Much has been written speculatively on the potential health hazards of carbon nano-tubes, usually as an afterthought to exciting reports of application prospects, in a variety of end uses. Given that carbon nano-tubes are expensive to make and have mostly been produced in very small amounts, the exposure potential has been low. But, not at zero hazard apparently. Some of the first tox tests with human implications, relative to carbon nano-tubes and spheres, were just reported on in Science News On-line, where we learned that:- "John T. James of NASA's Johnson Space Center in Houston, and his colleagues squirted nano-particles into the respiratory tracts of mice and then examined the rodents after 1 week and after 3 months. Although soot-like carbon nano-spheres caused no harm, an equal mass of commercially available carbon nano-tubes wreaked significant lung damage, even killing a few animals. In one especially graphic effect, immune system cells called macrophages trapped nano-tubes but then died. The ensuing inflammation scarred lung tissue by creating patches, called granulomas, that entombed the nano-tubes".This sort of testing needs corroboration before the hazard can be declared "known" and its significance is understood for manufacturing and product use. It may take several years more before we the reach the point of published consensus.
But, we (meaning society at large) don't have to wait to get at the other half of the risk equation. (Risk = Hazard X Exposure). Given the small size of individual carbon nano-tubes or tube fragments, they're likely to squeeze right through filters commonly found on lab or factory exhaust stacks, including HEPA filters. How to keep from exposing the neighbors? And what about personal protective gear or "breathing filters?" Same problem: exisiting-breathing filters in facemasks won't stop nano-tubes adequately.
Should it turn out that the hazards to human health are significant, how would lab and factory workers be protected? Will facility owners have to resort to pressurized respirators and glove boxes? Will manufacturing facilities have to direct exhaust through expensive and water/energy intensive scrubbers and incinerators? We certainly don't need a repetition of the mistakes made in the early days of chip fabs.
So here's the point. Our techno-optimism, such as it is, deserves to be informed. Sure, exposure controls can be delegated to people in white lab coats making happy press release noises. They'll figure it out as soon as they need to, right? Or not. Why wait to get the hazards nailed down before the exposure control technologies are defined? Or before the manufacturing heads offshore, to places where controls are unheard of?
If anyone has information on the types of controls that adequately trap carbon nano-tubes, comment away!
Image credit: Swiss National Computing Center