Arsenic and selenium in some Vietnamese acid sulphate soils

A large area in the Mekong delta is covered by acidic sulphate soils. Arsenic (As) and selenium (Se) are two potentially harmful elements that may accumulate in such sulphidic environments. Mapping of the abundance and fate of these elements during reclamation was therefore initiated. Results indicate that the soils are slightly enriched with As, but not with Se. The solubility of As varied considerably within the soil profiles and was much influenced by the redox conditions. Drainage, therefore, resulted in a downward shift of the zone with the highest As solubility. Selenium appeared to be practically immobile in all horizons studied. It was concluded that the drainage of these soils may result in high initial As concentrations in the drainage water, but also that As becomes largely unavailable to plants.