Oldest Evidence of Manmade Lead Pollution Found in Michigan

What is being reported as the oldest-discovered evidence of anthropogenic lead pollution on Earth has been found in northern Michigan -- researchers say the evidence of lead pollution is at least 8,000 years old.

The find suggests that metal pollution from mining and other activities appear far earlier in North America than in Europe, Asia or South America, according research by the University of Pittsburgh.

David Pompeani, lead author of the research said the environmental legacy of humans spans back to the ancient days of hunter-gatherer societies.

"Our records indicate that the influence of early Native Americans on the environment can be detected using lake sediments," Pompeani said in a statement.

"These findings have important implications for interpreting both the archeological record and environmental history of the upper Great Lakes."

Pompeani and a multi-disciplinary team which included a paleoclimatologist and a processor of catchment science, studied Michigan's Keweenaw Peninsula -- a strip of land jutting into Lake Superior in the northernmost part of the state -- as it is the largest source of pure native copper in North America. They investigated timing, location and magnitude of ancient copper mining pollution at the site.

Early surveys of the region uncovered hammerstones, ladders and pit mines - all indicators of an early human presence linked with prehistoric mining activity, a report from Pittsburgh University stated.

Sediments were collected from three lakes located near ancient mine pits.

Pompeani and his team analyzed the concentration of lead, titanium, magnesium, iron and organic matter in the collected sediment cores. They found observable 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 pre-agricultural societies mining copper on Keweenaw Peninsula starting as early as 8,000 years ago," said Pompeani. "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."

Metal pollution from Asia, Europe and South America only provide evidence for lead pollution during the last 3,000 years, a significant contrast to current findings, Pompeani said.

The researchers said they are hopeful their work can be used in the future to better understand past environmental changes. The same research team is currently investigating places near other prehistoric copper mines surrounding Lake Superior.

Pompeani and his colleagues' research is published in the journal Environmental Science & Technology.