Environmental contaminants in caribou in the Northwest Territories, Canada

Caribou (Rangifer tarandus) are strict herbivores with a winter diet consisting primarily of lichen. This simple food chain makes caribou a good species for monitoring changes in arctic terrestrial ecosystem contamination. The defined ranges of herds across the Northwest Territories (NWT) also enables examination of spatial trends in contaminant exposure. Caribou were collected from five locations in the first half of a study designed to examine levels of a broad spectrum of organochlorine, heavy metal, and radionuclide contaminants. A wide range of contaminants were detected, with most compounds found at relatively low levels. In general, organochlorine residues were significantly lower in caribou from the mainland Bathurst and Qamanirjuaq (Arviat) and the Southampton Island herds than in caribou from Cape Dorset and Lake Harbour on southern Baffin Island. Moderate levels of hexachlorobenzene (HCB) and alpha-hexachlorocyclohexane (alpha-HCH) were detected at all five study sites. HCB residues ranged from a lipid corrected mean of 32.83 ng/g in fat of Bathurst caribou to 129.41 ng/g in Lake Harbour animals. Alpha-HCH levels ranged from 8.11 ng/g in Bathurst animals to 37.9 ng/g in Cape Dorset caribou. Total polychlorinated biphenyl (sigma PCB) residues ranged from 6.24 ng/g in fat of Arviat caribou to 31.68 ng/g in Cape Dorset animals. Congeners 153 and 138 were the most dominant of the 43 congeners tested. Metal levels were also relatively low with the exception of cadmium, which had community means of 9.68- 33.87 micrograms/g in kidney tissue and 1.96-4.39 micrograms/g in liver tissue. Moderate levels of cesium-137 were detected, with community means of 33.2-184.1 Bq/kg in muscle tissue. Long-range atmospheric transport appears to be the primary source of the contaminants detected in this study.