Carbon nanotubes have unexpected negative impact on environment

Carbon nanotubes are stronger than steel, harder than diamond, light as plastic and conduct electricity better than copper.

It is no wonder they can be found in an increasing range of products, ranging from tennis rackets to solar cells and consequently end up in the environment in increasing quantities.

But much is still unknown about the effect of these nanotubes on the environment. Especially aquatic systems are of interest since that is where most nanoparticles eventually end up. New research now shows that carbon nanotubes at least are not toxic for green algae. Good news for the algae. Or is it?

Negative impact

Earlier findings have shown that carbon nanotubes are harmful for cells in the human body, more or less having the same effect on them as a spear has on game. Finding that the toxic effects on green algae are minimal was therefore a pleasant surprise.

When further examining the effects of the nanotubes on green algae Empa researchers found that they nevertheless have a negative impact on the growth of algae. The reasons for this are twofold: high concentrations of nanotubes form a layer that partly blocks sunlight and they stimulate algae to clump together depriving them of light and room.

Luckily these effects only occur at concentrations as high as one milligram per litre, a concentration that is unlikely to be met presently. But in a few years they may. Currently hundreds of tons of carbon nanotubes are produced each year, but this amount is on the rise and with it the quantity that can be released into the environment.

Proceed with caution

In itself the new results are not that alarming, although they do show a possible future threat to the environment. What is disquieting is that while some nanoparticles may show no direct toxicity for humans or the environment, they may still have a negative impact.

It shows that unfortunately the unexpected properties of nanoparticles are not limited to just the amazing ones that have made them into a whole new industry. Especially unbound nanoparticles because of their high reactivity ought to be carefully examined for their effects on the environment. Until then everybody should keep their nanoparticles safely inside.