Long-term changes in legacy trace organic contaminants and mercury in Lake Ontario salmon in relation to source controls, trophodynamics, and climatic variability

We used long-term (20+ yr) datasets to determine how the sum of 209 polychlorinated biphenyl congeners ([Sigma PCB]), dodecachloropentacyclodecane ([mirex]), para-para dichlorodiphenyltrichloroethane ([p,p'-DDT]), and total mercury ([Tot-Hg]) concentrations have changed in Lake Ontario chinook salmon (Oncorhynchus tshawytscha, 1983-2003) and coho salmon (Oncorhynchus kisutch, 1976-2003). Exponential decay models best describe temporal reductions of persistent organic pollutant concentrations [POPS], including [Sigma PCB], [mirex], and [p,p'-DDT], in chinook (r(2) = 0.68 - 0.77, p < 0.001) and coho (r(2) = 0.68 - 0.87, p < 0.001) salmon over the record. In comparison, declines in [Tot-Hg] were slight, with linear models best describing trends (r(2) = 0.49 - 0.50, p = < 0.001 - 0.001). Rapid declines of [POPs] from the mid-1970s through the early 1980s were attributed mostly to Canada-United States bans on usage and sedimentation; subsequent concentration oscillations were linked to salmonine stocking and nutrient abatement programs, climatic cycles, and alewife (Alosa pseudoharengus) population dynamics.