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

Abstract

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 (r2 = 0.68-0.77, p < 0.001) and coho (r2 = 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 (r2 = 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. © 2006, by the American Society of Limnology and Oceanography, Inc.