Graduate Thesis Or Dissertation


Assessing Chemical Dispersants Used During the Deepwater Horizon Oil Spill : Method Innovation and Application Public Deposited

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  • Large quantities of the chemical oil dispersant Corexit were applied in the Gulf of Mexico (Gulf) in response to the Deepwater Horizon oil spill. Large data gaps regarding the potential transport, persistence and impact of Corexit in the Gulf existed at the time of the emergency response. Analytical methods for the quantification of the individual surface-active-agent (surfactant) components of Corexit in seawater and sediments did not exist and needed to be developed for the support of environmental monitoring and laboratory experiments. The work presented in this thesis addresses important questions about the persistence and transport of the surfactant components of Corexit, namely DOSS, Span 80, Tween 80, and Tween 85 in marine systems. Unique challenges were uncovered and overcome along the way to answering these questions. Chapter 2 describes laboratory microcosm experiments quantifying the biodegradation of the Corexit surfactants in the presence and absence of oil using large volume injection liquidchromatography tandem quadrupole mass spectrometry (LC-MS MS). The extent of primary biodegradation differed for each surfactant and between treatments. Additionally, the microbial and abiotic hydrolysis of DOSS to its transformation intermediate EHSS was quantified. Significant biodegradation of DOSS was observed but mass balance with EHSS was not achieved, indicating that other transformation intermediates are formed during DOSS biodegradation. In contrast to a previous literature report, the abiotic hydrolysis of DOSS was not observed, suggesting that the abiotic losses observed by others were the result of the chemical biocide (sodium azide) employed in that study. Aqueous-phase surfactant concentrations were lower when Corexit was mixed with excess oil, due to partitioning of the surfactants into oil. The implication of this finding is that surfactant exposure concentrations depend on how Corexit is prepared. Chapter 3 describes the development and demonstration of an analytical method for the extraction and quantification of DOSS in marine sediments and sediment-trap materials using liquid chromatography quadrupole time of flight mass spectrometry (LC-QTOF). The use of QTOF resolved interferences without the need for sample cleanup that were observed in some samples analyzed by LC-MS MS. Chapter 4 describes the application of the method developed in Chapter 3 to a large set of sediments collected in the Gulf between 2010 and 2015. Publicly available, but unpublished data, on DOSS in gulf sediments generated as part of the natural resource damage assessment (NRDA) were also incorporated and use to identify an area of DOSS-impacted sediments. The temporal trend in DOSS concentration from 2010-2015 indicates long-term persistence of DOSS with quantifiable DOSS concentrations remaining for more than 5 years after the application of Corexit during the Deepwater Horizon oil-spill. Chapter 5 describes the quantification of Corexit surfactants in aerosols generated under laboratory conditions that simulate bursting bubbles that occur under breaking waves. The ejection of the Corexit surfactants as aerosols was demonstrated. Collectively, the research presented in this thesis overcame analytical challenges in the measurement of the Corexit surfactants and informed the transport and persistence of DOSS and other surfactants in marine systems.
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