It seems like a noble goal: amid growing concern about the health risks of nanoparticles, why not keep tabs on the health of people who work with the little buggers? But it turns out that's easier said than done.

"You could probably count the world's published literature on exposure to nanoparticles on both hands," says Paul Schulte, director of the Education and Information Division of the National Institute for Occupational Safety and Health (NIOSH). "And yet a lot of words have been written about nanotechnology, and it leads one to want to take action. We're struggling with finding a scientific basis on which to do that."

Unfortunately, he says, a NIOSH draft proposal—titled "Interim Guidance on Medical Screening of Workers Potentially Exposed to Engineered Nanoparticles''—is limited in the guidance it can provide. The reason: too little information. Scientists have only the broadest suspicions about harm that nanoparticles may cause. How, then, to recommend which workers should be screened and exactly what they should be tested for?

"In essence, you're going on a fishing expedition," says Andrew Maynard, a former NIOSH researcher who is now chief science adviser at the nonprofit Project on Emerging Nanotechnologies, part of the Woodrow Wilson International Center for Scholars in Washington, D.C. "We need to make this link to disease, but you can't just do that by randomly testing people."

NIOSH scientists are not the only ones scratching their heads over the possible dangers of nanotech. It is one of the world's hottest technologies, and experts agree that it poses unpredictable, potentially serious health risks. Beyond that, not much is known.

Nanotechnology involves the manipulation of teeny particles, measuring between one and 100 nanometers. (A nanometer is one billionth of a meter, or roughly 80,000 times smaller than the width of a human hair.) At that size, substances shed some of their usual rules of behavior, which is both the magic and the menace of nanotech.

Physically, nanoparticles are so minute that they can penetrate deep into the body. Animal studies have found, for example, that some can cross the blood–brain barrier, which normally protects the brain from toxins in the bloodstream. That may be great if you are using carbon nanotubes to deliver chemotherapy drugs to people with brain tumors, as cancer researchers in California (at City of Hope, a cancer research and treatment center in Duarte in collaboration with NASA's Jet Propulsion Laboratory in Pasadena), hope to do. It may not be so awesome if the particles enter the bloodstream by accident rather than as part of a medical treatment.

Some of the worry about exposure to engineered nanoparticles arises from their unintended counterparts, often found in air pollution. The puniest bits of soot in diesel exhaust, known as ultrafines, measure on the nanoscale. When inhaled, they journey into the smallest air passages in the lungs, which are off-limits to larger particles. There they cause respiratory problems and, more surprisingly, heart disease, according to University of Rochester researcher Günter Oberdörster and others.

Chemically, nanoparticles tend to be more reactive than larger amounts of the same substance, because they have more surface area and therefore more opportunity to interact with other substances. That means a chemical that's normally harmless might be toxic in minuscule doses. Animal studies show that inhaled nanoparticles can cause pulmonary inflammation, move from the lungs to other organs, and interfere with cell signaling. Shrink something to nanosize and it can do surprising things: change color, become soluble, conduct electricity.

At the same time, the potential benefits are enormous. Medical researchers hold out hope for "nanomiracles" ranging from drugs that fight radiation poisoning to a shoebox-size portable genetics testing lab. Current and potential green applications abound: window coatings that block heat but not light, more efficient solar panels, energy-saving traffic lights. Researchers at Lehigh University in Bethlehem, Pa., say that because of their size and reactivity, iron nanoparticles can decontaminate solvent-soaked soil up to 1,000 times faster than a conventional iron mixture.

Worldwide, sales of nano-enabled products reached $50 billion in 2007 and are projected to hit $150 billion this year, according to New York City–based Lux Research, an industry consultant on emerging technologies. Nanomaterials make clothing resist stains and sunscreen turn clear on your skin. Manufacturers put microbe-killing nanosilver in washing machines and plastic food storage containers. We can buy faster computer chips, lighter and stronger bicycles, fleece without static cling—all thanks to nanotechnology.

With more than 500 nano-enabled consumer products on the market, some people worry about stray particles finding their way into our food, air and water. But history tells us the most likely to experience any ill effects are the people who make the products, not those who buy them.

Coal miners used to take a canary into the shaft to warn them of deadly methane: if the canary passed out, it was time to come up for air. Historically, workers have often played the role of canary with other toxics. From leaded gasoline to mercury in felt hats, laborers absorb the highest exposures and are the first to get sick.

No wonder, then, that NIOSH is pushing for better understanding of the health effects of nanoparticles. But as Schulte notes, far more is unknown than known.

And as his colleague Doug Trout points out, it is a mistake to talk about nanomaterials as a single entity. "They're a whole universe," with no one-size-fits-all answers.

It is clear that inhaled nanoparticles can make their way into the bloodstream and throughout the body. Can they also penetrate the skin? What happens when they are ingested? Nobody knows. The size and shape of the particle are critical variables. And what about the amount? Nobody knows. Also, which companies are using nanomaterials, especially in sprays or powders that can easily be inhaled? How many workers might be affected? Nobody knows.

The reason: nanomaterials are completely unregulated; industry is under no obligation to keep records on potential hazards or anything else. NIOSH is a research institute; it can recommend that employers reduce worker exposure—and ways they might do that—but it has no enforcement power. Although the Environmental Protection Agency is a regulatory agency, it, like NIOSH, is in the early stages of gathering data. Last week, it released a long-awaited proposal asking businesses to voluntarily report safety data on engineered nanomaterials. Of the more than $1.3 billion budgeted for federal nanotech research in fiscal year 2006, only $38 million was targeted at investigating environmental, health and safety risks; the rest was earmarked for research and development.

There's currently a push from both inside and outside the government for the feds to do more. A recent Congressional Research Service report urges the multiagency National Nanotechnology Initiative (NNI) to establish an environmental and safety research agenda with real priorities—something NNI has been promising to do since 2006. U.S.

Rep. Albert Wynn, a Maryland Democrat who chairs the House Subcommittee on the Environment and Hazardous Materials, says he plans to hold hearings this year on "the serious gaps in the current statutory and regulatory framework." At the state level, Wisconsin legislator Terese Berceau (D-Madison) has asked her state's departments of Natural Resources, Health and Family Services, and Agriculture, Trade and Consumer Protection to work with her to create a registry of businesses that make nanoparticles as a first step toward tracking their use and potential health effects.

NIOSH is also interested in the possibility of establishing registries of workers exposed to nanoparticles. It is unclear who would run these registries, what information they would collect, or how the information would be used.

"A registry is not an end in itself," Patrick Conner, medical director for the Germany-based chemical company BASF, said during a recent meeting held by NIOSH in Cincinnati to get input on its nanotech draft proposal. "If you're going to gather data, you have to act on it."

And action is crucial, the Project on Emerging Nanotechnologies' Maynard says—not only to protect workers and consumers, but also to protect the promise of the technology itself.

"If you look at the potential of what we can achieve with nanotechnology, it's really quite incredible," he says. "But if we want to realize the long-term benefit, we've got to get these health, safety, ethical and social issues right as early as possible."

In the past, Maynard says, policymakers and businesses have developed technology and then tried to address problems as they emerge. "This is an opportunity," he notes, "to do things the other way around."

Carole Bass is an Alicia Patterson fellow, reporting on toxic exposures on the job.