Mechanisms of severe contamination in fish: Evaluating the probability of catching fat greenlings (Hexagrammos Otakii) highly contaminated with radiocesium off the coast of Fukushima

Abstract

On 1 August 2012, a total of 25,800 Bq/kg-wet of radiocesium ( 134 Cs = 9,800 Bq/kg-wet, 137 Cs = 16,000 Bq/kg-wet) was detected in the muscle tissue of two fat greenlings (Hexagrammos otakii) caught approximately 20 km north of the Fukushima Dai-ichi Nuclear Power Plant (FNPP). To estimate the contamination level of this fish species off the coast of Fukushima, we measured the radiocesium concentration in the muscle tissue of individual fat greenlings in 2012 and 2013. Radiocesium concentration of fat greenlings caught in southern coastal waters from the FNPP was significantly higher than that of fat greenlings collected in other waters off the coast of Fukushima. However, fat greenlings with a radiocesium concentration greater than 10,000 Bq/kg-wet were not detected, not even from highly contaminated areas. In addition, data obtained from specimens collected off the coast of Fukushima from April to December 2012 suggested that the probability of catching fat greenlings with a concentration greater than 16,000 Bq/kg-wet of 137 Cs was exceedingly low (less than 2.794 × 10 −6). In contrast, highly contaminated fat greenlings were frequently caught within the FNPP port. The geometric mean of 137 Cs was 55,400 Bq/kg-wet, as calculated from specimens obtained during December 2012 to May 2013. Our investigation suggests that fat greenlings with an extremely high concentration of radiocesium were contaminated within the FNPP port and then migrated offshore.