I’m looking at an electron microscope image of a carbon nanotube – as I cannot show it here, you’ll have to imagine it. It shows a long, straight, multi-walled carbon nanotube, around 100 nanometers wide and 10 micrometers long. There is nothing particularly unusual about this. What is unusual is that the image also shows a section of the lining of a mouse’s lung. And the nanotube is sticking right through the lining, like a needle through a swatch of felt.
The image was shown at the annual Society of Toxicology meeting in Baltimore last week, and comes from a new study by researchers at the National Institute for Occupational Safety and Health (NIOSH) on the impact of inhaled multi-walled carbon nanotubes on mice.
It’s highly significant because it takes scientists a step closer to understanding whether carbon nanotubes that look like harmful asbestos fibers, could cause asbestos-like disease…
Questions were raised about carbon nanotubes and their superficial similarity to asbestos fibers as far back as 1992. Yet it wasn’t until last year that research was published suggesting carbon nanotubes that look like harmful asbestos fibers could possibly also cause asbestos-like diseases—specifically the disease of the lungs’ lining mesothelioma.
The Poland study, published in the journal Nature Nanotechnology, indicated that development of the disease mesothelioma was theoretically possible following inhalation exposure. But it didn’t establish whether exposure could occur to asbestos-like carbon nanotubes in practice or, if they were inhaled, whether the nanotubes could move to and penetrate the sensitive outer layer of the lungs.
Both steps would have to occur for there to be a chance of mesothelioma developing.
The current study from NIOSH seems to close the loop on one of those steps. Some caution is needed here as the research has yet to be peer reviewed (see Richard Denison’s comments for instance). Yet the findings are so significant that NIOSH thought it important to keep people abreast of developments before the work is finally reviewed and published.
In the study, a suspension of carbon nanotubes was introduced into the mice lungs using the pharyngeal aspiration technique, and the movement of the nanotubes through the lungs subsequently tracked. The researchers found that some of the nanotubes migrated from the alveoli in the lungs (the tiny sacs where oxygen passes form the air to the blood) to the pleura—the delicate membrane surrounding the lungs. As seen in the image described above, there was direct evidence that some of these needle-like fibers physically penetrated through the lung lining, into the region where mesothelioma can develop.
The researchers are at pains to point out that these data are preliminary, and are not conclusive. The results could have been influenced by the way the nanotubes were delivered to the lungs, the amount of material applied, or the types of animals used. Nevertheless, they demonstrate that, in principle, some forms of carbon nanotubes have the potential to migrate to the outer layer of the lungs. And this, combined with the data from Poland et al., raises the stakes considerably regarding potential health impacts.
The data from this study will be peer-reviewed and published shortly, allowing a more critical evaluation. But given the significance of the preliminary findings, it seems there is an urgent need for a more extensive strategic research program to establish how harmful different types of carbon nanotubes are, and how they can be handled safely.
Without this, it’s hard to see how manufacturers will be able to make informed choices on good practices that don’t either endanger workers and users, or place an overwhelming burden on production processes.
In the meantime, the best advice seems to be: Take great care to avoid airborne exposures when working with carbon nanotubes that bear a physical resemblance to asbestos.