Carbon nanotubes: the new asbestos?
David Prentice
Calls for caution as nanotubes cause precancerous growths in mice.
Katharine Sanderson
Published online 20 May 2008 | Nature | doi:10.1038/news.2008.845
http://www.nature.com/news/2008/080520/full/news.2008.845.html
Nanotechnology experts are calling for prompt government action to
ensure that carbon nanotubes are properly regulated, after researchers
discovered that some carbon nanotubes can cause precancerous growths in
the same way that asbestos does.
Researchers led by Ken Donaldson of the University of Edinburgh’s
Centre for Inflammation Research, UK, found that in mice, long,
straight, multi-walled carbon nanotubes can cause the same kind of
damage as that inflicted by asbestos fibres when they are injected into
the lung's outer lining, called the mesothelium.
The lung clears out foreign bodies by wrapping them up in immune cells,
which can then be flushed out of the body. But straight fibres longer
than about 20 micrometres cannot be removed in this way because the
cells are too small to engulf them. As a result, the cells become
inflamed and form unwanted lumps, called granulomas, that can go on to
cause mesothelioma, a cancer of the mesothelium.
The researchers found that carbon nanotubes of this length led to the
formation of granulomas in the mice. “We have shown that if [carbon
nanotubes] do find their way to the mesothelium they are pathogenic,”
says Donaldson.
Toxic effects
The work doesn’t show that people exposed to nanotubes will get
cancer, Donaldson and his colleagues stress. There have not yet been any
studies on the effects of environmental exposure, or inhalation. “We
certainly need more research on the toxicology of these materials,”
says Donaldson.
The health effects of asbestos only came to light decades after workers
were exposed to the fibres. This needn’t happen with nanotubes, says
Anthony Seaton, a chest physician and co-author of the paper, published
in Nature Nanotechnology 1. “We are well ahead of the game,” he
says.
Andrew Maynard, co-author and chief scientific adviser for the project
on emerging nanotechnologies at the Woodrow Wilson International Center
for Scholars in Washington DC, says that he knows of 12 products that
openly declare the use of carbon nanotubes, such as tennis rackets and
bike components.
But Maynard suspects that this number is an underestimate. “My
suspicion is that this is the tip of the iceberg,” he says.
Size matters
"Up to now there has been considerable uncertainty about the hazards
that carbon nanotubes might pose," says Richard Jones, a
nanotechnologist at the University of Sheffield, UK. This research
begins to clarify things, he says. "Now we know that it is the longest
tubes that are most likely to cause problems."
Jones adds that nanotubes aren't normally handled in a state in which
they might be inhaled, but nevertheless sees a need to protect the
public, and the environment from any chance of exposure to nanotubes.
Maynard expects to see carbon nanotubes used in a wide range of
applications, from lightweight structural materials to
water-purification systems for the developing world. To do this safely,
the use of nanotubes must be properly regulated, he says.
Maynard calls the mouse study "a wake up call". “It has occurred at
an early enough stage that we can take action," he says. "If we think
carefully we can make carbon nanotubes reasonably safe.” He suggests
that only short, curly nanotubes, should be used. Alternatively, they
could be mixed with liquids, rather than using powders containing
straight nanotubes that might be inhaled.
Such regulation will require government and industry intervention, says
Maynard. “There has got to be regulation, but industry has got to take
responsibility.”
The UK government’s Department for Environment, Food and Rural
Affairs (DEFRA) has a voluntary reporting scheme for manufacturers that
use nanoscale materials in their products, and the United States has a
similar system. But until this kind of reporting is made mandatory, it
will be difficult to tell just where, and what kind of nanotubes are
being used by manufacturers.
References
1. Poland, C. A. et al. Nature Nanotech. doi:10.1038/nnano.2008.111
(2008).