Concentrations of Sr-90 and Cs-137/Sr-90 activity ratios in marine fishes after the Fukushima Dai-ichi Nuclear Power Plant accident

摘要

Strontium-90 (Sr-90) was released together with radioactive cesium (Cs) from the Fukushima Dai-ichi Nuclear Power Plant (FNPP) accident. Although the total amount of Sr-90 released into the marine environment from the FNPP was estimated to be a factor of 100 lower than that of Cs-137, the public have been concerned about the safety of commercial species because of the tendency of accumulation in bones of organisms, its long physical half-life and less information about Sr-90 concentrations in commercial species. In this study, we investigated the concentrations of Sr-90 in marine fishes off Japan before and after the FNPP accident. Except for within a 20-km radius from the FNPP, Sr-90 concentrations higher than the background level (0.046Bqkg(-1) wet) were only detected in 4 of 26 specimens collected off Fukushima. Furthermore, Sr-90 concentrations in all samples collected outside of Fukushima were under the detection limit (0.040Bqkg(-1) wet). Also, the concentrations of Sr-90 in marine fishes were notably lower than those of Cs-137, and thus the activity ratios of Cs-137 to Sr-90 in the whole body of teleost fishes were 5-190 times higher than that of before the accident. The activity ratio tended to decrease owing to a decrease in the Cs-137 concentration in marine fish. Our result together with ananalysis of other data sets indicated that the influence of the FNPP accident on Sr-90 in marine fishes was limited to the area near the FNPP and outside of the FNPP harbor area can be considered as negligible.