Carbon Nanotubes Dangerous to the Environment

Scientists from the research center Forschungszentrum Dresden-Rossendorf (FZD) have discovered worrying properties of carbon nanotubes, which indicate that nanotube production may be dangerous to the environment. Their discovery, they say, may halt an otherwise diverse and fertile research area.
Atomic force microscope image of carbon nanotubes on a nuclear track filter membrane. Apart from the nanotubes, the 50 nanometer sized filter pores are clearly visible. (Credit: E. Christalle)
Atomic force microscope image of carbon
nanotubes on a nuclear track filter membrane.
Apart from the nanotubes, the 50 nanometer
sized filter pores are clearly visible.
(Credit: E. Christalle)

Carbon nanotubes are molecule-sized tubes of carbon with exceptional properties. In the last fifteen years they have become the focus of extensive research as they are among the strongest fibers known with remarkable electronic properties. So far, commercial applications have been slow to develop mainly due to the high production costs of high quality nanotubes.

Researchers from the Forschungszentrum Dresden-Rossendorf say they have recently begun considering aspects previously overlooked by other scientists. “If the application of products and commodities containing carbon nanotubes will increase in the future, then there will be a higher probability for the tubes to get into the environment during their production, usage or disposal, to be distributed there, and to bind pollutants such as heavy metals on their way trough the environment”, says Harald Zaenker, a scientist at FZD.

Carbon nanotubes may leak into the environment via water. In their original state, the carbon fibers with diameter less than 50 nanometers are not water-soluble. This quality makes it seemingly unlikely for the substance to be able to spread through groundwater, lakes etc. However, carbon nanotubes are also capable of forming colloidal solutions (a type of chemical mixture where one substance is dispersed evenly throughout another) if their surface structure is altered. These changes may either occur intentionally during the production phase or happen due to natural causes after the tubes are released to the environment.

In a colloidal solution, unlike a true solution, the apparently dissolved substance is dispersed in the solvent, forming tiny particles. These particles are bigger than the solvent’s molecules and those of a dissolved substance in a true solution. As colloids in water, the nanoparticles can be easily transported to virtually anywhere on the planet. Another known feature of the nanotubes is their ability to penetrate cell walls. Furthermore, when the nanotubes’ surface properties change, their ability to bind heavy metals increases.

The scientists conducted their research on carbon nanotubes both in their natural state, and an oxidized state. They discovered that oxidized carbon nanotubes scatter light more strongly. “This is an indication that colloids have formed which do not settle”, explained Harald Zaenker.

The team also showed that the heavy metal uranium, which is abundant in the environment and water, is especially attached to the surface of treated nanotubes. They found that the uranium uptake capacity was increased by an order of magnitude in comparison to untreated carbon nanotubes. “Therefore, it is plausible to assume that carbon nanotubes, if released to the environment, influence the transport of uranium in environmental waters and even in biological systems. The possible impact on the environment and on human health has in general been considered too little”, Harald Zaenker says.

The high bonding capacity of carbon nanotubes for uranium and other heavy metals may suggest using them for the removal of heavy metals from waters. Unfortunately, at the moment, the new technology is not yet a cost-efficient alternative to classic water purifiers, Zaenker says. “Eventually, it is important at the moment to further study the behavior of carbon nanotubes in waters”, he says. “Only then can the positive and negative aspects of carbon nanotubes be better assessed.”

TFOT has recently covered the advantageous uses of carbon nanotubes, as researchers at Sandia National Laboratory in Livermore, California created the first carbon nanotube device capable of detecting light in the entire visible spectrum. Another story we brought you covered the development of flexible, transparent, nanotube based loudspeakers developed at the Tsinghua University and Beijing University.

To find out more on the possible dangers of carbon nanotubes, please visit the Forschungszentrum Dresden-Rossendorf news page.

Icon image credit: User Mstroeck on en.wikipedia

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