THE ROLE OF THE ZEBRA MUSSEL, DREISSENA-POLYMORPHA, IN CONTAMINANT CYCLING .2. ZEBRA MUSSEL CONTAMINANT ACCUMULATION FROM ALGAE AND SUSPENDED PARTICLES, AND TRANSFER TO THE BENTHIC INVERTEBRATE, GAMMARUS-FASCIATUS

To determine the contribution of ingested material to zebra mussel con taminant accumulation, contaminant assimilation efficiencies (fraction of the total contaminant exposure that is accumulated into tissue, AE ) from spiked algae and suspended sediment particles were measured for benzo(a)pyrene, the insecticide DDT, and selected polychlorinated bip henyl (PCB) congeners. Contaminant transfer from zebra mussel feces to the benthic invertebrate, Gammarus fasciatus, was determined by measu ring AE from PCB contaminated mussel feces to gammarids. Further, muss el contaminant AE values coupled with physiological and environmental parameters were used in a steady-state model to examine the relative i mportance of the algal, suspended sediment, and water-borne exposure r outes for a representative organochlorine compound, hexachlorobiphenyl (HCBP). The relative accumulation via the fecal and water exposure ro utes were modeled for gammarids. Mussel AE values for contaminant accu mulation were greater from algae than from suspended sediments. Model estimates indicated that when contaminant concentrations in the water were near detection limits, dietary exposure was the primary route of contaminant accumulation (61.5% of the total contaminant concentration ). Water was the most important route of contaminant exposure (89.5% o f the total contaminant concentration) when contaminant concentrations in water were IO times greater than the compound detection limit. Sus pended sediment was the major dietary source of contaminants at all wa ter concentrations. % AE for zebra mussel feces to gammarid transfer w ere high-79.0 and 89.4% for hexachlorobiphenyl and tetrachlorobiphenyl respectively-but not statistically different. Model estimates indicat ed that the dietary route of exposure was the primary source of PCB ex posure for gammarids and indicated a potential for PCB biomagnificatio n in the mussel-based detrital food chain. Results suggest that zebra mussels have the potential to change contaminant cycling in the Great Lakes by rerouting dissolved and particulate bound contaminants throug h zebra mussel food chains with possible biomagnification in upper tro phic levels.