Humans polluted with lead 8,000 years ago
U. PITTSBURGH (US) — The oldest evidence of lead pollution caused by humans has been discovered in Michigan’s Upper Peninsula.
The discovery suggests metal pollution from mining and other human activities appeared far earlier in North America than in Europe, Asia, and South America.
“Humanity’s environmental legacy spans thousands of years, back to times traditionally associated with hunter-gatherers,” says David Pompeani, a PhD candidate in the geology and planetary science department at the University of Pittsburgh.
“Our records indicate that the influence of early Native Americans on the environment can be detected using lake sediments. These findings have important implications for interpreting both the archeological record and environmental history of the upper Great Lakes.”
For the study, published in Environmental Science & Technology, researchers examined Michigan’s Keweenaw Peninsula because it is the largest source of pure native copper in North America. Early surveys of the region in the 1800s identified prehistoric human mining activity in the form of tools, including hammerstones, ladders, and pit mines.
The team investigated the timing, location, and magnitude of ancient copper mining pollution. Sediments collected in June 2010 from three lakes located near ancient mine pits. They analyzed the concentration of lead, titanium, magnesium, iron, and organic matter in the collected sediment cores—finding distinct decade- to century-scale increases in lead pollution preserved from thousands of years ago.
“These data suggest that measurable levels of lead were emitted by preagricultural societies mining copper on Keweenaw Peninsula starting as early as 8,000 years ago,” Pompeani says. “Collectively, these records have confirmed, for the first time, that prehistoric pollution from the Michigan Copper Districts can be detected in the sediments found in nearby lakes.”
By contrast, reconstructions of metal pollution from other parts of the world, such as Asia, Europe, and South America, only provide evidence for lead pollution during the last 3,000 years. “We’re hopeful that our work can be used in the future to better understand past environmental changes,” says Mark Abbott, associate professor of paleoclimatology.
The team is currently investigating places near other prehistoric copper mines surrounding Lake Superior.
The work was funded by a Henry Leighton Memorial Fund grant, the Geological Society of America, and the National Science Foundation.
Source: University of Pittsburgh