Carbon nanotubes may be as harmful as asbestos
Study finds they may be as deadly to workers as asbestos
Published 4:00 am, Wednesday, May 21, 2008
One of the most promising materials for the future of technology, carbon nanotubes, might be as harmful as asbestos if inhaled, according to a new study published Tuesday in the scientific journal Nature Nanotechnology.
Animal studies indicate that these long and very thin carbon molecules could cause a cancer called mesothelioma, which occurs in the lining of the lungs.
"The problem of asbestos was caused when it was released into the air, if it was handled inappropriately or incorrectly. Carbon nanotubes could do the same," said Andrew Maynard, chief science adviser to the Project on Emerging Nanotechnologies in Washington and one of the authors of the study.
"With this information, we should assume the worst, we should think of them as asbestos. But more research might relax that point of view."
Carbon nanotubes, 10,000 times thinner than a human hair, are among the materials many scientists believe will be used to build tiny electronics.
In 2001, IBM made an array of transistors out of carbon nanotubes. In 2004, General Electric created a carbon nanotube diode, and last year, UC Berkeley scientists used single carbon nanotubes to make the world's smallest radio.
Today, the most widespread application is in plastic materials reinforced by carbon nanotubes. Stronger than steel but light as plastic, carbon nanotubes are highly attractive to manufacturers of everything from sporting goods to airplanes. They can be found, for example, in some tennis rackets, baseball bats and bicycle frames.
"I would be very surprised if it is dangerous to use, let us say, a tennis racket or baseball bat containing carbon nanotubes," Maynard said. "But I do not think it is OK to tell people that we think it is safe - we've got to have evidence."
Such products, he said, should go through a number of tests investigating, for instance, what happens when they break or when the surface is rubbed against the ground. He also wonders what happens when the products are disposed of.
"Is there a chance that the nanotubes will enter the environment?" Maynard said.
The main concern, however, is the effect on people processing carbon nanotubes and manufacturing the materials containing them.
At Unidym, a Menlo Park company exploring the possibilities of using carbon nanotubes in such items as touch screens, precautions already have been taken.
"This is what we expected. It fits with the paradigm that long and skinny fibers can cause asbestosis. It does not really matter if they are made of carbon or asbestos. The key is not getting them into the body," said Ken McElrath, vice president for product development materials at Unidym's facility in Houston, which manufactures the carbon nanotubes.
To protect employees from breathing nanotubes, the manufacturing is conducted in closed ventilated systems. People working with the nanotubes also are protected by dust masks with respiratory filters.
McElrath said he found the study to contain some positive news: Shorter carbon nanotubes might not be harmful.
"We are using these kinds of findings in our product design," he said. "We try to stay away from things that potentially cause problems."
The research presented in Nature Nanotechnology used an animal model developed in the 1980s to study the development of mesothelioma, which can be caused by asbestos exposure.
Using this model, the nanotubes were injected into the abdominal cavity of mice, which is lined by tissue similar to the human lung and is a sensitive predictor of mesothelioma. After one week, there was an inflammatory response to longer versions of the nanotubes.
"This is a very important study; it is very well done. It shows that you do get an inflammation that is similar to asbestosis. What is not known yet is the long-term effect," said Vincent Castranova, involved in the nanotoxicology research at the National Institute for Occupational Safety and Health.
Also unclear is how this experimental model for mesothelioma translates into reality. Scientists do not know under which circumstances these long carbon nanotubes will form a breathable dust, or whether this dust will work its way into the lung.
"Here we run out of information," Maynard said.
Meanwhile, Castranova recommends people working with carbon nanotubes follow National Institute for Occupational Safety and Health guidelines for working with engineered nanomaterials, which involve the use of respirators and special filters to clean the air.