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EPA: oil-dispersant mix in Gulf is ‘moderately toxic’

A file photo of a mysid shrimp species from the Wkimedia Commons.

Second round of testing complete; more long-term monitoring planned


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By Bob Berwyn

SUMMIT COUNTY — The EPA says that the brew of oil and dispersants still swirling in the Gulf of Mexico can be highly to moderately toxic to marine organisms at certain concentrations determined in a lab setting. The agency did not say whether those acute toxic levels are present in the open waters of the Gulf.

According to the agency’s lab tests, the mix of Corexit and oil generally falls into the moderate category. The testing also found that the oil-dispersant mix is no more toxic than oil alone, EPA officials said, calling the unprecedented use of dispersant an “environmental tradeoff that’s not to be taken lightly.”

Visit this EPA website for the full press release, as well links to the study as well as an audio recording of the teleconference with reporter questions.

The tests were conducted on two species, the Gulf mysid shrimp (Americamysis bahia), an aquatic invertebrate and the inland silverside (Menidia beryllina) that lives in coastal estuaries. They were tested at juvenile life stages, when most sensitive to toxins. The two species are believed to representative of marine life in the area, according to the EPA.

Mysid shrimp form the basis of many aquatic food chains. Freshwater varieties live in the chilly waters of Dillon Reservoir, helping trout in the tailwaters below the Dillon Dam grow to Gold Medal size. A die-off of mysis shrimp in the Gulf would have far-reaching impacts up the food chain.

To establish the relative toxicity of the various mixtures, the concentrations were increased in the lab setting to concentrations far above those found in the Gulf. An earlier round of EPA testing found that the mix of oil and dispersant did not disrupt endocrine functions in the test subjects.

The EPA said no traces of dispersants have been found away from the failed BP well, or anywhere near coasts and wetlands.

“These data are important, but continued monitoring is necessary,” said EPA assistant administrator Paul Anasta. “We will continue monitoring efforts to ensure that dissolved oxygen levels do not decrease below levels of concern. To date, we have not seen dissolved oxygen levels fall below levels of concern to aquatic life,” he said.

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