Scientists solve the mystery of the widespread plunge in IQ across Europe 2,000 years ago

It was one of the most technologically advanced empires in history.

But the Romans may have been battling with cognitive decline due to pollution, according to a study.

Researchers suggest that widespread lead pollution – caused by mining – lowered the IQ of essentially the entire European population at the time.

For their study the team, from the Desert Research Institute in Nevada, examined ice cores – columns of ice up to 3,400m long that are extracted using enormous drills.

Gas bubbles trapped in the ice offer insights into the atmosphere of past eras, while the presence of pollutants such as lead can be used to indicate industrial activity.

Analysis of three ice cores revealed that European lead emissions sharply increased around 15 BCE following the rise of the Roman empire.

They remained high for around 150 years until the Empire began to decline.

By combining their findings with current research linking lead exposure to cognitive decline, the scientists estimated lead pollution during this time would have resulting in an average increase in childhood blood levels of around 2.5 micrograms per deciliter.

For their study the team, from the Desert Research Institute in Nevada, examined ice cores – columns of ice up to 3,400m long that are extracted using enormous drills

An, as a result, this would have led to widespread cognitive declines of 2 to 3 IQ points throughout the Roman empire.

‘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,’ Joe McConnell, lead author of the study, said.

‘The idea that we can do this for 2,000 years ago is pretty novel and exciting.’

Ancient lead pollution stemmed largely from silver mining, when the lead-rich mineral galena was melted down to extract silver.

Much of this lead was then released into the atmosphere.

In adults, high levels of lead exposure are linked to infertility, anaemia, memory loss, cardiovascular disease, cancer and reduced immune response.

Meanwhile among children, even low levels of exposure have been associated with reduced IQ, concentration challenges and reduced academic success.

‘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 said.

Gas bubbles trapped in the ice offer insights into the atmosphere of past eras, while the presence of pollutants such as lead can be used to indicate industrial activity

By combining their findings with current research linking lead exposure to cognitive decline, the scientists estimated lead pollution during this time would have resulting in an average increase in childhood blood levels of around 2.5 micrograms per deciliter. Pictured: Grass covered mounds mark the site of the Roman-era lead mine at Charterhouse on Mendip

‘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.’

Although ice core records show that Arctic lead pollution was 40-fold higher in the early 1970s – at its peak – the study reveals how ‘humans have been impacting their health for thousands of years through industrial activity’, the team said.

Their findings were published in the Proceedings of the National Academy of Sciences (PNAS).