The journal Nature has an article about carbon nanotubes, when placed into mice, can cause pleural placques and granulomas of the pleura similar to those seen from asbestos.
Carbon nanotubes are structures engineered from single atoms and molecules and scientists say they hold great promise for applications in medicine, electronics and especially new materials.
Note: the mice were exposed to carbon nanotubes by direct contact, not by aerosol exposure, and the mice were autopsied before they developed cancer, but the lung and pleura changes were similar to that which preceeds cancerous changes. and that has the scientists worried.
The worry is that since it took twenty years to discover the problems with asbestos, the same problems will be seen in the future with nanotubes.
As a student, we saw lots of mesotheliomas (cancer) and asbestosis related pulmonary fibrosis in World War II shipbuilders in the 1960′s and 1970s, but since then I haven’t seen any cases, because the asbestos used in insulating buildings is a different type and less likely to cause cancer. Also, of course, the government has been busy removing the asbestos insulation carefully using respirators.
Nanotubes are similar in size to the particles of asbestos that have caused problems after inhalation. In asbestos, since the largest particles don’t get inhaled down deep into the lungs, they get removed with cilia action and coughed up with sputum/phlegm. However, the smaller particles are eaten and removed from the body by immune cells, often causing local inflammation, and eventually fibrosis (scarring) of the lungs.
Fibers of 5 Âµm or more… are effectively cleared through mucociliary action. In comparison, fibers that are more slender tend to be deposited in small airways or airspaces, from which only a proportion of them are cleared.
The effect of fiber length is less certain, but straight fibers that are approximately 5-20 Âµm long, such as crocidolite fibers, are not cleared as effectively as others are, and they can cause intense inflammation and fibrogenic changes within the interstitium.
So it is the size of the nanotubes that started scientists to worry.
“Needlelike fibers of asbestos (left) and long carbon nanotubes (right) penetrate through macrophages, the bodyâ€™s trash collectors. An inability to fully engulf the fibers will cause these cells to die, fostering tissue-damaging inflammation.”.
Since nanotubes are “microscopic”, it is these longer tubes the size of the asbestos particles that are the biggest worry because the macrophage is destroyed trying to remove the particle.
Senior author Ken Donaldson of the University of Edinburgh succinctly summed up their results as “the long nanotubes were pathogenic – they caused inflammation and scarring. The short nanotubes were not.”
Another item that needs to be remembered is that the experiment is about inhaled particles, not nanotubes per se. And a lot of it has to do with the size and the flexibility of the particles, not with all nanotubes. Presumably smaller or longer nanotubes or flexible nanotubes would not pose as great a danger.
So the biggest danger might be in the manufacturing process, not in the finished item per se. There is also danger if the smaller particles are released from discarded products in landfills or other waste disposal areas.
The danger is not in all nanotechnology, nor has any experiments shown that inhaling the particles are a danger. Finally, there is no proof using items with the nanotech carbon fibers is dangerous, since there is no evidence that the particles flake off.
But it is something for scientists and OSHA regulators to start checking out.
Nancy Reyes is a retired physician living in the rural Philippines. Her website is Finest Kind Clinic and Fishmarket.