Natural Selenium Levels in Subtropical Soils of Southern Brazil

Selenium is an essential micronutrient for humans; however, in high quantities, it can become toxic. The aim of this study was to evaluate the natural Se levels in soils from southern Brazil. Fifty sampling locations were selected for their minimal anthropogenic interference and high pedological and geological diversity. Soil samples were collected from the A horizon up to a depth of 20 cm. Analyses of Ca, Mg, K, P, TOC, acidity, and texture followed standardized methods, while Se was analyzed after acid digestion and measured using ICP-OES. The natural Se levels ranged from 0.34 mg kg ^− 1 in a typical Alitic Haplic Cambisol to 11.25 mg kg ^− 1 in an organosolic Dystrophic Humic Cambisol. Se behavior in the soil is influenced by pH, P, Fe, Al, and Mn oxides, clay, and organic matter. Metamorphic rocks contain higher Se levels due to mineral recrystallization and trace element mobilization during metamorphism. Background values are crucial as they provide data for decision-making and area management.