ARE OXYGENATED HYDROCARBONS IMPORTANT OIL DEGRADATION PRODUCTS AFTER OIL SPILLS?

Abstract

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.