Stimulation of Microbial para-Dechlorination of Polychlorinated Biphenyls That Have Persisted in Housatonic River Sediments for Decades

Sediments were collected from PCB-contaminated Woods Pond in Massachusetts, and 2,5,3',4'-tetrachlorobiphenyl (25-34-CB) was added in an attempt to stimulate dechlorination. After three weeks of incubation, the formation of 25-3-CB was detected from the loss of the para chlorine. Over the next 13 weeks, about 90% of 25-34-CB was stoichiometrically converted to 25-3-CB. In addition to dechlorination of congeners bearing 235-, 234-, and 2345-chlorophenyl groups, there were also a few instances where congeners bearing 234- or 23456-chlorophenyl groups were dechlorinated to form congeners bearing 35- and 2356-chlorophenyl groups, respectively. It was hypothesized that the 25-34-CB selectively increased the PCB-dechlorinating microbial population by acting as an electron acceptor, but the data do not rule out other hypotheses.