Ever since humans first started refining metals – roughly 5,000 years ago – people have been unknowingly breathing, ingesting, and absorbing tiny particles of lead byproducts into their bodies.
A careful analysis of ancient human remains, buried at a site in Rome used continuously for more than 12,000 years and another site on the island of Sardinia has now revealed a close link between lead pollution and our history of mining and smelting.
In fact, researchers say the ebbs and flows of worldwide lead production are apparent in the very bones of people laid to rest in central Italy. Some who weren't even remotely involved in local mining or smelting still showed evidence of lead particles in their bodies.
From the start, the pollutant appears to have spread so quickly through the environment, all Romans needed to do was breathe the air, drink the water, and eat the local food to have the heavy metal gradually build up in their livers, kidneys, and bones.
"This documentation of lead pollution throughout human history indicates that, remarkably, much of the estimated dynamics in lead production is replicated in human exposure," explains geologist Yigal Erels from the Hebrew University of Jerusalem in Israel.
"Simply put: the more lead we produce, the more people are likely to be absorbing it into their bodies. This has a highly toxic effect."
Nearly every system in the human body can be poisoned by lead. Even at low levels, the heavy metal can be harmful, accumulating over time and potentially causing neurocognitive issues, organ damage, and reproductive issues in the long run.
The Romans actually knew this, but silver, gold, and even lead itself were simply too useful for them to ignore. They built their very plumbing with lead, delivering the heavy metal straight to their populace, despite some miners going mad or even dying due to exposure.
Still, it wasn't until coin production began roughly 2,500 years ago that the production of lead really took off in Roman society.
Careful analysis of ice from glaciers and soil from lakes suggests this is when lead pollution truly began to spread among the locals. Ancient human remains from Italy now also reflect that timeline.
Analyzing the bones of 132 individuals buried in Italy between 12,000 BCE and the 17th century, researchers have found a rise in lead pollution that closely matches worldwide lead production.
When Romans first began mining for lead and smelting it, the remains showed a clear rise in the ratio of lead to calcium found in their bones. When coins started to be produced, roughly 2,500 years ago, there was an even steeper increase in the concentration of lead found within the human remains.
Previous research has estimated lead production increased from the dawn of metallurgy to the height of the Roman Empire about fourfold. During this same stretch of time, the current study found the concentration of lead in human bones increased by 4,000 fold.
Only in the late Medieval Period did lead rates begin to decline, although by a thousand years ago, lead pollution was on the rise again, thanks to silver mining in Germany and the discovery of the New World's riches.
This time around, the rise in lead pollution among bodies in Italy was not quite so dramatic, possibly because lead production had shifted out of Europe into more remote parts of the world.
Even still, it was obvious to the researchers studying the burial site that there had been an increase in worldwide production of lead sometime in the last millennium.
The findings from history are a warning for the future. In much more recent years, lead production has fallen ever so slightly, but the demand for heavy metals, in general, is on the rise.
By 2050, some estimates predict there will be a more than 1,000 percent increase in the demand for lead, cobalt, and nickel, as demand for electronics, batteries, solar panels, and wind turbines grows to help us limit runaway climate change.
"This raises the concern that the current increasing use of several toxic metals (including lead) in electronic devices and the transition to low-carbon energy production may soon be reflected in elevated concentrations of these metals in humans, predominantly in those that are not fortunate enough to live in regulated and monitored regions," the authors conclude.
In 2017, for instance, the Institute for Health Metrics and Evaluation (IHME) estimated that lead exposure was responsible for more than 1 million deaths and nearly 25 million years of healthy life lost around the world. Low- and middle-income countries were by far the most exposed, carrying the highest health risks.
Children in these nations are especially vulnerable to heavy metals. Research suggests young humans absorb four to five times as much ingested lead as an adult, and because their bodies are still growing, the accumulating pollutant can have severe developmental impacts.
Already, a third of children worldwide have unhealthy levels of lead flowing through their blood. If the production of this heavy metal increases, the pollutant will no doubt accumulate to an even greater degree in the next generation.
"The close relationship between lead production rates and lead concentrations in humans in the past, suggests that without proper regulation we will continue to experience the damaging health impacts of toxic metals contamination," warns Erel.
History tells us it is so.