LYONS, BOULDER COUNTY, COLORADO
The Boulder County Public Health Department asked ATSDR to review the information available on burning tires as a partial replacement of coal as a fuel in the CEMEX, Inc. cement kiln. They requested help in addressing concerns by area residents about the potential health effects caused by the change in emissions. After a review of the source emissions testing report and site-specific air dispersion modeling of the CEMEX stack gases, ATSDR concluded that burning tires in the manner used during the November 2002 test is not anticipated to result in adverse public health effects in the communities near the plant. ATSDR classifies the stack emissions at this site "no public health hazard."
Lyons, Colorado is a small town located in Boulder County near the junction of State Highway 66 and US36. It is 14 miles north of Boulder and 8 miles west of Longmont on the eastern slope of the Rocky Mountains. Lyons, which has a population of 1585, is surrounded primarily by rural farmland and open space.
In July 2001, the CEMEX cement plant, located just east of Lyons, notified the North Boulder County Environmental Health Task Force of its intent to burn tire-derived fuel (TDF) in its rotary kiln as described in its air emissions permit issued by the State of Colorado. The proposed use of TDF at the plant has led to concerns by area residents about the potential health effects of emissions from the kiln. In response to these concerns, the Boulder County Public Health Department (BCPH) briefed its Board of Health in July 2001 on the proposed use of TDF at CEMEX. Subsequently BCPH agreed to analyze the use of tires at other cement kilns around the country to respond to the health concerns of the community. The BCPH analyzed stack test data with and without the burning of tires at other cement kilns and calculated the percent change in emissions after the conversion to TDF (BCPH 2002). The BCPH twice updated the Board of Health on this analysis and attended three public meetings, two held by CEMEX and one held by community groups (BCPH 2002).
In November 2002, the BCPH reported to the Board of Health that during their analysis of various cement kilns stack test data they did not find a definitive pattern of change in emissions with and without TDF. They requested CEMEX expand the planned stack test of its kiln emissions to analyze for a more extensive list of chemicals and conduct a risk assessment to determine if any health effects were possible in the community due to emissions from burning TDF.
CEMEX worked with BCPH and the Colorado Department of Public Health and Environment to develop an extensive stack test protocol to measure the emissions with and without the burning of tires in the kiln. Rather than a risk assessment, CEMEX prepared a "comparative risk assessment." This comparative risk assessment used, (1) stack test data, air dispersion modeling, and full risk assessments done for several other cement kilns to evaluate the effect of changes in emissions on risk for those communities, and (2) stack test data from the CEMEX plant when it was, and was not burning TDF. The assessment compared the emission rates at CEMEX with the emissions at the other plants and concluded that because CEMEX's emissions were similar to or lower than the stack emissions at the other plants the health risks to the Lyons community would be similar to the health risks found in the risk assessments for the other communities. They concluded, "Overall, the Lyons Plant emissions tests indicate no potential for adverse public health impacts from the use of TDF (Klingensmith 2003).
The BCPH initially contacted ATSDR in December of 2002 about evaluating this type of risk assessment. ATSDR agreed to do a health consultation if stack test data report, comparative risk assessment report, and other supporting documents were readily available for evaluation. The stack test for the CEMEX kiln was conducted in November of 2002 and the final report was issued in March 2003 (Dunmire 2003). The comparative risk assessment, Human Health Evaluation of Cement Kiln Emissions from Coal Supplemented with Natural Gas and Coal Supplemented with Tire (Klingensmith 2003), was also prepared in March 2003. After the public release of this data at a meeting in early May 2003, the BCPH requested that ATSDR evaluate the "comparative risk assessment" and the stack test report, and provide consultation on the potential public health effects that might result from burning TDF in the CEMEX cement kiln.
The community is concerned that replacing part of the coal, the current fuel, at the CEMEX plant with tires will make the stack emissions worse and cause adverse health effects. The community's representative, the Boulder County Public Health Department, asked ATSDR to address the general question of whether the change in fuel will cause adverse health effects, and to answer twelve specific questions (Milmoe 2003). See the section Reply to Specific Questions for the reply to their questions.
CEMEX, Inc. hired Air Pollution Testing, Inc. to sample their cement kiln stack emissions while burning only coal and while burning 19.2% tires with coal as fuel. The testing company used standard Environmental Protection Agency (EPA) stack sampling methods to collect the stack gas samples November 13 - 15 and November 20 - 22, 2002. The test burn protocol was well designed and the analytical data are representative of the concentration of chemicals present in the stack gases at that time. Four samples of each type of stack samples were taken when they were burning only coal and three samples of each type of stack samples were taken when they replaced 19.2% of the coal with whole tires. Normally three samples are taken, but due to sampling problems on one of the coal only tests, they discarded that sample and took a fourth sample (Dunmire 2003). Our only concern was the lack of adequate explanation as to what problem occurred that justified throwing out that one sample.
The detection limits achieved were below the health comparison values for each chemical. The quality control and quality assurance measures were very good, the percent isokinectics was excellent; probe, filter, and condenser temperatures were appropriate; and overall the laboratory QA/QC was very good. They did method blanks, field blanks, reagent blanks, spikes (both internal and surrogate spikes), and duplicate analyses. In summary, the data are acceptable for evaluating the potential for adverse public health effects.
To determine whether stack emissions will adversely affect public health ATSDR staff evaluate the ways by which the public can be exposed to the chemicals present in the gases-a pathways analysis. The primary exposure pathway for CEMEX stack emissions is inhalation. To evaluate whether the public will be exposed to concentrations of chemicals that could cause adverse health effects, we compared the chemicals' concentrations in the stack to health comparison values. Tables 1A and 1B (in Appendix A) contain the average concentrations of the chemicals detected in the three samples of CEMEX stack gases without tires and with 19.2% tires. The tables also list health comparison values for air that were available from a number of different sources (ACGIH 2002; ATSDR 2003).
Comparison values SHOULD NOT be used as predictors of adverse health effects or for setting clean-up levels. Media concentrations above a comparison value do not necessarily represent a health threat. They are used by ATSDR health assessors to select environmental contaminants for further evaluation.
Seventeen of the chemicals detected in the stack gases were over one or more comparison values in the stack, i.e., if someone stuck their head in the stack and breathed in, these chemicals might cause health effects. Table 2 and Table 3 list those chemicals. To determine what the concentrations of these 17 chemicals would be at ground level, where realistically the public could breathe them, ATSDR worked with the Colorado Department of Public Health and Environment to conduct air dispersion modeling using the following data:
- the stack gas velocity and exit temperature from the November 2002 stack test;
- one year of site-specific hourly meteorological data;
- site-specific parameters that affect the dispersion of stack emissions, such as building downwash, terrain elevations, and surrounding land uses;
- stack height, diameter, base elevation, and location; and,
- the EPA ISCST3 model.
Figure 1 summarizes the steps in the ATSDR evaluation of the CEMEX stack emissions. The model predicted that the maximally exposed individual resident (MEIR) would be exposed to a maximum 1-hour concentration of 1.2177 µg/m3 (micrograms of chemical per cubic meter of air) for each pound per hour (lb/hr) of that chemical released from the stack (Machovec 2003). This 1-hour concentration is the highest concentration that is likely to occur in a 1-year period, and is called the 1-hour dispersion factor. The hourly concentrations for the rest of that day and the following 364 days will be lower.
The dispersion factor for the maximum 24-hour concentration to which the MEIR will be exposed is 0.11851 µg/m3 for each pound per hour of that chemical released from the stack (Machovec 2003). This factor allows us to calculate the maximum air concentration to which anyone will be exposed for a 24-hour period during an entire year. All residents' exposure will be less than these concentrations for the following 364 days, and only persons at the MEIR location will be exposed to this concentration for that 24-hour period.
ATSDR compared the maximum 1-hour and maximum 24-hour concentrations of each chemical to "acute comparison values," such as, acute environmental media evaluation guides (acute EMEGs) (ATSDR 2003). ATSDR sets acute EMEGs as the concentrations below which the chemical is unlikely to pose a health threat if exposure occurs continuously for less than 14 days. If the maximum 1-hour and 24-hour ground level concentrations are below the corresponding acute EMEG then we know the acute EMEG value will not be exceeded for any 14-day period and acute type health effects are unlikely. The same would also be true if the maximum 1-hour concentration exceeded the acute EMEG, but the maximum 24-hour concentration did not exceed it, i.e., the 14-day average will be less than the acute EMEG and acute health effects are unlikely to occur.
The annual average concentration of a chemical to which the MEIR would be exposed is 0.00843 µg/m3 for each pound per hour of that chemical released from the stack (Machovec 2003). Using this dispersion factor, we calculated the average air concentration of each chemical in Table 2 to which the most exposed individual resident would be exposed for a full year. Table 2 lists these values. Ground level concentrations were calculated for the highest concentration of each chemical in Table 2, without regard to whether that concentration occurred when tires were being burned.
Table 3 lists the same chemicals as Table 2 along with the maximum pounds per hour emitted during any of the three runs when CEMEX was burning tires and when not burning tires. Using these maximum concentrations of each chemical, we calculated the maximum 1-hour, 24-hour, and annual ground level concentrations at the MEIR location. Table 3 represents the worst case exposures expected to occur in the community.
ATSDR compared the maximum and maximum average annual concentrations of each chemical in Tables 2 and 3 to available chronic, quarterly, or carcinogenic comparison values. None of the chemicals found in the CEMEX stack emissions were above any of the comparison values at the maximum projected ground level exposure concentrations.
Because the air pathway is the major route of public exposure to CEMEX stack emissions for residents in Boulder County and inhalation exposures are in most cases several orders of magnitude below the screening comparison values, we did not conduct a multi-pathway health assessment.
An issue that residents usually bring up when ATSDR uses test burn data to evaluate whether a facility will cause adverse health effects is,
There are fluctuations in stack emissions, as one can see by looking at the differences in the three stack samples taken during testing with and without tires (Dunmire 2003). Some of the factors that can affect the chemicals present in the stack gases of a cement kiln are:
- changes in the raw materials being processed;
- changes in the fuel being burned, e.g., high sulfur coal, low sulfur coal, liquid waste derived fuels, whole tires, shredded tires, natural gas, fuel oil;
- the location where the fuels or raw materials are fed into the kiln;
- a change in the percent of tires being burned;
- the temperatures in the pre-heater and kiln;
- the temperature in the baghouse(s);
- the time that the materials (fuels and raw materials) are in contact with the flame; and
- the mixing and turbulence that occurs in the kiln.
To make good cement the company must maintain extremely high temperatures, about 2700 degrees Fahrenheit, and keep the materials in contact with the flame for 80 to 90 minutes, which assures good destruction of the organic chemicals present in the fuel and raw materials (Rhodes 2001). To change the time that the materials are in the kiln or change the mixing and turbulence that occurs in the kiln would take a major modification of the facility, such as, the design of the kiln, its length or diameter, the angle of incline or speed of rotation. As long as there are no changes in the location, percentage, or manner in which the tires are fed into the kiln the emissions should not vary any more than is normal with coal. All of these factors can also affect the quality of the cement. Maintaining a consistent quality of cement is important to the company to maintain their customers, so management has a stake in maintaining the status quo.
Most cement manufacturers, like CEMEX, have their own quarries, grind, and blend their raw materials to make their raw material feed as consistent as possible. The CEMEX air permit requires periodic retesting of the stack emissions and testing when making major changes to the facility operation (Rhodes 1999). Because the kiln operating conditions that make good cement also cause good combustion, there is unlikely to be a wide variation in the stack emissions from a cement kiln while using the same fuel and raw materials.
The Boulder County Public Health Department asked ATSDR to review two documents, Source Emissions Testing Report for the CEMEX Lyons cement plant (Dunmire 2003), and Human Health Evaluation of Cement Kiln Emissions From Coal Supplemented with Natural Gas and Coal Supplemented with Tires, CEMEX, Inc. Cement Plant, Lyons, Colorado (Klingensmith 2003) and answer twelve questions (Milmoe 2003).
1. Were any quality assurance/control problems encountered that would jeopardize our confidence in the quality of the test?
ATSDR conducted a limited quality assurance and quality control (QA/QC) evaluation of the stack emissions testing. An important portion of a thorough evaluation involves observing the stack-sampling test and the accuracy of the recorded instrument readings. Although ATSDR staff were not present during the stack testing, no problems were noted during our review that would jeopardize our confidence in the test data. During stack sampling the isokinetic percentages were very good; probe, filter, and condenser temperatures were appropriate; and overall the laboratory QA/QC was very good; the percentage recovery for the spikes was good; they did field blanks, method blanks, reagent blanks, spikes (both internal and surrogate spikes), and duplicate analysis. The only concern we have is why an entire run was thrown out because of high acetone values. A detailed discussion should have been provided to justify why that data was not representative of CEMEX emissions and it was appropriate to discard the data.
There are several different ways of looking at the issue of what is a "significant" increase in emissions.
- From a mathematical perspective you can run statistical analyzes, such as Student-T test, to determine if a statistically significant numerical increase has occurred.
- Regulatory agencies may consider some percent over a regulatory standard or guidance level as significant.
- However, from a toxicological or public health perspective one must look at the actual dose an individual receives as a result of the increased emissions to determine if the increase will cause adverse health effects, i.e., be significant to public health. If health values have not been set for a chemical, the exposure concentration can be compared to the concentration of the chemical typically found in urban or rural air to gauge whether the increased concentration is likely to be significant to public health.
To illustrate the health perspective, if you took one aspirin for your headache, it would probably have little effect. A 100% or 200% increase in dose (taking 2-3 more tablets) would have positive health effects-provide better pain relief. However, if you had taken four aspirin to begin with and then increased the dose 100 - 200% (took 8 to 12 more tablets); you could have adverse health effects. It is not the percent of change that is significant-it is the dose of a particular chemical that is important.
3. Do the stack test results indicate a significant increase or decrease in emissions as a result of burning TDF?
No, the changes in the CEMEX stack emissions are not of public health significance-they do not increase the acute or chronic exposure concentrations enough to cause adverse health effects to the MEIR, the maximally exposed individual resident. Concentrations of stack gases in the rest of the community will be lower and not likely to cause adverse health effects even in more sensitive populations, such as children or the elderly.
1. Please comment on the methodology used in the report comparing the change in emissions reported in the CEMEX Lyons stack test and the results of the risk screening analyses conducted for the Davenport, Victorville, and Colton California cement plants. For example, is this type of comparative analysis common or novel? Is the approach credible with respect to the validity of results?
The comparative approach used to evaluate the potential human health effects of the CEMEX emissions when burning TDF is a unique approach, i.e., an approach we have not seen before. Comparing the CEMEX emissions to other cement kilns' emissions when tires were burned provides perspective on how well the CEMEX plant is designed and/or operated relative to other cement plants. However, without evaluating the public's exposure to the chemicals in the CEMEX stack gases, one cannot determine what the risk of adverse health effects is for the residents near CEMEX.
The brief description of the California risk assessment for the emissions from the Colton, California plant indicated that the stack emissions were modeled using the latest editions of ISC and ACE models. They used site-specific data to calculate the dispersion coefficients (also called dispersion factors) which were used to predict the exposure concentrations for the maximally exposed individual resident (MEIR) (Assiourn 1999). However, we have no information on the methodology used in the Davenport and Victorville cement plant risk analyses, so we cannot comment on their methodology.
The site-specific risk assessment approach used at the Colton plant sounds like the typical risk assessment methodology for stack emissions. Even if we assume the Colton, California, risk assessment was well done, we can not assume that the relationship between the CEMEX stack emissions and the concentrations of chemicals to which the Lyons' MEIR is exposed is the same relationship as the California facility and its MEIR. So many factors can affect the dispersion of stack emissions and therefore the concentration of each chemical to which local residents will be exposed (see the discussion in Evaluating Public Exposure) that it is not appropriate to apply dispersion factors for one facility to another facility-which is essentially what was done in the comparative analysis.
We used site-specific air dispersion modeling for the CEMEX facility to predict the exposure for the MEIR in Boulder County. When we compared the public's exposure to health comparison values, we concluded that the burning of TDF would not adversely affect public health.
2. Is the report technically correct?
We do not agree with the comparative risk methodology used in the report to determine if the stack emissions would adversely affect public health.
3. How relevant is the comparison between populations? Is it possible to use the California studies to indicate the potential impact on human health in Colorado without the availability of air dispersion modeling information, other exposure pathway data, etc?
As discussed in the reply to question B.1., ATSDR used site-specific dispersion modeling and exposure pathways analysis at the CEMEX Lyons facility to determine the potential impact of CEMEX emissions on human health in Colorado. See the Evaluating Public Exposure section, for a discussion of site-specific parameters that affect the dispersion of stack gases at a particular facility. Because there are a number of site-specific factors that affect the stack gases impact on the surrounding community, we do not think it is appropriate to apply California risk assessments to a Colorado plant.
4. Please comment on the risk assessment conducted by Parsons Engineering Science, Inc. for the California Portland Cement Plant in Colton, CA. For example, is this risk analysis credible based upon the memorandum provided in the stack test?
The brief description of the California risk assessments, which was provided in the memorandum/letter in the stack test, indicates that the stack emissions were modeled using the latest editions of ISC and ACE models and site-specific data to predict the exposure concentrations for the maximally exposed individual resident (MEIR) under both acute and chronic exposure scenarios. The letter also indicated that a site-specific exposure pathways analysis was conducted to address multi-pathway exposures (Assioun 1999). That type of site-specific analysis is necessary for a creditable risk assessment. Although we agree with the general description of the methodology that was used, without reviewing the actual risk assessment and supporting data we cannot comment on the overall quality of the assessment for the Colton, California plant.
5. With respect to the methodology used to compare the risk screening data, particularly the data developed by the California Integrated Waste Management Board, it appears that the change in percentage risk is fairly sensitive. How much a change in emissions would be necessary to produce a change in risk based on this data? Is the increase or decrease in emissions in the CEMEX Lyons Plant stack test enough to produce a change in risk based on this scenario?
As discussed previously, it is not valid to determine what the change in risk is based on merely a percentage increase or decrease in stack emissions without having site-specific air dispersion modeling to predict the corresponding increase or decrease in the public's exposure to those specific chemicals. ATSDR staff did not review the California Integrated Waste Management Board's report, therefore, we cannot comment on the methodology used. However, in reply to your last question, it is not appropriate to judge the risk at the Lyons Plant based on the California scenario.
ATSDR conducted a site-specific evaluation of (1) the concentrations of the various chemicals in the CEMEX stack gases to which the public is exposed and (2) the toxicological data for each chemical to determine the potential acute and chronic health effects for the Lyons community. Tables 1A and 1B contain the comparison values for chemicals detected in the CEMEX stack gases. ATSDR staff use comparison values to select environmental contaminants for further evaluation (ACGIH 2002; ATSDR 2003). Chemicals that exceeded one or more comparison value are listed in Table 2 and Table 3 for further evaluation. While a very small change in one chemical may trigger further evaluation, for another chemical it would take large changes (i.e., several orders of magnitude change) to exceed comparison values and indicate further evaluation is needed. Each site and each chemical must be considered separately.
For example, of all the chemicals in CEMEX stack gases (see Tables 1A and 1B) chromium exceeded the health screening values by the greatest amount (1E6-assuming the Cr is all Cr+6). However, the concentration the MEIR is exposed to (see Table 2) is ten times lower than the concentration expected to cause one cancer case in a million exposed individuals (a 1E-6 cancer risk-assuming the Cr is all Cr+6).
6. On page 6, the report states that "Emissions for these human health driver chemicals were generally low for the Lyons Plant, compared to plants in California." Do you concur with this statement given that chromium emissions in Davenport were two orders of magnitude higher in Lyons and increased by 50% and that benzene emissions increased by more than 3000%. Is it possible that these increases could indicate a potential increase in human health risk?
Tables 1A and 1B list chemicals or categories of chemicals detected in the stack emissions at the CEMEX plant along with corresponding health comparison values. At the Lyons site, 17 chemicals were above one or more health screening values in the stack-these chemicals needed further evaluation. Tables 2 and 3 list these chemicals and the projected ground level concentrations of them based on site-specific dispersions modeling. The modeling provided annual average concentrations (Table 2) and maximum annual concentrations (Table 3), which we used to evaluate chronic exposures and carcinogenic effects, and maximum 1-hour and 24-hour concentrations, which we used to evaluate acute exposures.
To answer your questions about chromium and benzene, they were among the 17 chemicals in the Lyons stack gases that required additional consideration in the ATSDR evaluation. Maximum ground level concentrations of benzene were several orders of magnitude below the comparison values (see Tables 2 and 3). Even if you assume all of the chromium in the Lyons plant stack gases is hexavalent chromium, the average and maximum annual ground level exposure concentrations are below the CREG. The 1-hour maximum concentration of chromium is below all other comparison values. Neither chemical is likely to cause adverse health effects in the community. See also the reply to question A.2. for a discussion on the use of percentages in evaluating health effects.
7. The report concludes that "emission rates are extremely low for all primary human health risk driver chemicals typically found in cement kiln emissions." It goes on, "Based on all data available, it can be concluded that there will be no significant adverse human health risks associated with the use of TDF at the Lyons Plant." Please comment on the accuracy of both of these statements. Is there enough information available to accurately support the conclusion reached in the second statement?
It is unclear what the author means by "extremely low." The ATSDR staff evaluation of the concentrations of the chemicals in the CEMEX stack gases at ground level shows that the chemicals are below levels expected to cause adverse, acute or chronic health effects. We classify the stack gases as "no public health hazard."
The report's conclusion that "there will be no significant adverse human health risks associated with the use of TDF at the Lyons Plant" is correct, i.e., is the same as ATSDR's conclusion. However, the basis for ATSDR's conclusion is site-specific air dispersion modeling and comparison of the predicted public exposure concentrations of the chemicals to health comparison values. To answer the last question listed above, there was not enough information in the report to support our conclusion-we needed additional information (air dispersion modeling and health comparison values) to reach that conclusion.
8. Page 6 of the report states that the risk range for the cement kilns located in California is "negligible." Do you concur with this statement based on the fact that risk increases from 6.26E-06 to 8.8E-06 in the case of the Victorville Plant? How would you characterize this increase in risk?
EPA and other regulatory agencies developed the risk assessment process to set consistent regulatory standards. Risk ranges have been a helpful tool to set sociological and environmental priorities, but they are not predictors of actual cases of cancer in a community. To determine whether actual adverse health effects are likely to occur in a community, ATSDR uses a site-specific exposure analysis. ATSDR evaluates the toxicity of the chemical and the level and duration of exposure to each chemical to determine public health impacts of a completed exposure pathway.
As stated in the ATSDR Cancer Policy Framework, "Emphasis is placed on the use of risk analysis as an organizing construct contingent on sound biomedical and other scientific judgment to define plausible exposure ranges of concern rather than single numeric conclusions that may convey an artificial sense of precision."(ATSDR 1993) We would not expect to see an actual increase in the number of cancer cases in a community if the risk range changed from 6.26E-06 to 8.8E-06.
9. Page 18, Table 9, uses a calculation to estimate emissions of hexavalent chromium from the test that analyzed for total chromium. The report estimates that hexavalent accounts for 16% of total chromium. Is this an accurate estimation method?
Page 18, Table 9 says that the 16% ratio of hexavalent chromium (Cr+6) to total chromium (Cr) was taken from the Davenport, California stack test. However the Colton, California facility stack test (Bell 1999) had the following ratios, without tires 65% Cr+6 (Page 55, Table 4-21) and with tires 29% Cr+6 (Page 56, Table 4-22). Because there is such a wide variation in the amount of total chromium that is hexavalent chromium in the stack emissions of cement kilns and other combustion sources, it is not possible to predict what the ratio is for the Lyons facility. Site-specific stack testing for Cr+6 is necessary to determine the amount present in the Lyon emissions when burning various mixtures of fuels. In Tables 2 and 3, we used site-specific dispersion modeling to predict the maximum chromium concentrations in the community. Even if we assume all of the chromium in the CEMEX stack gases is Cr+6, the chromium would not cause adverse health effects. In this situation, analysis of CEMEX stack gases for Cr+6 is not needed.
ATSDR has taken into account the unique vulnerabilities of infants and children to environmental contaminants during the evaluation of this public health issue and the preparation of this health consultation.
The following conclusions are based on
- the Source Emissions Testing Report, CEMEX - TDF/Coal Demonstration Test (Dunmire 2003),
- site-specific dispersion modeling performed by the Colorado Department of Health and Environment (Machovec 2003), which was used to calculate the maximum air exposure concentrations that would occur in the community, and
- comparison of those values to health guidelines (ATSDR 2003; ACGIH 2002).
ATSDR concluded that the concentrations of the chemicals detected in the stack gases of the CEMEX cement plant when burning coal or 19.2% tires with coal are unlikely to result in adverse public health effects in the communities near the plant.
ATSDR classifies the stack emissions at this site "no public health hazard."
ATSDR recommends the Boulder County Public Health Department provide health education for the communities near CEMEX to help them understand how their health is (and is not) affected by chemicals present in the CEMEX stack gases.
ATSDR recommends that agencies with regulatory authority over the CEMEX plant regularly inspect the facility, enforce operating conditions that will assure the stack emissions remain within the ranges measured during the source test, and require periodic retesting of the stack emissions.
If additional data or new information becomes available that would affect our conclusions regarding the public's exposure to stack gases from the CEMEX plant, we will provide review and consultation on the new data and information, if requested and if deemed appropriate at that time.
Betty C. Willis, MS
Environmental Health Scientist/Combustion Specialist
Program Evaluation, Records, and Information Services Branch
Division of Health Assessment and Consultation
Chris Poulet, MS
Environmental Health Scientist
ATSDR Region VIII
CDR Peter J. Kowalski, MPH, CIH
Environmental Health Scientist/Industrial Hygienist
Exposure Investigations and Consultations Branch
Division of Health Assessment and Consultation
|ACGIH 2002||American Conference of Government Industrial Hygienists. 2002. Two thousand two threshold limit values for chemical substances & biological exposure indices. Cincinnati.|
|Assioun 1999||Parsons Engineering Science, Inc. Letter to Mr. Jay M. Grady of California Portland Cement Company from Antoine Assioun concerning comparative health risk assessment. Pasadena. November 1, 1999.|
|ATSDR 1993||Agency for Toxic Substances and Disease Registry. January 1993. Cancer policy framework. Atlanta: US Department of Health and Human Services.|
|ATSDR 2003||Agency for Toxic Substances and Disease Registry. June 30, 2003. Air comparison values. Atlanta: US Department of Health and Human Services.|
|BCPH 2002||Boulder County Public Health. November 14, 2002. Air emissions stack test comparison: assessing the impact of tire derived fuel. Boulder|
|BCPH 2003||Boulder County Public Health. July 14, 2003. CEMEX use of tires as a supplemental fuel-briefing for Boulder County Board of Health. Boulder.|
|Bell 1999||Bell AC. September 1999. AB2588 emissions testing at California Portland Cement Company's Colton plant; coal firing and coal with tires firing. Orange, CA: Delta Air Quality Services, Inc.|
|Dunmire 2003||Dunmire JM. March 24, 2003. Source emissions testing report CEMEX - TDF/coal demonstration tests Lyons, Colorado cement plant. Denver: Air Pollution Testing, Inc.|
|Klingensmith 2003||Klingensmith JS. March 21, 2003. Human health evaluation of cement kiln emissions from coal supplemented with natural gas and coal supplemented with tires CEMEX, Inc. cement plant Lyons, Colorado. Boulder: Flatirons Toxicology, Inc.|
|Machovec 2003||Colorado Department of Public Health and Environment. Electronic mail to Betty Willis at ATSDR from Chuck Machovec regarding CEMEX kiln stack dispersion factors. June 24, 2003.|
|Milmoe 2003||Boulder County Public Health Department. Electronic mail to Chris Poulet at ATSDR from Pam Milmoe subject: questions on CEMEX Lyons stack test and human health evaluation. April 29, 2003.|
|Rhodes 1999||Rhodes C. September 1999. Technical review document for operating permit 950PB0082. Denver: Colorado Department of Public Health and Environment.|
|Rhodes 2001||Rhodes C. October 2001. Technical review document for minor modification to operating permit 950PB0082. Denver: Colorado Department of Public Health and Environment|
ACGIH = American Conference of Government Industrial Hygienists
Acute = Exposure for less than 14 days
ATSDR = Agency for Toxic Substances and Disease Registry
ave. = average
B(a)P = benzo(a)pyrene
BCPH = Boulder County Public Health
Chronic = Exposure for greater than 365 days
cpd = compound
CREG = Cancer risk evaluation guide for 1 x 10-6 excess cancer risk (ATSDR)
A = Human carcinogen (EPA)
B1 = Probable human carcinogen-limited human, sufficient animal studies (EPA)
B2 = Probable human carcinogen-inadequate human, sufficient animal studies (EPA)
2A = Probably carcinogenic to humans-limited human evidence, sufficient evidence in animals (IARC)
CV = comparison value
dscf = dry standard cubic feet
dscm = dry standard cubic meters
EMEG = Environmental media evaluation guide (ATSDR)
EPA = US Environmental Protection Agency
FR = (stack gas) flow rate
ft3 = cubic feet
g = grams
gr = grains
IARC = International Agency for Research on Cancer
Intermediate = Exposure for 14 to 364 days
lb/hr = pounds per hour
m3 = cubic meters
MEIR = maximally exposed individual resident
mg/m3 = milligrams (of chemical) per cubic meter (of air or stack gas)
min = minutes
MW = Molecular weight
NA = Not analyzed for
NAAQS = National Ambient Air Quality Standard (EPA)
NAAQS quarterly = NAAQS average for the quarter
ND = Not detected, or
NESHAP = National Emission Standard for Hazardous Air Pollutants (EPA)
ng = nanograms
NO2 = nitrogen oxides
NOx = nitrogen dioxide
PAH = polycyclic aromatic hydrocarbon
PCB = polychlorinated biphenyl
PM10 = particulate matter that is 10 microns or less in diameter
ppb = parts per billion
ppm = parts per million
QA/QC = quality assurance and quality control
RfC = Reference concentration (EPA)
SO2 = sulfur dioxide
SOx = sulfur oxides
STEL = Short-term exposure limit
TDF = tire derived fuel
TWA = 8-hour, time weighted average
µg/m3 = micrograms per cubic meter
> = greater than
< = less than
< # = Not detected at this detection limit - in calculating averages ½ the detection limit was used
Click here to Tables 1 - 3 in PDF format (PDF, 381KB)
For stack data to be compared to each other the data are corrected for the moisture content, temperature, and pressure of the stack gases and reported in dry standard cubic meters (dscm). As long as all the emissions data are reported in terms of "standard conditions" you can list them as cubic meters (m3) and compare them to air health comparison values (CVs).
Emissions data are usually reported as lb/hr, µg/dscm, ppm, or ppb. Occasionally gr/dscf (grains per dry standard cubic foot) and lb/ton dry feed will also be provided if the regulatory standard uses those units.
Health comparison values for air are usually in ppm, ppb, mg/m3, or µg/m3 units.
To compare emission concentrations to health guidelines the emissions data and CVs need to be converted to the same units. This appendix will provide the conversion factors and formulas that were used in preparing the tables in Appendix A, as well as some additional ones often used in reviewing air data.
To convert lb/hr stack concentration to mg/m3 stack concentration or vice versa:
To convert lb/hr stack concentration to µg/m3 concentration at ground level, you must have the dispersion factors (DFs) obtained from doing site-specific air dispersion modeling. DFs are given in µg/m3/lb/hr or µg/m3/g/s [which is µg/m3 of a chemical at ground level per lb/hr or g/second stack emission rate of that chemical]. The Dispersion Factors for the MEIR location for the CEMEX November 2002 stack test are:
|Time Period||Dispersion Factor|
|1 Hour||1.2177 µg/m3 per lb/hr|
|8 Hour||0.2695 µg/m3 per lb/hr|
|24 Hour||0.11851 µg/m3 per lb/hr|
|Annual||0.00843 µg/m3 per lb/hr|
Example 1 - Evaluation of benzene while burning tires
Table 2.10 (Dunmire 2003) reports the average emissions of benzene for the 3 runs was 1.01E-01 lb/hr (0.101 lb/hr) and the average stack-gas flow-rate was 146.6 kdscfm (146.6 kilo-dry standard cubic feet per minute or 146,600 ft3/min). The CREG for benzene is 0.1 µg/m3 and the Acute EMEG is 50 ppb (ATSDR 2003). Benzene MW = 78.11.
For Table 1A all values were converted to ppb for comparison.
NOTE: Often if you look through all the data in an emissions testing report you will find the data given in several different units and not have to do as many calculations. The 55.5 ppb in Table 1A was taken from Appendix 1 (Dunmire 2003); which compares favorably with the calculated value. Depending on how numbers are rounded on intermediate calculations, it is possible to get slight variations in the final number.]
Example 2 - Evaluation of benzene concentrations at ground level (while burning tires)
For Table 2 we calculated the concentration of benzene (and all other chemicals) to which the maximally exposed individual resident (MEIR) would be exposed on an annual basis, using the DFs above. We also had to convert the air comparison values from ppb to µg/m3, so all the values would be in the same units. The same calculations were done for Table 3-the only difference is we started with the maximum concentration in any run and used the FR for that run, if needed in the calculations.
Maximum 1-hour concentration of benzene at MEIR location:
0.101 lb/hr stack x 1.2177 µg/m3 per lb/hr = 0.12 µg/m3
Convert 50 ppb acute EMEG to µg/m3:
Example 3 - Evaluation of arsenic while burning tires
In Table 2.9 (Dunmire 2003) the arsenic average emissions are 4.69E-04 lb/hr. In Appendix 1 the average stack emission rate is given as 1.47E-03 mg/dscm. The CREG for arsenic is 0.0002 µg/m3, so to compare the metals emissions we only need to convert the CREG value to mg/m3.
0.0002µg/m3 ÷ 1000 µg/mg = 0.0000002 or 2E-7 mg/m3 [arsenic stack emission > CREG]