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Your Environment. Your Health.

Dispersants Frequently Asked Questions

These FAQs provide information about dispersants that is known to date. However, additional research is needed and is being conducted to explore exactly how dispersants work in various settings, and at various depths of water. Many of these questions and answers are related to the Gulf of Mexico Oil Spill in 2010, but much of the information is relevant to dispersants that might be used in any oil spill.

What are dispersants?

Dispersants are mixtures of different chemicals used to break down oil. They are one of several ways to try and clean up oil released from oil spills and accidents in water. Dispersants do not reduce the total amount of oil that is spilled or released into the environment. They change the properties of the spilled oil so that it breaks up in the water

Why are dispersants used?

Dispersants are used to break down oil on the surface of water. They work by breaking up larger oil slicks into smaller drops of oil. These smaller drops of oil then move more easily from the surface into the water. The smaller drops of oil can then be broken down more easily by bacteria that live in the water. Dispersants alone cannot get rid of oil in water, but they do make it easier for natural processes to break down the oil faster. They also limit the spread of oil  from the site of the spill  Dispersants were used during the Gulf oil spill to try to keep oil from reaching the shore.

When are dispersants used?

Dispersants have been used since the 1970s particularly when there has been an oil spill that could damage nearby delicate ecosystems (for example, wetlands) or coastal communities that rely on the ocean for food and recreation. Dispersants are used to try to keep oil from reaching coastal areas and damaging wildlife or people’s health They are also used when a large amount of oil has been spilled  when other clean-up methods (for example, skimmers, booms, or burning) are not enough. Dispersants work best on freshly spilled oil and are used within 1-2 days of oil being spilled. Dispersants may not work on older or “weathered” oil. Dispersants are also used to clean or remove oil from wildlife that has come into contact with oil. Dispersants are approved to be used for future oil spills.

How are dispersants used?

  1. Spraying: Dispersants can be directly sprayed onto the surface of a spill.
  2. Injection: Dispersants can be “injected” or pumped under the surface of the spill.

Where were the dispersants used in the Gulf oil spill?

Dispersants were used at the site of the Deepwater Horizon oil spill where fresh, dispersible oil was present (see map below). They were used underwater, where oil was leaking from the well, and on surface oil slicks.   By using the dispersants underwater, the amount of oil reaching the surface was reduced. They were also used throughout the Gulf where they were sprayed by plane on the water. Most of the dispersant application stopped a few days after the well was capped (July 15). In addition, using dispersants in the Gulf oil spill helped reduce the amount of the spilled oil that reached the shoreline.

map of dispersants in the gulf

Legend for dispersants map

The map above shows the area where dispersants were applied from airplanes in light shaded yellow (this is called the “aerial dispersant envelope” on the website). The orange lines are the flight lines or paths that the airplane(s) took while spraying dispersant over the surface of the water. Dispersants were sprayed from airplanes from late April through mid-July 2010. This map does not show where dispersants were used below the surface of the water. The color-coded areas along the shoreline correspond to levels of oiling that were determined by the Shoreline Cleanup and Assessment Technique or SCAT (see additional legends). The gray areas in the Gulf correspond to the number of days oil was observed in those areas (see additional legends). The After Action Report for Aerial Dispersant Response can be accessed by clicking on the highlighted text above or at: 


The Gulf oil spill Environmental Response Management Application (ERMA®) was developed by the NOAA, the University of New Hampshire, and the USEPA. The link to the website and the mapping tool for the ERMA® Deepwater Gulf Response is:

ERMA Deepwater Gulf Response

This online mapping tool was used to generate the map (shown above) and the area where dispersants were used in the Gulf oil spill (Environmental Response Management Application. Web application. Region. National Oceanic and Atmospheric Administration, 2014. Web. Accessed on 7-7-2015. (

What kinds of dispersants were used in the Gulf of Mexico oil spill?

The United States Environmental Protection Agency (EPA) allows 19 types of dispersants to be considered for use in oil spills ( USEPA National Contingency Plan Product List 2014). During the Gulf of Mexico oil spill in 2010, two dispersants were approved and used, COREXIT 9500A and COREXIT 9527A. Dispersants have been used in other oil spills including the Exxon Valdez spill (1989) and Ixtoc I oil spill in the Gulf of Mexico (1979).

What happens to dispersants when they are put into the environment, including water?

When dispersants are put into water they attach to both the oil and the water molecules (imagine a chain with a “hand” on either end). One end of the dispersant will grab onto an oil molecule, while the other end grabs onto a water molecule. The dispersant moves with the water and pulls small amounts of oil away from the larger spill. These small drops of oil can be broken down into smaller drops of oil which are further broken down by bacteria and weathering faster and more easily by bacteria already living in the water. Dispersants work best in moving water, for example water with waves, because waves help pull the oil drops apart from one another and down into the water below the surface.

Some dispersants can be spread in the air and may move many miles from where they were first sprayed. Dispersants that settle into the soil in very small amounts should not have any effects. Dispersants that enter the air may also be naturally broken down by natural processes such as sunlight.

How long do dispersants last in the environment, and in the water?

Dispersants break down quickly in water and the environment. An EPA study in 2014 found that dispersants on the surface of seawater broke down completely within a few days. Because of the large volume of dispersants used during the Gulf oil spill, there were detectable levels up to 8 weeks after the well was finally capped. Dispersants that were used below the water surface may take longer to break down, from weeks to several months. Dispersants like dispersed oil are broken down by bacteria living in the water. Smaller volumes of dispersants can break down within a few days to weeks.

Can dispersants get into my food or seafood?

Dispersants can get into seafood, but they have not been shown to bioaccumulate (build up in the body) or be present in harmful amounts. Dispersants can help break down oil up to 50% faster. This means there will be less dispersant or dispersant/oil mixtures for fish or shellfish to consume over time. After the Deepwater Horizon oil spill, the quality of seafood from areas where dispersants were used was checked. So far, no Gulf state programs or Consortium study has found any food or seafood sources with high levels of dispersants currently thought to be harmful.

Can I be exposed to dispersants in the air?

The general public had very low (minimal) or no exposure to dispersants in the air after the Deepwater Horizon spill because of restrictions on where dispersants can be used during oil spills. However, people who prepare or apply dispersants, or work where they are being used, should follow OSHA occupational safety guidelines and wear personal protective equipment to protect them from exposure. Information on OSHA safety guidelines can be found at

Can dispersants be harmful to me or my family?

If you breathe in or touch dispersants directly, they can be harmful, especially in high concentrations. Direct contact of the skin with dispersants breaks down the oil in your skin and causes drying. Breathing in dispersants in the air can cause irritation of the airways. Eye irritation can also occur with exposure to high concentrations in the air. Repeated or prolonged exposure without personal protection can cause blood, kidney or liver problems. If the dispersants are properly used, it is very unlikely that the general public would have exposure that would lead to any of these health problems. When proper-use guidelines were followed for the use of dispersants during the Deepwater Horizon oil spill, human health risk was low. These health effects should generally stop when exposure ends.  

What are the health effects of exposure to very low concentrations of dispersants, both in the air and in food?

Immediate health effects from very low concentrations of dispersants are not expected. When they do occur, the most common effects of short term exposure can include irritation of the eyes, throat, and lungs. These health effects should stop when exposure ends. Scientists are unsure if there are any health effects of very low concentration exposures to dispersants or about the long term health effects of exposure to dispersants. These effects are being studied further.

Are there any health effects on future generations that are known?

No chemicals in dispersants are known to cause cancer or birth defects.

Some coastal residents have raised concerns over 2-butoxyethanol, a chemical found in dispersants used during the Deepwater Horizon oil spill. The International Agency for Research on Cancer (IARC) and IRIS (EPA Integrated Risk Information System) found that 2-butoxyethanol was "not classifiable as to carcinogenicity to humans" and "not likely to be a human carcinogen (cause cancer)."

Are there any remedies for the health effects of exposure to dispersants, whether in air or food?

Medical care is needed if you are experiencing short-term effects from direct contact with dispersants. Many of the acute symptoms of direct contact go away when the exposure stops. It is therefore important to remove the individual from the exposure. The next step is to treat the symptoms related to exposure to the extent possible. These symptoms may include respiratory problems, eye irritation, skin irritation, and central nervous system problems like dizziness, headaches and nausea. Long term health effects are not known and research should be done to address this gap in our understanding and to develop preventions or treatments that might be necessary.

Can dispersants harm fish or other types of marine animals?

Longer contact to higher amounts of dispersants may result in greater harm to fish and other marine animals. In laboratory studies, fish appeared to be more affected than shellfish. Young or developing animals are generally more sensitive to dispersants than adult animals. Laboratory studies show that dispersants have relatively low toxicity compared to oil or oil mixed with dispersant. When oil is mixed with dispersant this causes the harmful chemicals in the oil to become more available to animals in the water, which is why dispersed oil is more harmful to some species than oil or dispersants alone. In natural settings, little is known about the effects of dispersants on marine animals, and research should be done to address the effects of dispersants on fish and marine animals when they are used in the marine environment.

The USEPA has recently proposed more stringent testing requirements for dispersants ( A scientific panel convened by the National Academy of Sciences has also recommended more testing of harmful effects especially for marine organisms that live in the water, including those that live in deeper water, and on the seafloor (

Are there any laws banning the use of dispersants?

Dispersant use is regulated by the National Oil and Hazardous Substances Pollution Contingency Plan. Dispersants that can be used must be on the EPA approval list ( Federal and state agencies also have agreements that limit the areas where dispersants can be used. Sites outside of the agreement areas must get approval from the EPA to be allowed to use dispersants. In the Gulf of Mexico, dispersants on the USEPA list are often pre-approved for use on oil spills that are 3-50 miles from the shoreline. To use dispersants anywhere between the shoreline and 3 miles offshore, an approval process including federal, state, and local agencies must be followed.

Can the dispersants harm shrimp workers/processors?

The greatest risk of harm associated with dispersants is for those that are applying them. Most of the clean-up workers did not come into direct contact with the undiluted dispersant.  The major groups of workers who could be affected by contact with dispersants were located within 5 miles of the wellhead or were those who prepared dispersant on land for the airplanes.

Does washing clean-up worker’s clothes with their family’s clothing harm them?

It is recommended that clean-up workers whose job exposed them to the crude oil or the dispersant, shower at work and separate their work clothing from the rest of the family’s laundry. If immediate health effects have occurred from direct contact with the oil or dispersants, those affected should seek medical care.

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