Speciation of uranium-series radionuclides in the leaf litter of willow family trees

In order to predict the barrier functions of the components of natural ecosystems in the migration of radionuclides,we studied the forms of U, 226Ra and 210Pb in fresh willow and aspen leaf litter collected in the taiga territory polluted by radium mining. In the course of the experiment, these radionuclides were sequentially extracted from fallen foliage with distilled water (water-soluble forms), 1M ammonium acetate (exchange forms), and 0.1M sulfuric acid solution (acid-soluble forms). Studied radionuclides differed in the degree of extraction from leaf biomass. After all the stages of extraction, 64-84 % of 226Ra and 85-88 % of 210Pb of their initial gross content were preserved in the litter. Among the mobile forms of radionuclides, exchange form (12-20 %) was the most characteristic for radium, and acid-soluble one (8-9 %) for lead. The amount of uranium extracted from leaf litter was higher in comparison with this. After all the extraction stages, the proportion of non-extractable uranium was 6-14 % and 20-23 % in the cases of willow and aspen, respectively. The results of the experiment indicate that in case of radioactive contamination of the taiga zone, the leaf litter of the studied representatives of the willow family is a good temporary depository of 226Ra and 210Pb. At the same time, uranium is expected to return quickly from the willow and aspen leaf litter to the abiotic components of the environment. Taking into account the degree of accumulation of the studied radionuclides in the green mass of woody plants, their widespread prevalence in the taiga, as well as the possibility of wind scattering of leaf litter, the obtained results complement the data necessary to predict the migration and concentration of natural uranium-series radionuclides in polluted taiga ecosystems.