XIV How safe is nanotech?

As the nanotech revolution gathers pace, few are giving a thought to the impact on health and the environment. We may live to regret this oversight.

As labs around the world churn out a burgeoning array of different nanoparticles, the potential benefit from these tiny objects is being championed like never before. Yet amid all the fanfare, nanotechnology is attracting a growing band of critics. They fear that ‘nanopollution’ from the carbon buckyballs, nanotubes and other particles could have a dire impact on health and the environment. With results presented this week suggesting nanotubes can damage healthy lung tissue, are their fears justified?

The possible hazards of nanotechnology were raised long before it was even possible to build molecular-scale objects. Some of the worst fears were hinted at in the 1986 book Engines of Creation by nanotech visionary Eric Drexler. He envisioned a time when a handful of self-replicating nanoscale robots can be thrown into a vat of raw materials and left to reproduce before putting together whatever they are programmed to make. Opponents feared that if such self-replicating nanoscale devices were ever realised, they could run out of control, with devastating consequences.

That much is science fiction. But there are more concrete reasons for concern. The way nanosized particles interact with other materials, not least body tissues, is not well understood. Last year, the US Environmental Protection Agency (EPA) called on researchers at the Center for Biological and Environmental Nanotechnology (CBEN) at Rice University in Houston, Texas, to present their concerns. The meeting spawned interest from regulators and led to calls from the ETC, a Winnipeg-based environmental group, to ban the manufacture of nanotubes until the health and environmental risks have been clarified.

Why are some scientists so worried now? After all, we’ve been using nanoscale carbon particles for decades in the form of carbon black, a filler for car tyres. “I don’t think these are fundamentally new, bizarre things,” says Christine Peterson, president of the Foresight Institute, a pro-nanotech think tank based in Palo Alto, California. “They’re carbon. This is stuff we’ve dealt with before. We are basically talking about soot.”

But it might not be that simple. Many materials that are safe in lumps are far more dangerous as fine particles, says Vicki Colvin director of the CBEN. Quartz, for example, is perfectly safe in bulk, but miners, rock cutters, and sand blasters who are exposed to quartz dust are at risk of silicosis – potentially fatal scarring of delicate lung tissue caused by inhaling the dust.

Fine particles can cause health problems elsewhere too. Even though hip and knee replacements are made from materials that are well tolerated by the body, they can shed fine particles into the surrounding tissues as they wear down, causing inflammation and, in the worst cases, loosening the implant, which must then be replaced.

Research presented at this week’s meeting of the American Chemical Society in New Orleans suggests there is good reason to be cautious about manufactured nanoparticles too. “This meeting is something of a watershed moment,” says Kevin Ausman, executive director of operations at CBEN. “It shows the community is taking the issue seriously.”

Chiu-Wing Lam, who studies the toxicity of nanotubes at the Wyle Laboratories of NASA’s Johnson Space Center in Houston, and Robert Hunter, a toxicologist at the University of Texas-Houston Health Science Center, reported the results of their study into whether nanotubes can damage lung tissue. They made up a suspension of nanotubes and placed a few drops directly into the lungs of mice. This allowed the researchers to carefully control the quantity of nanotubes that entered the animals lungs, which wouldn’t have been possible if the mice had simply inhaled an aerosol of nanotubes.

Hunter looked at the lung tissue around the sites where the nanotubes settled, first after one week and then after 90 days. He found that over time the nanotubes tended to clump together into bundles, and that these bundles were invariably surrounded by macrophages, immune cells recruited to flush the material from the body. This so-called “foreign body response” leaves scar tissue, damaging the original lung tissue. The researchers repeated the tests with nanotubes made by various different methods. Each produced a slightly different reaction. Hunter says the message is clear. “People should really take precautions. Nanotubes can be highly toxic,” he says. “There’s variability between different nanotubes and very little is known about it.”

David Warheit at DuPont’s Haskell Laboratory in Newark, Delaware, reported a similar study in which he also found immune cells gathering around clumps of nanotubes in rats lungs. At the highest dose of 5 milligrams per kilogram of body weight, 15 per cent of Warheit’s rats died – though not because of a toxic effect. Instead, the nanotubes had clumped together sufficiently to obstruct the bronchial tubes, suffocating the rats. Both Warheit and Hunter are now calling for studies to see if real inhalation rather than their experimental approximation causes similar damage.

For now, the only people at risk of inhaling nanotubes are those who manufacture or work with them, although few labs have measured the likely exposure. But because many nanotechnology studies are aimed at eventually using nano-sized particles in the body, much of the research into how safe they are is geared to these applications. David Allen at Texas Tech University in Amarillo, who also spoke at the conference, is looking at ways of using nanoparticles to target drugs to the brain. Other groups are also eager to use nanoparticles for drug delivery.

Aside from worries about the direct health implications of nanoparticles, there are concerns about how they might behave in the environment. “With any emerging technology, it’s almost a sure bet that there will be some negative environmental effects,” says Mark Wiesner, an environmental engineer at CBEN. “We need to conduct due diligence into the areas of what would happen to nanomaterials. Where will they go? What are the potential effects?”

Wiesner wants to see how far nanotubes could spread if they make it into groundwater. He is particularly concerned to see whether they might help spread other pollutants that would normally not travel far. Carbon nanotubes have such a high surface area that other molecules stick to them readily. If each nanotube picks up a few molecules of a pollutant, they could worsen existing contamination by spreading it far and wide. Conversely, binding to a nanotube might neutralise pollutants, reducing the harm they cause. As yet no one knows.

The EPA is taking the prospect of harmful nanopollution seriously. “There is an urgent need to evaluate the effectiveness of current water and air treatment techniques for the removal of potential nanoscale pollution,” says Tina Masciangioli, a policy fellow at the EPA. The agency will next month invite proposals for studies into any potentially hazardous side-effects of nanotech, and is offering to fund up to $5 million worth of research.

Pat Mooney at the ETC argues that until more results are in, commercial production of nanotubes should be banned. “We hope the potential benefit is all there. But with high benefits you also get high risks,” he says. Mooney fears that nanomaterials get the go-ahead for commercial use all too readily, simply because larger particles of the same materials are known to be safe.

Unsurprisingly, few agree with an all-out ban on nanotechnology. “Nobody is saying we shouldn’t look at potential problems,” says Peterson, of the Foresight Institute. “It seems to me though that people are already onto this one.”

Colvin at CBEN also feels a ban is not a good idea, but she does think some researchers are moving too quickly with their research, and that enthusiasm for nanotech’s potential might be leading them to pay too little attention to the risks. As with any new technology, she warns, sooner or later there will be problems.