Concentration and Risk Evaluation of Polycyclic Aromatic Hydrocarbons in Soils from the Vicinity of Selected Petrol Stations in Kogi State-Nigeria

Abstract

Polycyclic aromatic hydrocarbons (PAHs) are highly teratogenic, persistent, carcinogenic, and ubiquitous environmental contaminants. They present potential threats to the ecological environment and human health. Nine composite soil samples (three from each town) were collected at a depth of 0 – 30 cm using soil auger from the vicinity of selected petrol handling facilities (petrol stations) within three major towns in Kogi State-Nigeria, between September and October, 2020. The samples were analyzed for concentrations, distribution, sources and toxic potentials of emission of 16 USEPA priority polycyclic aromatic hydrocarbons (PAHs), since no such comprehensive study had been conducted in the area. The total concentrations of PAHs (∑PAHs) in soil samples from the vicinity of nine petrol stations within three major towns in Kogi State-Nigeria ranged from 2.66 to 5.64 μg/kg at Ankpa, 1.58 to 7.58 μg/ kg at Anyigba and 3.72 to 4.98 μg/kg at Idah, with an average of 4.03 μg/kg. Lower molecular weight PAHs (2 - 3 ring PAHs) dominated the PAH profiles, accounting for 69.2% of total PAH mass. The levels of individual PAHs in all the soil samples were below the Dutch maximum permissible concentration (MPC) for urban residential and agricultural soils. The average benzo[a]pyrene equivalent concentration (BaPeq) of the detected PAHs in the study area was 0.245 μg/kg, indicating a relatively low toxicity and carcinogenic potential. Diagnostic ratios of the results showed that PAHs in surface soil samples from the study area were of mixed origin (petrogenic and pyrolytic sources). The Pearson product moment correlation (PPMC) coefficient (r) explored the correlation between the environmental properties and the occurrence of PAHs. Among the physicochemical parameters studied, organic carbon and soil organic matter showed high positive correlation with PAHs concentration. When compared with the Maximum Permissible Concentrations for soil, statistical test at P < 0.05 revealed that the difference in PAHs concentrations is not significant. This is an indication that filling station soils in the study area within the period of investigation was safe. However, strict adherence to Department of Petroleum Resources (DPR) guidelines is highly recommended in siting and operating petrol handling facilities to further mitigate the presence of these pollutants.