Speciation of Thorium Isotopes in Water, Bottom Sediments, and Soils in the Region of the Former Radium Extraction Plant

Abstract

Speciation of natural thorium isotopes (²²⁸Th, ²³⁰Th, ²³²Th) in water, bottom sediments, and soils in the region of the former plant for radium extraction from highly mineralized stratal waters was studied. The isotope ratio in water and bottom sediments corresponded to the natural mixture, whereas in contaminated podzolic and alluvial-soddy soils with the mean thorium content of 26.0 and 2.74 μg g^–1 the enrichment in ²³⁰Th was observed. At the hydrochemical background of 0.06 μg L^–1 for waters of the river and industrial sites, the Th concentration varied from 0.02 to 0.73 μg L^–1 and correlated with the content of the organic matter dissolved in water and of iron ions. Thorium was present both in the solution and in the suspended material. Its relative content in the suspended material (0.45–3.5 μm) reached 50%, which is lower than the background level for the river. In bottom sediments and soils, Th mainly occurred in the insoluble residue. Its fraction linearly increased with an increase in the total thorium content of the soils. The relative content of Th in fractions of Fe and Mn oxides and hydroxides, amorphous silicates, and especially organic matter was higher than in other mobile fractions. This trend was more pronounced for podzolic soil than for alluvial-soddy soil.