Study identifies toxic by-products of nanotechnology
4 September 2007
In a warning to the emerging nanotechnology industry,
a new study of the by-products discharged to the environment during
production of carbon nanotubes (CNTs) has identified cancer-causing
compounds, air pollutants, and other substances of concern.
Photo credit: Anastasios John Hart
Carbon nanotubes, submicroscopic cylinders of carbon that are thousands
of times smaller in diameter than the width of a human hair, possess
characteristics not found in their larger, bulk counterparts, including
enhanced strength and high electrical conductivity. Carbon nanotubes are
expected to become the basis of a multi-billion dollar industry.
The research was reported at the 234th national meeting of the American
Chemical Society in August. Study co-author Desirée L Plata and colleagues
described their work as “totally new,” noting that past analyses of the
environmental impact of the emerging nanomaterials industry have been based
on the toxicity of ingredients used in the recipes, rather than the actual
pollutants formed during manufacture.
Recent experiences with other
industrial pollutants underscore the need to try to improve nanotube
manufacturing methods before serious problems arise, said Plata. These
pollutants include Freon refrigerants, the gasoline additive methyl t-butyl
ether (MTBE), flame retardants like polybrominated diphenyl ethers (PBDEs),
and the surfactant perfluoroctane sulfanate (PFOS), she noted.
other scientists have shown that carbon nanotubes, which come in many sizes
and shapes, can damage the lungs of mice, but their exact risk to human
health remains unknown. Even less is known about the potential effects of
the by-products of nanotube production, the researchers said.
expressing concern about the possible health and environmental effects of
nanotechnology by-products, Plata said the new data may be crucial as the
nanotechnology industry seeks to avoid the kind of unanticipated health and
environmental problems that have accompanied emergence of other new
Researchers said, for instance, that they foresee developing, in
collaboration with the CNT industry, “green chemical” reactions and
filtration systems to substitute for those with potentially hazardous
by-products and other ways of manufacturing carbon nanotubes that minimize
potentially adverse impacts.
“Without this work, the environmental and
health impacts of the carbon nanotube industry could be severe and costly to
repair,” said Plata, a doctoral student in chemical oceanography at the
Massachusetts Institute of Technology and Woods Hole Oceanographic
Institution. “We would like to help it develop in an environmentally
To evaluate the emission products formed during
nanotube production, Plata and her associates utilized a small-scale device
to simulate “chemical vapor deposition,” one of the main methods for making
CNTs. Using a carbon vapor source, the researchers produced CNTs and
analyzed chemical by-products from the reaction.
They found at least 15
aromatic hydrocarbons, including four different kinds of toxic polycyclic
aromatic hydrocarbons (PAHs) similar to those found in cigarette smoke and
automobile tailpipe emissions. The most harmful PAH identified was
benzo[a]pyrene, a known human carcinogen, the researchers said. They also
saw release of other hydrocarbons that can contribute to smog formation and
can trigger the formation of ozone in the lower atmosphere, which can in
turn cause respiratory problems in humans, Plata said.
“If nanotubes are
produced in the tonnes, there will also be tonnes of PAHs produced,” Plata
notes. She said that the key solution to the problem may also be to employ
special filters or ‘scrubbers’ in the production process to reduce the
formation of harmful by-products.
Another possible solution is to develop
new nanotube manufacturing processes that produce fewer toxins, said Plata,
who notes that the research team is currently working with four of the major
nanotube producers in the United States to help develop strategies to make
production more environmentally friendly.
CNTs are already produced on a
small industrial scale, and the researchers plan to measure actual emissions
at several industrial sites in the near future to get a clearer picture of
real-world pollutant emissions.
Collaborators in the study include graduate advisor Christopher M. Reddy,
Ph.D., of the Woods Hole Oceanographic Institution in Woods Hole, Mass. and
Philip M. Gschwend, Ph.D., of the Massachusetts Institute of Technology.
Save this page on del.icio.us