LAUSR

More than 9 years since the Fukushima Dai-ichi Nuclear Power Plant Accident (FDNPPA), the impact of FDNPPA on marine biota is being revealed. In this work, the evolution of FDNPPA derived 134Cs, 137Cs and 110mAg in dolphin fishes (Coryphaena hippurus) in the Northwest Pacific from Dec. 2011 to Sept. 2018 were studied. Bioconcentration factors (BCF) of radiocesium (29-69 with the average of 48) in dolphin fishes were calculated. The background level of 137Cs in dolphin fishes (<0.14 Bq/kgfresh weight) before FDNPPA was estimated. The radioactive levels of these three radionuclides in dolphin fishes decreased with time. Among them, 134Cs and 110mAg decreased at the half-lives of 158 days and 54 days at the population level, respectively. After May 2014, 134Cs and 110mAg cannot be detected and the activity of 137Cs returned to the background level before FDNPPA. Radiation dose assessment demonstrated that it was far from causing radiation harm to dolphin fishes in the open ocean of Northwest Pacific and humans who ingested them.