USE OF FRESH-WATER MUSSEL DREISSENA-POLYMORPHA TO ASSESS TRACE-METAL POLLUTION IN THE LOWER RIVER PO (ITALY)

Caged freshwater zebra mussels (Dreissena polymorpha) were transplante d for one month to Mo sites in the lower river Po, northern Italy. Tra ce metals accumulated in tissues were determined after 15, 30 and (1 s tation only) 60 days, and were also expressed as metal body burdens. M etals were also determined in Po water samples. No significant differe nces in metal accumulation in mussel tissues were observed between the two sites. Cd and Pb concentrations increased from 1.23 to 3.22 and 3 .40 to 5.93 mu g/g dry weight respectively at one site and the same tr end was observed at the second site, indicating that these metals accu mulated. Cu and Zn concentrations in mussel tissues did not change rel ative to time zero concentrations. The highest Cr and Ni levels were f ound after 15 days at both stations (10 and 27 mu g/g dry weight respe ctively). Low and relatively constant Hg concentrations (<0.10 mu g/g dry weight) were found in transplanted and native molluscs (D polymorp ha and Unio elongatulus). Concentration factors calculated for all tra ce elements assayed, ranged from 10(3) (Pb) to 10(4) (Zn).