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Reich Farm Health Assessment
(Dover Township) Toms River, New Jersey
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Description of Comparison Values
ATSDR's comparison values are media-specific concentrations that are considered to be "safe" under default conditions of exposure. They are used as screening values in the preliminary identification
of site-specific chemical substances that the health assessor has selected for further evaluation of potential health effects.
Generally, a chemical is selected for evaluation because its maximum concentration in air, water, or soil at the site exceeds one of ATSDR's comparison values. However, it cannot be emphasized strongly
enough that comparison values are not thresholds of toxicity. While concentrations at or below the relevant comparison value may reasonably be considered safe, it does not automatically follow that any
environmental concentration that exceeds a comparison value would be expected to produce adverse health effects. Indeed, the whole purpose behind highly conservative, health-based standards and guidelines
is to enable health professionals to recognize and resolve potential public health problems before they become actual health hazards. The probability that adverse health outcomes will actually occur as a
result of exposure to environmental contaminants depends on site-specific conditions and individual lifestyle and genetic factors that affect the route, magnitude, and duration of actual exposure, and not
solely on environmental concentrations.
Screening values based on non-cancer effects are generally based on the level at which no health adverse health effects (or the lowest level associated with health effects) found in animal or (less often)
human studies, and include a cumulative margin of safety (variously called safety factors, uncertainty factors, and modifying factors) that typically range from 10-fold to 1,000-fold or more. By contrast,
cancer-based screening values are usually derived by linear extrapolation with statistical models from animal data obtained at high exposure doses, because human cancer incidence data for very low levels of
exposure are rarely available. Cancer risk estimates are intended to represent the upper limit of risk, based on the available data.
Listed and described below are the types of comparison values that the ATSDR and the NJDHSS used in this Public Health Assessment:
Cancer Risk Evaluation Guides (CREGS) are estimated concentrations of contaminants in an environmental medium (such as drinking water) that are expected to cause no more than one excess cancer case for every
million persons who are continuously exposed to the concentration for an entire lifetime (equaling a risk of I x 10'). These concentrations are calculated from the USEPA's cancer slope factors, which indicate
the relative potency of carcinogenic chemicals. Only chemicals that are known or suspected of being carcinogenic have CREG comparison values.
Environmental 'Media Evaluation Guides (EMEGS) and Reference Dose Media Evaluation Guides (RMEGS) are estimates of chemical concentrations in an environmental medium (such as drinking water) that are not likely
to cause an appreciable risk of deleterious, non-cancer health effects, for fixed durations of exposure. These guides may be developed for special sub-populations such as children. EMEGs are based on ATSDR's minimal
risk level (MRL) while RMEGs are based on the USEPA's reference dose (RfD).
Other health-based guides may also be used as comparison values, including drinking water maximum contaminant levels (MCLS) established by the USEPA or the NJDEP.
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