Microbial reductive dechlorination of pre‐existing PCBs and spiked 2,3,4,5,6‐pentachlorobiphenyl in anaerobic slurries of a contaminated sediment of Venice Lagoon (Italy)

Abstract Reductive dechlorination of polychlorinated biphenyls (PCBs) pre‐existing (at ∼1 mg kg −1 ) in a marine sediment of Porto Marghera (Venice Lagoon, Italy) was investigated in anaerobic slurries developed in water of the same contaminated site. Some microcosms were pasteurized whereas others were amended with 2‐bromoethanesulfonic acid, molybdate or eubacteria‐inhibiting antibiotics (without and in the presence of exogenous carbon sources) to preliminarily characterize the microbial populations involved in the process. Bioconversion of highly chlorinated PCBs into tri‐ and di‐chlorinated, ortho ‐substituted biphenyls was detected from the 11th week of incubation both in the non‐amended and in the pasteurized microcosms, where a significant consumption of sulfate and no methane production were observed. Conversely, no significant PCB transformation was detected in the microcosms with molybdate, where no sulfate consumption and a significant methane evolution occurred. Neither was PCB transformation observed in the microcosms supplemented with antibiotics and exogenous carbon sources, where a strong methane evolution and no sulfate consumption were recorded until the 11th week. The addition of exogenous 2,3,4,5,6‐pentachlorobiphenyl showed preferential dechlorination at the meta and para positions, and did not significantly influence the onset of pre‐existing PCB dechlorination. These results indicate that endogenous PCBs pre‐existing in the marine sediment underwent reductive dechlorination. They also suggest that the process was not ‘primed’ upon 2,3,4,5,6‐pentachlorobiphenyl addition, and was likely to be mediated by sulfate‐reducing, spore‐forming bacteria.