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Testing the Toxicity of Oil Spill Dispersants

EPA scientists support federal response to the BP oil spill.

An oil rig platform

The U.S. Environmental Protection Agency (EPA) is providing full support to the U.S. Coast Guard, the leader of the coordinated federal response to the tragic events surrounding the BP Oil Spill in the Gulf of Mexico. A key component of EPA’s support is providing scientific and technical expertise.

Almost immediately after Louisiana sweet crude oil began gushing from the Deepwater Horizon oil well, scientists and engineers from EPA began mobilizing to set up environmental monitoring equipment and coordinate its support. EPA scientists are collecting and analyzing data from air, water, waste, and sediment samples from affected areas across the Gulf.

Among the first things EPA scientists were called upon to address was the need to conduct independent testing on the toxicity, including potential endocrine disrupting activity, of oil dispersants available for use in the Gulf.

Responding to the BP Oil Spill

The overall goal of actions taken in response to the unprecedented release of oil into the Gulf of Mexico is to minimize the known threat the released oil poses to the environment. Spill management strategies, practices, and technologies implemented include using sorbents, floating booms, and skimming operations to mechanically remove oil from the water, burning the oil in place, and applying dispersants.

Dispersants have properties that break down the oil, helping to prevent thick, sticky crude from fouling beaches or reaching ecologically sensitive coastal wetlands. Breaking the oil down into smaller droplets also promotes natural biodegradation, because the droplets can be ingested by tiny, oil-consuming marine microbes.

Toxicity Testing of Dispersants

To ensure that decisions about dispersant use in the Gulf of Mexico were grounded in the best available science, EPA began its own scientific analysis of eight dispersant products on the National Contingency Plan Product Schedule (NCP-PS). NCP-PS is a list of dispersants and other mitigating substances and devices that may be used to remove or control oil discharges.

The dispersant products EPA tested are: Dispersit SPC 1000, Nokomis 3-F4, Nokomis 3-AA, ZI-400, SAF-RON Gold, Sea Brat #4, Corexit 9500 A and JD-2000. (Corexit 9500 A is the dispersant BP applied offshore at the surface and in the deep ocean in response to the spill.)

During the first phase of testing, EPA scientists led a study assessing the acute toxicity of the dispersants alone (not mixed with oil) on the larval stages of two aquatic species considered representative of the sensitivity of many other organisms found in the Gulf of Mexico: mysid shrimp (Americamysis bahia), and the inland silverside fish (Menidia beryllina).  Toxicologists have used the two species for years, and a long record of scientific literature confirms their efficacy in such studies.   

In a related effort, over 80 in vitro tests from EPA’s ToxCast and endocrine disruptor research programs were used to test for endocrine activity and cytotoxicity (cell death).

EPA released peer reviewed results from the first phase of toxicity testing on June 30, 2010. The data showed that all eight dispersant products have roughly the same toxicity, and all fall into the “practically non-toxic” or “slightly toxic” category. Comparatively, JD-2000 and Corexit 9500A were generally less toxic to small fish and JD-2000 and SAF-RON GOLD were least toxic to mysid shrimp. Agency scientists also found that none of the eight dispersants displayed endocrine disrupting activity of biological significance.

The second phase of testing looked at the acute toxicity of multiple concentrations of Louisiana Sweet Crude Oil alone, and combinations of Louisiana Sweet Crude Oil with each of the eight dispersants. Again, mysid shrimp and the inland silverside fish were used to conduct the tests. 

Results of the second phase of tests, released on August 2, 2010 indicate that the toxicities of the eight dispersants mixed with oil are roughly similar to one another. The results also indicate that dispersant-oil mixtures are generally no more toxic to the aquatic test species than oil alone.

As expected, all eight dispersants were found to be less toxic than the dispersant-oil mixture to both test species. Oil alone was found to be more toxic to mysid shrimp than the eight dispersants alone. Oil alone had similar toxicity to mysid shrimp as the dispersant-oil mixtures, with the exception of the mixture of Nokomis 3-AA and oil, which was found to be more toxic.

"EPA is performing independent tests to determine the potential impacts of various dispersants. We will continue to conduct additional research before providing a final recommendation," said EPA Administrator Lisa P. Jackson. "We want to ensure that every tool is available to mitigate the impact of the BP spill and protect our fragile wetlands. But we continue to direct BP to use dispersants responsibly and in as limited an amount as possible."

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