Cs-137 in freshwater fish in Finland, Norway and Faroe Islands with examples of ecological half-times

The deposition from Chernobyl in spring 1986 was most unevenly distributed in Finland and elevated the 137Cs contents of freshwater fishes significantly. Finland can be divided into five categories on the basis of the average deposition of 137Cs in each municipality. High activity concentrations of 137Cs still occur in fish in certain Finnish lakes in the areas of the highest deposition. The observed ecological half-times of 137Cs in perch in certain Finnish lakes varied by a factor of about three. The longest halftime of 137Cs in perch was approximately 9 years and the shortest approximately 3 years, determined for the time period of 1988-2002. The Norwegian lakes differ also from each other with respect to the decrease rates of 137Cs in fish. In some cases there were clearly two components in the reduction of 137Cs. Ecological half-times of 137Cs in trout and Arctic char varied from 1.4 y to 4.7 y in 1988-1994. There is an indication of somewhat more rapid reduction of 137Cs in fish in certain Norwegian lakes compared to Finnish ones, although ecological half-times for the Norwegian and for the Finnish lakes were estimated for different time intervals in the examples, and are thus not directly comparable. (au)