Would you like a little less? Caesium-137 in different fish species

The radionuclide caesium-137 is easily detecable in fish from the German exclusive economic zone, however its concentration shows a decreasing trend. The peak in the beginning of the 1990ies with about 20 Bq Cs-137 per kg fresh weight originates from the input of the Chernobyl accident. Around 5% of the released Cs-137 was deposited in the eastern Blatic Sea and it took about 6 years until the maximum concentration was also reached in the western Baltic Sea. Since that time, the Cs-137 concentration in fish decreased continously. Obviously, the average concentration in Gadiformes (cod, whiting) was around 40% higher than the mean of all fish, while that of Clupeiformes (Herring and Sprat) was only 60% of the average of all fish. We conclude that this is the effect of different feeding of the fish and therewith their trophic level. While Clupeiformes forage plankton, Gadiformes feed on Clupeiformes, which leads to en enrichment of the Caesium in the former.