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Study: Mixing oil with dispersant made the BP oil spill worse

A new study by researchers at the Georgia Institute of Technology and the Universidad Autonoma de Aguascalientes in Mexico finds that mixing oil with dispersant made the BP oil spill worse. Georgia Tech reports that the two million gallons of dispersant used to clean up the 4.9 million barrels of oil that spilled into the Gulf of Mexico during the 2010 Deep Water Horizon spill made the oil 52 times more toxic.

The researchers discovered that mixing the dispersant with oil raised the toxicity of the mixture up to 52-fold over the oil alone. They found that the mixture’s impacts increased the death rate of rotifers, a microscopic grazing animal at the base of the Gulf’s food web.

Combining oil from the BP oil spill and Corexit, which is the dispersant mandated by the Environmental Protection Agency for clean up, the researchers measured the toxicity of oil, dispersant, and mixtures on five strains of rotifers.  Rotifers are often used by ecotoxicologists to calculate toxicity in marine waters because of their fast response time, ease of use in tests and sensitivity to toxicants.

Not only did the oil-dispersant mixture increase mortality in adult rotifers, as little as 2.6 percent of the mixture decreased rotifer egg hatching by 50 percent. These eggs hatch into rotifers each spring, reproduce in the water column and provide food for baby fish, shrimp and crabs.

“Dispersants are preapproved to help clean up oil spills and are widely used during disasters,” said study leader Roberto-Rico Martinez of the UAA in a statement. “But we have a poor understanding of their toxicity. Our study indicates the increase in toxicity may have been greatly underestimated following the Macondo well explosion.”

Mr. Martinez conducted the research while he was a Fulbright Fellow at Georgia Tech. The researchers hope that the study will encourage more scientists to look into how oil and dispersant impact marine life. They believe that more knowledge of this topic will result in better management of future oil spills.

“What remains to be determined is whether the benefits of dispersing the oil by using Corexit are outweighed by the substantial increase in toxicity of the mixture,” said Terry Snell, the chair of the School of Biology at Georgia Tech, in a statement. “Perhaps we should allow the oil to naturally disperse. It might take longer, but it would have less toxic impact on marine ecosystems.”

The study’s finding were recently published online by the journal Environmental Pollution.