Relationship of basic research in toxicology to environmental standard setting: the case of polybrominated biphenyls in Michigan.

The accidental contamination of dairy cattle feed in Michigan in 1973-74 with polybrominated biphenyls (PBB) led to the contamination of cattle and people consuming their products. This led to an extensive animal and product monitoring and disposal program conducted by the Michigan Department of Agriculture and the Department of Natural Resources. It also led to several studies of the people of Michigan, extensive research on the chemicals, and an unprecedented establishment by the Legislature of a Toxic Substance Control Commission. Only a few relatively minor components of the PBB mixture that contaminated Michigan are metabolized and another group of minor components seem responsible for the toxicity, which, similar to that caused by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), includes induction of microsomal enzymes, liver hypertrophy, thymic involution, porphyria, anorexia and chloracne. PBB were found to produce the "dioxin-like" toxicity with roughly 0.01% the potency of TCDD. Both non-toxic as well as toxic congeners were found to be tumor promotors. To date it is impossible to unequivocally conclude that any human health effects can be attributed to PBB. The Toxic Substance Control Commission was established as an independent oversight body with responsibility to gather information, investigate, coordinate and make recommendations concerning toxic substances and the handling of toxic substances incidents. The Commission has declared two toxic substances emergencies and made several recommendations for regulating and solving toxic substances problems but its major activities have evolved towards a role as an environmental ombudsman.