Rocky Mountain snow contains toxic metals from faraway mining

Snowpack in the Rocky Mountains acts like nature’s reservoir. It stores water during winter and supplies the American West through dry months. But snow now brings more than just water.

A new study from Desert Research Institute reveals that as storms deliver snow, they also transport mercury and other mining-related pollutants.

This work sheds light on how contaminants travel through the atmosphere. It raises concerns about both snowpack quality and long-term environmental consequences from mining operations.

Toxic metals found in snow

Published in Environmental Pollution, the study measured metal contaminants at nearly 50 sites across the Rockies. Researchers found elevated levels of mercury, zinc, cadmium, and antimony. These metals appeared most concentrated in the northern Rockies.

The likely source? Storms that originated in the Pacific Northwest, Idaho, and Montana — regions with a long mining history. Using storm-tracking techniques, the team followed weather patterns to pinpoint these sources.

“Metal pollution in the Rockies is relatively understudied,” Arienzo said. “Other studies have focused on certain parts, so the fact that we have this transect from Montana to New Mexico makes this study unique.”

Dust, snow, and the power to melt

While the contamination remains below EPA limits, the concern isn’t just toxicity. Dust from mining regions reduces snow’s reflectivity, causing it to melt faster. This changes how much water communities get and when they get it.

Beyond snowmelt timing, the study’s value lies in understanding atmospheric pollutant distribution. Combining physical samples with long-term datasets allowed researchers to build a broader picture of contamination patterns.

Long-range pollution patterns

In 2018, scientists collected snow samples across 48 Rocky Mountain sites. They measured metal levels, including calcium from natural sources. By comparing metals tied to both dust and human activity, they could isolate industrial impacts.

To test the strength of their findings, they added another layer — mercury and calcium data from the National Atmospheric Deposition Program, collected between 2009 and 2018. Patterns held steady.

“I was surprised by the amount of agreement we saw between all these different data sets we brought together,” Arienzo said.

“The snow samples showed us that contamination is higher in the northern Rockies, and that was really interesting. Looking at mercury contamination over time helped us say that 2018 is not just a fluke.”

“When you start to see these trends that are consistent between different records, it makes you feel more confident that something’s really happening here.”

Mining sites in the path of snow storms

Tracking storms gave the team another clue. Northern Rockies storms often came from the Pacific Northwest. Those in the southern Rockies mostly crossed the Mojave Desert.

By overlaying these paths with USGS maps of mining and smelting sites, they saw a clear link. Active and historical mines sat directly in the path of northern storms.

“Our idea is that the dust from current and historical mining sites gets carried up into the mountains and deposited across our study sites,” Arienzo said.

“This study shows the importance of continued scientific monitoring efforts, like the long-term USGS datasets we used here, as well as mitigation of current and historical mining sites.”

Studying mining pollution in snow

This research is part of a larger initiative funded by the National Science Foundation. In addition to studying snow, Arienzo and her team are examining tree rings as a natural archive of environmental pollution.

Trees, like snow, accumulate traces of mercury and other metals over time. By comparing the mercury levels found in snow to those recorded in tree rings, scientists aim to build a more complete picture of how contaminants move through ecosystems.

This comparison could reveal long-term trends in pollution levels, helping scientists understand not only where contamination is happening but how it changes over decades. These insights can inform environmental cleanup efforts, water management policies, and public health decisions.

Understanding how pollutants travel

As the climate shifts and industrial legacies resurface in unexpected ways, understanding how pollutants travel through the atmosphere becomes more urgent.

The snow that once symbolized purity now carries a story of industrial history, scientific discovery, and environmental responsibility.

With continued research, we may better understand these silent risks and work toward protecting the landscapes we depend on.

The study is published in the journal Environmental Pollution.

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