ARE OXYGENATED HYDROCARBONS IMPORTANT OIL DEGRADATION PRODUCTS AFTER OIL SPILLS?

ABSTRACT 2017-186 Oxygenated hydrocarbons (OxHC) are major and persistent hydrocarbon degradation products that are formed after oil spills. However, there are still knowledge gaps related to formation, fate and effect of these products. The objective of this study was to find if the OxHCs present in weathered oils are more or less toxic and bioaccumulative than their parent compounds. In this study, we first systematically investigated bioaccumulation potential and toxicity potential of oxygenated oil weathering products, using predictions based on Abraham Solvation Parameters. We then quantified OxHC in select crude and weathered oil samples from the 2010 Deepwater Horizon Oil Spill (DHOS). Seawater-dissolved concentrations were calculated using Raoult’s law, and baseline toxicity of the mixtures towards fathead minnow fish were estimated. We found that while OxHC generally had a lower bioaccumulation potential than corresponding n-alkanes, the baseline toxicity of OxHC was higher than that of their n-alkane precursors due to increased water solubility. After 30 days of weathering, toxicity of the oil residue decreased by a factor of ten. However, following six years of weathering, the calculated residual toxicity only dropped by a further factor of two. In the most weathered sample, toxicity was dominated by OxHC and not polycyclic aromatic hydrocarbons (PAHs). These preliminary data suggest that further research into OxHC toxicity is necessary. In future, additional factors such as reactive toxicity and biotransformation can be implemented to further explore OxHC toxicity and bioaccumulation in long-term environmental impacts of oil spills.

Biodegradation of petroleum in seawater at low temperatures

To evaluate the significance of biodegradation in the removal of polluting oil from cold oceans, freshly collected seawater samples were treated with petroleum and were incubated at controlled temperatures between 5 and 20 °C. Biodegradation was monitored by the measurement of CO2 evolution and by quantitative gas chromatographic analysis. Low water temperatures not only resulted in slower degradation rates, but caused increasing lag periods that preceded the onset of measurable biodegradation. A substantial portion of these lag periods was eliminated when, instead of fresh petroleum, a "weathered" sample was used. The results suggest that some volatile components of petroleum that are inhibitory to oil-degrading microorganisms evaporate only very slowly at low temperatures, and thus retard biodegradation.

IDENTIFICATION OF OIL LEAKS AND SPILLS

ABSTRACT Development of a tentative method of comparison of unknown petroleum leaks and spills with known sources is reported. Methods of sampling and preparation of a residue, free of water and solids, equivalent to a 24-hour weathered sample are described. The principal method of analysis is high-resolution temperature programmed gas chromatography. Additional analyses considered are sulfur, nitrogen, nickel, vanadium and infrared. Analyses of samples by 10 cooperating laboratories are reported.