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Dover Township Municipal Landfill & Silverton Private Well Contamination Investigation
Toms River, New Jersey
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Public Health Implications
The public health implications of the completed exposure pathways in the past will now be considered. Several contaminants were confirmed to be present in water from private wells at levels above health-based comparison values in both the DTML/Silverton
Road Groundwater Investigation and the Silverton Private Well Contamination Investigation. The NJDHSS and the ATDSR have further evaluated the public health significance of past exposures to these contaminants through an examination of relevant toxicologic
and epidemiologic information. In addition, this section will include a brief summary of the findings of an analysis of childhood cancer incidence data for Dover Township.
Childhood Cancer Incidence in Dover Township
The NJDHSS and the ATSDR reviewed cancer incidence data in the period 1979, to 1995 for Dover Township, as part of the Public Health Response Plan. Findings are fully described in a separate Public Health Consultation by the NJDHSS and the ATSDR (NJDHSS/ATSDR,1997).
Dover Township was the only municipality in Ocean County in which overall childhood cancer incidence (ages up to 19 years) was statistically elevated. Ninety cases were observed in the 17-year period, compared to 67 that would have been expected if childhood cancer
rates were the same in the township as in the entire State of New Jersey. Leukemia incidence was elevated in Dover Township, particularly in females under the age of five years. In the Toms River section of the township, overall childhood cancer was elevated
(24 observed vs. 14 expected). Both leukemia and brain/central nervous system cancers were elevated, with the excess occurring primarily in female children under age five.
Toxicologic and Epidemiologic Evaluation
Before actions were taken to interrupt the private well exposure pathways, it is clear that wells along Silverton Road adjacent to the DTML and in the Silverton section of Dover Township were contaminated with various VOCs and lead (for the Silverton Road private wells only)
for an undetermined length of time. Wells in the Silverton section of Dover Township were contaminated as early as 1981, when taste and odor problems were first reported. As previously indicated, the well contamination along Silverton Road is likely to be a result of contaminants
migrating in groundwater from the DTML. However, it is not known whether the contamination of the private wells in the Silverton section of Dover Township is related to the movement of contaminants in groundwater from the DTML.
DTML/Silverton Road Groundwater Investigation
Between 1987 and l989, nine private wells along Silverton Road were found to be contaminated with various VOCS. Of these nine wells, water fro m six of the wells contained benzene, tetrachloroethylene, or vinyl chloride slightly exceeding health-based comparison values
(wells D, E, F, G, H and I-- see Table 2). Because the levels found were close to the comparison values, a toxicological evaluation of these contaminants, taken on an individual basis, would not indicate that an adverse carcinogenic or non-carcinogenic health effect is
likely from past exposure to persons consuming water from these wells (ATSDR 1997a, 1997b, and 1997c). However, this evaluation is based only on one round of sampling, and there remains uncertainty as to the duration and levels of exposure that residents along Silverton
Road may have experienced before their wells were tested.
It should be noted that toxicologic evaluations of individual chemicals do not take into account the potential for adverse health effects from the combined exposure to mixtures of these contaminants, although research on the toxicity of mixtures indicates that adverse health
effects are unlikely when the mixture components are present at levels well below their individual toxicologic thresholds (Bond, 1997; Groton, 1997; Seed, 1995; and Yang, 1989). Because documented contaminant levels indicate that the exposures were well below their respective
individual toxicologic thresholds, the toxicological evidence suggests that VOC exposures to combinations of contaminants detected in private wells D, E, F, G, H, and I along Silverton Road are not likely to lead to adverse health effects.
Lead was detected in four private wells (Wells D, E, G and H -- see Table 2) at concentrations ranging from 6 to 161 jig/I. As previously noted, the presence of lead appears to be due to migration of lead from the site via groundwater. Lead is toxic to the nervous system,
particularly in the fetus and young children whose nervous systems are undergoing rapid development (ATSDR, 1993a). To protect against the neurotoxic effects of lead, the USEPA has promulgated an Action Level of 15 mgl for lead in drinking water for community water systems.
As indicated in Table 2, water from three wells contained lead concentrations well in excess of the Action Level. If the above lead concentrations in well water were sustained throughout the day, they could pose a public health hazard, particularly to a developing fetus or a young child.
Silverton Private Well Contamination Investigation
As seen from Table 3, 16 of the 20 private wells sampled in the Silverton section of Dover Township exhibited contamination above health-based comparison values. Five of these wells (Wells D, F, J, R and T) had levels of contaminants (either benzene, chloroform or carbon tetrachloride)
that were similar to their respective health-based comparison values. A toxicological evaluation of these contaminants, taken on an individual basis, would not indicate that an adverse carcinogenic or non-carcinogenic health effect is likely from past exposures to persons consuming
water from these private wells (ATSDR 1997a; ATSDR, 1997b; ATSDR, 1997d). This evaluation does not account for the possibility of the effects of combinations of contaminants. However, as discussed above, the available research indicates that exposures to these mixtures were well
below their respective toxicologic thresholds. Therefore, past exposure to residents using these five wells are not likely to lead to adverse health effects. However, as with the DTML/ Silverton Road well contamination evaluation above, this evaluation is based only on one round of sampling.
Therefore, there remains uncertainty as to the duration and levels of exposure that residents of the Silverton Private Well Contamination Investigation Area may have experienced before their wells were tested.
In eight of the Silverton wells (A, B, C, G, I, L, N and 0), the concentrations of carbon tetrachloride exceeded both the MCL (2 mgl) and the EMEG for intermediate (two weeks to one year) exposure duration (70 mgl) (ATSDR, 1994a). In several of these wells, the carbon tetrachloride
concentration also exceeded the 10-day USEPA Health Advisory level (200 Itg/1). Since these wells were used as a drinking water source for one year or more, the NJDHSS and the ATSDR conclude that past use of these wells could have posed a public health hazard for potential adverse non-carcinogenic health effects.
Carbon tetrachloride is metabolized in the liver to a free radical intermediate by the cytochrome P-450 enzyme system. This reactive intermediate can bind to cellular macromolecules resulting in damage to the liver (ATSDR, 1992b). The toxicity of carbon tetrachloride is dependent on the
action of the cytochrome P-450 enzyme system. Therefore, chemicals that activate this enzyme system can increase the toxicity of carbon tetrachloride. Such chemicals can include certain medications (such as barbiturates), chlorinated insecticides (such as DDT), and halogenated industrial chemicals
(such as polychlorinated biphenyls). In addition, it has been demonstrated that alcohol use or poorly controlled diabetes can increase the risk of carbon tetrachloride toxicity (ATSDR, 1992b).
Of the chemicals found in the Silverton wells, the non-carcinogenic toxicity of carbon tetrachloride was of greatest concern. In addition, all of the wells that contained elevated levels of carbon tetrachloride, also contained elevated levels of other chlorinated VOCS, such as methylene chloride,
1,2-dichloroethane, chloroform, 1,2-dichloropropane, TCE, and 1,1,2,2-tetrachloroethane. These chlorinated volatile organic chemicals are metabolized by the liver and excreted by the kidneys. Hence, these organs are often the targets for toxic effects caused by exposure to these chemicals
(ATSDR, 1989; ATSDR, 1993b; ATSDR, 1994b; ATSDR, 1996; ATSDR, 1997d; ATSDR, 1997e). While it is not possible to quantify the effect of concurrent exposure to mixtures of these chemicals, at the levels found, it is possible that the cumulative toxicity of exposure to the contaminated water would increase.
Several chemicals classified as known or probable human carcinogens were found in the Silverton wells. Benzene, found at levels up to 609 mgl, is classified as a human carcinogen by the USEPA, based on epidemiologic data. Carbon tetrachloride, chloroform, methylene chloride, 1,2-dichlornethane and TCE have
been classified as probable human carcinogens by the USEPA and/or the International Agency for Research on Cancer (ATSDR, 1993b; ATSDR, 1994a; ATSDR, 1994b; ATSDR, 1997d, LARC, 1995), based primarily on experimental evidence that exposure to high doses can cause cancer in laboratory animals.
The NJDHSS and ATSDR calculated estimates of the upper limit of cancer risk associated with exposures that occurred to adults and children, based on the maximum levels of the above contaminants found in the Silverton wells and the USEPA cancer slope factors. Assuming an approximate one-year duration of exposure,
the results of this evaluation indicate that there is a low increased risk of cancer in both adults and children. However, there is uncertainty in estimations of this kind since the duration and historical levels of exposure are not known.
Because of the excess incidence of childhood cancers in Dover Township, a specific discussion of contaminants at either the DTML/Silverton Road or the Silverton Private Well Investigation area that have been associated with leukemia's and/or childhood cancers follows. Benzene was found in both private well investigation
areas, PCE was found only in the DTML/Silverton Road investigation, and TCE was found only in the Silverton Private Well Investigation area.
Benzene
Occupational exposure to benzene and benzene-containing mixtures can result in damage to the blood-forming system (ATSDR, 1997b). Several studies of rubber workers have shown an increased risk of myelogenous leukemia and possibly other cancers. Experimental animal studies also indicate that high-level benzene
exposure can lead to the development of multiple tumor types. It is not known what effects exposure to benzene might have on the developing human fetus. Studies with pregnant animals show that breathing benzene has harmful effects on the developing fetus. These effects include low birth weight, delayed bone
formation and bone marrow damage (ATSDR, 1997b). Although some of the residents in the Silverton area who used benzene-contaminated well water for drinking and household uses were exposed to benzene at levels of public health concern for cancer effects, the exposure levels in the occupational epidemiologic studies
were much higher than those experienced by residents.
TCE and PCE
Following long-term, high level exposure, TCE has been shown to produce liver cancer in mice and kidney and testicular tumors in rats (ATSDR, 1997e; IARC, 1995). Chronic, high level PCE exposure produces liver cancer in mice and kidney tumors and mononuclear cell leukemia in rats (ATSDR, 1997a; IARC, 1995).
The exposure levels needed to cause these adverse impacts in laboratory animals are many times higher than exposure levels that could have occurred through the use of contaminated drinking water (ATSDR, 1997a; ATSDR, 1997e).
Epidemiological studies of occupationally exposed workers suggest an association between long-term inhalation exposure to high levels of TCE and increased risk of liver and biliary tract cancer and non-Hodgkin's lymphoma (L4, RC, 1995; ATSDR, 1997e). Increased risks of esophageal cancer, cervical cancer,
and non-Hodgkin's lymphoma have been observed in workers exposed to high levels of PCE (LKRC, 1995; ATSDR, 1997a).
Children may be particularly susceptible to the toxic effects of chemicals; fetuses may also be sensitive to toxic effects if the chemicals can cross the placental barrier. Recent epidemiologic studies suggest that fetal exposure to VOCs in drinking water could result in adverse health effects. The NJDHSS
evaluated the effects of VOCs in drinking water on birth outcomes in an area of northern New Jersey (Bove et al., 1995). This exploratory study found that maternal residence during pregnancy in areas with TCE-contaminated drinking water was associated with an increased risk of birth defects of the neural tube
and oral cleft. Exposure to PCE during pregnancy was associated with an increased risk of oral cleft defects. The authors concluded that their study by itself cannot determine whether the drinking water contaminants caused the reported adverse birth outcomes. A recent ATSDR study of exposure to VOCs in drinking
water and occurrence of adverse pregnancy outcomes was conducted at the U.S. Marine Corps Base at Camp LeJeune, North Carolina (ATSDR, 1997f). Decreased mean birth weight and increased small for gestational age babies were reported for two potentially susceptible subgroups: infants of mothers older than 35 years
of age and infants of mothers with histories of fetal death. This study provides limited evidence for a causal relationship between exposure to VOCs and the reproductive and developmental effects evaluated.
A study of childhood leukemia conducted in Woburn, Massachusetts, concluded that the incidence of childhood leukemia was associated with the mother's potential for exposure to water from specific wells contaminated with TCE and PCE, particularly for exposure during pregnancy (MDPH, 1997). The study did not find
any association between the development of childhood leukemia and the child's exposure to contaminated water after birth. The Woburn study should be interpreted with caution, however, since small numbers of study subjects led to imprecise estimates of risk. A study by the NJDHSS found a statistically elevated
rate of childhood leukemia in towns served by community water supplies contaminated with TCE and PCE in the years 1979 to 1987 (before current drinking water regulations had been implemented), compared to towns without a history of such contamination (Cohn et al., 1994). Overall, the associations drawn from
these limited epidemiological data in humans are suggestive, yet inconclusive, that exposure to these VOCs through drinking water may cause birth defects or childhood leukemia in children exposed while a fetus. ATSDR and others are conducting or sponsoring research to clarify this possible relationship.
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