Hydrogeochemical processes and health risks from heavy metal contamination in groundwater of the Toluca Valley, Mexico

Hydrogeochemistry of groundwater and its public health implications were evaluated in Texcalyacac, Mexico. Twenty-five groundwater samples were collected during the dry and rainy seasons. In situ measurements included pH, electrical conductivity, total dissolved solids (TDS), and dissolved oxygen. Major ions (Ca, Na, Mg, K) and trace elements were quantified by inductively coupled plasma (ICP), while nitrate, phosphate, sulfate, and chloride concentrations were determined using colorimetric methods. Most physicochemical parameters met drinking water standards. Seasonal variations reflected a dilution effect during the rainy season. Lead (Pb) concentrations exceeded permissible Mexican limits, representing a significant health risk. Heavy Metal Pollution Index (HPI) and Metal Index (MI) classified groundwater as non-potable in the dry season. Elevated levels of nitrate, phosphate, chloride, and sulfate, linked to agricultural and urban activities, indicate anthropogenic influence. Health risk assessment identified Pb as the primary contaminant, posing low chronic non-carcinogenic risks to adults and children. Groundwater was classified as a Ca–Mg–HCO 3 type. Gibbs and Mifflin diagrams suggested that rock–water interactions, evaporation, and mixing with local and intermediate flow systems govern groundwater evolution. Principal component analysis (PCA) indicated that mineralization, reflected by major ions and TDS, was the main control on groundwater chemistry, while a secondary component was associated with anthropogenic inputs affecting nutrient and organic matter levels. This study highlights an integrated approach combining hydrogeochemical characterization and health risk assessment. It effectively identifies priority contaminants and seasonal vulnerabilities and guides sustainable groundwater management in a small, water-dependent community. • Groundwater quality assessed in Texcalyacac using hydrogeochemical parameters. • Anthropogenic activities identified as key sources of groundwater contamination. • Heavy metal contamination quantified using multiple pollution indices. • Human health risk from groundwater metals exposure was evaluated. • Study supports improved groundwater management in the Toluca Valley.