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PETITIONED PUBLIC HEALTH ASSESSMENT

MCFARLAND STUDY AREA
MCFARLAND, KERN COUNTY, CALIFORNIA


SUMMARY

The community of McFarland, California petitioned the Agency for Toxic Substances and Disease Registry (ATSDR) to evaluate potential exposure to hazardous substances in their environment and any resulting public health effects. Previously, a childhood cancer cluster was identified, however, a causal association between health data and identified contamination could not be established. This health assessment addresses specific concerns regarding potential exposure to contaminants in municipal drinking water and soil. ATSDR reviewed water and soil sampling data collected and provided by the United States Environmental Protection Agency. Some metals and pesticides were identified in the municipal water system and in soil at various locations in the McFarland area. However, the contaminants identified were not at levels of health concern. Therefore, based on the available data, no adverse health effects would be expected from people coming into contact with soil or using the municipal water supply.


BACKGROUND AND STATEMENT OF ISSUES

In 1995, residents of McFarland, California and the community organization Healing Our Mother Earth (HOME) petitioned the Agency for Toxic Substances and Disease Registry (ATSDR) to address health concerns about potential environmental contamination in their community. McFarland is an agricultural community located 25 miles north of Bakersfield in California's Central Valley (Figure 1, Appendix A). The town has a population of approximately 7,970 and is surrounded by crop land, pastures, and orchards. Many residents are agricultural workers. The community is concerned about exposures to hazardous substances (for example, pesticides and toxic wastes) in soil and drinking water, and about the incidence of childhood cancer.

According to historical records, the McFarland area has been the site of a U. S. Army Air Force basic pilot training airfield during World War II, and had extensive agricultural activity, including crop production, chemical application, storage and shipment of agricultural products. From 1985 to 1989, the KCEHSD and CDHS with EPA assistance conducted environmental sampling in response to community concerns regarding potential soil contamination (1-3). Soils at various locations around McFarland were tested for metals, pesticides, and volatile organic compounds (VOCs) that might be present because of the types of historical activities described above. The KCEHSD and CDHS conducted environmental sampling for contaminants from 1985 through 1989, including soil in yards of families with cancer and compared them to residences without cancer cases (1-3). Drinking water wells, schools, parks, and drainage areas were also sampled and tested for pesticides, metals and other contaminants (3). No elevated levels of contaminants were detected except nitrates were found in some of the municipal wells. Interpretations of aerial photographs and measurements of electromagnetic fields did not reveal evidence of hazardous waste sites or unusual levels of electromagnetic radiation. Air sampling and deep soil analysis were not performed at that time. From 1997 to 1999, EPA conducted additional sampling of soil and drinking water in McFarland (3-5). A review of this current sampling data is provided.

Prior to 1976, water was provided to the community by wells 1, 2, 3, and 4; well 3 became inactive in December 1978. Two new wells, 5 and 6 were brought into operation in 1983-84. McFarland drinking water wells were sampled throughout the 1980s. Nitrates exceeded the Federal maximum contaminant level (MCL) in well 2 and a nitrate removal system was installed in 1983. Arsenic and 1, 2-dibromo-3-chloropropane was detected in well 5 which was subsequently deactivated in 1987. Wells 1 and 4 were used during peak demand periods usually in the summer. In 1985, wells 1, 2, 4, 5, and 6 were sampled by the State Department of Health Services. No contaminants were detected in those water samples. On November 1985, water samples were taken at the tap from ten homes of cancer victims, three randomly selected control (non cancer cases identified) homes in the city, and well 3 (deactivated in 1978) (McFarland Childhood Cancer Cluster-Phase I, Kern County Department of Public Health). Contaminants detected did not exceeded health comparison values.

The McFarland Municipal Water Company currently uses four active (in service) wells: 2, 4, 6, and the Garzoli well. Another well, well 1 was deactivated in 1997 and is now closed. The wells range from 600 to 1,400 feet deep and feed into a 750,000 gallon storage tank that provides water on demand to McFarland residences(4). During high demand, water may be diverted from the storage tank. Water from these four wells feed into a single system of interconnected pipes to deliver water within the community. All wells have chlorination/disinfection systems to remove harmful microorganisms from the water. Wells 2 and 4 have nitrate removal systems. Well 6 has a gas chlorination system to disinfect and remove hydrogen sulfide. Under the U.S. and the California Safe Drinking Water Act, all public drinking water must be sampled routinely for harmful microorganisms, chemicals, radioactive substances, and metals. In 1996, test results indicated that the McFarland municipal water system met all federal and state drinking water standards (4).

Demographics

McFarland was established in 1908 and the population has increased from 4,000 to 7,950 between 1949 and 1996. McFarland's economy is linked to the agricultural industry and the population increase is in part due to an influx of people seeking agricultural jobs. According to the 1990 U.S. Census, McFarland has a population of 7017 (Figure 2, Appendix A), 17% are children under 6 years, 8% are adults over 65, and 22% are females 15 to 44 years old.

Community Concerns

The community asked ATSDR, EPA, state, and local agencies to provide assistance in evaluating current health conditions in the area. Health concerns include a perceived increase in the number of childhood cancer cases, incidence of adult cancers, low birth weight, miscarriages, and developmental anomalies. The community is surrounded by agricultural fields where ground and aerial application of pesticides and fertilizers are reported to occur frequently. According to residents, during periods of heavy rain, surface water run-off appears to flow through the neighborhood into sump areas. Potential contaminated soil from surface water run-off is also of concern. The drinking water issue is of primary concern, specifically the status of municipal wells used for drinking water in the neighborhood.


DISCUSSION

ATSDR obtains the community's concerns, and other medical, toxicological, demographic, and environmental factors that may affect the health of a community exposed to hazardous substances. To determine if health effects are likely to occur within the community, ATSDR health professionals consider various factors: the toxicity of the contaminant, the concentration (how much), the time of exposure (how long), and how the chemical gets into the body (breathing, eating, drinking, or skin contact). Other factors: occupation, personal habits, age, nutritional status, general health, and genetics are also considered. These factors affect how a contaminant is absorbed, distributed, metabolized, and eliminated from the body. A health assessment evaluates contaminants to determine whether exposure to them has public health significance. ATSDR selects and compares on- and off-site concentrations of contaminants with ATSDR comparison values for noncarcinogenic and carcinogenic effects (Appendix B). Comparison values are concentrations of contaminants in specific environmental media (air, soil, and drinking water) that are not expected to produce adverse health effects in people who are exposed. These values are used only as screening values; therefore listing a contaminant in a table of "chemicals of concern" does not mean that it will necessarily cause adverse health effects if exposure occurs at that specified concentration. When the concentration of a contaminant detected on or off the site is above the comparison value, it is further evaluated to determine the potential for adverse health effects. The focus of the evaluation is on health effects that could plausibly result from exposures to site-related contaminants. ATSDR considers both adults and children when developing comparison values. The potential health effects on children is considered separately because in certain situations children may be more sensitive and more exposed to contaminants. ATSDR then presents its conclusions and recommends appropriate actions. (See Appendix B for additional information regarding comparison values).

Cancer Risk Evaluation Guide (CREGs)

Most of the chemicals identified as "chemicals of concern" at McFarland exceeded only ATSDR's cancer risk evaluation guide (CREGs) or pica child values. Media-specific CREGs for potential carcinogens in air, soil, and water, are typically derived from EPA slope factors by factoring in default values for body weight and daily intake of a particular medium (air, soil, or water). Therefore, EPA cancer risk assessments assumptions also apply to ATSDR's CREGs. The two most important of those assumptions are: the absence of a threshold value other than zero for carcinogens, and a lifelong exposure. These assumptions are generally not applicable to the contaminants and exposure conditions at actual sites. ATSDR CREGs, which assume the absence of such thresholds, and correspond to undetectable, one-in-a-million cancer risk levels, are generally much more conservative than are non-cancer comparison values. Unlike cancer-based comparison values, non-cancer values are based on established no observed adverse effects levels (NOAELs) or lowest observed adverse effects levels (LOAELs), and on identifiable safety margins. ATSDR uses CREGs as preliminary screening devices only, because CREGs cannot, by themselves, provide a credible basis for identifying real health hazards, even if they are exceeded by a substantial margin.

Pica Behavior

Pica behavior is the craving or eating of substances that have no food value such as starch, clay, plaster, paint, and gravel, that is exhibited by some young children (ages one to six years) and some pregnant women. The craving may be related to nutritional or emotional needs. It is not the same behavior exhibited by children up to 18 months who may put everything in their mouth (5). Most children do not exhibit pica behavior, but those who do, may be at an increased risk of exposure to contaminants or parasites in the material that they eat. Parents should take precautions to prevent or limit this behavior.

Soil comparison values based on pica behavior in children are much more conservative than other comparison values for soil; some pica child environmental media evaluation guides (EMEGs), and reference dose media evaluation guides (RMEGs) (for example, those for hexachlorobenzene, and bis (2-ethylhexyl) phthalate) are even lower than the corresponding CREGS. Therefore, like CREGs, these values have limitations when evaluating the potential health implications of plausible exposure at most sites. ATSDR converts chronic EMEGs and RMEGs for adults (which represent levels of chronic exposure expected to be safe over the course of a 70-year lifetime) by adjusting for the difference in default values for body weights and intake rates into corresponding values for children and pica children. However, the conversion does not take into account the fact that children grow up or that pica behavior typically persists only for the first few years in a small percentage of children.

In one study of soil ingestion by children, one out of 320 children (0.3%) ingested 5,000 milligrams (mg) of soil daily (ATSDR's default soil ingestion rate for pica children); 95 percent of the children studied ingested less than 100 mg of soil daily (the average was 40 mg) (6). Very young children who may exhibit pica behavior are unlikely to have chronic access to highly-contaminated soil, which is usually located on-site rather than in the yards of private residences. However, regardless of the source of the maximally-contaminated soil samples (ATSDR selects "contaminants of concern" on the basis of the highest concentrations detected), a pica child will probably not consume 5 grams of that same soil every day. Therefore, if the maximum concentration of a contaminant detected at the site exceeds only a pica child value or CREG, then that contaminant is unlikely to pose any public health hazard.

Water

In February 1997, ATSDR reviewed the EPA's McFarland Drinking Water Investigation Field Sampling Plan (FSP), prepared by Ecology and Environment, Inc., California (Contract No. 68-W6-0010, January 16, 1997). The EPA submitted the document to ATSDR for review of the proposed Phase I drinking water sampling plan, including a list of chemicals to be screened and suggested testing locations, the municipal water facilities at the wells, the distribution center (Figure 3, Appendix A). Some public and residential water taps were tested during Phase II (7).

EPA tested for over 300 chemical substances in the McFarland drinking water, including all national primary drinking water regulation chemicals, and agricultural chemicals (such as herbicides, fungicides, and other pesticides) (4). The list included pesticides that were, according to the State of California records, historically used in the McFarland area (4). Drinking water was tested at the well head, and at the taps in selected homes and public locations. This sampling was conducted to determine the quality of the water currently used by the community. Since limited data exists prior to 1984, the quality of the drinking water and potential past exposures at some locations before 1984 could not be determined. While other contaminants were detected in the drinking water, only those contaminants that exceeded ATSDR's health comparison values were selected for further evaluation (8).

ATSDR found that sampling procedures followed accepted methodology and quality assurance and quality control guidelines (8) for collecting, storing, shipping, and analysis, including field and laboratory controls (4, Section 4, Appendix C of the EPA McFarland Drinking Water Investigation Field Sampling Plan). ATSDR bases its health evaluation on the results of the sampling data provided by the EPA.

Municipal Water Supply (EPA Phase I Sampling)

The McFarland municipal water supply consists of four active wells (2, 4, 6, and the Garzoli well), one inactive well (1), and a 750,000-gallon storage tank. The wells range from 600 to 1,400 feet deep. All the wells are chlorinated to kill harmful organisms and some have hydrogen sulfide (well 6) or nitrate (wells 2 and 4) removal systems. In July of 1997, EPA conducted phase I of the water sampling plan; active and inactive municipal wells were tested at the source before going to the mixing and distribution center (4). Sampling results were reviewed for potential contamination in the drinking water after pretreatment. Arsenic was detected in the Garzoli well (15.5 µg/L), well 6 (13.9 µg/L), and the storage tank (13.2 µg/L) above ATSDR's chronic EMEG for a child (3 µg/L) and for an adult (10 µg/L).

Arsenic levels exceeded ATSDR's CREG in all drinking water wells tested (Table 1). However, ATSDR does not consider these levels a cancer hazard. ATSDR's CREG is based on an EPA slope factor, which is itself based on a large Taiwanese study in which consumption of arsenic-contaminated well water (170 to 800 µg/L) was associated with increased skin cancer. In the United States, the average levels of arsenic in drinking water ( 5 µg/L) are much lower and no excess skin cancer has been observed in people consuming even higher concentrations (9-11). It was suggested that in the Taiwanese study, underestimated arsenic exposure lead to an overestimation of risk. The villagers were exposed to high levels of arsenic in their food and in their drinking water. It is also likely that the protein- and methionine-deficient Taiwanese population was more sensitive than typical U.S. populations, due to a compromised ability to detoxify or methylate ingested arsenic (12, 13). At low exposure levels, toxic inorganic arsenic compounds are effectively detoxified by methylation and excreted in the urine. Blood arsenic levels increase only after the methylation capacity of the liver is exceeded, resulting in adverse health effects. Saturation of this detoxification mechanism may explain why both the cancerous and noncancerous effects of arsenic exhibit a threshold somewhere between 250 and 500 µg per day (12, 13). Because ATSDR's CREGs (or rather the cancer slope factors from which they derive) are based on a zero-threshold model for genotoxic carcinogens, they are not strictly applicable to non-genotoxic threshold carcinogens like arsenic. Although the arsenic levels in the McFarland groundwater exceeded ATSDR's CREG for drinking water, ATSDR does not consider them a carcinogenic hazard. Therefore, it is unlikely that people would suffer adverse health effects from drinking this water because they would not be exposed continually to this maximum dose.

Most radon levels detected in McFarland drinking water were at or below 300 pico-Curies per liter (pCi/L). Radon 222 levels detected in wells 2 (553 pCi/L) and 4 (471 pCi/L) exceeded by 40% this comparison value. Radon is a naturally occurring gas that may remain below the soil surface, move to the soil surface and enter the air, or may enter into the groundwater. People may be exposed from drinking water that contains radon, but most of the exposure occurs when radon in water is released rapidly into the air and breathed. A survey for radon in groundwater in the United States showed that radon levels in larger aquifers average 240 pCi radon-222/L of water while smaller aquifers average 780 pCi radon-222/L, depending on the type of rock formation in the area (14). It is estimated that the daily intake of radon from drinking water ranges from 100 to 600 pCi radon-222 per day, including drinking (assuming drinking two liters of water daily) and breathing radon released from the water (14). Limited studies indicate that the lung is the organ most affected by long-term exposure to radon and exposure to radon in the air may increase the chance of lung cancer (14). However, most of these studies are for work-related exposures at concentrations higher than those detected in McFarland.

The hypothetical cancer risks on which radon standards are based were extrapolated, assuming a linear, zero-threshold relationship, from excess cancer rates associated with high occupational exposures. However, low environmental radon exposure is unlikely to pose a cancer threat to exposed residents. In a large study of residential radon levels conducted by EPA and the University of Pittsburgh, lung cancer rates were lower in communities with naturally elevated radon levels in the air, compared to communities with lower levels of radon (15). Thus, in this study, which used radon data from 1,601 counties covering over 80% of the U.S. population, the observed relationship between lung cancer and residential radon directly contradicted the predictions of zero-threshold models. These results are consistent with some evidence indicating that low doses of radiation or chemicals may stimulate the body's natural defense mechanisms (16, 17).

Residential and Public Water Taps (EPA Phase II Sampling)

In June and July of 1998, the EPA conducted Phase II of the McFarland drinking water investigation (7). EPA resampled water from all four active municipal drinking water wells and the municipal storage tank. Additionally, EPA sampled and analyzed water from taps at 15 residential and 12 public locations (six schools, two parks, one gymnasium, the library, one health clinic, and one church) for contaminants. To protect the privacy of the tested residences, sampling locations were divided into quadrants: southeast, northeast, northwest, southwest, and central. These areas included the municipal water supply at the wells and distribution center and drinking water faucets at public and residential locations. The EPA reviewed and discussed the sampling results with participating individuals.

Table 1 contains a list of contaminants detected during the water sampling periods that were either above health comparison values or did not have a comparison value and were selected for further evaluation. Detected concentrations of trihalomethanes (chlorination by-products), bromodichloromethane or BDCM (ND-2.3 µg/L) and bromoform (ND-6.6 µg/L) were considerably lower than national drinking water standards (MCL 80 µg/L). In some wells, concentrations of BDCM and bromoform did exceed ATSDR's CREGs (Table 1). However, the cancer risk assessments from which these CREGs were derived are based on animal studies in which a daily bolus dose (for example, a single injected mass) of the chemicals was administered by gavage (force-feeding) in oil. Halogenated hydrocarbons are more soluble in oil than in water. However, chlorination by-products in drinking water are unlikely to pose a cancer hazard to humans, because doses are lower and distributed evenly throughout the day, instead of administered all at once as in a bolus dose. In chronically-exposed laboratory animals, high concentrations of the trihalomethanes, chloroform and chlorodibromomethane do not cause cancer when animals are allowed to drink water containing these chemicals freely (ad libitum) instead of by gavage in oil. Large, single doses can overwhelm the protective mechanisms of the liver and cause damage that eventually leads (via a non-genotoxic mechanism) to liver cancer, while the same total daily dose, spread out over the animal's waking hours, cannot. Unlike the larger bolus doses, the smaller individual doses that the animal receives when it drinks water may be effectively detoxified before any liver damage can occur that cannot be repaired before the next small dose.

Fusilade, an herbicide designed to control most weeds in a number of commercial crops (18), was detected at low concentrations in three samples: well 6 from the northwest quadrant (MW-35, 0.16 µg/L), the Garzoli well from the west central quadrant (MW-27, 0.06 µg/L), and from the southwest quadrant (DD-46, 0.17 µg/L). Fusilade is not a common contaminant of groundwater because it is rapidly broken down in water and has low mobility in soils. It is listed as an EPA class IV contaminant and is considered relatively nontoxic.

Arsenic was detected in water samples ranging from 0.5 to 18.2 µg/L, which is above ATSDR's chronic EMEG for a child (3 µg/L) and for an adult (10 µg/L).

Vanadium was detected in water samples collected at three of the quadrants in the McFarland area. The concentration ranged from 3.5 to 56.8 µg/L, the maximum concentration detected does not exceed ATSDR's intermediate EMEG of 100 µg/L for adults (19). It slightly exceeds (by 43% or 1.43-fold) ATSDR's child EMEG of 30 µg/L. However, ATSDR's oral MRL of 0.003 mg/kg/day for vanadium is based on a NOAEL in animals and contains a built-in, 100-fold safety factor. The maximum detected concentration of 56.8 µg/L, the daily oral dose of vanadium for a 10-kg child (0.0057 mg/kg/day) is within that safety factor. Therefore, the average concentrations of vanadium in drinking water should not be expected to produce any adverse health effects in people drinking this water.

Radon was detected above the health comparison value (300 pCi/L) in two municipal wells in the southeast quadrant, well 2 and well 4 at 500 and 420 pCi/L, respectively. These maximum detected concentrations would not produce any adverse health effects in exposed humans (See previous discussion on radon in municipal water wells).

Table 1. City Of McFarland-Phase II Drinking Water Sampling Resultsa

Contaminant

Sampling Locationb/Concentration Range(ug/Lc)

Comparison Value

Southeast Quadrant Northwest
Quadrant
West Central
Quadrant
Southwest
Quadrant
Northeast
Quadrant
Bromodichloromethane 1.1-1.6 1.9-2.2 0.3-2.3 0.27-1.9 0.69-2 100 MCLd 0.6 CREGe
Bromoform NDg ND ND 0.76-6.4 2.7-5.5 100 MCL 4 CREG
Fusilade ND ND-0.16 ND-0.06 ND-0.17 ND None
Arsenic 1.4-13.4 11.7-16.8 10-15.1 0.5-12.3 3.6-18.2 3/10 c EMEGf 0.02
CREG
Vanadium 3.5-56.8 32.4-38 32-52.2 3.9-51.7 8.4-47.5 30/100 EMEG
Radon 222 130-420 150-210 44-190 87-500 150-300 300 pCi/Lh

a United States Environmental Protection Agency (EPA) Phase II McFarland Drinking Water Investigation, June-July 1998
b Water samples were collected at municipal, public, and private water systems in McFarland
c µg/L= Microgram per liter
d MCL = EPA current maximum contaminant level for total trihalomethanes (bromodichloromethane, bromoform, chloroform, and dibromochloromethane)
e CREG = ATSDR cancer risk evaluation guide (see Appendix B)
f EMEG =ATSDR environmental media evaluation guide. child/adult
g ND = Not detected
h pCi/L= Pico curies per liter

Soil

Soil samples were obtained from various private, public, and industrial areas throughout the McFarland area. Samples were sent to six laboratories contracted by the EPA to conduct the various analysis for specific contaminants (20). The list of sampled contaminants is provided in the EPA McFarland Soil Investigation Phase I Summary Report (20). Only contaminants detected above ATSDR's health comparison values were further evaluated, as explained above, and are provided in the following tables.

A. Residential Areas

In 1999, the EPA sampled soil from eight residences labeled A through H (Figure 4, Appendix A) in McFarland. This land was reported to have been previously used for agricultural purposes and then converted to residential use between the late 1970's and the early 1980's. Some residents were concerned about possible soil contamination around their homes from potential dumping and from past and present pesticide applications. Two to three soil borings were drilled and 12 soil samples were collected at each residence at the surface (0.5 feet below ground surface (bgs) to nine feet bgs. Soil was also sampled at deeper intervals, 50 feet bgs at one residential location based on past disposal history.

Antimony, arsenic, cadmium, and chromium were detected in residential soils at levels below ATSDR's comparison values for a non-pica child or adult (Table 2). Maximum detected concentrations did exceed comparison values based on chronic exposure in pica children or on potential cancer effects. As discussed previously, most children do not exhibit pica behavior (5), but those who do may be at an increased risk of exposure to contaminants in the soil they eat. Therefore, parents should take precautions to prevent or limit this behavior.

The typical concentrations in California soils range from 0.6 to 11.0 mg/kg for arsenic and from 0.05 to 1.10 mg/kg for cadmium. ATSDR's most conservative comparison values for these elements are generally within normal background levels. Because none of the detected concentrations in soil exceed ATSDR's EMEGs/RMEGs for children or adults, exposures to contaminants detected in the residential soils tested should not be expected to produce adverse health effects.

Table 2. Soil Samples From Residential Areas-McFarlanda

Contaminant
Residential Locationsb/Concentration Range (mg/kg)c

A

B

C

D

E

F

G

H

Comparison Value/ Source
Antimony 0.79-2.5 1.3-2.2 0.79-1.9 0.27-1.1 0.92-2.2 0.73-1.6 1.7-2.5 0.54-1.1 0.8/20/3000 RMEGd
Arsenic 2.0-10.7 3.8-6.5 2.6-6.9 1.6-3 3.2-9.4 1.5-4.2 4.5-10.7 3.1-6.2 0.6/20/200 cEMEGe, 0.5 CREGf
Cadmium 0.56-1.3 0.58-1.1 0.8-2.5 0.53-1.7 0.45-1.1 0.69-2.2 0.72-1.2 0.42-0.69 0.4/10/1000 cEMEGe
Chromium 8.2-26.4 11.9-19 12.4-18.5 3.5-14.5 9.4-21.9 8.6-24.1 14.2-20.2 8.7-14.2 6/200/2000 RMEGd
a United States Environmental Protection Agency (EPA) McFarland Soil Investigation Phase I Summary Report (2000)
b Soil samples were collected at eight private residences in McFarland
c mg/kg= milligram per kilogram
d RMEG = ATSDR reference dose media evaluation guide, pica child/child/adult (see Appendix B)
e cEMEG =ATSDR chronic environmental media evaluation guide
f CREG = ATSDR cancer risk evaluation guide

B. Public Areas

Schools

Soil Samples were collected from four public schools: Browning Road School (Figure 5, Appendix A), Kern Avenue School (Figure 6, Appendix A), McFarland Middle School (Figure 7, Appendix A), and McFarland High School (Figure 8, Appendix A). Community members were concerned with potential pesticide build-up in the soil. Samples were collected at playgrounds and other highly accessible and heavily used areas at depths ranging from 0 to 0.5 (surface soil) and one to two feet below ground surface. These samples were tested for pesticides, metals, and other contaminants. Arsenic detected in soils tested from all four schools was within normal background levels (Table 3). Maximum values exceeded ATSDR's CREG and pica child EMEG, but not ATSDR's EMEGs for children or adults (CREGs are conservative screening values for carcinogenic substances that are based on daily, lifetime exposures [70 years]). Because children are not usually exposed to these maximum concentrations on a daily basis, adverse health effects are not expected.

Systhane or myclobutanil, (an agricultural chemical used as a fungicide, bacteriacide, and wood preservative) was detected only at the Browning Road school. A predicted dose at the maximum concentration detected would be 0.97 E-06 mg/kg/da. The oral reference dose (RfD) for Systhane is 0.025 mg/kg/da. Therefore the dose that a student might receive from occasional exposure to the soil is 25,000 times less than the safe level indicated by the comparison value. Such exposures would produce no adverse health effects.

Benzo(a)pyrene (BaP) was detected only in soil tested from the Browning Road School. The detected concentration (0.26 mg/kg) exceeded ATSDR's CREG by a factor of less than three. Benzo(a)pyrene is the most carcinogenic member of a natural class of compounds called polycyclic aromatic hydrocarbons (PAHs) (21). Because PAHs such as benzo(a)pyrene are natural substances produced during the combustion of virtually any organic material, they occur throughout the environment, even in the absence of industrial pollution. Inhalation of complex PAH mixtures (for example, cigarette smoke, roofing tar or coal tar pitch volatile, and coke oven emissions which contain many other carcinogens in addition to BaP) may cause cancer in humans, but the doses required are high and of long duration.

No studies suggest a direct link between oral or dermal exposure to PAHs (including BaP) and cancer in humans. Attribution of risk to humans exposed via these routes are based solely on studies in animals treated with high doses of BaP either through force-feeding (gavage) or painting on bare skin. The latter treatment involves repeated painting of shaved patches of skin with the test substance, followed by repeated treatment with 12-O-tetradecanoylphorbol-13-acetate (TPA) a potent promoter. In the gavage experiments, the rodent's most commonly affected organ was the forestomach. Humans obviously do not undergo such treatment. Additionally, humans do not have a forestomach and are unlikely to produce the relatively high levels of active (carcinogenic) BaP metabolites that rodents do. The enzyme (cytochrome P-450 1A1) required to convert BaP into carcinogenic metabolites is common in the liver of rodents but undetectable in most human livers. The liver is the organ primarily involved in the metabolism of ingested substances. Furthermore, since all cancer-based comparison values in the United States assume the absence of a threshold for carcinogenesis and correspond to a linearly-extrapolated one-in-a-million risk level, the CREG for benzo(a)pyrene is conservative by a much greater margin than the rodent data alone suggests. The zero-threshold theory assumes that cancer is a long-term product of genotoxicity. Genotoxic doses of benzo(a)pyrene in one strain of rat were 10 mg/kg and greater. To receive a similar dose of BaP from soil, a 10-kg child would have to eat almost 800 pounds of dirt containing the maximum detected level of BaP (0.26 mg/kg).

PAHs are, for the most part, readily metabolized and eliminated and, with the exception of some allergic reactions, their acute toxicity is low. Few adverse health effects clearly attributable to PAHs have ever been demonstrated in humans. Animals chronically exposed to 1 mg BaP/kg/day do not show adverse effects, cancer or non-cancer. To receive a dose numerically equivalent to this NOAEL, a 10-kg pica child would have to consume daily 5,000 mg of soil containing 2,000 mg/kg BaP, more than 7,700 times the maximum level detected at McFarland (0.26 mg/kg). The same child eating 5,000 mg of soil containing the maximum detected level of BaP in soil (0.26 mg/kg) at McFarland would ingest 1.3 ug BaP.

Parks

Three public areas in McFarland were sampled for potential contaminants: Browning Road Park (Figure 9, Appendix A), McFarland Park (Figure 10, Appendix A), and a drainage basin (Figure 11, Appendix A). Browning Road Park, a 10-acre area north of Browning Road School, was developed from agricultural land in the early 1970's. Community members were concerned with potential contamination from reports of military and agricultural dumping and pesticide build-up. In November 1998, Sage Earth Science which conducted a land survey did not find evidence of waste burial or dumping. Soil samples from accessible, high-use areas were collected and analyzed for pesticides, metals, and other contaminants.

The McFarland (Mouser) Park consists of 7.5 acres southwest of the intersection of Sherwood Avenue and Second Street. From historical aerial photographs, this property was agricultural land prior to the 1950's (3). A large excavation area was identified and may have been associated with the nearby construction of Highway 99 in the 1950's (3). This area is now a baseball diamond. EPA sampled soil at various locations around the park, including the playground, baseball diamond, and other high-use areas for children. Antimony, arsenic, cadmium, and chromium were detected in soil samples but the concentrations did not exceed child or adult comparison values established for exposure to soil through ingestion or skin contact (Table 4). These samples exceeded pica child values and arsenic concentrations exceeded the CREG. However, these values are typical of arsenic concentrations (0.6 to 11.0 mg/kg) found naturally in California soils. Exposure may be of consideration only to children exhibiting the type of temporary pica behavior described above who play in contaminated soil. However, adverse health effects are unlikely because children exhibiting pica behavior would be briefly exposed to soils in this area.

Drainage Basin

A 400 feet by 200 feet unlined drainage basin is located between Perkins Avenue and Brentwood Court, east of the Southern Pacific Railroad tracks (Figure 11, Appendix A). This drainage basin was constructed in the late 1970's to collect storm water runoff from the area east of Highway 99. Three concrete channels are located on the northwest, southern, and eastern sides of the basin. The area is surrounded by an earthen berm and a fence, and residences are located to the north and east. Concerns included hazardous waste build-up in the soil from storm water runoff into the area and potential military and agricultural dumping prior to construction of the basin. Soil samples were collected at various depths from 0 to 50 feet, especially near the discharge points of the concrete channels and the area of a historical agricultural water impoundment. No contaminants were detected above comparison values in soils tested in the drainage basin area. Exposure to these soils is unlikely to produce adverse health effects.

Table 3. Soil Samples From School Areas-McFarlanda

Contaminant School Locationsb/Concentration Range (mg/kg)c

Browning Road School

Kern Avenue School

McFarland Middle School

McFarland High School

Comparison Value Source
Arsenic

2.4-5.6

2.7-10.2

3.8-5.4

3.6-6.5

0.6/20/200 cEMEGd, 0.5 CREGe
Systhane

0.45-1.0

ND

ND

ND

RfD 0.025 mg/kg/da
Benzo(a)pyrene

0.26

ND

ND

ND

0.1 CREG
a United States Environmental Protection Agency (EPA) McFarland Soil Investigation 1999
b Soil samples were collected at four schools in McFarland
c mg/kg= milligram per kilogram
d cEMEG =ATSDR chronic Environmental media evaluation guide (pica child/child/adult )
e CREG = ATSDR cancer risk evaluation guide
f RfD = EPA reference dose
g RBC =EPA risk base concentration
h ND = Not detected


Table 4. Soil Samples From Park Areas-McFarlanda

Contaminant Park Locationsb/Concentration Range (mg/kg)c

McFarland Park

Browning Road Park

Comparison Value/Source
Antimony

0.29-1.5

0.6-5.2

0.8/20/3000 RMEGd
Arsenic

1.6-5.5

1.1-10.7

0.6/20/200 cEMEGe, 0.5 CREGf
Cadmium

0.14-2.8

0.29-3.1

0.4/10/1000 cEMEG
Chromium

3.0-22

6.7-29.1

6/200/2000 RMEG
a United States Environmental Protection Agency (EPA) McFarland Soil Investigation 1999
b Soil samples were collected at two municipal parks in McFarland
c mg/kg= milligram per kilogram
d RMEG = ATSDR reference dose media evaluation guide, pica child/child/adult (see Appendix B)
e cEMEG =ATSDR chronic environmental media evaluation guide (see Appendix B)
f CREG = ATSDR cancer risk evaluation guide

C. Industrial Areas

EPA selected nine commercial areas for further soil sampling after reviewing information from National Archive records, local libraries, current and past pesticide use reports maintained by the State of California and the Kern County Agricultural Commissioner's Office, and conversations with community members and local agencies (3). The areas include: the Kirkpatrick and Sons Potato Shed, Tri Cal, Renteria Farm Contracting, Montebello Rose Company, Brown and Bryant facilities, McFarland Cooperative Gin, Producer's Gin, Garza's Service Station, and Sunshine Service Station.

Elmo Highway Complex

For sampling purposes, the EPA defined the Elmo Highway Complex as the area containing the Kirkpatrick and Sons Potato Shed, Tri Cal, and Renteria Farm Contracting (3). The complex is south of Elmo Highway, along the eastern side of the Southern Pacific Railroad Tracks (Figure 12, Appendix A). Cultivated fields lie east of the Kirkpatrick and Sons Potato Shed and Tri Cal. A residential area lies east of the Renteria Farm Contracting. The community is concerned with pesticide and metal use during operations and storage activities, and discharges from drums and pits.

The Kirkpatrick and Sons Potato Shed was built in 1945 and used for various purposes from 1945 to 1970 (3). The facility was reportedly used to pack potatoes (1945-54, 1963-83), to store fertilizers and seeds (1955-62), to store rose growing supplies (1983-88), and to store other agricultural products on occasion (3).

Tri Cal is south of the Kirkpatrick and Sons Potato Shed (Figure 12, Appendix A). This facility was built between 1946 and 1952 (3) and used as a potato shed during the 1950's. In 1980, Tri Cal purchased the facility from Mount Arbor Nursery to store methyl bromide, chloropicrin, glue, and plastics. This facility was reportedly used only to store these chemicals and not to mix them. Since 1988, this facility has been vacant and fenced. In February 1989, the owners reported a leaking underground diesel storage tank and KCEHSD oversaw remedial activities, including tank removal and excavation of contaminated soil (3). Soil samples collected afterwards were tested for petroleum hydrocarbons, benzene, toluene, and xylene. The site is now considered remediated.

Renteria Farm Contracting is south of Tri Cal (Figure 12, Appendix A). Aerial photographs indicate that the facility was built between 1961 and 1967 and fenced in 1988 (3). The area is now a concrete pad containing rubble. It was formerly a plant nursery where rose plants were packaged and root stocks were raised. In 1987, the Agricultural Commissioners Office found labeled and unlabeled drums containing various pesticides (3).

Soil samples were collected at various depths from 0 to 20 feet at several locations at the Elmo Highway Complex, including the rail-car loading docks and the historical locations of pits, storage areas, and waste sites (Figure 12, Appendix A). Arsenic and mercury were detected at the Elmo Highway Complex but at concentrations that would not pose a threat to people who may occasionally enter the site (Table 5). The pesticides perthane, systhane, and benomyl were also detected in the soil, but either at or below concentrations detected in food samples by the U.S. Food and Drug Administration, or below EPA reference concentrations (Table 5). Therefore, occasional exposures at these concentrations would not result in adverse health effects.

South Industrial Street Complex

The South Industrial Street Complex contains two facilities; the Montebello Rose Company, Inc. and Brown and Bryant, Inc., on Industrial Street along the eastern side of the Southern Pacific Railroad (Figure 13, Appendix A). One residential area lies to the east and two residences lie north of these facilities. The Montebello Rose Company is at the southwest corner of "B" Street and Industrial Street (Figure 13, Appendix A). According to aerial photographs, between 1937 and 1946 an agricultural business was established there (3), in the 1960's a rose packing operation began, and in 1991 an underground gasoline storage tank was removed (3). Prior to 1956, Brown and Bryant Inc. reportedly operated an agricultural chemical manufacturing and pesticide application facility. Aerial photographs indicated that before 1937, a large building was constructed on the site which was later dismantled (from May 1973 through October 1974). Aerial photographs also indicated the existence of pits between these two facilities, south of the loading dock on the Montebello Rose Company facility. Elevated levels of arsenic, copper, mercury, lead, and zinc were detected in soil samples collected from these pits (3). Arsenic (254 mg/kg) and lead (222 mg/kg) were detected in one sample collected from a ditch near the railroad tracks at the Montebello Rose Company, subsequent sampling did not confirm these elevated levels. These levels do not exceed industrial levels set for arsenic (440 mg/kg) and lead (1000 mg/kg).

In response to concerns regarding pesticide, metal, dioxin, and other potential soil contaminants, samples were collected (0 to 0.5 feet below ground surface) especially near the loading docks, railroad areas, and areas identified by aerial photographs that showed ground disturbance and former building sites. Arsenic was detected in soils ranging from 3.9 to 13.6 mg/kg, below ATSDR's comparison value for a child or adult (Table 5). The pesticides iprodione (31 mg/kg) and bromacil (0.14 mg/kg) were detected in one soil sample each at this complex (Table 5). Occasional exposure to soil containing these pesticides at the concentrations detected would result in a dose well below comparison values established for a child or adult. Therefore, adverse health effects will not likely result.

Table 5. Soil Samples From Industrial Areas-McFarlanda

Contaminant Industrial Locationsb/Concentration Range (mg/kg)c

South Industrial St. Complex

Elmo Highway Complex

Comparison Value/Source
Arsenic

3.9-13.6

2.5-8.1

0.6/20/200 cEMEGd, 0.5 CREGe
Mercury

ND

0.02-28.9

0.6/20/200 RMEGf
(mercuric chloride)
Perthane (Ethylan)

ND

0.74

0.034/.005 ug/kg/da g USFDAh
Systhane (mycobutanil)

ND

0.65-0.75

0.025 mg/kg/da i RfD j
Benomyl

ND

0.06

0.05 mg/kg/da RfD
Iprodione

31

ND

0.04 mg/kg/da RfD
Bromacil

0.14

ND

0.09 mg/L HAk
a EPA McFarland Soil Investigation 1999
b Soil samples were collected at two industrial complexes in McFarland
c mg/kg= milligram per kilogram
d cEMEG =ATSDR Chronic Environmental Media Evaluation Guide (see Appendix B)
e CREG = ATSDR Cancer Risk Evaluation Guide
f RMEG = ATSDR Reference Dose Media Evaluation Guide, pica child/child/adult (see Appendix B)
g ug/kg/da = microgram per kilogram per day
h USFDA = United States Food and Drug Administration
i mg/kg/da = milligram per kilogram per day
j RfD = EPA Reference Dose
k HA = Health Advisory

McFarland Co-op Gin Inc. and Producer's Cotton Gin

The McFarland Cooperative Gin, established between 1949 and 1952, is located at the northeastern corner of Garzoli Avenue and Elmo Highway (Figure 14, Appendix A) (3). In July 1987, KCEHSD monitored the removal of a leaking underground gasoline storage tank and the placement of an asphalt cap over the contaminated area (3). Surface and subsurface soil samples were collected near pits, loading and storage areas, and areas with evidence of disturbed soil. Arsenic was detected in soil at concentrations ranging from 3.0 to 11.3 mg/kg and did not exceed the child or adult chronic EMEG, but did exceed the 0.5 mg/kg CREG. However, that value is based on a lifetime exposure and humans would not be exposed continually to soil at this location for that long. For reasons outlined in previous sections, arsenic in soil at levels that exceed no comparison values other than the CREG does not threaten public health.

Producer's Cotton Gin, at the northwestern corner of Davis Avenue and the Elmo Highway Complex (Figure 15, Appendix A) was a former cotton gin and manufactured cotton seed oil. The gin may have been operating between 1946 and 1952, but is only listed in the Polk City directory in 1962 (3). According to a Kern County Fire Department inspection report, the gin became vacant in 1995 (3). Surface and subsurface soil samples were collected from storage areas, depressions near the southern perimeter of the property, and a potential pit area southwest of the gin. Arsenic was detected in soil at concentrations ranging from 2.9 to 7.1 mg/kg and did not exceed the child or adult chronic EMEG, but did exceed the 0.5 CREG. However, that value is based on a lifetime exposure and it is unlikely that people who may occasionally access the area would be exposed to these low levels of arsenic in the soil. Therefore, these concentrations are not a threat to public health. Perthane was also detected at a concentration of 0.29 mg/kg in one soil sample in this area. The potential dose that a person might receive from intermittent ingestion of contaminated soil is well below acceptable concentrations detected in food samples by the U.S. Food and Drug Administration.

Garza Service Station and Sunshine Service Station

The Garza Service Station is located on Kern Avenue (Figure 16, Appendix A) and the Sunshine Service Station is located on San Juan Avenue (Figure 17, Appendix A). In response to community concern regarding potential leaking of underground gasoline storage tanks and waste, the EPA tested soil samples from these sites for lead, waste-oil associated compounds, solvents, and other hydrocarbons (3). Arsenic was detected in soil sampled at the Garza (2.3 to 4.8 mg/kg) and the Sunshine Service Stations (2.8 to 28.6 mg/kg). While these values exceeded the CREG comparison value based on a lifetime exposure, only the maximum value of one sample detected at the Sunshine Service Station was above ATSDR's child comparison value for arsenic. However, adverse health effects are unlikely because people would not continually ingest or inhale soil contaminated with these maximum concentrations (see discussions of arsenic in soil in previous sections).


PUBLIC HEALTH IMPLICATIONS

The California Department of Health Services (CDHS), the Kern County Environmental Health Services (KCEHSD) and the United States Environmental Protection Agency (EPA), Region IX investigated a potential childhood cancer cluster identified from 1984 through 1991 (1, 2). The epidemiological study concluded that McFarland, Fowler, and Rosamond had unusually higher rates of cancer. However, unusually low rates were found for other communities (Visalia, Sanger, and the Mendota area). The study concluded that the overall distribution of the various types of childhood cancers identified was the expected value. Twenty-one children (less than 15 years old) have been diagnosed with cancer between 1975 and 1995. During this investigation, the CDHS screened 1,700 children, analyzing blood and urine levels to identify any abnormalities. Some children were found to be anemic. CDHS concluded that while the cancer cluster was real, no causal association could be made between the health data and levels of toxic compounds identified by previous environmental sampling data (1).

A review of current environmental data did not identify levels of contaminants in drinking water or soil at levels of health concerns for cancer or non-cancer (low birth weight, miscarriages, or developmental) effects. Some metals (arsenic, vanadium), pesticides (fusilade, bromodichloroethane, bromoform) and radon were detected at concentrations below levels of health concern in the municipal water system. Soil samples were obtained from various private, public, and industrial areas throughout the McFarland area. Metals (antimony, arsenic, cadmium, and chromium) detected in residential and public area (parks and schools), and industrial areas (arsenic and mercury) were below health effects levels. Therefore, no adverse health effects would be expected.


CHILD HEALTH INITIATIVE

ATSDR recognizes that children react differently than adults when exposed to contamination in their water, soil, air, or food. They are more likely to be exposed for several reasons; children play outside more often than adults, increasing the likelihood that they will come into contact with chemicals in the environment, and because they are nearer to the ground, children breathe more dust, soil, and heavy vapors. Children are also smaller, resulting in higher doses of chemical exposure per body weight. The developing body systems of children can sustain damage if toxic exposures occur during certain growth stages.

ATSDR evaluated the likelihood of children being exposed to contaminants at levels of health concern while living in McFarland. Based on ATSDR's review of environmental data, adverse health effects would not result from drinking the municipal water or from exposure to soil.


CONCLUSIONS

ATSDR reviewed available municipal water and soil data. No adverse health effects would be expected, therefore, the McFarland site does not represent an apparent health hazard for water or soil.

Water

Municipal

1. Arsenic was detected in two municipal wells (Garzoli and 6) and the storage tank, above the current EPA Drinking Water Standard, but not at levels of health concern.

2. At the levels detected, adverse health effects for children and adults are unlikely to occur now or later. No data are available to evaluate past exposures.

3. Radon 222 in well 2 and 4 exceeded the current health comparison value. However, based on recent studies, the concentrations detected are not a hazard to public health.

Residential

1. Bromodichloroethane, bromoform, arsenic, and fusilade were detected in some residential taps, but not at levels of health concern for children or adults.

2. Vanadium was detected in residential taps in three of the quadrant areas in McFarland at maximum levels that slightly exceeded ATSDR's child EMEG. However, adverse health effects are unlikely at this concentration.

Soil

Residential

1. Antimony, arsenic, cadmium, and chromium were detected in residential soils but not at levels that exceed ATSDR's comparison values for children or adults.

2. Children exhibiting pica behavior are unlikely to be harmed by ingesting some of this soil, but this behavior should be prevented due to increase risk of exposure.

Schools

1. Concentrations of arsenic detected in soil tested at four schools were below child and adult levels of health concern.

2. Systhane and benzo(a)pyrene were detected in soil at the Browning School. Exposure to these substances at the maximum concentrations detected would pose no health hazard to school children.

Parks

1. Antimony, arsenic, cadmium, and chromium were detected in soil samples obtained from the Browning Road Park and the McFarland Park, but not at levels resulting in adverse health effects.

2. No contaminants were detected above ATSDR's health comparison values in soil tested in the drainage basin area.

Industrial

1. Arsenic, mercury, and the pesticides perthane, systhane, and benomyl were detected in some soil samples at the Elmo Highway Complex, but they did not exceed comparison values. Therefore, no adverse health effects are expected.

2. Arsenic and the pesticides iprodione and bromacil were detected in some soil samples tested in the South Industrial Street Complex, but not at levels of health concern.

3. Arsenic and perthane were detected in soil at the McFarland Cooperative Gin and the Producer's Cotton Gin, but not at concentrations that exceed ATSDR's comparison values established for children or adults.

4. Arsenic was detected in some soil samples collected at the Garza Service Station and the Sunshine Service Station, but not at levels that would result in adverse health effects.


RECOMMENDATIONS

1. Prevent children exhibiting pica behavior from eating soil and other materials that may contain contaminants.

2. Continue filtering out nitrates and chlorinating the municipal water supply. Continue routine monitoring.


SITE TEAM/AUTHORS

Adele M. Childress, PhD, MSPH
Environmental Health Scientist
Agency for Toxic Substances and Disease Registry
Division of Health Assessment and Consultation
Exposure Investigations and Consultation Branch

Frank Schnell, PhD, DABT
Toxicologist
Agency for Toxic Substances and Disease Registry
Division of Health Assessment and Consultation
Exposure Investigations and Consultation Branch


ACTION PLAN

1. ATSDR will review other water and soil data that becomes available, upon request.

2. ATSDR will review air data collected in McFarland by the EPA, when it is available.

3. ATSDR will provide the McFarland community with a health consultation evaluating the air sampling data for public health implications.


REFERENCES

1. California Department of Health Services. 1988. Epidemiologic Study of Adverse Health Effects in Children in McFarland, California, Phase II Report. Berkeley, CA: California Department of Health Services.

2. California Department of Health Services, Berkeley, CA: California Department of Health Services. 1996. The Four County Study of Childhood Cancer: Clusters in Context. Statistics in Medicine. Vol 15, 683-697.

3. EPA McFarland Soil Investigation Field Sampling Plan. Volume I. Contract No.68-W6-0010, Ecology and Environmental Inc. January, 1999.

4. EPA McFarland Drinking Water Investigation Field Sampling Plan. Contract No.68-W6-0010, Ecology and Environmental Inc. January 16, 1997.

5. Griffith, Winter H., M.D. The Complete Guide to Symptoms, Illness & Surgery. © 1995 The Putnam Berkley Group, Inc.

6. Gough, Michael. 1991. Human exposures from dioxin in soil-A meeting report. J. Toxicol. Environ. Health 32: 205-245.

7. EPA McFarland Drinking Water Investigation Phase II Sampling Report. 2000 May..

8. Agency for Toxic Substances and Disease Registry. ATSDR Public Health Assessment Guidance Manual 1992. DHHS (PHS).

9. Agency for Toxic Substances and Disease Registry (ATSDR). 1992. Toxicological profile for arsenic. Atlanta, GA:U.S. Department of Health and Human Services, Public Health Service.

10. ATSDR. 1993. Agency for Toxic Substances and Disease Registry. Toxicological profile for arsenic (Update). Atlanta: U.S. Dept. of Health & Human Services, Public Health Service; 1993 Apr. Report No. TP-92/02.

11. ATSDR. 1999. Toxicological profile for Arsenic (Update), Draft. Agency for Toxic Substances and Disease Registry, U.S. Dept. of Health & Human Services, Public Health Service; 1999, Feb.

12. Marcus WL, Rispin AS., 1998. Threshold carcinogenicity using arsenic as an example." In: Advances in modern environmental toxicology, Vol. XV. Risk Assessment and Risk Management of Industrial and Environmental Chemicals. Princeton Scientific Publishing Co., 1988.

13. Stohrer, Gerhard, 1991. Arsenic: Opportunity for risk assessment. Archives of Toxicology 1991; 65: 525-31.]

14. Agency for Toxic Substances and Disease Registry (ATSDR). 1990. Toxicological profile for radon. Atlanta, GA:U.S. Department of Health and Human Services, Public Health Service.

15. Cohen, B.L. 1995. Test of the linear, no-threshold theory of radiation carcinogenesis for inhaled radon decay products. Health Physics 68: 157-174.

16. Luckey, T.D. 1991. Radiation Hormesis. CRC Press, Boca Raton, FL.

17. Calabrese, E.J. 1994. Biological effects of low level exposures to chemicals and radiation. CRC Lewis Publishers, Boca Raton, FL.

18. Extoxnet-http://ace.orst.edu/cgi-bin/mfs/01/pips/fluazifo.htm

19. Agency for Toxic Substances and Disease Registry (ATSDR). 1992. Toxicological profile for vanadium. Atlanta, GA:U.S. Department of Health and Human Services, Public Health Service.

20. EPA McFarland Soil Investigation Phase 1 Summary Report. Contract No.68-W6-0010, Ecology and Environmental Inc. June 2000.

21. ATSDR. 1995. Agency for Toxic Substances and Disease Registry. Toxicological profile for polycyclic aromatic hydrocarbons (PAHs) (Update). Atlanta: U.S. Dept. of Health & Human Services, Public Health Service; 1995 August.

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