Dispersant Used to Clean Gulf Oil Spill Increases Toxicity in Marine Waters

Dispersant used to clean up oil released in the Gulf of Mexico during the Deep Water Horizon spill in 2010 is 52 times more toxic than the oil itself, reveals a new study.

The Deep Water Horizon spill (also known as the BP oil spill) caused one of the worst ecological disasters in the world. Around 4.9 million barrels of oil leaked in the Gulf, affecting the food chain of underwater creatures.

Now, a new research carried out by experts from the Georgia Institute of Technology and Universidad Autonoma de Aguascalientes (UAA), Mexico, has found that the two million gallons of dispersants used to clean up the oil has increased the toxicity in these marine waters.

Oil dispersants called Corexit 9527A and 9500A were emptied into the Gulf of Mexico in order to degrade the oil and prevent it from reaching the shore. But, when oil gets mixed with the Corexit dispersant, the mixture causes 52 times more toxicity in the waters, said the researchers.

The research team wanted to test the toxicity of the oil leaked in the Gulf, dispersants and mixtures of both on five strains of rotifers. They noticed that the oil-dispersant mixture caused mortality in adult rotifers. In addition, researchers also found that 2.6 percent of the mixture was enough to inhibit rotifer egg hatching by 50 percent.

The toxicity of the mixture affects the larvae from sediments by reducing the size of the next generation of organisms. This affects the food chain of marine animals, as rotifer eggs are known to hatch into rotifers each spring, which reproduces in the water and provides food for baby fish, crabs and shrimps.

The study findings are in contrast to the report released by the Environmental Protection Agency in August 2010. The report stated that the mixture of oil and Corexit is not more toxic than the oil alone to shrimps and crabs. However, the new study has revealed the mixture is more toxic than oil to embryos of several fish species, reported LiveScience.

"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 and his colleagues hope the study will encourage more scientists to carry out probes regarding the impact of oil and dispersant on marine food webs. This could help in better management of future oil spills, they said.

The findings of the study, "Synergistic toxicity of Macondo crude oil and dispersant Corexit 9500A® to the Brachionus plicatilis species complex (Rotifera)", are published online in the journal Environmental Pollution.