ABSTRACT
An ongoing problem for agencies such as the US Environmental Protection Agency is that of providing guidance as to health risk assessment of mixtures from a variety of sources such as wastewaters, hazardous waste sites, air particulates, or materials spilled in waters or soils. An interim procedure was proposed for estimating risks associated with chlorinated dibenzo-dioxins and dibenzofurans. This was revised in 1989. Toxicity equivalency factor approaches are also under consideration for individual congeners of polychlorinated biphenyl mixtures and for a set of polycyclic aromatic hydrocarbons. In its simplest form a comparative potency estimate is done on a mixture for which data are incomplete by carrying out a comparison to a similar mixture on which a human risk assessment has been done. Although there are references to the use of comparative potency to predict human health risks for endpoints other than cancer, the greatest use of the approach has been for cancer risk prediction.
