The US Environmental Protection Agency 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 conducted the tests as part of an effort to ensure that EPA decisions remain grounded in the best available science and data.
EPA's results indicate that the eight dispersants tested have similar toxicities to one another when mixed with Louisiana Sweet Crude Oil. These results confirm that the dispersant used in response to the oil spill in the gulf, Corexit 9500A, when mixed with oil, is generally no more or less toxic than mixtures with the other available alternatives. The results also indicate that dispersant-oil mixtures are generally no more toxic to the aquatic test species than oil alone.
"EPA has committed to following the science at every stage of this response - that's why we required BP to launch a rigorous dispersant monitoring program, why we directed BP to analyze potential alternatives and why EPA undertook this independent analysis of dispersant products," said EPA Administrator Lisa P. Jackson. "We have said all along that the use of dispersant presents environmental tradeoffs, which is why we took steps to ensure other response efforts were prioritized above dispersant use and to dramatically cut dispersant use. Dispersant use virtually ended when the cap was placed on the well and its use dropped 72 percent from peak volumes following the joint EPA-U.S. Coast Guard directive to BP in late May."
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 required rigorous, ongoing monitoring as a condition of authorizing BP's use of dispersant in the gulf. Dispersants prevent some oil from impacting sensitive areas along the gulf coast. 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. These results represent the second and final stage of the independent acute toxicity tests.
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