PORTLAND, Ore.—Nanotubes may not be toxic, as previously reported elsewhere, according to the Semiconductor Research Corp. (SRC). Rather, contaminants mixed in during their manufacture should be credited with their adverse health effects, according to a University of Texas study funded by SRC.
"Carboxylated single-walled carbon nanotubes indeed reduce the ability of mammalian cells to grow in culture, but by using simple filtration methods we were able to remove the contaminants introduced during manufacturing," said University of Texas professor Rockford Draper. "The resulting purified nanotubes were shown to have no ill effect on mammalian cells grown in culture."
The surprising finding can be applied immediately by research organizations using one of two methods outlined by the researchers in a paper entitled "Cytotoxicity Screening of Single-Walled Carbon Nanotubes: Detection and Removal of Cytotoxic Contaminants from Carboxylated Carbon Nanotubes," slated to be published in Molecular Pharmaceutics. Commercial manufacturers of nanotubes are expected to pick up the gaunlet and begin using these methods to offer pre-screened purified nanotubes which have already had the filtration process applied to them.
The research was conducted under the auspices of SRC's Center for Environmentally Benign Semiconductor Manufacturing, which supplies semiconductor manufacturers with a variety of guidelines on how to fabricate microchips in the safest and most economical manner that complies with worldwide efforts to use "green" materials and methods.
"During the manufacture of semiconductors using nanotubes, they are usually immobilized, preventing them from entering the environment," said Dan Herr, SRC director of nanomanufacturing sciences. "Nevertheless, we will continue to focus our efforts on minimizing their health impact and on insuring the safety of both the workers using these nanotube-based materials as well as on their potential hazards after manufacturing."
SRC is currently soliciting proposals for research that studies the entire lifecycle of carbon nanotubes and the semiconductors in which they will be used, as well as on different varieties of nanotubes, such as the multi-walled variety used in many bioelectronic applications.
Additional funding for the current research was provided by the National Institute of Environmental Health Sciences.
Single cell overlayed with the distribution in the cell of purified carboxylated single-walled carbon nanotubes (shown in yellow). No apparent effect was observed in the purified nanotubes, whereas unpurified nanotubes inside cells inhibited growth by 60 percent.
The researchers said they expect multi-walled nanotubes to also contain the contaminants, however the multi-walled variety are also much longer, so conceivably it could be their aspect ratio that cause an asbestos-like reaction (asbestos fibers are also very long, which causes them to get trapped in the lungs). That is why they have to text them next to find out whether its their aspect ratio or the contaminants.
I asked the researchers this question myself, but they said that many applications require carboxylation to functionalize the nanotubes, which produces the toxic byproducts. However, there are other ways of manufacturing them, and you are right to advise their makers to explore using those other methods (but in the meantime they should filter carboxylated nanotubes to remove the contaminants).
The title merely states the essense of the story, that reseachers say nanotubes are not toxic, which the story qualifies by stating that a certain kind have found to be nontoxic under certain conditions, and that those conditions are now being extended to the other types. This is standard journalist practice underwritten by the courts which do not require headlines to state the whole story, as long as the body of the story does.
The title and the first line tells completely different story. The title of this article says that Nanotubes are not toxic while the researchers claim only that Nanotubes may not be toxic. The whole article suggest the same thing that one particular instance of nanotube is found to be non-toxic but there might be other instances where it is otherwise.
We are not out of the woods yet, because the nanotubes that were said to be akin to asbestos were of the multi-walled variety rather than the single-walled ones tested here. However, they are looking at those now and there is no reason to think multi-walled nanotubes will also be given a clean bill of health.
I was surprised to think that there might be health considerations regarding nanotubes, so I looked up the previous article. Maybe we do actually learn from previous mistakes. It would have been very bad to have an equivalent to the asbestos fiasco all over again. Interesting stuff.