ASSESSMENT OF METAL MOBILITY FROM SEDIMENT OF LAKE VEGORITIS

In the framework of an extended study on the environmental contamination status of lake Vegoritis relatively high chromium and nickel concentrations were detected during the early stages of the investigation. The question whether these metals reached the lake due to anthropogenic activities or associated with elevated geochemical backgrounds, was not answered satisfactorily and therefore a sequential extraction technique was used to determine the chemical association of the heavy metals Pb, Cd, Zn, Cu, Cr and Ni. The methodology applied, the so called EC-Common procedure, was developed jointly by the BCR Brussels and the Joint Research Centre, Ispra, in collaboration with the University of Barcelona and the Macauley-Institute. Four metal fractions of the total concentration were distinguished: 1. The easily exchangeable and carbonate bound fractions 2. The fraction associated with easily and moderately reducible iron and manganese compounds 3. The fraction associated with the organic matter and sulfides and 4. The fraction associated with silicates and inert mineral phases. Most of the non-residual portion is bound to organic matter and to carbonates. The environmental relevance of the four fractions decreases from 1 to 4. The major result of the study was that the high concentrations of Cr and Ni are most evidently due to their origin from the erosion of ultramatic rocks as show the high concentrations in the residual fraction.