Even-n-alkane/alkene predominances in surface sediments from the Calabar River, SE Niger Delta, Nigeria

Abstract

We report the geochemical characterisation of hydrocarbons extracted from surface sediments of the Calabar River and coastal soils, SE Niger Delta, Nigeria using gas chromatography-mass spectrometry (GC-MS). As a result, a special group of organic compounds prevalent in the entire study area was identified. It consists of aliphatic hydrocarbons (7.3-22.2% of the total lipids) with several distinctive chemical features. These include a high abundance of even numbered n-alkanes (n-C(12)-n-C(26), maximising at n-C(18), n-C(20) and n-C(22)), n-alk-1-enes (n-C(14:1)-n-C(26:1), maximising at n-C(18:1) and n-C(20:1)), giving rise to Carbon Preference Indices (CPIs) between 0.15 and 0.82. An unresolved complex mixture (UCM) occurring in the range n-C(18)-n-C(35), and the presence of hopanes indicate petroleum contamination. The predominance of even numbered n-alkanes in the Calabar River sediments are thought to be derived from inputs of different microorganisms inhabiting an oil-polluted environment and contributing to the organic matter (OM). This paper, for the first time, gives an account of the unusual predominance of even numbered n-alkanes/alkenes in surface sediments from the Niger Delta of Nigeria and thus contributes to the information on the rare occurrence of such distributions in the geosphere.

Distributions and sources of polycyclic aromatic hydrocarbons in surface sediments from the Cross River estuary, S.E. Niger Delta, Nigeria

“…The weight of extract obtained is a measure of the amount of extractable organic matter. Asphaltenes were precipitated from the extracts by following the procedure described by Schoell et al (1983), Ekpo et al (2005), and Oyo-Ita et al (2010) with a dichloromethane and petroleum ether (b.p. 40-60 • C) mixture (1:30) and centrifuging at 3,000 rpm for about 20 min.…”

“…Details of the extraction method for soluble organic matter and fractionation were reported elsewhere (Ekpo et al 2005). Briefly, to reduce contamination, all glassware was cleaned with soap and water, rinsed with distilled water, heated in an oven at 550 • C for 8 h, and finally rinsed twice with ultra-pure hexane and acetone (1:1) mixture.…”

Even-numbered n-alkanes/n-alkenes predominance in surface sediments of Gabes Gulf in Tunisia

“…To the best of our knowledge, the only reported occurrence of even alk-1-enes with even alkanes in the range of C14-C22 corresponds to the Calabar River, Nigeria (Ekpo et al 2005). This unusual distribution is described in the present study at many stations.…”

Forensic Analysis and Source Partitioning of Aliphatic Hydrocarbon Contaminants in Surface Sediments from the Niger Delta, Nigeria

“…Conversely, an even/odd predominance has been reported to be associated with recent sediments having organic matter input from phytoplanktonic organisms such as diatoms and some bacteria [15], [25]. Even-numbered nalkane predominances are less common.…”

“…Fubara and others [14] have reported the predominances and source implications of even n-alkenes in surface sediments from coastal areas of the Niger Delta region. Even nalkane/alkene predominances [15] and predominance of ndocosane/docosene [16] have been reported for surface sediments from the Calabar River estuary, with the presence of unresolved complex mixture (UCM) indicating petroleum contamination at two stations along the estuary.…”