Offshore Oil Spills: Additional Information is Needed to Better Understand the Environmental Tradeoffs of Using Chemical Dispersants
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
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
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.
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) |
According to Coast Guard, the Interagency Coordinating Committee on Oil Pollution Research (ICCOPR) convened a working group to address GAO recommendations in August 2022. Since August, the working group has convened three additional times, and are scheduled to meet again with ICCOPR members in March 2024. Outcomes for recommendation 1 will be informed by the results of this working group as it examines the potential effects of the subsurface use of dispersants on ocean ecosystems in regions where the use of dispersants is viable. The working group estimates it will complete its efforts by April 2026.
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| 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) |
In December 2022, EPA said that it continues to take steps to implement this recommendation by participating with USCG and other related agencies in the Interagency Coordinating Committee on Oil Pollution Research (ICCOPR) quarterly meetings. More recently, EPA ORD and OEM participated in four monthly workgroup meetings (February - May 2023). The workgroup has crafted a draft charter of methodology to address the four GAO recommendations associated with this report, including recommendation 2, which EPA is responsible for. The methodology relies heavily on existing data and reviewing information that is cited within the GAO report. The workgroup plans to meet monthly as well as reporting out at the quarterly ICCOPR meetings (June, September, December, March).
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| 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) |
According to Coast Guard, ICCOPR convened a working group in August 2022 to address this recommendation. The ICCOPR working group met seven times in 2023 to address recommendations 3 and 4. The working group developed a framework for addressing the recommendations and anticipates the final report will be completed by November 2024. Among other things, the report will identify ways to improve the quality of information regarding the effectiveness of the subsurface use of dispersants.
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| 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) |
According to Coast Guard, ICCOPR convened a working group in August 2022 to address this recommendation. The ICCOPR working group met seven times in 2023 to address recommendations 3 and 4. The working group developed a framework for addressing the recommendations and anticipates the final report to be completed by November 2024. Among other things, the report will identify ways to better ensure that experiments about chemically dispersed oil toxicity and biodegradation result in quality information.
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