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.
In an experiment initiated after the Chernobyl accident, a herd of reindeer was followed before and after a temporary move from a highly contaminated area (greater than 20 kBq 137 Cs/m2) to a less contaminated area (less than 3 kBq 137Cs/m2) of natural pasture. The animals grazed in a highly contaminated area until they were moved to the low contaminated area where they grazed from late November to late April. The level of 137Cs in meat was about 12 kBq/kg at the time when the animals were moved (Nov.) to the low contaminated area and it decreased to about 3 kBq/kg with an effective half-time of about 1 month, after the animals were moved. In the low contaminated area the fractional transfer, fm, of 137Cs was determined to be 0.65 d/kg during winter pasture, mainly on lichens, and 0.30 d/kg during summer pasture, in the fields. The actual intake of radiocesium was determined by measurement of ruminal samples from slaughtered animals. The maximal radiation dose to reindeer in Sweden after the Chernobyl accident was estimated to less than 200 mSv/a with a dose rate of less than 1mSv/d during the winter period of maximum tissue concentration of radiocesium.