Orok E. Oyo-Ita

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

Polycyclic aromatic hydrocarbon (PAH) analyses of surface sediments from the Cross River estuary by gas chromatography–mass spectrometry indicated natural diagenetically derived PAHs in the upper estuary, with minor and variable amounts of petrogenic and combustion-derived PAHs from human activities (lower estuary). The occurrence of significant amounts of perylene (average 23% of all PAHs) with the diagenetic natural PAHs in the middle estuary bordered by mangrove forests supports its origin from terrestrial organic matter. The natural PAHs represent the highest percentage (average 76%) of the total PAHs in this tropical environment. The traditional geochemical parameters, including the petrogenic PAHs, confirmed trace petroleum contamination in the estuary. Specific PAH ratios such as Fl/Py and Fl/(Fl+Py) also support this source contribution.

Occurrence and Sources of Triterpenoid Methyl Ethers and Acetates in Sediments of the Cross-River System, Southeast Nigeria

Pentacyclic triterpenol methyl ethers (PTMEs), germanicol methyl ether (miliacin), 3-methoxyfern-9(11)-ene (arundoin), β-amyrin methyl ether (iso-sawamilletin), and 3-methoxytaraxer-14-ene (sawamilletin or crusgallin) were characterized in surface sediments of the Cross-River system using gas chromatography-mass spectrometry (GC-MS). Triterpenol esters (mainly α- and β-amyrinyl acetates and hexanoates, and lupeyl acetate and hexanoate) were also found. These distinct compounds are useful for assessing diagenesis that can occur during river transport of organic detritus. Poaceae, mainly Gramineae and Elaeis guineensis higher plant species, are proposed as primary sources for the PTMEs and esters in the sediments. PTMEs are biomarkers of specific higher plant subspecies, while the triterpenol esters are indicators of early diagenetic alteration of higher plant detritus.

Sources of Organic Contaminants in Solvents and Implications for Geochemistry and Environmental Forensics: An Example from Local Vendors in Nigeria

Two solvents, n-hexane and petroleum ether, commonly used for extract analysis of geological and environmental samples and purchased from chemical suppliers in Nigeria, were analyzed using gas chromatography-mass spectrometry for quantitative determination of organic background contaminants. Series of n-alkanes and n-alk-1-enes in the carbon number range of nC16–nC26, the latter with an even predominance (Cmax 16 and 18) were observed. Such alkanes, previously and exclusively assigned a biogenic origin in sediments from the Calabar and Cross River Estuary, are considered here to be derived as distillation residues (n-alkanes) and from leaching of by-products from the production of polyethylene/polyvinyl chloride plastic containers (n-alkenes) where these solvents were stored. Significant concentrations of low molecular weight parent and alkyl polycyclic aromatic hydrocarbons were detected (mainly naphthalene series) and most likely reached the solvents as production residues (crude distillation) and/or cross contamination during storage/laboratory transfer. Plastic additives such as DEHP and DOA(plasticizers) and tris(2,6-di-tert-butyl) phenylphosphate (anti-oxidant derivative) were detected at high levels, also most likely leached from the plastic storage containers by the solvents.

Source and Toxicological Assessment of Polycyclic Aromatic Hydrocarbons in Sediments from Imo River, Southeastern Nigeria

ABSTRACT Polycyclic aromatic hydrocarbons (PAHs) in sediments from the Imo River were analyzed to characterize their sources and assess their toxicity potential. The total PAH concentrations ranged from 409.43 to 41,198 ng/g dw with standard deviation of 4,796 ± 1,941. This wide variation reflects a localized contamination in the study area. The inadequacy in the use of traditional isomeric ratios for PAHs source characterization in sediment from tropical environments with shallow water depth of < 10 m was highlighted. A more robust principal component analysis coupled with n-alkanes unresolved complex mixture profiles approach to apportioned specific chemical signatures to samples was proposed. This approach differentiated stations that were heavily—from those that were mildly—impacted by oil and discriminated among stations that were influenced by pyrogenic sources. Effect range low (ERL) and effect range median (ERM) as well as risk quotients (RQwcs) revealed that only naphthalene, flourene, dibenzo(a,h)anthracene and low molecular weight PAHs were implicated with ERL and ERM exceeding the US National Oceanic and Atmospheric Administrations limit of concern and RQwcs > 1, as compounds of concern. The maximum toxicity equivalency value of 179.81 ng/g TEQscarc measured for the illegal petroleum refinery site indicated that this site requires some control measure and remedial action.

Reassessment of dibenzothiophene as marker for petroleum and coal contamination in sediments from Imo River, SE Nigeria

ABSTRACT Distributions of dibenzothiophene (DBT) and its historical trends of deposition in sediments from Afam, mangrove, estuary, and illegal petroleum refinery sites of Imo River, southeast Nigeria over the past approximately five decades were evaluated in order to reassess the compounds potential as a marker for petroleum and/or coal combustion emission source(s). The spatial distributions in the concentrations of DBT varied from 12.46 ng/g dry weight (dw) to 1,720.42 ng/g dw (mean 454.77±14 ng/g dw), maximizing and minimizing at locations adjacent to an illegal petroleum refinery site. There was no strong geographic element that influenced DBT distribution across the river. The concentrations of DBT down cores ranged from 13.54 ng/g dw at the middle layer (15–20 cm, approximately 1981–1989) of the Afam site to a maximum of 470.43 ng/g dw at near-top layer (5–10 cm) of the illegal petroleum refinery site. The later layer corresponds to a depositional time frame of approximately 1997–2005, coinciding with the period of intensive illegal petroleum refinery operations when coal was used as a refinery fuel in the illegal processing and oil bunkering/pipeline vandalization were at their peaks. The general decline in DBT levels from near-top layers (5–10 cm) to the most recent top layers (0–5 cm) was linked to the recent offer of amnesty to the Niger Delta militant groups by the Nigerian government and subsequent clamp down on economic saboteurs by the Nigerian joint armed forces. Due to its extra stability to microbial degradation relative to polycyclic aromatic hydrocarbons (PAHs), the study illustrated the greater potential of DBT as a marker for petroleum and/or coal combustion emission source contaminations than the commonly used markers such as PAHs.