Oil Source Identification Using Diagnostic Biomarker Ratio Analyses

Abstract

ABSTRACT The foremost questions asked about spilled oil are its source, quantity in various compartments of the environment, and the risk and consequences associated with various levels of oil within these compartments. The heterogeneous distribution of oil, with a continually changing composition due to weathering, causes considerable uncertainty in determining the source of a spilled oil and whether or not any notable impacts are due to the presence of that particular oil. Oil source-fingerprinting, an environmental forensics technique, is one way to determine the origin of oil in an unknown sample by comparison to a known oil source. Oil source-fingerprinting utilizes oil biomarkers that are naturally occurring in crude oils and most petroleum products which tend to be more resistant to environmental weathering processes compared to most other oil components. More importantly, vast amounts of geochemical research has established that distributions of oil biomarkers are unique for different types and blends of petroleum products and represent an oil-specific fingerprint to which samples can be correlated. In order to determine whether oil detected in coastal Louisiana marsh sediments originates from the Deepwater Horizon incident, an oil source-fingerprinting methodology using GC/MS and specific hopane, sterane, and triaromatic steroid ratios in Macondo 252 (MC252) source oil was developed and tested. A final suite of 15 diagnostic biomarker ratios were determined that will allow for the statistical comparison of diagnostic biomarker ratios of an “unknown” sample to the 15 diagnostic biomarker ratios of MC252 source oil. Unknown samples can then be classified into one of four operational and technically defensible categories: positive match, probable match, inconclusive, or non-match based on their diagnostic biomarker ratio score.