Climate change increases rare earth elements in Colorado’s Snake River
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2021-09-17
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The Snake River begins high in the mountains of Colorado, with headwaters near Loveland Pass. It weaves its way downstream through rocky fields to a wetland valley before eventually joining the Blue River, which cuts through Breckenridge and eventually dumps into the Dillon Reservoir. The river is important to the region: It supplies drinking water for Denver and is a popular fly-fishing spot.But the Snake could be heading for troubled waters: According to a recent study, climate change-driven changes in its hydrology are releasing more rare earth elements. It’s a finding that could have broader implications for water quality across the West.The study, published last month in the journal Environmental Science & Technology, found that higher levels of rare earth elements — a group of chemically similar metals — are ending up in Colorado’s water supply due to lower stream flows caused by drought and a shrinking winter snowpack.Lower stream flows mean that metals are not as diluted as they’ve been in the past. While previous research has connected this phenomenon to an increase in zinc concentrations, the latest study is the first to look at rare earth elements.“It’s definitely the first (study) to link increasing concentrations of rare elements with climate change-driven changes in hydrology,” said study author Diane McKnight, an engineering professor at the University of Colorado Boulder. “I don’t know of any other study that really looks at what’s the pattern of rare earth elements in a watershed at the scale of the Snake River, going all the way down to the drinking water supply.”Rare earth elements are ubiquitous today, used in cellphones, hard drives and solar panels. They occur naturally as a group of 17 metallic elements. While studies show that they’re toxic to small aquatic organisms and microbes, “we don’t have a big grasp on whether or not that extends to humans,” said lead author Garrett Rue, who was a master’s student at University of Colorado Boulder when the research was done. “These effects are understood at the bottom of the food web, but it’s very difficult to scale up what that means for fish or more complex biological life.”Rare earth elements are not considered a known toxicant by the Environmental Protection Agency; their concentrations aren’t monitored and no water quality standards have been set for them. Because they’re often found in acid mine drainages along with metals of concern, such as zinc and lead, it’s hard to isolate them and identify their effects. But their increasing use in medical products like MRI tracers means that rare earth elements are re-entering the ecosystem in the form of wastewater, prompting a renewed push to understand them.Documenting the increasing concentrations of rare earth elements together with the recent climate-driven changes in hydrology is important work, other experts in the field say.“As things dry up more and more, surface water and groundwater can be affected over the long haul, with water quality becoming worse,” said Kirk Nordstrom, a retired U.S. Geological Survey scientist who studied acid mine drainage extensively. (Nordstrom was not involved in the Snake River study.) “That’s something that almost nobody addresses, but this paper does that. Rare earth elements are a hot topic these days and nobody has data quite like they have in this paper.” The study, which used samples that spanned almost four decades, revealed a range of one to hundreds of micrograms per liter of the elements throughout the Snake River. The mere fact that researchers found concentrations high enough to warrant measuring in micrograms means that the river has an unusually high amount of rare earth elements. Concentrations in larger rivers are usually so small they’re measured in nanograms. “They tend to be in the parts per trillion range, and we’re seeing them now in the parts per billion range,” Rue said. “That unit is 1,000-fold higher.”Scientists also found that the elements are building up in stream insects at levels similar to toxic lead and cadmium.The highest concentrations were found near the headwaters and in areas receiving acid mine drainage from abandoned mines. Acid mine drainage occurs because rocks that contain certain minerals oxidize when exposed to air and water. The resulting chemical reaction creates sulfuric acid, which dissolves metals like iron and pulls rare earth elements out of rocks.
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