Interception and storage of wet deposited radionuclides in crops

Sammanfattning: The emission of radionuclides into the atmosphere from various sources, such as nuclear power plant accidents and nuclear bomb explosions, can result in the interception and uptake of radionuclides by crops in the agricultural ecosystem. These radionuclides e.g. radiocaesium (¹³⁴, ¹³⁷Cs) and radiostrontium (⁸⁵, 90Sr), can be transferred to foodstuffs via seeds or animal feed. Therefore, in this thesis, the goal was to study the amount of ¹³⁴Cs and ⁸⁵Sr that have been intercepted, taken-up and redistributed to different plant parts during wet deposition at different growth stages of spring oilseed rape, spring wheat and ley. For spring oilseed rape and spring wheat, the focus was on the transfer to the seeds after wet deposition of ¹³⁴Cs and ⁸⁵Sr. The dependence between the interception of radionuclides and the growth stage, e.g. the total standing plant biomass and the leaf area index (LAI) were also studied. There was a positive correlation between the interception of ¹³⁴Cs and ⁸⁵Sr and LAI for all three crops. A positive correlation between the standing plant interception and the biomass of ¹³⁴Cs and ⁸⁵Sr was found for spring wheat and ley, but not for spring oilseed rape. The highest interceptions of ¹³⁴Cs and ⁸⁵Sr were at shooting for spring oilseed rape, and at maturity for spring wheat. For ley, the highest interception was at the well-developed stages. Accumulation of ¹³⁴Cs and ⁸⁵Sr in the different plant parts increased when deposition was close to harvest and the crops accumulated more ¹³⁴Cs than ⁸⁵Sr. The concentration of ⁸⁵Sr was lower in spring oilseed rape than in wheat grains. There was an indication that the distribution of radionuclides between the above ground plant parts was independent of the way that they entered into the plant after deposition of ¹³⁴Cs and ⁸⁵Sr. The variation in transfer factors found in this thesis in comparison with results from other studies suggest, that the estimate of the risk of possible uptake to crops in the event of future deposition during the growing season, is still subject to uncertainties.