Assessment of Health Risks Associated with Potentially Toxic Elements in Groundwater Sources within a Petroleum Depot-hosting Community in Ibadan, Oyo State, Nigeria

Abstract

Groundwater is the main source of drinking water for residents of Adebisi Layout in Apata, Ibadan, Oyo State, Nigeria. However, the proximity of the Nigeria National Petroleum Corporation (NNPC) Depot to residential areas raises concerns about potential contamination of this critical resource. This study evaluated the physicochemical characteristics and concentrations of potentially toxic elements (PTEs)—cadmium (Cd), chromium (Cr), nickel (Ni), lead (Pb), and zinc (Zn)—in groundwater samples collected from ten locations within the community. Analytical methodologies included Atomic Absorption Spectrometry (AAS) for PTE quantification and standardized procedures for physicochemical assessments. The measured physicochemical parameters exhibited the following ranges: Total Dissolved Solids (TDS: 0.99–1.60 mg L⁻¹), Dissolved Oxygen (DO: 1.05–1.65 mg L⁻¹), pH (6.64–7.38), and temperature (27.2–29.2 °C). Heavy metal concentrations varied significantly, with Cd (0.04–0.18 mg L⁻¹) and Cr (ND - 0.03 mg L⁻¹) exceeding permissible limits in several samples, while Zn (ND–0.04 mg L⁻¹) and Ni (ND–0.16 mg L⁻¹) were detected at lower levels. Lead (Pb) concentrations remained below the instrument’s detection threshold. The elemental distribution followed a descending order of Cd > Ni > Zn > Cr, suggesting Cd as the dominant contaminant. Health risk assessments were conducted to evaluate carcinogenic and non-carcinogenic hazards associated with groundwater consumption. Carcinogenic risk analysis indicated no significant cancer threat within the study area. However, non-carcinogenic risk evaluations, expressed through hazard quotients (HQ), revealed elevated health risks for the local population, particularly from Cd exposure. The hazard index (HI) values exceeded the acceptable threshold (HI > 1), underscoring the urgency for mitigation strategies. These findings highlight the need for continuous monitoring and public health interventions to safeguard groundwater quality in petroleum depot-host communities.