Polycyclic aromatic hydrocarbons (PAHs) in surface sediments near a mining site in Okobo-Enjema, Nigeria: concentrations, source apportionment and risk assessment.

PAHs are pollutants of serious environmental and human health concerns. PAH studies in environmental compartments may assist in designing PAH control measures. The levels of selected PAHs in surface sediment samples of a stream near a mining site at Okobo-Enjema, Nigeria, were investigated. The data were used to determine the possible sources of the PAHs and to assess the potential health risk of the PAHs to humans which was evaluated based on the sediment quality, contamination level and cancer risk guidelines. Sediment samples were collected in replicates at various locations in the stream. A mixture of acetone, dichloromethane and n-hexane was used to extract the PAH compounds by sonication. The extracts were cleaned-up, concentrated and quantitatively analyzed using gas chromatography-mass spectrometry. The results indicated 14, 10 and 4 out of the 16 target PAHs were detected at various sampling stations. The total concentrations of the PAHs ranged from 0.09 to 1.2 mg/kg dry weight. High molecular weight PAHs dominated over the low molecular weight compounds at distances nearer to the coal mine. The PAH contamination came from pyrogenic and petrogenic sources. The results suggested that there was no eco-toxicological risk for organisms in the sediments beyond 400 m from the coal mine. The sediments were highly contaminated at ≤400 m from the coal mine; moderately contaminated at between 400 and 500 m from the mine; and lowly contaminated at beyond 500 m from the mine. The cancer risk is low on ingestion and skin contact with the sediments.