Lead pollution in the air impacted all ancient Romans

Ancient Rome thrived during the 200 years of peace known as Pax Romana, which occurred over the first and second centuries of the Common Era. But an unknown enemy poisoned nearly everyone in the empire. Lead air pollution spiked during this time and resulted in elevated blood lead levels and cognitive decline, a new study shows (Proc. Natl. Acad. Sci. 2024, DOI: 10.1073/pnas.2419630121).

Ancient Romans used lead in water pipes, utensils, and cosmetics. They even used it to sweeten wine. Those uses affected the elite in cities. But the rural majority was exposed to lead emissions from the smelting of lead-silver ores to make silver coins, says Joseph R. McConnell, a climate and environmental scientist at the Desert Research Institute. He and colleagues wanted to measure lead pollution across Europe and its consequences for health. “Our goal was to measure lead exposure for everybody,” he says.

The researchers first took measurements of lead deposited in three Arctic ice cores every year between 500 BCE and 600 CE using techniques they have reported before. They found that lead emissions shot up around 15 BCE, soon after the rise of the Roman Empire, and dipped around 165–180 CE with the end of Pax Romana.

The scientists then used atmospheric models to estimate that the Arctic deposits resulted from lead concentrations in air of about 150 ng/m³ near known Roman mining and metallurgy sites, the main sources of lead pollution in the world at the time. That in turn led to average lead concentrations of over 1.0 ng/m³ in the atmosphere above Europe. Finally, the team used modern epidemiological methods to translate those air concentrations to blood lead levels in children of about 2.4 μg/dl, which most likely resulted in a 2.5–3 point reduction in IQ. Today, levels below 1 μg/dl are considered safe.

Humans have faced higher levels of lead in recent times. Concentrations of the metal in both air and human blood in North America and Europe in the 1970s were over three times what the researchers estimated they were during Pax Romana. But “the idea that 2,000 years ago human industry was causing a third of the impact of the modern industrial era is pretty surprising,” McConnell says.

Bruce Lanphear, a health sciences professor at Simon Fraser University, calls this study novel for connecting the dots from lead pollution to cognitive deficits. “This study and other evidence indicate that people who minimized the contribution of lead poisoning to the decline of the Roman empire need to revisit the evidence on low-level lead poisoning.”