Wildfires in radiologically contaminated areas have raised concerns about radionuclide redistribution and increased radiation exposure. Most radionuclides, such as radiocesium (137Cs), remain in the charred residues and burned soil even after wildfires. This study investigated the impact of wildfires on 137Cs speciation in forest litter and soils following the Fukushima nuclear accident. Extraction tests of 137Cs from unburned litter and soil artificially combusted at 250, 375, and 500 °C were conducted. 137Cs leaching from charred residues and burned soil collected from the field after the wildfires was tested. Sequential extraction was performed on soil obtained after the fire. The results indicated that water-soluble 137Cs from burned litter increased with combustion temperature. However, in artificially combusted soil, the release of water-soluble 137Cs was significantly reduced. In the field, 137Cs leaching from charred residues was lower than that from unburned litter. The fraction of water-soluble 137C in burned soil did not differ significantly from that in unburned soil. This suggests that the combustion temperature was relatively low and insufficient to promote significant leaching or soil drying. Furthermore, the combustion of soil organic matter may have altered the exchangeable form of 137Cs. Overall, these findings suggest that wildfires enhance 137Cs retention in soil, potentially delaying its release.
Igarashi et al. (Sun,) studied this question.