Polychlorinated biphenyls (PCBs) are extensively occurring in freshwater and marine sediments. It has been documented that they might undergo in situ microbial dechlorination in a wide variety of anaerobic freshwater sediments mostly under methanogenic conditions. Despite of this, little is known about the occurrence of the same processes in PCB-contaminated marine sediments, including those of the Porto Marghera area (Venice Lagoon, Italy), where the occurrence of PCBs has been documented.
In a recent work, we could demonstrate the occurrence of microbial-mediated reductive dechlorination processes in 3 PCB-contaminated sediments of the Porto Marghera area (4). Then, we characterized the detected processes by showing that they were a) selectively directed at the meta- and para-chlorines of the molecules, b) not primed by the addition of exogenous PCBs and c) (apparently) mediated by sulfate-reducing spore-forming bacteria. A preliminary molecular characterization of microbial population enriched in the active microcosms partially confirmed the latter finding (6). To gain deeper insights on this, a culture enrichment program was started by developing new microcosm sets where the same sediment, spiked with 5 defined coplanar PCBs, was progressively applied at lower percentages. Spiked PCB-dechlorination rate increased by about 70% by moving from the primary to the secondary microcosms (all developed with sediment in site water at 25% v/v) and by over 100% to the tertiary microcosms (developed with 12% or 6% v/v of sediment). Molecular analysis of the microbial communities occurring in these enriched microcosms are currently in progress.
These and other results obtained on marine sediments of Venice Lagoon will be presented and discussed at the workshop.