Sediment analysis to support the recent glacial origin of DDT pollution in Lake Iseo (Northern Italy).

In the present study, a depth-related distribution of Persistent Organic Pollutants (POPs) in sediments of Lake Iseo, one of the major southern Alpine Italian lakes, is reported in order to further test the hypothesis of melting Alpine glaciers as a secondary source of contamination. In a previous paper, a "glacier contamination hypothesis" was suggested to explain the unexpected contamination of the biota of Lake Iseo, mainly fed by the Alpine melting ice. The sediment core analyses covered around the last 50 years. The organic matter profile evaluated as a Loss-On-Ignition percentage indicated transition of the basin from an oligotrophic to a mesotrophic status at around the early 1970s, but there was no evidence of the shift to eutrophy in the 1980s. Among DDTs, pp'DDE was the predominant metabolite, accounting on average for 79.4% of the total DDT concentrations and ranging from 6.4 to 447.5 ng g(-1)d.w. PCBs ranged from 5.0 to 163.7 ng g(-1)d.w. The maximum PCB concentrations were found in sediment layers corresponding to the 1970s when the highest production and use of these compounds occurred in Italy. In contrast, concentrations of DDTs showed a sharp increase from the early 1990s, long after their agricultural use was banned in Italy. This delayed pollution provides support for the hypothesis that the recent retreat of glaciers represents a secondary pollution source for old pesticides that were stored in the ice at the time of their use in agriculture.