U AND TH SPECIATION IN RIVER SEDIMENTS

A study of the distribution of some natural radionuclides in different chemical fractions of river bottom sediments has been carried out. Th e study has shown that the majority of the total U in sediments is loc ated in the non-residual fractions, while Th is more likely to be pres ent in the residual ones. This difference between U and Th reflects la rgely a much higher mobility of U relative to Th in surface and near-s urface environments. Coprecipitation with amorphous ferromanganese oxy hydroxides is the main process of U and Th incorporation from the wate r column into the soil particles. Moreover, the distribution of the ra dionuclides and the analysis of the Th/U mass ratios in different chem ical fractions of sediments has made an unequivocal connection between the enhanced U content in river sediments and the wastes discharged i nto the rivers by the operation of fertilizer industries.