Journal of Hazardous Materials 174 (2010) 641–647 Contents lists available at ScienceDirect Journal of Hazardous Materials journal homepage: www.elsevier.com/locate/jhazmat Polycyclic aromatic hydrocarbons in sediments and soils from oil exploration areas of the Niger Delta, Nigeria  O.S. Samuel Sojinu a,b , Ji-Zhong Wang c , O.O. Sonibare d , Eddy Y. Zeng a,∗ a State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China b Department of Chemical Sciences, Redeemer’s University, Klm 46/48 Lagos-Ibadan Express Way, Nigeria c CAS Key Laboratory of Crust-Mantle Materials and Environment, School of Earth and Space Science, University of Science and Technology of China, Hefei 230026, China d Petroleum and Environmental Geochemistry Research Group, Chemistry Department, University of Ibadan, Nigeria article info Article history: Received 19 July 2009 Received in revised form 17 September 2009 Accepted 18 September 2009 Available online 23 September 2009 Keywords: Polycyclic aromatic hydrocarbons Soil and sediment Oil field Ecological risk Fate Niger Delta abstract The distribution of polycyclic aromatic hydrocarbons (PAHs) in sediments from rivers and canals adjoin- ing some oil exploration sites in the Niger Delta and surface soils from host communities were examined. The concentrations of 28 target PAHs ranged from 65 to 331 ng/g (average: 168 ng/g) and from 24 to 120 ng/g (average: 80 ng/g) in the sediment and soil samples, respectively. Two-ring PAHs were the dominant components accounting for approximately 45% of the total PAHs detected. Assessment of the PAH compound ratios, phenanthrene/athracene (Phe/Ant) and fluoranthene/pyrene (Flu/Pyr), suggested that the PAHs in most sediment samples were predominantly of petrogenic origin which may have resulted from incessant oil pipeline leakages in the area. On the other hand, PAHs of pyrogenic sources were present predominantly in surface soils, an indication that gas flaring associated with oil exploration work in the Delta mostly affects the surface soils. An assessment using a set of widely cited sediment quality guidelines indicated that the majority of the sediment samples collected from the rivers of the delta does not pose a serious threat to the ecosystem except for two locations, Imo river and Oginni canal where PAH-contaminated sediments were likely to be acutely toxic to certain sediment dwellers. © 2009 Elsevier B.V. All rights reserved. 1. Introduction The occurrence of polycyclic aromatic hydrocarbons (PAHs) in surface soil and sediments from the Niger Delta area deserves major attention. Successive oil pollution in the area and natural gas flaring have significantly altered the region’s ecology [1,2]. The estuaries located in this area also receive organic pollutants from a num- ber of diverse sources including domestic sewage and wastewater, atmospheric fallouts, and boat engine exhausts [3]. The Niger Delta houses refineries and other petroleum-based industries; therefore, contamination of industrial effluents with oil-related residues is inevitable. At present, protection of streams and rivers from con- tamination by petroleum and its derivatives in the Niger Delta is one of the greatest ecological challenges in Nigeria. The Niger Delta is one of the major oil exploring regions in the world, with estimated 36.2 billion barrels of oil and 184 trillion cubic feet of natural gas in reserves [4]. Oil exploration activities started in the region in 1956 when the first oil well was discovered  “Capsule”: Occurrence and ecological risk of polycyclic aromatic hydrocarbons in soils and sediments near oil fields of the Niger Delta, Nigeria, are assessed. ∗ Corresponding author. Tel.: +86 20 85291421; fax: +86 20 85290706. E-mail address: eddyzeng@gig.ac.cn (E.Y. Zeng). by Shell-British Petroleum at Oloibiri. These activities have led to the release of various pollutants, including trace elements and PAHs into the soil, air, and water in the region. These pollutants can pose threat to the Nigerian ecosystem and residents. There have been many claims and counter claims by the inhabitants of the Niger Delta on pollution of rivers and streams by oil pipeline spillage, with alleged attendant reduction in the farmland yield which has heated up tension in the area and a great threat to the stability of the Nigeria state. The delta is vibrant with economic activities and accounts for over 30% of Nigeria’s gross domestic production, and about 2.5 million barrels of crude oil are drilled daily in the Niger Delta [4]. Numerous studies on the environmental pollution of the Niger Delta have been reported [5–8]. However, most previ- ous studies have been restricted to small areas and usually done on surface water and vegetation. At present, apparently limited data are available on the occur- rence and sources of PAHs in sediments and soils in the region; data available on PAHs in soils in the region covered a small area [9]. Therefore, the present study was conducted to examine the distribution and possible origins of PAHs in surface sediments and soils from some parts of the Niger Delta. It has been known that PAHs in the environment are mainly originated from pyrolytic and petrogenic sources. Pyrolytic PAHs are formed as a consequence of incomplete combustion whereas petrogenic PAHs are mainly 0304-3894/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.jhazmat.2009.09.099