From the article:

"The indications are that as particles get small, they become much more chemically reactive and, therefore, possibly much more toxic," said Dr. C. Vyvyan Howard, toxico-pathologist at the University of Liverpool and co-organizer of the conference.

I hope that this alludes to more than merely the geometric fact that as the size of particles decreases, the number of surface molecules per unit mass increases. That wouldn't qualify as a world-shattering insight.

Or, does reactivity rise further through uncovering more sites on each surface molecule when the notional geometric curvature of the surface increases as the particle diameter decreases? In the limit the particle will be a single molecule with all its reactive sites exposed. However, surface curvature doesn't increase very rapidly until particles sizes start to approach that limit.

It's worth noting that mechanochemical tools can use the latter effect to hide the reactivity of tool tips, by using negative surface curvature to expose little or no reactive sites at all until required. That's just another way of looking at sheathing, a role in which nanotubes will probably feature greatly.