Fractionation of Radium-, Uranium- and Thorium- in a Sod-podzolic-gley Soil and in Ortsteins of its Eluvial Horizon

The present research provides information about distribution and fractionation of radium-226, uranium-238 and thorium-232 in the sod-podzolic-gley soil’s profile, as well as in different-sized fractions of manganese-ferrous ortsteins, which occupy 17% of the eluvial horizon soil mass. Fractionation of radionuclides was carried out using the Pavlotskaya method adding the fraction of organic matter. It is shown that radionuclides’ specific activities are distrubuted along the profile according to an eluvial-illuvial pattern. The content of biologically available (water-soluble and exchangeable fractions) and geochemically mobile compounds (water-soluble, exchangeable and mobile fractions) decreases in order radium-226 (11.9-28.5 and 15.3-32.5% of the total activities respectively) > uranium-238 -(2.9-5.3 and 6.0-8.9%) > thorium-232 (0.2-4.4 and 1.1-7.4%). In compared to the host soil mass of eluvial horizon the ortsteins of all sizes accumulate the radionuclides; weighted average coefficients of the accumulation for radium-226, uranium-238 and thorium-232 are 2.1, 1.7 and 1.8 respectively. Regardless of the ortsteins’ size fractions, radium-226 is primarily increasing its content in the exchangeable compounds, uranium-238 - in the composition of the mobile fraction, while the uptake of thorium-232 depends on the neoformations’ size and occurs via mobile compounds and compounds, associated with organic matter and oxides of aluminum and iron. Within the soil profile the specific activities of the radionuclides significantly positively correlate with each other as well as with the content of eluvially-illuvially differentiated typomorphic elements, physical clay and silt, correlate negatively - with the content of manganese and organic matter. In the eluvial horizon direct correlation with iron and inverse correlation with calcium were shown for thorium-232.