Marine organisms and radionuclides. With special reference to the factors affecting concentration of 137Cs in marine fish

This review described findings on levels and behaviors of 137Cs in marine organisms and on factors affecting them since the radionuclide is major in the global fallout due to nuclear explosion experiments or accidents. The concentration of the radionuclide in the sea water is the primary factor for that in marine organisms and thereby data concerning those concentrations around Japan islands were presented and concentration factors in various fishes were considered. Levels of marine fish 137Cs are variable depending on the living area and food habit. Factors affecting 137Cs concentration in fish are thus biological and environmental. Time changes of 137Cs level in fish, which continuing to decrease after the Chernobyl reactor accident, enable to calculate its effective half life to be 13.4 y and the value had no significant difference from that in the sea water. 137Cs in fish can also be a ecological tool. 137Cs is thus the key nuclide for monitoring the environmental radioactive pollution. (K.H.)