IDENTIFICATION AND EFFECTS OF ANTHROPOGENIC EMISSIONS OF U AND TH ON THE COMPOSITION OF SEDIMENTS IN A RIVER ESTUARINE SYSTEM IN SOUTHERN SPAIN

A study of the distribution of natural radionuclides in different frac tions of river bottom sediments has been carried out. The study has sh own that the majority of the total U in the sediment is located in the non-residual fraction of the sediment, while Th is more suitable to b e present in the residual fraction of the sediments. Also, it has been found that coprecipitation with amorphous ferromanganese oxyhydroxide s is the main process of incorporation of U- and Th-isotopes from the water column to suspended matter or bottom sediments. The distribution of the radionuclides and the analysis of some relevant activity ratio s in different fractions of sediments has made an unequivocal connecti on between the enhanced U content in river sediments and the waste dis charged into the Odiel and Tinto rivers hy the operation in the vicini ty of phosphate fertilizer industries.