Hotter, drier mountains leach more metals from abandoned mines and natural deposits into streams

Garrett Rue grew up fly fishing in central Colorado, which is often surrounded by mountains dyed amber and maroon, and hikes along streams that seem to have borrowed these colors. Sometimes he would catch local trout, and then get nothing-because there is nothing to catch. Then he began to hear stories of people in nearby mountain communities who could not drink their own water. He began to wonder: "These streams have problems supporting the ecosystem and cannot be used for drinking. What happened here?"

Today, Rue, a postdoctoral scientist researching waterways at the University of Colorado’s Arctic and Alpine Institute, knows how to interpret the color codes of river ecology: rust red or orange represents iron oxide, pink white represents aluminum, and yellow represents manganese. This color reveals the presence of minerals that wash up the slopes; the result can be harmful to local aquatic life and endanger the drinking water system. Some mineralization and acidification occur naturally. But decades of research have shown that some are also the result of historic excavation and waste disposal practices in regional gold, silver and other mines (usually found in mountainous areas). Now, climate change seems to be accelerating this process.

This chemical reaction starts in alpine valleys, many of which have long been natural water towers in the world. Climate change is raising temperatures and increasing the frequency and intensity of droughts in high-altitude alpine environments that usually have mines. More and more research links these hotter, drier conditions with increasingly acidic water, which causes rocks to release more minerals into waterways. The list of entry into these waters is constantly increasing. These trends can damage the water quality of river basins anywhere in the world, the mountains of these basins contain high concentrations of minerals, from the Rocky Mountains to the Himalayas to the Andes.

The research co-authored by Rue is one of the latest entries in this area, and one of the first to link the increase in temperature rise with the increase in the concentration of dissolved rare earth elements in mountain streams. These metal elements are used in the polishing and coloring of glass, as well as in the manufacture of batteries and magnets for our ubiquitous mobile phones, TVs and cars. Rue said his research results, published in Environmental Science and Technology in August, may have more impact on the safety of surface water used for drinking and the long-term health of the ecosystems fed by these streams.

The rare earth elements identified by Rue are relatively new elements that have been studied around water quality issues. Little is known about the effects of these elements on human health, and the U.S. Environmental Protection Agency's drinking water regulations do not specify their thresholds. Rue said that they are usually one part per trillion in water—usually too low to detect. In samples collected for Rue’s recent research in the Snake River Basin in Colorado from 2012 to 2019, the team found that the dissolved rare earth metals lanthanum, cerium, neodymium, samarium, gadolinium, dysprosium, erbium, ytterbium, and yttrium contained Ten parts per billion. "They may not be a poison at low concentrations," Rue said, but "we may cross a threshold." Rue also reported finding rare earth elements in the bodies of stream insects, which indicates that these metals are entering the food web.

Even in parts of the Snake River Basin where there is no mining history, Rue has found that the concentration of rare earth elements in the waterways is rising. Research co-author Diane McKnight, a civil and environmental engineer at the University of Colorado, said this shows that mountain deposits that release these elements at a relatively stable rate for decades have, as temperatures rise and drought conditions worsen, It will also be more extensively leached. Boulder. There are no water quality standards related to rare earth elements. Therefore, McKnight and Rue refer to the American lead and cadmium water quality standards to estimate the potential risks that this leaching may bring. Researchers have found that the concentration of rare earth elements is higher than the level of lead and cadmium that are considered safe for aquatic organisms and human health.

Regardless of climate, the link between mines and downstream water quality issues—usually related to the release of various metals other than those that should be extracted—is common and, in some cases, lasting. Elsewhere in the Rocky Mountains, including the Coeur d'Alene River Basin in Idaho, a 1998 study tracked metals in old mines entering waterways. Researchers found metals in sediments and river rocks 50 miles downstream of historical mining. In recent decades, residents of Sardinia, Italy, have been dealing with groundwater pollution caused by acidification floods, which contain zinc, cadmium, and lead discharged from mines, including the Phoenician mine, which is thousands of years old. In Germany, it is reported that in the past 800 years, highly acidic water from silver, lead, copper and zinc mines continued to pollute groundwater 20 years ago.

In the above examples, there has been almost no formal investigation (if any) of the effects of climate change. However, if climate-related droughts are affecting downstream water quality elsewhere, there may be many locations to investigate in the United States alone. According to federal statistics, there are still more than 100,000 abandoned mines in the country. Rue estimates that more than 40% of the mountain sources of major rivers in the United States may be contaminated by heavy metals related to mines or their natural sources. In Australia, where the mining industry was also booming in the 1800s, a public policy think tank reported about 60,000 abandoned mines.

Traditional mining practices can lead to potential water pollution. For every ounce of gold, silver, copper, and lead mined, the miners hired to mine these veins generate tons of waste rock. It was not until the 1970s that American mining laws allowed private companies, individual prospectors, and factory operators to leave piles of such waste. The veins of minerals are usually intertwined, which means that these rock piles include various metals and target ores that emerge from the ground. Rue's research added rare earth elements to the list of potential constituents washed out of the rock.

Piles of waste rock may seem harmless, but mined metals are often found in rocks that also contain sulfides. When the air and precipitation weather over time, sulfide will degrade and produce sulfuric acid, which will shed residual aluminum, cadmium, iron, lead, zinc and other metals-including Snake in Rue and McKnight's research Rare earths from the River Basin site. Then melting snow or rain brings these metals downstream.

Adequate rainwater and melt water can dilute the impact of metals on downhill waterways, and wetlands can be used as water filters. But warmer, drier climates, along with longer and longer droughts, weaken these mitigating factors.

To understand in detail how these climate influences affect river health, the researchers reviewed river chemical samples collected in the Snake River Basin in central Colorado over the past 40 years. A 2012 study analyzing these data correlated the increase in summer temperature in the area with a five-fold increase in the concentration of zinc and other ecologically problematic metals in the basin’s waterways. The research geologist Andrew Manning of the US Geological Survey is a co-author of the study and conducted a study in 2013 that showed that as climate change extends the basin summers, those warm and dry months Will lower the water table-may expose deeper rock layers to weathering, producing corrosive sulfuric acid. Rue added that the reduction in snow accumulation due to global warming will also lead to an increase in the concentration of dissolved minerals in shrinking water bodies.

"It's amazing that when you start disturbing the climate, all these unforeseen consequences are connected," Manning said. "These ecosystems, especially in the Arctic and mountainous areas, are carefully woven together based on a fairly stable climate."

McKnight’s decades of research on the Snake River Basin have documented that more and more acidic water releases more heavy metals (possibly including rare earths) from the rocks. She recalled that when students first tested the pH of a stream at a location there, the result was extremely acidic at 2.7, "I said,'This can't be right.' It is true." A 2007 item The study concluded that acid rain is generally closer to neutral, around 4 in the pH range-this is also the level at which enough metals dissolve into the water to kill rainbow trout in the basin.

Downstream, dissolved metals can damage the water supply of human communities. For example, the Snake River Basin flows into the Dillon Reservoir to provide drinking water for Denver. Todd Hartman, a spokesman for Denver Water, said that dilution and sedimentation solved most of the problems, but utilities paid close attention to the issue of mine water being discharged into drinking water. McKnight added that if nearby ski resorts must rely on more mineralized and acidified water to make artificial snow, the problem will become more complicated. Melting in the spring can flush the metal collected in the artificial snow of the previous winter into a nearby stream in concentrated pulses.

Manning said that Rue's discovery is not so much a cause of alertness as it is a clue to further research.

"We have so few watersheds with long-term water quality data that we face a bigger question:'How common is this?'" said Manning, who recently sampled Colorado watersheds to try to answer this question. "This is a very worrying issue, but the big thing we are trying to figure out now is how worried we should be. We just don't know."

Rue's work witnessed him frolicking around New Zealand's waterways-some of which had iron oxide thick enough to dye his tennis shoes orange. About four years ago, during a trip there, Rue visited an abandoned coal mine with natural alkaline oyster shell tanks to neutralize the acid runoff from the old mine and reduce the metal load from it. He hopes to see similar innovations in the United States to solve the problem of polluted runoff from abandoned mines. As the demand for rare earth elements exceeds that of the global supply chain, if technical and legal obstacles can be overcome, extracting minerals from the sewage of these mountain streams can not only meet manufacturing needs, but also alleviate environmental problems.

"But it's not about finding the next prosperity," Rue said. "It's about finding sustainable solutions to environmental problems... We are already in trouble, so we must get rid of it scientifically."

Elizabeth Miller is an environmental journalist covering the West. Follow her on Twitter @WroteElizabeth.

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