PCB PROFILES IN SEDIMENTS OF LAKES MAGGIORE, COMO AND GARDA (ITALY)

Single PCB congeners were determined in dated sediment cores taken fro m 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 Aroc lor 1254 and 1260 (35:65). Qualitative and quantitative results are co nsistent with the amounts of Aroclor sold, showing a general trend tow ards less in recent sediments than in the 1970s. However, this decreas e was sharper in Lakes Maggiore and Come, which in the past had PCB co ncentration peaks of 197 ng g(-1) and 822 ng g(-1), respectively, 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 particulat e matter. A comparison of PCB loads in rain end 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 ind icates that this waterbody can be a source of pollution for the surrou nding area.