CHARACTERIZATION AND DISTRIBUTION OF POLYNUCLEAR AROMATIC HYDROCARBONS IN WET PRECIPITATIONS, SURFACE WATERS AND SOILS FROM SOUTH-EASTERN NIGERIA

Abstract

Polynuclear aromatic hydrocarbons (PAHs), are known as persistent organic pollutants (POP) which exist in different media as contaminants in parts of the environment’s atmosphere, seawater, sediments, soils, and vegetation. PAHs have been known for their mutagenic, carcinogenic, and toxic properties to humans through the food chain. This study is aimed to characterize and investigate the distribution of PAHs in wet precipitations, surface waters, and soils from Ikot Abasi, Ibeno, and Eastern Obolo Local Government Areas of Akwa Ibom State, Nigeria. PAHs were determined in the environmental components by gas chromatography-mass spectrometry technique. Two soil and two surface water samples were taken from selected locations and wet precipitation samples were harvested on event basis from the study areas .The results reveal the presence of the following priority PAHs at different concentrations: naphthalene, (0.02-0.09 mg/L);benzo[k]fluoranthrene (0.001 -0.09 mg/L); benzo[e]pyrene (0.001-0.08 mg/L); benzo[a]pyrene (0.001 -0.09 mg/L) ; 3-methylcholanthrene (1.27-7.21 mg/L) during the rainy and dry seasons in Ikot Abasi. The concentrations of naphthalene ranges (0.02-0.06 mg/L), 3-methylcholanthrene ranges (2.40-3.65 mg/L), while other PAHs levels were below detection limits in rainwater from Ibeno in both seasons. The concentrations of naphthalene ranges (0.02-0.05 mg/L); 3-methylcholanthrene (2.30 – 5.65 mg/L), while other PAHs levels were below detection limits in rainwater from Eastern Obolo in both seasons The PAHs levels indicated were higher than the World Health Organization (WHO) acceptable limit of PAHs (0.0007 mg/L) in drinking water. The PAHs detected in the surface waters were in the order: Ikot Abasi (11.09 ±0.02 mg/L) > Eastern Obolo (3.87± 0.002 mg/L) > Ibeno (1.94 ± 0.004 mg/L), during the rainy season, while the PAHs detected in the surface waters were in the order: Ikot Abasi (13.79 ± 0.03 mg/L) > Eastern Obolo (3.95± 0.008 mg/L) > Ibeno (2.45±0.011 mg/L), during the dry season. The PAHs obtained for the soils in the three study areas during the rainy season were in the order: Eastern Obolo (776 ± 5.92 ug/kg) > Ibeno (732 ± 8.33 ug/kg) > Ikot Abasi (8 ± 0.07 ug/kg), while, during the dry season, the results were in the order: Ibeno (872±11.05 ug/kg) > Eastern Obolo (105±9.03 ug/kg) > Ikot Abasi (20 ± 1.95 ug/kg). Soils from Eastern Obolo and Ibeno have PAHs levels greater than 700 ug/kg, which is categorized as slightly polluted, with toxic equivalent concentrations (TEQ) higher than permissible limit (33 ug/kg).This may cause ecological risk and raises public health concern that should attract more attention. Molecular diagnostic ratio analyses show that the sources of PAHs in the three study area are mainly pyrogenic.