Sources, Toxicity, Health and Ecological Risks of Polycyclic Aromatic Hydrocarbons (PAHs) in the Sediment of an Osogbo Tourist River

This study investigated twenty-three polycyclic aromatic hydrocarbons (PAHs) in the sediment of Osun River, spanning through both the peri-urban and urban areas of the river, to estimating their sources, ecological and health hazards. The sampling locations covered those beside major roads and agricultural farms. They were analyzed by gas chromatography-mass spectrometry. The concentrations of the PAHs ranged 88-1900 ng/g (average, 731 ng/g) with the predominance (56%) of benzo(e)pyrene (BeP). Though the PAHs had a similar trend of distribution in the sediment at both peri-urban and urban portions, total PAHs concentration at the peri-urban area was three times higher than that obtained in the urban area of the river due to relatively lower photo-degradation process caused by the thick rain forest in the area. Pyrolytic processes such as coal/wood burnings and emissions from gasoline and diesel engines were the PAHs sources. No dermal carcinogenic or non-carcinogenic health concerns were posed by the individual PAH; cancer risk and hazard quotient values were <10(-6) and <1.0, respectively. The sediment PAHs posed a low ecological risk in all the sampling locations as the mean effects range-median quotient of the individual USEPA priority PAHs was <= 0.04. The potential environmental toxicity of the priority PAHs showed that benzo(a)pyrene (BaP) and indeno[1,2,3-cd]pyrene (IDcdP) dominated, accounting for 37% and 44% of the total toxicity, respectively. The low health and ecological risks posed by the PAHs sediment became significant given the number of tourists Osun River attracts annually festival, as well as the effects on the river ecosystem.