Oil-Derived Polycyclic Aromatic Hydrocarbons and Total Petroleum Hydrocarbons in Surface Water of Okpare Olomu River, Niger Delta: Contamination Levels and Risk Evaluation

Abstract

This study investigates the contamination of surface water in the Okpare Olomu River, an oil-producing region in the Niger Delta, Nigeria, focusing on polycyclic aromatic hydrocarbons (PAHs) and total petroleum hydrocarbons (TPHs). Surface water samples from four stations were analyzed using gas chromatography. Sixteen priority PAHs were detected, with total concentrations ranging from 1006.19 µg/L at Station 1 to 2022.26 µg/L at Station 3, indicating a predominantly petrogenic origin. Twenty-eight TPH compounds were identified, with total concentrations ranging from 1914.31 to 5621.50 µg/L. Station 4 exhibited the highest TPH levels, followed by Stations 2, 1, and 3. Concentrations exceeded Nigerian and international guideline limits by several orders of magnitude, with WHO’s 10 µg/L guideline for drinking water surpassed by over 500-fold at some stations. Diagnostic ratios and the presence of low molecular weight hydrocarbons suggested crude oil–related inputs alongside evidence of weathering and partial biodegradation. Statistical analyses, including ANOVA and multivariate methods, confirmed significant spatial variation and a strong positive association between PAHs and TPHs, reflecting common pollutant sources. The contamination levels pose serious ecological risks to aquatic biota and potential human health hazards through water and food chain exposure. These findings align with earlier reports of petroleum hydrocarbon pollution in the Niger Delta but highlight even higher contamination levels in this locality. The study underscores the urgent need for remediation, continuous monitoring, and stricter enforcement of environmental regulations to protect the ecosystem and dependent communities Keywords: Total Petroleum Hydrocarbons (TPH), Polycyclic Aromatic Hydrocarbons (PAHs), Oil Pollution, Okpare Olomu River, Ecological Risk Assessment, Niger Delta