Carbon nanotubes are one of the most promising materials for future technological advances. Unfortunately, many news stories on such sites as SFGate.com and Washingtonpost.com have recently reported that carbon nanotubes may be as bad as asbestos. Carbon nanotubes could cause the same maladies as asbestos, according to a study by University of Edinburgh, which also showed that long-thin fibers cause the pathological response known to be a precursor to mesothelioma cancer in mice. Of course it has been known for a long time that asbestos is the cause of the devastating cancer mesothelioma that affects the lining of the lungs, heart and stomach.
In the eeTimes, an online electronics design site, University of Edinburgh professor Kenneth Donaldson is quoted as saying,."Long, thin carbon nanotubes showed the same effects as long, thin asbestos fibers," Nanotubes can have length to diameter ratios of one million to one, making them some of the thinnest structures known. The studies was originally published in the scientific journal Nature Nanotechnology in mid-May, 2008. This online journal shows an amazing photograph of a rat lung cell trying to injest a long nanotube. Since the tube is longer than the rat cell can stretch, it cannot fully injest the tube and therefore cannot remove it from the body. This is the same basic problem with asbestos, the body's inability to remove it from the lining of the lungs (mesothelium) and other tissue. The asbestos remains in the tissue causing long term harm including the cancer mesothelioma.
In the research protocol both carbon nanotubes and asbestos fibers were injected into the abdominal cavity of mice, a technique that is accepted in medical circles as a predictor of how pathogens affect lung tissue. The results showed that like asbestos, long nanotube fibers were thin enough to penetrate deep into lungs, but their length prevented the lungs' built-in mechanisms from removing the particles. It appears that this extreme length to width ratio is the basic problem with both asbestos and nanotubes.
Donaldson also said, "If nanotubes get into the lungs in sufficient quantity, there is a chance that some people will develop cancer—perhaps decades after breathing it." That could be either mesothelioma or an asbestos (or in this case nanotube) induced lung cancer.
Short nanotubes did not behave like asbestos, and were cleared from the bodies of experimental mice. The problem arose with long, thin nanotubes which tended to bunch together, causing inflammation and lesions that are known precursors of cancer. Short nanotubes may also be found to cause harm, according to the researchers, who said more research is needed.
Carbon nanotubes have high aspect ratios, only nanometers (one billionth of a meter) in diameter but sometimes microns (one millionth of a meter) long. Aspect ratios are often over 1000:1 and sometime 1,000,000 to 1. In semiconductors, nanotubes are usually safely affixed to a substrate, but their use in other industries could enable them to enter the water or air where they could become a health hazard.
If nanoparticles are breathed into the lungs, the researchers warned that the health affects would be as severe as breathing in asbestos. Asbestos exposure can cause lung cancer and mesothelioma in 30 to 40 years after initial exposure. It can also cause a debilitating lung condition called asbestosis.
In 2007, the National Science Foundation's (NSF) National Nanotechnology Initiative will spend $273 million, but only $28 million is earmarked for "societal dimension" studies, including testing and safety issues. The $28 million is divided among its Nanoscale Science and Engineering Centers, which are studying nanoparticle manufacturing wet environments, occupational safety during nanomanufacturing and the interaction between nanomaterials and cells. Studies are also underway to characterize nanomaterials. Health experts are calling for more spending on the safety issues involved with these and other new materials.
Particles affect the lung differently depending on what substances they are made from. Particles of the same material also may have different effects depending on their size and shape. For example, the risk from inhaling asbestos varies with the size and length of the asbestos fibers.
The nanotechnology industry creates extremely small particles of different substances, such as carbon, for various uses. These particles are called nanoparticles when they are less than 100 nanometers in size. For comparison, a human hair is about 100,000 nanometers in diameter, so it would take 1000 nanoparticles to equal the thickness of one hair. Animal and laboratory tests show that high concentrations of nanoparticles can be dangerous. But doctors do not know for certain the effects of the amounts and types of nanoparticles that workers in the nanotechnology industry are exposed to. Studies are being designed to evaluate the risks and to ensure that workers are protected.