Adsorption of Selenite in Tropical Soils as Affected by Soil Management, Ionic Strength, and Soil Properties

Considering that there are only few studies involving selenite sorption in tropical soils, mainly in Brazil, this study aimed to evaluate the influence of soil management, ionic strength (IS), and soil properties on selenite (SeIV) adsorption in tropical soils from the Brazilian Cerrado. A total of 16 soil samples were collected, being eight from cultivated fields and eight from the respective native area (uncultivated soils). Adsorption tests of Se(IV) were carried out in all soil samples, where solutions containing Se(IV) at concentrations of 100, 500, and 5000 μg L−1 were added in two IS, 15 and 150 mM. Results showed that all soils present high adsorption of Se(IV), mainly the clayey soils. For the sandy soils, higher Se(IV) adsorbed amounts were found for the uncultivated soils. Selenite retention was not affected by the tested IS, which indicate that the main adsorption mechanism of Se(IV) in these oxidic soils is by inner-sphere complex, which explains the low Se(IV) desorbed amounts found in the present study. Data from principal component analysis (PCA) showed that clay, S, Fe2O3, and Al2O3 positively correlated with the adsorption of Se(IV), while (P-rem) available P, FeOX, AlOX, PZSE, and pH have shown to affect negatively the Se(IV) adsorption. It can be concluded that Se(IV) is strongly adsorbed on Brazilian tropical soils, being this process unaffected by IS (which was not observed for selenate in a previous study) and affected by soil management and soil properties.