Plutonium is an alpha emitter, which means it will only harm you if particles are inhaled, ingested or embedded in you. Alpha radiation only travels about an inch and can be stopped by paper or skin. Gamma radiation is the bad stuff, it can pass through several feet of concrete shielding and kill you after only a few minutes of exposure to high levels. While I don't know what else they might put in a bomb to make it more efficient, nothing can be very radioactive because otherwise you wouldn't have a bomb after a short period of time.

A fizzle is possible, where the bomb almost but not quite makes it to a nuclear blast. This would produce a lot of radiation and radioactive material. But a full out misfire wouldn't rain much that was very dangerous around. And it might just go ahead and bury itself which would solve to problem pretty completely.