Carbon nanotubes (CNTs), as their name implies, are products of nanotechnology that has gained
popularity since it was discovered 15 years ago by Sumio Iijima, a Japanese Physicist, in his lab
at Nippon Electric Company (NEC) in 1991. CNTs attracted scientists and engineers due their
huge potential use for industrial applications in the fields of medicine, electronics, and materials
science.
In addition to being categorized into two major structures: single-walled nanotubes (SWNTs)
and multiple-walled nanotubes (MWCNTs), they existence in a wide range of length-to-diameter
ratio. Their unique properties such as electrical, thermal, as well as mechanical properties enable
them to be more applicable and manageable.
However, their large surface area/volume ratio is suspected of causing adverse health effects.
Scientific research has discovered that CNTs can bind to heavy metals, form colloidal solutions
and have adverse effects on aquatic life such as zebrafish. Animal studies indicate acute
pulmonary and/or respiratory toxicity; results similar to that of asbestos fibers. This is probably
why European Communities are currently reviewing the draft regulation on potential
occupational health effects for nanomaterials and designing exposure limits for nanotech
companies.
The health effects caused by MWCNTs are similar to that for asbestos so we did our risk
assessment on MWCNTs. The major routes of exposure include inhalation, transdermal
absorption, ingestion and ocular. We focused on inhalation because that is the main route of
exposure for occupational workers.
We did our risk assessment on Ryan-Rasmussen animal case study because the concentrations
used gave an idea of what might the NOAEL and LOAEL be because it had concentrations that
did and did not cause adverse health effects. Since there weren’t any exposure limits set for
MWCNTs, we made assumptions for NOAEL and LOAEL based on the experiment then
compared them with the limits set by other agencies for graphite and asbestos.
Based on our risk assessment, we believe the exposure limits for MWCNTs should be set below
the limits for asbestos and graphite for reasons such as size differences and lack of information
on health effects of MWCNTs. Instead of 0.1 fibers/cc/8hr, we believe it should be 0.008
fibers/cc/8hr.
According to our precautionary assessment, we concluded that the use of MWCNTs is not
supportive of health or community, there’s significant exposure, and highly hazardous because
we do not know much about MWCNTs. It is a serious concern that should be addressed.
For risk management, there should be more studies conducted to find more information about
MWCNTs and the adverse effects on humans, specifically workers. As for risk communication,
methods should be implemented to educate, protect, and monitor workers’ health. Production of
carbon nanotubes should be limited/halted until significant evidences prove they’re safe to use.