[js1138]

Plutonium burns. Mix chunks with a high-temperature combustant like thermite and you might get plutonium-oxide soot wafting into the atmosphere

I'm just guessing, but based on plutonium's mass, I don't think it would waft very far. So far, Anthrax seems to have gotten the most terror for the buck, in terms of disruption of everyday life.

[Poohbah]

I'm just guessing, but based on plutonium's mass, I don't think it would waft very far.

Far enough. Plutonium oxide can be a VERY fine dust--most of the Savannah River MUF is plutonium that ain't EVER getting out of the plumbing.