Evaluation of light petroleum biomarkers for the 3rd edition of the European Committee for Standardization methodology for oil spill identification (EN15522-2)

Abstract

As an expert body, the Oil Spill Identification Network of experts within the Bonn Agreement (OSINet) developed a common methodology for oil identification (denoted CEN/Tr 15522-2 for 1st and 2nd, and EN15522-2 for the upcoming 3rd edition) published by the European Committee for Standardization (CEN). OSINet decided that the 3rd edition of the methodology should expand on diagnostic ratios for light to mid-range petroleum distillates (LMPD). Many ratios involving light petroleum biomarkers have been proposed by the oil spill community, based on literature, in-house studies and case work experience. To establish a normative set of approximately 25 ratios for light biomarkers, OSINet decided to apply six criteria. Three criteria concern easily obtained information, on similarities in (1) retention time, and (2) mass-to-charge ratio, and (3) sufficient variation in compound classes. The present study was initiated to increase knowledge on the three remaining criteria: (4) documented weathering susceptibility of biomarkers, which was done by a biodegradation experiment of diesel in soil and supported by additional literature studies, (5) ubiquitous presence of proposed compounds in LMPD, and (6) good discriminative ability between sources. The last two criteria were studied using 87 unique non-weathered oil samples from 14 countries and supplementary literature data. The experimental results and the literature studies for criterion 4 demonstrated that LMPD will be susceptible to pronounced evaporation in an open environment, resulting in extensive information loss over time. Relative to evaporation, the processes of dissolution and photo-oxidation will generally play a limited part in weathering for these products. Signs of biodegradation will have reduced incidence of fatty acid methyl esters (FAMEs), n-alkanes and compounds including long straight-chain alkyl substituents. Of 78 ratios initially evaluated for criteria 5 and 6, many compounds were not detected at sufficient levels in LMPD or did not meet the requirements on analytical performance. After this collaborative study, 39 proposed ratios remained as candidates for a normative set. Based on information on all six criteria, OSINet aims at making an informed decision about diagnostic ratios for light petroleum biomarkers in the 3rd edition of the CEN methodology.