Radioactive impacts of the Fukushima Dai-ichi Nuclear Power Plant Accident on blue sharks in the Northwest Pacific.

The Fukushima Dai-ichi Nuclear Power Plant Accident (FDNPPA) derived Cs, Cs and Ag in blue sharks captured in the Northwest Pacific during 2011-2018 were assessed for the first time in the aspects of radioactive contamination, temporal variation, maternal-to-fetus transfer, tissue distribution and radiation dose, to demonstrate the impacts of the FDNPPA on blue sharks. The contribution of the FDNPPA derived radiocesium in blue sharks (>52%) was estimated based on Cs/Cs. The effective and ecological half-lives of the FDNPPA derived Cs (270 d, 410 d), and Cs (430 d, 450 d) were calculated. These contaminations decreased with time and returned to the level before the FDNPPA during the period of Sep. 2017-Sep. 2018.Cs and Cs tended to distribute in muscles, while Ag mainly distribute in their guts. Cs and Cs were also transferred to fetuses and the activities were up to ~30% of the maternal activities. Dose assessment demonstrated that the highest FDNPPA derived dose rate in blue sharks (~0.42 nGy/h) was far below the ERICA ecosystem screening benchmark of 10 μGy/h and the committed effective dose in humans from ingesting blue shark meat (0.06-0.90 μSv) was far less than that from annual consumption of food and water. It was far from causing radiation harm to blue sharks and humans, suggesting that the impacts of the FDNPPA on blue sharks were not significant.