REDUCTIVE DECHLORINATION OF POLYCHLORINATED-BIPHENYLS IN ANAEROBIC SEDIMENTS

To better understand the conditions which control PCB dechlorination in anaerobic sediments we examined the microbial activity in two freshwater sediments, Hudson River (NY) and Silver Lake (MA), and one estuarine sediment, New Bedford Harbor (MA). Two different reducing conditions were established, methanogenic and sulfidogenic; in addition, the effect of added organic substrates and the differences in the fate of preexisting and freshly added PCBs (100-400 ppm Aroclor 1242 or 1260) were examined. The most rapid dechlorination occurred in the methanogenic cultures established with Hudson River sediment to which Aroclor 1242 was added and supplemented with a fatty acid mixture. Meta and para chlorines were preferentially removed, resulting in accumulation of ortho-substituted mono-, di-, and trichlorobiphenyls. In cultures established with New Bedford Harbor sediment, dechlorination was slower and not as extensive, with di-, tri-, and tetrachlorobiphenyls accumulating. Dechlorination was observed with spiked Aroclor 1242 and with preexisting PCBs alone. In Silver Lake sediment cultures spiked with Aroclor 1260, dechlorination with accumulation of tri- and tetrachlorobiphenyls was observed. Dechlorination was slower than that for the Hudson River cultures. Both the Hudson River and Silver Lake cultures showed no additional dechlorination for the preexisting PCBs. The addition of fatty acids did not enhance activity in the New Bedford Harbor or Silver Lake cultures. No activities were detected under sulfate-reducing conditions with any of the sediments.