The first assessment of toxic heavy metal pollution in the Southern Hemisphere over the past 2,000 years

Human activity, from the burning of fossil fuels and fireplaces to contaminated dust produced by mining, is changing the Earth’s atmosphere in countless ways. Records of these impacts over time are preserved in eternal polar ice which serves as a sort of time capsule, allowing scientists and historians to connect the history of Earth with that of human societies. In a new study, ice cores from Antarctica show that lead and other toxic heavy metals linked to mining polluted the Southern Hemisphere as early as the 13th century.

The work is published in the journal Total Environmental Science.

“Seeing evidence that early Andean cultures 800 years ago, and later Spanish colonial mining and metallurgical exploitation, appear to have caused detectable lead pollution 9,000 km away in Antarctica is quite surprising,” said Joe McConnell, Ph.D., research professor of hydrology at Desert Research Institute (DRI) and lead author of the study.

The research was led by McConnell’s team at DRI with collaborators in Norway, Austria and Germany, as well as Florida. This is the first time scientists have assessed the impact of human activity on lead pollution in Antarctica 2,000 years ago. It is also the first detailed assessment of thallium, bismuth and cadmium pollution. In addition to lead, these heavy metals (with the exception of bismuth in low concentrations) are considered highly toxic and harmful to human health and that of ecosystems.

The team found that the first increase in heavy metal pollutants, particularly lead, began around 1200, coinciding with the establishment of urban communities by the Chimú people on the northern coast of South America.

“These settlements required large quantities of silver and other metals obtained through mining,” said Charles Stanish, an archaeologist and study co-author at the University of South Florida. Lead is often found in silver ores, and samples of lake sediments from the Potosí region of Bolivia also suggest lead emissions throughout the 12th and 13th centuries, consistent with ice records from the ‘Antarctic.

Longer lasting and more constant pollution began soon after the arrival of Spanish settlers in South America in 1532, when Potosí became the main source of silver for the Spanish Empire and the largest source of silver in the world. Ice records show a marked decline in lead pollution between about 1585 and 1591, when severe epidemics ravaged Andean communities. The team was able to compare silver records at the Potosí Colonial Mint to ice core data, finding that they were consistent with declining pollution in Antarctica.

“It’s pretty amazing to think that a 16th century epidemic in Bolivia changed pollution in Antarctica and throughout the Southern Hemisphere,” said Sophia Wensman, Ph.D., a postdoctoral researcher at DRI and co-author of the study.

“Although the remoteness of Antarctica, thousands of kilometers from South America and Australia, means that only traces of pollutants are deposited and preserved in the ice, the records precisely dated, year by year year, can provide insight into how and when human pollutants impacted the entire Antarctic hemisphere,” added co-author and atmospheric modeler Andreas Stohl, Ph.D., of the University of Vienna .

As expected, pollutants increased significantly after industrialization, with significant peaks at the start of lead mining in Australia in the late 19th century. There is also a marked decline in data corresponding to the two world wars and the Great Depression, demonstrating the global impacts of industrial activities and political events in the Northern Hemisphere.

The study resulted from the analysis of five different ice cores taken from the East Antarctic ice sheet at DRI’s Ice Core Lab, a unique facility with instruments capable of detecting traces of metals in ice and snow. McConnell and his team have refined their techniques over decades to advance scientific understanding of humans’ impact on Earth’s atmosphere over time and have tracked historical epidemics and wars using changes in levels of pollution in Greenland.

“We are arguably the only research group in the world to regularly perform these kinds of very detailed measurements, particularly in Antarctic ice, where concentrations of these trace metals are extremely low,” added Professor Nathan Chellman. research assistant at DRI and co-author of the study. doctorate

With these advances, this study offers a deeper insight into history than before. Previous studies have failed to identify the heavy metal pollution that preceded the industrial era because it was impossible to differentiate between metals produced by volcanic eruptions and those produced by human activity. For this study, the team used thallium levels recorded in the ice to estimate and subtract volcanic background levels of lead, bismuth and cadmium, which allowed them to identify when pollution from human origin began, as well as its scale.

“We found that levels of lead, bismuth, and cadmium all increased after industrialization by an order of magnitude or more,” says McConnell. “But the thallium hasn’t really changed, indicating little or no human emissions of thallium, so that’s what allowed us to use it as an indicator of volcanism over the last 2,000 years.”

McConnell says he and his team hope to use the techniques developed in this study to refine understanding of pre-industrial pollution levels in the Arctic, where mining and metallurgy were more pronounced much earlier in the history of the Arctic. humanity than in South America.