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In 2004, Oberdörster’s daughter, Eva Oberdörster, a toxicology researcher at Duke University, put largemouth bass into water containing buckyballs at the concentration of one part per million. After two days, the lipids in the brains of the fish showed 17 times as much oxidative damage as those of unexposed fish.

Carbon nanotubes, which are basically cylindrical versions of the spherical buckyballs, are one of the stars of nanotech, with potential uses in everything from solar cells to computer chips. But in 2003, researchers at NASA’s Johnson Space Center in Houston, headed by Chiu-Wing Lam, showed that in the lungs of mice, carbon nanotubes caused lesions that got progressively worse over time. Under the conditions of the experiment, the researchers concluded, carbon nanotubes were “much more toxic than carbon black [that is, soot] and can be more toxic than quartz, which is considered a serious occupational health hazard.”

Another extremely promising nanoparticle is the fluorescent “quantum dot,” now being explored for use in bioimaging. Researchers envision applications in which they tag the glowing nanodots with antibodies, inject them into subjects, and watch as they selectively highlight certain tissues or, say, tumors. Quantum dots are typically made of cadmium selenide, which can be toxic as a bulk material, so researchers encase them in a protective coating. But it is not yet known whether the dots will linger in the body, or whether the coating will degrade, releasing its cargo.

Sensible regulation of nanoparticles will require new methods for assessing toxicity, which take into account the qualitative differences between nanoparticles and other regulated chemicals. Preferably, those methods will be generally applicable to a wide spectrum of materials.

Today’s assays are not adequate for the purpose, says Oberdörster. “We have to formalize a tiered approach,” he says, “beginning with noncellular studies to determine the reactivity of particles, then moving on to in vitro cellular studies, and finally in vivo studies in animals. We have to establish that some particles are benign and others are reactive, then benchmark new particles against them.”

Separately testing every newly developed type of nanoparticle would be a Herculean task, so Rice’s Colvin wants to develop a model that indicates whether a particular nanoparticle deserves special screening. “My dream is that there would be a predictive algorithm that would say, for a certain size and surface coating, this particular type of material is one you’d want to stay away from,” she says. “We should be able to do it, with the advance we have made in computing power, but we have to ask the right questions. For instance, is it acute cytotoxicity, or is it something else?”

Amidst all the uncertainty about evaluating nanoparticles’ toxicity, regulatory agencies are in something of a quandary. In the United States, the Food and Drug Administration will assess medical products that incorporate nanoparticles, such as the quantum dots now being tested in animals; the Occupational Safety and Health Administration is responsible for the workplace environment in the factories that make the products involving nanoparticles; and the Environmental Protection Agency looks at products or chemicals that broadly permeate the environment, like additives to diesel fuel. In principle, these federal agencies have sweeping power over nanomaterials, but at the moment, their traditional focus, their limited resources, and the sheer lack of test tube and clinical data make effective oversight next to impossible.

For example, the National Institute for Occupational Safety and Health, the part of the Centers for Disease Control and Prevention in Atlanta responsible for studying and tracking workplace safety, acknowledges that “minimal information” is available on the health risks of making nanomaterials. The agency also points out that there are no reliable figures on the number of workers exposed to engineered nanomaterials.

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Tagged: Biomedicine, Materials

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