Selenium Geochemical Characteristics and Influencing Factors of Paddy Fields in Du'an County, Guangxi

Abstract

This study used 21 rock samples and 193 sets of paddy soil and rice grain samples collected form Baiwang Town, an area of clastic sedimentary rocks in Guangxi, China, to evaluate the potential for selenium-rich agriculture. We analyzed the concentrations of selenium and heavy metals in the soil and rice samples, and discuss the influencing factors by means of statistics and correlation analysis. The results showed that the selenium-rich rate of paddy soil and rice grain in Baiwang Town were 67.4% and 64.8%, respectively, but the content of cadmium in the selenium-rich soil samples was generally higher than the baseline value for China and the background value for Guangxi. In comparison to the screening value of soil pollution risk for agricultural land(GB 15618-2018), the over-standard rate of cadmium was 46.1%, while the over-standard rates of other heavy metals were negligible. The comparison shows that the selenium-rich rate of rice was 61.1% in the southern area of Baiwang Town with a negligible heavy metal content, and the advantages of green selenium-rich rice planting were clear. The correlation analysis showed that secondary enrichment was the main form of selenium enrichment in the study area. The soil pH and texture of the root-zone soil also affected the selenium content of the soil. The selenium content of rice seeds was mainly affected by the selenium content, active selenium content, pH, and aluminum oxide content of the root-zone soil. The risk assessment showed that the level of dietary exposure to cadmium is generally within safe limits, but it is still necessary to strengthen the monitoring of cadmium in rice and control cadmium pollution to reduce the levels of dietary exposure, especially in the central region of Baiwang Town.