Development, validation and limitations of toxic equivalency factors

Abstract

Halogenated aromatic hydrocarbons (HAHs) such as the polychlorinated dibenzo- p-dioxins (PCDDs), dibenzofurans (PCDFs) and biphenyls (PCBs) are complex mixtures of industrial compounds or by-products which have been identified as contaminants in almost every component of the global ecosystem. High resolution analytical techniques can unequivocally identify and quantitate most of the individual HAH congeners present in different matrices. The most toxic halogenated aromatic is 2,3,7,8-tetrachlorodibenzo- p-dioxin (TCDD) and, based on in vivo and in vitro studies, the relative toxicities of individual HAHs have been determined relative to TCDD ( i.e. toxic equivalency factors, TEFs). The derived toxic equivalents (TEs or TEQs) can be used for hazard and risk assessment of halogenated aromatic mixtures. This approach can be used for estimating the TEQs from high resolution analytical data obtained for PCBs, PCDDs and PCDFs; however, it is clear that this approach can only be used for those congeners which exhibit TCDD-like activity.