A Decade of Research Reveals Significance of Sunlight’s Effects on Floating Oil
– MAY 5, 2020
April 2020 marks ten years since the tragic Deepwater Horizon incident in the Gulf of Mexico. It also marks a decade of oil spill research that followed funded by the Gulf of Mexico Research Initiate (GoMRI), resulting in more than 1,350 peer-reviews studies published so far, that are helping us understand the oil’s fate and impacts and be better prepared for future spills.
The subject of how sunlight alters floating surface oil is one area that made significant strides. Scientists Collin P. Ward, Christopher M. Reddy, and Edward B. Overton describe these scientific advancements in a feature article in the American Geophysical Union’s science news magazine Eos Why Sunlight Matters for Marine Oil Spills.
The Eos article helps share the findings from a two-year synthesis effort that began at a 2018 workshop, which resulted in this peer-reviewed study: How the 2010 Deepwater Horizon spill reshaped our understanding of crude oil photochemical weathering at sea: a past, present, and future perspective.
Photo-oxidation is a weathering process that changes the chemical and physical properties of floating oil, and those changes have wide-ranging implications for ecosystem and human health and for spill response operations. Photo-oxidized oil is more difficult to clean up, contributing to persistent oil residues that wash up on valuable and sensitive coastline. However, prior to the recently-gained knowledge summarized in this Eos article, its role was not thought to be significant compared to evaporation and microbes degrading oil.
That’s changed now, thanks to a sustained period of focused research that revealed the rate and extent of Deepwater Horizon oil which was photo-oxidized far surpassed estimates based on early conceptual models of oil weathering.
The authors described the two pathways for oil photo-oxidation: Directly as crude oil compounds absorb natural sunlight and oxidize, and indirectly when a wide range of reactive oxygen species are produced by sunlight, which can then oxidize other oil compounds that did not absorb light directly. This indirect pathway dominated, making a much larger fraction of spilled oil vulnerable to photo-oxidation.
They also explained that there is synergy between photochemical weathering and emulsification. Sunlight produces surface-active compounds that reside at the oil-water interface and promote the formation of highly viscous and stable emulsions, which are very challenging to disperse. Sunlight chemically altered approximately half of the floating oil from Deepwater Horizon in a few days, creating openings for oxygen attachment and making Corexit less effective at dispersing the oil than anticipated.
The authors offered a unique perspective on the factors that aligned to make their discoveries possible following Deepwater Horizon:
- A continuous stream of floating oil that researchers could sample at different stages of weathering.
- Funding from GoMRI and other sources that allowed for sustained, in-depth analyses, which early on established the extent of oxidation that later studies built upon for understanding oxidation rates and pathways and their potential impacts on fate and transport models and response operations*.
- Technological breakthroughs in satellite-based remote sensing that estimated oil film surface area and thickness, critical for estimating photooxidation rates (Study Describes Oil Slick Differences in Natural Seeps and Deepwater Horizon); comprehensive two-dimensional gas chromatography coupled with flame ionization detection that helped determine the precursors of photooxidation (Oxygenated weathering products of Deepwater Horizon oil come from surprising precursors); Fourier transform ion cyclotron resonance mass spectrometry that helped determine photooxidation products and confirmed that indirect processes governed oxidation (Study Extends Precise Analysis of Oxygenated Products in Weathered Oil and Study Confirms Sun Exposure Increases Oxygen Molecules in Oil Slicks); and separation technologies that helped isolate and identify oil components that are produced by sunlight, partition to the oil-water interface, and promote emulsification (Fractionation of Interfacial Material Reveals a Continuum of Acidic Species That Contribute to Stable Emulsion Formation and Sunlight-Induced Molecular Progression of Oil into Oxidized Oil Soluble Species, Interfacial Material, and Dissolved Organic Matter).
- Diversified expertise through unprecedented interdisciplinary collaborations, including petroleum and environmental chemists, modelers and oil spill response scientists, and biogeochemists and isotope geochemists.
The scientific advancements gained following Deepwater Horizon provide a rare opportunity to continue advancing oil spill science. Workforces and laboratories are primed and ready for oil spill research, and cross-disciplinary connections are established. Priority areas for continued research include broadening applications to spills in other locations and different conditions, assessing emerging dispersant technologies, and incorporating photochemical processes into oil fate and response operation models.
*Oil spill studies on the extent of photooxidation, oxidation rates and pathways, and impacts on fate and transport models and response operations:
- Study Finds Oxygenated Compounds Formed in Weathered Oil Samples
- Study Extends Precise Analysis of Oxygenated Products in Weathered Oil
- Study Confirms Sun Exposure Increases Oxygen Molecules in Oil Slicks
- Study Finds Sunlight Reduced Dispersant’s Effectiveness During Deepwater Horizon
- Asphaltene Content and Composition as a Measure of Deepwater Horizon Oil Spill Losses within the First 80 Days
- Partial Photochemical Oxidation Was a Dominant Fate of Deepwater Horizon Surface Oil
- Oxygen Isotopes (δ18O) Trace Photochemical Hydrocarbon Oxidation at the Sea Surface
By Nilde Maggie Dannreuther. Contact firstname.lastname@example.org with questions or comments.
This research was made possible in part by grants from the Gulf of Mexico Research Initiative (GoMRI) for the review of research for synthesis (Collin Ward and Ed Overton) and to:
Tulane University for the project Toxicological Properties of Specific Aromatic Hydrocarbons Isolated from Fresh and Aged Crude Oil from the Deepwater Horizon Spill (Edward Overton)
Louisiana State University for these projects (Edward Overton):
- Analysis of Samples Collected to Measure Effects of Stressors on Coastal Wetlands
- Collection of Near-Shore Sediment Samples Associated with Potential Fishery Impacts
- Elementally Resolved Chemistry of the Evolution of the Oil Spill
- Investigating the Potential Ecological Impacts of the Deepwater Horizon Oil Spill and the Biologically-mediated Mechanisms of Removal of Polycyclic Aromatic Hydrocarbons (PAHs)
- Effects of Oil, Dispersant, and Remediation-related Human Activities on Marsh Plants and Associated Insects and Mollusks
Florida State University for the project The State-of-the-Art Unraveling of the Biotic and Abiotic Chemical Evolution of Macondo Oil: 2010-2018. (Christopher Reddy and Collin Ward)
The research consortium Deepsea to Coast Connectivity in the Eastern Gulf of Mexico or DEEP-C (Christopher Reddy)
The Center for the Integrated Modeling and Analysis of Gulf Ecosystems II or C-IMAGE II (Christopher Reddy)
Woods Hole Oceanographic Institution for the project Collection and Analysis of Oiled Sand Patties along the Gulf Coast (Christopher Reddy)
The Gulf of Mexico Research Initiative (GoMRI) is a 10-year independent research program established to study the effect, and the potential associated impact, of hydrocarbon releases on the environment and public health, as well as to develop improved spill mitigation, oil detection, characterization and remediation technologies. An independent and academic 20-member Research Board makes the funding and research direction decisions to ensure the intellectual quality, effectiveness and academic independence of the GoMRI research. All research data, findings and publications will be made publicly available. The program was established through a $500 million financial commitment from BP. For more information, visit https://gulfresearchinitiative.org/.
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