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Summer 2005 Vol. 5 No. 2

Table of Contents

©Photodisc Oil Spill Dispersants

Chemicals Used in Deep Waters Should Be Studied for Use Closer to Coastline

The National Research Council issued a report in 1989 that recommended chemical dispersants be considered as a first response option to oil spills. When the worst oil spill in U.S. history occurred later that year, cleanup crews tried to use oil dispersants at the scene of the Exxon Valdez disaster. Although sufficient supplies of a chemical dispersant were stored nearby, only one helicopter bucket spray system was available to apply the chemical to the slick, and the few applications that did take place were deemed ineffective.

Since then, dispersants have been used extensively in other parts of the world, and they have been successfully employed in response to several oil spills in the Gulf of Mexico. Nevertheless, continued difficulty in quickly mobilizing oil dispersal prompted the U.S. Coast Guard recently to require that more equipment and personnel be on hand to apply dispersants to spills in a timely manner. The use of dispersants is generally approved for spills at least five kilometers from shore and in water at least 10 meters deep, where dispersed oil's impact on marine life is likely to be low. But now that dispersal equipment will be more readily available, officials are wondering whether these agents should be used in nearshore, shallow waters, where most oils spills in the United States occur but also where much less is known about how even small droplets of oil affect the sea life and plants living there. Again, the Research Council was called upon to examine the current state of science surrounding the use of dispersants as a response to oil spills, particularly nearshore ones.


Oil spill dispersants are controversial because unlike traditional cleanup techniques, where booms and skimmers are used in attempts to remove oil altogether from the water's surface, dispersants do not reduce the total amount of oil entering the sea. They can, however, dissolve a slick before it reaches the shoreline, where the oil smears birds and marine mammals and turns beaches and coastal wetlands black. The chemical agents used as dispersants work by reducing the tension between oil and water, thereby enhancing the natural process of dispersion that takes place when waves mix large numbers of small oil droplets into the water beneath a spill. To be effective, however, they must be used in a hurry -- within 12 to 48 hours after a spill according to the committee that wrote the new report -- before fluctuations in water temperature change the oil's viscosity, possibly turning it into a semi-solid that cannot be dispersed.

As the report notes, the decision to use dispersants is a trade-off between decreasing the risk to organisms that thrive on the water's surface and coastline, and possibly increasing the risk to fish populations, sea grasses and coral reefs, and creatures that live on the seafloor. Better information is needed to decide whether to make that trade-off.

With limited funding -- less than $10 million annually -- for research on oil spill dispersants, the report recommends that federal and state agencies, along with industry and international partners, establish an integrated research plan focused on experiments to support decisions about when and where to use dispersants. For example, models need to be designed that can predict the concentration and underwater movement of dispersed oil more accurately and deliver rough estimates to emergency responders within hours of a spill. Monitors also should be rapidly deployed to the scene of any spill where dispersants are used in order to collect data on the fate of the dispersed oil. And more studies are needed on the toxicity of dispersed oil to sea life.

For now, experiments should be conducted in wave tanks, although field testing in actual water environments may be deemed necessary in the future, the report says.   -- Bill Kearney

Understanding Oil Spill Dispersants: Efficacy and Effects. Committee on Understanding Oil Spill Dispersants: Efficacy and Effects, Ocean Studies Board, Division on Earth and Life Studies (2005, approx. 248 pp.; ISBN 0-309-09562-X; available from the National Academies Press, tel. 1-800-624-6242; $40.00 plus $4.50 shipping for single copies).

The committee was chaired by Jacqueline Michel, president, Research Planning Inc., New Orleans. The study was funded by the U.S. Department of the Interior's Mineral Management Service, National Oceanic and Atmospheric Administration, U.S. Coast Guard, and the American Petroleum Institute.

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Copyright 2005 by the National Academy of Sciences