Distribution Behaviour of Polycyclic Aromatic Hydroarbons in Roadside Soil at Traffic Intercepts within Onitsha Metropolis, South-East Nigeria

Abstract

Polycyclic aromatic hydrocarbons (PAHs) pollution in roadside soil was conducted in a developing city environment of South-Eastern Nigeria during raining season to ascertain the contamination levels and their distribution behavior in soil. The concentration of polycyclic aromatic hydrocarbons was determined at nine locations of Onitsha city, 3m distances from roadside in soil covering all the major traffic intercepts within the city. The samples were extracted in acetone and dichloromethane (1:1) using soxhlet extraction. The total concentrations of 16 PAHs ranged from 14,260 to 14,289 µg/kg, with a mean of 14,276 µg/kg which were than the limit <10000 µg/kg set for PAHs in the soil and the seven possible carcinogenic PAHs accounted for 17.2 % of 16PAHs detected. Chrysene was the polycyclic aromatic hydrocarbons found in highest concentration at all the intercepts ranging between 4050 to 4053 µg/kg with the mean of 4052 µg/kg. Among different functional areas, the higher level of PAHs was found in Obosi junction (right) followed by Main market road junction (right). The composition of PAHs was characterized by the high molecular weight PAHs, among which fluoranthene, Indeno(1,2,3,-cd)Pyrene, Acenaphthene chrysene were most dominant components. A principal component analysis and PAHs isomeric ratios indicate that PAHs in Onitsha road soil mainly originated from combustion. The toxic assessment suggested that soil PAHs exposure is medium carcinogenic at present level.

Keywords: polycyclic aromatic hydrocarbons, Gas chromatography, season, traffic density, pollutants, principal component analysis, samples, concentration, carcinogenic.