Researchers examining a pristine ice core extracted in Peru reveal that mining and metallurgy activities polluted the Andean atmosphere over two centuries before the Industrial Revolution. The findings, published in Proceedings of the National Academy of Sciences this week, are the earliest evidence of widespread, anthropogenic air pollution in South America.

Previous work has documented the metallurgic activities of the Inca Empire from 1438 to 1532. And researchers know that in 1572, the Spanish introduced new silver extraction technology that significantly boosted production in the mountaintop mines of Potosí in present-day Bolivia. However, because evidence for pre-industrial atmospheric pollution in the Southern Hemisphere has been limited to a few, low-resolution geological archives, the timing and impact of these activities remain poorly understood.

Then in 2003, a team led by Paolo Gabrielli of Ohio State University extracted an exceptionally detailed ice core from the high-altitude drilling site of Quelccaya in Peru. These layers captured chemicals blown in from far away and preserved them under hundreds of years of snow and ice. When the team analyzed the elemental composition of dust deposited between 793 and 1989, they found that trace element concentrations were low and stable before 1450. Then came an increase in bismuth concentration around 1480, which corresponds with the expansion of the Inca Empire and bronze production. 

However, based on the ice core record, the Inca Empire's metallurgic activities had only a negligible impact on the atmosphere. During the pre-colonial period (that is, before 1532), the deposition of trace elements was dominated by windborne dust and of ash fallout from volcanic eruptions. A section of the ice core is pictured to the right.

As it turns out, the atmospheric emissions of a variety of toxic trace elements began to have a widespread environmental impact around 1540, less than a decade after the start of Spanish colonization. That means colonial mining and metallurgy in Bolivia were polluting the Andean atmosphere about 240 years before the Industrial Revolution. Other mines in the area contributed, but to a much lesser extent.

The boom in mining activity was further boosted by the 1572 shift from lead-based smelting to mercury amalgamation in silver production. This refining process introduced by the Spanish involves grinding silver ore (which contains way more led than silver) into a powder before mixing it with mercury. Starting just before 1600, the Quelccaya ice cap began capturing much larger quantities of antimony, arsenic, bismuth, molybdenum, and especially lead, and these high amounts lasted until the early 1800s, when South American countries declared independence from Spain.

“The fact that we can detect pollution in ice from a pristine high altitude location is indicative of the continental significance of this deposition,” Gabrielli says in a news release. “Only a significant source of pollution could travel so far, and affect the chemistry of the snow on a remote place like Quelccaya.”

Still, the deposition of toxic trace metals during the colonial era was several factors lower than 20th century atmospheric pollution—these remain the highest on record.

Images: Paolo Gabrielli/Ohio State University