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LINKING HISTORICAL ORGANOCHLORINE EXPOSURES IN THE GREAT LAKES CAUSALLY TO MAJOR FISH POPULATION CHANGES
Citation:
Cook, P. M. LINKING HISTORICAL ORGANOCHLORINE EXPOSURES IN THE GREAT LAKES CAUSALLY TO MAJOR FISH POPULATION CHANGES. Presented at Exposure Assessment: Its Role in Ecotoxicology, SETAC-Europe, Cardiff, Wales, UK, September 7-10, 1999.
Description:
The Great Lakes of North America are large aquatic ecosystems that have been greatly impacted by human activities in the 20th century. Introduction of non-native species, both advertently and inadvertently; reduction in populations through commercial fishing; habitat alternation; water quality degradation; and chemical toxicity are major categories of stressors that have been imposed. Diagnosing specific causes of fish population changes that are not part of natural cycles is facilitated through an eco-epidemiological approach within an ecological risk assessment framework. Since the Great Lakes have been, by their geographical location and hydrology, very susceptible repositories of persistent, hydrophobic organochlorine chemicals, population level effects due to toxicity are possible. The lake trout, Salvelinus namaycust, (LT) was determined to be the most sensitive fish species for early life stage mortality from exposure of eggs to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and structurally related chemicals that act through an aryl hydrocarbon receptor (AhR) mediated mode of action. Since LT populations declined to virtual extinction in all of the Great Lakes except Lake Superior during the 1940-1970 period of maximum organochlorine loadings, a chemical toxicity etiology was investigated by relating a reconstructed exposure history for Lake Ontario to risks for LT early life stage mortality. Recent exposures, directly determined through GC/MS analysis of LT eggs obtained from stocked LT, are slightly below the threshold for overt sac fry mortality, but within a range associated with effects that may contribute to the presently observed limited survival of young LT in the environment. Concentrations of AhR agonists in radionuclide-dated sediment corre sections provided acomplete record of exposures since 1900. Biota-sediment accumulation factors (BSAFs), adjusted for temporal trends in the sediment-water concentration quotient (IIscow), and TCDD toxicity equivalence factors (TEFs) were used to determine the TCDD toxicity equivalence concentrations in LT eggs (TEqCegg) over time. These TEqCeggs indicate populations and reproductive success are very consistent with this prediction. Independent exposure assessments also predicted these effects. This model may be appplied to other fish and wildlife species.