You are very correct on Plutonium. It is the most lethal substance known. Anything inhaled destroys the lungs.
BS. It's a low level, long life (very long life), alpha emitter.
You have stuff under your sink right now that is far more 'lethal' than plutonium.
Don't buy the crap the eco-commies feed you. Plutonium is a nasty and we should do all we can to keep it out of the environment, but it is far -- very far -- from being the most "lethal substance known."