01 Jul 2010:
Dispersants Used in Spill
Are Less Toxic Than Feared, EPA Says
The U.S. Environmental Protection Agency (EPA) says the chemical dispersants used to break up the oil spill in the Gulf of Mexico range from “practically non-toxic” to “slightly toxic
.” Paul Anastas, the agency’s assistant administrator for research and development, told reporters that EPA laboratory scientists had tested the effect of a variety of dispersants on shrimp and a small fish, the inland silverside. The agency determined that the most commonly used dispersant, Corexit, became lethal to half of the fish and shrimp in laboratory tests at concentrations of 130 parts per million, meaning it was “practically non-toxic.” Other dispersants killed half of the samples of fish and shrimp at lower concentrations and thus were labeled slightly toxic. The EPA did not test the toxicity of dispersants mixed with oil. Meanwhile, two teams of scientists said they are finding increasing evidence that extremely high levels of methane gas spewing from the Deepwater Horizon rig are beginning to create oxygen-depleted dead zones in Gulf waters
. Samantha Joye of the University of Georgia said the methane triggers the growth of microbes that break down the methane but also suck oxygen out of the water. She said she has found low-oxygen zones 1,000 to 1,300 meters below the surface. Scientists have said that high fertilizer loads from the Mississippi River and the spill are expected to create a larger-than-usual dead zone in the Gulf of Mexico this summer.
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