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 ([ΣPCB]), 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 [ΣPCB], [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.