NANOPARTICLES of iron could dramatically reduce the levels of toxic chemicals at tens of thousands of contaminated sites. Laboratory and field tests have shown that the particles can break down common pollutants such as trichloroethene, carbon tetrachloride and dioxins in a matter of hours.

A decade ago, chemists discovered that iron could play an important role in destroying polluting chemicals. Under the right conditions, the metal breaks down water to produce hydrogen, as well as reacting with oxygen to form iron oxide, better known as rust. But when other chemicals are present, the chemistry can be much more complex.

In 1994, Robert Gilham and Stephanie O'Hannesin from the University of Waterloo in Ontario, Canada, showed that iron particles could break down a number of common pollutants such as pesticides, organic dyes and chlorinated benzenes, albeit relatively slowly.

The reaction takes place on the surface of the iron. So when the ...