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Science / Medicine : A NATURAL RESPONSE TO TOXIC WASTE : When you bury an apple, it decomposes as soil organisms gobble it up. Such organisms also keep busy digesting sewage waste. Recently, scientists have begun to use microbes to destroy the worst hazardous substances that we throw out.

July 11, 1988|JUDY R. BERLFEIN | Berlfein is a free - lance science writer in Encinitas.

When the warehouse of Westchem Agricultural Chemicals Inc. in Minot, N.D., caught on fire in April, 1987, fire crews rushed in and hosed down the flames. Unfortunately, their quick response only led to more problems.

As it turned out, barrels of pesticides had been stored inside the warehouse, and the water that squelched the fire also washed the toxic chemicals into the soil, posing a threat to the local drinking water supply.

At first, it seemed that the only solution was to haul the contaminated soil to a landfill.

But upon reflection, Westchem's general manager, Harold Schultz, realized that that course of action only would have moved the toxic chemicals from his back yard to someone else's. Schultz had grown up in a farming community and felt strong ties to the land.

"Sooner or later," he said, "five or 10 centuries down the road, when we're all dead and gone, it's (dumping toxic materials) going to cause some problems on this earth."

As the excavation was still going on, a business associate told Schultz about a company that could clean up the contamination by stimulating microorganisms already present in the soil to munch away at the chemicals. The soil-dwelling organisms would do the job thoroughly and For a much lower price.

By June, a team from Ecova Corp., based in Redmond, Wash., was in place, ready to clean up the mess, using this biological method.

Within three months, the bacteria had destroyed 96% of the hazardous chemicals in the soil. Pesticide levels of substances such as 2,4,D and MCPA plummeted from 800 to 10 parts per million.

Using microbes to break down wastes isn't a novel idea. Knowingly or not, people have been doing it for centuries. When you bury an apple in the back yard, it decomposes as soil organisms gobble it up. Such creatures also keep busy at sewage plants, digesting the endless streams of waste.

Only in the last few decades, however, have scientists begun to tap the greater potential of microbes: using them to destroy hazardous substances.

In the '60s, scientists discovered that microbes living in the soil could be used to clean up petroleum waste products, although it wasn't until the early '70s that the new technology was put to work.

One of the first cleanups took place in Ambler, Pa., where a pipeline broke and contaminated the community drinking water supply with 130,000 gallons of high-octane gasoline from the spill. By adding nutrients and oxygen, the microbes in just over a year reduced the level of contamination to under 100 parts per billion--the level considered safe at the time. Without intervention, it might have taken 50 to 100 years, or more, to reach that level.

This technique, called bioremediation, has been used for many years on simple carbon-based petroleum compounds. But only in the last three or four years has the field entered a new arena.

Companies today are using microbes to degrade more complex chemicals, such as pesticides and solvents, although heavy metals and complex petroleum byproducts continue to present a challenge.

While many such firms have used microbes on a commercial basis, most of the work on biodegradation is still at the research stage. Scientists are searching for those "perfect bugs," as they are called, that have a yen for some rather unappetizing chemicals.

One such chemical group is polychlorinated biphenyls. Once used extensively in the electrical industry as a heat retardant, the manufacture of PCBs was banned in 1979 because of health hazards associated it.

But large quantities of the oily fluid still exist, sealed inside transformers and capacitors. The chemical repeatedly has made its way into the environment, including the food supply, through illegal dumping and accidents.

Chemists who synthesized PCBs in the late 1920s did such a good job that the chemical has proven nearly indestructible.

For the last six years, biochemist Ron Unterman, an expert on PCB bioremediation, and his colleagues at General Electric Co. have found several microbes that could begin to break down PCBs.

The group tested the bacteria last summer at a contaminated New York auto-racing site, where PCBs had been used for dust control. The microbes destroyed 25% of the hazardous chemicals at the site, bringing the contamination levels down from 500 parts per million to under 400.

Although 25% destruction is quite low, Unterman was pleased to see any activity at all. It showed that "you can degrade PCBs, even in the real world." Unterman said. "The rates are much slower (under real-life conditions), (but) that's not unreasonable considering the realities of temperature and . . . factors such as that."

However, the bacteria will have to achieve close to 100% destruction before they are put to work in the commercial arena.

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