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By Jonathan
Fildes
Science and technology reporter,
BBC News
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The inhalation of asbestos fibres
can cause lung diseases and cancers
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Carbon nanotubes, the poster child of
the burgeoning nanotechnology industry, could trigger diseases similar
to those caused by asbestos, a study suggests.
Specific lengths of the tiny fibres were found to cause
"asbestos-like" inflammation and lesions in mice.
Use of asbestos triggered a "pandemic of lung disease"
in the 20th Century.
There are high hopes for the tiny carbon molecules,
which have
remarkable properties that could be used for advanced electronics and
materials.
They are already known to be incorporated into
products such as tennis rackets, bicycle handlebars and baseball bats,
where they are used because of their strength and light weight.
Other undocumented products may also make use of them,
the
researchers said, but companies did not have a duty to report their
use.
"As a society, we cannot afford not to exploit this
incredible
material but neither can we afford to get it wrong - as we did with
asbestos," said Dr Andrew Maynard the Project on Emerging
Nanotechnologies at the Woodrow Wilson International Center for
Scholars in Washington DC, US.
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 For a fibre to be harmful, it has to be
thin, long and insoluble in the lung 
Ken Donaldson
University of Edinburgh
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However, of the known goods there was "little risk" of
exposure as
the nanotubes are encased inside, the researchers said. But, they
warned, there was a potential risk for workers exposed to the tubes
during manufacturing and disposal.
The nanotechnology industry welcomed the findings but
cautioned against drawing conclusions from a single study.
"Until now we have not had two studies that showed the
same
result," Dr Steffi Friedrichs, director of the Nanotechnology
Industries Association (NIA) told BBC News.
"The latest study suggests there could be a reason for
concern and suggests there is an effect but it needs to be validated."
Length-effect
Carbon nanotubes are often thought to epitomise the
nanotechnology industry.
The global market for these tiny cylindrical molecules
is
expected to grow to between $1bn and $2bn by 2014, according to some
estimates.
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CARBON NANOTUBES
Sheets of carbon atoms folded into
a cylinder
Can occur as single tubes or as a
series of concentric cylinders known as multi-walled nanotubes
Members of the fullerene family,
which includes buckyballs
Demonstrate unusual strength and
electrical properties
Promise to revolutionise
electronics, computers, chemistry and materials science
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However, the nanotubes show certain superficial
similarities to
other fibres, such as asbestos, which are known to cause harm and
diseases including cancers.
"For a fibre to be harmful, it has to be thin, long and
insoluble in the lung," explained Dr Ken Donaldson, one of the authors
of the paper published in Nature Nanotechnology.
Nanotubes' thinness and toughness are well established,
so the researchers set out to examine the effect of their length.
In a series of experiments, the researchers injected
different
lengths of multi-walled nanotubes - which comprise two to 50 concentric
cylinders - into the abdomen of mice.
Asbestos fibres and tiny flat sheets of carbon were
injected into other mice to compare the response.
The researchers looked in particular at a membrane that
forms
the lining of body cavities, such as the chest and the abdomen, called
the mesothelium. The lining around the lungs is known to be prone to
the cancer mesothelioma after exposure to asbestos.
"What we found was that the long nanotubes were
pathogenic -
they caused inflammation and scar formation. The short nanotubes were
not," said Dr Donaldson.
"The problem seems to be that the cells that usually
deal with particles can't deal with a long, straight shape."
The lung is equipped with a network of cells that engulf
foreign particles in a process known as phagocytosis.
"[The cells] can stretch to about 20 microns but beyond
20
microns they start to have trouble enclosing their membrane around a
structure," explained Dr Donaldson.
"Basically, it freezes them; they can't move properly so
they
can't clear material from the lung. They are in a hyperactivated state
which leads to inflammation, scarring and probably cancer in the long
term."
Long life
However, the researchers said the link between long,
straight, multi-walled carbon nanotubes and cancers was not proven.
"We are a long way from saying that any form of carbon
nanotubes causes mesothelioma," said Dr Donaldson.
Carbon nanotubes (top) show
similarities with asbestos (bottom)
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He said there were still many questions to answer,
including whether
the long, straight nanotubes would even reach the chest cavity lining
if they were inhaled.
A recent study showed that when mice inhaled nanotubes
they
developed inflammation that peaked within seven days of exposure, and
returned to normal within one or two months.
"Whether the material is asbestos-like is still a
question to
be debated," said Vincent Castranova, chief of a pathology research
unit at the National Institute for Occupational Safety and Health, who
conducted the study.
"Having a panic that you have the next asbestos is a
little bit premature in my view," he told Associated Press.
But other researchers still urged caution.
"These sorts of materials need to be handled very
carefully,"
said Dr Anthony Seaton, a medical doctor and co-author of the study,
who has treated a number of patients affected by asbestos.
"The Health and Safety executive in the UK needs to take
appropriate measures to ensure that people are not being exposed to
these things in the air."
He said this was particularly important for people
involved in
the manufacturing process, whether in industrial plants or academic
labs, and when products were disposed of.
Many people were affected by asbestos when buildings
which
contained the material were demolished. Related health problems
continue to be seen today.
"What happens if you demolish products, or you throw
products
into landfill sites or incinerate the products - is there a chance of
carbon nanotubes coming out then and exposure occurring?" said Dr
Maynard.
"We simply don't know the answer to that and I think
it's something that needs to be addressed."
He also called for greater transparency from the
nanotechnology industry.
"At the moment we don't know where carbon nanotubes are
being
used, what products they're appearing in, what types of nanotubes are
appearing in which products," he said
"I think the bottom line here is that we still have a
very
clear chance of making a difference with this technology - of getting
it right - if we take action now."
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