Natural lead occurs along with small amounts of uranium and thorium. These radioactive atoms have radioactive lead isotopes in their decay products. So natural

Natural lead occurs along with small amounts of uranium and thorium. These radioactive atoms have radioactive lead isotopes in their decay products. So natural lead is constantly replenishing its levels of radioactive isotopes. When lead is mined, it is separated from the uranium and thorium, so no new radioactive isotopes are produced. You just have to wait for the radioactive lead present to decay. This can take 2000 years evidently.