Offshore Oil Spills: Additional Information is Needed to Better Understand the Environmental Tradeoffs of Using Chemical Dispersants

GAO-22-104153 Published: Dec 15, 2021. Publicly Released: Dec 15, 2021.
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Fast Facts

In 2010, an explosion on an oil rig in the Gulf of Mexico resulted in 11 deaths and the largest oil spill in U.S. history.

Responders applied chemical dispersants to the surface oil slick—to break oil into smaller droplets. This can keep oil from reaching shoreline ecosystems, but may also increase toxic compound exposure for some sea life.

Responders also used dispersants at the wellhead, over 1,500 meters deep, without much information on the risks or effectiveness of doing so.

Subsurface dispersant use isn't well understood. We recommended that the Coast Guard and EPA find ways to improve understanding of using dispersants below the surface.

Use of Chemical Dispersants during a Subsurface Oil Spill

Illustration showing use of chemical dispersants during a subsurface oil spill

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Highlights

What GAO Found

When an oil spill occurs, responders have several options to manage the environmental effects, including using chemical dispersants (see figure). Chemical dispersants used on a surface oil slick can be effective at breaking up floating oil, which can help prevent the oil from reaching shore and harming sensitive ecosystems, according to studies GAO reviewed and stakeholders GAO interviewed. However, the effectiveness of applying dispersants below the ocean surface—such as in response to an uncontrolled release of oil from a subsurface wellhead—is not well understood for various reasons. For example, measurements for assessing effectiveness of dispersants applied at the subsurface wellhead during the Deepwater Horizon oil spill had limitations and were inconclusive. In addition, there are limited experimental data on the effectiveness of subsurface dispersants that reflect conditions found in the deep ocean.

Application of Chemical Dispersants at the Surface by Aircraft and Boat

Application of Chemical Dispersants at the Surface by Aircraft and Boat

Chemically dispersed oil is known to be toxic to some ocean organisms, but broader environmental effects are not well understood. Dispersants themselves are considered significantly less toxic than oil, but chemically dispersing oil can increase exposure to the toxic compounds in oil for some ocean organisms, such as early life stages of fish and coral. Other potentially harmful effects of chemically dispersed oil, especially in the deep ocean, are not well understood due to various factors. These factors include laboratory experiments about the toxicity of chemically dispersed oil that use inconsistent test designs and yield conflicting results, experiments that do not reflect ocean conditions, and limited information on organisms and natural processes that exist in the deep ocean.

Since the Deepwater Horizon oil spill, the U.S. Coast Guard, the Environmental Protection Agency (EPA), and other agencies have taken some actions to help ensure decision makers have quality information to support decisions on dispersant use. For example, the Coast Guard and EPA have assessed the environmental effects of using dispersants on a surface slick. However, they have not assessed the environmental effects of the subsurface use of dispersants. By assessing the potential environmental effects of the subsurface use of dispersants, the Coast Guard and EPA could help ensure that decision makers are equipped with quality information about the environmental tradeoffs associated with decisions to use dispersants in the deep ocean.

Why GAO Did This Study

In April 2010, an explosion onboard the Deepwater Horizon drilling rig in the Gulf of Mexico resulted in 11 deaths and the release of approximately 206 million gallons of oil. During the Deepwater Horizon oil spill, responders applied dispersants to the oil slick at the ocean surface as well as at the wellhead more than 1,500 meters below the surface. The subsurface use of dispersants was unprecedented and controversial.

GAO was asked to review what is known about the use of chemical dispersants. This report examines, among other things, what is known about the effectiveness of dispersants, what is known about the effects of chemically dispersed oil on the environment, and the extent to which federal agencies have taken action to help ensure decision makers have quality information to support decisions on dispersant use. GAO reviewed scientific studies, laws, regulations, and policies. GAO also interviewed agency officials and stakeholders from academia and industry.

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Recommendations

GAO is making four recommendations, including that the Coast Guard and EPA assess the potential environmental effects of the subsurface use of dispersants. The Department of Homeland Security agreed with the three recommendations GAO made to the Coast Guard, and EPA agreed with the one recommendation to the agency.

Recommendations for Executive Action

Agency Affected Recommendation Status
United States Coast Guard The Commandant of the Coast Guard should work with EPA and other agencies to conduct assessments—such as biological assessments or ecological risk assessments—examining the potential effects of the subsurface use of dispersants on ocean ecosystems in regions where this is considered a viable response option. (Recommendation 1)
Open
Homeland Security agreed with our recommendation. The Coast Guard Office Office of Marine Environmental Response plans to form a working group with EPA and other agencies to coordinate assessments that examine the potential effects of subsurface dispersant use during worst-case oil discharges. Currently the Coast Guard does not have the scientific expertise to conduct robust assessments and plans to leverage expertise in the interagency working group. The Coast Guard expects these assessments to take at least 4 years, with an estimated completion date of Spring 2026. Once the working group convenes, currently projected for Summer 2022, the Coast Guard will develop interim milestones and refine the estimated completion date.
Environmental Protection Agency The Administrator of EPA should work with the Coast Guard and other agencies to conduct assessments—such as biological assessments or ecological risk assessments—examining the potential effects of the subsurface use of dispersants on ocean ecosystems in regions where this is considered a viable response option. (Recommendation 2)
Open
EPA agreed with this recommendation. EPA plans to provide support to the Coast Guard and coordinate with the National Oceanic and Atmospheric Administration and other agencies to identify assessment methodologies and examine potential effects of the subsurface use of dispersants on ocean ecosystems for select regions. In Fall 2022, EPA plans to meet with the Coast Guard and other agencies to initiate this discussion.
United States Coast Guard The Commandant of the Coast Guard should ensure that the chair of the Interagency Coordinating Committee on Oil Pollution Research, in coordination with member agencies, convene a working group of the appropriate government, academic, and industry stakeholders, to identify ways to improve the quality of information about the effectiveness of the subsurface use of dispersants. (Recommendation 3)
Open
Homeland Security agreed with this recommendation. The Chair of the Interagency Committee plans to form a working group to develop a framework for improving the quality of information on subsurface dispersant use and effectiveness. Once complete, the Interagency Committee will present the finalized framework and any accompanying findings, which will be used to inform interagency assessments examining the effects of the subsurface use of dispersants. The Interagency Committee plans to convene this working group in Summer 2022 and anticipates completion by Fall 2023.
United States Coast Guard The Commandant of the Coast Guard should ensure that the chair of the Interagency Coordinating Committee on Oil Pollution Research, in coordination with member agencies, convene a working group of the appropriate government, academic, and industry stakeholders, to identify ways to better ensure that experiments about chemically dispersed oil toxicity and biodegradation result in quality information. (Recommendation 4)
Open
Homeland Security agreed with our recommendation. The Chair of the Interagency Committee plans to form a working group to develop a framework promoting that experiments involving chemically dispersed oil toxicity and biodegradation result in quality information. Once complete, the Interagency Committee will present the finalized framework and any accompanying findings in a report, which will be used to inform interagency assessments examining the effects of the subsurface use of dispersants. The Interagency Committee plans to convene this working group in Summer 2022 and anticipates completion by Fall 2023.

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