Bangalore: Carbon nanotubes, the molecular-scale tubes of graphitic carbon, that are gradually entering our lives—through electronic devices, health care, cosmetics, solar panels, to name a few applications—have lately fallen prey to the growing concern about safety of nanotechnology.
Now, a new research shows that the carbon nanotubes, or CNTs, resemble asbestos in inducing a certain type of cancer of the lungs.
In Wednesday’s issue of the journal Nature Nanotechnology, a group of researchers reports that in a pilot study in mice, straight and long CNTs behave like asbestos at the mesothelium (membrane that forms) lining of the body cavity, thereby confirming the earlier hypothesis that CNTs can cause mesothelioma. This type of cancer is almost exclusively found following asbestos exposure and was a major cause that led to the ban of asbestos in many parts of the world in the 1990s. India, however, continues to allow the use of asbestos.
“Not all carbon nanotubes look like asbestos fibres, and not all are likely to become airborne and be inhaled,” says Andrew Maynard, a co-author from the Woodrow Wilson International Center for Scholars in Washington. But, as early as 1992, concerns were raised that researchers should pay particular attention to whether this newly discovered material might lead to diseases usually related to asbestos, he adds.
“The cautions brought out in the paper on the use of multi-walled tubes (CNTs can be single or multi-walled) are definitely of high value,” says Ajay K. Sood, professor of physics at the Indian Institute of Science in Bangalore. Sood and his team discovered a path-breaking property of CNTs in 2003 when they showed that these tubes act as flow-sensors. That is, when liquid is passed over these tubes, electricity is generated in the direction of the flow, opening up opportunities for use in biomedical implants.
Sood, however, says it’ll be important to do studies on the same batch of samples of the tubes, “with the given surface chemistry, metal content, etc but with varying lengths”. India announced Rs1,000-crore national nanotechnology mission in 2007, and Sood, one of the lead architects of the programme, says such studies confirm that “projects on safety issues will be encouraged” in this mission.
It is estimated that nanotechnology will be associated with $2.6 trillion (Rs111 trillion) worth of manufactured goods by 2014, according to the fifth edition of Nanotech Report from Lux Research Inc. in 2006. And CNTs represent the broader field of nanotechnology, an area of research and development which comprises more than $10 billion in R&D investment around the world each year, says Maynard. It’s due to such promises that scientists believe exposure to CNTs needs to be controlled as the industry will suffer a setback through uncertainty and lack of trust “over the safety of emerging materials and products”.
“This is a young industry which promises to address some of the greatest problems being faced by society, including creating better drugs and cost-effective water purification,” says Maynard.
While researchers agree that more detailed investigations need to be carried out, the fact that diseases such as mesothelioma take years to develop and manifest makes it prudent to take precautionary measures early on in technology development. For instance, this paper throws a light on how the material might be made safer—by making the tubes “short and curly”. “The challenge now is to build on this research to develop ways of using the materials safely,” says Maynard. The field certainly needs more risk-research as CNTs have been used in the industry for some years now but it is not known what happens to them at the end of their life, for instance if they seep into groundwater.
“Eventually, CNTs may turn out to be toxic but it’s early to brand them so,” says O.N. Srivastava, professor of physics at Banaras Hindu University in Varanasi. Researchers (Maynard and colleagues) seem to have used the tubes straight from the market, without “functionalizing them” which can affect the outcome of the research, he cautions.
Functionalizing CNTs means giving them a series of chemical treatment so that they become more amenable to the body. Srivastava’s group at BHU makes carbon tubes and functionalizes them for use in research for delivering a cancer drug, amphotericin-B.