In the past week, a lot of writers – and, yes, that includes me – have focused on the chemical dispersants being sprayed into the Gulf of Mexico to help manage the ever-expanding oil spill from BP’s deepwater drilling rig.
For instance, I recently pointed out while dispersants do help break apart a slick into smaller and more biodegradable fragments, dispersed oil is a great deal more poisonous than crude oil. Further, that post, A Lethal Concentration, generated a great discussion, and one that taught me a lot.
I hadn’t considered that the thriving bacterial colonies of warm water environments like the Gulf may work to our advantage, breaking down oil far more rapidly than, say, in the Exxon Valdez disaster in icy Alaskan waters. And readers actually found better toxicity numbers than I had. Some of these strengthened my conclusion that BP’s chosen dispersant, Corexit, rather alarmingly increases the toxicity of crude oil. For instance, Corexit alone has an LC50 for silver fish of 25.2 parts-per-million. But the EPA’s dispersant data shows that Corexit plus fuel oil has an LC50 of 2.61, almost ten times as toxic.
This is not what you might think of as a happy synergy – I definitely don’t – but there are some trade offs here. Dispersants do help keep some of the oil from oozing its way on shore, where it does horrific damage. And – there’s some somewhat positive research cited in the comments – which reminds us that we don’t really know how rapidly these compounds are diluted in deep waters, how quickly bacteria may chew them up, or what chemical changes may occur as they filter down the water column.
Tomorrow, I want to take up the chemistry of crude oil itself, which is actually poisonous enough without help from dispersants. But today, I just want to say thanks to those who wrote in on the subject. I wish the people in charge knew as much as you do.