The oil spill resulting from the explosion of the Deepwater Horizon drilling rig has released an unprecedented amount of crude oil into the Gulf of Mexico. The oil is entering the sea from the bottom and either settles into a neutrally-buoyant subsurface layer or transits to the surface. During expulsion from the primary leak, transport and weathering, water-soluble components of the crude oil are slowly dissolving into the seawater. The composition and reactivity of these components are poorly constrained but are critically important to predicting the possible impact of this spill on marine life and ecosystem dynamics in the Gulf of Mexico.
With funding from this Grant for Rapid Response Research (RAPID), a research team at the Woods Hole Oceanographic Institution will use ultra-high resolution mass spectrometry to assess the composition of the water-soluble component of the leaking crude oil. The study will provide an initial assessment of compositional variability along temporal and spatial gradients near the active spill. The analytical capabilities of the Woods Hole team complement other planned analyses, and the results will be integrated with other chemical and biological data to provide a more complete analysis of the weathering and degradation of this oil spill.
Broader Impacts: An undergraduate summer will be part of the team working on this project, affording the student an opportunity to be involved in timely research on an environmental disaster. In addition, it will provide the student with experience with cutting-edge analytical chemical techniques and their synthesis with other physical, chemical and biological data available through collaboration with other scientists who are already funded to conduct research on the environmental aspects of the oil spill.
The Deepwater Horizon oil spill introduced millions of gallons of crude oil, natural gas, and dispersants into the Gulf of Mexico. Understanding the fate of these materials is paramount to ensuring ecosystem recovery. Our lab participated in the scientific response to this catastrophe by applying a sensitive detector to Gulf water samples to find the components of oil and dispersants that dissolved in seawater. Our detector, an ultrahigh resolution mass spectrometer, determines the mass of individual molecules with high precision and accuracy, and can resolve thousands of molecules within complex mixtures. We acquired water samples from the Gulf of Mexico, during and after the Deepwater Horizon blowout, through a collaboration with Dr. David Valentine at the University of California – Santa Barbara. The water samples spanned a range of distances from the wellhead as well as water column depths. We removed our target compounds from the seawater with extraction methods optimized for both the natural organic materials in seawater as well as for organic molecules within crude oil and dispersants. We analyzed these samples as well as the original crude oil, the dispersant mixtures and non-contaminated seawater. Our screening analyses revealed the presence of the dispersants in seawater samples acquired from the same depth as the gas and hydrocarbon plume observed by other investigators. We confirmed the identity of this compound as dioctyl sodium sulfosuccinate (DOSS), an anionic surfactant present in both formulations of the dispersant used at the Deepwater Horizon site. In collaboration with scientists at the U.S. EPA, we developed a sensitive assay for this compound that was 1000 times more sensitive than the available methods at the time. With this method, we quantified DOSS in all the water samples in our possession and established its spatial and vertical distribution in the water column. We noticed that the bulk of the DOSS was found at the plume depth and the concentrations matched those predicted from the application data available from public websites. In addition, the concentrations of DOSS decreased over 2 months but this decrease could be explained by passive dilution. We could not rule out biodegradation of DOSS as well but our results did not support significant degradation over time. This study was the first published work on the dispersant application at the Deepwater Horizon blowout. We continue to work on this project by comparing our full screening analyses to the original crude oil and to non-contaminated seawater. To date, we have observed that acid-containing molecules were present in water samples contaminated with oil. Our analytical method differs from standard methods in the oil spill community because it detects compounds that are water-soluble and contain oxygen, nitrogen and /or sulfur atoms. These compounds have rarely been tracked in previous oil spills but could contribute to the environmental impact of spills because they are preferentially transferred into water during a spill and because they harbor potentially higher toxicity to marine organisms. In our Gulf of Mexico water samples, we are working to identify any compounds that ultimately derived from the spilled crude oil in order to propose new marker compounds that could be used to track oil spills in the future. This project was an excellent example of the application of basic science techniques to a societal need, namely determining the fate of oil, gas and dispersants during and after the Deepwater Horizon oil spill. The application and eventual fate of dispersants were intensely debated by policymakers, scientists and the media during and after the Deepwater Horizon spill. Our work provided the first concrete data for this discussion and establishes the environmental concentrations relevant to ongoing and future toxicity studies for this spill. This information was shared with the public through interviews with media and industry groups, collaborations with government scientists and presentations at workshops and panels dedicated to the Deepwater Horizon aftermath.
