Clean-up makes Gulf of Mexico spill 52 times more toxic

If the 4.9 million barrels of oil that poured into the Gulf of Mexico during the 2010 Deep Water Horizon spill was an ecological disaster, the two million gallons of dispersant used to clean it up apparently made it even worse – 52-times more toxic.

A study from the Georgia Institute of Technology and Universidad Autonoma de Aguascalientes (UAA), Mexico, has found that mixing the dispersant with oil increased toxicity of the mixture up to 52-fold 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. The findings are published online by the journal Environmental Pollution and will appear in the February 2013 print edition.

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.

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 per cent of the oil-dispersant mixture inhibited rotifer egg hatching by 50 per cent.  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.