Forest Fires and Resuspension of Radionuclides into the Atmosphere

Problem statement: Forest fires are especially frequent around the Mediterranean Sea basin in the summer period and might be able to release naturally-occurring and man-made radionuclides from plant biomass and inject them into the atmosphere. The impact of this radioactivity on populations was not investigated before. Approach: Radionuclide analysis was performed in plants, in smoke from plant burning and in cigarette smoke to determine radionuclide concentrations by alpha spectrometry. Results: Concentrations of Pb and Po in trees such as olive trees, showed low concentrations in roots, trunk and leaves and minor translocation of radionuclides from the root to aerial parts. Soil to plant transfer ratios for Po and Pb in several plants were in the range from 10 to 10. Radionuclides from atmospheric depositions may be accumulated in plants by foliar uptake and for Pb this seems the main pathway, with plant aerial parts displaying Po/Pb ratios around 0.1, which is similar to the radionuclide ratios determined in atmospheric depositions. Experimental burning of wood from several tree species showed enhanced radionuclide concentrations in smoke compared to plant materials. Investigation of Po release from tobacco leaves used in cigarettes, showed especially enhanced concentrations of this radionuclide in the cigarette smoke particles. Conclusion: Radionuclide concentrations in cigarette smoke expose the lung tissues of regular smokers to high concentrations of Po that were considered carcinogenic. Although radionuclide concentrations in other plants analyzed were generally lower than in tobacco, globally the radionuclide activity in the plant biomass is elevated. Inhaled smoke particles from forest fires are likely to contribute to enhanced radiation doses in the human lung.