Scientists Traced Arctic Arsenic Back to a Montana Mine

Scientists have traced historical Arctic arsenic pollution back to a single dominant source thousands of kilometers away: the Anaconda Copper Mine in Montana.

For decades, researchers studying ice cores from Greenland, northern Canada, and the Russian Arctic noticed mysterious spikes in bismuth and antimony dating back to the early 20th century. While researchers concluded their presence was likely the result of pollution from the Second Industrial Revolution, the timing never quite lined up with continuing industrial growth.

“Why did these things peak in the 1910s, 1920s?” asked Joe McConnell, a climate and environmental scientist at the Desert Research Institute specializing in ice cores, as reported by Eos. Heavy metal particles travel through the air for only days or weeks before falling onto surfaces, creating a deposition pattern closely linked to emission dates.

To solve the puzzle, McConnell’s lab developed a method for measuring arsenic in ice cores. In a new study published in Nature Sustainability, researchers used this arsenic data to track the metallic fallout across 10 Arctic ice cores back to Montana.

“It’s a really neat piece of detective work,” said Karl Kreutz, an Earth scientist at the University of Maine who was not involved with the research, according to Eos. “What they presented [with arsenic] seems pretty convincing to me, that they can trace it back to one major mine in Montana. That’s the first time I’ve seen somebody try to do that with arsenic.”

Production statistics for the Anaconda Copper Mine matched the measured arsenic levels in the ice cores almost exactly. The data revealed a peak of about 15 times higher than preindustrial levels in 1914.

The research team evaluated several other North American smelting operations to test their models. A smelter in Tacoma, Wash., was excluded as being too small, lead isotopic ratios from Sudbury, Canada, did not line up, and a mine in Michigan’s Keweenaw Peninsula produced mostly native copper with relatively low heavy metal emissions.

Pollution levels dropped after 1919 despite the Montana mine remaining operational until 1947. This reduction followed the installation of electrostatic precipitators on the smelter, which the study estimates cut heavy metal emissions by about 65%.

Although an electrostatic precipitator was patented in 1908 and its inventor personally designed an installation plan for Anaconda, the facility delayed putting the devices into practice. “Montana government policy at the time was they only had to install pollution controls if it was profitable to the polluter,” McConnell stated to Eos.

That delay carried a heavy human toll. The researchers estimate the lag resulted in an additional 60,000 tons of arsenic and 24,000 tons of lead discharged into the environment.

By referencing 1910 and 1911 census records alongside atmospheric modeling, the study estimates that between 1898 and 1918, about 55% of Americans (50.5 million people) and 11% of Canadians (600,000 people) were exposed to arsenic levels that increased their risk of lung cancer. Elevated lead pollution also likely affected about 1.4 million people. According to the Environmental Protection Agency, there is no safe level of lead exposure for children.

Historical records show the Anaconda mine faced lawsuits from nearby farmers and ranchers and, eventually, the U.S. Forest Service, which alleged that the mine’s activities were damaging agriculture, poisoning livestock, and destroying forests. Today, the area is home to the country’s largest Superfund site.

“Anaconda, it turns out, was an infamous source of arsenic pollution,” McConnell said.