Dioxin-like and non-dioxin-like toxic effects of polychlorinated biphenyls (PCBs): Implications for risk assessment

Polychlorinated biphenyls (PCBs) are persistent, bioaccumulative, and toxic contaminants in the environment. Individual PCB congeners exhibit different physicochemical properties and biological activities that result in different environmental distributions and toxicity profiles. The variable composition of PCB residues in environmental matrices and their different mechanisms of toxicity complicate the development of scientifically based regulations for the risk assessment. In this article various approaches for the assessment of risks of PCBs have been critically examined. Recent developments in the toxic equivalency factor (TEF) approach for the assessment of toxic effects due to dioxin-like PCBs have been examined. PCB exposure studies that describe non-dioxin-like toxic effects, particularly neurobehavioral effects and their effective doses in animals were compiled. A comparative assessment of effective doses for dioxin-like and non-dioxin-like effects by PCBs has been made to evaluate the relative significance of non-orthto- and ortho-substituted PCBs in risk assessment. Using mink as an example, relative merits and implications of using TEF and total PCB approaches for assessing the potential for toxic effects in wildlife was examined. There are several advantages and limitations associated with each method used for PCB risk assessment. Toxic effects due to coplanar PCBs occur at relatively smaller concentrations than those due to non-dioxin-like PCBs and therefore the TEF approach derives the risk assessment of PCBs, in the environment. The need for the refinement of TEF approach for more accurate assessment of risks is discussed.