Concentration and Bioavailability Analysis of Heavy Metals in Mine Tailings from Morelos, Mexico

While mining is a highly important economic activity, it generates considerable environmental impact, especially during the grinding and extraction stages of metallic minerals, leading to the formation of waste known as mine tailings. These mine tailings, often abandoned in various regions of Mexico due to a lack of prior environmental regulations, contain heavy metals that pose a risk to both the environment and human health. In Huautla, Morelos, where metals such as silver (Ag), gold (Au), copper (Cu), lead (Pb), and zinc (Zn) were extracted from the 16th century until 1988, it is estimated that there are approximately 780,000 tons of mine tailings. These mine tailings are contaminated with heavy metals such as cadmium (Cd), Cu, chromium (Cr), manganese (Mn), Pb, and Zn, and the bioaccumulation and biomagnification of these metals have been documented in various plant and animal species in the region, indicating their bioavailability. The study conducted in this area consisted of determining the concentration of Cd, Cu, Cr, Mn, Pb, and Zn, as well as the sequential extraction of mine tailings 1 and 2 to identify metal bioavailability. The results showed for both mine tailings, that the metals with the highest concentrations were Pb (mine tailing 1: 1666 ± 317.7 mg/kg, mine tailing 2: 1329 ± 30.8 mg/kg) and Zn (mine tailing 1: 1327 ± 314.9 mg/kg, mine tailing 2: 1099 ± 34.3 mg/kg), found in fractions IV and VI, respectively. In mine tailings 1, the main bioavailable metals were Cd (75.3%), Mn (53%), Pb (39.8%), and Cu (36.4%), while in mine tailings 2, the bioavailable metals were Cd (56.8%), Pb (37.9%), and Cu (29.3%). In general, Cd and Pb exhibited the highest bioavailability in both mine tailings. According to the calculated risk indices, bioavailable Cd and Pb pose the highest pollution, ecological, and non-carcinogenic risk in both mine tailings, while bioavailable Cr showed the highest determined carcinogenic risk. This study demonstrated that the mining waste from Huautla contains high levels of bioavailable heavy metals, posing ecological and public health risks, and provides valuable information for the development of effective environmental remediation strategies.