DECHLORINATION OF POLYCHLORINATED-BIPHENYLS BY HUDSON RIVER SEDIMENT ORGANISMS - SPECIFICITY TO THE CHLORINATION PATTERN OF CONGENERS

Reductive dechlorination of polychlorinated biphenyls (PCBs) by Hudson River sediment organisms was investigated using the single congeners 2,3,4-, 2,4,5-, and 2,3,4,5,6-chlorobiphenyls (CBPs). In repeated enrichments, the sediment culture produced only 2,4-CBP from 2,3,4-CBP and was unable to remove para-Cl. However, the same organisms yielded 2,3,5,6-CBP from 2,3,4,5,6-CBP by para dechlorination as one of the products. In 2,4,5-CBP they produced primarily 2,4-CBP and a small amount of 2,5-CBP. However, with repeated transfers, the proportion of 2,5-CBP increased, becoming the only product in the fifth transfer. When this culture was transferred back to 2,3,4-CBP, it was only capable of meta-dechlorination, yielding 2,4-CBP. Therefore, dechlorination was not specific to the chlorine substitution position per se but was determined by the chlorination pattern on congeners. These enrichment experiments also suggested the existence of a threshold concentration for dechlorination. With 2,4,5-CBP, more than 35 mol % of the initial parent congener concentration was not accounted for, indicating that there might be anaerobic biotransformations other than dechlorination.