Scientists have uncovered evidence of widespread air pollution caused by a major copper mining and smelting operation in the United States during the early 20th century. Ice cores collected from Greenland, the Russian Arctic and northern Canada have revealed that toxic emissions from the Anaconda Copper Mine complex near Butte, Montana, travelled thousands of kilometres, exposing millions of people across North America to harmful levels of arsenic and lead.
The research published in the journal Nature Sustainability, was led by scientists from the Desert Research Institute (DRI), including Joe McConnell and Nathan Chellman alongside international collaborators. By examining historical pollution trapped in Arctic ice, the team reconstructed the scale, spread and potential health consequences of industrial emissions dating back more than a century.
Researchers analysed 10 ice cores collected from Greenland, the Russian Arctic and northern Canada. Their findings showed that atmospheric concentrations of arsenic and other toxic heavy metals increased dramatically between approximately 1886 and 1918.
Pollution levels during this period were around 15 times higher than pre-industrial levels, with the Anaconda Copper Mine identified as the primary source.
By combining measurements from the ice cores with atmospheric modelling and historical mining records, scientists estimated that the mine released approximately 10,000 metric tonnes of arsenic and 4,000 metric tonnes of lead annually during its peak production years.
The pollution travelled across much of North America and reached western Greenland, more than 4,000 kilometres from the source.
The researchers compared atmospheric pollution models with population data from the 1910 and 1911 censuses to estimate how many people may have been exposed.
Their analysis suggested that approximately 50.5 million Americans and 600,000 Canadians were exposed to arsenic pollution levels associated with increased risks of lung cancer and other serious health conditions.
People living closest to the mine in Montana, Wyoming and Idaho experienced particularly high exposure. For nearly three decades, arsenic concentrations in these areas reached or exceeded the World Health Organization’s current recommended maximum threshold of 6 nanograms per cubic metre for chronic exposure.
By comparison recent arsenic pollution levels in the United States and Europe are estimated to be between 0.1 and 0.5 nanograms per cubic metre.
The study also found that around 1.4 million Americans and Canadians were exposed to elevated lead pollution. Such exposure has been associated with cognitive decline, with researchers estimating a potential average reduction equivalent to 2.6 IQ points among affected populations.
Scientists emphasised that arsenic and lead can cause harm through several pathways, including contamination of crops, soil and water, although this particular study focused on airborne exposure.
To identify the source, researchers compared pollution patterns preserved in ice cores from different Arctic locations. Atmospheric modelling helped them determine where the toxic particles originated and how they travelled across the continent.
The team also examined historical records of mining and metal production. Arsenic measurements closely matched the production history of the Anaconda Copper Mine while lead isotope signatures in the ice provided further evidence linking the pollution to the facility.
Copper production expanded rapidly during the late 19th and early 20th centuries as demand increased for electricity infrastructure and industrial development. The Anaconda operation was one of the world’s largest copper producers during that period.
Its smelting processes involved roasting and processing sulphide ores, which released large quantities of arsenic, lead and other toxic metals into the atmosphere.
The research also highlighted how delayed environmental regulations contributed to decades of excessive pollution.
The installation of electrostatic precipitators at the Anaconda smelter began in 1919 and continued through 1923. These pollution control devices reduced heavy metal emissions by approximately 65%, a decline also visible in the Arctic ice records.
Although the technology had been patented in 1908 and adopted by several other smelters in the western United States and Canada, the Anaconda facility delayed its installation for roughly a decade.
According to the researchers if pollution controls had been introduced 10 years earlier, an estimated additional 54,000 metric tonnes of arsenic and 22,000 metric tonnes of lead emissions could have been prevented across much of North America.
At the time Montana’s regulatory policies required pollution control measures only when their installation was considered profitable for the polluting company.
Ice Cores Preserve a Century of Industrial Pollution History
The study also demonstrated the importance of ice cores as historical environmental records. Like tree rings, annual layers of accumulated snow preserve information about past atmospheric conditions, including industrial pollution, volcanic activity and forest fires.
Researchers directly measured arsenic in four of the 10 ice cores. For the remaining samples, they used bismuth as a reliable indicator because its concentrations closely tracked arsenic levels during the period.
The records showed that arsenic pollution began rising gradually between 1850 and 1887 before increasing rapidly towards the end of the 19th century. Concentrations peaked around the beginning of the First World War in 1914.
Levels subsequently declined following the introduction of pollution control technology, with another reduction recorded during the Great Depression between 1932 and 1934. Although pollution increased again later, it remained well below the levels recorded during the First World War era through 2020.
The Anaconda mining and smelting operation also caused serious environmental damage closer to its facilities. Contamination affected agricultural land, reducing crop growth and yields and contributing to livestock deaths. The resulting disputes between mine owners, farmers and ranchers continued for decades.
The Silver Bow Creek/Butte Area Superfund site is now recognised as one of the largest and most toxic environmental remediation sites in the United States.
The researchers say their findings provide important evidence of how a single major industrial source, combined with weak environmental regulations, can expose millions of people to toxic pollution over vast distances. The study also raises questions about the long term health consequences experienced by generations living downwind of major industrial facilities.
The research titled Widespread North American pollution and health impacts from early 20th C copper production, was published in Nature Sustainability in 2026.