Experimental wildfire induced mobility of radiocesium in a boreal forest environment

Wildfires are expected to increase with warmer climate, which can contribute to the mobility and the resuspension of long-lived and potentially hazardous radionuclides. The release of Cs-137 during combustion of dried litter, forest floor organic soil, and peat was investigated in a small-scale experimental set-up. Combustion conditions were varied to simulate different wildfire scenarios, and the fuels were dried organic material collected in a boreal environment of Sweden that was contaminated following the Chernobyl accident in 1986. The combustion-related release of Cs-137 to the air was on average 29% of the initial fuel content, while 71% of the initial Cs-137 remained in the ashes after the combustion. Peat and forest soil had the highest releases (39% and 37%, respectively), although these numbers should be viewed as potential releases since authentic wildfire combustion of these fuels are usually less effective than observed in these experiments. These results indicates that the Cs-137 has migrated downwards in the organic material, which imply potentially significantly more Cs-137 emissions in severe wildfires with intense combustion of the organic vertical profile in peatbogs and forests. More Cs-137 tended to be released during intense and efficient combustion processes, although no significant differences among combustion intensities were observed. The generated experimental data was used in an emission scenario to investigate the possible range in Cs-137 emissions from a wildfire. Our study shows that a severe wildfire in a contaminated area of 10,000 ha could potentially release up to 7 TBq of Cs-137. This is the first laboratory study to investigate Cs-137 release upon varying combustion conditions using real fallout contaminated organic material obtained from a boreal environment. (C) 2021 The Authors. Published by Elsevier B.V.

Automated summary

Wildfires are expected to increase with warmer climate, potentially contributing to the mobility and resuspension of long-lived and potentially hazardous radionuclides. Experimental findings suggest Cs-137 tends to remain in ash during combustion, with peat and forest soil showing higher releases.