A dispersant plane passes over an oil skimmer as it cleans oil from a leaking pipeline that resulted from last week's explosion and collapse of the Deepwater Horizon oil rig in the Gulf of Mexico near the coast of Louisiana Tuesday, April 27, 2010. (AP Photo/Patrick Semansky)
Oil-dispersing chemicals used to clean the vast BP spill in the Gulf of Mexico carry their own environmental risks, making a toxic soup that could endanger marine creatures even as it keeps the slick from reaching the vulnerable coast, experts say.
"The concentration of detergents and other chemicals used to clean up sites contaminated by oil spills can cause environmental nightmares of their own," said Terry Hazen, a microbial ecologist in Berkeley Lab's Earth Sciences Division who has studied such notorious oil-spill sites as the Exxon Valdez spill into Alaska's Prince William Sound.
"It's important to remember that oil is a biological product and can be degraded by microbes, both on and beneath the surface of the water," Hazen said. "Some of the detergents that are typically used to clean up spill sites are more toxic than the oil itself, in which case it would be better to leave the site alone and allow microbes to do what they do best."
Manufacturers argue that prompt use of such detergents, also called dispersants, can move oil more rapidly to those microbes. But BP announced late Wednesday that it would halt dispersant of the chemicals while agencies further assess its environmental impact.
Dispersants work on an oil spill as dishwashing detergent works on a greasy skillet: They break up oil into tiny droplets that sink below the water's surface where naturally occurring bacteria consume them. Without dispersants, oil stays on the water's surface, where bacteria can't get at them, said Mani Ramesh, chief technology officer of dispersant manufacturer Nalco.
The U.S. Environmental Protection Agency has approved 14 dispersants for use on oil spills, including Corexit 9500, which Nalco produces. Crews battling the spill have already used more than 156,000 gallons of dispersants including Corexit.
Nalco has exhausted its entire inventory and is producing more, said Mani Ramesh, Nalco's chief technology officer. Ramesh said Corexit's active ingredient is an emulsifier also found in ice cream; he disputed environmental groups' claims that it is harmful to marine life, although the exact chemical make up of the the product is a trade secret.
Coast Guard Rear Adm. Mary Landry, the federal on-scene coordinator, called the tests so far "very promising, very promising." He told the Associated Press that sonar and camera images from the first test last week appeared to show a reduction in oil on the surface, although federal officials said they want more information from planes that will examine the leak site from the air.
The problem, according to Jackie Savitz, a senior scientist at the marine environmental group Oceana, is that the dispersants themselves can be toxic to wildlife. Dispersants can also enhance oil's toxicity in the dispersion process.
"A decision is being made where it's the shore wildlife and oysters and beaches versus the animals that live in the water," Savitz said. "When they use a dispersant, it's taking the oil and essentially dissolving it in the water so that it doesn't wash up on the beach."
Hazen cities the aftermath of the Amoco Cadiz and the Exxon Valdez disasters, two spills where chemical detergents led to ecological problems. In 1978, the oil tanker Amoco Cadiz split in two three miles off the coast of Normandy, releasing about 227,000 tons heavy crude oil that ultimately stained nearly 200 miles of coastline. The spill site was so large that only the areas of greatest economic impact were treated with detergents. Large areas in the more remote parts of the coast went untreated.
"The untreated coastal areas were fully recovered within five years of the Amoco Cadiz spill," says Hazen. "As for the treated areas, ecological studies show that 30 years later, those areas still have not recovered."
A combination of detergents and bioremediation were used to clean up the 1989 spill from the Exxon Valdez. The detergents were nutrient rich, being high in phosphorous and nitrogen compounds. In addition, as part of the bioremediation effort, fertilizers were also used to promote microbial growth. After the first year, the treated areas were dramatically cleaner, Hazen says, but after the second year no improvements were observed. Long-term prospects for the treated area are grim.
"What happened was that we took a low-nutrient environment and added lots of nutrients to it to speed up the degradation of the oil, which we probably did," Hazen says. "However, we upset the ecological balance of the system, which could not handle the influx of nutrients. As a result, the severe environmental damage resulting from the spill is expected to persist for decades to come."
Improvements to detergents have been made over the years, including some degree of biodegradability. Allison Nyholm, a policy adviser at the American Petroleum Institute, noted that current dispersants are different from the thick solvents used in 1967 on an oil spill off the California coast at Santa Barbara.
But all agree that short of capping the leak, there are few good solutions to this ecological disaster.
Reuters contributed to this report.
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