Mobilization of trace metals and PCBs from contaminated marine sediments of the Mar Piccolo in Taranto during simulated resuspension experiment

The effects of sediment resuspension on the fate of metals and polychlorinated biphenyls (PCBs) were studied by using a short-term small reactor. Sediments and water were collected nearby the most contaminated site of the Mar Piccolo of Taranto. Contaminant partitioning was calculated between the solid and water phases and, in the latter, between the dissolved and particulate phases and related to physical-chemical variables. Before and after resuspension, metal concentrations in sediments did not vary remarkably. Except for Cd, all the analyzed metals exceeded by many folds both threshold effect level (TEL) and probable effect level (PEL) SQGs. Igeo index values for Hg designated the sediment quality as extremely polluted for Pb, Cu and moderately polluted for Zn. In the dissolved phase, Mn increased of about 70 times, Fe of about 7 times and Hg and Zn of 4 and 3 times, respectively. PCBs in sediments before and after resuspension did not vary for more than 15 %. PCB concentrations exceeded for more than ten times PEL values. After resuspension, PCBs increased from 0.82 to 4.82 ng L-1 in the dissolved phase and from 0.22 to 202.21 ng L-1 in the particulate one. The dissolved phase was initially enriched in light- to mid-weight compounds. After resuspension, the particulate phase was enriched in heavier congeners. In particular, hexachlorobiphenyl-153, 149 and 138 together with heptachlorobiphenyl-180 and 187 accounted for 57 % of total PCBs. The dissolved organic carbon (DOC) that increased from 1.31 to 8.55 mg L-1 likely influenced the fate of metals and PCBs in the dissolved and particulate phases. Despite that the residence time of the contaminated resuspended sediments in the water column is limited, they are still highly toxic for the pelagic trophic web.