Reductive dechlorination of weathered PCBs in the marine sediments of Brentella canal of Venice lagoon.

The occurrence microbial-mediated reductive dechlorination processes towards polychlorinated biphenyls (PCBs) has been documented in several subsurface sediments of contaminated freshwater and, less frequently, marine systems, spiked with exogenous PCBs and suspended in synthetic media. This work was aimed at detecting and characterizing the occurrence of reductive dechlorination processes towards weathered PCBs in contaminated marine sediments of Porto Marghera area (Venice lagoon, Italy) within slurry microcosms of sediments suspended in the water coming from the same contaminated site. Reductive dechlorination of weathered PCBs occurred in both sediments. The detected processes exhibited meta- and para-specificity and were not significantly “primed” after spiking with exogenous PCBs, that were rapidly and extensively dechlorinated. PCB dechlorination seemed to be mediated by sulfate-reducing bacteria, that probably started to use PCBs as electron acceptors during the sulfate reduction but in particular when their native electron acceptor was completely depleted. Such activities were detected under geochemical conditions that closely mimic those occurring in situ, and this allows to speculate that similar processes might also be in progress in situ.