Nigerian Journal of Science and Environment, Vol. 15 (1) (2017) 44 PETROLEUM HYDROCARBONS DISTRIBUTION IN SEDIMENTS FROM THE THAMES ESTUARY, UK Eferhire Aganbi Department of Biochemistry, Delta State University Abraka, P.M.B 1 Delta State Nigeria. E-mail: Eaganbi@gmail.com. Tel: ++(234) 8102570906. Accepted 28 th June, 2016 Sediment cores were collected from the Stanford-Le-Hope mudflats within 1 km distance from the Petroplus- Coryton BP and Shell Haven refineries located on the north shore of the Thames Estuary in Essex, 40 km east of Central London, UK (51 °30´N, 0 °27´E). The BTEX compounds (benzene, toluene, ethylbenzene, o-, m-, and p-xylenes) in surface sediment samples were non-detectable within the linear calibration range of 0 – 50 mg l -1 . n-Alkanes (C 11 - C 40 ) and polycyclic aromatic hydrocarbons (PAHs) quantified at different sediment depths (2 cm core portions up to a total depth of 18 cm) indicated a high distribution of n-alkanes in subsurface sediments at the 10 – 12 cm depth; up to an average concentration of 1353.4 μg g -1 dry weight. The highest summed PAH (∑PAH) concentration of 2.95 μg g -1 dry weight was also found at the 10 – 12 cm depth. Source identification based on the ratio of low-molecular weight (LMW) to high-molecular weight (HMW) n-alkanes and the pristane/phytane ratio (Pr/Phy) indicated n-alkane input from biogenic sources. Nevertheless, the dominance of C 1 -naphthalene among ∑PAH concentrations suggested possible input from petroleum-related sources. Key words: Polycyclic aromatic hydrocarbons, Thames Estuary, BTEX, n-Alkanes, Gas chromatography, Extractable petroleum hydrocarbons, Solvent extraction INTRODUCTION Estuaries and surrounding shelf waters are vulnerable to hydrocarbon pollution globally due to their use as quays and the establishment of a succession of industries on the banks of such estuaries. Polycyclic aromatic hydrocarbons (PAHs) in marine environments have been described as adhering to and persisting in sediments due to their low water solubility and hydrophobic nature (Da Silva and Alvarez, 2007; Trabelsi and Driss, 2005). Like benzene, many of the PAH compounds have carcinogenic properties and have been listed as priority contaminants by the U.S. Environment Protection Agency (US EPA). The BTEX compounds (benzene, toluene, ethylbenzene and xylenes isomers), which may be found in association with PAHs in contaminated sites, have been widely recognized as toxins of concern in petroleum products such as gasoline. These volatile organic compounds (VOCs) are highly soluble and pose a drinking water hazard when accumulated in groundwater. Several studies have reported the concentrations and distribution of various groups of hydrocarbons in estuarine sediments around the UK as well as other parts of the world (Vane et al., 2007; Wetzel et al., 2013; Nicolaus et al., 2015; Oliva et al., 2015; Iwegbue et al., 2016). Studies involving the distribution of VOCs such as benzene and toluene, and PAHs in estuarine sediments are important for monitoring the levels of these chemical contaminants to avoid potential toxicity to humans and various sediment dwellers (Spencer and MacLeod, 2002; Williams et al., 2014; Oliva et al., 2015). Understandably, available data on the distribution of BTEX and other VOCs in sediment samples from estuaries around the UK is limited due to the high solubility and volatility of these compounds. However, there is a rich repository of published data on PAHs distribution, and to some extent heavy metals status of sediments from estuaries around the UK. For example, Spencer and MacLeod (2002) described the distribution and partitioning of heavy metals in estuarine sediment cores collected from the Thames, Medway and Blackwater estuaries in south-east England and concluded that over 70% of metals detected in sub- surface sediments were labile in the Thames Estuary