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Aromatic Steroids in Crude Oils and Petroleum Products and Their Applications in Forensic Oil Spill Identification

Aromatic steroids including monoaromatic (MAS) and triaromatic steroids (TAS) are a series of naphthenoaromatic hydrocarbons, which consist of mixed structures of aromatic and saturated 6-carbon or 5-carbon rings. Although these aromatic steroids are in relatively low concentration in oils, their specific fingerprints and high weathering resistance make them desirable biomarkers for the characterization, correlation, differentiation, and source identification in environmental forensic investigations of oil spills. This study presents a quantitative GC/MS analysis of these aromatic hydrocarbons in a number of crude oils and refined petroleum products including light and mid-range distillate fuels, heavy fuels, and lubricating oils collected from various sources. TAS-cholestanes (C26), TAS-ergostanes (C27), and TAS-stigmastanes (C28) are the most distinguishable triaromatic steroids in most oil samples. C26 TAS-cholestane (20R) and C27 TAS-ergostane (20S) are coeluted and often present as the highest peak in m/z 231 chromatograms. A cluster of aromatic steroids were determined in nearly all the studied crude oils at various concentrations. These compounds are generally not detected in light fuel oil like gasoline and light diesel, but at variable abundance in heavy fuels and lubricating oils. In order to better understand the occurrence of aromatic steroids in refined petroleum products, a crude oil was compared with its products of laboratory fluid catalytic cracking (FCC) and hydrotreating processes. The effects of evaporative weathering and biodegradation on these compounds were evaluated with suites of weathered oil samples.