Abstract
Single PCB congeners were determined in dated sediment cores taken from the three greatest Italian lakes. The PCB profile is fairly constant with time in the three lakes and similar to that of a mixture of Aroclor 1254 and 1260 (35 : 65). Qualitative and quantitative results are consistent with the amounts of Aroclor sold, showing a general trend towards less in recent sediments than in the 1970s. However, this decrease was sharper in Lakes Maggiore and Como, which in the past had PCB concentration peaks of 197 ng g-1 and 822 ng g-1, repectively, than in Lake Garda (peak 38 ng g-1). There is disequilibrium between the top sediment layer and the water column due to freshly settled algae, which can adsorb PCBs to a greater extent than can abiotic particulate matter. A comparison of PCB loads in rain and in sediment shows that there are still local sources of contamination in Lake Como. The net flux of less chlorinated PCBs from Lake Maggiore to the atmosphere indicates that this waterbody can be a source of pollution for the surrounding area.
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