Contaminant trends in Great Lakes fish

Dramatic declines have been observed in the concentrations of PCB, DDT, dieldrin, and other organochlorine contaminants since fish were first monitored in the mid 1970s. These declines have, however, slowed or ceased entirely in recent years. PCB and DDT concentrations have not changed significantly in walleye from Lake Erie since 1982 and lake trout from the upper Great Lakes since 1986. In coho salmon from Lakes Michigan and Erie, PCB concentrations have increased significantly since the mid 1980s. The lack of recent declines and increases in contaminant concentrations appear to be the result of several factors including internal cycling of contaminants, continued loadings from the atmosphere, and changes in the food web brought about by the introduction of exotic species. Contaminant trends and probable causes will be discussed, as will the relationship between contaminant trends in the water column, top predator fish species and loading history.