Corexit:: the more we know the more we regret
A new modelling study shows the ineffectiveness of deepsea dispersant
Much has been made of the unprecedented use of the dispersant Corexit in the 2010 disaster, especially the unheard-of deepsea application. We at GRN have sued EPA because they backed down and approved the use of Corexit after they objected. In our lawsuit, we are asking our government to simply review the science before attempting large-scale chemical alterations to the Gulf--because we believe that the science will show that the scale of application and deepwater application are unnecessary and even harmful.
Some of the science has already said that Corexit is the most toxic of approved dispersants; that it was engineered for heavier Alaska crude, and not for Louisiana's oil; and that the natural weathering of the oil catches up with any short-term benefit of chemical dispersants--if your stream of oil pollution is doing to last longer than a month, there is no long-term benefit to rapidly dispersing the oil.
Newer research has come out against Corexit completely--arguing that the oil and Corexit mix is more toxic than oil alone, and that Corexit is actually toxic to the bacteria it is supposed to help feed.
New research this month in Environmental Science and Technology argues that deepsea dispersant application wasn't needed at all. Apparently, modelling shows that the physical pressure of the BP's underwater geyser dispersed the oil itself, without the need for chemical assistance.
Although there were many other things learned about the movement of oil in the deepwater Gulf as a result of this modelling effort, the principle whereby BP's oil self -emulsified is well known. This video from 2010 demonstrates the principle how a deepwater plume forms under pressure in saltwater. This is the deepwater plume that BP denied existed for so long.
Screencap from the UNC video. On the left, a turbulent plume emulsifies the oil into a denser liquid that doesn't come to the surface. On the right, oil released without turbulence floats to the surface.
Now, modelers at University of Miami have shown that the same plume forms in a simulated Gulf of Mexico, and they have shown that the turbulence of the geyser itself disperses the oil more than chemicals can.
Although oil is less dense than water, and normally floats, the action of the geyser creates an oil / water emulsion that is denser than water. The oil / water plume settles out at the depth above which the water is less dense than the oil / water emulsion. More interesting, perhaps, is that that same geyser--that tremendous amount of heat and pressure--emulsifies the oil into droplets surrounded by water, so that the geyser itself physically disperses the oil--no chemicals necessary.
Dispersants have their place in oil response, specifically to keep oil from coating our marshes. But they are a precision tool.
You can't use a socket wrench as a hammer, and you can't use dispersants to "clean" oil from the water. Dispersants are designed for limited spills, applied to the water (not the air) at the surface, and work over weeks. Corexit itself was designed for Alaskan oil, and is only 50% effective on Louisiana sweet crude--BP admitted to the fact that it only used Corexit because of its existing "availability." The industry push to use dispersants as a "one-size-fits-all" response is strong enough that we must forcefully ask our government to review the science.
When the next oil disaster comes, we hope that dispersants won't be used in such quanitities. It would always be better to skim and recover what oil can be recovered.
If as many resources were applied to spill response as were applied to exploration and drilling, the Gulf would have the capacity and the technology to respond to oil spills. Until then, we'll keep hammering nails with a socket wrench.
Scott Eustis is GRN's Coastal Wetland Specialist