Applicability evaluation of the diagnostic ratios consisting of bicyclic sesquiterpanes to source identification for seriously weathered spilled oils
Marine oil spills often cause long-term great harm to the polluted environment. The absence of many important components makes it more difficult to identify the source of oil spill. Traceability identification of seriously weathered oil spill has always been a difficult point due to influence of complicated weathering process. Therefore, it is particularly important to screen and verify the new indexes to solve the problem of identification of severe weathering oil spill. As a kind of common biomarker, bicyclic sesquiterpanes is a research hotspot in the field of identification for spilled oils. The stability and applicability of bicyclic sesquiterpanes in oil spills in different time has been assessed by comparing laboratory simulation weathering experiment and beach weathering experiment samples. By using the commonly used oil spill identification method including t-test, similarity method and repeatability limit method，12 new diagnostic ratios (DRs) of bicyclic sesquiterpanes were screened and appraised. These diagnostic ratios are applicable to the identification of unweathered crude oil samples coming from different regions. In both severe weathering processes, only the ratio total pentamethyldecahydronaphthalene to total pentamethyldecahydronaphthalene and hexamethyldecahydronaphthalene mained relatively stable. This has a good indication for the identification of the source of severe weathering oil spill. If it has been verified by a variety of oil products, it can be recommended as the identification index of severe weathering oil spill.