In Gulf oil spill, how helpful – or damaging – are dispersants?

www.csmonitor.com...

The one BP is using to break up the Gulf oil spill has been approved by the EPA. But it's an older mixture that contains toxic ingredients, and it's not among the top tier of recommended dispersants.

Two dispersants BP has been using to break up the oil spewing from an undersea wellhead in the Gulf of Mexico carry the federal stamp of approval. But they are not rated as effective or as safe for marine life as at least 12 other government-approved dispersants on the market.

Why would they do this you ask , when the other ones are more effetive and safer?
See here : www.nytimes.com...

So far, BP has told federal agencies that it has applied more than 400,000 gallons of a dispersant sold under the trade name Corexit and manufactured by Nalco Co., a company that was once part of Exxon Mobil Corp. and whose current leadership includes executives at both BP and Exxon. And another 805,000 gallons of Corexit are on order, the company said, with the possibility that hundreds of thousands of more gallons may be needed if the well continues spewing oil for weeks or months. But according to EPA data, Corexit ranks far above dispersants made by competitors in toxicity and far below them in effectiveness in handling southern Louisiana crude.