Atmospheric lead pollution likely caused cognitive decline among citizens of the Roman Empire, according to research published Monday in the Proceedings of the National Academy of Sciences.
Researchers analyzed ice core records for an approximately thousand-year period corresponding roughly with the period from the Roman Republic through the decline of the Empire, focusing on the two-century period known as the Pax Romana. They used computer modeling of lead in the atmosphere to estimate atmospheric levels across the European continent, hypothesizing that IQ levels fell two to three points in Europe.
Research has long shown a link between lead exposure and cognitive decline, particularly in low-income areas where lead infrastructure has yet to be replaced. However, researchers said the study is the first to extrapolate effects on populations from thousands of years ago.
“This is the first study to take a pollution record from an ice core and invert it to get atmospheric concentrations of pollution and then assess human impacts,” lead author Joe McConnell, a research professor of hydrology at Nevada’s Desert Research Institute (DRI), said in a statement. “The idea that we can do this for 2,000 years ago is pretty novel and exciting.”
Unlike the 20th century, when lead poisoning was primarily due to exposure to leaded gasoline fumes, Roman-era lead exposure was predominantly a byproduct of silver mining. The mining and smelting process involved melting down galena, an ore of lead that produced thousands of ounces of lead during the process.
“Lead is known to have a wide range of human health impacts, but we chose to focus on cognitive decline because it’s something we can put a number on,” co-author Nathan Chellman, an assistant research professor of snow and ice hydrology at DRI, said in a statement. “An IQ reduction of 2 to 3 points doesn’t sound like much, but when you apply that to essentially the entire European population, it’s kind of a big deal.”
