Oluwadayo O. Sonibare

Polycyclic aromatic hydrocarbons in sediments and soils from oil exploration areas of the Niger Delta, Nigeria

The distribution of polycyclic aromatic hydrocarbons (PAHs) in sediments from rivers and canals adjoining 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.

Thermo-oxidative reactions of Nigerian oil sand bitumen

Abstract The thermal behavior of the Nigerian oil sand bitumen in an oxidizing environment was studied using non-isothermal thermogravimetric analysis (TGA) and differential thermal analysis (DTA). This condition can occur during in situ thermal recovery. The kinetics of the reactions was also determined by Arrhenius plot method. Three regions of weight loss corresponding to low-temperature oxidation, fuel deposition and high temperature oxidation were identified. Increasing the heating rate caused a shift in the reaction regions and peak temperatures to higher temperatures. No effect of gas flow rate was observed on the reactions. The oil sands have lower peak temperatures and activation energies compared with their corresponding bitumen extracts, suggesting a catalytic effect of sand on the reactions. The DTA revealed the exothermic nature of the reactions. The exothermicity increased with increasing heating rate. The results of this study showed that the heating rate and the presence of sand have significant effect on the thermo-oxidative reactions of the bitumen.

Assessing anthropogenic contamination in surface sediments of Niger Delta, Nigeria with fecal sterols and n-alkanes as indicators

The occurrence of sterols and n-alkanes in surface sediments from rivers and canals in the Niger Delta, Nigeria, determined with a gas chromatography-mass spectrometry method, was used to assess the impacts of anthropogenic activities in the area. The concentrations of total sterols (∑₈Sterol) and n-alkanes (∑₂₈n-alkane) in the sediments ranged from 133 to 2040 ng/g and 474 to 79,200 ng/g, respectively. An evaluation of the source diagnostic indices indicated that petroleum related sources (petrogenic) were the main contributor of n-alkanes in the samples, with minor contribution from higher plants waxes (biogenic), while the sterols were mainly of biogenic origin. The ratio of α-cholestanone/(α-cholestanone+β-cholestanone), a commonly used source diagnostic index, implicated no fecal contamination in most of the sediment samples under investigation. These results have established the occurrence of anthropogenic contamination in Niger Delta sediments with significant contributions from petrogenic sources.

Biomonitoring potentials of polycyclic aromatic hydrocarbons (PAHs) by higher plants from an oil exploration site, Nigeria.

Higher plants sampled from a moderately polluted exploration site were analyzed with gas chromatography-mass spectrometry to determine the occurrence and sources of polycyclic aromatic hydrocarbons (PAHs). The concentrations of the sum of 28 target PAHs (designated as Σ(28)PAH) in the leaves of higher plant samples ranged from 365 to 2870 μg/kg with an average of 1430 μg/kg. The majority of the target compounds were detected except 9,10-diphenyl anthracene and dibenzo(a,h)anthracene, which were below the detection limits in most plant samples. In addition, the concentrations of the 2- and 3-ring PAHs, especially naphthalene and its alkylated derivatives, were generally higher than the 4-, 5- and 6-ring PAHs. Based on the results obtained in the present study, higher plants, especially non-woody annual and perennial plants could serve as good phytoremediators for a PAHs polluted sites.

Assessment of organochlorine pesticides residues in higher plants from oil exploration areas of Niger Delta, Nigeria

The concentrations and distributions of organochlorine pesticides (OCPs) in some higher plant samples collected from oil exploration areas of the Niger Delta, Nigeria were examined. The concentrations of Σ(25)OCP ranged from 82 to 424, 44 to 200 , 34 to 358, 33 to 106 and 16 to 75 ng/g in Olomoro, Oginni, Uzere, Irri and Calabar plants, respectively. The compositional profiles of the analysed OCPs in most of the plants showed no fresh inputs in the area. The OCPs detected in the samples could have resulted from pesticide usage for intense farming activities cum the use of pesticides to control household pests and insects in the area. Drilling fluids and corrosion inhibitors used in petroleum explorations also have chlorinated compounds as additives thereby serving as potential sources of OCPs. Among the studied plants, elephant grass showed high bioaccumulation and phytoremediation potentials of OCPs. The ΣHCH concentrations exceeded the allowable daily intake limit thereby serving as potential threat to humans.

Concentrations of polycyclic aromatic hydrocarbons in soils of a mangrove forest affected by forest fire

Surface soils affected by forest fires from Igbanko mangrove forest in Nigeria were analyzed for 16 EPA priority polycyclic aromatic hydrocarbons (PAHs) using gas chromatography–mass spectrometry (GC–MS). The total PAHs concentrations in the soils ranged from 63 to 188 µg kg−1 dry weight (average: 108 µg kg−1). The three predominant PAHs in the soils were naphthalene (Na), fluoranthene (Flu), and benzo(b)fluoranthene (BbF). Compared to the control sample (19 µg kg−1), elevated PAHs concentrations were observed in the soils, an indication of some level of PAHs contamination. PAHs source diagnostic ratios of Flu/(Flu + Pyr) and Ant/(Ant + Phe) indicated that the PAHs have a pyrogenic origin which may have resulted from combustion of grass, wood, or coal. An assessment based on Canadian soil quality guidelines indicated that the studied locations do not pose any serious adverse risk on human health.

Terpenoid composition and origin of amber from the Cape York Peninsula, Australia

The terpenoid composition of fossil resin from the Cape York Peninsula, Australia has been analysed by pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) to determine its origin. The pyrolysis products were dominated by cadalene-based C15 bicyclic sesquiterpenoids including some C30–C31 bicadinanes and bicadinenes typical of Class II resin derived from angiosperm plants of Dipterocarpaceae. This observation contrasts with the Araucariaceae (Agathis sp.) source previously suggested for the resin based on Fourier transform infrared (FTIR) analyses. Dipterocarpaceae are not known in Australian vegetation but grow abundantly in Southeast Asia including New Guinea, indicating that the geological origin of the amber is not the Australian mainland but could be traced to Southeast Asia.

Hydrocarbon-Generative Potential of Coal and Interbedded Shale of Mamu Formation, Benue Trough, Nigeria

Abstract Coal and its interbedded shale samples were collected from Okaba, Onyeama, and Okpara seams in the Mamu Formation, Lower Benue Trough, Nigeria. In the present study, source rock evaluation and biomarker distribution in the samples were investigated by Rock-Eval pyrolysis, vitrinite reflectance measurement, and gas chromatography–mass spectrometry (GC-MS) analysis. All of the samples analyzed contained the minimum of 0.5 wt.% and 2 mg/g of total organic carbon (TOC) and genetic potential (GP) respectively of organic matter required to serve as good source rock for oil and gas. Several plots from the Rock-Eval pyrolysis classified the organic matter in the samples as type II/III kerogen. The abundance of hopanes, homohopanes (C31–C35), benzohopanes, and C29 steranes in most of the samples indicates terrigenous materials, phytoplankton, and cyanobacteria contributions to the organic matter that formed the coal. High Pr/Ph ratio (1.73–12.47) and n-alkane distribution in the samples showed that Mamu samples consisted of terrestrial organic matter with marine incursion deposited under oxic/suboxic-oxic in lacustrine-fluvial/deltaic environments. The distribution patterns of C32–C35 benzohopanes in the samples confirmed the redox condition of organic matter deposition within the formation. The occurrence of olean-18-ene, olean-13 (18)-ene, and olean-12-ene in Okaba samples favors terrestrial organic matter deposited in lacustrine-fluvial/deltaic environment. The vitrinite reflectance values (0.48–0.60% Ro) and all the maturity parameters derived from the Rock-Eval analysis and biomarker distributions showed that Okaba samples are immature, whereas Okpara and Onyeama are at the beginning of the oil window.

Aromatic Hydrocarbons Distribution in Nigerian Coal and Their Geochemical Significance

Abstract Aromatic fractions obtained from thirteen Nigerian coals collected from two formations (Awgu and Mamu) were analyzed by gas chromatography-mass spectrometry. C1-C3 naphthalene, C0-C2 phenanthrene, and C0-C2 dibenzothiophene are the major aromatic hydrocarbons identified in the coals. 1,6-, 1,7-, and 2,6-DMNs are more pronounced in Mamu Formation compared to Awgu samples, suggesting more terrestrial organic matter input. The presence of 1,2,5- and 1,2,7-TMN in all the samples indicates both angiosperm and gymnosperm contribution to their organic matter. Also, there is occurrence of 1,2,6-TMN in the samples, reflecting microbial input. Paleoenvironmental parameters computed from the phenanthrene and dibenzothiophene and their alkyl derivatives show that the organic matter was deposited in lacustrine and/or fluvio-deltaic environment. Various maturity ratios calculated indicate that the Awgu samples are in the late oil window while Mamu samples are at the beginning of the oil window. The calculated vitrinite reflectance values from the aromatic distributions are in close agreement with vitrinite reflectance values obtained from petrographic analysis.

Aliphatic biomarkers distribution in crude oil-impacted soils: An environmental pollution indicator

Abstract The occurrence and distributions of aliphatic biomarkers in oil contaminated soils from Owaza, Niger Delta, Nigeria, were investigated by gas chromatography-mass spectrometry (GC-MS). The concentrations of the n-alkanes Σ(nC14 to nC29) in the soils ranged from 18,680.4 to 35,615.8 μg/g (average 24,664.0 μg/g). The abundance of n-alkanes in the soils extracts show that the effect of environmental degradation on the impacted soils has been minimal. N-alkanes diagnostic indices, source and maturity parameters computed for the terpanes and steranes in the soils extracts indicate Niger Delta oil as the source of contamination. This study reveals the significance of aliphatic biomarkers in serving as organic pollution source indicator.