Selenium-rich soils in the area of Ruyuan, Guangdong, China: Se geochemistry and evaluation of factors controlling Se enrichment

A survey of 422 surface soil samples in the Ruyuan Yao Autonomous County of Guangdong Province was done to determine the geochemistry and spatial distribution of Se, and to evaluate factors that could influence Se distributions in soils in the study area. Results showed that the average content of Se in soil of the study area was 0.65 mg·kg^－1, which was 1.97, 2.71 and 2.95 times that of the background values of Shaoguan City, Guangdong Province, and the national average, respectively. The selenium-rich soil is mainly distributed in the central and western regions of the study area, and a total area of 2061.31 km² of selenium-rich soil is delineated, accounting for 89.66% of the total study area. Soil Se concentrations vary by land use type: forest land > garden land > grassland > cultivated land. The enrichment of Se in the soil of the study area is mainly controlled by the parent material. The type of parent material with the highest soil Se content is soil formed by the weathering of argillaceous rocks, where soil selenium is enriched 93.33% relative to parent rock. Secondly, it is affected by the supergene geochemistry and the adsorption and fixation of S, N and other elements in the study area, which is conducive to the enrichment of Se in soil. There was a significant negative correlation between Se and pH in the soil of the study area, that is, the lower the pH value, the higher the Se content. These insights provide a scientific basis for the rational planning and utilization of local selenium-rich land resources, especially for considering agricultural land uses. Se can provide an essential nutrient or adversely affect crops, depending on Se concentrations and chemical form.