Hydrocarbon source identification and weathering characterization of intertidal and subtidal sediments along the Saudi Arabian coast after the Gulf War oil spill

Abstract

One year after the Gulf War oil spill, approximately 200 intertidal and subtidal (surface and subsurface) sediments were collected in the areas of Dawhat al Musallamiyah, Dawhat ad Dafi, and Ras Tanaqib along the Saudi Arabian coast as part of the Nearshore Geochemistry Processes Study (Leg II: 16 March–5 April 1992) of the Mt Mitchell Gulf survey. The sediment samples were analysed for total petroleum hydrocarbons and the environmentally important saturated hydrocarbon (SHC) and polycyclic aromatic hydrocarbon (PAH) components of the spilled oil. The target analytes included n-alkanes (C 10–C 34) and selected isoprenoids, individual and alkyl homologues of the two- through six-ringed PAH compounds and sulphur-containing heterocyclic compounds (38 individual and alkyl-PAHs), and selected cycloalkane biomarkers (steranes and triterpanes). These target analytes were also determined for reference crude oil samples. SHC, PAH alkyl homologue, and triterpane distributions in environmental samples were compared with reference crude oils—Kuwait crude oil, Light Arabian crude oil, and Iranian crude oil—to determine the source(s) and extent of weathering of the spilled oil. Diagnostic hydrocarbon parameters and ratios, especially the plots of the ratios of the C 2- and C 3-alkyl homologues of the dibenzothiophenes and phenanthrenes/anthracenes (i.e., C 2D/C 2P vs. C 3D/C 3P) and the same homologues of the dibenzothiophenes and chrysenes/benzanthracenes (i.e., C 2D/C 2C vs. C 3D/C 3C), and the ratio of the source indicator triterpane/trisnorhopanes, T M/T S were useful in differentiating hydrocarbon source(s) and characterizing the weathering of the spilled oil in the samples. From the chemical diagnostic parameters, the Kuwait reference crude oil was determined to be very similar to the Gulf War spilled oil collected during a shoreline survey of oil-impacted beaches of Saudi Arabia in June 1991, shortly after the Gulf War. Asphaltic pavement residual oil found at intertidal sites on Abu Ali and in isolated locations in Dawhat ad Dafi were chemically identified using chemical biomarkers as originating from a source other than oil spilled from the Gulf War. With the SHC and PAH data, a set of chemical characteristics was identified that corresponded to stages of spilled oil weathering. Sediments from exposed habitats generally exhibited an advanced weathering stage; whereas, the moderately exposed and sheltered habitat sediments were typically less weathered at a moderate weathering stage. The advanced stage of weathering was also apparent in the asphaltic pavement sediment. The hydrocarbon characteristics of the subtidal samples were usually dominated by background concentrations of hydrocarbons consisting of both petrogenic PAH and biogenic saturated hydrocarbon signatures.