ORGANIC CONTAMINANT EXPOSURE IN THE LAKE ST-CLAIR FOOD-WEB

Chemical concentrations and distributions in an aquatic food web were studied to quantify the relative importance of chemical properties ver sus food web processes in determining exposure dynamics of organic con taminants in aquatic ecosystems. Five organochlorines were measured (P entachlorobenzene QCB, Hexachlorobenzene HCB, Octachlorostyrene OCS, D ichlorodiphenyldichloroethylene DDE and Polychlorinated Biphenyls PCBs ) in the food web of Lake St. Clair. Levels of QCB in aquatic organism s ranged from 1.0 to 25 mug kg-1 lipid, and levels of HCB ranged from 10 to 410 mug kg-1 lipid. More elevated concentrations of OCS (13 to 3 92 mug kg-1 lipid), DDE (162 to 11 986 mug kg-1 lipid) and PCB (650 to 64 900 mug kg-1 lipid) were observed. Organism - water equilibrium ra tios were calculated for all species sampled to quantify the importanc e of food web processes in regulating contaminant exposure dynamics. C orrelations of organism - water equilibrium ratios with body size were not significant for QCB, HCB and OCS (P>0.1), but were found to be si gnificant for DDE and PCB (P<0.01). Results support the conclusion tha t both chemical properties and food web dynamics regulate the distribu tion and concentration of organochlorines in aquatic ecosystems. Food web processes are important, however, for chemicals, that are not meta bolized and have octanol - water partition coefficients (log K(OW)) gr eater than 5.5.