Surface Water Quality in a Rapidly Urbanizing Region of Southwest Nigeria: Hydrogeochemical Characterization, Trace Metal Pollution, Irrigation Suitability, and Ecohealth Risk Evaluation

This study presents a comprehensive hydrogeochemical characterization and human-ecological risk assessment of trace metals in surface waters of Ondo Town, Nigeria. Surface water samples (n=20) were analyzed for physicochemical parameters and trace metals (Fe, Pb, Cu, Cr, Mn, Zn, Ni, Co, Cd) using atomic absorption spectrophotometry (AAS). Hydrogeochemical analysis revealed Ca-Mg-HCO₃ as the dominant water type, indicating silicate weathering and ion exchange as key processes controlling water chemistry. However, anthropogenic influences were evident, with elevated concentrations of Fe (0.12–7.54 mg/L), Pb (0.01–0.99 mg/L), Cr (0.01–0.13 mg/L), and Cd (0.002–0.004 mg/L) exceeding WHO permissible limits in several samples. Multivariate statistical analyses (PCA, HCA) identified geogenic weathering, agricultural runoff, and industrial effluents as major contamination sources. Pollution indices (CF, CD, PLI, MI, NPI) indicated moderate to very high contamination, particularly for Fe, Pb, and Cd. The Water Quality Index (WQI) classified 25% of samples as "excellent," 20% as "good," 20% as "poor," 20% as "very poor," and 15% as "unsuitable" for drinking. Ecological risk assessment (PERI) highlighted considerable risks from Fe (Eᵣ = 36.82), Pb (Eᵣ = 26.46), and Cd (Eᵣ = 68.70), posing threats to aquatic ecosystems. Health risk assessment revealed higher non-carcinogenic risks (HQ > 1) for children due to Pb and Co exposure, while carcinogenic risks from Cd and Cr were significant for adults. The study underscores the need for urgent remediation, stricter industrial regulations, and community awareness programs to mitigate contamination. Recommendations include water treatment interventions, sustainable agricultural practices, and long-term monitoring to safeguard public health and aquatic biodiversity in the region.