Polycyclic Aromatic Hydrocarbons (PAHs) in Urban Park Dusts from Lagos, Nigeria: Pollution levels, Sources and Exposure Implications

Dust is a significant source and reservoir for polycyclic aromatic hydrocarbons (PAHs) in metropolitan areas globally. This study investigates the pollution levels, sources and exposure risks associated with PAHs in dust collected from twenty vehicle parks in Lagos, Nigeria, one of Africa's fastest-growing cities. The concentrations of PAHs in the dust samples were analysed using Gas Chromatography-Mass Spectrometry (GC-MS). The origins of the PAHs were identified through the Positive Matrix Factorization (PMF) technique and diagnostic ratios. Total PAH concentrations ranged from 4.81 to 8.48 mu g/g, with four-ring PAHs, particularly Fluoranthene (Flan), being the most prevalent, exhibiting concentrations between 0.26 and 1.33 mu g/g across the parks. Among the seven PAHs classified as carcinogenic, Benzo(k)fluoranthene from road traffic sources was identified as the most prominent, with concentrations ranging from 0.31 to 0.99 mu g/g. The PMF model revealed eight distinct sources of PAHs: biomass combustion, gasoline vehicle exhaust, coke oven emissions, lubricating oil burning, unburnt fossil fuel, diesel combustion, petrol combustion, and fugitive dust. Utilizing a probabilistic cancer risk model, the average cancer risk associated with exposure in the studied vehicle parks was calculated to be 1.27 x 10-5 for children and 1.41 x 10-5 for adults, both of which fall within acceptable risk levels. The findings of this research are essential for epidemiological studies, urban planning efforts, public awareness initiatives, and policy development in Lagos and other African cities.