FOOD-CHAIN STRUCTURE IN ONTARIO LAKES DETERMINES PCB LEVELS IN LAKE TROUT (SALVELINUS-NAMAYCUSH) AND OTHER PELAGIC FISH

The trophic structure of pelagic communities in lakes of glaciated regions is highly variable due to restricted dispersal of glacial relict taxa and recent species introductions. Much of the enormous between-lake variability in PCB levels in lake trout flesh (15-10 000ng/g) from the St. Lawrence system results from differences in the length of pelagic food chains. Data (1978-81) on PCB concentrations in lake trout flesh indicate that PCB concentrations increased with the length of the food chain and tissue lipid content, and decreased with distance north of urban-industrial centres. Each trophic level contributed about a 3.5-fold biomagnification factor to the PCB concentrations in the trout, and the lipid content of predicting PCB levels in pelagic salmonids and forage fish (smelt and coregonids) indicated that biomagnification of small atmospheric inputs of persistent lipophilic contaminants can explain the frequent occurrence of high levels of contaminants in some biota from remote areas, and that species introductions that lengthen food chains will lead to significant increases in levels of atmospherically dispersed persistent organic contaminants in top predators. -Authors