Regional Studies in Marine Science 9 (2017) 9–16 Contents lists available at ScienceDirect Regional Studies in Marine Science journal homepage: www.elsevier.com/locate/rsma Bioavailability of polycyclic aromatic hydrocarbons (PAHs) and Environmental Risk (ER) Assessment: The case of the Ogbese river, Nigeria Isaac Ayodele Ololade a,* , Busayo Olubamise Adetiba a , Francis Femi Oloye a,b , Oluwaranti Olubunmi Ololade c , Nurudeen Abiola Oladoja a,d , Samuel Babatunde Obadawo a , Mayowa Monday Anifowose a , Thompson A. Akinnifesi a , Daniel Akerele a , Adenike Bosede Alabi c , Adedapo Oluwasanu Adeola a a Department of Chemical Sciences, Adekunle Ajasin University, PMB 001, Akungba-Akoko, Ondo-State, Nigeria b Chemistry Department, University of Aberdeen, Scotland, UK c Federal University of Technology, Akure, Nigeria d Institute of Water Quality Control, Technical University Munich, Gerching, Munich, Germany highlights • Greater influence of sediment clay particles in partitioning of PAHs over other factors. • High molecular weight PAHs were more sensitive to the OC changes than low molecular weight PAHs. • Variability in specific interactions and unequal partition efficiencies with sediment organic matter under natural condition. • Partition effect of PAHs with SOM increases more rapidly with increasing molecular weight. • Natural organic matter is an important sedimentary hydrophobic domain in PAH assessment. article info Article history: Received 18 July 2016 Received in revised form 19 September 2016 Accepted 9 November 2016 Available online 12 November 2016 Keywords: PAHs Sediment Pore water Soil organic carbon Partitioning abstract 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 (R 2 = 0.978) in partitioning of PAHs over other factors. Total concentration of PAHs in the sediments and porewater ranged 14.45 μgg -1 to 26.78 μgg -1 (n = 8, dry weight) and 6.25 μgL -1 to 13.93 μgL -1 (n = 8) respectively. The measured partition coefficients (i.e., K oc 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 K oc (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. © 2016 Published by Elsevier B.V. 1. Introduction Polycyclic aromatic hydrocarbons (PAHs) belong to ubiquitous class of organic pollutants which mainly originate from the * Corresponding author. E-mail addresses: olisa200@yahoo.com, isaac.ololade@aaua.edu.ng (I.A. Ololade). incomplete combustion of carbonaceous materials. The United State Environmental Protection Agency (US EPA) have listed 16 PAHs as priority pollutants due to their toxicity, mutagenicity and carcinogenicity (Elmquist et al., 2007; Honda et al., 2007; Lohmann et al., 2009; Parinos et al., 2013). These organic compounds are found in all environments especially at locations involving intense human activities (Kannan et al., 2005; Botsou and Hatzianestis, 2012; Manzetti, 2013). The reactive products resulting from http://dx.doi.org/10.1016/j.rsma.2016.11.004 2352-4855/© 2016 Published by Elsevier B.V.