Sequential Extraction And Column Chromatography Method For Speciation Study Of The Selenium In Soil

The Tessier sequential extraction technique was applied to selenium speciation of the selenium(Se) in soil and compared with column chromatography separation. The content and distribution of selenite, selenate and humic substances bond Se in exchangeable, carbonates and organic matter fraction in soil of Keshan disease area in Chuxiong and Mouding in yunnan province was determined. The plant available Se and maximum available Se in soil were evaluated. The feasibility of the Tessier sequential extraction technique for the determination of plant available Se in soil was analyzed. The relative standard deviation of the sequential extraction procedure is generally lower than 4.50%, the total recovery rate is between 90.1%-93.4%. Tessier sequential extraction technique is reliable for the determination of different forms of Se in soil. The Se fraction in exchangeable, carbonates, Fe-Mn oxides, organic matter and residual were 9.7 μg/kg, 8.8 μg/kg, 16.1 μg/kg, 27.8 μg/kg, and 10.7 μg/kg respectively, the sum of the Se in exchangeable Se, carbonates and organic matter is 75 times of water soluble Se in soil. The proportion of various fraction of Se in soil of study area is as follows: organic matter(31.8%) > Fe-Mn oxides(18.4%) > Residua(12.2%) > exchangeable(11.0%) > Se bound to carbonates(10.1%). The proportion of Se bound to organic matter is the biggest fraction in Keshan disease affected villages. The content of Se bound to Fe-Mn oxides and the Se in residual are increased with more cases of the disease, and the content of exchangeable Se and Se bound to carbonates is decreased at the same time. There was a significant positive correlation between exchangeable Se and Se bound to carbonates, Se bound to organic matter(P<0.05). The Se in exchangeable, carbonates and organic matter fraction could be transformed from one to another. The proportions of selenite and selenate in changeable, carbonates and organic matter are very small, but are still more than ten times of that in water soluble Se in soil. The sequential extraction procedural dissociated selenite and selenate in soil which is not water soluble. The Se in exchangeable, carbonates and organic matter fraction, in total 8.78 μg/kg, are not all plant available in the study area. The plant available Se, selenite and selenate by column chromatography were only 0.162 μg/kg, 1.84% of the sum above. The Conversion efficiency of the Se in soil is very low in the study area, the bioavailability of Se for plants is very poor. Tessier sequential extraction method could be used for analysis of soil selenium morphological characteristics, the valence state analyses of column chromatography is the better measure for plant available Se in soil.