Analysis of the contamination process of the extremely contaminated fat greenling by Fukushima-Derived radioactive material

Abstract

We analyzed the contamination process by which the fat greenling, which was caught in the area off the mouth of the Ota River of Fukushima prefecture on August 1, 2012, concentrated radiocesium ( 134 Cs + 137 Cs) to the level of 25,800 Bq/kg-wet. The radioactivity environment of the area was insufficient to maintain or increase the radiocesium concentration in the fish at the time. Distribution of the radioactive materials in the otolith of the fat greenling estimated by beta-ray emissions suggested that the fat greenling was in a highly contaminated environment during the period immediately following the Fukushima Dai-ichi Nuclear Power Plant (FNPP) accident. We used a biokinetic simulation of the 137 Cs concentration to demonstrate that the fat greenling had to have been exposed to radioactivity from the FNPP to achieve such a high radiocesium concentration. Thus, the extremely contaminated fat greenling originated in the heavily contaminated environment of the FNPP port or the adjoining area in the period just after the accident.