BROMINATED BIPHENYLS PRIME EXTENSIVE MICROBIAL REDUCTIVE DEHALOGENATION OF AROCLOR-1260 IN HOUSATONIC RIVER SEDIMENT

The upper Housatonic River and Woods Pond (Lenox, Mass.), a shallow im poundment on the river, are contaminated with polychlorinated biphenyl s (PCBs), the residue of partially dechlorinated Aroclor 1260. Certain PCB congeners have the ability to activate or ''prime'' anaerobic mic roorganisms in Woods Pond sediment to reductively dehalogenate the Aro clor 1260 residue. We proposed that brominated biphenyls might have th e same effect and tested the priming activities of 14 mono-, di-, and tribrominated biphenyls (350 mu M) in anaerobic microcosms of sediment from Woods Pond. All of the brominated biphenyls were completely deha logenated to biphenyl, and 13 of them primed PCB dechlorination. Measu red in terms of chlorine removal and decrease in the proportion of hex a- through nonachlorobiphenyls, the microbial PCB dechlorination prime d by several brominated biphenyls was nearly twice as effective as tha t primed by chlorinated biphenyls. Congeners containing a meta bromine primed Dechlorination Process N (flanked meta dechlorination), and co ngeners containing an unflanked para bromine primed Dechlorination Pro cess P (flanked para dechlorination). Two ortho-substituted congeners, 2-bromobiphenyl and 2,6-dibromobiphenyl (2-BB and 26-BB), also primed Process N dechlorination. The most effective primers were 26-BB, 245- BB, 25-3-BB, and 25-4-BB. The microbial dechlorination primed by 26-BB converted similar to 75% of the hexa-through nonachlorobiphenyls to t ri- and tetrachlorobiphenyls in 100 days and removed similar to 75% of the PCBs that are most persistent in humans. These results represent a major step toward identifying an effective method for accelerating P CB dechlorination in situ. The challenge now is to identify naturally occurring compounds that are safe and effective primers.