Risk assessment and multi-criteria ranking of groundwater contamination by multiple metal(oid)s in the Rio das Velhas...

This study assessed groundwater quality in the Rio das Velhas Basin (Minas Gerais, Brazil)-a mining‑influenced watershed under strong anthropogenic pressure-using data from 35 observation wells monitored between 2004 and 2023. A total of 26 parameters were evaluated, including metal(oid)s (aluminum, arsenic, barium, chloride, fluoride, nitrite, nitrate, sulfur, cadmium, lead, copper, chromium, iron, manganese, mercury, nickel, selenium, sodium, zinc) and microbiological indicators (thermotolerant coliforms and Escherichia coli). Water quality was assessed through the groundwater quality index (GWQI), carcinogenic and non-carcinogenic risk analyses, and irrigation-related risks (sodium adsorption ratio, SAR; residual sodium carbonate, RSC). These parameters were further analyzed using a multi-criteria decision framework to identify critical points. Results showed that groundwater quality is primarily altered by water-rock interactions, while anthropogenic inputs also contribute, as evidenced by fecal indicators detected in at least one sample during monitoring. Even at minimum contaminant concentrations, 57% of the wells posed carcinogenic risks through ingestion and dermal contact pathways, being lead, nitrate, sulfide, and manganese the most critical elements identified. In contrast, groundwater was deemed suitable for irrigation, posing no significant risks to soil health. Overall, five wells were identified as critical points based on the multi-criteria analysis. Beyond anthropogenic and geological factors, climate-induced impacts may further exacerbate water quality degradation. These findings emphasize the need for integrated water resources management and targeted mitigation strategies. Moreover, this study highlights the global importance of groundwater monitoring amidst rising water demands and the intensifying effects of climate change.