Dispersants are a class of chemicals that enhance natural dispersion of oil in marine environments. When chemical dispersants are applied to oil slicks, the dispersant molecules interact at the oil-water interface, reducing the interfacial tension, and allow oil droplets to break away from slicks or sheens. Once separated from the surface slick, the droplets remain in the mixed layer and naturally disperse. Learn more>>
In order for dispersants to be effective, the water must be turbulent. The mixing energy provided by wind and waves allows the oil to break down to smaller size droplets. Katz (2009) used holographic imagery to capture how this process occurs view final report here>>. The stretching of the droplet into a curved "dumbbell" shape is caused by turbulence and the lowered interfacial tension of the oil as a result of the dispersant. This process produces a range of droplet sizes, referred to as a droplet size distribution. The size distribution is a function of the magnitude of turbulence and the type and amount of dispersant applied. Droplet size is one of the key factors dictating the fate and behavior of the oil. The ultimate goal of dispersants is to dilute the oil to an extent that it represents a low risk to the environment. This is accomplished through dispersing oil droplets into the water column, where they enter the mixed layer (ML) and disperse via currents and natural diffusion in three dimensions. Dispersants do not decrease the quantity of oil, they force dilution of the oil droplets into a large volume of water. Once dispersed, these oil droplets can have various potential fates including: sedimentation; dissolution; biodegradation; re-coalescence; and uptake by biota, either through ingestion or absorption (i.e., via direct contact on membranes or body surfaces).
Click on the photo to the right to view the video (Joseph Katz, UNH).
A Comprehensive Dispersant Hazard Assessment Based on Nearly 50-Years of Aquatic Toxicity Data, Adriana Bejarnao, Research Planning Inc
Critical Review and Analysis of Aquatic Toxcity Data on Oil Spill Dispersants, Adriana Bejarnao, Research Planning Inc
A Comparative Assessment of the Aquatic Toxicity of Corexit 9500 to Marine Organisms, Brandi Echols, Langdon, Stubblefield, Rand and Gardinali (2018).
BSEE large study comparative report here>>
Deepwater Horizon Dispersant Use meeting report (May 26 & 27, 2010) here>>
Deepwater Horizon Dispersant Use meeting press release (May 27, 2010)
Dispersant Research Information here>>
Dispersed Oil Research Forum Presentations - February 1-2, 2007 here>>
U.S. EPA/ORD Dispersant In Vitro Testing Analysis of Eight Oil Spill Dispersants Using In Vitro Tests for Endocrine and Other Biological Activity here>>
USEPA Dispersant Toxicity Testing (June 30, 2010) Comparative Toxicity of Eight Oil Dispersant Products on Two Gulf of Mexico Aquatic Test Species
Australian Maritime Safety Administration (August 2009)
Large-Scale Cold Water Dispersant Effectiveness Experiments with Alaskan Crude Oils and Corexit 9500 and 9527 Dispersants. The paper was published in Marine Pollution Bulletin (MMS)
A bibliography compiled and edited by John Conover, Associate Librarian at LUMCON
11/17/07 presentation by Francois Merlin (Cedre)
SPREEX: Spill Response Experience WP2-T2.4 - Use of Dispersants - State of the Art
Francois Xavier Merlin and Georges Peigne (Cedre)
Understanding Oil Spill Dispersants: Efficacy and Effects
This National Academy report is available online
Research & Development Needs For Making Decisions Regarding Dispersing Oil, September 20-21, 2005
The workshop report is available in pdf here>>
The Center hosted a short course, Efficacy and Effects of Dispersants in Oil Spill Response: Progress since the 2005 NRC Report, at the 2008 International Oil Spill Conference on May 4, 2008.