Great Lakes: old contaminant concentrations improve slowly, new contaminants worsening

The news regarding toxic chemicals in the Great Lakes is mixed. A recently published paper shows statistically significant decreases in the concentrations of chlorinated and persistent bioaccumulative and toxic (PBT) contaminants (PCBs, DDT, dieldrin, cis-chlordane, oxychlordane, cis-nonachlor) in lake trout in Lakes Huron, Ontario, and Michigan over the period of 1999 to 2009. At current rates of decline, the levels of these chemicals in Great Lakes fish may decline to below levels of concern in about 30 years. There is no similar trend in Lakes Superior and Erie but concentrations of these toxic substances are lower in fish in these two lakes than in the other three.

Another study published earlier this year shows that concentrations of brominated flame retardants, also persistent, bioaccumulative and toxic substances, are increasing in Lakes Michigan and Ontario. The concentration in sediment of one BFR is currently doubling every 3–5 years in Lake Michigan and approximately every 7 years in Lake Ontario.

The paper showing decreases in PBTs (free abstract; pay for full text)  is available at

The paper showing increasing concentrations of BFRs (free abstract; pay for full text) is at

See also a more detailed summary of the results of these two research projects at

GallonDaily’s editor was a participant in a team effort to promote actions reducing flows of toxic substances to the Niagara River, the Great Lakes system connection between Lakes Erie and Ontario, in the 1980’s. Progress in reducing levels of toxic contaminants in the Great Lakes is certainly slow.

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