Background levels of selenium in some selected Brazilian tropical soils

- Background levels of Se in soils from São Paulo state are very low.
- In the top surface layer, Se amounts were correlated with pH, oxides, and clay contents.
- In subsurface samples, only pH and Al oxide contents were correlated with Se.
- Correlation between Se amount and parent material was observed.

Selenium is an essential trace element required in low amounts by humans and animals, but it can be toxic when ingested at high concentrations. Information regarding Se background levels in soils is important to prevent Se deficiency, to optimize human nutrition, and to prevent toxicological effects. Background Se levels in Brazilian soils were evaluated and correlated with other soil characteristics. Se concentrations were quantified in samples from the superficial layer (0-0.2 m) and from the subsurface layer (the highest portion of the B horizon) for 58 soils. Soils were selected across a wide range of soil types and parent materials. Se concentrations ranged from < 0.08 to 1.61 mg kg− 1, with a mean of 0.19 mg kg− 1. Concentrations of Se in the samples collected in the superficial layer were positively correlated with cation exchange capacity, as well as with clay, organic matter, and oxide contents of the soils. In the subsurface samples, only pH and aluminum oxide content were correlated with Se concentrations.