The isotope in question (Lead-210) is indeed a decay product of Uranium-238. However, not all lead is Pb-210, most of it is made of other, stable isotopes. Sin

The isotope in question (Lead-210) is indeed a decay product of Uranium-238. However, not all lead is Pb-210, most of it is made of other, stable isotopes. Since mining and refining lead removes the U-238 that would decay into more Pb-210, if you wait long enough (and shield it underwater), you get almost radiation-free lead, as the Pb-210 existing at the time of mining/refining eventually decays into non-radioactive Pb-206.