How do green algae react to carbon nanotubes?

November 4, 2011, Empa

Nanoparticles such as carbon nanotubes (CNT), which are found in an ever-increasing number of products, are ending up more and more frequently in our surroundings. If and how they affect aquatic ecosystems are questions which are still unanswered. An Empa study shows that while CNTs do not have toxic effects on green algae they do inhibit its growth by depriving the plant of light and space.

Carbon nanotubes (CNTs) are up to 100,000 times thinner than a and as light as plastic. Despite this they have a higher tensile strength than steel, are harder than diamond and better than copper. These properties make CNTs a raw material with a very promising future. All over the world possible applications are being investigated, including use in , plastics, batteries, medical technology and the purification of drinking water.

Carbon nanotubes are not poisonous to green algae, but they do slow the growth of these organisms at high concentrations because they cause clumping which leads to the algae receiving less light. Left: intact algae (green) in a clump of carbon nanotubes (black). Right: "normal" photosynthetic activity of the algae (red) made visible by fluorescence.

With the increasing industrial production of CNTs now reaching the level of hundreds of tons per year, the quantity of these particles which could be released into the environment has also risen. Certain studies have raised the possibility that CNTs lodged in the lungs might cause similar health effects as do . An interdisciplinary team of scientists from Empa and the Agroscope Reckenholz-Taenikon (ART) Research Station have now begun investigating the fundamentals of how CNTs behave when they are deposited in waterways and lakes.

Algae remain healthy but grow slower

In the course of the project, which is financed by the Swiss National Funds, researchers further developed a standard chemical method in order to measure the growth and photosynthetic activity of exposed to CNTs. They discovered that even in the presence of high concentrations of CNTs the algae retain normal levels of photosynthesis, although growth rates are reduced. Also noticeable was that when CNTs are added to the algae suspension, its color darkens and the algae forms with the nanotubes. Despite this there is no evidence that the nanotubes are absorbed by the plants.

The investigators came to the conclusion, therefore, that the algae grow more slowly because they stick together as a result of the presence of CNTs and therefore receive less light. To prove this, they developed two further tests which allowed them to measure quantitatively the shadowing and agglomeration effects the nanotubes had on the algae. The results show that the slower growth of the organisms is in actual fact primarily due to these two factors. The conclusion is therefore that CNTs are not directly toxic to green algae, as earlier studies indicated. In the presence of CNTs, algae simply do not enjoy ideal growth conditions because, like land plants, they need sufficient room and light to do so.The clumping and shadowing effects which were observed only manifest themselves at elevated CNT concentrations of more than one milligram per liter, however. These levels of carbon nanotubes concentrations are currently unlikely to be met in the environment.

Explore further: Carbon Nanotubes heralded as ideal candidates for next generation Nanoelectronics

More information: Are Carbon Nanotube Effects on Green Algae Caused by Shading and Agglomeration? F. Schwab, et al. Environmental Science & Technology, DOI: 10.1021/es200506b

Related Stories

Study on cytotoxicity of carbon nanotubes

December 22, 2008

Owing to the novel properties of carbon nanotubes (CBNs), a series of problems associated with in vitro toxicity assessments of carbon nanotubes (CNTs) have appeared in many literatures. In order to properly evaluate the ...

Carbon nanotube composites for enzymes and cosmetics

September 6, 2011

Japanese researchers have developed a low cost and efficient method for producing electrically conducting composites based on electrostatic adsorption of CNTs onto resin and ceramic particles for applications including enzymes ...

Carbon nanotubes could go antiballistic

November 9, 2007

CSIRO (Australia) has been granted $2 million under the Defence Capability and Technology Demonstrator (CTD) Program to demonstrate the capabilities of carbon nanotubes as strong, lightweight antiballistic materials.

Recommended for you

New technology for diagnosing immunity to Ebola

January 15, 2018

A promising new approach to detect immunity to Ebola virus infection has been developed by researchers from i-sense in a collaboration between UCL and Imperial College London.


Adjust slider to filter visible comments by rank

Display comments: newest first

1 / 5 (2) Nov 07, 2011
So now carbon nano-tubes can be used to combat the algae plumes caused by too much nitrogen being carried in our rivers and streams due to pollution from human activities?

Wow, what wonderful thing will they do next?
1 / 5 (1) Nov 07, 2011
it would be better to create river filters with basins of swamp plants and convert them to fuel, maybe a new type power plant that works reversed-polluting.
1 / 5 (1) Nov 07, 2011
So now carbon nano-tubes can be used to combat the algae plumes caused by too much nitrogen being carried in our rivers and streams due to pollution from human activities?

Wow, what wonderful thing will they do next?

I really hope you are being facetious and not serious.

CNT's are deadly to larger life forms, how are you going to direct the CNT's to stop microbial growth without contaminating larger species?

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.