It's one of the most intriguing aspects of nanotechnology: Commonplace materials assume unpredictable and incredible characteristics at the molecular level. Tiny rolled-up "nanotubes" of carbon graphite suddenly turn superstrong and highly conductive, inert materials become highly reactive, and particles that once emitted red light appear blue on the nanoscale.
As more and more nano-based consumer products arrive, scientists are beginning to worry that these unpredictable particles are holding back a few surprises -- ones that could harm human health or the environment. Researchers have conducted only a handful of studies on the health implications of nanotechnology. "We absolutely know how [these materials] behave when they are larger," says Karluss Thomas, of the nonprofit Health & Environmental Sciences Institute (HESI). "But when you engineer something that small, it changes all the fundamentals. Some are so new we don't even have adequate testing methods."
"Nobody is saying here it's a minor threat or a major threat -- we just don't know," adds Andrew Maynard, of the National Institute of Occupational Safety & Health (NIOSH).
ONE SIZE DOESN'T FIT ALL.
The term "nano" describes a size range between 1 and 100 nanometers, the difference of one-billionth and one-hundred-millionth of a meter. The width of one human hair, for example, is about 80,000 nanometers. In that range, thousands of different types of particles exist, some possibly dangerous but many others completely harmless.
"We're looking at a whole slew of nano-materials," says Nancy Monteiro-Reviere, a scientist at North Carolina State University who's researching how several different carbon structures and tiny silicon quantum dots (atoms so isolated that the movement of a single electron can be detected) affect skin cells. "You can't go classify all nano-materials as bad or all as good."
After all, people have encountered and ingested nanometer-size particles since the invention of fire -- soot is a good example. So are air pollutants such as smog. "NIOSH has had many years of experience working with particles of nanometer size," say Maynard.
Some of the new concerns center on metal-containing nano-materials such as titanium dioxide and zinc oxide. Compounds like these have always been used as sunblocks -- the thick solid-colored lotions you see on lifeguards' noses -- but once mixed into the lotions at a nano level, they turn translucent. Scientists fear that if the metallic atoms in these lotions get into the body, they'll create free radicals and undergo oxidation reactions, literally pulling cells apart in a fashion similar to the way alcohol consumption and cigarette smoking destroy cells.
But no one knows whether these particles ever actually separate from the sunscreen. So far, studies have differed, says Maynard. Researchers can't tell whether or not these particles penetrate the skin, much less cause such damage.
The Food & Drug Administration approved the products, as did the Scientific Committee on Cosmetic & Nonfood Products, which advises the European Commission. Don Marlow, agency standards administrator for the FDA, says that could change if further research proves otherwise, as is the case with all products, nano or not. "We would evaluate any new products on the basis of new information," he says. How big is the risk? Fairly small, according to current research. But truth is, no one really knows for sure.
Another worry about special nano-material properties that could cause harm: Scientists are experimenting with brain medications that use nano-materials to more easily target and enter trouble spots. But the easy maneuvering enabled by these tiny particles' size could prove a detriment. One study from 2004 found that, when present in water, carbon structures called buckyballs slipped into the brains of large-mouth bass and killed cells. The study, however, was inconclusive and intended only to open the door for more research.
This year, agencies including the Environmental Protection Agency, NIOSH, and the National Institutes of Health have earmarked $9.3 million for research into health implications. The money represents part of the $106 million funding plan to study the upside of nanotechnology -- how it can be used to help in medicine.
Some science interest groups, HESI among them, also contend that while many outstanding questions remain, it's hardly time to sound the warning bells. "I don't necessarily believe that there's a need to be alarmist -- we have been exposed to some of the materials for a while," says Thomas. "But certainly there's enough novelty and enough new [production] going on that it's worth evaluating."
As it was for many other new technologies, it will take years years before anyone knows for sure.
Helm is a reporter for BusinessWeek Online in New York