The concentration and extent of degradation of petroleum components from intertidal and subtidal sediments in Saudi Arabia following the Gulf War oil spill

Geoff C. Smith

A b s t r a c t: The hydrocarbon concentration and the extent of oil degradation were measured from sediments at several sites that had been contaminated during the Gulf War oil spill. No change in hydrocarbon concentrations could be determined in sediments at a low-energy site and a low-energy tar-covered site after periods of 27 months and 17 months respectively. By using the proportion of the unresolved complex matrix (UCM) to the total weight of hydrocarbons extracted as an indication of the extent of hydrocarbon degradation, it was seen that mote oil breakdown occurred at a high-energy study site than at a low-energy site and that at the low-energy tar-covered site no change could be determined over the sampling period. The sites with least hydrocarbon degradation would appear to be some of the more heavily oiled ones (47 g/kg) and the sediments lying beneath tar pavements (91 g/kg). The use of hydrocarbon component proportions such as n-C17/pristane and n-C18/phytane must be questioned for some of the degraded sediment samples due to the increased presence of n-C17 and n-C18 hydrocarbons which are probably of biogenic origin. This caused the indices of well-degraded samples to increase over time whereas the indices of the less degraded, tar-covered and heavily oiled sediments decreased significantly. Gas-chromatographic spectra of the liquid oil in many of the relic crab burrows showed significant degradation with respect to the straight-chain aliphatic and branched hydrocarbon components. Analysis of subtidal sediments indicated that petroleum hydrocarbons were most noticeable, but low in concentration (l040 g/kg), at inshore sites closest to the most heavily oiled intertidal sediments. Offshore subtidal sediments contained negligible hydrocarbon concentrations. Correlation analysis of trace metal concentrations associated with the oil (Ni and V) with the percentage subtidal fine-grained sediments (< 63 µm) was significantly high and suggested that the route of petroleum hydrocarbons to these sites was probably via the transport of small tar balls and possibly via sorption of weathered oil onto fine-grained sediments. Preliminary observations of the proportions of Ni and V in oiled samples suggested that V is more readily removed than Ni over time. This could serve as an indicator of the state of oil degradation after the organic components that form the degradation indices (n-C17/pristane) have diminished.

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