[Sprool]

In our industry, anything nano is now suddently considered suspect, like the bubble has burst, our enthusiasm for new emerging nanotech industry to cure world problems has waned, everyone realises its just tiny stuff and now theres poor science journalism running smear campaigns on nanoparticles for cosmetics use, sunscreens, etc. Is there a risk or is it just scaremongering?

[damocles]

A smear campaign regarding cosmetics use and sunscreens? Isn't language a strange thing!

To seriously address the original post though: I think that there is a significant risk, but one that can and should be routinely addressed. I do not think it appropriate that 'nano-' should become a 'dirty word' to be avoided at all costs.

Taking a hypothetical example for illustration: zinc oxide and coconut oil are both fairly innoccuous materials. A normal paste or slurry of these two materials could be prepared, and it could safely be assumed that the MSDS sheet descriptions of the two individual materials would combine to cover this new preparation.

But if the zinc oxide particles in a dispersion were at the nanoscale -- perhaps if more than 10% had a particle size below 0.5 µm -- this could no longer be assumed.
(1) The tiny particles of zinc oxide might pass through pores or filters that would block the passage of larger particles.
(2) For larger particles, the contact area with another phase or material is relatively small, and surface effects produce a minor perturbation of the properties. With nanoparticles, contact areas become huge, and tend to dominate the properties of the material.

So in my view a separate MSDS evaluation is needed for any nanoparticle based material or mixture. But that does not imply any greater hazard than is involved with the deployment of any new material.

[evan_au]

Asbestos fibres tend to split longitudinally to create nanoscale-wide spears that cannot be broken down by the body's defences, and can cause mesothelioma, especially to people with workplace exposure.
This "nano" is a definite "no-no".
Depending on the application, carbon nanotubes may come as long tubes ("long" compared to the size of a cell), and so there is some geometrical similarity to asbestos, but the chemical behaviour in the body is radically different, and environmental breakdown processes will be quite different. Carbon nanotubes should be separately assessed for health hazards, and not grouped with "asbestos". It may be considered "safe" as long as it is in a form that cannot be ingested.

Every nanomaterial should be considered on its own merits - perhaps to the extent of determining at what scale the behaviour deviates significantly from the Material Safety Data Sheet (MSDS) for the "macroscale" material.