Carbon nanotubes (CNTs) add strength and design flexibility to many materials, from reinforcing adhesives and materials used in electronics to enhancing the design of carbon fiber composites for use in cars and aerospace applications. But there's been increasing evidence that they, along with other nanoscale materials, may pose risks to human health and the environment. In ongoing research efforts to determine just how toxic they actually are, researchers at Texas Tech University have come up with a new method for detecting CNTs in soils.
The university's environmental biologists built an apparatus that can quantify how much CNT is present in a given soil sample. That's not an easy task since they're so small: mean outer diameters of 13nm to 16nm are common in multi-walled tubes. The apparatus was developed as part of the researchers' ongoing work in locating CNTs in biological environments and examining how they to accumulate in soil, plants such as food crops, or other organisms.
Researchers at Texas Tech University have come up with a new method for detecting CNTs in soils, which will help determine their toxicity. CNTs are so small that mean outer diameters of 13nm to 16nm are common in multi-walled tubes, shown here as grains partially smeared on paper (scale in centimeters). (Source: Shaddack/Wikimedia Commons)
The testing apparatus works by exposing soil samples to microwaves, which can reveal even mere trace quantities of CNTs. That's because, in the presence of microwaves, CNTs produce very high quantities of heat, much higher than most materials. The effect is so extreme that, if you put CNTs in your kitchen microwave oven, the carbon will spontaneously ignite. The researchers used this fact to heat samples to different temperatures to determine different concentration levels. The method has also been used to determine the amount of CNT loading in plant samples and earthworms.
The news about CNTs' toxicity is more than a little unwelcome, since graphene, the tubes' constituent substance, is the hardest known substance. When layers of it are rolled up into tubes, the resulting CNTs constitute a fiber that is 100 times stronger than steel and weighs one-sixth as much. That combination, along with qualities such as mechanical strength and electrical and thermal conductivity, makes them highly unusual and ideal building blocks for industrial uses.
Earlier this year, a joint study by the University of Missouri and the US Geological Survey showed CNTs to be toxic to various species of invertebrate aquatic organisms that live in sediment, including mussels, worms, and crustaceans. These researchers note that CNTs, which may contain metals as well as carbon, tend to accumulate in sediment when released into water. Both the metals -- including nickel, chromium, and other metals used in manufacturing that may remain as impurities -- and the carbon in CNTs can reduce growth rates or even kill certain types of marine life. The degree of toxicity varied depending on the type and source of CNT, the species of test organism, whether the materials had been cleaned using acid, and what method was used for dispersing the materials.
Researchers of the joint study say one of the biggest potential contamination risks occurs during the manufacture of carbon composites, but careful waste management and handling procedures can reduce that risk. More information is also needed on what happens when the composites begin to break down.
Ann, this is indeed a concern. Like many of the clever solutions to engineering problems, we have to think of the effect on living organisms, not just humans. Semiconductor manufacturing also uses many toxic chemicals, for example, and these have to be controlled. This is true at the point of manufacture and at the point of disposal. I recall that even the ink used in thermal printers, such as those that are used to print receipts at stores, can be toxic. We need to be careful in handling exotic, engineered materials.
One question I do have is about the detection method. Since microwaves are used, I assume that the tests done on earhtworms are destructive. Soil, even after being exposed to microwaves, is still just soil. An earthworm on the other hand...
Good article explaining the detection method for CNT's in soil. Are there toxicity concerns for CNT's in product? Also, are there concerns with the processing method used to add the CNT's to the base material?
Its carbon, the thing that loves to react with oxygen... Light it up :) Let's find out how fast this material will decay or adhere to larger particles. How much of it is released in the industry, as well as from end use products and compare it with the amount of material required for it to be a threat prior to hitting the panic button.
It's good to have that voice of reason to set some perspective. Still, it's better to find it now and accomodate its problems than much, much later when it's everywhere. Asbestos comes to mind in that regard.
Asbestos is absolutely safe (inorganic and non-reactive). It's the genetic material that rides along with it when asbestos (because it's ends are needle sharp) puncture a cell's wall that kills. Which is why asbestos was used everywhere without any concern for human health (in schools, ships, tile floors). Human history is full of examples of "safe" technology that that was over-exploited before realizing the dangers.
Carbon nanotubes probably have similar mechanical effects. I was told by an ME friend that carbon fiber (yes, not nanotubes, but still relevant) is much more dangerous than fiberglass. Where you get fiberglass on or in your skin, it works its way out. Carbon fiber works their way in ...
I read in Science News a few years ago, nanotubes in the environment do NOT disperse like other polutants (perhaps this is a good thing?)
In any case, if they are so reactive to microwave's, perhaps this is the solution. Just blast the contaminated soil with a high enough dose to destroy the bonds and turn them back into simple carbon.
Interesting comments. This is the first I've heard about toxicity concerns in CNT's. Guess it's time to dump my stock in graphene futures! When I hear about toxicity concerns, the scientist voice inside my head always asks, "But what is the mechanism at work?". As you point out, it may be an issue of mechanics rather than chemistry. Once this is understood, then a potential solution is usually at hand. In the meantime I'll start using a HEPA filter when I sharpen my #2 pencil.
It seems that the alleged toxicity of these nanotubes must be a mechanical thing, although none of the reports bothers to say anything about the mechanism of toxicity. The good news is that these nanotubes don't occur naturally, at least I have not heard of them being natural. So the proliferation should be quite a bit less. Also, they are kind of expensive, I think, so perhaps users may be motivated to avoid spilling them.
It would be good if those who go around bleating out noninformational phrases could somehow be motivated to provide more actual information and less intention toward causing hysteria.
Of course, if the nanotubes are locked into a composite material they may be a lot less free to cause any type of problems, although it would seem that machining the composite could be a bit hazardous.
If microaves can heat up the CNT then they can destroy them. Collect the waste and bath it with microwaves, waste disposal problem solved. Light them up! A plasma furnace would also work and other metals can be recovered. iRobot can probably build a Roomba robot that will do manufacturing cleanup and CNT destruction at the same time.
Inspired by the hooks a parasitic worm uses to penetrate its host's intestines, the Karp Lab has invented a flexible adhesive patch covered with microneedles that adheres well to wet, soft tissues, but doesn't cause damage when removed.
Engineers at the University of California, San Diego are designing a robotic arm that takes inspiration from the loose, flexible, yet very strong structure of the armored plates on a seahorse's tail.
Researchers at the Missouri University of Science & Technology have designed a new nanoscale material that can transmit light faster than the 186,000 miles per second it usually takes to travel through air.
It has often been said that as California goes, so goes the nation. This spring, the state's wind power is setting energy generation records and solar energy generation is expected to rise sharply during the second half of 2013.
From Dell / Intel® New Paradigms in Design Work Scott Hamilton, vertical market strategist for Dell Precision workstations, 5/2/2013 3
Early in my career, I worked as a draftsman and remember the days of drawing on vellum with numbered pencils and Mylar with plastic lead. This was a fun experience in the sense that I ...
I've been using workstations for more than 10 years and love finding ways to get more performance from my system. With demanding professional applications that require more power each ...
A lasting memory from my first job as an engineer in an auto assembly plant is standing on hard concrete at six in the morning, vending-machine coffee clutched in hand, listening to ...
A quick look into the merger of two powerhouse 3D printing OEMs and the new leader in rapid prototyping solutions, Stratasys. The industrial revolution is now led by 3D printing and engineers are given the opportunity to fully maximize their design capabilities, reduce their time-to-market and functionally test prototypes cheaper, faster and easier. Bruce Bradshaw, Director of Marketing in North America, will explore the large product offering and variety of materials that will help CAD designers articulate their product design with actual, physical prototypes. This broadcast will dive deep into technical information including application specific stories from real world customers and their experiences with 3D printing. 3D Printing is
To save this item to your list of favorite Design News content so you can find it later in your Profile page, click the "Save It" button next to the item.
If you found this interesting or useful, please use the links to the services below to share it with other readers. You will need a free account with each service to share an item via that service.
Tweet This
4 
