Concentrations, distribution and influencing factors of selenium (Se) in soil of arid and semi-arid climate: A case from Zhangye-Yongchang region, north-western China

Selenium (Se) is an essential trace element for human health. It is therefore important to investigate Se geochemical characteristics in the environment. However, less attention has been paid to the supergene geochemistry of selenium in alkaline soils. Based on a recently-completed geochemical survey in the Zhangye-Yongchang region of north-western China, this paper first summarizes the concentrations and spatial distribu-tion of Se in the topsoil therein, and then discuss the influencing factors through multivariate statistical analysis, and study the bio-availability of soil Se. Our results showed that the contents of Se in the topsoil of the Zhangye-Yongchang range from 0.07 to 0.88 mg/kg, and the average concentration was 0.255 mg/kg. The Se-rich soil samples were mainly distributed in the Zhangye city and surrounding counties and towns, mainly including Dongyuan town, Shandan County, and Huocheng town of Minle county, and the potential Se-deficiency areas contain northern Dongyuan Town where develops sandy land, and Shigangdun town that covered by Gobi Desert. Relatively high Se background in local strata points out that the soil parent material is the dominant controlling factor of the Se concentrations in the topsoil. Results from factor analysis, cluster analysis and cor-relation analysis suggest a positive relationship between Se and F, Mo, Sr, U, MgO, CaO, and organic matter, but negative relationship between Se and SiO2 and pH value. Organic matter and certain oxides are likely to be the adsorbent of soil Se. Moreover, a high proportion of water-soluble and ion-exchange state Se (7.66 % of the total contents) and a high Se enrichment rate of crops (>30 %) indicate high bio-availability of soil Se in the Zhangye-Yongchang region, where could probably develop a green industry of Se-rich agricultural products in the future.

Automated summary

This paper summarizes the concentrations and spatial distribution of selenium in the topsoil of the Zhangye-Yongchang region in north-western China, and discusses the influencing factors and the bio-availability of soil selenium. The results show that the average concentration of selenium in the topsoil is 0.255 mg/kg, and the soil samples with high selenium content are mainly distributed in specific areas. Factor analysis, cluster analysis, and correlation analysis indicate certain relationships between selenium and other elements, as well as the role of organic matter and certain oxides in selenium adsorption. The high water-soluble and ion-exchange state selenium content and the high enrichment rate of selenium in crops suggest the potential for developing a green industry of selenium-rich agricultural products in the future.