Reduction of Aryl Hydrocarbon Receptor-Mediated Activity of Polychlorinated Biphenyl Mixtures Due to Anaerobic Microbial Dechlorination

Abstract

Aroclors 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 monoortho-substituted PCBs. Calculated 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) equivalents (TEqs calc ) for the PCB mixtures were 5.7, 0.08, and 0.05 pM TEq calc /mole of PCBs for non-, RR-, and SL-dechlorinated Aroclor 1242, and 7.8, 1.6, and 1.0 pM TEq calc / mole of PCBs for non-, RR-, and SL-dechlorinated Aroclor 1254, respectively. Correspondence between TEqs assay determined using the H4IIE bioassay and TEqs calc 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.

Biological activity associated with noncoplanar polychlorinated biphenyls after microbial dechlorination of aroclor 1242® and aroclor 1254®

“…The reason for these different results lies in the fact that the biological activities measured previously were mediated by coplanar congeners but those measured in our study involve noncoplanar and lightly chlorinated congeners [21]. Clearly, the conversion of Aroclors by anaerobic dechlorination to product mixtures containing a higher fraction of more lightly chlorinated, ortho-substituted congeners produces a loss of Ah-receptor-mediated activities [4] because of the loss of coplanar congeners with chlorine in the meta and para positions in the biphenyl molecule [2]. In contrast, no loss or, in certain cases, a gain in the biological activity in the product mixtures can be attributed to the predominance of noncoplanar and lightly chlorinated congeners.…”

“…Coplanar congeners act primarily through binding to the Ah-receptor, in contrast to noncoplanar congeners, which act by increasing intracellular free calcium and activating signal-transduction pathways through mechanisms not yet completely understood [10,[17][18][19][20]. Whereas previous reports indicated a loss of PCB-related inhibition of in vitro fertilization [3] and induction of CYP1A1 activity [4] occurred when product mixtures identical to those used in the present study were evaluated, our results indicate no loss of biologic activity when two different cellular functions were examined. The reason for these different results lies in the fact that the biological activities measured previously were mediated by coplanar congeners but those measured in our study involve noncoplanar and lightly chlorinated congeners [21].…”

“…Results are presented as the mean Ϯ standard error of the mean. Data from the insulin-release studies were analyzed us- [3,4]. c Congeners listed together eluted in the same chromatographic peak.…”

Dietary accumulation efficiencies and biotransformation of polybrominated diphenyl ethers in farmed Atlantic salmon (Salmo salar)

“…Intestinal microbes or enzymes are also capable of debrominating PBDEs in carp and probably in other fish species (Stapleton et al 2004c). It has been observed that microbes preferably dehalogenate polybrominated and polychlorinated biphenyls from the meta-and parapositions, whereas the halogen substituents in the ortho-position are more recalcitrant (Bedard and Van Dort 1998;Quensen et al 1998). Some evidence also exists for preferential meta-debromination (positions 3 and 5) and selective accumulation of certain PBDE congeners in fish.…”

Congener‐specific model for polychlorinated biphenyl effects on otter (Lutra lutra) and associated sediment quality criteria

“…First, microbial reductive dechlorination in sediments, together with reduced input of PCBs and associated dilution by deposition of cleaner sediment, may lead to a gradual decline of dioxin-like toxicity of PCB mixtures [10][11][12]. Microbial reductive dechlorination of PCBs in anaerobic sediments is an important environmental transformation [13,14].…”