Geochemical Behavior of Potentially Toxic Elements in Historic Mine Tailings in Taxco, Mexico: A Comprehensive Review of Environmental Transfer and Human Exposure

Taxco, Mexico, has centuries of polymetallic Ag–Zn–Pb mining. This review synthesized published information on potentially toxic element (PTE) geochemistry, environmental distribution, biological exposure, and ecological and human health risk along the Cacalotenango River. The maximum concentrations in La Concha tailings (mg/kg) were 11,800 As, 780 Cd, 43,700 Pb, and 37,994 Zn, whereas those in El Fraile were 5725, 384, 22,900, and 39,145, respectively. La Concha was neutral to alkaline and carbonate-rich, while El Fraile was more acidic and contained more secondary sulfates and Fe oxyhydroxides. Acidic conditions at El Fraile favored PTE mobility, although secondary minerals and cemented horizons provided attenuation. As and Pb were mainly associated with less labile fractions, whereas Zn and Cd were more labile. Soils and sediments near the impoundments showed the greatest contamination. Blood-Pb exceeded 5 µg/dL in 94% of children and 87% of women living relatively far from the impoundments, suggesting additional Pb sources. However, multiple sources, confounding stressors, particulate contamination, and reliance on total rather than bioaccessible concentrations limited attribution of biological effects. An integrated assessment combining source tracing, PTE speciation and bioaccessibility, biomonitoring, and longitudinal health studies is required to establish source–exposure–effect relationships and provide a scientific basis for a regional control program to protect human health.