PTE and multi-isotope assessment of spring water used for human consumption in the historical mining region of Taxco de Alarcón in southern Mexico

Abstract

The concentration of potentially toxic elements (PTE) and the isotope compositions (87Sr/86Sr, δ34S, 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios) were determined in spring water, sulfide minerals, and rocks samples to evaluate spring water used for human consumption in the historical mining region of Taxco de Alarcón, southern Mexico. The springs samples were collected from the most representative rock units of the study area, from older to younger, to the Taxco Schist, Morelos, Mexcala, Balsas, and Tilzapotla formations. The spring water samples were classified as HCO3–Ca and HCO3–Ca–Na–Mg. The concentrations of Cd, Pb, Sb, Ni, Cu, Zn, Mn, Ba, and Al in the spring water samples were below the recommended values for human consumption according to Mexican and international agencies. However, Al, Ba, Mn, Li, Tl, and Ga concentrations may represent adverse health effects. The average concentrations in the springs followed the decreasing order Tl > Cd > Pb > Sb > Ni > Cu > Li > Zn > Ga > Mn > Ba > Al. This order is similar to that of the rocks rather than the sulfide mineralization, which suggests a major water-rock interaction, and therefore, a genetic link with the rocks. The water-rock interaction is supported by the Sr isotope data, mainly with the rocks belonging to the Tilzapotla Fm. According to the S isotope composition of the springs, two groups were identified: (1) springs characterized by lighter δ34S values, similar to those of the disseminated pyrite hosted in rocks from the Mexcala Fm; and (2) springs with heavier δ34S values, which were within the compositional range of the sulfide mineralization and Morelos Fm rocks. The Pb isotope compositions and mixing models indicated that the rock formations, particularly the Morelos Fm rocks, and the sulfide mineralization, influenced the composition of the spring water. This type of research is crucial to assess PTE contents and sources of spring water used for human consumption, particularly in developing countries, where the lack of infrastructure is common in rural areas.