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(38-57) DDTs and other organochlorine insecticides distribution in the sediments of a contaminated region. Guzzella, L.*,1, De Paolis, A.1, 1 IRSA-CNR, Brugherio, Milan, Italy ABSTRACT- The study of lake sediments provides important time-integrated information on changes within a lake and its watershed. Lake Maggiore, the second largest Italian lake, is located in a heavily industrialised and densely populated subalpine area. Its drainage basin covers 6599 km2 and it receives several inputs from anthropogenic point sources as well as from diffuse natural sources. In 1993-94 the analysis undertaken by Laboratorio Cantonale of Lugano (CH) showed DDT concentrations greater than 1000 ug/kg in some fresh muscle samples of the twaite shad fish collected in the Lake Maggiore. The Italian Government was therefore asked by the International Commission for Italian-Swiss Water Protection to investigate on the possible origin of the DDT contamination in the Lake. In the present study lacustrine sediments were sampled in the whole Lake Maggiore and in the main lake tributaries and analysed for organochlorine pesticide content. The OCs analysis showed the presence of a point source contamination in the Pallanza basin: the higher abundance of the pp'-DDT compared with its main metabolites demonstrated the recent origin of the pollution phenomenon (a local industrial activity). The decreasing trend of the DDT contamination observed from Toce core station to Stresa one is in a good agreement with the particulate matter deposition of suspended material from the Toce river to the lacustrine open water. In contrast with the consistent scientific opinion, no significant correlation was found between DDT contamination and sedimentary organic carbon in these cores. A non-equilibrium ripartition between DDT in water and in suspended matter might explain the observed discrepancy. This phenomenon probably reflects local industrial discharges more than water-sediment interaction processes. Contamination by other OCs in the lake sediments was very low in all the samples analysed and could be attributed to diffuse contamination sources. Key words: sediments, organochlorine insecticides, DDTs, industrial origin |
