Comment by leonidasrup

The man-made radioactive isotope caesium-137 can be detected in the bodies of all living humans and it was there even before the Chernobyl accident. The first nuclear explosion in 1945 spread, for the first time, the isotope caesium-137 over the whole planet. We have so sensitive methods of detecting caesium-137 that we can use them to check if a bottle of wine was produces before 1945

https://www.npr.org/sections/thesalt/2014/06/03/318241738/ho...

Of-course there were radionuclides in our bodies even before the first nuclear test in 1945. For example Potassium-40 or Carbon-14. The presence of Carbon-14 in organic matter is the basis of the radiocarbon dating method to date archaeological, geological and hydrogeological samples.

The big question is how much radionuclides is safe and how much radionuclides is a health risk.

https://en.wikipedia.org/wiki/Dose%E2%80%93response_relation...

https://en.wikipedia.org/wiki/Radiation_dose