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

In ancient Rome, lead was widely used in glazed table wares, paints, cosmetics, and was intentionally ingested as well as being present in air pollution from mining and smelting.

"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."