The Chronicle of Higher Education has a
special report on nanotechnology’s benefits and risks (subscription required). The take-home on toxicity: yep, these things seem to be toxic. The toxicity appears to be proportional to surface area, not weight. They cause cell damage and cell death, and they travel to the brain through nerves.
Kind of neat, eh? I guess that’s why the FDA approved nanoparticles for use in sunscreen in 1999 — a move criticized in the article — and why they’re already being incorporated into clothing.