Evaluation of diagnostic ratios of phenanthrenes and chrysenes for the identification of severely weathered spilled oils from the simulation weathering and the Sinopec pipeline explosion at Huangdao, 2013

The composition and physical properties of spilled oil undergo great changes during a serious weathering process. This causes great difficulties for identifying the source of an oil spill. So stable and trustworthy diagnostic ratios (DRs) for the accurate identification of severely weathered spilled oils are very important. An explosion in the Sinopec pipeline happened on November 22, 2013 at Qingdao, China. Local beaches at Jiaozhou Bay were polluted by spilled oils. After the accident we collected original spilled oil samples from an area free from human interference near the oil leakage point. Synchronized with actual beach weathering, laboratory experiments were conducted to simulate oil weathering for 360 days by using the collected original spilled oil samples. Based on the t-test and the repeatability limit method, 46 diagnostic ratios (DRs) of phenanthrenes and chrysenes were screened. 18 DRs maintained remarkable stability during the simulated weathering experiments and field weathering process. These stable ratios can retain the characteristics of the oil source during weathering. They are very beneficial for improving the accuracy of identifying the source of severely weathered oil and can be used as an effective supplement to the existing index system for source identification.