Present status of POP contamination in Lake Maggiore (Italy)

In the last decade, Lake Maggiore has been subject to heavy DDT contamination due to a chemical plant located near the main influent of the Baveno Bay. The freshwater bivalve zebra mussel (D. polymorpha) was used as a bioindicator of several POPs (DDTs, PCBs, HCB, HCHs) to follow their concentration trend after a heavy flood in autumn 2000. Sampling of mollusc specimens were carried out monthly from April 2001 to October 2002 at two different stations in and outside the bay. Results showed worsening of DDT pollution due to the transport of insecticide from contaminated sediments and soils still present in the closed chemical plant site. Levels of about 4.5 μg/g lipids in soft tissues of specimens from the most contaminated site and 2.0 μg/g lipids outside it were found, which are twice those measured before the flood. HCHs and HCB values were always very low, but it was noticed since winter 2001–2002 a sharp increase of PCB pollution, with values of about 3–4 μg/g lipids, not due to the 2000 flood, but probably to improper discharge or release of contaminated sediments from numerous dams located in the watershed. Concentrations of total dioxin-like PCBs reached dangerous levels for the water community. Fish consumption may be a risk for human health especially for resident population, bearing in mind that fish usually have a higher POP concentration than zebra mussel.