Temporal Variation of Radionuclide Contamination of Marine Plants on the Fukushima Coast after the East Japan Nuclear Disaster

As a result of the Great East Japan Earthquake and associated tsunami in March 2011, the Fukushima Daiichi Nuclear Power Plant (FDNPP) released a large amount of radioactive material into the environment, resulting in contamination of many marine organisms. In this study, 15 marine algal species and a seagrass species were collected from the sublittoral zone of the Iwaki Coast of Fukushima Prefecture from May 2012 to June 2015 and analyzed for variations in Ag-110m, Cs-134, and Cs-137 over time. The results indicated that (1) (110)mAg, (CS)-C-134, and Cs-137 were present in all marine plants collected in May 2012, (2) the concentration of Ag-110m in the seagrass Phyllospadix iwatensis decreased significantly over time while the ecological half-life of Ag-110m in P. iwatensis was longer at locations closer to the FDNPP, and (3) the Ag-110m/Cs-137 radioactivity ratio of P. iwatensis was remarkably high until 2015, indicating that detectable 11 mAg was present in the coastal environment 4 years after accident. The concentration of Ag-110m in P. iwatensis was higher than those in other marine algae, demonstrating a species specific mechanism of accumulation.