Though much of the concern about nanotechnology is hype, there is one thing that causes concern which might be real. This is the similarity of some small features to asbestos fibres. Nanotubes could be like this. There is some US work which is relevant, though unconfirmed. It means that those making the tubes should take precautions.
Not my field, but I came across the research when looking at nanotechnology
possibilities for a large company.