Radioactive caesium in fish in Swedish lakes 1986–1988 —General pattern related to fallout and lake characteristics

Abstract

The aim of this work is to provide a picture of how the concentration (=activity) of 137Cs varied geographically in Sweden during 1986, 1987 and 1988 in different fish species (especially pike, perch, char and trout), to study how different lake properties (water chemistry and morphometry) influence the 137Cs uptake in fish, to try to develop a load diagram for lakes when 137Cs in fish is used an an effect parameter, and to study how the caesium concentration set of data from 644 Swedish lakes. The median 137Cs concentration in fish increased between 1986 and 1987 by between 13% (trout) and 240% (pike). The increase between 1987 and 1988 has stagnated for most species, but not for pike where the concentration increased 82% in ‘the median lake’. The in-lake, between-lake and temporal variations are large and differ from species to species. About 14 000 laks in Sweden had fish (‘100 g perch’) with 137Cs concentrations above 1500 Bq/kg (w/w) (the Swedish guideline) during the autumn of 1987. Apart from the radioactive fallout, the water retention time is the individual factor of greatest importance for the variability of 137Cs concentration in fish between these lakes — longer water retention time gives higher 137Cs concentrations in fish. Lake water hardness and/or conductivity also influence the uptake of 137Cs in fish — lakes with high values of these parameters tend to have lower concentrations of 137Cs in fish.