Understanding the thermal degradation patterns of hopane biomarker compounds present in crude oil

Abstract

In-situ burning (ISB) is a common oil spill response technique used for managing marine oil spills. The burnt residues generated from ISB can have several toxic compounds and therefore their impacts on aquatic ecosystem are of major environmental concern. When quantifying the fate of the toxic compounds in ISB residues, C30-αβ hopane is routinely used as a conservative biomarker since it has shown to be resistant to most natural weathering processes. However, a recent laboratory study has shown that C30-αβ and other hopane compounds have the potential to degrade when crude oil was physically burnt under controlled conditions. When crude oil is burnt, the temperature of the oil can raise up to 350–500 °C; however, so far, no one has studied the fate of hopanes when crude oil is simply heated to very high temperatures. In this study, we hypothesize that heating crude oil to very high temperatures would result in the degradation of hopane compounds. Results of our study show that C30-αβ hopane in crude oil will start to degrade at around 160 °C and the degradation pattern follows first order kinetics. Other types of hopanes and their diagnostic ratios can also change when the oil is exposed to severe heating conditions. We conclude that removal of hopane biomarkers via thermal degradation is a possible depletion pathway during ISB. Therefore, caution should be exercised when using hopanes as conservative biomarker compounds for characterizing ISB residues.