The presence of lead in things like gasoline and paint up until the 1970s presented a bevy of problems for Americans, not the least of which is a drop in IQ that studies have documented over the years. A new study by an international group of researchers found that lower IQs linked to lead exposure isn’t a new phenomenon and actually dates back to the time of the ancient Romans.
The study, published Jan. 6 in the Proceedings of the National Academy of Sciences journal, examined ice samples from Greenland that contained lead particles that blew over from the European continent during the Pax Romana period between 27 B.C.E. to 180 C.E. They found that average lead exposure in the Roman Empire was approximately one-third what it was in the United States in the 1970s before the Clean Air Act when leaded gasoline use was at its peak.
“Human or industrial activities 2,000 years ago were already having continental-scale impacts on human health,” study lead author Joe McConnell told NBC News. “Roman-era lead pollution is the earliest unambiguous example of human impacts on the environment.”
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It all has to do with how the Romans made their currency. Smelting silver for coins released lead that would attach to dust particles in the atmosphere, some of which eventually made its way to Greenland.
“For every ounce of silver you might produce, you might produce 10,000 ounces of lead,” McConnell explained. “As you’re producing silver, the Romans were smelting and mining silver for their coinage, for their economy, and they were introducing a lot of lead into the atmosphere.”
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The lead exposure was so bad, the study found, that it likely lowered the average person’s IQ by 2.5 to 3 points. This is in line with other studies that have found a link between lead exposure and lower IQ, including a 2022 study that found an average lower IQ of 2.6 points among Americans exposed to lead in childhood. Overall, ancient Romans were exposed to roughly twice the lead levels that American children are today.
If you’re concerned about lead in your house, consider buying a lead detector kit to examine all your items.