Interpretation of Bicyclic Sesquiterpane Petroleum Biomarker Results for Environmental Forensic Investigations

Forensic Environmental Chemistry
Oral Presentation

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Petroleum biomarkers are components of crude oils, derived from the original organic source material, and produced during the maturation of the petroleum over the millennia. They are thought to originate from algae, bacteria and higher plants. Several classes of biomarkers have been recognized for decades and are used extensively in oil exploration. Compared to other crude oil components biomarkers are resistant to many degradation processes and their relative proportions are diagnostic for the specific reservoir where the crude oil originates. These features make them valuable markers for differentiating and correlating different crude sources. Although they are more recalcitrant to weathering losses than many of the paraffinic materials comprising the bulk of most crudes, there are typically differences in degradation rates between different members of the same class of biomarkers. This provides an avenue to evaluating the degree of weathering crude oils and their refined products may have been exposed to after release into the environment, particularly where less recalcitrant biomarkers like isoprenoids have degraded. Bicyclic sesquiterpanes are a relatively low molecular weight class of biomarkers that are useful for source and weathering evaluation of middle distillate fuel releases such as diesels and heating oils. Many of the higher molecular weight biomarkers are removed during the middle distillate refining processes whereas the bicyclic sesquiterpanes are concentrated in these fractions. Their use in forensic oil spill investigations was proposed in the early 2000s and significant advances in their use have appeared over the past decade.

This presentation will describe practical considerations for collecting and submitting samples for forensic biomarker analysis including bicyclic sesquiterpanes, and the laboratory processes used for processing samples. It will also show typical report examples and describe how the information is interpreted.

Different approaches have been proposed for the use of bicyclic sesquiterpane data in oil spill investigations, often based on specific case objectives. This presentation will also present results of case studies and review the more commonly used approaches to such investigations. It will describe the pros and cons of the different approaches and identify which approaches are currently being employed in the main forensic investigation protocols currently in use.