OCS Study BOEM 2018-036. U.S. Department of the Interior, Bureau of Ocean Energy Management (BOEM), Alaska Outer Continental Shelf Region, and the University of Alaska Fairbanks. 46 pp.
OCS Study BOEM 2018-036. U.S. Department of the Interior, Bureau of Ocean Energy Management (BOEM), Alaska Outer Continental Shelf Region, and the University of Alaska Fairbanks. 46 pp.
In the event of an oil spill in the Arctic Ocean, the use of chemical dispersants is one potential option for oil spill response. Corexit 9500A is currently the principal chemical dispersant stockpiled and is likely to be applied to an oil spill in the Arctic, should it receive regulatory approval. Before its risks can be fully assessed, there is a need to determine the fate and persistence of Corexit 9500A in the Arctic marine environment. In this project, we quantified biodegradation of the chemical dispersant Corexit 9500A in Arctic seawater and determined how the presence of crude oil alongside dispersants affects the biodegradation of both dispersants and oil. Using advanced molecular tools, we identified microbes active in oil and dispersant biodegradation in Arctic seawater. We found that crude oil and surfactant components of Corexit 9500A can undergo substantial biodegradation within 28 days in Arctic surface seawater: 36– 41% of oil; 33–77% of bis-(2-ethylhexyl) sulfosuccinate (DOSS); 96% of Span 80. In near-shore seawater, crude oil degraded slightly more extensively than in offshore waters. Overall, the nonionic surfactant components of Corexit 9500A (Tween 80+85 and Span 80) were more labile than DOSS, with the nonionics dropping to below detection limits within 2–5 days, while DOSS was more persistent, especially in the presence of oil. Molecular analyses of the microbial communities were performed in the 2013–14 incubations. The microbial population size grew more extensively in response to Corexit 9500A than oil alone within 28 days, suggesting that some components are more readily biodegraded and utilized as growth substrates. In general, different members of the microbial community appear to be responsible for Corexit 9500A and oil biodegradation; however, throughout the incubation, a subset of taxa (Oleispira, Colwellia, Lutibacter, and an unclassified Flavobacteriaceae spp.) and functional genes associated with oil biodegradation (alkB, nagG, and pchCF) increased in response to both oil and Corexit 9500A, suggesting that some organisms may biodegrade both Corexit 9500A components and oil. Together, these findings indicate that the indigenous microbial community in the Chukchi Sea in summer and fall can perform substantial oil and dispersant biodegradation within 28 days, although the longer-term fate of the residual components is yet-to-be-determined.