Oil Dispersant

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Oil dispersants are a common tool used after oil spills to break up oil slicks on the water surface and increase the oil's rate of biodegradation. By breaking up large slicks, oil dispersants are intended to reduce harmful oil exposures to birds, fish, and other wildlife in proximity to spills. Two oil dispersant products were used heavily in the BP oil leak: COREXIT 9500 and 9527, both produced by Nalco. BP used over 1,800,000 gallons of dispersant since the start of the oil leak (Buchanan).

How Oil Dispersants Work

Oil dispersants work by separating an oil slick into small droplets of oil. Wind, waves, and other turbulence in the water break up these droplets and disperse them throughout the water column. Once dispersed, the oil droplets are consumed by naturally occurring bacteria or they are carried out into the open ocean. The goal of using oil dispersants is to protect fragile coastal areas from oil coming ashore.

Nalco Website and Video on How Oil Dispersants Work

The Chaos of Cleanup: Analysis of the Potential Health and Environmental Impacts of Chemicals in Dispersant Products

Download the report today!

This report highlights key findings from research on the 57 chemicals found in the oil dispersant products listed by the EPA as appropriate for use in response to oil spills. Additionally, the report disects issues of concern with the approval process for dispersant products and makes suggestions on improving regulations so that the safest dispersant is used in each unique spill.

Oil Dispersant Glossary

Throughout the oil dispersant section you may come across a word, phrase, or abbreviation that you are not familiar with. Visit the oil dispersant glossary for definitions and explanations of these terms.

Oil Dispersant Chemicals

There are a total of 57 chemical ingredients that are found in the oil dispersant products approved for use by the US Environmental Protection Agency. View a chart of the potential effects on human health and the aquatic environment.

Oil Dispersant Products

Click on a product name for information on the chemicals found in it, potential effects on human and environmental health, as well as data on its effectiveness at dispersing oil.

Environmental Toxicity

Oil dispersants begin to break down within 16 days of application in aquatic environments (CDC 2010).

Dispersing oil can have both positive and negative impacts on the environment and wildlife. "They expose marine life in the water column to more oil than would be the case for untreated oil, which floats at the surface" (Torrice 2010.) However, "Oil in the water column...won't reach wetlands on shore, where it could wreak greater havoc" (Torrice 2010).

The potential environmental impacts of oil dispersants are dependent on various factors, described below.

Species of Wildlife

  • Different species of aquatic wildlife react differently to oil dispersant exposure, as evaluated by the exposure level that causes a 50% mortality rate under particular exposure conditions. For example, grass shrimp can withstand exposure to higher concentrations of Corexit oil dispersants than the Pacific oyster. Analysis of tests done on a variety of species of aquatic life show that crustaceans (a group of animals including crabs, shrimp, and barnacles) are more sensitive to oil dispersant exposure than fish (George-Ares, 2000).
  • One study found that the species with the least amount of protective shell or external tissue are most sensitive to oil dispersant exposure (Scarlett et al., 2005).
  • Another study found that the use of oil dispersants increased the levels of hydrocarbons, which are found in crude oil, in rockfish. Fish exposed to high levels of hydrocarbons may show changes in their physiology. Study researchers state that similar effects could be seen in other ovoviviparous fish, fish that give birth to live young instead of eggs (Jung et al., 2009).
  • A study was performed to see if the use of oil dispersants affected fish intake of PAHs (polycyclic aromatic hydrocarbons, a chemical compound that exists in oil). Researchers found that the use of oil dispersants did in fact increase exposure and uptake of PAHs by fish, especially fish that live throughout the water column of coastal areas, the ocean, and lakes. They also state that "the risk of PAH toxicity ... especially to sensitive life stages such as eggs and larvae, is enhanced by chemical dispersion (Ramachandran et al., 2003)." "Concentrations of LMWPAHs and HMWPAHs (low and high weight PAHs) are higher in the water column following application of chemical dispersants to surface slicks" (Couillard et al. 2004).
    • PAHs have been studied and shown to cause cardiac problems, abnormal accumulations of fluid in the body, and spinal and cranial deformation of fish embryos (Incardona et al., 2004). Chronic exposure to PAHs has also been shown to cause increased rates of parasite infection, which may cause disease and death in fish.

Life Stage of Wildlife

  • Early life stages of aquatic organisms (embryo, larval, and juvenile) have a higher sensitivity to oil dispersants. The George-Ares study states, "Corexit 9500 and Corexit 9527 are moderately toxic to early life stages of fish, crustaceans, and molluscs." Studies have shown that the age, down to the hour, can have an impact on the species' level of sensitivity to oil dispersants. For example, "Herring eggs at time of fertilization were more sensitive to the dispersants ... than herring eggs 6 hours after fertilization" (the herring eggs were exposed to a different type of oil dispersant) (George-Ares, 2000).

Duration of Exposure

  • The longer the period of exposure to oil dispersants is, the worse the impacts on particular species can be. In several studies, species continually exposed to oil dispersants for a 96-hour period were more susceptible to a 50% mortality rate than species exposed to oil dispersants just one time. Releasing oil dispersants into the water for days, weeks, or months at a time will increase the dispersants' level of toxicity.
  • In a study that compared the toxicity of oil, dispersants, and oil plus dispersants on shrimp, minnows, and silverside fish, researchers found that oil plus a dispersant, in this case Corexit 9500, had an equal or lower toxicity than just the oil. However, this test was to reflect a one-time application of dispersant. When dispersant is continuously applied, effects of toxicity are more readily seen in the test species. The longer the dispersant is applied, the more toxic it becomes (Fuller et al., 2004).

Water Temperature

  • Studies have shown a direct correlation between water temperature and wildlife's sensitivity to oil dispersants. The warmer the water is, the more toxic the oil dispersants are to aquatic life. In studies, both grass shrimp and scallops were able to withstand significantly higher concentrations of oil dispersants in water at lower temperatures. A 10 to 20C degree increase in water temperature dramatically increased their sensitivity to oil dispersants (George-Ares 2000).
  • Current Gulf of Mexico Water Temperatures from NOAA

Concentration of Dispersant

  • The higher the concentration of oil dispersants in water, measured in parts per million (ppm), the more likely it is for the dispersants to affect wildlife. Certain species can withstand very high concentrations of oil dispersants, while others show negative impacts at very low concentrations. Negative effects on particular aquatic species have been shown to be reversible at low concentrations, but the higher the concentration, the more likely that the effects will be irreversible (Scarlett et al., 2005).
  • The maximum recorded concentration of oil dispersants in open water is 13ppm (Scarlett et al., 2005). Studies have shown that in many cases the oil dispersant concentrations are less than 1 ppm within hours of application (George-Ares 2000).

Geography and Type of Water Body

  • Areas where water is more stagnant or protected, such as estuaries, enclosed bays, and reefs, are more susceptible to high concentrations of oil dispersants than more open or large bodies of water.
  • Without wave action and turbidity, oil dispersants have a lower rate of dissipation (Scarlett et al., 2005).


Buchanan, Susan. "Dispersants Add to Gulf Spill's Toxi Threats." The Louisiana Weekly. 1 June 2010. Web. 01 June 2010. <http://www.louisianaweekly.com/news.php?viewStory=2862>.

"CDC - Oil Spill Response - Dispersant Information for Health Professionals." Centers for Disease Control and Prevention. 19 May 2010. Web. 03 June 2010. <http://emergency.cdc.gov/gulfoilspill2010/dispersants_hcp_info.asp>.

US EPA EPA Response to BP Spill in the Gulf of Mexico http://www.epa.gov/bpspill/

Fuller, Chris, James Bonner, Cheryl Page, Andrew Ernest, Thomas McDonald, and Susanne McDonald. "Comparative Toxicity of Oil, Dispersant, and Oil plus Dispersant to Several Marine Species." Environmental Toxicology and Chemistry 23.12 (2004): 2941-2949.

George-Ares, A., and J. R. Clark. "Aquatic Toxicity of Two Corexit Dispersants." Chemosphere 40 (2000): 897-906.

Incardona, John P., Tracy K. Collier, and Nathaniel L. Scholz. "Defects in Cardiac Function Preceded Morphological Abnormalities in Fish Embryos Exposed to Polycyclic Aromatic Hydrocarbons." Toxicology and Applied Pharmacology 196.2: 191-205.

Jung, Jee Hyun, Un Hyuk Yim, Gi Myeong Han, and Won Joon Shim. "Biochemical Changes in Rockfish, Sebastes Schlegeli, Exposed to Dispersed Crude Oil." Comparative Biochemistry and Physiology C.150 (2009): 218-23.

Ramachandran, Shahunthala D., Peter V. Hodson, Colin W. Khan, and Ken Lee. "Oil Dispersant Increases PAH Uptake of Fish Exposed to Crude Oil." Ecotoxicology and Environmental Safety 59 (2004): 300-08.

Scarlett, Alan, Tamara S. Galloway, Martin Canty, Emma L. Smith, Johanna Nilsson, and Steven J. Rowland. "Comparative Toxicity of Two Oil Dispersants, Superdispersant-25 and Corexit 9527, to a Range of Coastal Species." Environmental Toxicology and Chemistry 24.5 (2005): 1219-227.

Torrice, Michael. "Cleaning up the Gulf Oil Spill." Chemical and Engineering News 88.20 (2010):36-37.

Breaking News Stories

Oil Dispersant News from Environmental Health News

Environmental Health News
( Links to articles in today's press about environmental health. Many more links available today at www.EnvironmentalHealthNews.org )
When the next oil disaster happens, the US will be better prepared, researchers say.
Teams from the University of Southern Mississippi will track Gulf floor sediment, will attempt to close gaps in what is known about Gulf fish and their diets and will study fish RNA.
A Thai oil firm, Indonesian seaweed farmers and Australian regulators. What happened after the Montara oil spill?
Eight years after the blowout, legal action against the company responsible is ramping up, even as the true extent of the damage caused remains a mystery.
Consequences of Deepwater Horizon oil spill ongoing.
Government and academic specialists at a Capitol Hill briefing Oct. 17 offered a sampling of what has been done, is being done and needs to be done as they discussed the consequences of the 2010 disaster.
Deepwater Horizon casts long shadow over BP drilling in Bight.
Like the uncontrolled release of oil in the Deepwater Horizon disaster in the Gulf of Mexico, BP has long been haemorrhaging credibility and corporate goodwill into the pristine waters of the Bight.
BP platform leaks 95 tons of oil into North Sea.
An oil spill 46 miles off Shetland is being monitored by air and said to be heading away from land and dispersing.
Inside the institute charged with exploring how chemicals affect human health.
Fifty-year-old National Institute of Environmental Health Sciences is the U.S.’s top environmental health research agency.
BP's planned response to any Great Australian Bight oil spill too slow, says expert.
BP is proposing to drill for oil in the Great Australian Bight using plans that fall a long way short of industry best practice and would not be allowed in some other regions, according to an expert in oil spill disasters.
Indonesian seaweed farmers to file $200m class action over Timor Sea oil spill.
More than 13,000 Indonesian seaweed farmers are launching a $200m class action against the company they claim was responsible for Australia’s worst offshore oil spill, which sent millions of litres of oil towards their shores.
'Dirty blizzard' carried Deepwater Horizon contaminants to seafloor.
Scientists have discovered the mechanism that transported contaminants from the Deepwater Horizon oil spill to the bottom of the Gulf of Mexico.
Can oil spills make you fat?
Understanding the role of chemicals in the growing obesity epidemic will save lives, reduce healthcare costs and improve public health.
Deepwater Horizon spill altered shipwreck ecosystems.
The thriving of microbial communities in the presence of oil could put historic shipwrecks at risk.
VIDEO: BP oil spill altered coral, shipwrecks in gulf, scientists say.
Oil from the BP Deepwater Horizon disaster and the dispersant used to break the oil into tiny droplets might have affected the genetic balance of deepwater corals in the Gulf of Mexico.
Blaise and the Phoenix Coast.
Can an area of outstanding beauty ever recover from a massive oil spill?
Study of effects of oil on fish begins at Mote Marine Laboratory.
The next phase in a multi-year study to look at the effect oil has on fish could have lasting impacts on our knowledge of how oil and dispersants used during the BP spill affects life in the Gulf of Mexico.
Study: Dispersants did not help oil degrade in BP spill.
The chemical sprayed on the 2010 BP oil spill may not have helped crucial petroleum-munching microbes get rid of the slick, a new study suggests.

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