Fate and Transport of Fukushima-Derived Radiocesium in the Environment: Key Findings and Challenges for the Future

Author(s): Alexei Konoplev, Yoshifumi Wakiyama, Yasunori Igarashi, Kenji Nanba

Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident in March 2011 led to extensive environmental contamination by radiocesium isotopes ¹³⁴Cs (half-life T_1/2=2.06 years) and ¹³⁷Cs (T_1/2=30.17 years). Numerous research studies of environmental behavior of radiocesium in the context of geoclimatic conditions of Japan were undertaken. A lot of thought was given to what makes Fukushima environmental impacts different from previous nuclear disasters. This review paper summarizes key findings of post-Fukushima studies of radiocesium fate and transport in abiotic soil-water environment and discusses some challenges for future research. After the Fukushima accident scientific evidence was obtained to confirm that radiocesium behavior in the environment is governed by its speciation in fallout and site-specific environmental characteristics. Given strong binding of Fukushima-derived ^137Cs to soil and sediment particles, its potential bioavailability appeared to be reduced. Incorporation of the deposited ^137Cs in glassy hot microparticles insoluble in water and slowly decomposing in the environment was another salient feature. The Fukushima contaminated areas are noted by relatively high annual precipitation and steep slopes, resulting in significant erosion and intensive radiocesium wash-off, especially during devastating typhoons. Extreme floods during typhoons Etou in 2015 and Hagibis in 2019 caused major redistribution of ^137Cs on river watersheds and floodplains, and, in some cases, natural self-decontamination. Significantly, for all special features and characteristics of Fukushima areas, the recently obtained knowledge is in line with the basic perceptions of modern environmental chemistry regarding radionuclide behavior in the environment. Challenges for future research include, to name a few, tackling radiocesium leaching from glassy hot particles and studying dynamics of radiocesium in the environment over long term, better understanding of dissolved radiocesium seasonality in water bodies and addressing radiocesium remobilization from rivertransported sediments at the freshwater-seawater interface.