Biodegradation of low sulfur fuel oil HDME 50 in seawater at sub-arctic temperatures with and without dispersants

Abstract Dispersant has been used effectively to enhance biodegradation rate of spilled oil in marine environment even at low temperature. However, the introduction of new ultra-low sulfur fuel oils (LSFO) to meet the new regulation for sulfur emission from ships, poses new challenges for oil spill response. There is limited knowledge regarding the dispersibility of the new oil type when applying dispersant, how toxic are the dispersed oils and how fast are the biodegradation of the oil components. Our current study tested biodegradation potential of chemically dispersed new LSFO, Hybrid Wide Range Gas Oil (HDME 50) and the un-dispersed oil film in seawater at 13 and 5 °C. Our study demonstrated that both dispersed HDME 50 and un-dispersed oil were biodegraded by bacterial communities in the seawater which was collected from Lofoten, Norway during September and March. The depletions of total hydrocarbon content after 64 days were 44, 38 and 23% for the dispersed oil and oil film microcosms at 13 °C, and oil film microcosms at 5 °C, respectively. The half-lives of n -alkanes and naphthalenes were shortest for the dispersed oil at 13 °C, followed by the oil film at the same temperature, and longest for oil film at 5 °C. Bacteria genera Polaribacter, Colwellia, Comamonas, Glaciecola and the unclassified Methylophilaceae became dominant in both dispersed oil and oil film microcosms tested at 13 °C. There was a delay of the temporal succession for genera Polaribacter and Colwellia at 5 °C compared to 13 °C. Genus Colwellia presented with higher abundance at 5 than 13 °C. Beside the common bacterial taxa for both temperatures, there were other bacterial taxa that only increased in oil treated winter seawater such as unclassified Flavobacteriaceae and unclassified Nitrincolaceae (formerly Oceanospirillaceae ) .