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 (K_d) of ash was significantly lower than that of soil for ¹³⁷Cs, while for ⁹⁰Sr there was no significant difference in K_d 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.