Ice cores record Earth’s secrets, even the dirty ones.
Some of the cylindrical sections of ice extracted from the Arctic contain elevated levels of arsenic, lead and other heavy metals that circulated in our planet’s atmosphere in the late 19th and early 20th centuries. Those pollutants, which have been tied to declines in IQ and higher rates of certain cancers, were probably emitted by a mining and smelting company in Montana whose grounds are now designated as multiple Superfund sites, the researchers report November 3 in Nature Sustainability.
The ice cores contain tiny particles that were once airborne — including pollutants, volcanic ash and salt from ocean spray — and fell to our planet’s surface within a few days or weeks. In polar regions, that fallout combines with snow and is preserved as ice.
Joseph McConnell, an environmental scientist at the Desert Research Institute, and his collaborators recently analyzed 10 ice cores collected across Canada, Greenland and Russia. The cores contained material that had fallen to Earth as early as 210 BCE, but the interval spanning the Industrial Revolution in the United States — from roughly 1870 to 1914 — was what caught the team’s collective eye.
In the ice layers from that period, arsenic concentrations in some of the ice cores were up to 15 times higher than pre-Industrial Revolution levels. Because the heavy metal exposure has been tied to upticks in the rates of certain cancers, McConnell and his team set out to determine the most likely source of all that pollution.
The largest increases in arsenic existed in the ice cores from Greenland. That finding was a big hint, McConnell says, because atmospheric circulation patterns tend to move material from west to east. “The only way you can explain that pattern of deposition is if the emissions are coming from North America,” McConnell says. “Had it been from Europe, we would have seen much larger increases in the Russian Arctic.”
The most likely source, the team concluded, was a massive copper mining and smelting operation in southwestern Montana operated by the Anaconda Copper Mining Company. It was one of the largest in North America during the Industrial Revolution and, unlike other copper mining operations in the area, it worked with copper ore that contained heavy metals like arsenic and lead. It was no secret that those toxic metals were entering the atmosphere, says Fred Quivik, a historian and the author of Smoke and Tailings, a book about the environmental history of copper smelting in Montana. “Ranchers and farmers started seeing their livestock die from arsenic poisoning.”
Based on the concentrations of arsenic in the ice cores and models of how material disperses in the atmosphere, McConnell and his colleagues estimated that the Anaconda Copper Mining Company was emitting roughly 30 tons of arsenic per day into the atmosphere in the late 19th and early 20th centuries. By comparison, Chile, currently the world’s largest producer of copper and home to more than 20 mining operations, collectively emits roughly one quarter as much arsenic today.
Beginning in 1919, the Anaconda Copper Mining Company installed devices near its smokestacks and other facilities to capture arsenic and prevent its release into the atmosphere. Arsenic emissions dropped by about 60 percent as a result, the ice core data showed, but by then hundreds of thousands of nearby residents had already been exposed for decades. That exposure could have been lessened, McConnell says, if the Anaconda Copper Mining Company hadn’t waited so long to install the pollution-abatement technology. “They delayed installation for about a decade.”
These new findings should be combined with census records to trace the effects of this pollution on human health in the 19th and 20th centuries, McConnell and his team suggest. “We hope that epidemiologists will take this information and really investigate potential impacts on human populations.”
