Levels of Polycyclic Aromatic Hydrocarbons in Soils of Ibeno, Nigeria; Distribution, Sources and Potential Risk

Abstract

The contamination of PAHs in soils may result in accumulation in the food chain, leading to potential health risks. This study was designed to determine the levels of PAHs in soils of Ibeno, Nigeria and evaluate their potential ecological and health risks. Soil samples were collected at Ukpenekang, Mkpanak, and Iwuchang districts of Ibeno and analysed for eighteen PAHs using gas chromatography- mass spectrometry. Carcinogenic and ecological risk assessments were performed using USEPA models. The total concentration of the 18 PAHs ranged from 10.3 to 276.6 µg/kg with a mean value of  71.9 µg/kg in Ukpenekang; 9.3 to 176.5µg/kg with a mean value of 58.7 µg/kg in Mkpanak and 11.4 to 179µg/kg with a mean value of 71.4 µg/kg in Iwuchang. The total PAHs in the soils were higher than guideline values for agricultural soils. The higher molecular weight (HMW) compound which constitute the 4 to 6-ring, were the most abundant components of the soil with percentage composition of 58.2 – 65.5%. The diagnostic ratios show fuel combustion as the source of PAH in the area, predominantly from gas flaring and venting in the area. The soils are potentially carcinogenic with total carcinogenic toxic equivalency factors (BaPeq) values ranging from 103.05 to 148.8µg/kg-Bapeq dry weight. Ecotoxicity studies revealed minimal effect of PAH on soil functions, with mean effects range median quotient (m-ERM-q ) values ranging from 0.06 to 0.08. Continuous environmental monitoring, total elimination or improvement in the efficiency of gas flaring system used by oil prospecting companies can reduce the risks associated with these hazardous compounds.