Use of stable isotope ratios to distinguish sources of lead exposure in wild birds

We used stable lead (Pb) isotope ratios to attempt to discriminate between several potential sources of elevated environmental Pb exposure in several wild bird species. For juvenile herring gulls (Larus argentatus) from the Canadian Great Lakes, the mean Pb-206:Pb-207 ratio in bone (1.137 +/- 0.007) was within the range characterizing Pb from gasoline combustion in Canada (1.13-1.16). By contrast, very few Canadian waterfowl, loons or eagles that had experienced elevated Pb exposure had Pb-206:Pb-207 ratios similar to that of Pb originating from Canadian gasoline combustion. Pb in soils, sediments and biota derived from leaded gasoline combustion was not the primary source of elevated Pb exposure and toxicity for most individuals of these species. The range and pattern of the Pb-206:Pb-207 ratios for Pb-exposed waterfowl and eagles was very similar to that for Pb shot pellets purchased or recovered from lake sediments, consistent with the contention that the ingestion of Pb shot (or Pb sinker in the case of common loons) is the main cause of elevated Pb exposure in these species. In addition, the isotope ratios for all species were higher than that characterizing Pb from Precambrian mining and smelter sources (Pb-206:Pb-207 = 0.93+/-1.07), indicating that none of the birds examined in the present study had experienced elevated Pb exposure from Precambrian mining or smelting wastes. We conclude that stable Pb isotope analysis is useful for distinguishing between potential sources of Pb exposure in wildlife and that Pb shot ingestion is the cause of most of the elevated Pb exposure in waterfowl and their predators in Canada.