Et tu, Plumbum? Then Fall, Caesar’s IQ!

Lead is a very, very bad thing to be exposed to. Children poisoned by lead suffer permanent negative health impacts, particularly with regards to development of the central nervous system, while lead exposure in adults can lead to high blood pressure, cardiovascular disease, and kidney damage. Leaded gasoline blighted an entire generation of children in the 1960s and 1970s, costing those born during those years an average 6 or 7 IQ points. Fortunately, with the banning of leaded gasoline in 1996, children now only have microplastics to stunt their intellectual development.

One might imagine that lead poisoning is a modern-day problem, a result of the Industrial Revolution and internal combustion engines. But that’s not the case. Despite physicians of the era recognizing lead as a poison and documenting cases of lead poisoning, it was very prevalent during the age of both the Roman Republic and Empire. A popular theory in the 1980s even posited that Rome’s fall could be directly linked to lead exposure.  

That hypothesis has been largely debunked, but ancient Romans were undeniably exposed to large amounts of lead, and a recent study published in PNAS has been able to quantify both how much lead the Roman civilization poured out and what the cognitive effects of so much lead pollution were. To do this, they analyzed cores of ice from places like Greenland and Antarctica, where atmospheric lead has settled among the slowly building glaciers. These cores, some as long as 11,000 feet, contain records of atmospheric anomalies stretching back eons. 

For a pre-industrial civilization, the Romans were exceptionally skilled at pouring lead over the course of their thousand-year history, mostly as a byproduct of large-scale silver mining all over the empire. Galena, the mineral the Romans pulled silver from, also contains lead, so much so that for every ounce of silver they extracted, a thousand ounces of lead were released into the atmosphere. 

While the atmospheric lead concentrations during Roman times were a fortieth of what was reached during the 1970s, the Romans still managed to release over 500 kilotons of lead into the atmosphere during the 200-year Pax Romana at the start of the first millennium AD. This was enough to raise childhood blood lead levels by 2.4 mcg/dL — today, 3.5 mcg/dL is enough to necessitate medical intervention — and reduce the average IQ of the European population at the time by 2-3 points. 

That “doesn't sound like much, but when you apply that to essentially the entire European population, it's kind of a big deal,” study coauthor Nathan Chellman of the Desert Research Institute in Nevada said in a press release. Indeed, with a bit less lead in the air, perhaps Caesar could have had the foresight to see that knife coming.