It was during the period known as the Pax Romana, a time of stability in the Roman Empire that lasted for about two hundred years between 27 BC and 192 AD. Mining and smelting operations throughout Europe were likely a a source of lead contamination,

Researchers measured lead pollution and its impact on human health through Arctic ice-core samples. View on euronews

The mass production of silver coins in the Roman Empire had an unintended effect: spewing so much lead into the atmosphere that it may have lowered citizens’ IQs.

"A 2 to 3 points lower IQ doesn't sound like much, but when you apply that to the entire European population, it's quite a lot."