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Can Asbestos Help Us Understand Nanotoxicity?
Roland Piquepaille writes "Occupational Hazards is running an interesting article about how using our knowledge of asbestos could help us to assess the risks from nanoparticles, or their nanotoxicity. Today, it's unknown if nanomaterials under development are dangerous to human beings or to our environment. Some people think that nanoparticles can move to our lungs or our brains, presenting a significant threat to our health. Other scientists think there is no danger because we have been exposed to nanoparticles for thousands of years, such as ashes from volcanic eruptions. For example, nanotubes which are now used for many industrial developments, have similar shapes as fibers like asbestos, being long and extremely thin. And like nanomaterials today, asbestos was considered as harmless when humans were exposed to it. While the comparison has some merit, more research needs to be done before drawing any conclusion."
I'm not sure if asbestos is an appropriate analog for nano-based respiratory hazards. When Dr. Irving J. Seilkoff published his report on the link between asbestos and respiratory ailments, there was already an abundant record of impairment in the form of asbestosis. Asbestosis is a scarring and sedimentation of the lung due to particulate inhalation. It is in a general family of respiratory ailments known as pneumoconiosis. That group includes silicosis (affects quarry workers) and black lung (coal miners). The link that Seilkoff is credited with is the connection of asbestos to lung cancer, which is has only one known asbestiform species in direct connection: crocidolite. This blue amphibole was used in ship construction and in homes in and around Australia (sorry mates!). This asbestiform mineral has been directly connected to one of the most virulent forms of lung cancer, mesothelioma. This cancer of the plural lining is fatal within months of diagnosis.
Connections between other asbestiform minerals and cancer is more complex. Tremolite and serpentenite have also been linked to lung cancer, but the connection is much more tenuous. Another factor that would complicate the study of asbestos as an analog is the size: an asbestos fiber is counted for toxicological purposes only when it fits a 5:1 aspect ratio and is >5 micron in length. That is the geometry that is most likely to fit into the alveoli. This deep penetration of asbestos into the tissues of the lung is presumed to be the mechanism that leads to cancer. Plaques form around the embedded spines of asbestos as microphages attack and envelope the fibers. This process leads to a general lessening of the effective surface area for gas transfer leading to shortness of breath. The mechanics leading to cancer, however, are dubious and have plagued researchers for more than two decades.
I can't see how the study of asbestos can illuminate any area of occupational health. I can, however, see how injury claims attorneys would use the experience of asbestos litigation in any future attack on the nano-industry.
"Rocky Rococo, at your cervix!"
The real question comes in why asbestos causes harm. Is the the morphology (shape) of it that is the key? Or is it the chemical properties? Or is it both?
I must plead my ignorance when I say I don't know if that question has been fully answered yet. I do know that from certain Taconite mining operations they have found non-asbestos minerals that have a similar shape to asbestos, and have found higher rates of rare cancers, of the kind known that asbestos can cause, in the region around the mines. That might suggest the shape itself is important. You can find an example in this article.
If I recall coreectly, people working on the space elevator (Lawrence Livermore Labs) were creating long strings of bucky balls (carbon nanotubes) as it is a very strong, very light material. The problem that they discovered (this was a few years ago) was that if you put 0.5 parts per billion of buckyballs into a fish tank (500 gallon aquarium), within 3 days, 20% of the fish start exhibiting signs of mental retardation. Within 5 days, the number soars to 80%, accompanied by 10% of the most severely affected fish dying. Within one week, all of the fish are either showing signs of extreme mental retardation, or have died. The part that they found most troubling was that if predatory fish ate those dead or dying fish, then they too would experience the same symptoms, and die in exactly the same way and in the same length of time. Preliminary disections showed that the carbon nanotubes could get past the membrane that surrounds the brain. Once they got in, they tended to cause severe damage to the brain. At least one report is here: http://www.newscientist.com/article.ns?id=dn4825
That study is somewhat old hat. Have a look here and you'll see that the mechanism is now understood.
:v)
In short, you can make toxic, or non-toxic buckyballs. The more bits you dangle on the outside of the buckyballs, the less toxic they become. Nanomachine designers will be aware of this and act accordingly.
Vik
You seem to be under the impression that we have stopped using asbestos (and asbestos related minerals) as a fire resistant material. You see those shingles on your roof? Asbestos. You see those ceiling tiles in your office? Asbestos.
My friend works for an asbestos testing lab. On a trip to home depot he pointed out dozens of building materials with a "Warning: This contains xxxxxxx" where xxxxxxx is some mineral that has the exact same properties as asbestos, and sometimes is just asbestos, but with a confusing name.
So why do we still use it if we know of the dangers? It's because it works. One of the easiest ways to test for asbestos fibers in a sample is to burn it at a very high temperature and see if anything is left. Asbestos and related minerals are almost impervious to fire. Manufacturers have gotten around various bans by using it in small quantities and with other, non-banned, minerals that have the exact same properties, bad and good.
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