A LAKE-ONTARIO GULF OF ST-LAWRENCE DYNAMIC MASS BUDGET FOR MIREX

Mirex, a flame retardant and pesticide, is unique among the organochlorine contaminants in the Great Lakes as its occurrence is restricted to Lake Ontario due to its two sources at the Niagara and Oswego Rivers. Because of its high lipophilicity and extreme persistence, mirex has entered the entire Lake Ontario food chain. It is being removed from Lake Ontario (exclusive of sedimentation and burial) primarily by outflowing water and migrating biota. Mirex concentrations in water and suspended and bottom sediments of Lake Ontario and downstream thereof in the St. Lawrence River and its estuary are useful indicators of its present and past movements in this system. We report here new mirex data in sediments as far downstream as the Gulf of St. Lawrence and on the development of a mass budget for this contaminant. This mass budget incorporates results measured and modeled data on the contaminant in the food chain of the St. Lawrence estuary and a top predator. Our analysis showed that over the last 4 decades a total of approximately 2700 kg of mirex has entered Lake Ontario, of which approximately 550 kg has been removed, mainly by transport to the St. Lawrence estuary.