How Pollution in Ancient Rome Lowered IQ of Population

By Aristos Georgiou
The site of a Roman lead mine. Grass covered mounds mark the site of a Roman-era lead mine at Charterhouse in the United Kingdom. A study has shed light on how atmospheric lead exposure may have impacted health during the Roman Empire.
The site of a Roman lead mine. Grass covered mounds mark the site of a Roman-era lead mine at Charterhouse in the United Kingdom. A study has shed light on how atmospheric lead exposure may have impacted health during the Roman Empire.

Lead pollution likely led to widespread declines in IQ during the ancient Roman era, a study has found.

The negative health effects of lead exposure in modernity have been widely recognized. Over the past 150 years or so, atmospheric lead pollution has largely resulted from burning fossil fuels, particularly the ubiquitous use of leaded gasoline starting in the 1920s-a practice that has now been phased out.

But while this might seem like a distinctly modern problem, historical and archaeological evidence -such as ancient texts and skeletal remains-indicate that people living across Roman territory thousands of years ago were subjected to significant levels of atmospheric lead exposure that potentially impacted human health.

Although there were a number of lead exposure routes in antiquity, including the use of glazed tableware, paints, cosmetics and intentional ingestion, the most significant source for the non-elite, rural majority of the population may have been through background air pollution arising from the mining and smelting of silver and lead ores.

These activities, which took place on a large scale, were a significant part of the ancient Roman economy.

In the study published in Proceedings of the National Academy of Sciences, researchers used Arctic ice core records and atmospheric aerosol modeling to estimate the concentrations and potential health impact of lead pollution during the Roman era.

Ice core records are long cylinders of ice drilled from the thick ice sheets in polar regions. They essentially function as time capsules, preserving detailed information about Earth's climate and environment over hundreds of thousands of years.

The study authors analyzed three ice cores spanning the period 500 B.C. to A.D. 600, which revealed that European atmospheric lead concentrations increased sharply around 15 B.C.-following the rise of the Roman Empire-and remained relatively high until the decline of the Pax Romana, starting around A.D. 165.

The Pax Romana was a roughly 200-year period of relative peace, stability and prosperity across the Roman Empire, beginning with the rule of the first emperor Augustus in 27 B.C. and lasting until around A.D. 180.

The atmospheric lead pollution levels seen after 15 B.C. were not exceeded again until the early 2nd millennium during the High Middle Ages.

Based on modern epidemiological studies, the researchers estimated that these levels would have led to an increase in the quantity of lead in the blood of young children during the Roman era. Considering the size of this increase, the authors suggest that childhood lead exposure would have led to widespread cognitive declines of roughly 2.5-3 IQ points throughout the Empire.

Lead exposure has been associated with a range of health impacts, with even relatively low levels known to affect the cognitive development of children.

Immune system impairment has also been linked to low-level exposure. So it is "intriguing" that the destructive Antonine plague-the first great epidemic of the Roman Empire that killed an estimated 5-10 million people, or roughly 10 percent of the population-immediately followed roughly two centuries of highly elevated atmospheric lead emissions, the authors wrote in the study.

Do you have a tip on a science story that Newsweek should be covering? Do you have a question about ancient history? Let us know via science@newsweek.com.

Reference

McConnell, J. R., Chellman, N. J., Plach, A., Wensman, S. M., Plunkett, G., Stohl, A., Smith, N.-K., Vinther, B. M., Dahl-Jensen, D., Steffensen, J. P., Fritzsche, D., Camara-Brugger, S. O., McDonald, B. T., & Wilson, A. I. (2024). Pan-European atmospheric lead pollution, enhanced blood lead levels, and cognitive decline from Roman-era mining and smelting. PNAS, 121(0), e2419630121. https://doi.org/10.1073/pnas.2419630121

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Aristos Georgiou
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Aaron Moody is a sports and general reporter for the News & Observer. Here is a second sentence for the bio because it will probably be longer than this. Maybe even longer I don't know. Support my work with a digital subscription

This story was originally published January 6, 2025 at 3:00 PM