Geopedology-climate interactions govern the spatial distribution of selenium in soils: A case study in northeastern Brazil

Abstract

Selenium (Se) is an essential trace element in humans with critical roles in immune functioning and antioxidant systems. Plant foods growing on soils with sufficient Se levels are the primary dietary sources of selenium. Therefore, knowing the factors that drive the concentration of Se in soils is essential to map Se deficiencies and toxicities and implement biofortification programs to enhance foodstuffs' mineral composition. Here, we assessed how geopedology-climate interactions govern the background concentration and spatial distribution of Se in soils from two northeastern Brazil states. A soil geochemical survey covering roughly 110,000 km2 collected 198 composite samples in sites with minimal anthropogenic influence and wide variation concerning soil types, geological and climatological settings. The samples had their Se concentrations determined by hydride generation atomic absorption spectroscopy (HGAAS) after microwave acid digestion. The results indicate that climate (precipitation) and bedrock are the main broad-scale factors on regional soil Se distribution, while soil contents of clay and organic matter influence Se values locally. Geographically weighted regression (GWR) showed that these factors change over space and exist in a spatial non-stationarity relationship with selenium. Se-deficient soils are most likely to occur in semi-arid settings overlying crystalline rocks, in which pedogenesis and climate drive low contents of clay and soil organic carbon, and Se air-borne inputs are low. The risk of inadequate Se intake by humans and animals in the region is high. This study can aid public policies addressing Se malnutrition in the study region and similar geopedological and climate settings worldwide.