If the 4.9 million barrels of oil that spilled into the Gulf of Mexico during the 2010 Deepwater Horizon spill were an ecological disaster, the 2 million gallons of dispersant used to clean it up apparently made it 52-times more toxic.
That's according to new research from the Georgia Institute of Technology and Universidad Autonoma de Aguascalientes, Mexico, Science Daily reported.
The study found that mixing the dispersant with oil increased the toxicity of the mixture as much as 52-fold over the oil alone. In toxicity tests in the lab the mixture's effects increased the mortality of rotifers, a microscopic grazing animal at the base of the Gulf's food web.
The findings were published online by the journal Environmental Pollution and will appear in the February 2013 print edition.
Using oil from the Deepwater Horizon spill and Corexit, the dispersant required by the Environmental Protection Agency for cleanup, the researchers tested the toxicity of oil, dispersant and mixtures on five strains of rotifers.
Rotifers have long been used by ecotoxicologists to assess toxicity in marine waters because of their fast response time, ease of use in tests and sensitivity to toxicants. In addition to causing mortality in adult rotifers, as little as 2.6 percent of the oil-dispersant mixture inhibited rotifer egg hatching by 50 percent. Inhibition of rotifer egg hatching from the sediments is important because these eggs hatch into rotifers each spring, reproduce in the water column and provide food for baby fish, shrimp and crabs in estuaries.
"Dispersants are pre-approved to help clean up oil spills and are widely used during disasters," UAA's Roberto-Rico Martinez, who led the study, told Science Daily. "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."
Martinez performed the research while he was a Fulbright Fellow at Georgia Tech in the lab of School of Biology Professor Terry Snell. They hope that the study will encourage more scientists to investigate how oil and dispersants affect marine food webs and lead to improved 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," Snell, chairman of the School of Biology, told the publication. "Perhaps we should allow the oil to naturally disperse. It might take longer, but it would have less toxic impact on marine ecosystems."