Long-term trends in contaminant exposure were examined in eggs of two aquatic-feeding species, the Herring Gull (Larus argentatus) and the Snapping Turtle (Chelydra serpentina), collected from locations within the Hamilton Harbour Area of Concern, an industrialized area historically associated with high concentrations of legacy persistent organic pollutants, metals and other compounds. Significant declines in concentrations of sum polychlorinated biphenyls, four organochlorine pesticides and 2,3,7,8-tetrachlorodibenzo-p-dioxin were evident in Herring Gull eggs collected from nesting colonies within the harbour (range in % declines = 86%–94%) and in Snapping Turtle eggs from two area of concern wetland/creek locations (range in % declines = 36%–89%) from the 1980s to 2012. Temporal trends in polychlorinated biphenyl congener profiles in eggs were examined by grouping polychlorinated biphenyl congeners according to structure-activity relationships based on their susceptibility to be metabolized by the cytochrome P450 system. Significant temporal changes in the percentages of non-metabolizable congeners (i.e. increase) and congeners metabolized by P450 1A enzymes (i.e. decrease) were evident in eggs of both species. It is not clear if these distinct temporal patterns are related to changes in metabolism following reductions in polychlorinated biphenyl burdens or changes in bioavailability of congeners in the environment. Large decreases in contaminant burdens in eggs of these two species at two different geographic scales within the area of concern (i.e. local scale for Turtles and regional scale for Gulls) are reflective of improved environmental conditions within the harbour and support their utility as top-predator wildlife bio-indicator species.

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