Hydrogeochemical assessment of groundwater in Iwo, Ikonifin and Ife-Odan, Osun and Oyo states, Southwest Nigeria

Hydrogeochemical assessment of groundwater in some communities (Iwo, Ikonifin and Ife-odan) of Southwest Nigeria was carried out. The physicochemical parameters determined include pH, temperature, redox potential (Eh), electrical conductivity and depth of wells. The concentration of heavy metals was determined using Bulk Scientific model of atomic absorption spectrophotometer. Flame photometer was used to determine Na and K, while titration method was used to determine Mg and Ca. The obtained results indicate that the majority of the sampled wells were deep (>16 m) and the values of redox potentials (EH) recorded were mainly positive with the exception of a few. Most parameters were within the WHO-recommended limits in drinking water. DO was significantly higher at Ife-Odan with values of 4.96 ± 0.34 mgL⁻¹, while wells from Ikonifin were significantly deeper than others. The PO₄ ³⁻ and SO₄ ²⁻concentrations were significantly high, both in Ife-Odan and Iwo, which was attributed to possible runoff from diffuse sources (wastes). The piper diagram showed that the dominant cations were Na⁺ and K⁺, while the dominant anions were CO₃ ²⁻ and HCO₃ ²⁻, suggesting that the major ions are from water–rock interactions. The concentration of lead (Pb) was found to be higher than the recommended WHO limit of 0.05 mgL⁻¹ in drinking water from most (80 %) of the samples. Significantly (P < 0.05) high Pb concentration values were recorded from Ife-Odan (0.53 ± 0.04 mgL⁻¹) and Ikonifin (0.6 ± 0.06 mgL⁻¹). The cadmium (Cd) concentration was found to be slightly higher than 0.003 mgL⁻¹, theWHO-recommended limit for all locations.