Leaching behavior of selenium from the karst infillings of the Hydrogeological Experimental Site of Poitiers

Abstract The selenium enrichment in groundwater may be caused by the contact with sedimentary formations. In many French regions, geogenic sedimentary sources of Se were identified as responsible of the Se concentrations exceeding the European limit in many wells designated to produce drinking water. This study focuses on the black argillaceous infillings of the Hydrogeological Experimental Site of Poitiers (HESP) and aims to better understand the Se release mechanisms at the interface between these infillings and aqueous media using batch experiments with variable pH and contact time. The Se behavior as function of pH was similar in the ultrapure water and in the HESP water and can be discriminated in three main domains. For very acidic domain the speciation of the released Se, that can be associated to the dissolution of some mineral phases, was majorly unidentified. For 2  in-situ data confirm the diversity and the complexity of the release mechanisms of Se that is not associated with a specific carrier phase but disseminated within the sedimentary matrix.