Fingerprinting complex mixed oil spills at refineries: Source identification, quantitative source apportionment, and biodegradation assessment.

Chemical fingerprinting is well-established for source identification of marine oil spill, however cases for contaminated industrial sites are much more complicated. This study applied an integrated framework (combining source identification, source apportionment, and biodegradation assessment) for a forensic investigation of a 50,000 m2 Light Non-Aqueous Phase Liquid (LNAPL) plume. Comprehensive analysis of 28 samples (16 floating oils, 10 petroleum products, 2 crude oils) revealed four distinct oil mixtures within the LNAPL plume, each comprising varying proportions of reformulated gasoline, catalytic cracking diesel, straight-run diesel, and crude oil. More importantly, this work made three key methodological advances: (1) We developed a new source apportionment method to quantify oil mixing ratio of ternary oil mixtures (gasoline-diesel-crude oil). The new method overcame the limitations of conventional biomarker-based approaches that was not applicable to light distillates or multi-source contamination; (2) A novel biodegradation index (BdgrI) was developed to reconcile source-specific mixing ratios with conventional biodegradation ratio, enabling standardized assessment of biodegradation degree in oil mixtures; (3) We also demonstrated that the commonly used biomarker "bicyclic sesquiterpanes" were unable to achieve accurate source identification for middle distillates with the same crude oil feedstocks and similar distillation cut temperatures, since the distribution characteristics of bicyclic sesquiterpanes in crude oil were "inherited" by middle distillates with similar distillation cut temperatures, even if they were processed through different refining technologies. These innovations significantly enhance forensic capability for complex petroleum contamination, improving source identification accuracy, guiding targeted bioremediation strategies, and providing quantitative scientific support for environmental liability allocation and remediation cost-sharing at contaminated refinery sites.