Distribution of Radioactive and Rare-Earth Elements in Soils of the Guangdong Province, China

Аннотация

The mineral and geochemical features of soils with increased natural radioactivity in the southern China province of Guangdong have been studied. The distribution patterns of uranium (U), thorium (Th), lanthanum (La), cerium (Ce), neodymium (Nd), samarium (Sm), europium (Eu), terbium (Tb), ytterbium (Yb), and lutetium (Lu) in the profile of ferrallitic soils (Ferralsols) have been examined for the first time, using a wide range of research methods. The method of neutron activation analysis has revealed increased concentrations of radioactive and some rare earth elements. Electron microscopy, fragmentation radiography, and X-ray phase analysis have been applied to study the forms of the elements. The correlation between the particle-size distribution of soils and element concentrations in particular particle-size fractions has been revealed. The mineralogical composition of soils has been studied, and minerals-concentrators of radioactive and rare-earth elements—monazite, zircon, xenotime, thorite, and a rare-earth cerium phase with thorium—have been determined. A high Th concentration in the soil has been pointed out. Its significant part migrates with the destroyed material of alkaline thorium granites represented by fine solid particles with an admixture of accessory minerals. The anomalous levels of U, Th, Ce, and La in the studied soils are mainly related to the high content of these elements in the soil-forming rocks. The dependence of the increase in radon activity due to the uranium release from structural lattices of minerals and transition to other forms (adsorbed in particular) has been revealed. A possible effect of high concentration of radionuclides in rocks, soils, and groundwater and of the increased radon activity on the development of malignant tumors in people has been pointed out. According to the World Health Organization, the Guangdong province is characterized by the highest rate of nasopharyngeal cancer in the world.