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PUBLIC HEALTH ASSESSMENTMORGAN FALLS MUNICIPAL SOLID WASTE LANDFILL
ROSWELL, FULTON COUNTY, GEORGIA

EPA ID No. GAD980559413

October 28, 2004

Prepared by:

The Georgia Department of Human Resources
Under a Cooperative Agreement with
Agency for Toxic Substances and Disease Registry




Potential Exposure Pathways

A table listing potential exposure pathways is located in Appendix B.

Groundwater

Impacts to groundwater underlying landfills typically include contaminant sources such as landfill gas (LFG), leachate, and operational sources (e.g., Underground Fuel Storage Tanks). LFG contains a complex mix of gases consisting predominantly of methane and carbon dioxide, and a limited amount of nitrogen, oxygen, and various non-methane organic chemicals. At Morgan Falls landfill, a stronger correlation exists between the types of VOCs in LFG and groundwater than between VOCs in leachate and groundwater. Therefore, because of the partitioning of VOCs from gas into the groundwater, LFG is the predominant source of VOCs present in on/off-site groundwater [1].

Residences in Morgan Falls Station and the surrounding area are connected to municipal water, which comes from surface water intakes on the Chattahoochee River. Since 1997 groundwater samples have been collected and continue to be collected on a quarterly basis as part of the landfill's Post-Closure care groundwater monitoring plan. The extent of groundwater contamination has been determined to have reached the southern part of Morgan Falls Station, approximately 800 feet south of Morgan Falls landfill. Contaminated groundwater has migrated that distance because of geologic fractures, and other secondary openings caused by regional stresses in the area [1]. Maximum historical groundwater contaminant levels above CVs detected in monitoring wells located from Morgan Falls Station include arsenic (41 ppb), beryllium (5 ppb), lead (63 ppb), methylene chloride (5 ppb), and vinyl chloride (5 ppb). Maximum historical groundwater contaminant levels above CVs detected in monitoring wells located in and near the Morgan Falls landfill include [1]
  • arsenic (105 ppb)
  • beryllium (84 ppb)
  • cadmium (21 ppb)
  • copper (10,200 ppb)
  • lead (89 ppb)
  • thallium (2 ppb)
  • benzene (7 ppb)
  • cis-1,2-dichoroethylene (324 ppb),
  • methylene chloride (9 ppb)
  • tetrachloroethylene (103 ppb)
  • trichloroethene (30 ppb)
  • vinyl chloride (7 ppb)
Ongoing LFG collection at the landfill minimizes the impact to groundwater, thereby reducing the potential for off-site migration of contaminated groundwater. Because residents living at Morgan Falls Station have always had access to municipal water, as well as residents in the vicinity surrounding the landfill, an exposure pathway does not exist. Therefore, toxicological evaluations of the contaminants affecting groundwater will not be addressed in this public health assessment.

Indoor Air

Volatile contaminants from groundwater might be released as a vapor to the overlying soil (soil gas) and migrate through the soil to the ground surface. Therefore, the potential exists for some of the VOCs present in shallow groundwater to migrate upward to the ground surface at Morgan Falls Station, and enter lower level apartment buildings through utility openings and floor cracks or similar defects. As a result, concentrations of contaminants in groundwater beneath an apartment building could be present in indoor air in buildings overlying the contamination. Indoor air sampling has not been conducted at Morgan Falls Station. contaminated overburden and bedrock groundwater monitoring wells have, however, been detected at depths of 25 feet and approximately 50 feet below ground surface, respectively [1]. At these depths attenuation factors will minimize the potential for vapor intrusion, so that vapor intrusion is not likely to be asignificant exposure pathway and and therefore not likely to lead to adverse health effects.

Outdoor Air

Exposure is possible to outdoor air containing chemicals that overlie shallow groundwater contamination. Contaminants present in shallow groundwater plumes could migrate upward towards the ground surface and enter outdoor air. As a result of dilution with large quantities of outdoor air, however, contaminant concentrations released to that outdoor air will - typically - dissipate quickly.

The potential for exposure to contaminated air from the upward migration of methane and VOC vapors also exists, but impacts are confined at or near the edges of the site in the hydraulically downgradient direction of the landfill [2]. Air samples were collected from methane monitoring points (MMPs) and groundwater monitoring well headspaces and analyzed for the presence of VOCs. MMP-16, which is the MMP nearest Morgan Falls Station (40 feet above, and approximately 90 feet diagonally from the nearest apartment building), was sampled and found to contain benzene, 1,4-dichlorobenzene, and vinyl chloride above CVs. Table 6 summarizes air-sampling results from the methane monitoring probe located nearest Morgan Falls Station.

Table 6: Air Sampling Results from Methane Monitoring Probe MM16-B Located Approximately 89 Feet Above Morgan Falls Station Apartment Complex.
Contaminant Health Based Comparison Values**(g/m3)VOC Air Sampling Data Ambient Air Concentration(g/m3)
Benzene 0.1 CREG
12.8* EMEG/MRL1
30 RfC

75
1,4-Dichlorobenzene 601.2 EMEG/MRL1
800 RfC
620
Vinyl Chloride 0.1 CREG
77* EMEG/MRL1
100 RfC
80
g/m3: micrograms per cubic meter
CREG: Cancer Risk Evaluation Guide
EMEG: Environmental Media Evaluation Guide (see Appendix B)
MRL: Minimal Risk Level (ATSDR Health Guidelines, Spring 2004)
RfC: Reference Concentration
*Intermediate EMEG: Environmental Media Evaluation Guide for exposures between 15-364 days
1For the purposes of this table, EMEG/MRL values given in parts per billion (ppb) have been converted to g/m3 using a conversion factor:Conversion Factor, where the chemical concentration in g/m3 = concentration in ppb x molecular weight of chemical 24.45
**Source: ATSDR, Air comparison values (Spring 2004)


Note that the air samples were taken inside the actual monitoring well or methane probe shafts. Also, overburden and bedrock groundwater monitoring wells are at depths of 25 feet to greater than 100 feet bgs [2]. Ground surface concentrations of VOCs are likely to be much lower because of attenuation factors associated with the depth of the groundwater. Moreover, contaminant concentrations released to outdoor air will be quickly reduced as a result of dilution with large quantities of outdoor air. Exposure to VOCs originating from Morgan Falls landfill from outdoor air is not expected to result in any increased risk of adverse health effects to golfers or to those living at Morgan Falls Station.

Fish Uptake

Between Morgan Falls Dam and Peachtree Creek, which is a section of river west of and downstream of Morgan Falls landfill, the GEPD has sampled for environmental contaminants largemouth bass, carp, brown trout, and jumprock sucker. No consumption restrictions were placed on largemouth bass, brown trout, and jumprock sucker; however, PCBs were found in Carp, thus the recommendation was that no more than 1 meal per month be consumed [19]. PCBs are common in fish tissue in rivers in Georgia, but the landfill is not a suspected source. Fish tissue sampled did not contain manganese or vanadium (contaminants found in the Chattahoochee River above CVs).

Children's Health Considerations

To protected the health of the nation's children, ATSDR has implemented an initiative to guard children from exposure to hazardous substances. In communities faced with contamination of their water, soil, air, or food, ATSDR and GDPH recognize that the unique vulnerabilities of infants and children demand special emphasis. Due to their immature and developing organs, infants and children are usually more susceptible to toxic substances than are adults. Children are more likely to be exposed because they play outdoors and they often bring food into contaminated areas. They are also more likely to encounter dust, soil, and contaminated vapors close to the ground. Children are generally smaller than adults, which results in higher doses of chemical exposure because of their lower body weights relative to adults. In addition, the developing body systems of children can sustain permanent damage if toxic exposures occur during critical growth stages. At the Morgan Falls site, children with repeated access to the area could have been exposed to contaminants in soil, surface water, sediment, and air in the past; however, historical data does not exist. Currently, children are not being exposed to contaminants at levels of health concern, and increased exposures in the future are unlikely.

Community Health Concerns

GDPH released the results of the Morgan Falls Public health assessment for review and public comment from August 8 through September 8, 2004. No community health concerns have been received by the GDPH.

Conclusions

GDPH developed the following conclusions and assigned a public health hazard category to the site. A description of public health hazard categories is provided in Appendix D.

Using the data evaluated, GDPH considers this site to pose no apparent public health hazard. Specifically:
  1. The calculated exposure doses to aluminum, arsenic, vanadium, and benzo(a)pyrene present in the soil at Morgan Falls Station are substantially lower than respective exposure doses known to be associated with health effects; hence, adverse health effects from ingestion, dermal contact, and inhalation are not expected from past, current, and future exposure to soil at Morgan Falls Station.
  2. The numeric risks for cancer from exposure to arsenic and benzo(a)pyrene, over a lifetime of exposure are, for adults and children, insignificant.
  3. The calculated exposure doses to manganese present in the Chattahoochee River and Morgan Falls Lake are substantially lower than doses to manganese known to be associated with health effects; hence, adverse health effects from dermal absorption are not expected to result from current and future exposure to soil at Morgan Falls Station.
  4. Ingestion of surface water and sediment is possible, but the likelihood of swallowing sediment or drinking river or lake water in volumes large enough to be of concern is not very likely.
  5. Although concentrations of surface water manganese that might have existed in the past are unknown, adverse health effects from past exposure to manganese are not likely because the likely site-specific exposure doses would be too low.
  6. The calculated exposure doses to vanadium present in the Chattahoochee River sediment are substantially lower than exposure doses to vanadium known to be associated with health effects; hence adverse health effects from dermal absorption are not expected to result from current and future exposure to sediment from the Chattahoochee River. Although concentrations of surface water vanadium that may have existed in the past are unknown, adverse health effects from past exposure to vanadium are not likely because the likely site-specific exposure doses would be low.
  7. The residents of Morgan Falls Station and in the vicinity of Morgan Falls landfill have had, and presently have, access to municipal water; therefore, a current exposure pathway from groundwater does not exist.
  8. Although indoor air sampling has not been conducted at Morgan Falls Station, the depth of groundwater is such that attenuation factors will likely minimize the potential for vapor intrusion, so that vapor intrusion is not likely to lead to exposure.
  9. Outdoor air samples were taken inside the actual monitoring well or methane probe shafts where VOC concentrations would be higher than potential surface emissions released. Moreover, reduction as a result of dilution with large quantities of outdoor air and attenuation factors related to the depth of groundwater will occur.
  10. Adverse health effects from inhalation of VOCs inherent in LFG were and are not expected to result from past, current and future exposure to outdoor air from individuals playing golf or trespassing onto the golf course, as well as residents living at Morgan Falls Station.
  11. To date, residents have not voiced any health concerns regarding contamination from the Morgan Falls landfill.

Recommendations

There are no recommendations at this time.

Public Health Action Plan

Actions Completed

In 2002, Morgan Falls Station management was informed by GEPD and the EPA that landfill gas (methane) might potentially underlie the apartment complex buildings.

Actions Planned
  • The GEPD will continue to require on - and off-site groundwater monitoring and remedial activity at the landfill.
  • As additional data become available, GDPH will review the information and take appropriate actions. GDPH will respond to all requests for information regarding health issues associated with the landfill.

References

  1. Weston Solutions, Inc. Assessment of corrective measures study, revision 1. August 2003.
  2. US Environmental Protection Agency. Final expanded site investigation report: Morgan Falls Landfill, Roswell, Fulton County, Georgia. April 30, 2003.
  3. National Transportation Safety Board. Pipeline accident brief. . Washington DC; adopted 22 March 1999.
  4. 3. Weston Solutions, Inc. Morgan Falls semiannual statistical analysis report. December 2003.
  5. Agency for Toxic Substances and Disease Registry. Public health assessment guidance manual. Atlanta: US Department of Health and Human Services; March 1992.
  6. Hawley JK. 1985. Assessment of Health Risk to Contaminated Soil. Risk Anal 1985;5(4):289-302.
  7. Agency for Toxic Substances and Disease Registry. public health assessment guidance manual (update). Atlanta: US Department of Health and Human Services; March 2002.
  8. Golub MS, Donald JM, Gershwin ME, Keen CL. Effects of aluminum ingestion on spontaneous motor activity of mice. Neurotoxicol Teratol 1995;11:231-35.
  9. Tseng WP, Chu HM, How SW et. al. Prevalence of skin cancer in an endemic area of chronic arsenicism in Taiwan. J Natl Cancer Inst 1968;40:453-63.
  10. US Environmental Protection Agency. Integrated risk information system. Cincinnati, Ohio: Office of Health and Environmental Assessment, Environmental Criteria Office; 2001. Available at : www.epa.gov/iris. Last accessed 23 October 2004.
  11. Wu MM, Kuo TL, Hwang YH, and Chen CJ. Dose-response relation between arsenic concentration in well water and mortality from cancers and vascular diseases. Am J Epidemiol 1989;130(6):1123-32.
  12. Chen CJ, Wang CJ.. Ecological correlation between arsenic level in well water and age-adjusted mortality from malignant neoplasm. Cancer Res 1990;50(17):5470-74.
  13. Chen CJ, Chen CW, Wu MM, and Kuo TL. Cancer potential in liver, lung bladder and kidney due to ingested inorganic arsenic in drinking water. Br J Cancer 1992;66(5):888-92.
  14. Agency for Toxic Substance and Disease Registry. Toxicological profile for vanadium and compounds. Atlanta: US Department of Health Human Services; July 1992.
  15. Domingo JL, Llobet JM, Tomas JM et al. Short-term toxicity studies of vanadium in rats. J Appl Toxicol 1985;5:418-21.
  16. Agency for Toxic Substance and Disease Registry. Toxicological profile for polycyclic aromatic hydrocarbons. Atlanta: US Department of Health Human Services; August 1995.
  17. Brune H, Deutsch-Wenzel RP, Habs M, Ivankovic S, and Schmahl D. Investigation of the tumorigenic response to benzo(a)pyrene in aqueous caffeine solution applied orally to Sprague-Dawley rats. J Cancer Res Clin Oncol 1981;102(2):153-57.
  18. Knauf L and Rice G. Memorandum to R. Schoeny, US EPA, Cincinnati, OH re: statistical evaluation of several benzo(a)pyrene bioassays. 1992.
  19. Thyssen JJ, Althoff JKG, and Mohr U. Inhalation studies with benzo(a)pyrene in Syrian golden hamsters. J Natl Cancer Inst;1981;66:575-577.
  20. Agency for Toxic Substance and Disease Registry. Toxicological profile for manganese and compounds. Atlanta: US Department of Health Human Services; September 2000.
  21. US Environmental Protection Agency. Risk assessment guidance for Superfund (RAGS), Volume I: Human health evaluation manual (Part E, supplemental guidance for dermal risk assessment) interim-review draft for public comment. Washington, DC: September 2001.
  22. US EPA. Issuance of final guidance: ecological risk assessment and risk. Chapter 3:risk assessment data and tasks during the remedial investigation. Appendix B: screening tables and reference values for the water pathway. Available at: www.epa.gov/superfund/programs/risk/ragse/appendix_b.pdf. Last accessed 22 October 2004.
  23. Georgia Department of Human Resources. Guidelines from "Eating Fish from Georgia Waters." Atlanta: 2003 (Update).
  24. Georgia Department of Human Resources. Georgia comprehensive cancer registry. Atlanta: February 2004.
  25. US Environmental Protection Agency. Air emissions from municipal solid waste landfills - background information for proposed standards and guidelines. Washington DC: EP-450/3-90-011a;1991.

Authors, Technical Advisors

Franklin Sanchez, REHS
Program Consultant, Chemical Hazards Program
Georgia Division of Public Health

Reviewers

Jane Perry, MPH
Director, Chemical Hazards Program
Georgia Division of Public Health

CDR William T. Going III, MPH
Technical Project Officer
Agency for Toxic Substances and Disease Registry

Jeff Kellam
Technical Project Officer
Agency for Toxic Substances and Disease Registry

Robert E. Safay, MS
Senior Regional Representative
Agency for Toxic Substances and Disease Registry

Appendix A: Figures

Figure 1 - Morgan Falls Landfill - Intro Map

Figure 2 - Site Layout Map

Figure 3 - Side Site Layout Map

Figure 4 - Aerial Photograph of Morgan Falls Landfill, 1997

Appendix B: Potential Exposure Pathways

Exposure Pathway Elements Time
Sources Medium Point of Exposure Route of Exposure >Exposed Population
Movement of contaminants discharged onto landfill along with high background levels some metals Groundwater Sampling Groundwater Direct contact Workers Past
Present
Future
Volatilization/mixing of contaminants from groundwater to landfill gas to outdoor air Outdoor air Outdoor air at methane monitoring probes and groundwater monitoring wells Inhalation Residents, Recreational visitors, Workers Past
Present
Future
Vapor intrusion from volatilization of contaminants from groundwater Indoor air Air within Building overlying the groundwater plume Inhalation Residents, Workers Past
Present
Future
Discharge of contaminants from groundwater, soil, surface water runoff Fish uptake Chattahoochee River Ingestion Residents, Recreationists, Fisherman Past
Present
Future


Appendix C: Explanation of Evaluation Process

Step 1 - The Screening Process

To evaluate the available data GDPH used comparison values (CVs) to determine which chemicals to examine more closely. CVs are contaminant concentrations found in a specific media (for example: air, soil, or water) and are used to select contaminants for further evaluation. CVs incorporate assumptions of daily exposure to the chemical and a standard amount of air, soil, or water that someone may inhale or ingest each day. CVs are generated to be conservative and non-site specific. These values are only used to screen out chemicals that do not need further evaluation. CVs are not intended to be environmental clean-up levels or to indicate that health effects occur at concentrations that exceed these values [1].

CVs can be based on either carcinogenic (cancer-causing) or non-carcinogenic effects. Cancer-based comparison values are calculated from the U.S. Environmental Protection Agency's (EPA) oral cancer slope factor (CSF) or inhalation risk unit. CVs based on cancerous effects accounts for a lifetime exposure (70 years) with an unacceptable, theoretical excess lifetime cancer risk of 1 new case per 1 million exposed people. Non-cancer values are calculated from ATSDR's Minimal Risk Levels (MRLs), EPA's reference doses (RfDs), or EPA's Reference Concentrations (RfCs). When a cancer and non-cancer CV exists for the same chemical, the lower of these values is used as a conservative measure. The chemical and media specific CVs utilized during the preparation of this PHA are listed below:

An Environmental Media Evaluation Guide (EMEG) is an estimated comparison concentration for which exposure is unlikely to cause adverse health effects, as determined by ATSDR from its toxicological profiles for a specific chemical.

A Reference Dose Media Evaluation Guide (RMEG) is a comparison concentration that is based on EPA's estimate of daily exposure to a contaminant that is unlikely to cause adverse health effects.

A Cancer Risk Evaluation Guide (CREG) s a comparison concentration that is based on an excess cancer rate of one in a million persons and is calculated using EPA's cancer slope factor (CSF).

A Maximum Contaminant Level (MCL) is a contaminant concentration that EPA deems protective of public health, and may consider the availability and economics of water treatment technology.

Step 2 - Evaluation of Public Health Implications

The next step in the evaluation process is to take those contaminants that are above their respective CVs and further identify which chemicals and exposure situations are likely to be a health hazard. Separate child and adult exposure doses (or the amount of a contaminant that gets into a person's body) are calculated for site-specific scenarios, using assumptions regarding an individual's likelihood of accessing the site and contacting contamination. A brief explanation of the calculation of estimated exposure doses for the site are presented below. Calculated doses are reported in units of milligrams per kilogram per day (mg/kg/day).

Ingestion of contaminants present in Soil

Exposure doses for ingestion of contaminants present in soil were calculated using the average and maximum detected concentrations of aluminum, arsenic, vanadium, and Benzo(a)pyrene from the sample data, in milligrams/kilogram (mg/kg). The following equation is used to estimate the exposure doses resulting from ingestion of contaminated soil :

EDs = C x IR x EF x CF

BW

where;
EDs = exposure dose soil (mg/kg/day)
C = contaminant concentration (mg/kg)
IR = intake rate of contaminated medium (based on default values of 100 mg/day for adults; 200 mg/day for children, and 5000 mg/day for a children with pica)
EF = exposure factor (based on frequency of exposure, exposure duration, and time of exposure). The exposure factor used is 0.08, based on 5 years of exposure, 2 hours/day, 7days/week, 50 weeks/year, and 365 days/year.
CF= kilograms of soil per milligram of soil (10-6 kg/mg)
BW = body weight (based on average rates for adults: 70 kg; children: 25 kg, children with pica: 16kg)

Because of the transience of apartment living, a conservative time period of 5 years was used as the length of time an individual would reside in the same apartment or apartment complex.

Soil Dermal Absorption Calculation

Exposure doses from dermal absorption of contaminants present in soil were calculated using the average and maximum detected concentrations of aluminum, arsenic, vanadium, and Benzo(a)pyrene from the sample data, in milligrams/kilogram (mg/kg), and default soil adherence values. The following equation is used to estimate the exposure doses resulting from dermal absorption of contaminated soil:

EDs = C x A x AF x EF x CF

BW

where;
EDsd = exposure dose soil from dermal absorption (mg/kg/day)
C = contaminant concentration (mg/kg)
A = total soil adhered (based on default values of 326 mg for adults; and 525 mg for children)
AF = bioavailability factor (represents, as a percent, the total amount of substance ingested, inhaled, or contacted that actually enters the bloodstream and is available to harm a person). An FF of 0.1 was used (unitless)
EF= exposure factor (based on frequency of exposure, exposure duration, and time of exposure). The exposure factor used is 0.08, based on 5 years of exposure, 2 hours/day, 7days/week, 50 weeks/year, and 365 days/year. (unitless)
CF= kilograms of soil per milligram of soil (10-6 kg/mg)
BW = body weight (based on average rates for adults: 70 kg; children: 25 kg, children with pica: 16kg)

Direct Skin (Dermal) Contact with Contaminants Present in Surface Water

Exposure doses from dermal absorption of contaminants present in soil were calculated using the average and maximum detected concentrations of aluminum, arsenic, vanadium, and Benzo(a)pyrene from the sample data, in milligrams/kilogram (mg/kg), and default permeability coefficient values []. The following equation is used to estimate the exposure doses resulting from dermal absorption of contaminated water:

EDwd = C x P x SA x ET x CF

BW

where;
EDwd = exposure dose soil (mg/kg/day)
C = contaminant concentration (mg/L)
P = permeability coefficient (cm/hr)
SA= exposed body surface area (cm2). Default values used include 19,400 cm2 for adults, and 14,900 cm2 for children.
ET = exposure time (hr/day). 1hr/day was used for these calculations. cm2
CF= conversion factor (1 L/1,000 cm3)
BW = body weight (based on average rates for adults: 70 kg; children: 25 kg, children with pica: 16kg)

Non-cancer Health Effects

The doses calculated for exposure to individual chemical are then compared to an established health guideline, such as an MRL or RfD, in order to assess whether adverse health impacts from exposure are expected. These health guidelines, developed by ATSDR and EPA, are chemical-specific values that are based on available scientific literature and are considered protective of human health. Non-carcinogenic effects, unlike carcinogenic effects, are believed to have a threshold, that is, a dose below which adverse health effects will not occur. As a result, the current practice to derive health guidelines is to identify, usually from animal toxicology experiments, a No Observed Adverse Effect Level (NOAEL), which indicates that no effects are observed at a particular exposure level. This is the experimental exposure level in animals (and sometimes humans) at which no adverse toxic effect is observed. The NOAEL is the modified with an uncertainty (or safety) factor, which reflects the degree of uncertainty that exists when experimental animal data are extrapolated to the human population. The magnitude of the uncertainty factor considers various factors such as sensitive subpopulations (for example, children, pregnant women, and the elderly), extrapolation from animals to humans, and the completeness of the available data. Thus exposure doses at or below the established health guideline are not expected to cause adverse health effects because these values are much lower (and more human health protective) than doses, which do not cause adverse health effects in laboratory animal studies. For non-cancer health effects, the following health guidelines are described below in more detail. It is important to consider that the methodology used to develop these guidelines does not provide any information on the presence, absence, or level of cancer risk [1]. Therefore, a separate cancer evaluation is necessary for potentially cancer-causing contaminants detected at this site.

Minimal Risk Levels (MRLs) - developed by ATSDR

ATSDR has developed MRLs for contaminants commonly found at hazardous waste sites. The MRL is an estimate of daily exposure to a contaminant below which non-cancer, adverse health effects are unlikely to occur. MRLs are developed for different routes of exposure, such as inhalation and ingestion, and for lengths of exposures, such as acute (less than 14 days), intermediate (between 15-364 days), and chronic (365 days or greater). At this time, ATSDR has not developed MRLs for dermal exposure.

Reference Doses (RfDs) - developed by EPA

An estimate of the daily, lifetime exposure of human populations to a possible hazard that is not likely to cause non-cancerous health effects. RfDs consider exposure to sensitive subpopulations, such as children, the developing fetus, and the elderly. EPA RfDs have been developed using information from the available scientific literature and have been calculated for oral and inhalation exposures.

If the estimated exposure dose to an individual is less than the health guideline value, the exposure is unlikely to result in non-cancer health effects. If the calculated exposure dose is greater than the health guideline, the exposure dose is compared to known toxicological values for the particular chemical and is discussed in more detail in the text of the PHA. The known toxicological values are doses derived from human and animal studies that are summarized in the ATSDR Toxicological Profiles. A direct comparison of site-specific exposure and doses to study-derived exposures and doses found to cause adverse health effects is the basis for deciding whether health effects are likely to occur.

Cancer Risks

Exposure to a cancer-causing compound, even at low concentrations, is assumed to be associated with some increased risk for evaluation purposes. The estimated risk for developing cancer from exposure to contaminants associated with the site was calculated by multiplying the site-specific adult exposure doses by EPA's chemical-specific Cancer Slope Factors (CSFs). Which are available at www.epa.gov/iris. This calculation estimates a theoretical excess cancer risk expressed as a proportion of the population that may be affected by a carcinogen during a lifetime of exposure. For example, an estimated risk of 1 x 10-6 predicts the probability of one additional cancer over background in a population of 1 million [1]. An increased lifetime cancer risk is not a specified estimate of expected cancers. Rather, it is an estimate of the increase in the probability that a person may develop cancer sometime in his or her lifetime following exposure to a particular contaminant.

Because of conservative models used to derive CSFs, using this approach provides a theoretical estimate of risk; the true or actual risk is unknown and could be as low as zero. Numerical risk estimates are generated using mathematical models applied to epidemiologic or experimental data for carcinogenic effects. The mathematical models extrapolate from higher experimental doses to lower experimental doses. Often, the experimental data represent exposures to chemicals at concentrations orders of magnitude higher than concentrations found in the environment. In addition, these models often assume that there are no thresholds to carcinogenic effects - a single molecule of a carcinogen is assumed to be able to cause cancer. The doses associated with these estimated hypothetical risks may be orders of magnitude lower that doses reported in toxicology literature to cause carcinogenic effects. As such, a low cancer risk estimate (less than 10-6) may indicate that the toxicology literature support a finding that no excess cancer risk is likely. A cancer risk estimate (greater than 10-6), however, indicates that a careful review of toxicology literature before making conclusions about cancer risks is in order [2].

Appendix C References
  1. Agency for Toxic Substances and Disease Registry. Public health assessment for North Railroad Avenue plume, Española, Rio Arriba County, New Mexico. Atlanta: US Department of Health and Human Resources; March 7, 2003.
  2. US EPA. 1999. Guidelines for carcinogenic risk assessment. Draft revised guidelines. NCEA-F-0644; November 29, 2001. Available at: http://cfpub.epa.gov/ncea/raf/cancer.cfm. Last accessed 22 October 2004.


Appendix D: ATSDR Public Health Hazard Conclusion Categories

No Public Health Hazard

A category used in ATSDR's public health assessment documents for sites where people have never and will never come into contact with harmful amounts of site-related substances

No Apparent Public Health Hazard

A category used in ATSDR's public health assessments for sites where human exposure to contaminated media might be occurring, might have occurred in the past, or might occur in the future, but where the exposure is not expected to cause any harmful health effects

Indeterminate Public Health Hazard

The category used in ATSDR's public health assessment documents when a professional judgment about the level of health hazard cannot be made because information critical to such a decision is lacking.

Public Health Hazard

A category used in ATSDR's public health assessments for sites that pose a public health hazard because of long-term exposures (greater than 1 year) to sufficiently high levels of hazardous substances or radionuclides that could result in harmful health effects

Urgent Public Health Hazard

A category used in ATSDR's public health assessments for sites where short-term exposures (less than 1 year) to hazardous substances or conditions could result in harmful health effects that require rapid intervention.



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