A long-term study of anaerobic dechlorination of PCB congeners by sediment microorganisms: Pathways and mass balance

Abstract

Abstract Reductive dechlorination of PCBs by Hudson River sediment microorganisms was investigated using individual congeners, 2,3,4,2′,4′,5′-, 2,4,5,2′,4′,5′-, 2,3,4,5,6-, 2,4,2′,4′-, and 3,4,3′,4′-chlorobiphenyls (CBPs) in long-term studies lasting 15 to 20 months. The dechlorination of 2,3, 4,2′,4′,5′-CBP yielded 2,4,5,2′,4′-, 2,4,2′,4′-, 2,4,2′,5′-, and 2,4,2′-CBPs; notably absent was 2,2′-CBP. Yet, the total molar concentration of all congeners decreased with time and at 15 months accounted for only 25% of the initial concentration of the parent compound. 2,3,4,5,6-CBP produced 2,3,5,6-, 2,4,6-, and 2,6-CBPs. At 15 months the sum of all congeners accounted for only about 50% of the initial amount of the parent congener. On the other hand, 2,4,5,2′,4′,5′-CBP yielded six daughter products, including 2,2′-CBP, and did not show any decrease in total molar concentration even at 20 months. 2,4,2′,4′-CBP did not show any change at 15 months. These results indicate that anaerobic PCB biotransformation may include mechanisms other than dechlorination and that the mechanisms are congener dependent. Biphenyl was detected with 3,4,3′,4′-CBP, indicating complete dechlorination; however, it accounted for < 10% of the total molar loss. 14C-labeled tracer of this congener showed that all radioactivity was in the hexane fraction, suggesting that transformation products were hydrophobic.