METAL POLLUTION RECORDED IN EXTINCT DREISSENA-POLYMORPHA COMMUNITIES,LAKE-BREITLING, HAVEL LAKES SYSTEM, GERMANY - A LASER-ABLATION INDUCTIVELY-COUPLED PLASMA-MASS SPECTROMETRY STUDY

Shells of probable former living communities of Dreissena polymorpha w ere found within sediments of the shallow polytrophic to hypertrophic hard water Lake Breitling (Havel-Lake system, Germany). Corresponding sediments have been deposited between approximately 1940 and 1970 and reflect increasing eutrophication and heavy metal pollution of the Lak e during this period (Schettler, 1992). Single shells from various sed iment depths were analysed by laser ablation inductively coupled plasm a mass spectrometry (LA-ICP-MS) along a line on the outer part of the shell. The response of these freshwater mussels to increasing heavy me tal pollution is clearly reflected in the distribution of Pb, Cu, Cd a nd Zn within their valves. In general, Cd, Cu, Pb and Zn contents are lower, and the distribution more even, in the outer harts of the deepe st (oldest) shells compared to shells from higher in the cared sedimen ts. Notably higher contents of Cu, Pb and Zn were recorded from the ce ntral (umbonal) part of the more recent shells, but this behaviour is not recorded for Cd. Metabolic changes brought an by worsening environ mental conditions are proposed to explain this phenomena. Acidity prod uced during anaerobic metabolism can be neutralised by dissolution of the carbonate part of the shell. Copper, Zn and Pb, which show an affi nity for the organic component of the shell, may thus accumulate by re peated dissolution and reprecipitation of the shell during the lifetim e of an individual organism. Cadmium, which is bound mainly in the ara gonite of the shells, is released during the dissolution of carbonate and is not concentrated in the umbonal area of the shell.