I remember reading (I think on this board) that all (most?) iron and/or some other metals currently produced are slightly (more) radioactive because of the A-bomb tests conducted since the 40s and that metal from ship wrecks that occurred before the 40s is retrieved and used for building less contaminated structures for certain scientific experiments.
I was discussing this yesterday with a friend and I couldn’t recall the specifics and I also got slightly suspicious - why would currently mined metals be significantly contaminated while shipwrecks wouldn’t? Is that just due to the protection provided by water? Is water that much more efficient than rock in that regard?
I can’t find the thread I first read it (if it exists at all), so any info is appreciated, even if it’s just a link.
Edit: Just looking at your question a bit more closely: Steel isn’t an element. You could, presumably, use steel that had been buried sufficiently deeply underground pre-45 as well.
I also see from that thread that it’s not merely the effects of the bomb tests, but also the shielding from cosmic rays over long periods that makes the element (lead in this case) so non-radioactive.
The cosmic rays are far more significant than human activity, and recently-mined metal will be contaminated from radioactive material in the ground. It’s only relevant for a few extremely sensitive experiments, though (mostly neutrino detectors).