SPATIAL DISTRIBUTION AND ECOLOGICAL RISK OF PETROLEUM HYDROCARBONS AND HEAVY METALS IN THE ANAMBRA RIVER BASIN, NIGERIA
Authors/Creators
- 1. Department of Geography and Meteorology, Faculty of Environmental Sciences, Enugu State University of Science and Technology (ESUT), Enugu
- 2. Department of Agronomy and Ecological Management, Faculty of Agriculture and Natural Resource Management, Enugu State University of Science and Technology (ESUT), Enugu
Description
This study assessed the spatial distribution, seasonal dynamics, and ecological risks of petroleum hydrocarbons and heavy metals around the Anambra River near ANAR-1 crude-oil production site in the Anambra Basin, southeastern Nigeria. Soil samples (0–15 cm and 15–30 cm) and water samples (surface and groundwater) were collected during both dry and wet seasons, analyzed for Total Petroleum Hydrocarbons (TPHs), Polycyclic Aromatic Hydrocarbons (PAHs), and heavy metals (Cd, Pb, Ni, Cr, Zn, Fe, Mn, Cu), and integrated with geostatistical and GIS models. Ordinary kriging and Getis-Ord Gi* hotspot analyses revealed statistically significant (p < 0.01) contamination clusters, with severe hotspots occurring within 0–200 m of the location of the crude oil transportation barges extending downstream along the Anambra River corridor. Although concentrations attenuated with distance, they remained above FEPA/WHO limits up to 1000 m, indicating persistent pollutant diffusion into agricultural and residential zones. Ecological Risk Assessment (ERA) using contamination factor (CF), pollution load index (PLI), and potential ecological risk index (RI/PERI) highlighted cadmium (Cd) and lead (Pb) as the most critical contaminants. Cd consistently presented extremely high risk (Eᵣᵢ > 320; RI > 600 in near-point source soils during wet season), while Pb contributed considerable ecological risks (Eᵣᵢ = 80–160). Composite RI values classified near-field soils and waters as “very high risk zones.” Seasonal analysis confirmed that rainfall-driven runoff, infiltration, and vertical leaching amplified contamination footprints, with wet-season concentrations and risks consistently higher than those in the dry season. The findings demonstrate that inland basins such as Anambra, though less studied than the Niger Delta, are highly vulnerable to petroleum-related contamination. They also highlight the effectiveness of integrating GIS and geostatistics with ERA metrics as early-warning tools for environmental monitoring and targeted remediation. The study provides vital baseline data for policy interventions, ecological risk management, and community health protection in Nigeria’s emerging inland oilfields