Aliphatic Hydrocarbons in recent dated Sediment Cores of Imo River,
SE Nigeria: Environmental/Historical Implications
Four sediment cores (0-30 cm long) from Afam (AF), Mangrove (MG), Estuary (ES) and illegal Petroleum refinery (PT) sites of Imo River, Southeast Nigeria were analyzed by Gas Chromatography-Mass Spectrometry (GC-MS) to characterize the sources of organic matter (OM), examine their depositional history and assess human-induced changes in the last ca. 5 decades using biomarker and 210Pb/137Cs radiometric approach. Evaluation of carbon preference indices (CPIs, 2.01 - 2.19), carbon number maxima (Cmax, 29, 31) and atomic C/N (16.51-31.32) for the top layers (0-5 cm) revealed greater wash-in of land-derived OM, attributable to the 2012 flood episode. The bottom layer (PT1, 25-30 cm,) of PT deposited ca. 1964-1972 exhibited CPI of 0.97 and pristane/phytane (Pr/Ph, 3.75), suggesting illegal oil refinery had begun in the region ca. 8 years after the first commercial discovery of oil in Nigeria in 1956. The occurrence in high abundance of heptadecane in the middle layer (ES4, 10-15 cm) of ES corresponded with the period of eutrophication that blocked the waterway in the late 1980s. Measurement of a marked unresolved complex mixture in the near-top layer (AF5, 5-10 cm) of the AF indicated that the heaviest contamination by petroleum hydrocarbons occurred at ca. 1997-2005.
Keywords: Aliphatic hydrocarbons, Biomarker, Historical trend, Imo River, Source.