HEALTH CONSULTATION

Analysis of the Human Exposure Pathway via Surface Water, Sediment, andBiota in Churchill County

FALLON LEUKEMIA PROJECT
FALLON, CHURCHILL COUNTY, NEVADA

TABLES

SIC (Standard Industry Classification) codes:

0241: dairy farm
1629: heavy construction
4911: electric services
4952: sewerage system
9711: national security
NA: not available

CEMEG: chronic environmental media evaluation guide
CREG: cancer risk evaluation guide for 1×10^-6 excess cancer risk
CV: comparison value
EMEG: environmental media evaluation guide
NA: not available
Pica: A craving to eat nonfood items, such as dirt, paint chips, and clay. Some children exhibit pica-related behavior.
PRG: preliminary remediation goals
RMEG: reference dose media evaluation guide
SSL: soil screen level
UL: tolerable upper intake level

CEMEG: chronic environmental media evaluation guide
CREG: cancer risk evaluation guide for 1×10^-6 excess cancer risk
CRMEG: chronic reference dose media evaluation guide
CV: comparison value
LTHA: long term health advisory
MCL: maximum contaminant level
MCLG: maximum contaminant level goal
NA: not available
PRG: preliminary remediation goals
RMEG: reference dose media evaluation guide
UL: tolerable upper intake level

NDEP: Nevada Division of Environmental Protection
USGS: US Geological Survey
USFWS: US Fish and Wildlife Service
USBR: US Bureau of Reclamation
USBIA: US Bureau of Indian Affairs
EPA: US Environmental Protection Agency

APPENDIX A: LIST OF ATSDR DOCUMENTS FOR CHURCHILL COUNTY

1. Agency for Toxic Substances and Disease Registry. Pathway Assessment for Churchill County Surface Soil, Residential Indoor Dust, and Electromagnetic Fields. Atlanta: US Department of Health and Human Services; 2003


2. Agency for Toxic Substances and Disease Registry. Air Exposure Pathway Assessment, Fallon Leukemia Cluster Investigation. Atlanta: US Department of Health and Human Services; 2003


3. Agency for Toxic Substances and Disease Registry. Fallon Naval Air Station Evaluation of Potential Exposures from the Fallon JP-8 Fuel Pipeline. Atlanta: US Department of Health and Human Services; 2002


4. Agency for Toxic Substances and Disease Registry. Public Health Assessment, Naval Air Station Fallon. Atlanta: US Department of Health and Human Services; 2003


5. Agency for Toxic Substances and Disease Registry. Analysis of Human Exposure Pathways for Pesticide Use in Churchill County. Atlanta: US Department of Health and Human Services; 2003


6. Agency for Toxic Substances and Disease Registry. Health Consultation for Churchill County Tap Water. Atlanta: US Department of Health and Human Services; 2003

APPENDIX B: ATSDR COMPARISON VALUES AND DEFINITIONS

ATSDR comparison values (CVs) are media-specific concentrations of chemicals that are considered safe under a default exposure scenario. CVs are used as screening values for the identification of contaminants (site-specific substances) that require further evaluation to determine the potential for adverse health effects.

Generally, a chemical is selected for further evaluation because its maximum concentration in air, water, or soil at the site exceeds one of ATSDR's comparison values. However, it cannot be emphasized strongly enough that comparison values are not thresholds of toxicity. Although concentrations at or below the relevant comparison value might reasonably be considered safe, it does not automatically follow that any environmental concentration that exceeds a comparison value would be expected to produce adverse health effects. Indeed, the whole purpose behind these highly conservative, health-based standards and guidelines is to enable health professionals to recognize and resolve potential public health problems before they become actual health hazards. The probability that adverse health outcomes will actually occur as a result of exposure to environmental contaminants depends on site-specific conditions and individual lifestyle and genetic factors that affect the route, magnitude, and duration of actual exposure, and not on environmental concentrations alone.

Screening values based on noncancer effects are obtained by dividing NOAELs (no-observed-adverse-effect levels) or LOAELs (lowest-observed-adverse-effect levels) determined in animal or (less often) human studies by cumulative safety margins (variously called safety factors, uncertainty factors, and modifying factors), which typically range from 10 to 1,000 or more. By contrast, cancer-based screening values are usually derived by linear extrapolation from animal data obtained at high doses, because human cancer incidence data for very low levels of exposure simply do not exist, and probably never will.

Listed and described below are the comparison values that ATSDR has used to select chemicals for further evaluation for this health consultation, along with the abbreviations for the most common units of measure.

EMEG	environmental media evaluation guide
RMEG	reference dose media evaluation guide
MRL	minimal risk level
MCL	maximum contaminant level
ppm	parts per million, for example, mg/L or mg/kg
ppb	parts per billion, for example, µg/L or µg/kg
kg	kilogram (1,000 grams)
mg	milligram (0.001 grams)
µg	microgram (0.000001 grams)
L	liter
m3	cubic meter (used in reference to a volume of air equal to 1,000 liters)

Acute exposure is defined as exposure to a chemical for a duration of 14 days or less.

Cancer risk evaluation guides (CREGs) are estimated contaminant concentrations in water, soil, or air that would be expected to cause no more than one excess cancer in a million persons exposed over a lifetime. CREGs are calculated from EPA's cancer slope factors.

Chronic exposure is defined as exposure to a chemical for 365 days or more.

Environmental media evaluation guides (EMEGs) are concentrations of a contaminant in water, soil, or air that are unlikely to be associated with any appreciable risk of deleterious non-cancer effects over a specified duration of exposure. EMEGs are derived from ATSDR minimal risk levels by factoring in default body weights and ingestion rates. Separate EMEGs are computed for acute (<14 days), intermediate (15-364 days), and chronic (>365 days) exposures.

Intermediate exposure is defined as exposure to a chemical for a duration of 15-364 days.

Lowest-observed-adverse-effect levels are the lowest exposure level of a chemical in a study, or group of studies, that produces statistically or biologically significant increase in frequency or severity of adverse health effects between the exposed population and its appropriate control.

Maximum contaminant levels (MCLs) represent contaminant concentrations in drinking water that EPA deems protective of public health (considering the availability and economics of water treatment technology) over a lifetime (70 years) at an exposure rate of 2 liters of water per day.

Minimal risk levels (MRLs) are estimates of daily human exposure to a hazardous substance that is likely to be without an appreciable risk of adverse noncancer health effects over a specified route and duration of exposure.

National Primary Drinking Water Regulations (NPDWR or primary standards) are legally-enforceable standards that apply to public water systems. Primary standards protect drinking water quality by limiting the levels of specific contaminants that can adversely affect public health and known or anticipated to occur in water. They take the form of MCLs or Treatment Techniques.

National Secondary Drinking Water Regulations (NSDWR or secondary standards) are nonenforceable guidelines regarding contaminants that may cause cosmetic effects (such as skin or tooth discoloration) or aesthetic effects (such as taste, odor, or color) in drinking water.

No-observed-adverse-effect level is the dose of a chemical at which there were no statistically or biologically significant increases in frequency or severity of adverse health effects seen between the exposed population and its appropriate control. Effects may be produced at this dose, but they are not considered to be adverse.

Uncertainty factor (UF) is a factor used in operationally deriving the MRL or reference dose or reference concentration from exposure data.

APPENDIX C: DOSE CALCULATIONS

ATSDR established acute (1-14 days) and intermediate (14-365 days) MRLs for inorganic mercury as 0.007 and 0.002 mg/kg/day, respectively. For chronic (more than 365 days) exposure, the MRL for methyl mercury is 0.0003 mg/kg/day. MRLs are estimates of daily human exposure to mercury that are likely to be without an appreciable risk of adverse health effects over a certain time period. The acute and intermediate MRLs for inorganic mercury are based on the no-observed-adverse-effect level (NOAEL) for renal effects in rats, with an uncertainty factor of 100 for extrapolation from animals to humans and human variability. The chronic MRL for methyl mercury is based on the NOAEL for neurodevelopment effects in human, with an uncertainty factor of 4.5 for human variability and modifying factor of the selected study. Organic and inorganic mercury is not known to be carcinogenic by the oral ingestion route [24].

Although most of the mercury found in the environment is in the form of metallic mercury and inorganic mercury compounds, microorganisms convert inorganic mercury to methyl mercury–the form that can accumulate in the food chain. Methyl mercury is also the form of mercury most easily absorbed by the human body. Inorganic mercury does not accumulate in the food chain to any extent [24]. Therefore, the chronic MRL for methyl mercury is used to estimate exposure dose.

The following assumptions were made to estimate maximum concentrations that could result in exceeding chronic MRLs in edible portion of fish, ducks and other biota materials:

1. The average intake of fish, duck, and other biota materials for freshwater anglers is 8 grams per day (EPA exposure factors hand book), the average intake for children is 4 grams per day.
2. The average body weight for adults is 70 kilograms (kg) and the average body weight for children is 10 kg.
3. Total mercury concentrations were used as concentrations of methyl mercury.
4. Fish and duck consumption is the major source of mercury intake from food and other sources.

The following mathematical formula was used to estimate minimal concentration that could result in exceeding the MRL:

Cmin = (IDf × BW)/(CRxEF)

Where:
Cmin = minimal concentration that could result in exceeding the MRL in edible portion of fish, duck, and other biota materials in milligrams per gram (mg/g)
IDf = ingestion dose in mg/kg/day (respective oral MRLs for mercury)
CR = consumption rate of fish or duck or other biota materials (g/day)
EF = exposure factor (unitless–conservatively assumed to be 1.0)
BW = body weight (kg)

Therefore:
C min for chronic methyl mercury exposure (adult) = (0.0003 mg/kg/day × 70 kg)/ (8 g/day × 1)
= 0.0026 mg/g = 2.6 ppm

C min for chronic methyl mercury exposure (child) = (0.0003 mg/kg/day × 10 kg)/ (4 g/day × 1)
= 0.00075 mg/g = 0.75 ppm

The Federal Emergency Management Agency National Insurance Program Flood Insurance Maps for Churchill County were digitized for spatial analysis. The following maps were digitized.

APPENDIX F: COMMENTS AND ATSDR RESPONSES

ATSDR released a public comment version of this document to the Fallon community in February 2003. Comments were received from various sources, including US Fish and Wildlife Services, USGS, Kennametal Inc., Stone Lions Environmental Corporation, and Pheasant Services. All comments were reviewed by ATSDR staff. The following is a summary of comments and ATSDR responses:

Comment:

Additional data was provided to increase the database for the document. Those reports are:

Hoffman, R.J., and Taylor. 1998. Mercury and suspended sediment, Carson River Basin, Nevada–loads to and from Lahontan Reservoir in flood year 1997 and deposition in reservoir prior to 1983. U.S. Geological Survey Fact Sheet FS - 001- 98.

Hoffman, R.J., R.J. Hallock, T.G. Rowe, M.S. Lico, H.L. Burge, and S.P. Thompson. 1990. Reconnaissance investigation of water quality, bottom sediment, and biota associated with irrigation drainage in and near Stillwater Wildlife Management Area, Churchill County, Nevada, 1986–87. U.S. Geological Survey Water–Resources Investigations Report 89-4105.

Rowe, T.G., M.S. Lico, R.J. Hallock, A.S. Maest, and R.J. Hoffman. 1991. Physical, chemical, and biological data for detailed study of irrigation drainage in and near Stillwater, Fernley, and Humboldt Wildlife Management Areas and Carson Lake, west-central Nevada, 1987-89.

Response:

ATSDR reviewed the first report listed above and added a summary paragraph to the appropriate sections of the document. For the second and third reports, ATSDR reviewed and verified that data in the above reports were included in the federal facility information management system (FFIMs) database used to generate summary tables in the document. In addition, ATSDR verified that biota data in the above reports were also presented in reference 12 used for this document (i.e., US Geological Survey. Detailed study of irrigation drainage in and near wildlife management areas, west central Nevada, 1987-90. Part A, B, C. Carson City, Nevada. US Department of the Interior; 1994). The three reports were added as references.

Comment:

ATSDR uses the term "hazardous substances" when referring to naturally occurring substances. This statement creates the impression that all of the chemicals evaluated in the health consultation are "hazardous", therefore, their mere presence have some inherent risk to the residents of Fallon.

Response:

ATSDR changed the term "hazardous substances" to "chemicals" in the final document.

Response:

1. For the first comment, ATSDR changed the document accordantly.
2. In the final document, ATSDR clarified that the hydrographic areas listed are for areas in the state of Nevada only. The majority of the Sierra canyons of the west and east forks of the Carson River are located in California. For the second part of the comment, ATSDR changed the document accordantly.
3. Lake Tahoe is the largest reservoir providing water to the Newlands project. The Newlands project covers parts of both California and Nevada. The Lahontan Reservoir is the only large storage reservoir in the Carson River Basin in Nevada. Therefore, the document remains the same.

Comment:

In the surface water evaluation section, why use comparison values that are only applicable to drinking water exposures while the surface waters are classified as Class C?

Response:

Although the surface waters are classified as Class C, which indicates that surface water is not used as drinking water, there still is a completed exposure pathway existing for Fallon residents who work or participate in recreational activities in area lakes, the Carson River, and canals. Drinking water standards are used as screening values for the identification of contaminants (site-specific substances) that require further evaluation to determine their potential for adverse health effects. This is an extremely conservative approach for hazard evaluations. For substances detected at concentrations above the screening values (e.g., arsenic, mercury, and certain pesticides at the site), ATSDR uses site-specific exposure scenarios and performs an in-depth evaluation. For the Fallon area site-specific exposure scenarios, the most likely human exposure at the site is occasional ingestion and/or infrequent dermal contact with contaminated surface water by persons working or participating in recreational activities. This kind of infrequent exposure to the contaminated surface water is not likely to result in any adverse health effects.

Comment:

The phase "community concern" should be better defined or removed from the report.

Response:

ATSDR removed the phase "community concern" from the document.

Comment:

The mercury concentrations reported in the document appear to be far higher than those the USGS personnel noted in a brief review of several USGS and USFWS reports.

Response:

ATSDR conducted an extensive cross-reference check for data used in the document for mercury concentrations in sediment. Communications with staff of the Nevada office of the USGS indicated that an error was made in entering all the samples taken on September 15, 1998, and September 16, 1998, into the National Water Information System Web site water-quality data retrieval system. ATSDR revised the final document to reflect the changes. In addition, actions were taken to update local and Web databases by USGS personnel.

Comment:

The report refers to the double-lined evaporation ponds at Kennametal as "leach fields". Generally, leach fields are designed to encourage percolation of fluids into the soil. These evaporation ponds are designed specifically to prevent such percolation.

Response:

ATSDR changed the document to reflect an accurate description of the ponds as "evaporation ponds".

Comment:

The term EMEG is used with no explanation. A list of acronyms would help this report.

Response:

Actually, EMEG was defined at the beginning in the section of ATSDR's evaluation process. ATSDR added an appendix (Appendix B–ATSDR Comparison Values and Definitions) in the final document.

Comment:

For the evaluation of flooding as a potential point of exposure for case and control houses, information on accurate GPS latitude-longitude reading for all wells sampled and site description of where the wells were located relative to structures should provide accurate information needed to reduce any error of mapping house locations.

Response:

ATSDR received GPS latitude-longitude reading for all wells sampled and site descriptions of where the wells were located relative to structures after the public comment release of this document. Therefore, the discussion of flooding events for case and control houses in the final document was revised to reflect the accuracy of new information.

Comment:

Appendix B, assumptions: The assumption used total mercury concentrations for methyl mercury gives exceedingly conservative estimates of risk, particularly in this environment. This area has high total mercury concentrations, with world-class low percentages of methyl mercury. Nonetheless, the absolute concentrations of methyl mercury are among the highest reported in the literature.

Response:

ATSDR acknowledges that using total mercury concentrations to calculate risk resulted a conservative estimate. However, most available data on mercury for this area were for total mercury instead of methyl mercury. Therefore, in the document, ATSDR listed site-specific exposure scenarios which could significantly reduce mercury exposures. The site-specific exposure scenarios included the following statements related to this issue:

1. The total mercury concentrations are the sum of inorganic and organic mercury compounds. The true methyl mercury concentrations would likely be lower than those used for the risk evaluation.
2. The absorption and bioavailability of methyl mercury in food might be affected by other dietary components, such as dietary fiber, phytate, and selenium.

Response:

ATSDR revised the final document according to the suggestions and the ATSDR Style Manual, FY 2000.

FIGURES

Figure 1. Carson River Basin - Nevada/California: Hydrologic Features

Figure 2. Newlands Project, Nevada/California: Major Project Works

Figure 3. Carson River Basin, Nevada: City of Fallon Vicinity, Canals and Drains

Figure 4. Gaging Station in the Study Area, Churchill County, Nevada

Figure 5. Annual Peak Flow from 1980 Through 2000

Figure 6. Location of Case and Control Group Houses and the Floodplain

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