Proposed PCB congener groupings for epidemiological studies.

Polychlorinated biphenyls (PCBs) have been the target of many epidemiological studies because of their toxic potential and widespread prevalence in the environment. Advances in analytic techniques have made it possible to distinguish routinely among the 209 different congeners, which vary widely in their biological properties. We propose here a classification system for the most commonly detected congeners. Group 1 (potentially estrogenic, weak phenobarbital inducers); Group 2 (potentially antiestrogenic and immunotoxic, dioxinlike); and Group 3 (phenobarbital, CYP1A and CYP2B inducers, biologically persistent). Group 2 is further subdivided according to non- and mono-ortho substituted vs. di-ortho substituted, in analogy with toxicity of dioxin congeners.