Bioremediation

In 1975 a massive leak at a military storage facility spilled eighty thousand gallons of kerosene-based jet fuel outside a quiet suburb of Charleston, South Carolina. Although the cleanup effort contained the spill, it could not prevent the fuel from seeping into groundwater. In less than ten years, highly toxic chemicals, such as cancer-causing benzene, had reached residential neighborhoods.

Studies conducted by the U.S. Geological Survey (USGS) found that microorganisms in the soil were actively consuming the toxic compounds. As they ate, they transformed the compounds into harmless carbon dioxide. By stimulating the bacteria with nutrients, the USGS team found they could increase the bacteria's activity. Through specially made infiltration systems, the nutrients were pumped into the contaminated soil. Tainted groundwater was filtered out and cleaned. In one year the contamination was reduced by 75 percent.

The process of using microbes as miniature cleanup crews is now called bioremediation, and it is big business. More than fifty bioremediation companies use microbes to clean the soil at former industrial plants, military ammunitions sites, and old gasoline stations.

Gasoline is the most common contaminant of groundwater throughout the United States. Thousands of steel tanks buried beneath old gas stations are corroding and leaking gas into the soil. "These tanks are everywhere; it's a nationwide problem,"24 says Loring Nies, an assistant professor of environmental engineering at Purdue University. Before microbes were used, the soil had to be completely removed down to depths of several feet—an expensive and labor-intensive process.

Rusty barrels containing toxic materials can release toxins into the soil. Using microbes to clean up such waste has become a common practice.

Now microbes that occur naturally in the soil are "fed" by pumping phosphorus and nitrogen into the ground, promoting rapid bacterial growth.

Another type of bacteria that likes to eat poison is cleaning up old contaminated mining sites. Gold is traditionally separated from ore using cyanide, a highly toxic substance that can kill within minutes if ingested. After processing, the cyanide is washed away and ends up in nearby streams and creeks. The Homestake Mine in South Dakota, the largest gold mine in North America, had been washing cyanide into Whitewood Creek for more than a hundred years. The creek was so polluted that it was thought to be sterile: Nothing could live in it. But when researchers tested the creek water, they found that one type of bacteria was thriving. That bacterium used the poisonous cyanide as its main food source. Now that bacterium is being used to clean up other mining sites as well.

Researchers around the world search for bacteria with useful appetites. Some, like the mining microbes, are found in nature, while others are discovered in an endless array of laboratory tests. At the University of West Florida scientists tested more than twenty thousand mutant strains of bacteria before they found one that turned a toxic industrial chemical, TCE (trichloroeth-ylene), into a harmless substance. Today bacteria are used to detoxify soil and water polluted by PCBs (poly-chlorinated biphenyls), creosote, DDT, and other tough, toxic compounds.

The USGS estimates that cleaning up existing environmental contamination in the country would cost as much as $1 trillion. With bioremediation the cost may be cut drastically and the cleanup will be less stressful on the environment. But much of what bioremediation promises has yet to be realized. Designer microbes will eventually take the place of naturally occurring ones and will be able to do the job faster and more efficiently. One recent project at the Oak Ridge

National Laboratory in Tennessee involved adding a bioluminescent gene to one toxin eater to make it glow so that human cleanup crews could see the bacteria at work.

Even The Guinness Book of World Records "World's Toughest Bacterium"25 is being put to work. Dein-coccus radiodurans was discovered in 1956 inside a can of meat that had spoiled despite being sterilized by radiation. This amazing bacterium can withstand and actually grow during exposure to 3 million rads of radiation, which is more than one thousand times the amount of radiation needed to kill a human. The bacterium does become damaged during exposure, but in less than one day, it is able to repair its damaged chromosomes. Scientists working with the Department of Energy are looking into the possibility of using these microbes, or hybrids of them, to clean up radioactive sites left over from the production of nuclear weapons.

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