Scientists from the University of Maryland and Tulane University investigated the possibility of using food-grade materials for oil spill remediation.
Their goal was to find alternatives to synthetic detergents, such as Corexit 9500A, that are currently used for this purpose. As a first step towards this goal, they examined the stability of emulsions of crude oil in seawater in the presence of various food-grade materials. They found that a blend of lecithin (from soybean) and Tween 80 (a material used in ice cream) generated more stable emulsions than did Corexit 9500A. The team published their findings in the August 2014 issue of Langmuir: An effective dispersant for oil spills based on food-grade amphiphiles.
Responders to the Deepwater Horizon oil spill used about two million gallons of Corexit to disperse the oil into discrete droplets that remained submerged in the water column, preventing slicks from reaching coastlines and promoting microbial degradation. Corexit, the only readily-available and federally-approved dispersant, includes the surfactant dioctyl sodium sulfosuccinate (DOSS) which is a potential toxin and a known eye and skin irritant that can persist in the environment for years. In an effort to create a safer dispersant, researchers examined the ability of mixtures of Tween 80 and soybean-based lecithin, which are already used in pharmaceutical and food products, to emulsify crude oil in seawater.
The team tested the compounds individually and blended together. The components were ineffective emulsifiers by themselves as lecithin is too hydrophobic (oil-soluble but not water-soluble) and Tween 80 is too hydrophilic (water-soluble but not oil-soluble). However, a blend containing a 60/40 ratio of lecithin/Tween 80 generated effective, stable emulsions regardless of the type of oil, water, or solvent tested. The blend produced relatively stable emulsions even at low concentrations of the two molecules. The researchers explained that the synergy between lecithin and Tween 80 is related to three distinct aspects: lecithin and Tween 80 molecules pack tightly around oil droplets; the low water-solubility of lecithin makes molecules less likely to travel through water from droplet to droplet, anchoring the molecules to the oil droplets’ surface; and the high water-solubility of Tween 80 repels other oil droplets in favor of the surrounding water, preventing coalescence.
Comparison experiments revealed differences between the emulsification capabilities of the lecithin/Tween 80 blend and those of Corexit 9500A. The dispersed oil formed in the Corexit experiment initially remained stable, then rapidly recombined into a surface oil layer after a few minutes. Microscopic images revealed large drops (about 100 micrometers) and even larger “blobs” at the onset of the experiment. The dispersed oil that formed in the lecithin/Tween 80 emulsion experiments remained stable even after several hours, and the droplet size remained small (about 5 micrometers).
The researchers acknowledged that in an ocean setting the function of Corexit is to disperse surface oil into droplets so waves will transport those droplets down into the water. They also note that, while there remains an open question about the measurable differences between dispersion and emulsification, the smaller the droplets and the greater their resistance to coalescence, the better the overall extent of oil dispersion.
With this study’s results, they concluded that the lecithin/Tween 80 blend could serve as a cost-effective and potentially safer or more biocompatible candidate for oil-spill treatment than Corexit. The study’s lead investigator, Professor Raghavan from the University of Maryland, noted that “The discovery that lecithin/Tween 80 blends are effective emulsifiers of crude oil was a serendipitous one.” His team was already familiar with lecithin from prior lab work, then as Raghaven explains, “It was my students, specifically Jasmin Athas, who discovered its synergistic interaction with Tween 80. Thereafter, we collaborated with Professor Vijay John at Tulane University to confirm this effect. We hope our work will prove to be an important first step in the design of safer alternatives to current dispersants for oil-spill treatment.”
The team plans to conduct comparison studies of the blend and commercial dispersants using models to simulate the dispersion of a thin layer of oil into seawater, with a specific focus on the role of solvents. Future studies will also seek to confirm the nontoxicity of lecithin/Tween 80 blend on marine organisms.
The study’s authors are Jasmin C. Athas, Kelly Jun, Caitlyn McCafferty, Olasehinde Owoseni, Vijay T. John, and Srinivasa R. Raghavan (Raghavan website).
This research was made possible by a grant from the Gulf of Mexico Research Initiative (GoMRI) to the Consortium for the Molecular Engineering of Dispersant Systems (C-MEDS).
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 http://gulfresearchinitiative.org/.