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 bet ween several potential sources of elevated environmental Pb exposure i n several wild bird species. For juvenile herring gulls (Larus argenta tus) from the Canadian Great Lakes, the mean Pb-206:Pb-207 ratio in bo ne (1.137 +/- 0.007) was within the range characterizing Pb from gasol ine combustion in Canada (1.13-1.16). By contrast, very few Canadian w aterfowl, loons or eagles that had experienced elevated Pb exposure ha d Pb-206:Pb-207 ratios similar to that of Pb originating from Canadian gasoline combustion. Pb in soils, sediments and biota derived from le aded gasoline combustion was not the primary source of elevated Pb exp osure and toxicity for most individuals of these species. The range an d pattern of the Pb-206:Pb-207 ratios for Pb-exposed waterfowl and eag les was very similar to that for Pb shot pellets purchased or recovere d from lake sediments, consistent with the contention that the ingesti on of Pb shot (or Pb sinker in the case of common loons) is the main c ause of elevated Pb exposure in these species. In addition, the isotop e 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 ex perienced elevated Pb exposure from Precambrian mining or smelting was tes. We conclude that stable Pb isotope analysis is useful for disting uishing 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.