Bioavailability of polycyclic aromatic hydrocarbons (PAHs) and Environmental Risk (ER) Assessment: The case of the Ogbese river, Nigeria

Pollution from PAHs in porewater and surficial sediments of the rapidly contaminated Ogbese River, Ondo State, Nigeria was investigated. Samples were extracted using Hexane/methylene chloride mixture and the complex PAH mixtures were analyzed by gas chromatography-mass spectrometry. There was greater influence of sediment fine particles (R2=0.978) in partitioning of PAHs over other factors. Total concentration of PAHs in the sediments and porewater ranged 14.45 μg g−1 to 26.78 μg g−1 (n=8, dry weight) and 6.25 μg L−1 to 13.93 μg L−1 (n=8) respectively. The measured partition coefficients (i.e., Koc values) of the individual PAHs between sediment organic matter (SOM) and porewater across all locations ranged from 5.027 (±0.157 SD) to 5.074 (±0.169 SD). The correlation in log Koc (observed vs predicted) for high molecular weight/low molecular weight-PAHs suggests variability in specific interactions and unequal partition efficiencies with SOM under natural condition. Based on equilibrium partitioning and narcosis model, three PAHs {benzo(b)fluoranthene, benzo(a)pyrene and dibenz(a,h)anthracene }has toxic unit (TU) values of concern. These results represent a baseline report for future monitoring programs of PAHs.