That's why they discuss hydrology: if the stuff goes into drinking water, then oops. IIRC Litvinenko was killed with something like 10^-4 g (hundred micrograms

That's why they discuss hydrology: if the stuff goes into drinking water, then oops. IIRC Litvinenko was killed with something like 10^-4 g (hundred micrograms) of polonium-210 added to his food. That stuff is quite active (half life of less than half a year), but still.