Stable carbon isotope ratios of crude oil exposed to environmental degradations

Abstract

Crude oil is a complex mixture of thousands of different organic compounds formed from a variety of organic materials that are chemically converted under differing geological conditions over long periods of time. Oils from different sources have distinct chemical compositions, which can be used to identify the source of oil pollution. The chemical compositions of spilled oils, however, can be altered in the environment by a number of physicochemical and biological factors, making source characterization by GC or GC/MS ambiguous. Source identification of spilled oil requires more discriminative parameters that are relatively resistant to weathering processes. The stable isotope compositions of individual compounds in weathered oil are known to remain relatively less affected than molecular compositions and therefore can be effectively used as a correlation parameter. However, under extensive degradation, isotopic composition of crude oil can also be affected and thus it is important to understand isotopic changes during environmental weathering for clearer source identification. In this study, a crude oil was exposed to natural environmental weathering during a simulated oil spill using an in-situ experimental mesocosm. The crude oil was also exposed to various artificial weathering processes in controlled lab experiments including evaporation, dissolution, adsorption, photooxidation and microbial degradation. s have distinct chemical compositions, which can be used to identify the source of oil pollution. The chemical compositions of spilled oils, however, can be altered in the environment by a number of physicochemical and biological factors, making source characterization by GC or GC/MS ambiguous. Source identification of spilled oil requires more discriminative parameters that are relatively resistant to weathering processes. The stable isotope compositions of individual compounds in weathered oil are known to remain relatively less affected than molecular compositions and therefore can be effectively used as a correlation parameter. However, under extensive degradation, isotopic composition of crude oil can also be affected and thus it is important to understand isotopic changes during environmental weathering for clearer source identification. In this study, a crude oil was exposed to natural environmental weathering during a simulated oil spill using an in-situ experimental mesocosm. The crude oil was also exposed to various artificial weathering processes in controlled lab experiments including evaporation, dissolution, adsorption, photooxidation and microbial degradation.