By context, surely the page about flowers that you linked can be assumed to be the Cardamine flower I was talking about? Guess not.
Malta Cardamine is a plant (razor-blade grass) but the 'active ingredient' is a gas. It would slowly spread into the atmosphere from the fields (and then into the food, water, animals etc.), but can be actively synthesised into a concentrated gas that they used in space and... for ODing with, early on. How would it seep into the air if it was just a powder? Rebreather masks work a lot better when you can actually breathe through them.
It's stupid, but that's how it is.
