Greenland and Arctic ice cores link a 15-fold arsenic rise to Anaconda copper smelting in Montana

Researchers at DRI's Ice Core Lab, led by Joe McConnell and Nathan Chellman, reported in Nature Sustainability on Nov. 10 that Arctic ice preserves a record of air pollution from the Anaconda Copper Mine complex near Butte, Montana, according to miragenews.com miragenews.commiragenews.commiragenews.comOpen source ↗. The team analyzed 10 ice cores from Greenland, the Russian Arctic and northern Canada. Arsenic and other toxic heavy metals in the ice rose about 15-fold during the peak period, from about 1886 to 1918.

Ice cores point to the source

Arsenic and lead stay in the air for only days before they are deposited. For this reason the team compared cores from three regions, and together with atmospheric modeling this pointed to northern North America as the source. The researchers then checked production records from the USGS and Canadian reports. Anaconda's record matched the arsenic found in the ice almost perfectly, and lead isotopes were also consistent with Anaconda as the main source.

Arsenic was measured directly in four of the ten cores. Bismuth levels were closely linked to arsenic in that period, so bismuth served as a proxy in the other six cores. Sulfur, sodium and calcium helped identify annual layers, and cerium set a background level for natural dust.

In a central Greenland core, arsenic rose slowly between 1850 and 1887, then quickly until 1895, and peaked around 1914 at about 15 times the level before industrialization. It dropped by 1920. The authors link the decline after 1919 likely to electrostatic precipitators installed at the Anaconda Smelter. Through 2020 arsenic stayed well below the peak miragenews.commiragenews.commiragenews.comOpen source ↗.

Exposure estimates

Combining ice data, atmospheric modeling and the mine's records, the team estimates emissions of 11 thousand tons of arsenic and 4.4 thousand tons of lead per year during two to three decades of peak production. Using the 1910/1911 census, they estimate that about 50.5 million Americans, along with some Canadians, were exposed to arsenic above 1 ng/m3, a level associated with higher lung cancer risk.

People closest to the mine, in Montana and parts of Wyoming and Idaho, lived for nearly 30 years with arsenic at or above 6 ng/m3, the current WHO maximum for chronic exposure. Recent levels in the U.S. and Europe are 0.1 to 0.5 ng/m3. About 1.4 million Americans and Canadians were exposed to lead above 1 ng/m3, potentially linked to cognitive decline equivalent to 2.6 IQ points. The authors considered only air exposure, not deposition on crops, soils and water.