Radiocesium in Swedish reindeer after the Chernobyl fallout: seasonal variations and long-term decline.

Data about 137Cs activity concentrations in reindeer muscle were collected from different parts of Sweden during 1986-1992. The data were used to evaluate seasonal and geographical variations and long-term decline of 137Cs in reindeer. The seasonal variation is shown in an example from one of the most contaminated areas, the Saami community Vilhelmina Norra, where 137Cs activity concentrations in reindeer during winter exceed those found during summer by about 20 times. Activity concentrations of 137Cs in reindeer were fairly well correlated to ground deposition. The ratio between 137Cs in reindeer (kBq kg-1 wet weight) and ground deposition (kBq m-2) was calculated to be 0.76 m2 kg-1 for the winter period, January-April, in 1987. Activity concentrations of 137Cs in reindeer decreased significantly during the years 1986-1992. The decline was generally more rapid during September, November, and December [corresponding to an effective ecological half-life (TEff) of 3.2 y] than during January-April when TEff was calculated to 4.2 y. There was a general trend toward a slower decrease during the last of the observed years.