I can try to answer at least part of the first question.
If you take, for example, titanium dioxide, which is used in sunscreens, when you use particles that are not in the nanometric size but that are larger, you have a cream that is white. When you decrease the size of the particle to the nanometric size, that cream can become completely colourless, so from the point of view of marketing, it is extremely interesting. Then, when you look at the efficiency of intercepting UV rays, the efficiency will increase with nanoparticles as compared to with micrometric particles. So you have an increase in the efficiency and also a benefit from the point of view of marketing.
This is applied on the skin. However, you can look at, for example, toxicity in the lungs. Regarding the toxicity of titanium dioxide, when you expose rats or animals to titanium dioxide through the lungs, it is normally considered to be a rather inert particle. When you decrease the size of the titanium dioxide to nanometric size, the toxicity increases enormously.
In the U.S. about three or four years ago, NIOSH--the National Institute for Occupational Safety and Health--made recommendations that the standard for workers' exposure to titanium dioxide in the workplace be lowered from 1.5 milligrams per cubic metre down to 0.1 milligrams per cubic metre. This suggests that the toxicity of titanium dioxide would increase by a factor of 15, just due to the size of the particle. If you exposed a worker to the same mass through the lungs, you would substantially increase the toxicity.
What we find in the literature is that almost all of the particles that are in the nanometric size will be more toxic than will be the same mass of particle in micrometric size. So we have to take care of potential risks related to the size of these particles.