EPA Says Corexit 9500A Less Toxic Than Originally Thought

EPA Releases Second Phase of Toxicity Testing Data for Eight Oil Dispersants

The US Environmental Protection Agency (EPA) today released peer reviewed results from the second phase of its independent toxicity testing on mixtures of eight oil dispersants with Louisiana Sweet Crude Oil. EPA has found that a new round of independent testing showed that Corexit 9500A was similar to the toxicity of seven other dispersants pre-approved for combating oil spills. Previously, the EPA had said Corexit 9500A was among the most toxic chemicals and had ordered BP PLC to find a less toxic alternative. BP insisted that Corexit 9500A was the best option. The dispersant is made by Nalco Holding Company.

EPA also concluded that Corexit 9500A and most other oil-dispersant mixtures were also less toxic to the fish than oil alone, suggesting the use of dispersants was "a wise decision." The EPA authorized the use of dispersants in order to keep oil from reaching the shores, mindful of the risk of unknown damage to fish and other aquatic life. The agency and the U.S. Coast Guard later ordered BP to cut back its use of dispersants.

The Center believes that dispersants are toxic and their use added to the pollution produced by the Deepwater Horizon oil spill. Yet, in the final analysis, we have to agree with the EPA when it concluded:

"...while it might not have agreed with every [Coast Guard] waiver, it believed that dispersant use "has been an essential tool in mitigating this spill's impact."

The standard acute toxicity tests were conducted on juvenile shrimp and small fish that are found in the gulf and are commonly used in toxicity testing. The tests were conducted on mixtures of Louisiana Sweet Crude Oil and eight different dispersant products found on the National Contingency Plan Product Schedule – Dispersit SPC 1000, Nokomis 3-F4, Nokomis 3-AA, ZI-400, SAFRON Gold, Sea Brat #4, Corexit 9500 A and JD 2000.

The same eight dispersants were used during EPA’s first round of independent toxicity testing. All eight dispersants were found to be less toxic than the dispersant-oil mixture to both test species. Louisiana Sweet Crude Oil was more toxic to mysid shrimp than the eight dispersants when tested alone. Oil alone had similar toxicity to mysid shrimp as the dispersant-oil mixtures, with exception of the mixture of Nokomis 3-AA and oil, which was found to be more toxic than oil. While there has been virtually no dispersant use since the well was capped on July 15 – only 200 gallons total applied on July 19 – EPA’s environmental monitoring continues.

EPA’s position has been that BP should use as little dispersant as necessary and, on May 23, Administrator Jackson and then-federal on-scene coordinator Rear Admiral Mary Landry directed BP to reduce dispersant usage by 75 percent from peak usage. EPA and the Coast Guard formalized that order in a directive to BP on May 26. Before directing BP to ramp down dispersant use, EPA directed BP to analyze potential alternative dispersants for toxicity and effectiveness. BP reported to EPA that they were unable to find a dispersant that is less toxic than Corexit 9500, the product then in use. Following that, EPA began its own scientific testing of eight dispersant products. EPA released the first round of data – on the dispersant products alone – on June 30. Today’s results represent the second and final stage of the independent acute toxicity tests. View the toxicity test results. (EPA, WSJ, 8/2/1020)