"The new work helps explain the very fine particles and extraordinarily high concentrations found by an earlier UC Davis study, the first to identify very fine metallic aerosols in unprecedented amounts from Ground Zero. It will be essential to understanding the growing record of health problems."

.......

"The new study also confirms, Cahill said, that the very fine particles observed were almost totally from the trade center debris pile and not from other upwind sources, such as power plants and the diesel trucks used to haul away the debris.

When the trade center towers burned and collapsed, tons of concrete, glass, furniture, carpets, insulation, computers and paper were reduced to enormous, oxygen-poor debris piles that slowly burned until Dec. 19, 2001.

In that hot pile, some of the debris' constituent elements combined with organic matter and abundant chlorine from papers and plastics, and then escaped to the surface as metal-rich gases. These then either burned or chemically decomposed into very fine particles capable of penetrating deeply into human lungs.

In the trade-center air samples, Cahill identified four classes of particles that have been named by the EPA as likely to harm human health:

* Fine and very fine transition metals, which interfere with lung chemistry.
* Acids, in this case sulfuric acid, which attack cilia and lung cells directly.
* Very fine, un-dissolvable (insoluble) particles, in this case glass, which travel through the lungs to the bloodstream and heart.
* High-temperature organic matter, many components of which are known to be carcinogens.

"For each of these four classes of pollutant, we recorded the highest levels we have ever seen in over 7,000 measurements we have made of very fine air pollution throughout the world, including Kuwait and China," Cahill said.

After the debris fire was out, pollution levels dropped, Cahill said. DELTA Group measurements at the trade-center site made in May 2002, with the American Lung Association of New York, showed that levels of almost all of the very fine components had declined more than 90 percent,"