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 transplanted for one month to Mo sites in the lower river Po, northern Italy. Trace metals accumulated in tissues were determined after 15, 30 and (1 station only) 60 days, and were also expressed as metal body burdens. Metals were also determined in Po water samples. No significant differences 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 trend was observed at the second site, indicating that these metals accumulated. Cu and Zn concentrations in mussel tissues did not change relative to time zero concentrations. The highest Cr and Ni levels were found after 15 days at both stations (10 and 27 mu g/g dry weight respectively). Low and relatively constant Hg concentrations (<0.10 mu g/g dry weight) were found in transplanted and native molluscs (D polymorpha and Unio elongatulus). Concentration factors calculated for all trace elements assayed, ranged from 10(3) (Pb) to 10(4) (Zn).