When did humans start choking themselves with atmospheric lead? Common wisdom has it that lead levels rose dramatically during the Industrial Revolution of the 1700s and 1800s, when a boom in factories and other industrial processes began pumping pollution up into the skies. But that assumption could be wrong.
As Nicola Davis reports for The Guardian, new research using ice cores and historical data suggests that humans may have polluted the atmosphere for much longer than previously thought. Researchers detail their findings in a paper published this week in the journal GeoHealth.
Glacial ice acts like a kind of historical record, capturing lead levels from the atmosphere over time in thin layers like rings on a tree. The team used new technology to track these changes back some 2000 years, plotting out the tiny variations from year to year.
The results of this analysis suggest that lead levels have been remarkably high throughout the entire 2000-year period studied. The only time lead levels dropped to what the researchers believe are the "natural" background levels occurred between 1349 and 1353. During this time, the Black Death pandemic ravaged Europe, killing at least 25 million people—an estimated 60 percent of the entire European population—and completely disrupted daily life.
This discovery suggests three things: The higher lead levels before and after were human-caused; humans have been polluting the atmosphere for way longer than scientists assumed; and past lead levels, which scientists assumed were due to natural, “background” levels of lead, actually reflected pollution that was anything but natural.
Based on their analysis of historical records, the team suggests that the source of this ancient pollution was likely smelting and mining in Britain—an ocean away from the ice's origin in the Colle Gnifetti glacier in the Swiss-Italian Alps. Lead mining has been taking place since the Iron Age, and archaeological evidence shows that it picked up speed during the Roman occupation of Britain.
The team also found other drops in lead levels related to epidemics and economic slowdowns. And they’re still studying the ice cores to figure out what additional secrets it might hold.
“We have basically been poisoning ourselves for about 2,000 years,” Alexander More, a historian and scientists who co-authored the paper, tells Davis. Lead is unsafe to humans in any concentration, particularly affecting infants and young children. Lead poisoning can cause a variety of symptoms, including impacts to the nervous, immune, cardiovascular and reproductive systems.
The knowledge that man-made air pollutants have been around for millennia is sobering. But each new piece of knowledge about the past could hold clues for Earth's future.