Inyang O. Oyo-Ita

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.