When I worked at Brookhaven National Lab, the sewer system had radiation detectors in it, to ensure there was no improper disposal of radioactive stuff. It was said that it was sensitive enough to detect someone flushing a banana down the toilet.
The Assistant Director of the lab at the time, had had a radionuclide angiography, and I guess the radio marker is emitted in the urine, because he claimed to have set the alarms off after coming back to the lab post-procedure.
Possibly apocryphal story that supports the assertions of BED, I read somewhere long ago that the Monticello nuclear power plant sheds less radioactive stuff into the Mississippi river than the water treatment plant 100 miles downriver at Pigs Eye in St. Paul because of flushed medical diagnostic residues.
Off topic: around the same time I read that there's a statistically significant difference (a rise) in the level of caffeine in the Mississippi as measured above and below the Twin Cities.
The Assistant Director of the lab at the time, had had a radionuclide angiography, and I guess the radio marker is emitted in the urine, because he claimed to have set the alarms off after coming back to the lab post-procedure.