Tiny particles of iron with special polymer shells might serve as guided missiles to seek and destroy organic solvents that contaminate groundwater at thousands of sites nationwide, Carnegie Mellon University researchers reported yesterday.

The "smart" particles, described yesterday at the American Chemical Society meeting in Anaheim, Calif., are engineered to destroy underground pockets of trichloroethylene, or TCE, a solvent widely used to clean metal parts.

No satisfactory method of cleaning up subsurface contamination by TCE is available, said Greg Lowry, a CMU professor of civil and environmental engineering who specializes in subsurface remediation. About 60 percent of the 1,400 hazardous waste sites on the Environmental Protection Agency's National Priorities List are contaminated with the suspected carcinogen.

TCE pollution of groundwater wells was the focus of a 1995 book by Jonathan Harr and a 1999 John Travolta movie, both titled "A Civil Action."

The particle that the CMU team has developed with colleagues at the Energy Department's Idaho National Engineering and Environmental Laboratory includes a core of iron, which oxidizes TCE, ripping off chlorine atoms and leaving behind ethane and other harmless byproducts.

The problem, Lowry said, has been delivering the iron to the TCE. The solvent doesn't mix with water and is heavier than water, causing it to percolate down through porous soils and accumulate in tiny pockets. Drops of TCE can be steadily released from the pockets into the groundwater.

Even detecting all of these tiny pockets of TCE is beyond technical abilities, he noted.

To deliver the iron to the TCE, the researchers needed to make it soluble, so it could travel through water, and keep the iron from reacting with water or other molecules before it reaches the TCE.

So the research group of Krysztof Matyjaszewski, a chemist who directs the Center for Macromolecular Engineering, designed special polymers, called block copolymers. The long, chain-like molecules have a compound on one end that binds to the iron, then a "water-hating" polymer that protects the iron core. On the outer end of this copolymer is a second, "water-loving" polymer that serves as the particle's outer shell and allows it to travel through water.

When block copolymer comes in contact with the solvent, Matyjaszewski said, the water-hating polymer near the center of the particle swells, creating openings that allow the reactive iron to come in contact with the TCE and destroy it.

Lowry said the particles are now being characterized in lab tests. At the end of the current, three-year program, sponsored by a $1.7 million grant from the Department of Energy, the hope is to begin field testing of the particles in special tanks at the Idaho lab.

The main way that TCE pollution is now treated is by pumping water out and treating it -- a tactic that can contain the pollution but not eliminate. Consequently, pumping and treating can continue indefinitely at tremendous cost.