Carbon Nano Tubes is like asbest? the future of nano?

[Fearless]

You've probably heard about the isolating material asbest which was used a lot around the turn of the 1900's. It got these long fibers that pierces the cell and accelerates rapid cell growth. This cell growth more than often gives the recipient cancer in the lung.

In the recent issue of nanotechnology nature (maybe it was in the pre-articles) they've modeled long and short CNT in the lining of the lung and in some lungtissue in mice. The long nanotubes behaved almost like asbest, causing cell change and piercing the cell from wall to wall. The short nanotubes didn't act like asbest.

So what do you people think about this? CNT's are here to stay, or is this a deathsentence to that field in nanotechnology?

I personally think that there needs to be more articles and more research, and that the long CNT's be handled with caution at the very least. I think this could get very serious effetcs on the nano-industry and getting funding for nano-research, I so hope this won't kill the industry in it's cradle.

 

[Moonbear]

It would be helpful for the discussion if you could provide references to the studies about which you're referring.

In general, when one considers the risk/benefit balance for a product, the exposure risk needs to be considered in addition to what damage they can cause once an exposure occurs. What is the likely application of these long nanotubes, and who could potentially be exposed to them? The problem with asbestos was that it was used all over the place, in building insulation for example, and people worked with it unaware of the health risks, so not only were there occupational exposures to people who didn't know they should use protective equipment, but also exposure risks to the general public working in buildings where the material was used who would not be wearing protective equipment.

Can working with them be made safe? Are there adequate respirators to filter them from getting into the lungs? Where are they used and who could be exposed to them? Are all the applications in industrial settings where PPE can be used, or is there a consumer end-product where exposure risks are high in the general population who would not wear PPE to work with whatever the end product is? That's going to be important in determining if this is a blow to the technology in general.

Examining the studies on health risks, on the other hand, are more useful in addressing how to deal with an exposure, on the need to prevent exposure, and if there is a way to treat long-term illness in people exposed too late to mitigate early damage (if such a risk really exists...which is what I guess this thread is intended to discuss).

 

[Fearless]

I will try to find the study again as soon as I can and have access to the nature nano-journal.

And good questions by the way. I will try to answer them too when I have the time. :)

 

[mgb_phys]

It was media hype, the author of the report said in the conclusion it wasn't a problem.
Basically long fibre nanotubes are hazardous, but were only present while being manufactured. Once embeded in the matrix they were used in, they were safe and since the manufacturing process required them to be handled in hyper-clean sealed enviroments it was unlikely any worker would come into contact with them.

The paper I read specifically said - this is NOT like asbestos where the long fibres are in the user's enviroment.

 

[BoomBoom]

So what do you people think about this? CNT's are here to stay, or is this a deathsentence to that field in nanotechnology?

I personally think that there needs to be more articles and more research, and that the long CNT's be handled with caution at the very least. I think this could get very serious effetcs on the nano-industry and getting funding for nano-research, I so hope this won't kill the industry in it's cradle.

I vote emphatically that they are here to stay! There are hundreds or perhaps thousands of different uses for these little nano-wonders. I'm sure any hazards they may pose will be discovered and dealt with with little impact on this new technology.

I often browse the abstracts at this site to see what they are up to:

http://pubs.acs.org/NanoLett/"

 

[Moonbear]

It was media hype, the author of the report said in the conclusion it wasn't a problem.
Basically long fibre nanotubes are hazardous, but were only present while being manufactured. Once embeded in the matrix they were used in, they were safe and since the manufacturing process required them to be handled in hyper-clean sealed enviroments it was unlikely any worker would come into contact with them.

The paper I read specifically said - this is NOT like asbestos where the long fibres are in the user's enviroment.

Thanks. That's what I was wondering, and your response addressed my question pretty well. Now, does anyone have any references to support any of this? Not that I don't trust you folks, I just want to see the papers too so if I hear people fretting over this, I'll be more informed and can give them proper citations as well.

 

[mgb_phys]

No sorry - it was probably linked from theregister or slashdot or somewhere.
And I can't remember the author's name - but it was available online.

 

[Mike H]

The paper is, unless I'm mistaken, an Advance Online Publication available http://www.nature.com/nnano/journal/vaop/ncurrent/abs/nnano.2008.111.html".

Craig A. Poland, Rodger Duffin, Ian Kinloch, Andrew Maynard, William A. H. Wallace, Anthony Seaton, Vicki Stone, Simon Brown, William MacNee & Ken Donaldson. "Carbon nanotubes introduced into the abdominal cavity of mice show asbestos-like pathogenicity in a pilot study." Nature Nanotechnology. doi:10.1038/nnano.2008.111

And perhaps the relevant quote from the paper on the issue that mgb_phys brought up, unless I'm mistaken...

Although the study suggests a potential link between inhalation exposure to long CNTs and mesothelioma, it remains unknown whether there will be sufficient exposure to such particles in the workplace or the environment to reach a threshold dose in the mesothelium.

 

[Moonbear]

Thanks Mike. Reading the abstract, I can see why the media is all excited about this; their final line in the abstract sounds very dire. Someday someone should explain to the media that they need to read beyond the abstract, however. On the other hand, the authors or editors should have realized such a statement right up in the abstract would sound sensational.

 

[mgb_phys]

On the other hand, the authors or editors should have realized such a statement right up in the abstract would sound sensational.

Oh I'm sure they did !

 

[Moonbear]

Oh I'm sure they did !

Yes, though media recognition is a double-edged sword if they end up misrepresenting your work.

 

[Mike H]

Someday someone should explain to the media that they need to read beyond the abstract, however.

You can lead a horse to water, but you can't make him drink...

I do think that the authors could be been a little more prudent in their abstract regarding the likelihood of reaching a critical threshold point. Of course, now the door is open to possible grant applications with "We have shown that mesotheliomas can occur due to CNT exposure, however, we need to quantify the rate of damage under expected industrial/environmental conditions. Please give us as much money as you can spare."

 

[maverick_starstrider]

Even in the absolute worse-case scenario where nano-tubes are incredibly toxic there are LOADS of applications where it's not a problem. I mean if you use their conductive properties for example you just make sure to hermetically seal the device and you're fine. Or else develop a coating or something. If people had to wear bio-hazard suits to work in areas where it's being used it still wouldn't put that much of a dent in the possible applications of nanotech.

 

[maverick_starstrider]

They just might not put it in your cereal (or in your insulation)

 

[f95toli]

This is only an issue in factories where FREE nanotubes are fabricated in large quantities(which, as far as I know, means ONE quite small factory in Japan).
In most real-world application of nanotubes the tubes will probably be grown in-situ on the chip and they will be permanently sitting there, integrated in a circuit.
It is only when studying one or maybe a few nanotubes that it is feasible to use free nanotubes dispersed in a solution as a starting point (since you can't really control where they end up on the chip), i.e. while this is still a common method in research it is not likely to be used in commercial applications.

So yes, it might be an issue in "bulk" applications of nanotubes ("ropes" etc) but in electronic applications this is simply not an issue.

I share a lab with colleagues that work with nanotubes (mainly measurements of electronic/thermal properties) but for us H&S it is simply not an issue in this case; it is highly unlikely that anyone would be able to inhale a sample(!) and even if that happened a few nanotubes would obviously not make any difference whatsoever.

Note that nanotubes are actually present in the exhaust fumes from diesel engines, meaning most of us have probably already inhaled quite a few tubes in our lifetimes.

 

[Fearless]

The paper that Mike H brought up is the one I am citing.

Of course I am with most of you that say this will not be a problem. But, technologies are not always used as they are meant (yesterday at my summerjob a guy used a knife as a key) and sometimes will be used in rather stupid ways.

CNT's are commonly used in rather mundane objects. Like sports equipment, cars (in the carbody), the materials industry and the likes. So the use is not restricted to in situ growing them on a chip or having them in a isolated cleanroom. Of course they have been around for at least as long as we have had combustion of coal. But I think they come out as rather bundled and not separated into long and short CNT's. Therefore they are much less dangerous.

The things I found interesting in the article is that Long CNT's were "dangerous" and short were not. Another thing is that they showed how the long CNT's penetrated the cells in a similar fashion to that of asbestos.

 

[mgb_phys]

CNT's are commonly used in rather mundane objects. Like sports equipment, cars (in the carbody), the materials industry and the likes. So the use is not restricted to in situ growing them on a chip or having them in a isolated cleanroom. ...
Long CNT's were "dangerous" and short were not

But when they are in materials they are bonded in a matrix (glue) in a similair way to fibreglass. The article admitted that it was only in the free form that they were dangerous and there is no practical way to get them out of the glue.
This is different to asbestos where it is very easy to release the fibres from drywall.

They are dangerous in the factory before they are mixed with the glue, but this is likely to be in carefully contolled conditions, you aren't going to have stockpiles of long tube CNTs with workers carrying shovels. This isn't just for workers health, any fine dust of a combustible material is a definite hazard - factories have been destroyed by exploding custard powder!

There is a saying in chemistry that "poison is just dose", anything is dangerous in high enough quantities, we might have to add that "size is also poison". Carbon is fairly safe as lumps of coal, is dangerous as PM2.5 from diesel smoke and now dangerous as long tube CNTs.
We are going tohave to start considering the size effects rather than just assuming that because some chemical is 'safe' in solution or as a solid lump it is necessarily safe as all forms of dust.

 

[Fearless]

I am curious as to what happens when you recycle the bulk produce that have a lot of CNT-long in them?

 

[Mike H]

I would venture that it will depend on how the materials are recycled. It could perhaps be an issue with certain methods, however, someone else will have to chime in as I'm not overly familiar with the latest in recycling technology. It could be that we might have to separate out materials with high concentrations of CNT for specialized recycling for whatever methods might be developed in the future.

 

[Moonbear]

It really sounds like the only place one might risk exposure to these long carbon nanotubes would be in an industrial setting, in which case, simply working with proper safety equipment to prevent inhalation, much as people who remove asbestos today know they need to do to protect themselves, is all that's needed to prevent health problems.

 

[K.J.Healey]

How thermally stable is a CNT? What energy is required to break the c6 bonds? (the benzene-like ring)