Regional variation of ¹³⁷Cs in freshwater fishes in Finland

STUK, Radiation and Nuclear Safety Authority, Research and Environmental Surveillance, P.O. Box 14, 00881 Helsinki, Finland

Abstract

The aim of this study was to see if differences in the transfer and behaviour of ¹³⁷Cs in fishes can be found in large fishery areas. Based on watercourses the country can be divided into eight large areas. The study is focused mainly to four of these areas, most important for freshwater fishing in Finland and based on long-term analysing programmes of freshwater fishes carried out after the Chernobyl deposition in each area. Deposition from Chernobyl was distributed most unevenly in Finland. Average depositions of ¹³⁷Cs to the areas studied varied from 4 kBq/m² to 34 kBq/m². The transfer of ¹³⁷Cs into fishes differed somewhat in various areas. Regional averages of ¹³⁷Cs in fishes per unit deposition varied between 0.04 to 0.2 m²/kg. Average concetration ratios of ¹³⁷Cs in predatory, non-predatory and intermediate fish and water were 7000, 2400 and 6200, respectively, in 1998. After peak values ¹³⁷Cs in fishes decreases with a half-life of 2.2 - 7.5 years in the four large fishery areas. The type of the catchment plays an important role in the long-term behaviour of ¹³⁷Cs both in surface water and in fishes.