What was worse, the 4.9 millions of oil that gushed into the Gulf of Mexico from the Deepwater Horizon disaster or the 2 million gallons of dispersant used to help clean up the spill?
If you answered both, you would be correct, according to a new study.
The ecological disaster from the oil is a given, however, the two million gallons of dispersant used to clean it up apparently made it even worse: About 52 times more toxic, according to new research from the Georgia Institute of Technology and Universidad Autonoma de Aguascalientes (UAA), Mexico.
The study found that mixing the dispersant with oil increased toxicity of the mixture up to 52 times over the oil alone. In toxicity tests in the lab, the mixture’s effects increased mortality of rotifers, a microscopic grazing animal at the base of the Gulf’s food web. Using oil from the Deep Water Horizon spill and Corexit, the dispersant required by the Environmental Protection Agency for clean up, the researchers tested toxicity of oil, dispersant and mixtures on five strains of rotifers.
Ecotoxicologists use rotifers 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 preapproved to help clean up oil spills and are widely used during disasters,” said UAA’s Roberto-Rico Martinez, who led the study. “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 the study will encourage more scientists to investigate how oil and dispersants impact 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,” said Snell, chair of the School of Biology. “Perhaps we should allow the oil to naturally disperse. It might take longer, but it would have less toxic impact on marine ecosystems.”
The findings are online at the Environmental Pollution publication and will appear in the February 2013 print edition. There is a cost to download the report.