I'll go down this rabbit hole for you because I was also curious.

https://www.scientificamerican.com/article/ancient-roman-lead-physics-archaeology-controversy/

All lead mined on Earth naturally contains some amount of the radioactive element uranium 235, which decays, over time, into another radioactive element, a version of lead called lead 210. When lead ore is first processed, it is purified and most of the uranium is removed. Whatever lead 210 is already present begins to break down, with half of it decaying on average every 22 years. In Roman lead almost all of the lead 210 has already decayed, whereas in lead mined today, it is just beginning to decay. (Of course, many lead 210 atoms have already decayed in this ore, too, but the supply is constantly replenished by uranium in unprocessed lead). "The longer since it was originally processed, the lower its intrinsic radioactivity," Gonzalez-Zalba says.