How do green algae react carbon nanotubes?

How do green algae react to carbon nanotubes?

1:14 AM, 14th November 2011
How do green algae react to carbon nanotubes?
Carbon nanotubes are not poisonous to green algae, but they slow growth of the organisms at high concentration because they cause clumping, leading to algae receiving less light. (L) Intact algae (green) in a clump of carbon nanotubes (black). (R) Normal photosynthesis activity of algae (red).

DUBENDORF, SWITZERLAND: Nanoparticles such as carbon nanotubes (CNT), which are found in an ever-increasing number of products, are ending up 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 human hair and as light as plastic. Despite this they have a higher tensile strength than steel, are harder than diamond and conduct electricity better than copper. These properties make CNTs a raw material with a promising future. With increasing industrial production of CNTs, 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 asbestos fibre. An interdisciplinary team of scientists from Empa and Agroscope Reckenholz-Taenikon (ART) Research station have now begun investigating fundamentals of how CNTs behave when they are deposited in waterways and lakes.

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

The investigators came to the conclusion, that algae grow slowly because they stick together as a result of 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 slower growth of 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 presence of CNTs, algae simply do not enjoy ideal growth conditions such as land plants, they need sufficient room and light to do so.

“Our study shows how difficult it is to understand in detail, effect of nanomaterials on organisms,” said Fabienne Schwab, Researcher, Empa and ART. The results will help to test other nanoparticles to ensure that the safety of humans and their environment is guaranteed. Empa Researcher Bernd Nowack advised that until comprehensive, long term results are available for complex organisms such as green algae, nanoparticles (particularly unbound nanoparticles) should not be released into our environment.

(C) Empa - a Research Institute of the ETH Domain News




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