Objectives 1. To determine tissue residue levels of metals and radionuclides in caribou given its importance as a country food species. 2. To monitor contaminant exposure in caribou as a representative species of the terrestrial arctic ecosystem. 3. To examine metal speciation and isotopes ratios (uranium, thorium, strontium, titanium) which may provide insight into the source of contamination (anthropogenic vs. natural). 4.To provide information on temporal trends in radionuclide and metal levels in several caribou herds to determine whether levels are increasing, decreasing or remaining the same over time. 5. To determine the efficacy of international controls in reducing or eliminating pollutants entering the Canadian Arctic terrestrial ecosystem. Barren-ground caribou are found across northern Canada, and are a major component of the traditional diet in communities across the Northwest Territories (NWT) and Nunavut. Caribou are a good indicator species for terrestrial ecosystem contamination given their wide distribution across northern Canada, the simple air-lichen-caribou food chain, the existing baseline data set, and their importance as a country food species. Three (3) caribou herds from across the NWT and Nunavut have been selected as sentinel herds, with a different herd to be sampled each year to determine tissue residue levels and monitor temporal trends. Field collections will be conducted in cooperation with local Hunter’s and Trapper’s Organizations and/or local aboriginal organizations, utilizing local hunters in planning and conducting the field work. Samples will be tested for a wide range of environmental contaminants including 10 heavy metals and 7 radionuclides.