Recent DDT and PCB contamination in the sediment and biota of the Como Bay (Lake Como, Italy).

Due to its peculiar geographical and morphological characteristics, Lake Como (Northern Italy) represents an interesting study-case for investigating the sub-basin scale circulation of persistent organic pollutants (POPs) that, despite being banned since the 1970s, have reached surprisingly high concentrations in some southern alpine lakes as a consequence of their release from melting glaciers in recent years. In particular, the Como Bay, which is located in the city of Como, seems noteworthy because its waters have a longer residence time than the other areas of the lake. The analyses of the historical concentration of PCBs, pp'DDT and its metabolites in a sediment core sampled from the Como Bay covering a time-period from their ban to recent times, showed that the DDTs have never experienced a significant (p b 0.05) decrease over time, with concentrations of the most abundant homologue, pp'DDE, ranging from 27 to 75 ng g-1 d.w. Conversely PCBs significantly (p b 0.05) decreased towards recent times, reaching concentrations around 80 ng g-1 d.w. The contribution of high altitude and local sources was recorded also in the food web: both zooplankton and the zooplanktivorous fish agone were mainly contaminated by pp'DDE (81.4 ng g-1 w.w. and 534.6 ng g-1 w.w. respectively) and by the PCB metabolite hexa-CB (449.7 ng g-1 w.w. and 1672.1 ng g-1 w.w. respectively). The DDT concentrations in the agone (sampled during the years 2006-2009) never exceeded the limits for human consumption in Italy,while concentrations of six selected PCBs exceeded human health advisory recommendations in one of the fish samples analysed, when it was approximately two times higher than the recommended value of 125 ng g-1 w.w.