Apart from sanitation, medicines, education, wine, public order, irrigation, roads, the fresh water system and public health, what did the Romans ever do for us? asks an exasperated Reg in Monty Python’s Life of Brian.
One answer, according to a new study, is widespread cognitive decline across Europe, courtesy of the vast quantities of lead pollution churned out by the booming metals industry that shaped the empire.
Researchers have said the massive expansion of mining and the processing of metal ores in particular caused airborne lead pollution to soar during the peak of the empire, leading to an estimated 2- to 3-point drop in IQ across the land.
“It’s amazing that we were able to quantify atmospheric air pollution over Europe nearly 2,000 years ago and assess potential health impacts on the ancient Roman civilisation,” said Dr Joseph McConnell at the Desert Research Institute in Nevada.
“Our findings demonstrate that anthropogenic emissions from industrial activities have resulted in widespread damage to human health for over two millennia, which is pretty profound in my view,” he added.
Roman physicians were aware of the dangers of lead poisoning, but the metal was still widely used for water pipes and cooking pots and found its way into medicines, cosmetics and toys. The metal was also ingested on purpose after Romans discovered that lead-containing syrups helped to preserve and sweeten wine.
While lead poisoning through contaminated food and wine were more likely to be concerns for the upper classes, the entire population would have inhaled airborne lead produced from the empire’s huge mines and smelting operations, with lead being a byproduct of silver and gold refineries.
To track levels of airborne lead pollution back through Roman times, McConnell and an international team of researchers analysed ice cores drilled from the Arctic. The cores provided a timeline of atmospheric lead concentrations from 500BC to AD600.
Writing in Proceedings of the National Academy of Sciences, the researchers describe how the ice cores revealed a sharp increase in lead pollution around 15BC after the rise of the Roman empire. The levels then remained high until the decline of the Pax Romana, a 200-year stretch of relative peace and prosperity that ended in AD180. Over the period, McConnell estimates that the empire released more than half a million tonnes of lead into the atmosphere.
To work out what impact the pollution might have had, the scientists turned to atmospheric models to map how the lead would have spread across Europe. They then drew on modern studies to calculate how much of the neurotoxic metal would have built up in children and the impact it might have had on their IQ.
On average, lead levels in children’s blood at the peak of the Roman empire could have risen 2.4 micrograms per decilitre, the researchers found, reducing their IQ by 2.5 to 3 points. When taking background lead into account, childhood blood levels may have reached about 3.5 micrograms per decilitre.
By some estimates, the Roman empire amounted to more than 80 million people at its peak, meaning that about a quarter of the world’s population could have been exposed to the lead pollution generated by mining and smelting. The effects of lead poisoning can be so severe that scholars have debated whether it contributed to the fall of the empire.
“A 2.5- to3-point reduction in IQ may not sound like much but it was across the entire population and would have persisted for the nearly 180 years of the Pax Romana,” McConnell said. “I leave it to epidemiologists, ancient historians, and archaeologists to determine if the levels of background atmospheric lead pollution and health impacts we have identified … were sufficient to change history.”
While airborne lead pollution fell after the Roman empire, it rose again in the high middle ages and soared in the 20th century with the Industrial Revolution and the burning of fossil fuels, including leaded fuels for vehicles. A 2021 study by the Centers for Disease Control and Prevention in the US found blood levels in children aged one to five years fell from 15.2 to 0.83 micrograms per decilitre between the late 1970s and 2016 as leaded fuels were banned.