Concentrations and health risk assessment of Polycyclic aromatic hydrocarbons in Soils of an urban environment in the Niger Delta, Nigeria

The concentrations and compositional patterns of the United States Environmental Protection Agency (US EPA) 16 priority polycyclic aromatic hydrocarbons (PAHs) were determined in surface soils of an urban environment in the Niger Delta of Nigeria with a view to providing information on the sources, extent of contamination and human health risks of PAHs in these soils. The analyses were performed by means of gas chromatography-mass spectrometry (GC-MS) after extraction of the soils with hexane/dichloromethane and clean-up of the extracts. The concentration of Σ16 PAHs in the urban soils ranged from 188 to 684 µg kg−1, while the ΣPAH7c (carcinogenic PAHs) ranged from 28.5 and 571 µg kg−1. The estimated carcinogenic and mutagenic potency factors for these sites ranged from 2.34 to 197 and 9.66 to 195 µg kg−1 respectively. The composition of PAHs in these soils follows the order: 5-rings>4-rings>3-rings>6-rings>2-rings, and higher molecular weight PAHs accounted for a significant proportion of the Σ16 PAH concentration in this study. The results indicated that there is a high potential risk of cancer development as a result of exposure of PAHs via ingestion, dermal contact and inhalation. The diagnostic ratios indicate that the PAHs in these soils originated mainly from pyrogenic processes, such as combustion of petroleum, fossil fuels and biomass such as woods, charcoal straw and grasses. The results of this study provided information on the concentrations and compositional patterns of PAHs, which is useful in understanding the effects, sources, fate and transport of PAHs in soils, as well as environmental quality management and environmental forensic studies.