After ordering BP last month to find and switch to a less toxic chemical dispersant than Corexit — which BP has sprayed in record quantities into the Gulf of Mexico -- the EPA announced today that based on initial testing, all eight dispersants the agency is studying “are roughly equal in toxicity.”

So far, however, the dispersants have been tested only on their own — not in combination with oil, which some scientists believe is more toxic than either oil or dispersant alone.

These are not the first toxicity tests conducted on these dispersants: according to an EPA fact sheet released today, the manufacturers “already tested both the toxicity and the effectiveness of each of these dispersants.” In a conference call today, Paul Anastas, the EPA's assistant administrator for research and development, said the toxicology tests are “an important part of the listing criteria” for a product to be placed on the National Contingency Plan Product Schedule — the EPA’s list of authorized dispersants. 

Here’s the kicker, though: The toxicity tests are part of the listing criteria only in the sense that they must be done and the paperwork must be filed with the EPA. But there’s no maximum toxicity for products to be included on the EPA’s list.

That means the 14 products, once deemed to be above a certain threshold of effectiveness, could be placed on the list as long as toxicity tests were done and the paperwork was complete, regardless of what the toxicity tests found. (To be applied to an oil spill, however, a product that is authorized must still be approved by the federal on-scene coordinators and regional response teams.)

The EPA has chosen eight of the 14 products to test now, based on three criteria: toxicity, quantities available for the spill, and immediate availability for testing. Note that first criterion.

But until now, the agency has not independently verified the toxicity testing done by the manufacturers. It started doing so only about a month into the BP disaster, by which time hundreds of thousands of gallons had already been applied. More than 1.5 million gallons have been applied in the Gulf to date.

When I asked Anastas about the lack of a toxicity limit for placement on the EPA’s authorized list (an issue I first heard about from Richard Denison, a senior scientist at the Environmental Defense Fund), he acknowledged that BP’s disaster in the Gulf has “raised important questions about how these previous existing regulations may need to be re-examined and revisited.”

More testing will be conducted, he said, to look at the oil and dispersant combination before any decisions are made.