Health risk assessment of potentially toxic elements in water from a geothermal exploration zone in Mexico

The present study evaluates the occurrence and human health risk of potentially toxic elements (PTEs) in surface and groundwater from a geothermal exploration zone in Acoculco, Puebla, Mexico. Twenty-five water samples were collected during dry and rainy seasons and analyzed using inductively coupled plasma mass spectrometry (ICP-MS) and inductively coupled plasma optic emission spectrometry (ICP-OES). Physicochemical parameters and the concentrations of 12 PTEs (Al, As, Cd, Cr, F, Fe, Mn, Ni, Pb, V and Zn) were measured. Concentrations of aluminum (Al), arsenic (As), iron (Fe), manganese (Mn) and vanadium (V) frequently exceeded the maximum permissible limits set by NOM-127-SSA1-2021, WHO (2017), and USEPA (2018). Meanwhile, copper (Cu) and nickel (Ni) were generally compliant with regulations, although exceedances occurred at specific locations and times, reflecting spatial and seasonal variability. The Water Quality Index (WQI), calculated using the Canadian Council of Ministers of the Environment (CCME) methodology, classified 40 % of the samples as "marginal" or "poor," especially during the rainy season. This deterioration in water quality was primarily associated with elevated concentrations of Al, As and Fe and is likely influenced by geothermal and hydrothermal processes typical of the region. Human health risk was assessed using hazard quotient (HQ), hazard index (HI), and carcinogenic risk (CR). HI values exceeded 1.0 in most locations, indicating potential non-carcinogenic risk, and CR values for As surpassed the acceptable limit (1 × 10^-6) in all samples. These results underscore the need for continuous, spatially explicit, and seasonally representative monitoring in geothermal regions, particularly in rural communities without access to treated water.