A quad-engine plane applies dispersant on the oil slick at the BP Deepwater Horizon spill site. In spite of an EPA directive to cease the application of dispersants, BP continued to spray aerially and inject them at the well. J. Henry Fair / industrialscars.com

By Bob Berwyn
3 December 2012 The massive amounts of oil that spilled into the Gulf of Mexico after BP’s Deepwater Horizon drill rig exploded was devastating to marine life, but the dispersant used in the aftermath to try and break down the oil slicks may have been even worse for some species, according to new research done by scientists with the Georgia Institute of Technology and Universidad Autonoma de Aguascalientes, Mexico. Based on laboratory toxicity tests, the study found that the oil-dispersant mix was up to 52 times more toxic to tiny rotifers, microscopic grazers at the base of the Gulf’s food chain. The researchers tested a mix oil from the spill and Corexit, the dispersant required by the Environmental Protection Agency for clean up, 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. Other studies the past two years have shown similar results. Essentially, the mixture of oil and dispersant is more easily absorbed by organisms, raising the question of whether the benefits of using dispersant are enough to offset the negative effects. One study showed a dramatic change in the composition of microbial communities on some Gulf beaches, while another found traces of a toxic blend of oil and dispersants present in the surf line, where swimmers and surfers could be exposed. Scientists with the Woods Hole Oceanographic Institution found that plumes of the dispersant lingered in deep Gulf waters for many months after the spill. The Deepwater Horizon spill marked the first time dispersant was used in such massive quantities, being mixed directly with the oil spewing out of the broken well. The latest research shows the mixture caused mortality in adult rotifers, and 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.” […] The findings are published online by the journal Environmental Pollution and will appear in the February 2013 print edition.

Study: Dispersant Made Oil 50 Times More Toxic To Gulf Of Mexico Microorganisms