REDUCTIVE DECHLORINATION OF POLYCHLORINATED-BIPHENYLS IN ST-LAWRENCE-RIVER SEDIMENTS AND VARIATIONS IN DECHLORINATION CHARACTERISTICS

Sediment cores taken near three industrial plants on the St. Lawrence River (Reynolds Aluminum, General Motors, ALCOA) showed evidence of in situ dechlorination at all sites except at Reynolds 001. The extent o f dechlorination varied widely from site to site, ranging from 2 to 45 %, based on the average number of Cl's per biphenyl. The absence of de chlorination at Reynolds 001 was not due to the lack of competent micr oorganisms but appeared to be associated with a high level of cocontam inants. There was no correlation between sediment PCB concentrations a nd the extent of dechlorination. Even though the three sites were prim arily contaminated by the same Aroclor, laboratory dechlorination assa ys with single congeners and Aroclor 1248 revealed significant differe nces in dechlorination characteristics, suggesting wide difference in dechlorinating populations among the three sites. The differences in d echlorination pattern between native sediments and laboratory sediment s suggested the involvement of sediment characteristics in the selecti on of dechlorinating populations.