Hydrocarbons biodegradation and evidence of mixed petroleum source inputs to surface sediments from the Cross River system, S. E. Nigeria

Abstract

Chromatographic analysis of extracts from the Cross River system show evidence of variable composition of biogenic n-alkane profile with dominance of terrigenous over aquatic organic matter present (LHC/SHC-0.36-10.57) at upstream location reflecting the natural background levels and marked levels of petroleum residues (UCM-0.16-11.3) at various sampling stations (downstream). The mild hydrocarbons biodegradation status of these sediment is partly indicated by the pristane/nC17 (0.9-
2.56) and phytane/nC18 (0.10-0.85) ratios. Although the 17á(H)25-norhopane detected in the system represent heavy biodegradation, the n-alkane signatures show some characteristics typical of mild  biodegradation, suggesting inputs of mixed/different petroleum origins. In addition, examination of the mass chromatograms of the hopane series shows evidence supportive of inputs from different petroleum source locations, reflected in their thermal history differences, variation in biodegradation patterns and biomarker composition. This distinction is a reflection of utilization of petroleum products derived from different source locations imported into the Nigerian economy.