Use of toxicity equivalence factors in assessing the hazard of related compounds in occupational settings and at Superfund Sites

For certain classes of chemicals, bioassay data are not available for most members of the class. In order to provide an estimate of toxicity for all chemicals in a class, one approach is to use toxicity equivalence factors (TEF). Briefly this involves using bioassay data to establish the potency of one member of the class and then using information such as short term tests and structure- activity relationships to predict the potency of analogues relative to the benchmark chemical. The assumption is that all the chemicals in the class share the same mechanism of action such that their potency can be ranked relative to the benchmark chemical. This report briefly describes the application of the TEF approach to dioxins and polynuclear aromatic hydrocarbons.