REDUCTIVE DECHLORINATION OF PREEXISTING SEDIMENT POLYCHLORINATED-BIPHENYLS WITH LONG-TERM LABORATORY INCUBATION

The dechlorination potential of polychlorinated biphenyl (PCB)-contami nated sediments from the St. Laurence River was investigated in labora tory incubations over a 39-month period. During the first 4 months, de chlorination reduced the average total chlorines in the General Motors 001 sediments from 3.2 to 2.5 per biphenyl, an additional 22% beyond the in situ level, for an overall 36% reduction from the original Aroc lor 1248 contaminant. With continued incubation, however, an additiona l dechlorination of a single peak 2,4',5+2,4,4'-chlorobiphenyl ensued after a lag that reduced the average chlorines from 2.5 to 2.4. After this, there was no further transformation until the end of incubation. The extent of dechlorination and congener pattern of Aroclor 1248-spi ked sediments were similar to those of the native sediments after a co mparable period of time despite differences in sediment sources and st arting congener composition. The results indicate that most dechlorina tion occurs during a relatively short period of the initial rapid phas e and any further transformation, if it occurs, would be extremely slo w, and its contribution to the total dechlorination may not be signifi cant.