Effects of Large-Scale Wildfires on the Redistribution of Radionuclides in the Chornobyl River System

Wildfires in radiologically contaminated areas raise significant concerns due to potential radionuclides redistribution and increased public radiation exposure. This study examined the impact of the 2020 Chornobyl wildfire on the redistribution of radionuclides, specifically ¹³⁷Cs and ⁹⁰Sr, in the Chornobyl River system. We determined the quantities and speciation of ¹³⁷Cs and ⁹⁰Sr in charred residues and soil after wildfires and analyzed the riverine concentrations of these radionuclides based on long-term monitoring data. Our findings indicate that the inventories of ¹³⁷Cs and ⁹⁰Sr in the charred residues and soil decreased with increasing distance from the nuclear power plant, which is consistent with the initial deposition patterns. However, the transfer of ¹³⁷Cs and ⁹⁰Sr from soil to charred residues did not correspond to the distance, type of contamination source, or fire type. Speciation analysis revealed that the water-soluble fractions of ¹³⁷Cs and ⁹⁰Sr in the charred residues were significantly higher than those in the soil, implying increased mobility. Following the wildfires, no significant increase in ¹³⁷Cs concentration was observed in a river catchment in Chornobyl. However, ⁹⁰Sr concentrations showed a significant increase, exceeding the permissible levels in drinking water (2 Bq/L) in Ukraine. This increase is attributed to hydrologically driven mobilization processes: (1) during snowmelt in spring and (2) the transport of soluble ⁹⁰Sr from charred residues and surface soil into the river during high suspended solid concentration events. Collectively, our findings highlight the importance of continuous monitoring of radionuclide dynamics in postwildfire environments to better assess potential radionuclide redistribution and radiation exposure risks. These results provide valuable insights into the behavior of ¹³⁷Cs and ⁹⁰Sr in river systems affected by wildfires, contributing to a more accurate understanding of their environmental impacts and potential countermeasures.