Comparison of heavy metal bioaccumulation in freshwater molluscs of urban river habitats in Vienna.

Two bivalve species (Anodonta sp. and Unio pictorum) and two gastropod species (Radix ovata and Viviparus sp.) were tested as bioindicators in moderately metal-polluted Danube River habitats of Vienna. Molluscs, two sediment fractions and water samples were collected between April 1993 and May 1994 at six sampling sites located at five waters in Vienna. The unionid clams were dissected into viscera, gill, mantle, adductor muscle and shell, gastropods into soft body and shell. Analyses of Cd, Pb, Cu and Zn were carried out with atomic absorption spectrophotometry. Bioaccumulation of metals varied strongly according to sampling site, metal and mollusc species. Cd, Cu and Zn loads of the molluscs exceeded environmental concentrations, but not so for the apparently less bioavailable Pb. Sampling site had a significant influence on metal bioconcentrations, e.g. the Neue Donau sampling sites, where traffic emissions probably caused increased metal contents. High environmental metal concentrations in Danube harbours were poorly reflected by the bioindicator species. The gastropods showed about 20-fold higher concentrations than the bivalves. This may indicate a higher Cu regulation capacity of bivalves. The suitability of the investigated mollusc species as bioindicators depends on their specific relationship to the environmental compartment. Anodonta sp. and R. ovata concentrations were more likely related to the contents of the fine sediment fraction, which may be explained by their close association to the sediments. The metal concentrations of the deposit- and filter-feeder Viviparus sp. correlated more closely with suspended matter and filtrate contents.