After a series of tests to determine if chemical dispersants would be safe and effective to help break up the oil spill at the source of the oil leak in the Gulf of Mexico, a mile below the surface of the ocean, the U.S. Coast Guard and U.S. Environmental Protection Agency today announced they have authorized BP to use dispersants at depths of 5,000 feet.

“Based on the scientific analysis of the EPA and NOAA and review by the National Response Team," said Coast Guard Admiral Thad W. Allen, the national incident commander for the spill, "it has been determined that the use of dispersants at the subsea source is the prudent and responsible action to take along with other tactics including surface dispersant, skimming and controlled burns."

Coast Guard officials say that preliminary testing results indicate that subsea use of the dispersant is effective at reducing the amount of oil from reaching the surface – and can do so with the use of less dispersant than is needed when the oil does reach the surface.

BP first deployed the dispersant near the source of the oil leak at the broken riser soon after the response shifted to large-scale oil spill control efforts. But because the dispersants had never been used a mile below the surface of the sea--and the environmental impacts of deep-sea deployment of the chemicals were largely unknown--EPA and Coast Guard suspended the use of subsea dispersant until NOAA could gather more information.

Dispersants are largely considered less harmful than the highly toxic oil leaking from the source and they also biodegrade in a much shorter time span.

Dr. Jane Lubchenco, the Undersecretary of Commerce for Oceans and Atmosphere at NOAA, said research suggests the chemicals used in the dispersants are one-tenth to one one-hundreth less toxic than the oil. "Their use is a trade-off decision," said Lubchenco earlier this week.

But not everyone is convinced. A group of toxicology experts are suggesting that the stew of chemical dispersants and crude oil might be doing more harm than good.

“The dispersants used in the BP cleanup efforts, known as Corexit 9500 and Corexit EC9527A, are also known as deodorized kerosene,” said Dr. William Sawyer.

“With respect to marine toxicity and potential human health risks, studies of kerosene exposures strongly indicate potential health risks to volunteers, workers, sea turtles, dolphins, breathing reptiles and all species which need to surface for air exchanges, as well as birds and all other mammals," said Dr. Sawyer.

And even though the exact chemical breakdowns of the dispersants are unknown to the general public--because the chemical companies that make them claim the need to maintain proprietary control of their products--EPA Administrator Lisa P. Jackson said that the process of approving chemicals used as oil dispersants is something EPA takes seriously.

“There is a process of getting on the list (of approved dispersants) that requires toxicity testing by regulatory agencies,” said Jackson. “This is not something that is done lightly.”

In terms of the volume of dispersant that will ultimately deployed in the Gulf of Mexico, British Petroleum, Inc. has already dumped more than 400,000 gallons of chemical oil dispersants into the Gulf of Mexico. BP says that the makers of the Corexit line of chemical dispersants, Nalco Energy Services of Nashville, can deliver as much as 75,000 gallons of dispersants a day indefinitely.

Said EPA Administrator Jackson about the amount of dispersants used to control the impacts of the BP oil spill in the Gulf of Mexico, "I think it's fair to say that when it comes to this volume, we're in uncharted waters."