NATICK LABORATORY ARMY RESEARCH
(a/k/a U.S. ARMY SOLDIER SYSTEM COMMAND (SSCOM) - NATICK)
NATICK, MIDDLESEX COUNTY, MASSACHUSETTS
The Natick Laboratory Army Research (a|k|a U.S. Army Soldier System Command, SSCOM) is a Department of Defense site listed on the Environmental Protection Agency's National Priorities List (NPL). The Agency for Toxic Substances and Disease Registry (ATSDR) is mandated to conducted a public health assessment (PHA) on every site listed on the NPL. The purpose of the PHA is to determine the public health hazard associated with pathways of exposure to environmental contamination at the site. ATSDR released a PHA on the SSCOM site for public comment in May 1997. Using the data and information reviewed for the PHA, ATSDR determined that the site posed no apparent public health hazard.
Community concerns are an important aspect of the PHA process. Community concerns for the SSCOM site have centered around the repeated finding of low levels of volatile organic compounds (VOCs), namely tetrachloroethylene (PCE), in one of the Natick public water supply wells during the period from the late 1980s to early 1990s. Local residents have expressed concern about whether these potential past exposures could have resulted in adverse health effects. ATSDR developed this Health Consultation to address these concerns in greater detail than in the PHA.
Members of the Restoration Advisory Board (RAB) for the SSCOM site and the local community requested that ATSDR evaluate the public health hazard from potential past exposure to VOCs in the Town of Natick public water supply. In response, ATSDR conducted a comprehensive review of the available animal and human health literature to determine whether potential past exposure to PCE, at the highest levels detected in the municipal water supply wells, posed a health hazard to the local community. The community specifically asked about adverse health outcomes related to reproductive and developmental toxicity and cancer. Neurological effects of PCE were included in the evaluation because they are a sensitive effect of PCE exposure and may be related to adverse effects of PCE on reproduction and development (ATSDR, 1995a).
As part of the PHA for the SSCOM site, ATSDR used several screening-level approaches to evaluate potential past exposures to PCE in the Natick water supply. This involved developing conservative exposure scenarios and determining whether such exposures would be likely to result in adverse health conditions of concern to the local community. ATSDR estimated exposure doses for Natick residents assuming exposure to PCE at the highest levels ever detected in any of the municipal water supply wells and making assumptions about patterns of exposure (e.g., how much water was consumed and for how long). Exposure estimates were then compared with minimum-effect levels of exposure (or lowest-observed-adverse-effect levels, LOAELs) and levels of exposure below which no adverse effects have been observed (no-observed-adverse-effect levels, NOAELs) reported in studies of laboratory animals and humans. Exposure estimates for Natick residents were also used to estimate the potential hazard for non-cancer outcomes and potential lifetime cancer risks using standard toxicity and cancer potency values.
In this report, ATSDR used an additional weight-of-evidence approach to evaluate public health hazards from potential past exposure to PCE in the Natick water supply. This was a more in-depth and less conservative approach, but one that better reflects what is known and not known about the hazards posed by PCE and the scientific uncertainties of the available literature.
First, an extensive review of the scientific literature was conducted to identify animal and human health studies pertaining to adverse effects on reproduction and development, nervous system toxicity, and cancer. Each study identified in the literature was evaluated to determine:
- Strength of associations between exposures and adverse effects and the basis for establishing levels of effect;
- Merits and limitations with regard to study design, findings, and interpretation of findings; and
- Relevance of the reported findings (e.g., contaminant types, levels of exposure, duration and frequency of exposure, and routes of exposure) for evaluating health hazard from exposure to PCE predicted for Natick residents.
From this evaluation, ATSDR determined the overall sufficiency and strength of the available animal and human health data, including some level of confidence in the data. From this, ATSDR determined the public health hazard, for the health outcomes of concern to the local community, from potential past exposures to PCE at the highest levels detected in the Natick municipal water supply wells.
Overall, the weight-of-evidence approach used in this report constituted a more thorough evaluation
than the screening-level approaches used in the PHA. The weight-of-evidence approach addressed
issues often not considered in screening level approaches, such as strength of causal relationships
reported between exposures and adverse effects, consistency of findings from animal and human
studies, and applicability of animal studies to humans. When considered together with the results of
screening-level approaches, ATSDR feels that the weight-of-evidence approach provides a more
realistic and responsive approach to public health protection.
Our findings are as follows:
- The town of Natick's Evergreen and Springvale municipal drinking water well fields have been shown to be contaminated by VOCs including PCE and trichloroethylene (TCE). The highest levels of VOCs were found in the Evergreen Well No. 1 during the period from 1988 to 1991. The highest levels of VOCs detected in this well were 15.9 µg/L PCE and 2.7 µg/L TCE (in 1991). Routine sampling of the well was not required prior to 1988. Voluntary sampling in 1980 and 1984 did not show contamination by VOCs. Because the data are limited, it is not known how long the contamination was present and at what levels prior to 1988.
- The water from Evergreen Well No. 1 was routinely blended with water from other Natick municipal water supply wells prior to distribution to households. The average annual levels of VOCs in municipal water supplied to households never exceeded the enforceable standards for contaminants in public drinking water supplies during the period from 1988 to 1991. The water treatment system recently installed by the town of Natick is an important measure to ensure that the public water supply remains protected from VOCs contamination in the future.
- ATSDR used conservative (e.g., worst-case) assumptions about how long exposures to VOCs in the Natick water supply may have occurred and at what levels. ATSDR assumed that exposures occurred to the highest levels of PCE ever detected in the Evergreen Well No. 1 and that exposures occurred daily over the entire 17-year period (1974-1991) the well was in operation. Water pumped from this well was blended before being distributed to households. Levels of PCE in water distributed to households never exceeded 5 µg/L during the period from 1988 to 1991, so that actual exposures to PCE were overestimated for this period.
- Exposures were assumed to occur from ingestion of drinking water, inhalation of vapors released from water during showering and bathing, and skin (dermal) contact with water during household use.
- ATSDR used a weight-of-evidence approach to evaluate the public health hazard from potential past exposures to contaminants in the Natick public water supply. This included an in-depth review of the available scientific literature for PCE exposure and the health outcomes of concern to the local community, namely adverse effects on reproduction and development, nervous system toxicity, and cancer. ATSDR used information from pharmacokinetic models and related studies to determine how PCE may cause toxicity following exposure by ingestion, inhalation, and contact with the skin at the levels of exposure predicted for Natick residents.
- When available, human health studies were preferable to animal studies as a basis for evaluating public health hazard for Natick residents. Using toxicologic studies as the basis to assess hazard in humans is complicated by the need to extrapolate findings from animals to humans in terms of routes, duration, frequency and levels of exposure as well as differences in biological systems which affect toxicity.
- The findings from animals and human studies suggest that exposure to VOCs during pregnancy
(in utero) results in adverse effects on reproduction and development. However, the
available information does not provide substantial quantitative evidence for a causal relationship
between chronic exposure to PCE and reproductive and developmental toxicity.
Only one animal study identified in the literature provided evidence that the developing nervous system in young animals may be sensitive to the effects of acute PCE exposure in utero. However, the findings from this study were not entirely relevant for evaluating health hazard from long-term exposure to PCE by Natick residents because of important differences in routes, levels and duration of exposure to PCE for animals and Natick residents.
No human health studies were found to support the findings from animal studies that PCE exposure during pregnancy (in utero) results in adverse effects on nervous system development and behavior in offspring. Overall, the findings from human health studies provide suggestive evidence for a causal relationship between exposure to VOCs and reproductive and developmental toxicity. They do not provide substantial quantitative evidence for a causal relationship between chronic PCE exposure and adverse effects on reproduction and development.
PCE has been found in the breast milk of women living near dry-cleaning facilities who were exposed daily to PCE in air. Adverse health effects in the nursing infants, including obstructive jaundice and liver toxicity, were reported but not found to be statistically elevated compared to unexposed infants. Exposure to PCE in ambient air was found to contribute to PCE body levels more than breastmilk. The exposure doses predicted for children in Natick were many times lower than the minimum-effect level reported for adverse effects in infants in this study. Based on data from animal and human studies, potential past exposure to PCE by Natick residents does not pose a health hazard for adverse reproductive or developmental effects.
- The findings from animal and human health studies indicate that PCE exposure, at high enough doses, results in adverse effects on the nervous system. Most adverse effects of PCE have been observed for inhalation exposure. The most relevant studies for determining potential public health hazard for Natick residents are those involving workers chronically exposed to PCE. The daily exposure doses predicted for Natick residents were many times lower than the minimum-effect level reported in occupational studies and as regulatory standards for the protection of workers. Collectively, the available studies suggest that past exposure to PCE, at the levels predicted for Natick residents, does not pose a health hazard for nervous system toxicity.
- The findings from animal and human studies provide some evidence that PCE causes cancer. Data from chronic cancer studies in animals indicate that PCE, at high enough levels, produces cancer of the liver in mice and monocellular leukemia (and kidney cancer) in rats. Cancer development in rodents is thought to occur by species-specific mechanisms that are not as important in humans. No significant increases in cancer of any type have been reported in animals at the low level of PCE exposure predicted for Natick residents.
No common outcome for PCE carcinogenicity has been reported for animals and humans. Too few human health studies are available to see a definite pattern of cancers related to VOC exposures. In addition, the studies conducted to-date have important limitations with regard to classification and quantification of human exposure. The findings from human health studies are not adequate for defining a causal relationship between PCE exposure and cancer at the levels of exposure predicted for Natick residents. Additional studies may be warranted under conditions where exposures can be adequately characterized and quantified and the cancer outcomes of concern are biologically plausible.
Overall, the available animal and human studies indicate that potential past exposure to Natick residents does not pose a health hazard for cancer.
In conclusion, potential past exposures to VOCs, at the highest levels ever detected in a single municipal water supply well (e.g., Evergreen No. 1 ), are not likely to have resulted in reproductive or developmental toxicity, adverse effects on the nervous system, or cancer.
The average annual concentrations of PCE in the Natick water supply never exceeded enforceable standards for public drinking water supplies during the period from 1988 to 1991 when sampling was required. Voluntary sampling prior to 1988 did not show contamination by VOCs. The town of Natick has recently installed a treatment system for the public water supply. ATSDR recommends use of the treatment system to ensure that the public water supply remains protected from VOCs in the future. ATSDR recommends that no additional follow-up is necessary.