Fukushima and Chernobyl: similarities and differences of radiocesium behavior in the soil-water environment

In the wake of Chernobyl and Fukushima accidents radiocesium has become a radionuclide of most environmental concern. The ease with which this radionuclide moves through the environment and is taken up by plants and animals is governed by its chemical forms and site-specific environmental characteristics. Distinctions in climate and geomorphology, as well as ¹³⁷Cs speciation in the fallout result in differences in migration rates of ¹³⁷Cs in the environment and rates of its natural attenuation. In Fukushima areas ¹³⁷Cs was found to be strongly bound to soil and sediment particles, its bioavailability being reduced as a result.  Up to 80% of the deposited ¹³⁷Cs on the soil were reported to be incorporated in hot glassy particles (CsMPs) insoluble in water. Disintegration of these particles in the environment is much slower than of Chernobyl-derived fuel particles. The higher annual precipitation and steep slopes in Fukushima contaminated areas are conducive to higher erosion and higher total radiocesium wash-off. Typhoons Etou in 2015 and Hagibis in 2019 demonstrated the pronounced redistribution of ¹³⁷Cs on river watersheds and floodplains, and in some cases natural self-decontamination occurred. Among the common features in ¹³⁷Cs behavior in Chernobyl and Fukushima is a slow decrease in ¹³⁷Cs activity concentration in small, closed, and semi-closed lakes and its particular seasonal variations: increase in summer and decrease in winter.