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Evaluation Methods

While evaluating BHMWS, ATSDR used the weight-of-evidence approach, which considers the strength of all of the evidence to evaluate potential health effects. ATSDR also used quantitative risk assessment to estimate cancer risk levels. These estimated risk levels are one of the factors considered by ATSDR in its professional judgment to define exposures that present a potentially significant human health hazard [26].

ATSDR generally knows two things about health effects associated with a particular contaminant: 1) the level of exposure at which ATSDR would consider most individuals to be "safe" (such as comparison values), and 2) the level of exposure at which adverse health effects have been reported in the scientific literature, generally in occupational workers. ATSDR's comparison values may be hundreds or thousands of times below the levels for which adverse health effects have been reported. Comparison values include a margin of safety to protect sensitive populations. Therefore, ATSDR knows a concentration for which health effects might be expected and a concentration for which health effects would not be expected. ATSDR is uncertain what may happen when individuals are exposed to concentrations that are in between these values. ATSDR performs a health assessment to determine whether health effects would be likely or unlikely at a given concentration in a site-specific exposure scenario. Other risk factors, which are unique to each individual, also may play a role in determining whether an individual will actually become sick. These are risk factors such as smoking, alcohol consumption, diet, nutrition, and exposure to other chemicals at home or at work. ATSDR does not know the risk factors for each individual in a community, so ATSDR's health assessments focus on the community as a whole, realizing that the risk of an individual becoming sick depends on that individual's risk factors.

ATSDR performs health assessments in two phases. The first phase is a screening phase in which ATSDR compares health comparison values with concentrations of contaminants to which the community could be exposed. Exposures at levels less than or equal to these comparison values are not expected to make people sick and are thus considered to be "safe" levels. For example, comparison values for chronic-duration (long-term) exposures are based on lifelong, continuous exposure. While it is unlikely that anyone would be exposed this frequently or for this duration, it represents a worst-case condition. If a contaminant concentration does not exceed a comparison value, ATSDR generally concludes that there is no need to evaluate the contaminant any further, because even under the maximum conditions of exposure, an individual would not be expected to get sick.

If a contaminant concentration exceeds a comparison value, but is below levels where adverse health effects have been reported, ATSDR performs a more in-depth evaluation using realistic exposure scenarios. This is a way to describe the exposure, relative to other exposures. It does not predict whether an individual will get sick. For example, if an individual were exposed to a contaminant half as much as another individual, his risk would be half as great. This risk does not mean that the individual would get sick. ATSDR does not know if either individual would get sick, but ATSDR uses this way of describing an individual's risk of getting sick from a specific exposure to a specific contaminant as compared to another individual's risk of getting sick from a different exposure to the same contaminant or to a different contaminant. ATSDR also evaluates combinations of contaminants in relevant exposure pathways such as drinking water.

If the risk of getting sick from exposure to a contaminant is low (no increased risk or no apparent increased risk), ATSDR does not need to evaluate the contaminant any further. If the risk from exposure to a contaminant is high, ATSDR further evaluates the contaminant and the exposure during the second phase of the health assessment. This consists of a qualitative evaluation of the likelihood of adverse health outcome is determined.

Professional judgment plays an important role in the evaluation and judgement is based on the principles and knowledge of toxicology, physiology, biochemistry, anatomy, epidemiology, and other scientific disciplines to describe the likelihood of adverse health effects occurring in an exposed population. Risk assessment is one of the quantitative tools that a health assessor uses in considering all evidence. Because of the conservative nature of risk assessments, ATSDR is reasonably assured that no one is likely to become sick if the risk assessment does not indicate a very high level of risk. Refer to Appendix E for a complete description of ATSDR's methodology for data evaluation.

Municipal Water

Recent VOC Levels in BHMWS
Municipal water sampling results from 1988 and 1991 include the chemical analyses of water samples collected before going through the air stripping (raw water) and water flowing out of the air stripping ( finished water) [11]. These sampling results are in Table 4 and Table 5. The raw water samples were collected at the wellhead or a header valve (i.e., a common valve in the hydraulic system where flowstreams from individual wells are co-mingled) before chlorination and distribution. The finished water samples were collected after air stripping and chlorination, but before distribution. Monitoring results show a reduction in VOC levels after the water passes through the air strippers. Levels of trihalomethanes which are made up of chlorodibromomethane, chloroform, bromochloromethane, and bromoform have increased since 1988 (Table 4). Trihalomethanes are formed during the chlorination process of water and this increase was most likely from chlorination of organic compounds. The total trihalomethane level in the municipal water is below regulatory standards. Table 4 lists the VOC levels in water samples from the BHMWS during 1988, and Table 5 lists the VOC levels in water samples taken during 1991 (to show the decrease in VOC concentrations). VOCs are monitored in the BHMWS every two weeks [12]. Current concentrations of VOCs in BHMWS are below regulatory standards and in compliance with the Safe Drinking Water Act [12].

Past VOCs in BHMWS
VOC levels were also analyzed in municipal water samples collected from 1979 to 1986 before the installation of air strippers in 1988. Table 6 lists the VOC levels detected in BHMWS before residential distribution, mostly at wellheads [13-18, 19-24]. Although water samples straight from the taps of homes connected to BHMWS are not available, the people who used this municipal water before the installation of air strippers in 1988 were probably exposed to VOCs. Many of these chemicals were detected above ATSDR or EPA's comparison values (CV) and were selected for further toxicological evaluation (see Table 6 and Table 8).

Public Health Implications of Municipal Water Exposure

Estimated exposure doses were calculated for each contaminant that was detected above a chronic (long-term exposure) or carcinogenic comparison value to evaluate the potential adverse health effects from past exposures. These estimated exposure doses were compared to the health based guidelines, such as Minimal Risk Levels (MRLs) and chronic Reference Doses (RfDs) [26]. These are exposure estimates that are considered safe and are not likely to cause adverse health effects. Since no water samples were collected at the taps of each home, the highest chemical concentration detected in the distribution lines of the municipal water system was used to determine an individual's estimated exposure dose to that chemical. However, it is unlikely that an individual would be consistently exposed to a chemical at this concentration.

Trichloroethylene, bis(2-ethylhexyl)phthalate, carbon tetrachloride, and nitrobenzene exceeded chronic comparison values based on non-cancer health effects. These chemicals were further evaluated to determine specific exposure doses and potential health effects associated with the exposures:

Human studies have shown that VOCs can be detected in breath samples following inhalation and dermal exposures from bathing, showerin and ingestion of VOCs contaminated water [30,31]. Because of their high vapor pressures, these chemicals volatilize easily into ambient air. Therefore, these studies demonstrate that approximately equal amounts of VOCs from water can enter the body by three different routes (i.e., inhalation, dermal and ingestion) of exposure. VOCs are metabolized primarily in the kidneys and liver, and the active metabolites of these chemicals are responsible for the toxic effects observed in humans central nervous system, liver, kidneys and heart. The estimated levels of exposure are below levels known to cause adverse health effects in animals and humans. It is unlikely that past exposure to the VOC contaminated water from BHMWS resulted in adverse health effects.

Also, assuming that BHMWS containing the maximum level of 15 parts per billion (ppb) of TCE was routinely consumed (one and two liters per day for children and adults, respectively), the resulting exposures would be about 0.0009 mg/kg/d for children and 0.0004 mg/kg/d for adults (see Table 7). These estimated exposure doses for TCE are below the RfD of 0.006 mg/kg/d. Therefore, no adverse health effects would be expected to result from past exposure to TCE in this water. Similarly, a child's estimated exposure dose for bis(2-ethylhexyl)phthalate was 0.0083 mg/kg/d and 0.018 mg/kg/d for an adult (see Table 7). These estimated exposure doses are below the RfD (0.02 mg/kg/d) for bis(2-ethylhexyl)phthalate. Therefore, past exposure to bis(2-ethylhexyl)phthalate at these levels are not expected to have caused adverse health effects.

The estimated exposure dose for nitrobenzene was 5 to10 times greater than its RfD (0.0005 mg/kg/day). Methemoglobinemia is the dominant adverse health effect resulting from oral exposure to nitrobenzene in drinking water and from inhalation exposure. In this condition, less oxygen is released from hemoglobin (oxygen carrying protein in blood) to body tissues and all body functions tend to slow down. However, no reliable human studies were located to indicate that methemoglobinemia develops in humans at similar exposure doses calculated for nitrobenzene at this site. An animal study showed that a one time exposure of rats to 200 mg/kg/d of nitrobenzene resulted in methemoglobinemia [28]. This level of nitrobenzene was equivalent to 4,000 parts per million (ppm) of nitrobenzene in animal feed [28]. Nitrobenzene levels at this site are below levels known to cause adverse health effects in animals. Although the estimated exposure doses for adults and children to nitrobenzene exceeded the RfD, it is unlikely that methemoglobinemia developed. No studies were located regarding hepatic (liver) respiratory, cardiovascular (heart), gastrointestinal (stomach and intestine), ocular (eye) or dermal (skin) effects in humans or animals following oral exposure to nitrobenzene [28].

Cancer Risk Evaluation
ATSDR also evaluated the potential cancer risks associated with exposure to the maximum chemicals concentrations detected in municipal water that exceeded comparison values based on cancer. ATSDR estimated past cancer risks through ingestion of contaminated water 7 days per week for 38 years based on the establishment date of nearby industries and the installation of air strippers in August 1988 (see Table 8). ATSDR found no apparent increased risk for cancer development at this site from past exposure to VOCs and other contaminants detected in the BHMWS.


The NJDHSS analyzed cancer incidence data in response to concerns expressed by residents of the in Borough of Hawthorne and Passaic County regarding the occurrence of leukemia and its relationship to municipal water quality [7].

The Standardized Incidence Ratio (SIR) is used by epidemiologists to analyze cancer incidence in a population [27]. An SIR is calculated by dividing the observed number of cases in a population that is being studied by an expected number of cancer cases. The expected number is determined from a comparison population where the cancer rates would be stable and represent the normal number expected in a population of that size. The SIR is tested for significance or whether the observed number of cases is truly elevated or possibly due to factors such as a small population size, years observed, inaccurate data, or life style. The 95% confidence interval is a statistical tool used to evaluate the probability that the SIR may be greater than 1.0 due to chance alone [27]. In this analysis of leukemia incidence, the NJDHSS adjusted the SIR with respect to age.

NJDHSS compared data obtained for leukemia and lymphoma cases reported in Hawthorne from 1979 through 1983. During this time period, the observed number of total cancer and lymphoma cases for both males and females living in Hawthorne was not significantly different that the expected number of cases for this population. The observed number of leukemia cases was determined to be greater than the expected number of cases; however, the increase was not statistically different from that expected. Likewise, no clustering was observed in the population and the cases appeared randomly distributed within the population.

The second report issued in 1993, compared data obtained for leukemia cases reported in Hawthorne between 1979 through 1988 [7]. The analysis demonstrated that while the SIR was greater than one for both males and females, this ratio was not statistically significant. The NJDHSS concluded that the observed number of leukemia cases for both males and females was not greater than what would be expected in the Hawthorne population.

The NJDHSS conducted an updated analysis of leukemia incidence in Hawthorne on July 22, 1997, using 17 years of State Cancer Registry data from 1979 through 1995. The NJDHSS reported that the SIR for leukemia (all age groups combined) over this period was 1.28 for males and 1.20 for females. Therefore, the observed number of leukemia cases for both males and females was not found to be significantly elevated over the expected number of cases in the population.

In summary, the NJDHSS analysis indicates that during the 17-year period of observation, 1979 through 1995, the age-adjusted incidence rate of leukemia in Hawthorne, New Jersey is not significantly different from the number of cases expected in the population.


ATSDR's Child Health Initiative recognizes that the unique vulnerabilities of infants and children demand special emphasis in communities faced with contamination of their water, soil, air, or food. Children are at a greater risk than adults from certain kinds of exposures to hazardous substances emitted from contaminated sites. They are more likely to be exposed to certain media (soil, surface water, etc.) because they frequently play outdoors; 2) children are shorter than adults, which means they breathe dust, soil, and vapors closer to the ground; and 3) children are also smaller, allowing exposure to higher doses of chemical exposure per body weight. ATSDR is committed to evaluating children at sites such as the Borough of Hawthorne.

ATSDR evaluated the likelihood that children using water from BHMWS may have been exposed to chemical substances in the past. ATSDR did not identify any chemicals that children have been exposed to at levels of health concern. Children were probably exposed to VOCs in the municipal water supply before the installation of the air stripping towers; however, it is unlikely that they will develop any health effects related to those exposures.

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