About a century ago, the Anaconda Copper Mine complex near Butte, Montana was emitting vast amounts of air pollution into the atmosphere. As small particles of arsenic and other heavy metals were carried by winds over the Arctic, storms eventually helped pull them to the ground, where they joined layers of history embedded in the ice. Now, DRI's Ice Core Lab has analyzed these natural archives to help us better understand the scope of just how much air pollution this mining and smelting operation sent over the continent, and who was most impacted.
The research, published Nov. 10th in the journal Nature Sustainability , was led by DRI's Joe McConnell and Nathan Chellman, along with colleagues from around the world. They analyzed 10 different ice cores collected from Greenland, the Russian Arctic, and northern Canada to reconstruct atmospheric levels of arsenic and other toxic heavy metals during the second Industrial Revolution. The peak pollution period, recorded in Arctic ice from about 1886 to 1918, saw increases in these toxins of about 15-fold that the team traced back to the Anaconda Copper Mine operations, one of the world's largest producers of copper at the time. By measuring the levels of these metals in the ice, combining the data with atmospheric modeling, and cross-referencing their findings with the mine's own historical records, they estimate emissions of 11 thousand tons of arsenic and 4.4 thousand tons of lead per year during the mine's two to three decades of peak production. This pollution potentially led to widespread health impacts for the more than half of Americans (55%) and about 11% of Canadians who lived downwind of the mine's pollution plume at the time.
"It's pretty wild to think that a single, albeit massive source of pollution could have affected effectively the entire North American continent and western Greenland more than 4000 kilometers or 2500 miles away," McConnell said.
By examining American and Canadian census data from 1910/1911 and overlapping them with their atmospheric models, the researchers found that approximately 50.5 million Americans and 600,000 Canadians were exposed to levels of arsenic pollution (>1 ng/m3) associated with higher risk for lung cancer and other serious conditions. The people living closest to the mine in Montana and parts of Wyoming and Idaho were exposed for nearly 30 years to arsenic levels that meet or exceed the current maximum threshold of 6 ng/m3 for chronic exposure recommended by the World Health Organization. For context, recent arsenic pollution levels in the U.S and Europe range from 12 to 60 times lower (0.1 to 0.5 ng/m3).
The study also found that 1.4 million Americans and Canadians, including all Montana and Wyoming residents, were exposed to elevated lead pollution levels (>1 ng/m 3) potentially linked to cognitive decline equivalent to an estimated reduction of 2.6 IQ points. Although the researchers acknowledge that arsenic and lead emissions have health impacts that extend beyond air pollution, including due to deposition over crops, soils, and water supplies, they focused on air pollution levels in this study. Public health research has established that no level of exposure to arsenic or lead is without harm, including increased risks of cancer, diabetes, cognitive decline, and heart disease.
Tracing Pollution from the Arctic to Anaconda
Using an array of ice cores from across the Arctic region allowed the researchers to look at how deposition patterns changed over time and space. When combined with advanced atmospheric modeling techniques, which allow scientists to track and visualize atmospheric circulation patterns, they could pinpoint northern North America as the source of these emissions. Heavy metals like arsenic and lead have fairly short "atmospheric lifetimes," meaning they're typically only carried by air for mere days before being deposited. This made it important for the team to compare and contrast pollution levels from ice cores collected from Greenland, the Russian Arctic, and northern Canada.
Once they had pinpointed northern North America as the likely source of emissions, they looked at the largest mining and smelting sites during that era, including copper and other metal production rates based on historical U.S. Geological Survey (USGS) and Canadian reports. When McConnell compared the records from Anaconda to the arsenic pollution rates found in the ice, it was almost a perfect match. Lead isotope records found in the ice were also consistent with Anaconda being the primary source of emissions.
"Everything points to Anaconda — an infamous source of arsenic pollution in this country," McConnell said. "We can use atmospheric modeling and the deposition pattern of pollution to estimate the magnitude of the emissions. So we know where it's coming from, and we know its magnitude. And with this information, we can then forward model how that pollution would have spread around North America."
Copper smelters are among the largest sources of arsenic pollution, and demand for copper and other metals surged in the late 19th and early 20th century during a period of rapid electrification. This era also saw the rise of other industrial and military uses during the buildup to World War I. Copper production in Montana was almost entirely from sulfide ores mined near Butte, and the emissions from roasting and smelting of these sulfide ores were well-established sources of sulfuric acid and volatile heavy metals at the time. Consequences from arsenic pollution, such as reduced crop growth, lower crop yields, and livestock deaths, resulted in decades of litigation between the owners of Anaconda and nearby farmers and ranchers, and eventually the U.S. Forest Service. The Silver Bow Creek/Butte Area Superfund site is now one of the largest and most toxic environmental remediation sites in the country.
This is one of the first studies to analyze arsenic levels in Arctic ice cores because it is a more challenging element to measure and analyze than others such as lead. Arsenic, bismuth, lead, and antimony are all metals found in metal-bearing sulfide ores and fossil fuels, and their volatility means that they are co-emitted by industrial processes. The study team directly measured arsenic levels in four of the ten ice cores but found that bismuth levels were closely linked to arsenic during this period. This allowed them to use bismuth as a proxy for arsenic in the other six ice cores. They also measured sulfur, sodium, and calcium, elements linked to volcanic eruptions, sea spray, and soil dust, which allowed them to identify annual layers in the ice like tree rings. Cerium was measured to establish a background level for natural dust emissions.
In an ice core from central Greenland, the team found that arsenic levels rose slowly between 1850 and 1887, then rapidly to 1895, before peaking at around 15 times higher than pre-Industrial Revolution levels around the start of World War I in 1914. They then fell rapidly following the end of the war to 1920, recovered slightly, and dropped again during the peak of the Great Depression between 1932 and 1934. While arsenic levels increased again following the Great Depression, they remained well below the peak pollution rates of the World War 1 era through 2020.
A Direct Link to Lax Environmental Regulations
The research team has worked with Arctic ice cores for many years and had been struck by a consistent pattern they were seeing. Why were levels of certain heavy metals so much higher in the early 20th century in some parts of the Arctic than they were in later decades, when industrial output was much higher? Focusing on arsenic, one of the most toxic heavy metals out there, helped untangle this persistent mystery.
The research showed a significant drop in arsenic pollution levels in the years following 1919. This is likely due to the installation of electrostatic precipitators at the massive Anaconda Smelter at this time, which as recorded in Arctic ice, reduced heavy metal emissions by around 65%. Historical documentation shows that although this technology was patented years earlier, in 1908, and quickly adopted by many smelters in the Western U.S. and Canada, the Anaconda smelter delayed their installation for a decade. At the time, Montana regulatory policy required the installation of pollution controls only if profitable to the polluter. Installation of air pollution controls ten years earlier would have prevented an additional 60 thousand tons of arsenic and 24 thousand tons of lead pollution over much of North America.
"We hope this is not the end of the use of these data and conclusions about the health impacts," McConnell said. "Our goals were to document the patterns of arsenic and other heavy metal pollution in the Arctic and use the patterns to establish the timing, sources, and magnitude of this pollution to better understand the level of human exposure. But we're not epidemiologists, and our findings provide important insights into the public health impacts of air pollution that impacted millions of Americans and Canadians. The parents and grandparents of many Americans alive today were exposed to this heavy metal pollution, so the health impacts are quite recent and close to home."
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More information: The full study, Widespread North American pollution and health impacts from early 20th C copper production, is available from Nature Sustainability at DOI: 10.1038/s41893-026-01975-9
To see photos and videos from an expedition to Greenland to drill ice cores, visit DRI's Storymap: Working Under the Midnight Sun
Study authors include: Joe McConnell (DRI), Nathan Chellman (DRI), Sophie Wensman (DRI), Alison Criscitiello (U. of Alberta), Andreas Plach (U. of Vienna/Stockholm U.), Dorthe Dahl-Jensen (U. of Copenhagen/U. of Manitoba), Diedrich Fritzsche (AWI), Kira Holland (U. of Alberta), Drake McCrimmon (DRI), Matthew Osman (U. of Cambridge), John Sandlos (Memorial U.), Andreas Stohl (U. of Vienna)
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