Impacts of wildfire on desorption of radionuclide and subsequent wash-offs in the Chornobyl Exclusion Zone

The Chornobyl wildfires of 2020 raises concerns regarding radionuclides wash-off from post fire sites. The objective of this study is to determine the speciation of 137Cs and 90Sr in the ash and soil. And to reveal the impact of the wildfires on concentrations of 137Cs and 90Sr in river water in Chornobyl. To accomplish this objective, extraction tests were conducted using ash and soil samples collected immediately after the 2020 fires to determine the water-soluble and exchangeable fractions of 137Cs and 90Sr in the ash and soil. Long-term river-water radionuclide concentration records were also analyzed. The results showed that the solid–liquid distribution coefficient (Kd) of ash was significantly lower than that of soil for 137Cs, while for 90Sr there was no significant difference in Kd between ash and soil. Analysis of river water data indicated that 90Sr concentrations higher than the Ukrainian drinking water standard (> 2 Bq/L) were observed more frequently following wildfires in the Sakhan River catchment. The fires increased 90Sr concentrations over the following two years, particularly in the spring, when snowmelt causes substantial releases, and in the summer and autumn, when surface flows occurred. High 90Sr concentrations were observed only within the Chornobyl Exclusion Zone, so additional human uptake of or dose exposure to 90Sr from river water is not expected. The Chornobyl wildfires, which is a short period when radioactive contamination levels are elevated in the ecosystem, affected radionuclide speciation, turning the catchment into a location where radioactive contamination levels are significantly higher than in the surrounding area for the redistribution of radionuclides.