Water integrity, ecological profiling, and health risk quantification of hand-dug wells in the Oghara-sub-Saharan Ecozone

Water is essential for human physiological and socio-economic activities; however, increasing dependence on hand-dug wells (HDWs) for domestic water supply in the Oghara-Sub-Saharan Ecozone raises concerns regarding water integrity, ecological quality, and potential human health risks. This study assessed the physicochemical characteristics, heavy metal contamination, pollution status, and associated health risks of groundwater from HDWs in Oghara, Ethiope West Local Government Area, Delta State, Nigeria. Groundwater samples were collected from nine HDWs used for domestic purposes over 3 months using standard procedures. Water quality variables analysed included pH, dissolved oxygen, biochemical oxygen demand (BOD 5 ), total dissolved solids, total suspended solids, phosphate, nitrate, chloride, sulphate, zinc, iron, manganese, lead, bicarbonate, and sodium. Heavy metal contamination and groundwater quality were evaluated using the Water Quality Index (WQI), Modified Water Quality Index (MWQI), Pollution Index of Groundwater (PIG), Nemerow Integrated Pollution Index (NIPI), Quantification of Contamination (QoC), Contamination Degree (CD), and Contamination Factor (CF). Human health risks associated with heavy metal exposure were also assessed. All physicochemical parameters differed significantly among sampling stations ( P < 0.05 ). WQI values were high at Stations 1 and 4–9, exceeding recommended standards. The PIG identified Station 1 as being strongly influenced by Zn, Fe, and Pb contamination, whereas elevated NIPI values at Stations 4, 5, 6, and 9 were mainly associated with Mn. Contamination levels fluctuated considerably among stations, with CF indicating high contamination at Stations 2–9 and low contamination at Station 1. QoC results suggested that heavy metals originated from both geogenic and anthropogenic sources. Non-carcinogenic risk estimates were below acceptable thresholds, indicating no significant non-carcinogenic health risk. However, the carcinogenic risk associated with Pb suggested potential health concerns from prolonged consumption. Overall, groundwater quality varied substantially across the study area. Improved control of anthropogenic activities, particularly indiscriminate agricultural chemical use, and further microbiological investigations are recommended to safeguard public health.