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This study examines the hydrogeochemical and heavy metal parameters of groundwater in Ojo District to determine its suitability for use, potential sources, and human health implications. Ten groundwater samples were assessed, and hydrogeochemical modelling was performed via the Aquachem software. The chemical ions were in the following order: EC > (107.78–448.65 μS/cm) > TDS (182.02–320.77 mg/l) > TH (46.22–182.45 mg/l) > pH (5.55–6.35); HCO3− (64.13–125.82 mg/l) > Na+ (36.87–96.49 mg/l) > Ca2+ (47.65–58.88 mg/l) > SO42− (19.94–53.67) > NO3− (15.55–44.25 mg/l) > Cl− (20.43–27.16 mg/l) > Mg2+ (11.09–16.87 mg/l) and K+ (2.55–7.86 mg/l). The concentrations of heavy metals in groundwater were in the range of: Fe (0.11–0.27 mg/l) > Mn (0.003–0.16 mg/l) > Ni (0.05–0.12 mg/l) > Zn (0.003–0.05 mg/l) > Pb (0.001–0.03 mg/l) > As (0.001–0.005 mg/l) > Cr (0.002–0.005 mg/l) > Cd (0.001–0.003 mg/l) and Cu (0.001–0.0002 mg/l), with Pb, Mn, and Ni exceeding their allowable limits. The Schoeller and Gibbs plots revealed that the major mechanisms controlling the aquifer groundwater in Ojo region are geological rock weathering and mineralization, with a minimal influence of saltwater intrusion. The piper trilinear diagram also revealed that none of the cation was dominant while the anions were strongly dominated by HCO3− (weak acids). The hydrogeochemical facies which describes the geochemical characteristics of the groundwater were classified into 3 types; “Ca2+–Mg+–HCO3– (65 %)”, “mixing zones (30 %)”, and “Na+–K+–Cl––HCO3– (5 %)”. The hydrogeochemical modelling revealed that the groundwater is characterized by forward cation exchange, while rock–water interactions (silicate dissolution) were heavily involved in the geochemical processes. The single pollution index showed that Pb, Ni, and Mn contributed significantly to contamination, and the multi–pollution indices showed that the groundwater was slightly-moderately polluted. The integrated groundwater quality index revealed that only 10 % were clean, 50 % were poor or moderately unclean, 30 % were highly unclean, and only 10 % were extremely unclean (unfit for utilization). The water pollution index showed that 70 % of the groundwater was good. The irrigation indices suggest that the groundwater would enhance soil quality and support plant growth. Multivariate analysis revealed that the groundwater is being influenced by geogenic factors and anthropogenic activities. The health risk assessment (Hazard Quotient and Hazard Index) showed that exposure of adults to the investigated groundwaters could result in noncarcinogenic adverse effects. The cancer risk values also exceeded the minimum limit (1.0 x 10−6) and thresholds (1.0 x 10−4) for adults, indicating the carcinogenic potential of the groundwater.

Background: Lagos and Ologe Lagoons are parts of the Lagos Lagoon Complex, which provide fish as an animal protein source to the locals. However, these fish species have a high propensity to accumulate pollutants including Potentially Toxic Elements (PTEs) from their environment. This potentially constitutes a health risk to fish consumers. Therefore, this study investigated concentrations of some PTEs (As, Cd, Cr, Cu, Fe, Pb, Ni, and Zn) in water, sediment, and fish (Sarotherodon melanotheron) from Lagos and Ologe Lagoons, the ecological and health risks associated with the consumption of the fish as well as the likely sources of the PTEs. Methods: Water, sediment, and fish (S. melanotheron) samples were collected monthly for ten months (June 2022 - March 2023) from three sites: Badore and Baiyeku in Lagos Lagoon and Ologe Lagoon. The concentration of PTEs was determined in the environmental matrices {water, sediment, and three organs (gill, muscle, liver)}. The range of values for method detection limits (MDL), limits of detection (LOD), limits of quantitation (LOQ), and recovery rates were 0.01 – 0.025 mg kg−1, 0.00002 – 0.002 mg L−1, 0.0001 – 0.0067 mg L−1 and 97.19±2.45 - 99.85±1.16% respectively. The ecological risk of PTE in water and sediment was assessed by various indices. Estimated dietary intake (EDI), health risk index (HRI), and target hazard quotient (THQ) were the human health risk assessment indices employed. The distribution and source of the PTEs were analyzed using the coefficient of variation, Pearson's correlation matrix, principal components analysis, and hierarchical cluster analysis. Results: The water and sediment quality assessment indices indicated that the water and sediment from the lagoons had low contamination with respect to the eight PTEs studied. EDI values were generally less than 1 except for Fe and Zn. THQ for all PTEs in the three sampling stations and across the different population groups was less than 1 except for Fe. PCA revealed two major sources of PTE pollution which are natural and anthropogenic. As, Cd, Cr, Cu, and Pb were probably due to anthropogenic inputs like agricultural operations and industrial activities while Fe, Ni, and Zn may have occurred due to lithological sources like rock weathering and volcanic events. Conclusion: Based on the result of the study, the waters from the lagoons are still suitable for agricultural usage. The sediments are also largely uncontaminated with respect to the eight PTEs studied. The EDI and THQ show that consumption of S. melanotheron from the sites may not constitute any significant health risk to humans and the sources of the PTEs are lithologic and anthropogenic.