Autopurification effect of the lithology of geological outcrops under a semi-arid climate: case study of the Wadi Mellegue catchment (northwest Tunisia)

The northwest of Tunisia comprises more than 81% of surface waters and contains 95% of the country's mines and mineral deposits. The Mellegue catchment, located in this area, contains 10 mines extracting lead, zinc, iron, strontium, fluoride and phosphates. The impact of tailings from these mines on surface waters, was evaluated on the basis of several sampling campaigns. The results of ICP/MS analysis of the samples show that they are rich in Al, As, B, Ba, Br, Cd, Co, Cr, Cu, Hg, Mo, Ni, Sr, U and Zn. Tests for these elements in the waters of the Mellegue, its tributaries and in the Nebeur reservoir found that concentrations did not exceded the drinking water thresholds set by the WHO. The reduced water contamination with metals observed in this study may be due to: the presence of geological outcrops formed by limestone, clays and evaporite rocks, the absence of streams draining the tailings directly, and the formation of secondary minerals that strongly adsorb heavy metals and the extent of uncontaminated area in the catchment. Editeur Z.W. Kundzewicz Citation Mlayah, A., Ferreira Da Silva, E.A., Lachaal, F., Khadhar, S., Charef, A., et Noronha, F., 2013. Effet auto-epurateur de la lithologie des affleurements geologiques dans un climat semi-aride: cas du bassin versant de l'Oued Mellegue (Nord-Ouest de la Tunisie). Hydrological Sciences Journal, 58 (3), 686705.