Assessment of Selenium Bioavailability in Natural Selenium-rich Soil Based on Diffusive Gradients in Thin Films

Abstract

BACKGROUND Available selenium is an important index to evaluate the supply capacity of selenium from the soil to plants. Unfortunately, there is no general method for the determination of available selenium in soil in China. Chemical extraction and soil solution methods are commonly used to evaluate bioavailability of selenium. Furthermore, there are problems such as the lack of universally applicable extractant types, incomplete extraction of target states, and dissolution of non-target states. The diffusive gradient in thin-films (DGT) technique is a method based on dissociation and diffusion kinetics which has been successfully used to assess the bioavailability of selenium. However, it is not clear whether the DGT technique can be used in natural selenium-rich soil. OBJECTIVES To investigate the feasibility of the DGT technique to evaluate the bioavailability of selenium in natural selenium-rich soil. METHODS Natural selenium-rich soils from Shangshu and Fenkou in Zhejiang Province were chosen as the research objects. Fe-oxide DGT, Zr-oxide DGT, chemical extraction, and soil solution methods were used to evaluate selenium bioavailability. RESULTS (1) The average of available selenium measured by Fe-oxide DGT was 0.17±0.076μg/L, whereas the average of available selenium measured by Zr-oxide DGT was 0.20±0.13μg/L. Zr-oxide DGT cannot be used effectively to reflect the content of selenium in plants due to the specific adsorption characteristics to Se4+. Fe-oxide DGT was suitable for the bioavailability evaluation of selenium in soil rather than Zr-oxide DGT. (2) There was a significant positive correlation between the selenium content in plants (Cplant-Se) and the available selenium content determined by the three methods. The correlation between available Se by Fe-oxide DGT and Se concentration in plants (r=0.705) was greater than the chemical extraction method and soil solution method. (3) The Kd value and R value calculated from DGT and soil solution methods indicated that the soil of the Shangshu area had stronger selenium mobility than the Fenkou area, but the rate of Se supply from the soil solid phase to the soil solution was less than the Fenkou area. CONCLUSIONS DGT is more suitable for evaluating selenium bioavailability compared with chemical extraction and soil solution methods because it has more advantages in testing performance and reflecting the information of soil dynamics process.

Keywords

• chemical extraction methods
• diffusive gradients in thin films technique
• soil solution method
• selenium
• bioavailability
• natural selenium-rich soil