Microplastics found in freshly fallen snow in Sierra Nevada

Microplastics are everywhere — including in Nevada’s snowpack.

After years of skiing on freshly fallen snow in remote locations across the Sierra Nevada, Aleksandra Karapetrov — an environmental toxicologist at the University of California, Riverside — wondered how pristine the snow really was. 

Over six months, Karapetrov and a team of University of California, Riverside scientists tested fresh snowfall at seven sites across the Sierra Nevada and found something they did not expect: a steady delivery of tiny plastic fibers, even in the most remote locations.

“It was surprising the consistency at which we found microplastics everywhere,” Karapetrov said. “It’s kind of disrupting this narrative of pristineness. I hope it brings awareness to the circularity and widespreadness of pollution. There’s this boomerang effect, and it’s important we recognize that.”

The study was published this month in the journal Environmental Science and Technology.

Though the study did not determine how much plastic ultimately reaches drinking water, the findings could be significant as the Sierra Nevada snowpack supplies about 60% of freshwater in northern Nevada. 

Microplastics appeared in snow at both remote and populated sites, but populated sites had roughly three times the average concentration. Most commonly, the researchers found plastics commonly used in clothing and packaging.

“There were a handful of studies at the time looking at microplastics and snow, but folks weren’t really getting out to what I would consider remote,” Karapetrov said.

Microplastics research is still in its infancy, said Karapetrov. No one knows how widespread microplastics in drinking water and snowpacks really are. There is still no standardized method to test for them either. And no one knows what dose may be safe to consume, since the human health effects are also largely unknown.

But researchers have found that some chemicals used in plastics have documented health effects including hormone disruption, inflammation, and cellular damage.

The plastic particles found were made of different materials and range in size from 1 micron — the size of one one-thousandth of a millimeter — to 5 millimeters.

The study also describes how snow scavenges airborne plastic from the atmosphere and carries it to the ground, far from population centers and places where the plastic is produced or used. 

Researchers think microplastics enter the air when plastic products shed fibers or wear down into small fragments. Those fibers are eventually blown by winds and then – through mechanisms which are not fully understood – transported long distances through the atmosphere.

Longer dry periods were associated with higher concentrations of microplastics following storms, possibly reflecting atmospheric buildup, said Karapetrov.

As snowflakes fall, they collect some of these tiny plastic particles suspended in the air. This process, called scavenging, helps explain why researchers measured substantially more plastic arriving with the falling snow than during dry weather.

“Snowflakes have such a big surface area, it’s well known that they’re good for scavenging particles in general, like dust particles and minerals, from the atmosphere,” Karapetrov said.

The University of California, Riverside study examined how much is being deposited on the ground during individual storms, allowing researchers to connect measurements with particular weather events.

“We’re reporting the amount of microplastics coming out in a single storm, and that’s like what the novelty here is,” Karapetrov said. “We can calculate the rate of microplastics that were deposited in a storm, and so that time point resolution is what’s really unique.”

To explore where the plastics may have originated, the researchers traced masses of air that ushered in the storms sampled in the study. Most of the storm air passed over California’s Fresno and Madera counties, suggesting the Central Valley may be a region contributing these particles. 

“There’s local transport, so coming from nearby towns in a 10 to 20 mile radius, but also there’s regional transport that’s happening with these sizes of microplastics,” Karapetrov said.

Earlier research has already established that microplastics occur in snowpack across the west and globally. Plastic pollution has been found from the summit of Mount Everest to the depths of the oceans. Previously, research groups have found plastics in the atmospheric fallout of Dongguan, China, Tehran in Iran, and Paris, France.