Insight into the metropolitan levels, spatial distribution and health risks of polycyclic aromatic hydrocarbons in roadside soil of Ibadan, Nigeria

This study examined the distribution, sources, levels and health risk assessment of polycyclic aromatic hydrocarbons (PAHs) in roadside soil of Ibadan metropolis. Six locations were chosen based on heavy traffic density, industrial activities and low traffic density. Samples were collected at five different spots at each location on monthly basis for the period six month covering the two seasons. The concentrations of PAHs in roadside soil were analysed using Gas Chromatography–Flame Ionization Detector. The PAHs ranged from 0.54 mg/kg to 1156 mg/kg. The PAHs were more predominant in roads with heavy traffic density. The total concentration of the 16 PAHs ranged from 232 mg/kg to 990 mg/kg. The distribution of PAHs ring size is in the order 6 ring > 5 ring > 4 ring > 3 ring > 2 ring. Among the PAHs compounds, Benzo(g,h,i)perylene was predominant. Carcinogenic fraction of PAHs represent 81.1% of the total PAHs. The total concentration of carcinogenic PAHs ranged from 196 mg/kg to 728 mg/kg. Benzo(a)pyrene was found in all the locations ranging from 26.0 to 46.0 mg/kg. The monthly increasing order of Σ 16 PAHs is November > June > July > August > December > January. Lower molecular weight (LMW) PAHs were more abundant in dry season than wet season while higher molecular weight (HMW) PAHs were more abundant in wet season than dry season. The source diagnostic ratios analysis indicated the PAHs are more of pyrogenic source. Cancer health risk assessment of PAHs showed that children of the study area are more vulnerable to cancer than adult. The study revealed increasing accumulation of carcinogenic PAHs in roadside soil in Ibadan metropolis.