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A bowl of popcorn

Nanoparticles can be found in a host of products, including popcorn.

The little things

University brings nanoparticle researchers together to contemplate implications of fast-growing technology

By Deane Morrison

Published on October 7, 2005

Stuck in traffic behind a diesel-burning truck, your thoughts may turn to the obtrusive presence of particles in the air. But air pollution is probably the farthest thing from your mind when you're buttoning up that nice new stain-resistant shirt, slathering on sunscreen, or digging into a bowl of fresh, buttery-tasting microwaved popcorn. No, you don't worry--but workers in the factories that made those products have cause to. Ultrafine particles, called nanoparticles, are incorporated into those products to help them resist stains, prevent sunburn, or taste buttery, and factory workers who inhale the nanoparticles may develop severe respiratory difficulties. Such is the value of these tiny particles that society is not likely to abandon their use. The trick is to get out in front of the problems associated with them so that the technology can be developed with minimal health risks. The University has a strong research program in nanoparticles, and this week mechanical engineering professor David Pui, along with Andrew Maynard of the Robert A. Taft Laboratory in Cincinnati, hosted an international symposium to get researchers up to speed on the nature of nanoparticles and how to forestall health problems they may cause. "In order to continue development of nanotechnology we really have to include the consideration of the safety issue and the issue of public perception in parallel," said Pui, a Distinguished McKnight Professor. "We hope this symposium will lead in this direction. You can't develop new technologies without public acceptance." Held October 3-6 in the Radisson Metrodome, the 2nd International Symposium on Nanotechnology and Occupational Health drew 400 scientists and engineers from 20 countries. It focused on protecting the health of industrial workers but included talks on virtually every aspect of nanoparticles. (Nanoparticles are not strictly defined, but generally, they have at least one dimension measuring 100 nanometers--100 billionths of a meter--or less.) It began with a series of tutorials on such topics as what nanoparticles are, why at least some of them are toxic, the behavior of nanoparticle aerosols, and how scientists determine the physical and chemical properties of gas-borne nanoparticles (taught by mechanical engineering department head Peter McMurry).

In a keynote speech Thursday, U professor Kenneth Keller urged the audience to think about nanoparticles, and all new technologies, in more ways than only "Is it safe?"

One recurring theme was that substances have one set of properties in bulk but another when they appear as nanoparticles. For example, nanoparticles of gold appear red. Gold and other particles take on more sinister properties in the nano realm because their smaller size allows them to penetrate cells or move through the body. The most important factor appears to be their surface area; thus, particles that are long and thin may make more contact with a cell and do more damage. But it's dangerous to generalize. A ball-shaped molecule with 60 carbon atoms (known as buckministerfullerene or "buckyballs" because its shape recalls the geodesic domes of Buckminster Fuller) can punch holes in cell membranes to wreak havoc. On the other hand, buckyballs and molecules derived from them hold great promise as components in nanoelectronic devices. Some nanoparticles appear able to migrate to the brain from the nasal area, said researcher Gunter Oberd?rster of the University of Rochester, New York. Besides nanoparticles of carbon, they include gold; viruses such as herpes, polio, and rabies; and manganese oxide, which is given off during welding. "Epidemiological data shows that welders often come down prematurely with Parkinson's disease," said Oberd?rster. "This might--and I stress, 'might'--be from the manganese oxide." In his lab, Oberd?rster is testing how various nanoparticles interact with cells such as those in the linings of lungs and blood vessels. Pui, his collaborator, is well along in developing a system to deliver single, unaggregated nanoparticles for Oberd?rster to test. Also, some nanoparticles may also penetrate skin, according to research by Sally Tinkle of the National Institute of Environmental Health Sciences and others. The health implications of nanoparticle exposure are under investigation, but one example stands out. Workers in popcorn factories have suffered severe lung damage, which has been linked to the chemical that produces buttery flavor. Add to that the fact that nanoparticles are produced by all kinds of combustion, and the specter of burned popcorn becomes even more unpleasant. So do unavoidable, but short-lived, generations of nanoparticles from home heating, barbecuing, and even, according to one researcher, mopping up with PineSol. On a brighter note, mechanical engineering professor David Kittelson described filters for diesel engines that remove essentially all the particles produced and that will be featured on all trucks starting in 2007. One type of filter does, however, generate very tiny particles whose environmental significance is unknown, he said. Mechanical engineering student Dabrina Dutcher presented data showing that as the percentage of ethanol in gasoline rises, engines emit smaller-sized particles of a pollutant called PAH, which are believed to be less apt to cause cancer than large PAH particles. Warm engines are less problematic than cold ones, she said, and Kittelson emphasized that most problems arise from old, worn-out engines. Among companies displaying their wares was TSI of Shoreview, which was founded in 1961 by University engineering graduates Mike Fingerson and Lowell Nystrom. TSI's Dick Borotz, also an alumnus, exhibited a machine that measured the exposure of a person's bronchial tubes and alveoli to airborne nanoparticles. It read about 5,000 particles per cubic centimeter in the Radisson--a low level. "If people were smoking, it would go to 100,000," said Borotz. Also on hand was TSI scientist Avula Sreenath, who holds a doctorate from the School of Public Health. "Particles are hardest on people with heart disease, respiratory disease, or immune dysfunction," he said. In a keynote speech Thursday, University professor Kenneth Keller urged the audience to think about nanoparticles, and all new technologies, in more ways than only "Is it safe?" The professor of chemical engineering and materials science reminded them that information technology brought to the surface issues of privacy that had lain dormant, such as the use of credit cards over the Internet or government and corporate access to data. He also pointed out that technologists must deal with both real and perceived risk, and that nothing gets better by sitting on the shelf. "If we don't use [technologies], we don't improve them," said Keller, who is also a professor of science, technology, and public policy in the Humphrey Institute. He hosted a conference on oversight of nanotechnology on September 15. Symposium attendees gave the gathering high marks. "Your university has a significant research program in nanotechnology," said George Bockosh of the National Institute of Occupational Safety and Health (NIOSH). "David Pui served on the NIOSH Emerging Technologies National Occupational Research Agenda team, and he volunteered to organize this conference. I've heard comments from others that the tutorials on the first day were great--they brought people to the same level of competence. As for me, I've learned too much to describe."