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Frontiers
Pow! Bam! Zap! Pollution Fighters Crowd the Horizon

January 1998

They stand ready to zap, vaporize, or otherwise transmogrify "bad" chemicals into "good" ones. A bunch of hardy cartoon heroes? No, they're the next generation of NSF-funded pollution fighters.

Take plasma generators. At the University of Illinois in Urbana Champaign, engineer Mark Kushner and others are developing tools to make diesel fuel's noxious chemicals harmless. The device will pass the post combustion fumes through a plasma, an ionized gas with free electrons.

Unlike conventional combustion, which relies on heat of atoms and molecules to break molecular bonds and initiate a chemical reaction, plasma chemistry is a kind of cold combustion. Applying an electrical field excites the charged electrons without directly affecting the plasma's neutral atoms.

Because the electric field moves the lightweight electrons ("think of ping pong balls," says Kushner), and not the heavier atoms ("think bowling balls"), the gas doesn't get very hot while the energetic electrons break bonds more selectively than their atomic cousins. As a result, scientists have more control of the reaction.

The idea, still being optimized on the computer drawing board, is to design a plasma generator, about as big as a muffler, in which electrons collide with the nitrous oxides (a contributor to acid rain) in the exhaust and convert them to harmless nitrogen and oxygen molecules. One of the remaining problems, says Kushner, is power efficiency. Computer models are helping to address this and other issues.

Another group of pollutants targeted for change is toxic metals. Soils filled with toxic metals have to be carted away and stored as hazardous waste. But at the University of Georgia in Athens, geneticist Richard Meagher and his team have genetically engineered a variety of plants that soak up mercury through their roots and convert the metal to the less toxic elemental mercury, used in tooth fillings. The trick is performed by a bacterial gene that produces an enzyme --MerA-- hungry for toxic mercury. So far Meagher's group has placed the bacterial gene into mustard plants, tobacco, canola and even yellow poplar trees. "And they all thrive on mercury", he says.

The researchers aren't sure yet whether the converted mercury transpires up to the leaves, where it vaporizes, or simply diffuses through the roots, "but in any case, we don't find mercury in the plant itself." With the help of their vast root system, transgenic plants could theoretically clean up hundreds of acres of mercury contaminated land at a percent of what it would cost using conventional methods.

Meagher hopes that this approach--called phytoremediation--will prove helpful in water as well as in soil. He's found another verison of the bacterial enzyme --MerB-- that munches methyl mercury, the kind that shows up in fish from polluted waters and can cause severe neurological damage. Meagher's team has also begun experimenting with MerA to see if they can "each" it through test tube evolution to soak up other toxic metals as well, including copper, cadmium, and nickel.

Other NSF-sponsored pollution fighters crowd the horizon, from compressed carbon dioxide as a safer alternative to harmful organic solvents to a new Engineering Research Center whose goal is to find a cleaner way to manufacture microchips.

Who knows? Today's fantasy may be tomorrow's superhero.


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