Evaluation of selenium bioavailability in natural selenium-rich soil by gradient diffusion film technology and chemical extraction method: a case study in Yanqi Basin, Northwest China

Abstract Effective selenium is an important indicator for evaluating the supply capacity of selenium to plants in soil. The chemical extraction method and soil solution method have been applied to determine available selenium in soil, but it is not clear whether they can be applied to evaluate selenium bioavailability in natural selenium-rich soil. To explore the feasibility of using gradient diffusion film technology to evaluate the bioavailability of selenium in natural selenium-rich soil, the natural selenium-rich soil distributed in the Yanqi Basin of Xinjiang was taken as the research object, and the chemical extraction method, soil solution method, and DGT technology were employed to evaluate the bioavailability of selenium in the soil. The results showed that: ① The average content of CDGT measured by Fe-oxide DGT was 0.19 ± 0.083 µg/L, and the average content measured by Zr-oxide DGT was 0.25 ± 0.11 µg/L. The difference in available selenium content measured by the two types of DGT was not significant, however, because Zr-oxide DGT had specific adsorption characteristics for Se4+, Zr-oxide DGT could not effectively reflect the selenium content level in plants. For the determination of soil selenium bioavailability, Fe-oxide DGT was better than Zr-oxide DGT; ② The selenium content in plants Cplant-Se and the effective selenium content measured by the three methods were significantly positively correlated, but the correlation coefficient (r = 0.6805) of the effective selenium content measured by Cplant-Se and Fe-oxide DGT was greater than that measured by the other two methods; ③ The R-value (the ability of soil particles to supplement selenium to soil solution) and Kd value (the distribution coefficient between soil solid and liquid phases) calculated based on the DGT technology indicated that the soil selenium in the Hejing County research area had stronger mobility than that in the Heshuo County research area, however, the rate of the supplement of selenium ion to soil solution by soil solid phase was smaller than that of Heshuo County research area. In summary, the DGT method was superior to the chemical extraction and soil solution methods in terms of the evaluation of selenium bioavailability in natural selenium-rich soil, and had more advantages in testing the performance and reflecting the information of the soil dynamics process.