Trace Elements in Brazilian Oxisols

Résumé: Trace elements (TE) are a global concern and some of them (e.g., cadmium, lead, and arsenic) are of special interest due to their high toxicity to animals and humans and increasing number of soil contamination records worldwide. In Brazil, arsenic abnormal soil levels are found nearby gold and coal mining areas, whereas Cd and Pb are associated with Zn mining. In addition, there are also innumerous unknown cases of TE addition to soils via agricultural inputs (pesticides, fertilizers, sewage sludge, etc). Yet little data is still available on many TEs in Brazilian soils. A better knowledge of TE behavior in variable-charge soils like Oxisols is thus mandatory to help risk assessments as well as regulation purposes (risk management). This presentation will focus on the sorption behavior and background levels of Cd, Pb, and As in Brazilian soils. We highlight the Oxisols, because they comprise ~ 40% of the Brazilian territory, and are highly weathered, acid soils, with many pH-dependent charges, low-medium OM content, low CEC and a mineralogy dominated by kaolinite, gibbsite, goethite, and hematite. We also focus on the effects of pH and ionic strength, as these variables affect not only the adsorption/desorption behavior of TEs, but also Oxisols surface charge thus affecting TE mobility and availability in the soil. -------------------------------------------------------------------------------- Séminaires Minéralogie --------------------------------------------------------------------------------