Lead Pollution in the Roman Empire

Air pollution has been impacting human health for more than 2,000 years, according to a study published this month in the Proceedings of the National Academy of Sciences. The study indicates that silver mining and smelting in the ancient Roman Empire caused harmful amounts of lead pollution in the air. The neurotoxin released into the atmosphere during the mining process was significant enough to lower Romans’ intelligence. 

To gather their data, the researchers analyzed the composition of Arctic ice cores preserved from ancient times. They discovered that as Roman smelting was occurring, the amount of lead deposited in the Arctic ice spiked. During the midst of Roman silver production, air currents carried the lead particles across Europe. The researchers estimate that 6 to 9 million pounds of lead pollution were being released each year and that blood lead levels among children probably increased by 2 to 5 micrograms per deciliter. 

The Effects on IQ

The authors estimate that the exposure was enough to reduce the typical IQ by up to 3 points across the empire, making Rome’s Pax Romana (its roughly 200-year golden age) one of the earliest examples of industrial pollution harming human health. 

Sadly, it’s far from the last.

During the peak era of leaded gasoline in the United States (from the late 1960s to early 1980s), lead pollution was so heavy that the average level for a child was about 15 micrograms of lead per deciliter of blood, which corresponded to a decline in IQ of 9 points. (Fortunately, the level of airborne lead in America has decreased rapidly since then.)

According to a Washington Post article about the study, the findings could add fuel to a long-standing debate about whether mass lead poisoning could have contributed to the fall of the Roman Empire.

 A version of this article appears in the March 2025 issue of The Numismatist (money.org).