1Graduate School of Agricultural and Life Sciences, The University of Tokyo, Bunkyo, Tokyo 113-8657, 2Head Office, Marine Ecology Research Institute, Shinjuku, Tokyo 162-0801, Japan
Using published data for 8,683 samples obtained off the coast of Fukushima during the two-year period after the Fukushima Daiichi Nuclear Power Plant accident in 2011, the state of radioactive cesium (134Cs+137Cs) for 95 species (a total of 97 fishery items including two species that are marketed separately for the adult and immature stages) were clarified. All data available from a government website were used for this analysis. The results of cluster analysis using parameters of the annual average and standard deviation of radioactive cesium concentration indicate that the 97 items can be categorized into four groups. Group A had lower concentrations and lower variability both for the first and the second years (60 items). Group B showed a decline of concentration in the second year but it was still high (21 items). Group C had extremely high initial concentrations but levels were almost undetectable in the second year (1 item). Group D was highly contaminated throughout the two years (15 items). Almost all the items of groups A and C satisfied the government food-safety standard in the second year. On the other hand, products in groups B and D do not satisfy the standard and must be closely monitored.