, co-exposures to other contaminants, and exposure of
potentially more sensitive populations, such as children and individuals with pre-existing
respiratory disease. Exposures in this range will be evaluated using a site-specific
strength of evidence approach.
Peak exposures (5 -minutes) above 10 ppb SO2 to 400 ppb SO2 are described as a doseresponse continuum (Table B-1 below) where higher concentrations in this range are
more likely to cause a response in a greater number of sensitive individuals than lower
concentrations in this range. Clinical exposures in this range resulted in a response in
healthy mild-to-moderate asthmatic adults and adolescents who were exercising (at an
increased ventilation rate). Persons with severe asthma, unhealthy individuals, and
children were not included in these studies. These populations might be more sensitive
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than the populations that were included in the clinical studies. The lowest effect level
reported in human clinical studies was 100 ppb SO2 via mouthpiece exposure (oral
breathing) which bypasses the protective effect of the nasal mucosa [1, 2]. The lowest
level reported for effects in free-breathing or oronasal breathing subjects occurred about
200-250 ppb SO2 [3, 4]. An estimated 5 - 30 % of persons with asthma are believed to be
sensitive to exposures between 200 and 300 ppb SO2 and experience moderate or greater
decrements in lung function (greater than or equal to a 100% increase in sRaw (airway
resistance) and/or greater than or equal to a 15% decrease in Forced Expiratory Volume
in 1 second, or FEV1) [7]. Further, an estimated 20% – 35 % of exercising persons with
asthma experience moderate or greater lung function decrements at SO2 concentrations
400 – 500 ppb [5].
Acute effects reported in exercising adult and adolescents with asthma exposed to <400
ppb SO2 (5 minutes) are considered less serious than those exposed to > 400 ppb SO2
(exposures <500 ppb do not usually require the individual to cease the activity, do not
usually require medication, and do not usually require the individual to seek medical
attention). Effects up to 250 ppb SO2 are equivalent to reported effects of asthmatic
responses to exercise alone [6]. Effects such as bronchoconstriction might not be
perceived by the exposed individuals at the lower end of this range and symptoms
(coughing, wheezing, dyspnea) begin to appear > 400 ppb SO2.
Exposures of 10 ppb to 400 ppb SO2 (5 minutes) might be considered of variable public
health concern, depending on the intensity, frequency and duration of SO2 exposure.
Although about 200 ppb is the lower level of mild to moderate asthmatics experiencing
effects while at increased ventilation rates in clinical studies, these studies did not include
potentially more sensitive individuals. These studies were performed at laboratory
conditions of controlled humidity and temperature, whereas actual exposures might occur
at colder and dryer conditions that have been reported to result in an increased response
[7, 8].
Current scientific literature links health effects with short-term exposure to SO2 ranging
from 5-minutes to 24-hours. The Environmental Protection Agency (EPA) examined
potential 5-minute health benchmark values in the 100 – 400 ppb range in the second
draft of the Risk and Exposure Assessment to Support the Review of the SO2 Primary
National Ambient Air Quality Standards [9]. In addition, the frequency and duration of
exposures might increase the risk for longer-term health effects leading to respiratory or
cardiac disease. For example, increased frequency and duration of exposure to SO2
leading to a 24-hour average concentration of 140 ppb SO2, the former EPA National
Ambient Air Quality Standard (NAAQS) may be considered a public health hazard to all
populations. In epidemiologic studies, SO2-related respiratory effects were consistently
reported at lower concentrations than the clinical studies observed and in areas where the
maximum ambient 24-hour average SO2 concentration was below the former 24-hour
average NAAQS level of 140 ppb.
A decrease in heart rate variability has been reported in adults with asthma exposed to
200 ppb SO2 for 60 minutes [10]. The significance of these short-term effects to chronic
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cardiac endpoints is still being investigated but such exposures suggest the need for
public health concern.
>400-1000 ppb SO2
Exposures >600 ppb and less than 1000 ppb SO2 (5 minutes) might cause adverse health
effects in an estimated 35% - 60 % of exercising persons with asthma and an unknown
portion of other sensitive populations [5]. Effects in exercising adult or adolescent
persons with asthma exposed to this concentration range might include more serious
health effects that necessitate (1) stopping the exercise, (2) taking medication, or (3)
seeking medical attention. Exposures in this concentration range might be considered a
public health hazard to sensitive populations at elevated ventilation rates.
>1000 ppb SO2
Exposures to >1000 ppb SO2 (5 minutes) are considered an acute public health hazard to
all populations.
Sensitive populations
The following populations are considered sensitive or potentially sensitive to SO2
exposures in that the response to SO2 might be more severe or occur at a lower threshold
than the general population.
Asthmatics
Many persons with asthma are sensitive to SO2 exposure [11]. The referenced SO2
exposure ranges above are based on exposure to exercising asthmatic adults and
adolescents.
Children
Children might be at increased risk from exposure to ambient air contaminants with
respect to both toxicology and exposure. That children are more toxicologically sensitive
to SO2 but might be more vulnerable because of increased exposure is not clear.
Although physiologically based pharmacokinetic modeling has suggested that children
might be more vulnerable in the pulmonary region to fine particulate matter, it also
suggests that children’s airways might not be more sensitive than adults to reactive gases
such as SO2 [12].
Factors that might contribute to enhanced lung deposition in children include higher
ventilation rates, less contribution from nasal breathing, less efficient uptake of particles
in the nasal airways, and greater deposition efficiency of particle and some vapor phase
chemicals in the lower respiratory tract. A child breathes faster compared with an adult,
which might result in increased uptake [13]. Children spend three times as much time
outdoors as adults and engage in three times as much time playing sports and other
vigorous activities [14]. Based on these parameters, children are more likely to be
exposed to more outdoor air pollution than adults. Epidemiologic evidence suggests that
air pollution effects (lung function decrements) in children might not be fully reversible,
even if the exposure stops, although SO2 was not a major contaminant in these studies
[15].
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Other SO2 sensitive or vulnerable populations
Other sensitive populations might include obese individuals, individuals who have
chronic pro-inflammatory state like diabetics, older adults (65+ years), and individuals
with pre-existing respiratory and cardiopulmonary disease [16]. Vulnerable individuals
are those who spend time outdoors at increased exertion levels and might include
children, outdoor workers, and individuals who play sports or exercise outdoors.
Adverse health effects.
What constitutes an adverse health effect has long been debated [17]. Whether a less
serious observed effect to SO2 exposures in the 100 – 400 ppb range is considered an
adverse health effect is still the subject of uncertainty. Some scientists consider a
biological effect as an adverse effect only if the effect is medically significant in that the
subject must take medication, seeks medical treatment (hospital or medical practitioner
visit), or must stop the activity in which the subject was engaged. Other scientists
consider a biological effect to be adverse if the exposure reduces the reserve function of
the lung, reducing the subject’s ability to withstand additional insults.
ATSDR recognizes the variability in asthmatic response and uncertainty associated with
adopting any single health comparison value. ATSDR has described the reported range of
health effects from the scientific literature in the range of most uncertainty, 10 – 400 ppb
SO2. ATSDR needs to make a site-specific assessment to characterize the likelihood of
health effects occurring in this range. A site-specific evaluation would consider the
location of SO2 concentrations, the frequency, duration, time of day and day of week, and
co-exposures to other contaminants.
Severity and incidence of respiratory symptoms has been shown to increase with
increasing concentrations between 200 and 600 ppb SO2 in free-breathing exercising
adults with asthma following peak exposures (5-10 minutes). Statistically significant
increases in symptoms (chest tightness, coughing, or wheezing) are observed at
concentrations > or = 400 ppb SO2.
Exposure to concentrations at or above 200 ppb SO2 is considered by ATSDR to
potentially result in a diminished capacity to respond to exposures to other agents in
sensitive individuals at elevated ventilation rates. The diminished capacity results from a
moderate or greater decrement in lung function (i.e. increases in sRaw > or = 100% or
decrease in FEV1 > or = 15% in 5-30% of exercising asthmatics at 200-300 ppb SO2 with
5-10 minute exposures). This diminished capacity from the decrement in lung function is
considered an adverse health effect. This adverse health effect might be considered a
public health hazard to sensitive populations at elevated ventilation rates depending on
the potential impact of site-specific frequency and duration of exposure and the temporal
and spatial considerations and co-exposure potential. In addition, exposure must occur to
a sensitive individual while at an elevated ventilation rate.
Exposure to concentrations at or above 400 ppb SO2 might result in the increasing
potential for the development of symptoms (chest tightness, coughing, and wheezing) in
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sensitive populations at elevated ventilation rates. SO2 induces moderate or greater
decrements in lung function (described above) in 20%-60 % of persons with asthma at
400 – 1000 ppb SO2 with 5-10 minute exposures.
Exposure to concentrations at or above 600 ppb SO2 is considered a public health hazard
to sensitive populations at elevated ventilation rates because of the increasing potential
that medical intervention may be appropriate.
These conclusions are based on clinical investigations reported in peer-reviewed
scientific literature. These clinical investigations are based on responses in typically mild
to moderate healthy adults with asthma at elevated ventilation rates in controlled
temperature and humidity environments. Because of ethical considerations,
investigations do not usually involve persons with severe asthma, children, or unhealthy
individuals. These and other potentially sensitive or vulnerable individuals (obese
individuals, individuals with pro-inflammatory state like diabetics, adults greater than 65
years, and individuals with pre-existing respiratory and cardiopulmonary disease) might
be at risk for effects at lower SO2 concentrations or more severe effects at equivalent
concentrations. In addition, sensitive populations might experience an exacerbation of
effects from exposure to dry, cold air or co-exposure to other agents such as particulate
matter or ozone. Therefore, adverse health effects could occur to the more vulnerable or
sensitive individuals at levels below 200 ppb SO2. Although clinical investigations have
not addressed free-breathing levels below 200 ppb, mouthpiece investigations have
reports effects at 100 ppb.
Epidemiologic studies have provided consistent evidence of an association between
ambient SO2 exposures and increased respiratory symptoms in children, particularly those
with asthma or chronic respiratory symptoms. Multicity studies have observed these
associations at a median range of 17 to 37 ppb (75th percentile: -25 to 50) across cities for
3-hr average SO2 and 2.2 to 7.4 ppb (90th percentile: 4.4 to 14.2) for 24-hr average SO2
[18].
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Table B-1. Sulfur Dioxide Concentrations of Interest
Peak exposures
Respiratory effects in clinical studies. Peak exposures < 15 minutes.
10 ppb
MRL
% asthmatics affected
Less serious effects in exercising asthmatics
More serious effects in exercising asthmatics
100 ppb
Lowest
oral
exposure
effects
500-600 ppb
Take medication
Seek medical attention
Stop activity
200-250 ppb
Lowest
oronasal
exposure
effects
5 - 30 %
(200-300 ppb)
400 ppb
Symptoms:
cough
wheeze
dyspnea
20 – 35 %
(400 – 500 ppb)
Short-term exposure
75ppb
1-hour (short-term)
NAAQS (99th percentile daily maximum concentration averaged over three consecutive years)
1
EPA has revoked their previous short-term 24-hour standard and annual average standard.
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1000 ppb
Lowest
Non-sensitive
Populations
35 - 60 %
(600 – 1000 ppb)
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Health Guideline Values
The following are health-based guidelines for sulfur dioxide.
Short-term health-based criteria (based on human clinical studies)
ATSDR Acute MRL screening level (10 min)
UK/N Ireland (15 minutes)
(60 minutes)1
WHO 2005 Guidelines 2 (10 minutes)
CA EPA1
(60 minutes)
EPA3
(1-hour current standard)
Chronic health-based criteria (based on epidemiological studies)
EPA4 (24-hour NAAQS-Revoked in 2010)
Northern Ireland (24 hour)5
CA EPA2 (24-hour)
WHO 2005 Guidelines (24-hour)
10 ppb
100 ppb
135 ppb
190 ppb
250 ppb
75 ppb
140 ppb
48 ppb
40 ppb
8 ppb
EPA (Annual Average NAAQS—Revoked in 2010) 30 ppb
1
2
3
4
5
not to be exceeded more than 24 times/calendar year
not to be exceeded value
not to exceed the 99th percentile of 1-hour daily maximum
concentration averaged over three consecutive years
not to be exceeded more than once per year
not to be exceeded more than 3 times/calendar year
ATSDR’s acute minimal risk level (MRL) [19]. Acute exposures <10 ppb SO2 are not
likely to cause adverse health effects. The MRL is a screening level below which
exposure is believed to be without adverse (non-cancerous) health effects to all
populations, including sensitive groups. The MRL is not a threshold for health effects,
but exposures to concentrations above the MRL will be evaluated further using the
strength of evidence approach and site-specific factors.
EPA acute exposure guideline levels (AEGLs) for sulfur dioxide. AEGLs are intended to
apply to once-in-a-lifetime exposures to the general population including infants and
children, and other individuals who might be sensitiveand susceptible.
AEGL1 (10 minutes – 4 hours)
AEGL2 (10 minutes – 4 hours)
200 ppb
750 ppb
AEGL 1 – general population and susceptible individuals could experience notable
discomfort, irritation, or certain asymptomatic, non-sensory effects. Effects are not
disabling and are transient and reversible upon cessation of exposure.
AEGL 2 – general population and susceptible individuals could experience irreversible or
other serious, long-lasting adverse health effects or impaired ability to escape.
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References
1. Sheppard D, Saisho A, Nadel JA, et al. 1981. Exercise increases sulfur
dioxide-induced bronchoconstriction in asthmatic subjects. Am Rev Respir
Dis 123:486-491.
2. Trenga CA, Koenig JQ, Williams PV. 2001. Dietary antioxidants and ozoneinduced bronchial hyperresponsiveness in adults with asthma. Arch Environl
Health. 56(3):242-249.
3. Horstmann DH, Roger LJ, Kehrl HR, and Hazucha MJ. 1986. Airway
sensitivity of asthmatics to sulfur dioxide. Toxicol Ind Health. 2:298-298.
4. Boushey HA, Bethel RA, Sheppard D, Geffroy B, et al. 1985. Effect of 0.25
ppm sulfur dioxide on airway resistance in freely breathing, heavily
exercising, asthmatic subjects. Am Rev Respir Dis. 131:659-661.
5. US Environmental Protection Agency. 2008. Integrated Science Assessment
for Sulfur Oxides – Health Criteria. National Center for Environmental
Assessment. Office of Research and Development. Research Triangle Park,
North Carolina. EPA/600/R-08/047-F.
6. Horstman DH, Seal E, Folinsbee LJ, Ives P, and Rogers LJ. 1988. The
relationship between duration and sulfur dioxide induced bronchoconstriction
in asthmatic subjects. Am Ind Hyg Assoc J. 49:38-47.
7. Bethel RA, Sheppard D, Epstein J, Tam E, Nadel JA, Boushey HA. 1984.
Interaction of sulfur dioxide and dry cold air in causing bronchoconstriction in
asthmatic subjects. J Appl Physiol, 57, 419-423.
8. Linn WS, Shamoo DA, Anderson KR, Whynot JD, Avol EL, Hackney JD.
1985. Effects of heat and humidity on the responses of exercising asthmatics
to sulfur dioxide exposure. Am Rev Respir Dis, 131, 221-225.
9. US Environmental Protection Agency. Risk and Exposure Assessment to
Support the Review of the SO2 Primary National Ambient Air Quality
Standards: Second Draft. Office of Air Quality Planning and Standards.
March2009. EPA-452/P-09-003.
10. Tunnicliffe WS, Hilton MF, Harrison RM, and Ayres JG. 2001. The effect of
sulphur dioxide exposure on indices of heart rate variability in normal and
asthmatic adults. Eur Respir J. 17:604-608.
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11. US Environmental Protection Agency. 1994. Review of the National Ambient
Air Quality Standards for Sulfur Oxides: Assessment of Scientific and
Technical Information. Supplement to the 1986 OAQPS Staff Paper
Addendum (Final Report). Research Triangle Park, NC: Office of Air Quality
Planning and Standards.
12. Ginsberg GL, Foos BP, and Firestone MP. 2005. Review and analysis of
inhalation dosimetry methods for application to children’s risk assessment. J f
Toxicol Environ Health A. 68(8):573-615.
13. Koenig JQ and Mar TF. Sulfur Dioxide: Evaluation of current California air
quality standards with respect to protection of children. Prepared for the
California Air Resource Board, California Office of Environmental Health
Hazard Assessment. September 1, 2000.
14. US Environmental Protection Agency. Exposure Factors Handbook. 1997.
Washington, DC.
15. Gauderman WJ, Avol E, Gilliland F, Vora H, Tomas D, et al. The effect of air
pollution on lung development from 10 to 18 years of age. N Engl J Med.
2004. 351(11):1057-1067.
16. US Environmental Protection Agency. 2007. Integrated Science Assessment
for Sulfur Oxides- Health Criteria. First External Review Draft. National
Center for Environmental Assessment-RTP Division. Office of Research and
Development. EPA/600/R-07/108.
17. American Thoracic Society. 2000. What constitutes an adverse effect of air
pollution? Am J Respir Crit Care Med. 161:665-673.
18. US Environmental Protection Agency. 2008. Integrated Science Assessment
for Sulfur Oxides- Health Criteria. Second External Review Draft. National
Center for Environmental Assessment-RTP Division. Office of Research and
Development. May 2008. EPA/600/R-08/047.
19. Agency for Toxic Substances and Disease Registry. 1998. Toxicological
Profile for Sulfur Dioxide. US Department of Health and Human Services.
Atlanta, GA.
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| File Type | application/pdf |
| File Title | Microsoft Word - Midlothian TX NAAQS HC Approved PC 11 14 12 |
| Author | rlm6 |
| File Modified | 2012-11-15 |
| File Created | 2012-11-15 |