The Rocky Mountains, known for their natural beauty and as a critical water source for communities throughout the Western United States, undergo a transformation in winter when storms blanket them in snow. However, these storms are not merely covering the peaks with a pristine layer of white; they are also introducing contaminants that pose a potential threat to the environment and public health.

A recent study led by Monica Arienzo, a researcher at the Desert Research Institute’s Division of Hydrologic Sciences, presents alarming findings regarding the presence of metal pollutants in the snow covering the Rockies. Published on March 26 in the journal Environmental Pollution, the study highlights the ecological repercussions of mining activities in the region and the ways in which environmental processes transport hazardous materials.

Arienzo and her research team embarked on an extensive investigation to assess contamination levels of metals including mercury, cadmium, zinc, and antimony in the snow that blankets the Rocky Mountains. “Metal pollution in the Rockies is relatively understudied,” Arienzo shared in a statement. “While previous studies have concentrated on specific areas, our research spans a transect from Montana to New Mexico, making this study notably unique.”

In the spring of 2018, the team collected snow samples from 48 different locations across the Rockies. They meticulously analyzed the concentration of various metal contaminants in these samples. To accurately identify the amount of contamination attributable to human activities, the researchers compared the levels of metals originating from natural dust, such as calcium, to those resulting from both natural sources and human activities.

“When you start to see these trends that are consistent across different records, it reinforces your confidence that something significant is occurring here,” Arienzo explained.

The findings indicated that the snow in the northern Rocky Mountains exhibited higher concentrations of metal contaminants from human activity compared to the southern Rockies. Key states such as Montana, Idaho, and Northern Wyoming were highlighted for their elevated levels of these pollutants. Fortunately, the researchers noted that the concentrations detected remained within the safety guidelines established by the U.S. Environmental Protection Agency for drinking water and aquatic life.

To validate their results, the team compared their findings with data from the National Atmospheric Deposition Program, which documents calcium and mercury levels in rain from 2009 to 2018. Notably, this comparison reinforced their conclusions, demonstrating a correlation between snow and rain data.

“I was surprised by the amount of agreement we observed across all these different data sets we compiled,” Arienzo reflected. “The snow samples indicated that contamination is greater in the northern Rockies, which was particularly fascinating. The analysis of mercury contamination over time allowed us to determine that the patterns we observed in 2018 are not anomalies. Repeated trends give us greater confidence that a significant issue is at play.”

The researchers also reconstructed the trajectory of winter storms in 2018 and found that many storms affecting the northern Rockies originated from the Pacific Northwest. In contrast, storms impacting the southern Rockies primarily came from the Mojave Desert. This led them to surmise that the heightened levels of metal contaminants in the northern Rockies snow are likely the result of dust carried from mining sites in the Pacific Northwest, Idaho, and Montana.

“Our hypothesis is that dust from both active and historical mining operations gets lifted into the atmosphere by storms and subsequently deposited across our study sites,” Arienzo noted. “This study underscores the necessity for ongoing scientific monitoring efforts and the urgent need to address both current and historical mining sites.”

Even amid the seemingly untouched snow of the Rocky Mountains, the lasting impact of human activity is palpable, leaving behind a legacy that demands attention and action.