Summary

Description

Exposure to detrimental concentrations of lead has been documented in waterfowl in Alaska. In spectacled eiders Somateria fischeri and longtailed ducks Clangula hyemalis, lead exposure has been demonstrated on the YukonKuskokwim Delta YK Delta at levels that have negative population effects Franson et al. 1995, Flint et al. 1997, Flint and Grand 1997, Flint and Herzog 1999. Additionally, Stellers eiders Polysticta stelleri breeding near Barrow on the North Slope showed high levels and rates of exposure Trust et al. 1997; A. Matz, U.S. Fish and Wildlife Service, unpubl. data, and 11 percent of longtailed ducks captured northeast of Teshukpuk Lake on the North Slope in 1980 had lead shot in their gizzards Taylor 1986. Breeding populations of Stellers and spectacled eiders in Alaska have declined dramatically and both are listed as threatened species. King eiders S. spectabilis, common eiders S. mollissima and longtailed ducks are listed as species of concern by the Alaska Natural Heritage Program. Common eider population trend information is sparse, but a migration study at Barrow suggests a large 50 percent decline from 1976 to 1994. The presumed source for avian exposure above background is ingestion of lead shot, which waterfowl consume either intentionally or accidentally while feeding in wetlands where hunting has occurred. Lead shot settles slowly, with some shot potentially available more than three years after deposition Flint 1998; P. Flint, unpubl. data. Alternatively, birds could be exposed to background lead associated with naturally occurring sediment concentrations or dispersed sources such as emissions from combustion of automotive gasoline or industrial processing. While use of leaded gasoline has declined overall in the Northern Hemisphere since the 1970s, combustion of leaded gasoline from Europe and Asia is still the major source of atmospheric lead in the Arctic Dietz et al. 1998, Barrie et al. 1997. Baseline lead levels in the Arctic are typically low, however, except near point sources such as smelters, mining sites, and military installations such as Distant Early Warning DEW sites e.g., Braune et al. 1999. Avian exposure to lead from shot can be determined using radiographs or dissection, if shot are present within the bird. However, lead isotope analysis can identify sources even when no lead shot are found. Ratios of lead isotopes e.g., 206 Pb 207Pb can distinguish between different environmental sources, such as gasoline, natural deposits, or lead shot Scheuhammer and Templeton 1998, Gelinas and Schmit 1997, Blais 1996. This technique has been used to identify lead shot as the major source of exposure for loons, waterfowl, and eagles in Canada Scheuhammer and Templeton 1998. Our study goals were to identify the isotopic signatures of potential sources of lead exposure for nesting eiders and longtailed ducks on the YK Delta and along the North Slope, and to examine variation in lead isotopic signatures over a range of blood lead concentrations in the same species. We were also interested in determining if the standard clinical blood lead threshold of 0.2 ppm Friend 1985 was applicable to eiders and other waterfowl in Alaska, because nesting YK Delta spectacled eider blood lead concentrations did not have an expected specific breakpoint at 0.2 ppm between background concentrations and elevated concentrations. Lack of a definitive breakpoint suggested that the level above which eiders should be considered poisoned by or even exposed to lead above background was unclear, based on standard blood lead residue analyses. We therefore compared blood isotopic signatures to those from reference matrices sediments and shot to define blood concentrations indicative of exposure to lead shot.