Yeah, it's rare. Probably was never really in the food system. Well no more than gold or silver. Not a good idea to ingest heavy metals. They have a higher cross-section and so interact with the background radiation more than most of the material in you body. The interaction creates free radicals which is was actually do the molecular damage in your body. Radiation damage is an indirect thing.
As a caveat it's more than 15 years since I've studied this stuff, but I think I remember a few of the basic.
It's also used in the electronics industry for some IR detectors (InGaAs detectors).
