Distribution of natural radionuclides in sequentially extracted fractions of sediments from a marsh area in Southwest Spain: U isotopes

A study of the distribution of U in different fractions of intertidal sediments collected in a marsh area enhanced by the radioactive wastes discharged from a fertilizer complex has been carried out. The study has shown that U isotopes are mainly located in non-residual fractions of the sediments. Coprecipitation with amorphous ferromanganese oxyhydroxides is the main process of incorporation of this element from the water column into the sediment. The residual fractions only contain some 5% of the total U in the sediment. Moreover, all fractions seem to reflect the same pattern of contamination, with in fact a quite good relationship between the U in most extracted fractions. Thus, those sediments located along the Odiel river basin have higher U concentrations in all the sequentially extracted fractions. Concentration ratios for Spartina densiflora have also been studied. In this paper, it has been considered that not all the substrate sediment takes part in the uptake of elements by the plant but only the non-residual fractions. Thus, a study of the dependence of these concentration ratios on the concentration in the non-residual fraction of sediments has been carried out.