Characterization and Sources of Aliphatic Hydrocarbons of the Sediments of River Oluwa at Agbabu Bitumen Deposit Area, Western Nigeria

Abstract

Aims: This research is aimed at determination of the distribution, concentrations, sources and origins of petroleum hydrocarbon in sediment. Study Design: River sediment samples were collected from five sampling sites from the sediments of River Oluwa at Agbabu bitumen deposit area and analyzed for n-alkanes content. Place and Duration of Study: Samples were collected from Agbabu bitumen deposit area, Western Nigeria, in years 2008 and 2009. Methodology: Analysis was carried out using gas-chromatography flame ionization detector. Diagnostic parameters used in identifying and estimating the origins of n-alkanes in the study area included Carbon Preference Index (CPI), Average Carbon Chain (ACL) and %Plant Wax Contribution. Results: n-alkanes ranged from 54.72mg/kg to 2002.4mg/kg, which were all higher than the recommended limit of 10 mg/kg. Sampling station OLSW1 had CPI value of 1 in the two sampling seasons, showing petrogenic source. The remaining sampling stations had CPI values that ranged from 0.22 and 0.52, showing bitumen related sources. ACL values were constant at 28 in all the sampling stations, except sampling stations OLSW1 (27.19) and M2SW (27.71), where they were lowered due to petrogenic contamination in the study area. Analysis of variance of the concentrations of n-alkanes with SPSS at α = .05 showed statistically non-significant differences. Conclusions: The sediments of River Oluwa at Agbabu bitumen deposit area were heavily contaminated with n-alkanes due to bitumen deposit, microbial activity, phytoplankton and algae, insects and plant waxes, and anthropogenic activities which included petroleum product transportation, fishing and laundry. Source diagnostic analysis of petroleum hydrocarbons with CPI gave values that were less than 1 at all sampling points, except OLSW1, indicating that bitumen deposit in the study area had impacted on the sediments of River Oluwa at Agbabu bitumen deposit area as a result of the predominance of even numbered n-alkanes.