Facts about Dispersants

Friends from Prince William Sound Reaching Out to Communities on the Gulf

Joe Banta, Environmental Monitoring Project Manager, from PWSRCAC, provides information on dispersants through the following links:

~May 5, 2010~

The dispersants being used on the Deepwater Horizon drilling disaster has brought about many questions in regard to their safeness to the water and wildlife above and beneath the Gulf.  The following is a Q&A provided by Kristina Peterson of the University of New Orleans CHART with Joe Banta, Project Manager for Environmental Monitoring of Prince William Sound Regional Citizen’s Advisory Council.  Mr. Banta’s organization has done research on dispersants for many years.  ***A PDF of this Q&A is available for download on the “PDF’s To Download" page.

1. What dispersant is being used?  Is it one or a combination, what are the chemical properties?
We do not have a direct link in to the Unified Command that is managing the spill response so we don’t know for sure all of the types of dispersants being used.  The most prevalent dispersants in our country are Corexit 9527 (an older formulation) and Corexit 9500 (a newer formulation) originally developed by Exxon.  We understand that all the dispersants stockpiled in our region of Alaska have been requested by the UC and are being shipped there.  This was reported to be a stockpile of around 85,000 gallons of mostly Corexit 9527. 

I will attach a variety of web links below that provide additional information, including some articles that refer to types of dispersant being used in the Gulf of Mexico.  One of the articles states that over a third of the world’s dispersant stockpiles have already been used on the spill.  We have seen no statements on the efficacy of the dispersants use on this spill and by the size of the slick it appears that the dispersants are not having much of an impact.

Dispersants used on the waters of the United States must be approved by EPA and can by found listed in the Federal Register National contingency Plan Subpart J.  There are 14 approved dispersants at this time.  Because there are this many dispersants, it should be safe to assume that multiple dispersants are being used and that there may be some mixing of them, as a limited number of aerial application packages are being used.  Here is a link to a factsheet about Subpart J - http://www.epa.gov/oem/docs/oil/ncp/NCPfactsheet.pdf.  And here is Subpart J listing the 14 approved dispersants - http://www.epa.gov/oem/docs/oil/ncp/schedule.pdf. 

As far as their chemical properties, dispersants are chemical substances applied to spilled oil that disperse oil into the water column rather than leaving it floating on the surface in a slick.  This  is similar to the effect of the use of soap on greasy dishes.  One useful resource that provided information on the chemical ingredients and effects of dispersants is a Materials Safety Data Sheet (MSDS).  A web search for the dispersants name and “MSDS” will find multiple sites with the MSDS sheets and discussions on them. 

2. Does the dispersant have any residuals?
Dispersants use is based on the concept of them dissolving the oil into droplets that will then dilute and spread out the oil and over a long time period allow microbial degradation to break down the hydrocarbons in the droplets.  If they aren’t spread over the oil they then will not mix with it and could remain on/in the water surface for some time.  One of our organizations concerns that has been shown in the research is that the dispersed oil tend to resurface and re-coalesce.  Some of the links below will provide information to explore this issue further.

3. How long will it remain in the environment, and in what form?
That question is really difficult to deal with based on the immensity of the spill and the lack of information coming out of the Unified command with regard to the efficacy of the dispersant applications.  Based on the discussions above, if mixed with the oil successfully, dispersants should remain with the oil, and, as it has oil components to it, it will likely break down in a similar rate as the oil.  While our organization has concerns about oil remaining in the environment up here for years ( we can still find EVOS oil on beaches more that 20 years later) and for dispersants not being effective in our colder waters on North Slope crude, the warmer waters and temperatures of the Gulf of Mexico may help speed the breakdown of oil and dispersants, but a timeframe is very difficult to come up with on that subject. 

4. What effect will the dispersant have on marine life; from spawning to adult?
This is difficult to answer easily due to the many differences in marine species and the exposures based on their life cycles, but it is clear that sensitive life stages like eggs and larvae are more sensitive to dispersed oil than adults of various species.  In general, oil is more toxic that most modern dispersants.  Our organization has determined that most research on dispersants and dispersed oil is  from an acute toxicity perspective and that much less work has been done on chronic toxicity impacts.  We have recently begun to study this issue of chronic hydrocarbon toxicity and should have study results in the next one to two years. 

We also have tried to track dispersants research in a comprehensive manner in an effort to provide a one-stop source for dispersants research.  You can find that research on our website - http://www.pwsrcac.org/projects/EnvMonitor/dispers.html at the lower section of the page  in an Excel spreadsheet - “A database for the 2008 dispersants literature surveys” and in a written summary on the issues - “A Review of Literature Related to Oil Spill Dispersants 1997-2008.”  This review summarizes studies done on many species and could be of use to explore the issues in this question further. 

5.  Can the dispersant create a toxic situation, for plant, animal and/or human life?  Are we exchanging a toxin we can see (floating crude) for one we cannot (dispersed crude with chemical attachment)?
The research summarized in our report “A Review of Literature Related to Oil Spill Dispersants 1997-2008” provides information about studies on plants and animals, including some on species from the Gulf of Mexico region.  Human health effects are discussed in MSDS sheets for dispersants (as referred to above).

There are trade-offs between removing oil from the surface and leaving it on the surface.  Leaving oil on the surface increases exposure to water surface users, usually macro-fauna such as seabirds and marine mammals, as well as fish that come to the surface for air  or to jump, etc. or seaweeds.  Dispersing oil into the water column exposes the sealife in the water column to the hydrocarbons, i.e. fish, larval forms of fish and shell fish, invertebrates, etc.  This is discussed further in our review discussed above and in the National Academy of Sciences Report cited below. 

Websites and Links for More Information:

• News Articles discussing dispersants use:


• PWSRCAC Resources

• Research Resources and Other Sites
2005 National Academy of Sciences Report - Oil Spill Dispersants: Efficacy and Effects
International Maritime Organization


More Information on Dispersants

These facts are provided through the Office of Personnel Management, FSC, Emergency Actions Group in Washington D.C.  Our thanks to Mark A. Lewack, Emergency Actions Coordinator for providing this information.

Some Facts about Dispersants and Alternative Response Strategies.  To be used in U.S. Waters

  1. They must be on the approved dispersants list, maintained by EPA.  The latest list of dispersants can be found at:  http://www.epa.gov/emergencies/content/ncp/#schedule.  This web site also contains links to information about the approved dispersants, their use, requirements for use, etc. 


  1. There is a dispersant job aid.  See: http://bit.ly/aoaobF.  This web site is sponsored by the National Oceanic and Atmospheric Administration Office of Response and Restoration, the Coast Guard’s Scientific Support Coordinator (DOI also is a Scientific Support Coordinator for inland U.S. spills and other areas, which escape my memory cells at the moment.  The observer guide to dispersant application, can be found at:


  1. Just because it is on the approved dispersant list, the user cannot take it upon him/her to use it without first going through a specific use, approval process.  The dispersant must first be approved by the Regional Response Team (RRT), a regional planning/incident management group consisting of the Coast Guard, EPA, NOAA SSC, the State Environmental Authorities from member states of the region, and others. There is an area-specific, expedited approval guide for the RRT VI which covers Gulf States / offshore areas west of the Alabama/Mississippi border to the Texas/Mexico border.  This guide can be found at:  http://bit.ly/b9wQMk


Besides dispersants, there are other agents that can be used, including biological agents.  Information can be found in:


a.       A guide to alternative countermeasures can be found within EPA’s Oil Spill Response Book (Chapter 3): http://www.epa.gov/OEM/docs/oil/edu/oilspill_book/chap3.pdf

b.       A joint NOAA, USCG, EPA and American Petroleum Institute Pub called: Characteristics of Response Strategies: http://response.restoration.noaa.gov/book_shelf/910_response.pdf