Post-Remediation Evaluation of Heavy Metals and Hydrocarbon Interactions in the Olero-Abiteye Oil Spill Corridor, Niger Delta

This study presents a post-remediation assessment of soil quality at the Olero-Abiteye oil spill corridor in the Niger Delta, following intervention via evacuation and Enhanced Natural Attenuation (ENA) techniques. The investigation evaluates the persistence and interactions of Total Petroleum Hydrocarbons (TPH) and heavy metals across two soil depths (0 - 15 cm and 15 - 30 cm) and two seasons (wet and dry), in comparison with control samples. Results indicate that TPH concentrations remain significantly elevated across all sampled horizons, with dry season surface soils recording 3945.14 ± 1342.22 mg/kg—well above the EGASPIN intervention threshold of 500 mg/kg. Heavy metals, notably copper (Cu), also exceeded permissible limits in all depths and seasons, with Risk Quotients (RQ) consistently greater than 1.0. Multivariate analyses reveal strong correlations (r > 0.75, p < 0.01) between TPH, Cu, Pb, and Total Organic Content (TOC), suggesting synergistic sorption mechanisms that hinder contaminant mobility but also prolong environmental persistence. Principal Component Analysis (PCA) and Hierarchical Cluster Analysis (HCA) further highlight the seasonal and depth-based stratification of pollutants, driven by hydrological and physicochemical dynamics. These findings demonstrate that current remediation methods, while partially effective, fall short of fully restoring ecological integrity, particularly within organic-rich surface soils. The study underscores the need for integrated, depth-targeted, and seasonally adaptive remediation strategies to address the coupled behaviour of hydrocarbons and heavy metals in tropical oil-impacted landscapes. Post-remediation monitoring and enhanced contaminant-specific interventions are recommended to ensure sustainable recovery and land reuse.