Spatial distribution of total cadmium, copper, and zinc in the zebra mussel (Dreissena polymorpha) along the upper St. Lawrence River

The zebra mussel (Dreissena polymorpha) was utilized to assess the spatial distribution of three trace metals, cadmium, copper, and zinc, in the tippe r St. Lawrence River and to test the hypothesis that outflow from Lake Onta rio influenced levels of these metals in near-shore biota. Zebra mussels, c ollected from twelve sites along the southern shore, were analyzed for tota l cadmium, copper, and zinc in their soft tissues. Total cadmium and copper concentrations were elevated at all sites compared to relatively uncontami nated waters and were highest at sites near the outflow of Like Ontario and an industrial area farthest downstream. Total zinc concentrations approach ed levels found at uncontaminated sites. Concentrations were rarely related to animal size at any site. However, body burdens (metal content per indiv idual) showed strong positive relationships with size. To facilitate compar isons among sites, body burdens were calculated for standard length (2.0 cm ) mussels. Highest body burdens occurred at the outflow of the lake and at one relatively uncontaminated site downstream. Lowest body, burdens occurre d at sites in the industrial area, although concentrations in the tissues w ere high. Expected total cadmium concentrations in tissues were estimated u sing a bio-energetic based kinetic model. Observed cadmium concentrations w ere lower than predicted, suggesting that near-shore areas may comprise sig nificant depositional areas subject to enrichment with contaminants carried in the outflow from Lake Ontario. Long-term studies of inter-annual variab ility in metal concentrations, metal burdens, and growth rates should enhan ce the usefulness of D. polymorpha as a biomonitor and help in understandin g the fate of trace metals in the upper St. Lawrence River.