Abstract
AbstractAroclors 1242 and 1254 were anaerobically dechlorinated by microorganisms eluted from polychlorinated biphenyl (PCB)‐contaminated River Raisin (RR) and Silver Lake (SL) sediments. Dechlorination occurred primarily from the meta positions. H4IIE rat hepatoma cell bioassays for ethoxyresorufin‐O‐deethylase (EROD) induction potency, a measure of aryl hydrocarbon receptor‐mediated toxic potential, revealed that the potencies of the Aroclors were considerably reduced after dechlorination. The decreases in EROD induction potencies were dependent on the extent of dechlorination of the non‐ortho‐substituted and mono‐ortho‐substituted PCBs. Calculated 2,3,7,8‐tetrachlorodibenzo‐p‐dioxin (TCDD) equivalents (TEqscalc) for the PCB mixtures were 5.7, 0.08, and 0.05 pM TEqcalc/μmole of PCBs for non‐, RR‐, and SL‐dechlorinated Aroclor 1242, and 7.8, 1.6, and 1.0 pM TEqcalc/μmole of PCBs for non‐, RR‐, and SL‐dechlorinated Aroclor 1254, respectively. Correspondence between TEqsassay determined using the H4IIE bioassay and TEqscalc indicated that no unexpected synergistic interactions occurred among components of the dechlorinated mixtures. These results indicate that the dioxinlike toxicities of PCB mixtures are substantially reduced by microbial reductive dechlorination, and that a constant ratio of TEq to total PCBs cannot be assumed in risk assessments.
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