New publications answer questions about dispersants used during the Deepwater Horizon oil spill

By: Larissa Graham / Published: Mar 03,  2016

Over the past year and a half, our oil spill outreach team has talked with more than 1,000 people along the Gulf Coast. We’ve asked them what questions they have about the Deepwater Horizon oil spill, and what comes up over and over again? DISPERSANTS.

People want to know why dispersants are used to respond to oil spills and what impact they had on breaking down the oil. They also wonder how dispersants used during the Deepwater Horizon oil spill impacted people, wildlife, habitats and water quality.

Our team has pulled together the latest science on dispersants and packaged it in three outreach publications to start answering these questions. Here are a few highlights from each of the publications that are available on our team’s website:

Chemical Dispersants and Their Role in Oil Spill Response – This publication focuses on why and how dispersants are used during oil spills and how they were used during the Deepwater Horizon oil spill. The main take-home messages are: 

  • During the Deepwater Horizon oil spill, emergency responders sprayed nearly 1.1 million gallons of dispersant (Corexit 9500A and 9527A) on oil slicks at the surface and 0.77 million gallons were sprayed at the site of the wellhead.
  • Emergency responders sprayed dispersants to break oil into smaller droplets so it could mix into the water column. This helps to prevent shorelines from becoming oiled and creates smaller oil droplets that are more available to nature’s oil-eating bacteria.
  • Response plans define what types of dispersants emergency responders can use during an oil spill. Federal agencies also have guidelines to monitor how dispersants are used and how effectively they are working during a spill so they can change application techniques, if needed.

Fate, Transport and Effectiveness of Dispersants Used in the Deepwater Horizon Oil Spill – This publication focuses on how effective and persistent dispersants are in the environment and whether it was necessary to use dispersants at the subsurface. The main take-home messages are: 

  • The Deepwater Horizon oil spill was the first time that dispersants were used at the subsurface.
  • Depending on where dispersants were used, scientists have shown that they can persist in the environment for up to 4 years after the spill.
  • There is still some uncertainty as to whether or not the use of dispersants at the subsurface was effective. Ongoing research on this topic continues in the scientific community, which is hoping to have a better understanding for future spills.

Responses of Aquatic Life in the Gulf of Mexico to Oil and Dispersants – This publication focuses on how dispersants impact aquatic life in terms of life stage and species and how lab and field studies can provide a more complete picture of the implications of exposure to oil and dispersants. The main take-home messages are: 

  • While there are many compounds that make up oil, polycyclic aromatic hydrocarbons (PAHs) are the source of most concern. The availability of PAHs to aquatic life tends to increase when oil is mixed with dispersant.
  • At the level of individual organisms, aquatic life typically has one of several responses to oil-based compound (e.g., PAH) exposure:
    • Some animals, like jellyfish and copepods, accumulate PAHs in their bodies
    • Fish break down oil-based compounds in their bodies – and that can be used by scientists to detect exposure to oil
    • Effects differ based on stage of life and environmental conditions
    • Oil exposure can impair vital development and bodily function
  • Note that while the effects of PAHs to individual organisms can be negative, scientists have not seen these impacts scale up to populations (of fish). More studies are needed to understand if there are any long-term effects on populations or communities of aquatic life.

Our team also has two other publications that were recently released. Our Top 5 Frequently Asked Questions about the Deepwater Horizon oil spill publications provides short answers to the questions that everyone is curious about. Another publication, Navigating Shifting Sands: Oil on our Beaches, explains how oil from the Deepwater Horizon oil spill was buried, how it moves around and how scientists track it. 

If you still haven’t had your fill, be sure to visit the presentations page on our website to see what types of science seminars we have coming up in the next few months. We also record all of our seminars. So, if there is one that you’ve missed, be sure to catch the recording. And, as always, please call (251-348-5436) or email if you have any questions!

The oil spill outreach program is a partnership between the Sea Grant programs in the Gulf of Mexico and the Gulf of Mexico Research Initiative (GoMRI). The Gulf of Mexico Alliance manages and administers funding for GoMRI. The purpose of the outreach program is to share oil spill science with people whose livelihoods depend on a healthy Gulf. The oil spill science outreach team organizes science seminars and creates outreach publications that answer questions about the oil spill with the latest science. To learn more about the program, visit To be updated about the oil spill science outreach team activities, seminars and publications, sign up for their email list (click here). 






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