Photo: Michael Ströck

Tube Tangle: Nanotubes could enable batteries to be recharged thousands of times instead of just hundreds, but they may damage the environment or threaten human health.

The electronics industry is at the forefront of this revolution. For example, all hard-disk storage today is based on a magnetic effect that occurs at the nanoscale level, where ones and zeros are changes in the magnetic poles of the nanoparticles. In fact, you’ll find the vast majority of nanomaterials in electronics—in computer memories, batteries, displays, solar cells, capacitors, fuel cells, filters, antistatic coatings, and flame retardants. In the future, nanowires may power medical implants or cellphones by generating tiny currents when subtle movements make them vibrate and displace ions. Carbon nanotubes, which conduct electricity much more efficiently than traditional wires, could form the basis of batteries that could be recharged thousands of times. Carbon nanotubes can also be used in flat screens that are more efficient than today’s displays [see photo, “Tube Tangle”].

as nanotechnology spreads across industries, concerns about its environmental and health effects are spreading as well. The concerns stem from the small size of nanoparticles as well as from the atoms that compose them. Consider the class of airborne pollutants known as particulates. The U.S. Environmental Protection Agency (EPA) and many U.S. states currently regulate “coarse” particulate matter, less than 10 000 nm in diameter. In air pollution terms, nanoparticles are considered ultrafine particles, less than 0.1 micrometer or 100 nm. Airborne particles are released, for example, from fuel combustion or brake linings. Coarse particles and smaller ones can trigger asthma, bronchitis, and other respiratory diseases, make cold symptoms worse, and decrease lung function. Children and the elderly are especially at risk.

As a general rule, the health effects of smaller particles are more worrisome than effects from larger ones. Nanoparticles can be smaller by ­factors of 100 to 10 000 than the air pollutants we are just now beginning to regulate, and they could be even more harmful. Günter Oberdörster, a professor of environmental medicine in the school of medicine and dentistry at the University of Rochester, New York, studying ultrafine particles in 1992, found a nonlinear relationship between toxicity and particle size: as nanoparticles get smaller, their toxicity increases disproportionately.

Coarse particulate air pollution can damage lungs, but such particles are simply too big to get past the lungs and enter other parts of the body. Nanoparticles, on the other hand, can be more invasive. Nancy Monteiro-Riviere, a professor of investigative dermatology and toxicology at North Carolina State University, in Raleigh, discovered last year that some nano­particles can penetrate the skin and could enter the bloodstream. Similarly, when swallowed, nanoparticles may be able to pass through the wall of the stomach or lining of the intestines.

In 2003, Chiu-wing Lam of NASA’s Johnson Space Center, in Houston, instilled carbon nanotubes into the lungs of mice and reported that they triggered granulomas, or areas of ­inflammation. In a similar experiment, David Warheit at Dupont’s Haskell Laboratory for Toxicity and Industrial Medicine, in Newark, Del., found such inflammation in rats’ lungs in the same year. Perhaps most troubling of all, nanoparticles can make their way into the brain by passing from the nose through the blood-brain barrier, a membrane that protects the brain from chemicals in the blood while allowing oxygen, carbon dioxide, sugars, and certain amino acids to pass through unaltered.

In 2004, experiments by Eva Oberdörster, a lecturer in bio­logical sciences at Southern Methodist University, in Dallas, found that the buckyball, a nanostructure made of carbon atoms, can penetrate the brains of bass via the gills. There, the nanoparticles trigger a reaction in brain enzymes called oxidative stress, a change in brain chemistry that indicates harm. Eva Oberdörster (a daughter of Günter) also discovered that buckyballs are toxic to daphnia, tiny freshwater fleas used to test toxicity in aquatic systems [see photo, “Aquatic Mine Canaries”]. The buckyballs did not clump together and sink harmlessly to the bottom of the test sites as researchers had expected.

In 2005 Daniel Watts, of the New Jersey Institute of Technology, in Newark, reported that nanoparticles of aluminum oxide slowed plant growth; the same nanomaterials are used in some scratch-resistant coatings.