Ice cores serve as frozen archives of Earth’s history, preserving not only climate data but also traces of industrial contamination.
Cylindrical ice samples drawn from the Arctic reveal heightened concentrations of arsenic, lead, and other heavy metals that circulated through the atmosphere during the late 19th and early 20th centuries. These pollutants—linked to cognitive decline and elevated cancer risk—likely originated from a mining and smelting operation in Montana, now designated as multiple Superfund sites, according to research published November 3 in Nature Sustainability.
Ice cores trap microscopic particles that were once airborne, including pollutants, volcanic ash, and sea salt. This fallout typically settles within days or weeks. In polar regions, it merges with snowfall and becomes locked into the ice.
Joseph McConnell, an environmental scientist at the Desert Research Institute, together with colleagues, examined ten ice cores collected across Canada, Greenland, and Russia. While the cores captured material dating back to 210 BCE, the researchers focused on the period of U.S. industrialization, roughly 1870 to 1914.
Ice layers from that era showed arsenic concentrations up to 15 times higher than pre-industrial levels. Given the established links between heavy-metal exposure and increased cancer incidence, McConnell’s team sought to identify the pollution’s source.
The most pronounced arsenic spikes appeared in Greenland ice cores. McConnell notes that this pattern points to North America, as prevailing atmospheric currents generally carry materials from west to east. “The only way to explain that deposition pattern is if the emissions originated in North America,” he said. “Had the source been Europe, we would have observed far larger increases in the Russian Arctic.”
The team identified the likely culprit as a large-scale copper mining and smelting operation in southwestern Montana run by the Anaconda Copper Mining Company. Among the largest in North America during the Industrial Revolution, it processed ore containing arsenic and lead—unlike other regional operations. Contemporary accounts confirm the hazard; historian Fred Quivik, author of Smoke and Tailings, noted that ranchers and farmers began losing livestock to arsenic poisoning.
Using arsenic concentrations in the ice cores and atmospheric dispersal models, McConnell and his colleagues estimated that the company released approximately 30 tons of arsenic daily during the late 19th and early 20th centuries. For context, Chile—the world’s top copper producer, with over 20 active mining operations—currently emits about one-quarter that amount.
In 1919, Anaconda installed equipment near smokestacks and other facilities to capture arsenic before it entered the atmosphere. Ice-core data indicate emissions fell by roughly 60 percent, but by that point, hundreds of thousands of nearby residents had endured decades of exposure. McConnell argues the harm could have been mitigated had the company acted sooner. “They delayed installation for about a decade,” he said.
McConnell and his team recommend correlating these findings with census data to assess the pollution’s impact on human health during the 19th and 20th centuries. “We hope epidemiologists will use this information to investigate potential effects on human populations,” McConnell said.
