https://phys.org/news/2018-05-earliest-evidence-pollution-balkans-bc.html

We already knew about these Bronze Age Balkans from patchy archaeological records of axes, adzes and beads. But we are now able to learn more about them thanks to traces of pollution they left behind.

Metal is extracted from its ore through a process known as smelting. This releases microscopic particles of lead into the atmosphere, which are then transported long distances by winds until they settle on the ground.