Use of Sesquiterpanes, Steranes, and Terpanes for Forensic Fingerprinting of Chemically Dispersed Oil

Abstract

Biomarkers, as complex hydrocarbons in oil from formally living organisms, have been widely used for offshore oil spill fingerprinting. The application of oil dispersants may affect the suitability of existing biomarkers in oil fingerprinting during physicochemical weathering. The existence and concentrations of some biomarkers in chemically dispersed oil (CDO) may differ from those in crude oil and weathered oil. Such differences could affect the diagnostic ratios among different biomarkers and cause difficulties in oil spill fingerprinting. This study thus examined the stability and suitability of three groups of biomarkers, i.e., sesquiterpanes, steranes, and terpanes, for CDO characterization in seawater after application of a representative chemical dispersant (Corexit 9500A). The results indicated that the suitability of sesquiterpanes as biomarkers for CDO identification was affected due to less number of stable diagnostic ratios and overlapped ranges of diagnostic ratios compared to other reference oils. On the contrary, most of the steranes and terpanes could still be applied as biomarkers for CDO characterization. All the selected diagnostic ratios of terpanes were suitable for identification of oil sources. By considering both the stability and suitability, the recommended ranking of biomarkers for CDO was terpanes > steranes > sesquiterpanes. The findings would help improve offshore oil spill fingerprinting methods particularly after application of chemical dispersants.