Is mirex still a contaminant of concern for the North American Great Lakes?

Mirex, historically used as a pesticide and fire retardant, was released to Lake Ontario during the 1960s. Even after 35-40 years of cessation of its production and bans on use during the 1970s, mirex is considered a contaminant of concern. In this study, we present a comprehensive view of long-term trends and significance of mirex/photomirex levels in fish from the Canadian waters of the Great Lakes. Majority of measurements (except for Lake Ontario) were below detection, especially in recent years. Concentrations of mirex in Lake Ontario fish decreased by approximately 90% between 1975-2010, and both mirex and photomirex decreased by 75% between 1993-2010. Half-lives of mirex and photomirex for the entire period ranged from 4-10 years, but were lower at 2.5-8 years in recent times indicating expedited recovery possibly in response to remedial actions performed in the 1990s. Simulated fish consumption advisories generated by considering only mirex and photomirex indicated that mirex/photomirex is a minor concern. We predict that within 15 years mirex/photomirex levels in Lake Ontario fish will drop to levels that will result in advisories of at least 8 meals/month. In either case, the presence of other contaminants in Lake Ontario fish contributes to more stringent advisory than generated by mirex/photomirex. It is recommended that the routine monitoring of mirex/photomirex be replaced with periodic surveillance to reduce analytical costs. Dechlorane family compounds (that mirex is a part of) need to be evaluated further for their monitoring needs once in-depth toxicological information becomes available.