Dispersants Are the ‘Soap’ That Saved Louisiana’s Coast, Says Top Scientist
By Veronica Del Bianco
Dr. Edward Overton in his lab at LSU, Baton Rouge, La.
“Dispersants saved our coast. You can quote me on that!” says Dr. Edward Overton of the Department of Environmental Sciences School of the Coast and Environment at Louisiana State University.
In Overton’s view, hundreds of miles of coastal marsh were protected by the decision to use dispersant offshore on the Deepwater Horizon oil well — a decision he calls the lesser of two evils.
“It is not correct to say the use of dispersants causes no damage. It does cause damage, but it looks to be minimal damage.”
Overton recently testified before the U.S. Senate Committee on Environment and Public Works about the effects of dispersants on oil spills.
According to Overton, when an oil spill occurs, the majority of oil floats on the water’s surface and can be moved inshore by wind and tide, reeking havoc on vulnerable coastal habitats. To prohibit the oiling of a coast, the generally accepted practice is to add dispersants to floating oil, dispersing it into the water column. The animals living in the water column are, in the process, exposed to the dispersant.
“The good news,” says Overton, “is that when you are way offshore, most animals that swim can sense something and will go the other way. So they will practice avoidance. If you have something that can’t swim — a reef on a rig, all of the barnacles — they can’t move, so if the dispersed oil goes over them, that can cause a problem.”
There are higher concentrations and larger populations of these sedimentary, vulnerable organisms, such as oysters, living inshore versus offshore. So the generally accepted practice for minimizing the environmental impact of an oil spill is to use dispersant in water deeper than 300 feet. The deeper the water, the more diluted the dispersed oil will become.
The ingredient list of Corexit 9500 — the Nalco-manufactured dispersant used on the spill — is no mystery. People who insist otherwise are ignoring the scientific facts, Overton says, and may have a political agenda for doing so.
“A lot of people have insisted that we don’t know what’s in dispersants and that’s not true,” says Overton. “We do know what’s in this dispersant. Nalco has told what’s in its dispersant.”
The U.S. patent for Corexit 9500 is available to the public online and lists the components of the dispersant but not the ratio.
“Virtually all of the products are licensed by the FDA for consumption either in food or around food,” reports Overton. “They don’t have persistent organic chemicals. All of them are biodegradable. There are no heavy metals in them. And there are no unusual toxicities.”
Also, in an independent study that was funded by Nalco, Corexit 9500 showed 78 percent biodegradation in 28 days and a bioaccumulation factor (BAF) in the range of 2.6 to 208, well below the regulatory bioaccumulation threshold for concern — 1,000. For comparison, the infamous pesticide DDT’s had a BAF range of 12,000 to 80,000, depending on the species.
“Dispersants are a variety of chemicals that basically dissolve oil in the water — it’s a soap,” says Overton. “We use soap for our hands. Dispersant is a soap for oil.”
A soap that, in Overton’s opinion, helped save the Louisiana coast from becoming dirty with millions of gallons of oil.
Graph from Dr. Overton’s statement to the U.S. Senate Committee on Environment and Public Works.
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