Urban mine tailings and efflorescent crusts: unveiling health implications in Nacozari de García, Mexico

Nacozari de García situated in Mexico's second most significant porphyry Cu district hosts the largest urban historical mine tailings in Sonora. This study aimed to comprehensively evaluate mineralogy, bioaccessibility (Al, Mn, Cu, Zn, and Cd), and associated risks in this region. Three distinct mine tailings, their corresponding efflorescent crusts, and street dust were subjected to thorough investigation. X-ray diffraction analysis unveiled the presence of silicates originating from neighboring lithologies. In the mine tailings, secondary minerals like jarosite and gypsum indicated extensive oxidation due to environmental exposure. Efflorescent minerals, including chalcanthite, hexahydrate, szomolnokite, poitevinite, and halotrichite, were identified, reflecting the influence of the semiarid climate. Among the samples analyzed, the highest elemental concentrations emerged within the efflorescent crusts (Al = 55,584 μg/g; Mn = 36,619 μg/g; Cu = 90,366 μg/g; Zn = 35,391 μg/g; Cd = 137 μg/g). Subsequently, the 10 μm fraction of mine tailings displayed lower concentrations (Al = 19,651 μg/g; Mn = 914 μg/g; Cu = 5626 μg/g; Zn = 936 μg/g; Cd = 3.2 μg/g). Regarding bioaccessibility, the efflorescent crusts exhibited notably high oral bioaccessibility percentages (> 80%) for Cu, Zn, and Mn, potentially leading to non-carcinogenic effects upon oral exposure. However, lung exposure did not present significant risks for the studied elements. Despite generally low Cd concentrations, the enrichment of Cd in efflorescent crusts raised concerns about possible carcinogenic effects. These results underscore the potential human health hazards associated with efflorescent crusts, emphasizing the urgency of implementing appropriate measures to mitigate potential risks.