Index-Based Assessment of Groundwater Vulnerability, Metal Pollution and Human Health Risk: A Case Study of Oghe Area, Southeastern Nigeria

Groundwater resources (GWR) are among the most important sources of freshwater for human populations. Assessing groundwater for pollution and protecting it from contamination is crucial, as remediation of contaminated groundwater is challenging. Given the limited freshwater resources, the presence of coal, and the heavy reliance on a few accessible sources, assessing the vulnerability and pollution status of groundwater in the Oghe area is critical. Vertical electrical sounding (VES) was conducted at 20 locations to collect field data for estimating geohydraulic parameters and generating vulnerability indices using manual and computer modeling techniques. Physicochemical analysis was carried out using the American Public Health Association standard methods (APHA) on eight groundwater samples from different locations in the study area. To assess the potential toxic elements (HM) pollution index and the health risks (HR) associated with its consumption, Atomic Absorption spectrophotometer (AA-7000 Shimadzu, Japan) was used. The VES results revealed four to five geoelectric layers, with twelve characteristic curve types with resistivity range of 59.6 Wm (VES 7) to 2445.4 Wm for the topmost (VES 1). The third and fourth layers were observed as the aquifer layers in different study locations with its resistivities varying from 135.8 Wm to 79552.1 Wm and 803.7 Wm to 14457.1 Wm respectively. The dynamic intrinsic vulnerability index classified the study area into moderate and high-vulnerability categories. The hydraulic conductivity ranged from 0.01 m/day (VES 5) to 3.968 m/day (VES 1), porosity ranged from 25.686 % (VES 5) to 31.567 % (VES 1), tortuosity values ranged from 0.284 (VES 1) to 0.301 (VES 5). The permeability values estimated in two different units ranged from 0.003 m2 (VES 5) to 1.017 m2 (VES 1) and from 21.253 mD (VES 5) to 8571.435 mD (VES 1). Physicochemical analysis showed that the groundwater is slightly acidic (pH 5.8) to slightly alkaline (pH 7.1). The metal index and Nemerow's pollution index classified the groundwater in all the locations as highly polluted (Class V). Additionally, the results of non-carcinogenic and carcinogenic risk assessments indicated high chronic health risks with in Iwollo Oghe I, Iwollo Oghe II and Amansiodo Oghe groundwater revealing a high chronic risk of the fourth level with target hazard indices of 42.943, 41.327, and 34.386 for children and 17.24, 16.591 and 13.805 for adult respectively. Children are more vulnerable due to unique behavior, higher metabolic rates, and immature detoxification systems. Elevated THI in children as observed around Neke Oghe II, suggests increased risk for neurological disorders, developmental problems, and chronic illness, as they absorb pollutants like lead up to 40% more efficiently than adults. Arsenic, which contributed the most to the THI, is known to enter groundwater through several means, especially through natural processes, though human activity accelerates its release and through coal mining. All these processes are common within the study area. These observations could be used as a signpost to the inhabitants and health professionals in formulating measures that will help to preserve the quality of groundwater in Oghe area. It is also strongly recommended that urgent steps should be taken by the relevant authorities to remediate the polluted zone.