Romans, Lead and IQ

Ancient Romans were surrounded by lead in daily life. It was used in water pipes, cooking utensils, cosmetics, and even as a sweetener in wine (lead acetate). We now know lead is highly toxic, damaging both body and brain. Some historians have linked chronic lead exposure to erratic or brutal behaviour among certain emperors and even to the long-term decline of the Roman Empire.

However, a recent study highlights a far more widespread and invisible source of exposure: atmospheric pollution from industrial activity[1]. This pollution reached not only city dwellers but also the large rural population across the Empire and beyond. Researchers describe it as the first major pollution event driven by human industry—occurring roughly 1,500 years before the Industrial Revolution.

To measure this, scientists analysed deep Arctic ice cores from Greenland and Russia (up to 3.3 km deep), which preserve a detailed record of atmospheric pollution from 500 BC to 600 AD. The data revealed a sharp rise in lead levels starting around 15 BC and peaking until about 180 AD — precisely during the Pax Romana, Rome’s Golden Age.

The main culprit was large-scale silver mining and smelting. Romans extracted silver from lead-rich galena ore to produce coins and other goods. For every gram of silver, roughly 10,000 grams of lead were released, much of it as toxic vapour or dust into the atmosphere. Ice-core evidence suggests the Empire emitted between 3,000 and 4,200 tons of lead per year during this period, totalling over 500,000 tons across nearly 200 years.

Atmospheric modelling shows that lead concentrations in the air exceeded 1 ng/m³ across most of Europe, with peaks near mining sites (such as the massive Rio Tinto in Andalucia, Spain) reaching up to 150 ng/m³ or more.

Using modern epidemiological data on lead exposure and child brain development, researchers estimated that this airborne pollution alone raised blood lead levels in Roman children by about 2.4 µg/dl. This level is associated with an average IQ reduction of 2.5 to 3 points across the population.

While a few IQ points may seem minor for an individual, a widespread, multi-generational drop in cognitive ability across a large empire could have had significant societal consequences — affecting innovation, decision-making, and resilience.

Two modelling scenarios were tested: one assuming most pollution came from the massive Rio Tinto mines, and another distributing emissions across multiple mining regions. Both showed similar overall effects, with the strongest impact in southern Spain and noticeable exposure extending into Gaul, Britannia, and even areas beyond direct Roman control.

Context
American children in the 1970s had much higher average blood lead levels (around 15 µg/dl) from leaded gasoline and paint, linked to roughly a 9-point IQ drop[2]. Roman exposure was lower but still substantial and chronic, affecting an entire civilization during its peak.

[1] McConnell et al: Pan-European atmospheric lead pollution, enhanced blood lead levels, and cognitive decline from Roman-era mining and smelting in Environmental in Sciences in Proceeding of the National Sciences of the USA - 2024. See here.
[2] McConnell et al: Pervasive Arctic lead pollution suggests substantial growth in medieval silver production modulated by plague, climate, and conflict in Sciences in Proceeding of the National Sciences of the USA – 2019. See here.