Altered biologic activities of commercial polychlorinated biphenyl mixtures after microbial reductive dechlorination

The reductive dechlorination oi polychlorinated biphenyls (PCBs) by anaerob ic bacteria has recently been established as an important environmental fat e of these compounds, This process removes chlorines directly from the biph enyl ring with replacement by hydrogen, resulting in a product mixture in w hich the average number of chlorines per biphenyl is reduced. in this study , dechlorination of commercial PCB mixtures (Aroclors 1242 and 1254) by mic roorganisms eluted from PCB-contaminated sediments of the River Raisin (Mic higan) and Silver lake (Massachusetts) caused a depletion in the proportion of highly chlorinated PCB congeners and an accumulation oi lesser-chlorina ted congeners. Dechlorination occurred primarily at the meta and, to a much lesser extent, para positions of biphenyl. The concentrations of the copla nar congeners including 3,3',4,4',5-pentachlorobiphenyl, the most potent di oxinlike congener, were significantly lowered by reductive dechlorination. Microbial reductive dechlorination of commercial PCB mixtures caused a subs tantial reduction in biologic activity in several instances. It significant ly lowered or eliminated the inhibitory effects of Aroclors on fertilizatio n of mouse gametes in vitro. Similarly, the dechlorinated product mixtures had substantially lower ethoxyresorufin-O-deethylase induction potencies an d showed less ability to induce activating protein 1 transcription factor a ctivity as compared to the unaltered Aroclors, in other assays the same dec hlorinated product mixtures demonstrated biologic activities similar to the nondechlorinated Aroclors, including the ability of PCB mixtures to stimul ate insulin secretion and cause neutrophil activation. The data presented h ere establish that the biologic activities of commercial PCB mixtures are a ltered by microbial reductive dechlorination and that an assessment of thei r toxic potential requires an array of tests that include the different mec hanisms associated with PCBs.