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

Abstract

Strontium-90 (90Sr) was released together with radioactive cesium (Cs) from the Fukushima Dai-ichi Nuclear Power Plant (FNPP) accident. Although the total amount of 90Sr released into the marine environment from the FNPP was estimated to be a factor of 100 lower than that of 137Cs, 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 90Sr concentrations in commercial species. In this study, we investigated the concentrations of 90Sr in marine fishes off Japan before and after the FNPP accident. Except for within a 20-km radius from the FNPP, 90Sr concentrations higher than the background level (<0.046 Bq kg−1 wet) were only detected in 4 of 26 specimens collected off Fukushima. Furthermore, 90Sr concentrations in all samples collected outside of Fukushima were under the detection limit (<0.040 Bq kg−1 wet). Also, the concentrations of 90Sr in marine fishes were notably lower than those of 137Cs, and thus the activity ratios of 137Cs to 90Sr 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 137Cs concentration in marine fish. Our result together with ananalysis of other data sets indicated that the influence of the FNPP accident on 90Sr in marine fishes was limited to the area near the FNPP and outside of the FNPP harbor area can be considered as negligible.