Mix carbon nanotubes and asbestos together (metaphorically) and you get an explosive mix—at least if news coverage of the latest publication coming out of Professor Ken Donaldson’s team is anything to go by. The research—published on-line today in Nature Nanotechnology—is the first to explicitly test the hypothesis that long carbon nanotubes behave like long asbestos fibres in the body.
In brief, the study (which I was a co-author on) used an established method to test whether a fibrous material has the potential to lead to the disease mesothelioma—a cancer of the outer lining of the lungs that can take decades to develop following exposure. In the method, samples of material are injected into the abdominal space of mice, where inflammation and the formation of granulomas in the lining tissue (the mesothelium) are studied over a seven-day period. Previous research has established that the combined presence of fibres, inflammation and granulomas is a very strong indicator that mesothelioma will occur in the long-term. While the method uses lining of the abdominal space, it is highly predictive of what happens in the same tissue surrounding the lungs, if it is exposed to durable fibres.
Five materials were tested in this study: short amosite asbestos fibres, long amosite asbestos fibres, short and/or tangled multi walled carbon nanotubes (two samples), long straight multi walled carbon nanotubes (two samples), and carbon black (compact graphite-based particles. The results: fibres longer than 15 micrometers to 20 micrometers (whether asbestos or carbon nanotubes) led to a positive response; short/compact particles did not.
This is the first study to demonstrate that carbon nanotubes that physically resemble harmful asbestos fibres, can also behave like harmful asbestos fibres.
What the study does not address is whether exposure to long straight carbon nanotubes will occur or, if it does, whether these fine fibres will reach the mesothelium surrounding the lungs, and go on to cause mesothelioma.
But the results are sufficiently compelling to suggest urgent action is needed if we are to prevent a long lasting legacy of harm from some forms of carbon nanotubes, and ensure the emergence of safe and trusted carbon nanotube applications.
First and foremost, targeted research is needed to validate this study, assess the magnitude and nature of likely carbon nanotube exposures—from material production to product disposal—and evaluate whether inhaled nanotubes can work their way to the outer lining of the lungs. The current U.S. federal strategy for nanotechnology-related environmental, health and safety research (PDF, 2.2 MB) does not specifically address the health impacts of carbon nanotubes (despite a recommendation from the UK Royal Society and Royal Academy of Engineering in 2004 to carry out exactly this type of research). Perhaps it’s time to rethink what is important here.
But action is also needed now to ensure carbon nanotube exposures to workers and users are kept as low as possible. This means developing appropriate exposure measurement methods, applying effective control and containment protocols, and agreeing on benchmark exposure levels to use in the absence of more formal exposure limits. The recent BSI Guide to safe handling and disposal of manufactured nanomaterials (PD 6699-2:2007, see also“Safe nanotechnology in the workplace: A practical guide”) recommends a benchmark exposure level of 0.01 fibres/ml for carbon nanotubes in the absence of any other information—this would seem to be good advice for long carbon nanotubes, until more is known about their exposure potential and hazardous nature. Long multi-walled carbon nanotubes can currently be purchased from outlets like CheapTubes Incorporated for as little as 40 cents a gram (as long as you by them in kilogramme quantities), yet the health and safety advice still assumes these are as harmless as graphite—this has to change.
And thirdly, action is needed to ensure transparency—making sure regulators, industries and consumers know which types of carbon nanotubes are being used, where they are being used, and what precautions should be taken to ensure safe use.
Carbon nanotubes have great potential as a unique material that can be used in many unique and beneficial ways—from reducing our environmental impact to curing diseases. But mis-steps now could easily undermine trust in this nascent industry, and prevent the material’s potential from being realized.
The comparison with asbestos is firmly grounded in the physical resemblance between certain forms of the two materials, and this alone should stimulate clear action to ensure safe use. But the health impacts of asbestos exposure still resonate through society—deaths from asbestos-related disease are not expected to peak for another ten years—and the mere suggestion of similarities between nanotubes and asbestos fibres could cause investors and users to shy away from this new technology unless there are clear assurances that health and safety concerns are being fully addressed.
Widespread pickup in the media of the current study suggests that people care about carbon nanotubes, and whether they are safe. The good news is that we still have time to ensure they are used safely—but only if we act now and act fast.
Carbon nanotubes display asbestos-like behaviour – a SAFENANO commentary by Ken Donaldson
This post first appeared on the SAFENANO blog in May 2008