Radiocesium in caribou and reindeer in northern Canada, Alaska and Greenland from 1958 to 2000

This study summarizes the spatial and temporal trends of fallout 137Cs concentrations in caribou and reindeer (Rangifer tarandus ssp.), reported in various programs in Canada, Alaska and Greenland, over a 40-y period. During the 1960s, the highest 137Cs concentrations (2000–3000 Bq kg−1 wet weight in muscle) were found in the large caribou herds of central northern Canada, with levels about 50% lower in Alaska and Greenland. Concentrations varied by up to a factor of 6 between spring and fall. Concentrations in reindeer were comparable to those in caribou from the same regions. The highest 137Cs concentrations (750 Bq kg−1) in the late 1980s were found in the Caniapiscau herd of central Québec. The contribution from the Chernobyl accident in 1986 was estimated from 134Cs measurements to be 10–40% of the total 137Cs. Present concentrations have declined to 200–300 Bq kg−1. The effective half-life (Teff) of 137Cs in Canadian caribou herds was estimated to be about 6 y. The potential impact on the health of northern residents is discussed.