CHANDELEUR ISLANDS, La. — In the scramble to keep oil off wetlands and beaches in the Gulf of Mexico, British Petroleum has sprayed and pumped so much chemical dispersant into the water that its supplies by Thursday were running out as the first oil began to come ashore.
The dispersants, which work much like detergent on greasy dishes, are being used in amounts that may exceed anything ever tried. They break up the oil slick floating on top of the water and spread it in tiny droplets that mix deep down into the water, preventing it from reaching shore.
At the same time, though, the toxic brown brew could damage or destroy the fish, coral, oysters and other creatures that live under the surface. So far, no one is predicting what the consequences might be for humans.
"It's a really hard decision to make, because it's a tradeoff between what you want to save and what you expose to more toxic material," said Carys Mitchelmore, an associate professor of environmental toxicology and chemistry at the University of Maryland's Chesapeake Biological Laboratory who researches the effects of chemical dispersants and oil on marine life.
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British Petroleum said in a statement Wednesday that it had sprayed more than 250,000 gallons of a dispersant called Corexit onto the surface of the water, was down to its last supplies and was ordering another 250,000 gallons. Charlie Pajor, a spokesman for Nalco, the Illinois company that makes Corexit, said he'd never heard of it being used on such a big scale.
The dispersant has a low to moderate toxicity. Nalco won't reveal its exact makeup, because the information is proprietary, Pajor said. The company is trying to make more of it as fast as it can, he said.
Corexit changes the physical and chemical properties of the oil, Mitchelmore said. Instead of a dark slick on the surface, it becomes tiny droplets that disperse into the water below.
It all being done with a scant understanding of what damage Corexit might be doing.
Mitchelmore worked on a 2005 National Research Council report that summarized what was known about dispersants and called for more studies, including how marine life is exposed to it and ultimately what are the effects of the dispersant and dispersed oil.
"There's research out there that shows that dispersed oil is more toxic than the oil itself, and then there are studies that say it's the same," she said. "The big questions are what are the long-term or delayed effects, and how will the different routes of oil exposure due to dispersant use affect exposed organisms? Those are topics that really haven't been looked at in detail and were highlighted in the NRC report."
Oysters, for example, could take in the droplets as they feed, she said. Fish can ingest the droplets by drinking water, or the droplets can stick to fish gills, suffocating them. The droplets also bind to other organisms, including those that are part of the food chain.
Some studies, however, find that having oil in the form of small droplets is helpful because it allows microorganisms to degrade the oil.
The oil droplets also can sink to the sea floor where they would cover coral.
Mitchelmore conducted lab studies with soft coral to study how they reacted to a mix of Corexit 9500 and dispersed oil. The coral died or failed to grow well.
Overall, the toxic effects depend on the kind of organism and the amount of exposure, she said. Generally chemical dispersants are "not ideal," but they can be the right choice if they keep oil away from sensitive habitats along the shore.
The Environmental Protection Agency said in a statement Thursday that it authorized BP to use the dispersant, but only if it took steps to protect the environment and health of nearby residents. The EPA was monitoring air quality.
Bill Seeman of Gulfport, Miss., took his open fishing boat out near the Chandeleur Islands on Wednesday to see for himself what was happening. He passed through calm waters where a highway of fluorescent orange strands ran past the islands. Seeman scooped up a water sample. Small, clear gelatinous droplets beaded up on his hand.
National Oceanographic and Atmospheric Association official Jacqueline Michel, who's overseeing the search for onshore oil, said Thursday that the first oil came ashore on the Chandeleur Islands.
She said it was "light orange, moussey looking stuff," and that crews were working to clean the islands' wetlands and beaches.
"It's pretty amazing we've had the oil in the water for this period of time and so little shoreline oiling," Michel said.
Jeremy Symons, senior vice president of the National Wildlife Federation, also surveyed the area by boat. Eighteen miles from the Biloxi wetlands he ran into heavy brown sludge on the water and a smell like spilled gasoline.
Near the islands, chemical dispersants had turned the ocean itself brown down to a depth of 5 to 15 feet, Symons said.
"People are expecting to see birds covered in heavy crude, but the real suffering in effects is happening out at sea out of sight of the cameras," he said in a report on his trip.
The chemical dispersant is approved for use three miles offshore in water deeper than 30 feet, where the huge volume of water dilutes it.
It's not clear if some of the large amount of dispersants sprayed on the spill had reached shallow waters.
A safety data sheet for Corexit 9500 said it had a low to moderate toxicity to humans. It also said that no toxicity studies had been conducted on it. Another version of the dispersant could cause damage to red blood cells, kidneys or the liver through "repeated or excessive exposure," the safety sheets said. The company recommended people handling Corexit wear protective clothing and gear.
The oil itself contains chemical components that evaporate, causing vapors that are a potential health risk. The contaminants also can accumulate in the food chain.
In an experiment never tried before, BP used robots to pump dispersants on the sea floor near the leak about 5,000 feet below the surface. The test stopped Tuesday night until scientists could evaluate how well it worked.
(Schoof reported from Washington. Lee reports for the Sun Herald in Biloxi, Miss.)