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 110m Ag, 134 Cs, and 137 Cs over time. The results indicated that (1) 110m Ag, 134 Cs, and 137 Cs were present in all marine plants collected in May 2012, (2) the concentration of 110m Ag in the seagrass Phyllospadix iwatensis decreased significantly over time while the ecological half-life of 110m Ag in P. iwatensis was longer at locations closer to the FDNPP, and (3) the 110m Ag/ 137 Cs radioactivity ratio of P. iwatensis was remarkably high until 2015, indicating that detectable 110m Ag was present in the coastal environment 4 years after the accident. The concentration of 110m Ag in P. iwatensis was higher than those in other marine algae, demonstrating a species-specific mechanism of accumulation.