Fingerprinting technique is a universal method for tracing oil spill. It is usually achieved by means of diagnostic ratios (DRs) of biomarkers. In the process of severely weathering, the important components usually change greatly and the relevant diagnostic ratios may also change. Therefore, it is more difficult to trace severely weathered oil to its source. On 22 November 2013, the huge explosion of Sinopec pipeline occurred in Qingdao, China. The beaches near the explosion site were contaminated and damaged by oil spills. After the explosion, an actual weathering experiment was carried out on an oil-polluted beach. The original and weathered spilled oil samples have been collected from this site. Synchronized with actual coastal weathering, a 360-day Lab simulated weathering experiment was carried out using the sampled original oil spill samples. According to data analysis techniques including similarity, t-test method and repeatability limit analysis, 27 new diagnostic ratios of dibenzothiophenes and fluorenes in the weathered oil samples were selected and verified. 6 of them maintained good stability during both of the simulated and actual weathering process. It is recommended that these stable DRs be used for tracing the source of severely weathered oil spills to promote the efficiency and accuracy.
Keywords: Seriously weathered; diagnostic ratios; dibenzothiophenes; fluorenes; oil spill; source identification.