Vertical distribution of radionuclides in soils of varying pedochemistry

Natural gamma-emitting radionuclides (40K, 226Ra and 232Th) and Chernobyl-derived radionuclide 137Cs were determined in soil profiles representing typical soil types of Belgrade (Serbia). The influence of soil properties and content of stable elements on radionuclide distribution down the soil profiles (at 5 cm-intervals up to 50 cm depth) was analyzed. The relationships between soil properties and radionuclides suggested the association of 40K, 226Ra and 137Cs with fine-grained soil fractions. The activity concentration of 137Cs correlated significantly with organic matter content, cation exchange capacity, saturated hydraulic conductivity and specific electrical conductivity. The strong positive correlations between 226Ra and 232Th activity concentrations and Fe and Mn indicate their association with oxides of these elements in soil. The correlations observed between 40K and Cr, Ni, Pb and Zn and also between 137Cs and Cd, Cr, Pb and Zn could be contributed to their common affinity for clay minerals. The results of this study provide insight into the the main factors that affect radionuclide migration in the soil, which contribute to the understanding of radionuclide behaviour in the environment and factors governing their mobility within terrestrial ecosystems.