HEAVY-METAL DISTRIBUTION AND MOBILIZATION IN SEDIMENTS FROM A DRINKING-WATER RESERVOIR NEAR A MINING AREA

This study was prompted by concern about the possible heavy metal contamination of the Flumendosa lake, a drinking water reservoir located downstream from the Funtana Raminosa mining area, in Sardinia (Italy). Extremely high concentrations of Pb, Cd and Cu were found in the Rio Sarraxinus, a small tributary of the Flumendosa river which drains the mining area. Sediment cores from the reservoir showed high contents of all three metals. In order to investigate the partitioning of the metals in the main components of the sediments, a scheme of sequential extractions was used. The results indicate an important role of the organic matter in binding Pb and Cd in the sediment of the reservoir. Percentages of non-residual Pb and Cd bound to the organic matter were significantly higher in the reservoir sediments than in those from the tributaries, while the highest percentages of Cu were associated with the organic matter both in lake and in river sediments. However most of the Cd and Pb both in lake and fluvial sediments were bound to the carbonates and to Fe-Mn oxides, which are exposed to chemical changes and then susceptible to metal remobilization in the water.