| New bio- remediation agent: A Bacterium That Gobbles Up Poison
By JONATHAN MILLER
The New York Times(2003년 10월19일)
[AIRFIELD, N.J] - The Caldwell Trucking Superfund site, a few miles west of the Willowbrook Mall, is a nine-acre repository of poison-laced sewage, hauled here and dumped until the 1970's, when the threat of drinking-water contamination was recognized.
About 50 private wells and two public wells had to be shut down, and even more drinking water was threatened as contamination spread toward the Passaic River. The contamination has now mostly been contained, but the latest cleanup stage has progressed fitfully at best.
And so three years ago, the federal Environmental Protection Agency started a daring project to pump into the ground a mysterious and little- understood bacterium that munches on the type of pollutants to be found here.
By all accounts, the use of the half-micron-long bacterium with the official name Dehalococcoides ethenogenes has been a success. Technically, the bacterium - a few thousand could fit on the head of a pin - ingests the toxic chemicals the way that people breathe oxygen.
"It looks like the process is really working," said Tom Porucznik, remedial project manager for the E.P.A. The agency will be looking at more results throughout the fall, and will likely decide sometime in the spring whether to continue with the treatment.
The bacterium was discovered in 1997 by a team of scientists at Cornell University. They found that it had a strange natural affinity for devouring dangerous industrial chemicals like the one found at Caldwell Trucking - trichlorethylene, or TCE, which was often used as a heavy cleaner and is suspected of being a carcinogen. The bacteria have an unusual cell wall, and are tiny even by bacterial standards. "They're really weird organisms," said Dr. Stephen H. Zinder, the chairman of the microbiology department at Cornell University.
Using the "bugs" - as both he and others refer to D. ethenogenes - is a vast improvement over the pump-and-treat method, a tactic used at many polluted sites that essentially pumps water to the surface in the hope of removing contamination.
"The bugs flow where the contamination is, because they're following the water," said Peter Herzberg, a lawyer for eight companies responsible for the cleanup at the Caldwell site. "And you're getting to places where you couldn't get to mechanically with a pump-and-treat system."
Once they get where they are going, the bugs find the TCE or other poisons and begin devouring the chlorines from the molecules, leaving as a byproduct a harmless substance called ethene. The procedure, called bioremediation, has been used in pilot programs in California, Delaware, Texas and elsewhere to battle potential groundwater contaminants. Many sites lie near Air Force bases, where a mixture of jet fuel and TCE often seeped into the ground. Here, scientists and government officials have watched with surprise as the bacterium has significantly reduced the levels of TCE, in some places by 90 to 95 percent.
To those who may wonder about replacing poisons with bacteria in groundwater, officials and scientists say that thus far they see no ill effects. David W. Major, a scientist for GeoSyntec, a company that produces a widely used strain of the bacteria used at the site, said that once the feeding of D. ethenogenes stops, the organism simply dies, with little impact on the environment. Still, Dr. Zinder of Cornell, who along with James M. Gossett discovered the organism, said that unintended consequences were always a possibility.
"I'd say, you never know for sure, which makes people nervous," he said, "but I think as technologies go, I wouldn't consider these pathogens. There's just no evidence."
In fact, over the past decade, bio- remediation has been used a number of times. Fertilizer has been used to attack oil spills. In phytoremediation, plants are used to clean up toxic metals.
On a clear, bright day, a little chilly by early October standards, a single propeller plane passes overhead on its way to Essex County Airport,
and it seems that little is detectably wrong at this nine-acre spot in northern New Jersey. But the whine of a generator and the site of seven milky-white 55-gallon drums rising from the ground quickly dispel that notion.
These drums are a kind of feed bag for the bacteria. Each day, Joe Huffman, a geologist, sends a concoction of nutrients, including lactate, into the ground. "It's like a buffet for the homeless," he said.
Chris Young, a project manager for the site, is stomping over what was once the "central lagoon," where the heaviest contamination from the
septic sludge remains. Now, millions of poison-munching bacteria are burrowing into the soil's convoluted pathways where only a bacterium
can go.
"In those tortuous paths," Mr. Young said, "we're just trying to get these nutrients down, get them feeding the organism in place, and get these
populations growing."
Obviously, the more they increase, the more they eat.
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