Groundwater contamination and health risks near waste dumps and mechanic workshops: A seasonal perspective

Background: Groundwater is an essential source of drinking and domestic water in most developing countries. In the absence of an effective public water supply, residents often drill boreholes and use groundwater without adhering to standards set by the World Health Organization (WHO) and the Nigerian Standard for Drinking Water Quality (NSDWQ). Objective: This study assessed the health impacts of groundwater quality in Aba, Abia State, Nigeria, focusing on areas near waste disposal sites and mechanic workshops. Methods: Water samples were collected from ten boreholes during the dry and rainy seasons, and analyzed for physicochemical properties and heavy metal concentrations using standard methods. The Water Quality Index (WQI), pollution indicators, and health risk assessment were calculated. Results: All sampling sites showed acidic pH levels, ranging from 3.42 to 6.1 during the rainy season and 4.72–6.28 in the dry season. Temperatures ranged from 31.8°C to 32.8°C in the dry season which was above the WHO recommended standard, and 28°C in the dry season, which falls within permissible limits. Elevated concentrations of biochemical oxygen demand (BOD) (61.8 mg/L and 86.8 mg/L), chemical oxygen demand (COD) (136.5 mg/L and 73.9 mg/L), and dissolved oxygen (DO) (18.9 mg/L and 12.8 mg/L) were detected across all samples during both seasons, exceeding WHO drinking water guidelines. However, total dissolved solids (TDS), chloride (Cl⁻), nitrate (NO₃⁻), and magnesium (Mg²⁺) levels were below recommended limits in both seasons. Heavy metals such as cadmium and chromium showed concentrations ranging from 0.047 to 0.109 ppm and 0.04–0.078 ppm, respectively, in the dry season, and from 0.04 ppm to 0.078 ppm and 0.00–0.023 ppm in the rainy season, these values exceeded WHO standards. The calculated water quality index (WQI) ranged from 239.61 to 581.33 in the dry season and 156.15–464.60 in the rainy season, indicating that all samples were unsuitable for drinking. The ecological risk index for cadmium classified all sites as posing a very high ecological risk during both seasons, while Cr, Zn, Pb, Fe, and Cu presented low ecological risks across all sites. Despite low pollution load indices, health risk assessments revealed hazard quotients and indices exceeding 1 for both adults and children, indicating significant non-carcinogenic risks. Carcinogenic risk values for chromium and lead also exceeded acceptable limits (10⁻⁶ and 10⁻⁴, respectively). Cadmium contamination was primarily ascribed to anthropogenic sources, while zinc was linked to natural lithogenic origins. Conclusion: Groundwater quality in the study area presents a serious threat to public health and is currently unsuitable for consumption. Immediate intervention is required to ensure the safety of water used for drinking and domestic purposes. This includes the implementation of appropriate water treatment technologies at the point of use and the enforcement of stricter regulations governing the siting and construction of boreholes, particularly near pollution-prone areas.