ARSENIC AND SELENIUM IN SOME VIETNAMESE ACID SULFATE SOILS

A large area in the Mekong delta is covered by acidic sulphate soils. Arsenic (As) and selenium (Se) are two potentially harmful elements th at may accumulate in such sulphidic environments. Mapping of the abund ance and fate of these elements during reclamation was therefore initi ated. Results indicate that the soils are slightly enriched with As, b ut not with Se. The solubility of As varied considerably within the so il 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 hor izons studied. It was concluded that the drainage of these soils may r esult in high initial As concentrations in the drainage water, but als o that As becomes largely unavailable to plants.