EDF's cancer and noncancer risk scores are generated by a method that considers
variations in both a chemical's inherent toxicity and human exposure
potential. This offers a substantial advantage over scoring systems
that either do not consider exposure at all (such as TRI toxicity
weights) or rely on surrogate measures of exposure potential (such as
WMPT effects scores). These other methods do not attempt to quantify the
dose of a chemical that people receive as a result of releases to air or
water. The total dose of a chemical that people receive from ingestion
of contaminated food and water, inhalation of contaminated air and
dermal contact determines the health risks posed by that chemical.
EDF cancer risk scores are expressed in terms of toxic equivalency potentials, which
require selection of a reference carcinogen. EDF has selected benzene
as its reference compound for carcinogens. The added cancer risk that
may result from total human exposure to a one pound release of a
carcinogen to air is normalized by comparison to the added risk
associated with a one pound release of benzene to air. All carcinogen
releases are converted into pounds of benzene-equivalents.
It is important to note that EDF's method does not take into account
qualitative differences in the types of cancer that chemicals may cause,
or in the weight of evidence supporting the identification of a chemical
as a carcinogen. Benzene is a known human carcinogen that causes
leukemia. Expressing the potential health risk of other carcinogens in
benzene-equivalents does not indicate they are known human carcinogens,
or that they will cause leukemia; it indicates only the relative
magnitude of added cancer risks associated with a one pound release.
EDF noncancer risk scores are expressed in terms of toxic equivalency potentials, which require selection of a reference toxicant. EDF has selected toluene as its reference compound for noncarcinogens. The hazard index that may result from total human exposure to a one pound release of a toxicant to air is normalized by comparison to the hazard index associated with a one pound release of toluene to air. All noncancer toxicant releases are converted into pounds of toluene-equivalents. It is important to note that EDF's method does not take into account qualitative differences in the types of health effects that chemicals may cause, or in the weight of evidence supporting the identification of a chemical as a human health hazard. Toluene is a recognized developmental toxicant. Expressing the potential health risk of other chemicals in toluene-equivalents does not indicate they are developmental toxicants; it indicates only the relative magnitude of the hazard index associated with a one pound release.
