A curious thing about PU, people exposed at Los Almos were carefully monitored for long term health effects. It was called the " I pee PU club" after frequent urine testing. Everyone in it had ingested PU, but for a substance reputed so deadly there was a puzzling lack of late life cancers the stuff they expected just never showed up.
Thats a good reason not to thing in a 1 gram of PU dirty bomb as anything but a distraction.