Assessment of Potentially Toxic Elements in Water from the Protected Natural Area Barranca de Metztitlán, Mexico, and Human Health and Ecological Risk

Water is a critical resource for both environmental integrity and human health. This study assessed the concentrations of potentially toxic elements (PTEs)—Pb, Cd and Hg—in surface waters adjacent to six urban settlements within the Barranca de Metztitlán Biosphere Reserve (MBR), Mexico. Ecological and health risks were evaluated for vulnerable groups, including children, adolescents, and the elderly. Cd and Hg water concentrations surpassed the national and international water quality criteria at three locations. Ecological and health risk analysis of Pb was not conducted as Pb concentrations were below LOD (0.02 ppm). Ecological risk analysis revealed a low potential risk for Cd exposure but a high risk for Hg at its highest concentration in the reserve. Health risk assessment revealed that Cd and Hg pose a non-carcinogenic risk, particularly to children under three years old. Hazard quotients (HQ) and cumulative risk indices (HI) exceeded safe thresholds at multiple sites. Infants (0–11 months) were the most susceptible, even at contaminant levels near detection limits. These findings emphasize the importance of routine monitoring and early intervention strategies to mitigate exposure risks, especially in vulnerable populations within the MBR.