Does Corexit 9500 Correct it?

I've been thinking about starting a blog for some time now, to present my field, toxicology, to the layperson. There are a lot of scary things out there these days, and the fact that BP is spraying hundreds of thousands of gallons of a chemical dispersant, Corexit, provided the impetus for me to get the ball rolling. Hope you find this educational, informative, and alarming.


Corexit 9500 is the latest in a series of chemical dispersants produced by the Nalco corporation. The purpose of oil dispersants is to break up large pools of oil into bite-sized morsels. This allows the oil to sink into the water, where it can be more easily consumed by marine bacteria. It also helps with the image problem, because as we know from the Exxon Valdez spill, nothing galvanizes people like oil-covered wildlife.

Everyone agrees this is tragic, and should be prevented at all costs. But, by dispersing oil, we are shifting the burden from birds to the less visible species that live below the sea.


Corexit, as well as other dispersants, work by forming micelles around oil droplets. Oil and water don't mix, so you add a chemical that contains a polar (charged) head, and a nonpolar (uncharged tail). Like dissolves like, so when you add a dispersant to an oil/water mixture, the uncharged tails associate with the oil (and each other), while the heads line up to face the water side. This is how soap works. Soap is good, right? Well, not necessarily...

Part of the job of a "dispersant" is to disperse. So, where does all the oil go? Some settles to the bottom of the ocean, and some of it gets solubilized into the water. This can be bad.

Below is a figure from Anderson et al.¹

Using Corexit 9500, the dispersant used in the Gulf right now, the authors found more oil dissolved in the water when Corexit was used. So, it's doing the job.
In subsequent experiments, they tested the effect of this dissolved oil on Topsmelt fish. Without Corexit, there was not enough oil in the water to affect these fish. With Corexit, enough oil was dissolved to kill adult fish as well as cause developmental abnormalities in embryos (birth defects).

If you know about the food chain, you know this is bad. First of all, we might be killing an entire generation of developing fish, causing population decline. Thich provides less food for bigger fish, birds, and so on. Secondly, some of the compounds in oil are able to mutate DNA, so we may be causing heritable effects on marine life. Not good.

A study by Ramachandran et al.² showed that Corexit dispersant increases uptake of carcinogens in fish exposed to crude oil. This is a particular problem because these nasty compounds in oil are lipophilic, meaning they get stored in our fat when we eat them. Well, they do that in fish, too--this is bioaccumulation, and is a major concern, especially if we plan on eating any seafood from the gulf from any time soon...


This entire post ignores the possible toxicity of the dispersants themselves...I'll delve into that next time.


References:

1. Brian S. Anderson, Diane Arenella-Parkerson, Bryn M. Phillips, Ronald S. Tjeerdema, David Crane, Preliminary investigation of the effects of dispersed Prudhoe Bay Crude Oil on developing topsmelt embryos, Atherinops affinis, Environmental Pollution, Volume 157, Issue 3, March 2009, Pages 1058-1061, ISSN 0269-7491, DOI: 10.1016/j.envpol.2008.10.013.
2. Shahunthala D. Ramachandran, Peter V. Hodson, Colin W. Khan, Ken Lee, Oil dispersant increases PAH uptake by fish exposed to crude oil, Ecotoxicology and Environmental Safety, Volume 59, Issue 3, November 2004, Pages 300-308, ISSN 0147-6513, DOI: 10.1016/j.ecoenv.2003.08.018.