Heavy Metal Contamination and Ecological-health Risks in the Santiago River, Mexico: A Multiyear Water Quality Assessment

Introduction: Water security threatens the world's population, so the evaluation of the quality of water in reservoirs is one of the priority issues and represents a challenge for the sustainability of ecosystems and the human population. The Rio Grande de Santiago is considered the most polluted river in Mexico, as a result of the discharge of water from the industrial corridors of the region, agricultural activities in the area and wastewater from the Guadalajara Metropolitan Area (GMA) and riverside populations without adequate treatment, causing an increase in diseases, ecological deterioration and low quality of life. Aims: The objective of this research is to evaluate the physicochemical parameters and heavy metals of the water of the Santiago River to determine the water quality indices and estimate the ecological and health risks in this century. Study Design: An ecological study was carried out using indices of water quality, pollution, and ecological and health risks in the Santiago River during the period 2009-2024. Methodology: The water quality data of the Santiago River was obtained through the Jalisco State Water Commission. The analyses were carried out on a monthly basis from 2009 to 2024. Subsequently, the CWQI, WQI, ISQA, NP, HPI, HEI, DC, PERI, HQ, HI, THI, CR and TCR indices were calculated to determine water quality and ecological and health risks. Results: The distribution of parameter concentration showed great spatial and temporal variation. The physicochemical parameters are within both national (NOM-001-SEMARNAT-2021) and international (CCME) standards with the exception of fluorides, and total dissolved solids and suspension. The heavy metals Al, As, Cr, Cu, Fe, Hg, Ni, Pb and Zn have concentrations above the national and international standard. Pearson's correlation analysis showed that trace elements have negative correlations that show different sources; and positive correlations of both natural and anthropogenic origin. The water quality at all monitoring points according to the WQI is between 100 and 200, which is categorized as poor quality, while the CWQI shows poor water quality (20-30). The ISQA showed average values of 40 considered as poor quality. According to the NP index (0 to 14500), the concentrations of heavy metals showed very high levels of contamination. The HPI index (89) showed moderate to high levels of heavy metal contamination. The HEI index showed average levels of 30, indicating high pollution. The DC presented an average of 21, classified as a high degree of contamination. The PERI index showed that the ecological risk from heavy metals is moderate to high. Non-carcinogenic hazard indices indicate that river water is not suitable for drinking, and poses a high health risk via ingestion, while dermal contact poses no health risk to residential and recreational recipients, while the carcinogenic hazard index for Cr begins to pose risks. Conclusion: According to the water quality, ecological risk and health indices, the water quality of the Santiago River is poor, with a high degree of contamination by heavy metals and represents ecological and health risks (carcinogenic and non-carcinogenic).