Review on Characteristics of Selenium in Soil and Related Analytical Techniques

BACKGROUND Selenium is an essential micronutrient for humans. The spatial heterogeneity of selenium in soil is the main cause of various diseases and environmental problems. Selenium in soil is unevenly distributed across the globe, with most soils being low in selenium. Globally, the average selenium content in soil is 0.4mg/kg, while it is 346-2018mg/kg in typical high-selenium areas. Thus, accurate analysis of selenium in soil is of great significance in research on seleniferous soil. The reasonable use of reference materials can aid in the effective monitoring of the quality of analysis. OBJECTIVES To summarize the status of research on selenium in soil, and the development of the corresponding analytical methods and reference materials. METHODS This article describes the distribution characteristics, speciation, and migration and transformation characteristics of selenium in soil. Furthermore, the methods for extracting selenium speciation in soil, the progress of research on selenium content analysis technology, and the status of the development of soil selenium reference materials in recent years are summarized. RESULTS Because of limited advancements in the development of analytical techniques, research on the mechanism of migration and transformation is still incomplete. The emergence of sequential extraction techniques provides a new way to study the distribution, migration, and transformation of soil selenium speciation. However, this method is still under development and has many shortcomings, such as inadequate selectivity and inevitable speciation transformation. Atomic fluorescence spectroscopy is the mainstream approach for the analysis of selenium content in soil, especially in China. Mass spectrometry, with high precision and a low detection limit, and synchrotron radiation X-ray technology, with in-situ speciation analysis capabilities, offer significant advantages in the analysis of trace and ultra-trace elements and speciation analysis. There is a significant gap in the research on reference materials with gradient content and certified speciation content. CONCLUSIONS Methods with a low detection limit, high sensitivity, and matrix interference resistance are urgently needed. The combined application of sequential extraction, mass spectrometry, and X-ray fluorescence can promote research on selenium in soil. Moreover, related certified reference materials with gradient content and certified speciation content are in short supply.