From 2020 Science:
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.
[Read the original article at http://2020science.org/2009/03/26/new-carbon-nanotube-study-raises-the-health-impact-stakes/]