The Nature of Selenium Species in the Hydrogeological Experimental Site of Poitiers

High concentrations in selenium - above the quality limit of 10 ppb - were detected in some wells of the Hydrogeological Experimental Site (HES) of Poitiers. Speciation measurements show that Se migrates mainly as selenate in the Dogger's aquifer water. The characterizations of drill core samples tend to attribute a geogenic origin to the selenium species observed in the Dogger's aquifer and to identify specific argillaceous levels fulfilling some karst cavities as selenium host matrix. Chemical extractions applied to these argillaceous samples show that most of Se is mobilized in parallel with the base-soluble organic matter part as Se(IV) species and other reduced forms.