Researchers used ice cores collected from the Alps along the Swiss-Italian border to retrace historic lead levels in the atmosphere. Photo by Nicole Spaulding/Climate Change Institute/University of Maine.
May 31 (UPI) -- Analysis of ice cores, as well as historic health and economic records, suggests humans have been polluting the air for at least 2,000 years, challenging the assumption that environmental degradation began during the Industrial Revolution.
Researchers determined the natural concentration of lead in the air is close to zero. Ice cores show unnatural lead levels were detectable in the atmosphere several centuries before the Industrial Revolution.
When the Black Death pandemic decimated European populations, halting mining and smelting operations between 1349 and 1353, researchers observed a return to normal atmospheric lead levels.
"These new data show that human activity has polluted European air almost uninterruptedly for the last circa 2000 years," researchers wrote in their study, newly published in the journal GeoHealth. "Only a devastating collapse in population and economic activity caused by pandemic disease reduced atmospheric pollution to what can now more accurately be termed 'background' or natural levels."
Because scientists have previously assumed pre-industrial lead levels to be natural, regulators have deemed pre-industrial lead levels safe. The latest research suggests scientists and public health officials need to reconsider their definitions of "natural" and "safe."
Scientists reconstructed historic lead levels by analyzing ice cores drilled in the Swiss-Italian Alps. Researchers found lead levels dropped suddenly in the section of the ice cores corresponding to the four years between 1349 and 1353, when historical records suggest smelting and mining ceased almost entirely.
"In different parts of Europe, the Black Death wiped out as much as half of the population. It radically changed society in multiple ways," Alexander More, a historian at Harvard University, said in a news release. "In terms of the labor force, the mining of lead essentially stopped in major areas of production. You see this reflected in the ice core in a large drop in atmospheric lead levels, and you see it in historical records for an extended period of time."
Though researchers didn't identify any similar precipitous drops in lead levels, other declines in lead were linked to economic downturns and smaller pandemics.
Researchers say their interdisciplinary approach offers a new way to study climate history.
"This research represents the convergence of two very different disciplines, history and ice core glaciology, that together provide the perspective needed to understand how a toxic substance like lead has varied in the atmosphere and, more importantly, to understand that the true natural level is in fact very close to zero," said Paul Mayewski, director of the Climate Change Institute at the University of Maine.