Tuesday, February 07, 2006

Screening for Toxic Nanoparticles

Researchers suggest a strategy that could weed out dangerous nanoparticles.

By Kevin Bullis

The novel properties of nanoparticles mean they could find uses in applications as different as solar power and cancer treatment. Indeed, some nanoparticles have already made it into commercial products, notably, cosmetics.

Many experts worry, however, that the unique properties of these particles could make them toxic, and fear over the potential dangers of nanoparticles has led to increasing calls for tests and regulations (see New Nano Law? and Can EPA Regulate Nano?). But the sheer number of new nano materials will make evaluating all of them impossible. The result: either harmful materials could reach consumers, or, in an effort to play it safe, restrictive regulations could be created that clamp down on innovation.

The authors of a review of past studies published last week in the journal Science suggest a strategy for screening the most dangerous nanoparticles more efficiently, which could help avert potential disasters and allow the development of new technologies to continue. The strategy would use "predictive toxicology," which looks for subtle signs that the cells in a culture are starting to defend themselves, indicating that the particles they've been exposed to could be dangerous.

Andre Nel, professor of medicine at UCLA, and one of the authors of the paper, says that existing work on the toxicity of particles that are byproducts of industrial and natural processes should help researchers to identify the telltale danger signs in cell-culture screening of nanoparticles.

According to the review, researchers studying particle toxicology have already identified molecular mechanisms that are triggered when dangerous particles come into contact with living cells. They've found that dangerous particles create reactive forms of oxygen that damage cells. At low concentrations of these molecules, cells can defend themselves by producing anti-oxidants. As concentrations increase, however, cells become inflamed or die. At each stage, the cell produces signs that can be screened for, using cell cultures that have been exposed to these new particles.

Nel says that engineered nanoparticles are likely to produce similar effects, as was found with early studies on fullerenes. By testing engineered particles on cell cultures, he says, researchers could identify those particles that are most likely to be dangerous.

Nel's proposed screening method won't catch everything, though. "There may, in fact, be some novel mechanisms for toxicity that nanoparticles might produce," says Kevin Ausman, executive director of operations at the Center for Biological and Environmental Nanotechnology at Rice University in Houston. This could mean that some dangerous particles get through.

But, for now, signs of reactive oxygen "seem to be a natural place to start looking," says Ausman, adding that others have suggested similar ideas. "Should it be looked at to the exclusion of all else? No. But given the fact that we have limited resources to look at this really huge field, with a wide-open set of questions, we have to be able to focus."

Indeed, Nel emphasizes that their tests won't prove that a particle is safe. But, as nanoparticles appear in more products, the need for some sort of efficient screening is growing. "We don't have the luxury at this stage to wait for a mature toxicology for each particle," Nel says. "We need to do something proactive."