I have to disagree. Just having nanotubes flying around your blood stream could probably lead to cirrhosis as the nanotubes of a certain length or more would get trapped inside the liver, causing scaring and damage ( http://www.ncbi.nlm.nih.gov/pubmed/19801780) similar to how miners can get miner's lung (http://en.wikipedia.org/wiki/Pneumoconiosis).

Ultimately it depends on what form the nanotubes are in, but I don't want them just going nilly-willy around an environment.