You all probably know the feeling of reading a book that completely alters your outlook of the world, and of our future. When I read K. Eric Drexler’s Engines of Creation, I set down the book convinced that the future would be an amazing place powered by molecular replicators–by nanotechnology. We haven’t reached the capabilities that Drexler envisioned 20 years ago, but nanotech is part of our daily world now; it’s in our sunscreens, stain-resistant slacks, sports equipment, electronics, cosmetics, and experimental medicine.
Recently medical science has thrown up a yellow flag over nanotechnology. Very small particles, like those found in diesel fumes kill thousands every year through inhalation. Also, tiny fibers of asbestos lodge in the lungs and lead to a cancer-inducing inflammation called asbestosis. Studies in cell cultures and rodents have suggested that nanomaterials, such as carbon nanotubes or C60 “buckyballs”, may suffer these same major drawbacks. Today’s Published Research Synopsis examines a review article that looks at the state of nanomaterial toxicity research and concludes that while there may be cause for concern, nanomaterial research should proceed cautiously forward.
Citation (online at CiteULike.org):
Nel, A., Xia, T., Madler, L. and Li, Ning (2006). Toxic Potential of Materials at the Nanolevel. Science 311(5761), pp. 622-627.
Synopsis:
The authors review several possible paths for nanomaterial toxicity including reactive oxygen stress, membrane dissolution, protein denaturing, triggered immune reactions, and particulate clumping. They focus primarily on reactive oxygen stress because more is known about the dangerous effects of particulates through this channel than any other. Reactive oxygen stress results from the formation of highly reactive O2- radicals in the blood. Tiny particulates are capable of generating large quantities of radicals in part because of their enormous surface areas; diesel exhaust is dangerous partly for this reason. The surfaces of particulates often have reactive molecular groups that are capable of forming radicals, and the more of them that are exposed on the surface, the more radicals are formed per particulate. The authors note that intravenously-administered C60 carbon buckyballs have been shown to be acutely toxic in smaller doses (though still extremely high doses, and their toxicity may require a UV or visible light trigger) than larger particulates that have been better studied. But, when the relative surface areas of the nanomaterials are considered rather than just the mass dosage, buckyballs have the same toxicity as larger particulates.
A study involving intra-trachaelly administered carbon nanotubes in rats resulted in lung inflammation, interstitial fibrosis, and foreign body granuloma formation (similar to the symptoms of asbestosis). And, the extremely high doses required to induce these symptoms also resulted in asphyxiation due to nanotbue clumping in the airways as well. The authors note that iron impurities on the surfaces of the nanotubes may be to blame for the toxicity of the nanotubes, rather than the fact that they are tiny fibers like asbestos. Though inhalation doses are not expected to be acute in real-world manufacturing situations, there is the possibility that chronic exposure could have a similar effect, though it is not yet well studied.
Acute intravenous doses are extremely unlikely to occur outside the lab settings, but there are many other routes for nanomaterials to enter the body, such as through the skin or gastro-intestinal tract, or even directly into the brain through the olfactory nerves. Smaller doses could lead to immune responses and other negative effects. None of these routes of entry have yet been demonstrated to lead to toxicity, however. For instance, studies have shown that little uptake occurs when rats swallow radioactively-labeled C60 molecules. The authors conclude that not enough is yet known to determine the toxicity of nanomaterials.
Context:
Though the general public is not, as yet, tuned in to the potential toxicity of nanomaterials, certain environmental groups have called for a moratorium on nanomaterial research. Given the review of nanomaterial toxicity presented in this paper, it appears that those concerns are exaggerated, or at least premature. Note that I have only listed the reasons that nanomaterials may be dangerous, not the reasons that they may be safe, so the above synopsis is inherently pessimistic. If manufacturing conditions can be controlled to minimize inhalation, then the most likely path for toxicity can hopefully be avoided. Because unlike airborne particulates, large quantities of nano-particles will not be spewed out during their manufacture or use.
This entire discussion has focused on the toxicity of passive nanomaterials. As our ability to work at the nano-scale progresses, we will eventually develop active nanomolecules that are capable first of catalyzing reactions, then eventually utilizing molecular energy sources for true self-powered movement. This is even still a step shy of the molecular replicators that Drexler had in mind when he wrote his first book on nanotechnology. The final step in nanomachine progression will be to create molecules capable of reproducing themselves, just as does biological life. This prospect has truly frightened some people (including Michael Crichton in Prey), leading them to suggest the “Grey Goo” hypothesis in which replicators get out of control and destroy the entire biospehere of Earth, leaving behind only a grey or green goo. Like the idea of the Earth’s atmosphere catching fire with the explosion of a particularly large atomic bomb, the Grey Goo hypothesis is only credible because of considerable ignorance.
More academic (though no less vocal) criticism of Drexler’s ideas came from the late Richard Smalley, the Nobel-prize winning co-discoverer of C60. He claimed that the idea of molecular replicators is yet so far in the future that giving significant funding to their research is wasteful. More practical in the short term, he believed, was purely chemical nanotechnology. Unfortunately, Smalley’s relatively early death last year, at the age of 62, is a loss for all nanotechnology research even for those who fall on Drexler’s side of the camp.
General Explanations:
None this time! If you would like anything cleared up a bit, just comment.
More specious arguments based on questionable research. For instance: the rat research done above. No one ever mentions that powerfully irritating solvents were used along with the carbon nanotubes. These sort of unsubstantiated reports and questionable research procedures are the hallmark of alarmists attempting to gain noteriety. Lets wait a bit (especially since most if not all of these materials are still constrained to the lab) before we pass damning judgement.
By the way, dihydrogen monoxide is a nanoparticle composed of just three atoms and would you like to do without that?
The Guy,
Hey, I’m not anti-nanotech by any means. The “specious arguments” I presented were in summary of a review article in the journal Science. I would be inerested in seeing a reference for the irritating solvents thing, because the authors of the review paper did not mention that either. I think you need to show a bit more evidence for your claims of researchers being alarmist, or that their research is questionable.
I pass no damning judgement in this piece, not by any means. I’m not sure if you read my entire article, because in the Context section I make it pretty clear that I feel the toxicity research shows that we can proceed with nanotech research with caution. After all, a few billion dollar class-action lawsuits will kill any industry, so a bit of caution is necessary.
hi iam student and i hoped that obtain information this site
Layman alert!!
Could someone enlighten me as to the scale of the “molecular machine” in relation to a human hair etc.
Much appreciated.