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Canadian shorebirds are exposed to environmental contaminants throughout their annual cycle. Contaminant exposure among species varies with diet, foraging behaviour and migration patterns. We sampled twelve species of shorebirds from four locations across Canada to assess their exposure to PCBs, organochlorine pesticides, as well as four trace elements (Hg, Se, Cd, As). SigmaPCB and SigmaDDT followed by SigmaCHL were most frequently found above trace level in the shorebird carcasses. In general, the plover species (American golden, semipalmated, black-bellied) appear to be the most contaminated with organochlorines, whereas Hudsonian and marbled godwits appear to be the least contaminated. Among adult birds, the greater and lesser yellowlegs had the highest hepatic Hg concentrations (2.4-2.7 microg g(-1) dw), whereas American golden plovers as well as Hudsonian and marbled godwits contained relatively low levels of Hg (<1 microg g(-1) dw). Renal Se concentrations varied from 3.2 to 16.7 microg g(-1) dw and exhibited little interspecific or seasonal variation. Renal Cd levels in adult birds were highest in Hudsonian godwits from Quill Lakes (43 microg g(-1) dw) and Cape Churchill (12 microg g(-1) dw), and lowest (0.8-1.5 microg g(-1) dw) in greater and lesser yellowlegs from Cape Churchill and Bay of Fundy. Renal As concentrations varied from 0.06 microg g(-1) dw in golden plovers from Cape Churchill to 4.6 and 5.1 microg g(-1) dw in dunlin samples from the Pacific coast. There is no evidence that contaminants were adversely affecting the shorebirds sampled from the Canadian locations in this study.

Thick-billed murres (Uria lomvia) originating from breeding colonies in the Canadian Arctic were collected on their wintering grounds off the coast of Newfoundland. Murres had been previously banded such that the age of each bird could be determined upon collection. This allowed us to explore the possible relationships between age and contaminant levels in the thick-billed murre. Samples of breast muscle were analyzed for organochlorines (chlorobenzenes, hexachlorocyclohexanes, DDTs, chlordanes, mirex, dieldrin, and PCBs) and metals (selenium, cadmium, mercury, and lead). Levels of both organochlorine and metal residues were sufficiently low so that toxic effects were unlikely. First-year birds contained lower levels of DDTs, mirex, dieldrin, and PCBs compared with older birds, reflecting lower levels of contamination of these compounds in food chains at breeding colonies located at higher latitudes. Higher levels of chemical residues in older birds may reflect greater direct input of those organochlorines into the wintering grounds via the highly contaminated St. Lawrence River. Levels of chlorobenzenes, hexachlorocyclohexanes, and chlordanes, which reflect atmospheric deposition, were not detected at higher levels in older birds. Of the metals, only cadmium was detected at higher levels in older birds.