Assessment of groundwater contamination using Duncan multiple range test and associated descriptive techniques in selected local government areas of Oyo State South-West Nigeria

Groundwater is a major source of fresh water for the global population and is used for domestic, agricultural, and industrial uses. This study assessed the various Groundwater contaminations in selected local government areas of Ibadan Oyo State. Water samples were collected from 10 wells per location (50 wells in total) and insitu measurement of pH, Temperature, Electrical Conductivity (EC), and Total dissolved solids (TDS) were determined using a Hanna Combo Tester. Two bottles were each filled with water from the well, notably samples for the Cations analysis were acidified by adding a drop of Nitric acid (HNO3) in a sample in order to bring down the pH of the water and ensure that the metals are inert prior to analysis. The second samples for Anions test were labeled accordingly. The two water quality parameters analyzed were physical parameters, and chemical parameters. The concentration of Sodium and Potassium in water sample was determined using a flame photometer calibrated using the standard stock solution of sodium and potassium having a 30ppm concentration. Anion-selective electrode which is the most cost-effective, efficient and reliable analytical method for determination of the fluoride level was used for the water samples. Data for physical parameters in water samples were subjected to Analysis of variance (ANOVA) and Duncan multiple range test (DMRT) to evaluate the significance level. The result showed that mean pH concentration ranged from 4.7±0.15 to 8.9±0.21b, Temperature, 26.7℃±3.06c to 30.9℃±1.63b, TDS, 119±0.58a to 599.7±9.07g (mg/L), EC 15.6±0.51a to 82±2.0f (μS/cm). Significant variations (p≤0.05) were observed in the water concentrations sampled across the study area. The mean concentration of pH, EC, TDS and temperature were within the 2021 World Health Organization permissible limits. Quantitative analysis was carried out on the samples to determine Cations and Anions concentrations in the water samples. The concentration of the cations (Na+, K+ Ca2+ and Mg2+) and Anions (HCO3−, SO42-, Cl−, F-, NO3-) varied across the water sample with most samples having concentrations that were within the World Health Organization WHO maximum permissible limit. Most water samples fall within WHO permissible limit for drinking water except Oja-Oba samples whose cations and anions levels were significantly high, and therefore, most unsuitable for drinking purposes and consequently recommended for comprehensive treatment.