The detrimental effects of modern lead exposure on human health are widely recognized. Evidence from the Roman era indicates substantial lead exposure that potentially impacted human health more than 2,000 y ago. The most significant exposure for the rural, nonelite population may have been to background air pollution from silver mining and smelting that underpinned the Roman economy. Using detailed records of Roman-era lead pollution measured in Arctic ice cores and atmospheric modeling, we show that lead emissions from these activities elevated air concentrations throughout Europe. Based on modern epidemiological studies, this air pollution enhanced childhood blood lead levels (BLLs) by about 2.4 µg/dl leading to widespread cognitive decline including an estimated 2.5-to-3 point reduction in intelligence quotient.
Rome collapsed due to the contradictions of its slave economy. In order to pay its soldiers, Rome promised them land and slaves. In order to acquire those, Rome had to conqueror more territory, which required more soldiers, who were paid with land and slaves, so Rome had to conqueror more territory…etc. etc. repeat over and over.
Eventually they resorted to the use of mercenaries. Multiple assassinations of high ranking leaders caused civil wars, instability, etc. This made them vulnerable to invasion, which is exactly what happened and the Visigoths sacked Rome. They moved the capital and continued for several hundred years, but had declined to a fraction of what they once were.
There was also a huge plague that killed a quarter of the population and a mini-ice age which decreased agricultural yields enormously and forced migration from the Eurasian steppe.
I’d make a case for environmental factors being the biggest cause of collapse rather than economic contradictions.