Impact assessment of Hg–Sb wastes to urban soils and shallow groundwater in the mining region of Huitzuco, Guerrero (southern Mexico) using mineralogical, geochemical and Sr–Pb isotopic tools

Concentrations of Hg, Sb and the related potentially toxic elements (RPTEs) As, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, V and Zn were determined in tailings from the Hg–Sb mining region of Huitzuco, Guerrero (southern Mexico) to evaluate their impact on urban soils and shallow groundwater. Tailings are entirely composed of fragments from the ore-hosting Morelos Formation and contain residues of cinnabar, terlinguaite, livingstonite, stibnite and Fe–Ti oxides, whereas urban soils are derived from rocks of the Tilzapotla Formation with a minor contribution from the Morelos Formation. Tailings typically contain lower concentrations of Hg, Sb and RPTEs than urban soils strongly suggesting more than one source of elements. Shallow groundwater is of Ca–HCO₃ and Ca–SO₄ types with most samples having concentrations of Hg and Sb above the Mexican and EPA guidelines and concentrations of all RPTEs below these guidelines. At Huitzuco, tailings are the most important source of Hg and Sb and a significant source of Mn, Fe, Cr and Ni, whereas As, Pb, Cd, Cu, Zn, V and Co derive from neighboring lithologies. Neighboring rocks are also significant contributors of Sb, Mn, Fe and Ni. Besides lithology and mineralization, the Pb isotopes indicate the participation of a still unidentified, low radiogenic source in urban soils and groundwater with an isotopic signature similar to house paints. Unlike other nearby mining zones, at Huitzuco, only Hg and Sb represent a serious menace to ecosystems and inhabitants, Cu a moderate risk around tailings, and Pb, Zn and Cd a low risk.