If the nanotubes break of and form dust, it would have health issues similar to asbestos dust. No company would dare to make or use them for fear of lawsuits. The trial lawyers would salivate at that prospect.
Asbestos is particularly harmful (some species) because they have fishhook-type barbs that attach to the bronchial walls at the bottom of lungs and irritate the lining with the resultant scarring and death of the wall and cilia
Ordinary dust causes a condition characterized as silicosis.