Plane spraying over waterA U.S. Air Force plane sprays chemical dispersants over the oil spill in the Gulf of Mexico.Photo: Deepwater Horizon ResponseEPA chief Lisa Jackson, along with other EPA officials and representatives from the National Oceanic and Atmospheric Administration, gave a press teleconference on use of dispersants in the Gulf Wednesday afternoon. I attended and got in a question.

I wanted to hone in on the hazardous ingredients in the dispersants now in use, which I discussed at length in a post last week. Last week, the government’s Deepwater Horizon Response website confirmed the use of two dispersants: Corexit 9500 and Corexit 9527A, which were developed and originally marketed by Exxon and are now owned by a company called Nalco.

Corexit 9527A is the older product, and considered more toxic. According to its Material Safety Data Sheet, it contains a chemical called 2-butoxyethanol — at a level of between 30 percent and 60 percent by weight (the public information on these products is maddeningly inexact). Since writing the post last week, I’ve come upon the entry for 2-butoxyethanol on the website of Haz-Map, a service of the National Library of Medicine that provides “information about the health effects of exposure to chemicals.”

This is not charming stuff, according to Haz-Map:

Severe hemoglobinuria and changes in the lungs, kidneys, and liver are seen in mice after 7-hour lethal concentration studies. Volunteers showed no evidence of adverse effects other than mucous membrane irritation after 8 hour exposures to 200 ppm. … For ethylene glycol ethers, there is limited positive evidence of spontaneous abortions and decreased sperm counts in humans and strong positive evidence of birth defects and testicular damage in animals.

Moreover, such effects seem to happen at low concentrations — as low as 20 parts per million. So I asked Jackson and her crew to “drill down” (pun not intended, I promise) on just what sort of effect dumping hundreds of thousands of gallons of a substance that contains lots of 2-butoxyethanol would have on the Gulf.

Jackson gave the floor to Paul Anastas, assistant administrator for EPA’s Office of Research and Development and the Science Advisor to the Agency. His answer surprised me. Rather than discuss the toxicity of 2-butoxyethanol, Anastas sought to assure us it was no longer in use — because the Gulf cleanup crew had already dumped all of the Corexit 9527A it had in hand into the Gulf, and were now using only Corexit 9500.

“Corexit 9527 has been around since the 80s, and over time, the dispersing agents have become more and more effective and more environmentally friendly,” he said. For Corexit 9500, Nalco has switched to “other solvating agents that obviate the need for 2-butoxyethanol,” he added.

He went on to say that “9527 was being used originally, but due to supply, the 9500 is now being used at the current time.”

So how much 9527 went into the Gulf before supplies ran out? We can get a very rough estimate from information that emerged from the meeting.

At one point, Jackson said that the Gulf cleanup team had received a total of 500,000 gallons of dispersants, and had used 400,000 gallons by May 10. Another 805,000 gallons are on order, she added.

Someone asked her how much of each dispersant — 9500 and 9527A — had been used. Jackson said she didn’t know for sure, but she understood that use so far had been “roughly 50/50″ between the two.

If 9527A made up half of the volume of dispersants used by May 10, that means that something like 200,000 gallons of the dodgy stuff went into the Gulf. And we don’t know whether more is on the way; Jackson said she had no information on the 805,000 gallons of dispersant on order.

This information raises hard questions about what’s happening in the Gulf. Unfortunately, I didn’t get to ask them; followup questions were not allowed.

For one, knowing that spills are always a risk, why isn’t the oil industry required to keep a ready supply of the least toxic dispersants available on hand at any given time? If it’s common knowledge that dispersants have become “more effective and more environmentally friendly” since Corexit 9527A’s ’80s heyday, then why is 9527A still playing a key role in addressing oil spills?

To me, the dispersant situation is yet another instance of the oil industry being allowed to take tremendous drilling risks without being forced by regulators to take corresponding precautions. If dispersants are indeed a critical tool for limiting the damage of spills, the industry as a whole should be charged with ensuring that there’s a sufficient global stockpile of the best dispersants, optimized for maximum effectiveness and environmental friendliness.

In the second part of my question at the press conference, I asked about supply. Given that we’ve burned through so much so fast, and given the strong possibility that the leak will maintain current levels or even increase for the next three months, are there sufficient dispersant supplies on hand? What happens if we run out? Jackson replied in vague terms that her operations team had assured her that supply wasn’t a problem. The numbers she gave told a different story, though. So far, we’re using about 200,000 gallons of dispersants per week. Jacskon says there’s 800,000 on order — about a four-week supply. Is there more if needed? And will BP have to revert to older, more toxic dispersants if stocks of 9500 run low? None of these questions were addressed.

I also wish I had gotten the chance to get Anastas to drill down into the composition of Corexit 9500. It may be more environmentally benign than 9527A, but there are also key questions about its toxicity. As I wrote in my last piece, the solvent that replaced 2-butoxyethanol in 9500 is a substance called “petroleum distillates,” which, according to its Chemical Scorecard, “is harmful to aquatic organisms.” Moreover, the Material Safety Data Sheet for 9500 contains the chilling line, “Component substances have a low potential to bioconcentrate.”

I am currently trying to get an interview with Anastas, and will report back when I have more information.