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A complete "total oil analysis method" suitable for monitoring chemical composition changes and studying the fate of 12-year-old weathered oil residues from an arctic beach is described. The characterizations not only are through analyses of individual aliphatic, aromatic, and biomarker compounds but also are through "pattern recognition" plots involving more than 100 important oil components and component groupings. The weathered percentages of residual oil in Baffin Island oil spill samples are quantified using C29 and C30 a/Miopane in the "fresh" source oil as internal oil references. The values of the weathered percentages show excellent correlation to the total solventextractable materials (TSEM), total petroleum hydrocarbons (TPH), aliphatic, aromatic, and biomarker compound analysis results. Biodegradation is demonstrated to have played an important role in the degradation and removal of the residual oil. Twelve years after the spill, the composition changes due to weathering progress much more slowly, and this slower rate of change will continue under these arctic conditions.

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A rapid, reliable, and effective method for direct determination of benzene, toluene, ethylbenzene, and o-, m-, and p-xylenes (BTEX) and alkyl-substituted benzene components in oil has been developed using GC/MS in selected ion monitoring mode. Using this method, 58 alkyl-substituted benzene components in a light crude oil, Alberta Sweet Mixed Blend, were positively identified, and the concentrations of the individual BTEX compounds and C3-benzene isomers in over 200 different crude and weathered oils were quantified. The effects of weathering on compositional changes of alkylbenzenes were also studied. The plots of the concentrations of BTEX and BTEX + C3-benzenes versus weathering percentages can be used to estimate the weathering extent of weathered oil samples, especially for those short-term weathered oils for which the loss of BTEX and C3-benzenes is significant For environmental and toxicity concerns, BTEX levels in oil are a very important parameter. BTEX is the collective name of benzene, toluene, ethylbenzene, and the xylene isomers (p-, m-, and o-xylenes). BTEX compounds are the most common aromatic compounds in petroleum (the amount of BTEX can be up to a few percent of the total weight for some crude oils) and often occur in greater amounts than other aromatics. BTEXs constitute the most soluble, most mobile fraction of crude oil and many petroleum products. BTEXs have many chemical applications and are widely used in the manufacture of paints, synthetic rubber, agricultural chemicals, and chemical intermediates. The concentration of BTEX in petroleum can directly affect the physical and chemical properties of petroleum such as density, viscosity, flash points, dispersibility, emulsion stability, solubility, and weathering processes. On the other hand, BTEX compounds frequently enter soil, sediments, and groundwater because of accidental oil spill, leakage of gasoline and other petroleum fuels from underground storage tanks and pipelines, and improper oil-related waste disposal practices. In these cases, BTEX compounds can also be used as markers in identifying the presence and determining the composition of these weathered fuels originating from leaking underground fuel tanks or pipelines. BTEXs are hazardous carcinogenic and neurotoxic compounds and are classified as priority pollutants regulated by Environment Canada1 and the U.S. Environment Protection Agency (EPA),1 2 especially benzene, which has a very low tolerance standard in drinking water of 5 jtg/L.