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

摘要

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 compound's 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 neartop 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.