Radionuclides in the lichen-caribou-human food chain near uranium mining operations in northern Saskatchewan, Canada

The richest uranium ore bodies ever discovered (Cigar Lake and McArthur Riv er) are presently under development in northeastern Saskatchewan. This suba rctic region is also home to several operating uranium mines and aboriginal communities, partly dependent upon caribou for subsistence. Because of con cerns over mining impacts and the efficient transfer of airborne radionucli des through the lichen-caribou-human food chain, radionuclides were analyze d in tissues from 18 barren-ground caribou (Rangifer tarandus groenlandicus ). Radionuclides included uranium (U), radium (Ra-226), lead (Pb-210), and polonium (Po-210) from the uranium decay series; the fission product (Cs-13 7) from fallout; and naturally occurring potassium (K-40). Natural backgrou nd radiation doses average 2-4 mSv/year from cosmic rays, external gamma ra ys, radon inhalation, and ingestion of food items. The ingestion of Po-210 and Cs-137 when caribou are consumed adds to these background doses. The do se increment was 0.85 mSv/year for adults who consumed 100 g of caribou mea t per day and up to 1.7 mSv/year if one liver and 10 kidneys per year were also consumed. We discuss the cancer risk from these doses. Concentration r atios (CRs), relating caribou tissues to lichens or rumen (stomach) content s, were calculated to estimate food chain transfer. The CRs for caribou mus cle ranged from 1 to 16% for U, 6 to 25% for Ra-226, 1 to 2% for Pb-210, 6 to 26% for Po-210, 260 to 370% for Cs-137, and 76 to 130% for K-40, with Cs -137 bio magnifying by a factor of 3-4. These CRs are useful in predicting caribou meat concentrations from the lichens, measured in monitoring progra ms, for the future evaluation of uranium mining impacts on this critical fo od chain.