There is a safe radiation dose, because all living beings concentrate in them several radioactive isotopes (14C, 40K, 48Ca), so they are more radioactive than t

There is a safe radiation dose, because all living beings concentrate in them several radioactive isotopes (14C, 40K, 48Ca), so they are more radioactive than the environment. Also, for example I have a dental bridge made of platinum-gold alloy and dental crowns made of zirconia ceramic. Platinum is one of the most radioactive natural elements after uranium and thorium, while any piece of zirconia also contains radioactive isotopes of zirconium and hafnium. Despite this, the people who wear platinum jewelry are not worried (though perhaps that is due more to ignorance than to rational risk assessment, since those who sell platinum jewelry do not advertise them as being radioactive). Because the living beings have evolved in a radioactive environment (and the radioactivity of the environment was many times higher in the past, before most of the potassium 40 decayed) all have mechanisms for repairing the damage caused by radiation. The efficiency of the repair mechanisms vary a lot between different living beings, but all of them can withstand the relatively low radioactivity levels of most environments on Earth.