From an informative graphic novel "Trinity: A Graphic History of The First Atomic Bomb" by Jonathan Fetter-Vorm, I discovered that due to the frequent testings of atomic bombs in Nevada in the 1950s and 1960s,
each of our bodies [especially those who live in the U.S. and surrounding countries - ed.] contains some amount of radioactive material, lingering trace of atomic testing.
When I read that, I said to myself...damn, I thought traces of radioactive materials do exist in nature?
But then again, further research on the topic concludes that the plutonium traces from those Nevada testings are significantly less than the exposure we get from regular sunlight, or the Radon we get from being in a basement/enclosed car park.
Hence our radioactive world.