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, published this month in the journal Environmental Science and Technology, found significant amounts of microplastics in fresh snowfall at both remote and populated sites across the Sierra Nevada, which supplies about 60% of freshwater in northern Nevada. 

While populated sites had roughly three times as many microplastics as more remote locations, all sites tested contained microscopic bits of the plastic commonly used in clothing and packaging. 

The remote location of the sites revealed that airborne plastic from the atmosphere is being carried into the Sierra Nevada snowpack from communities miles away, rather than directly deposited by human activity.

Microplastics enter the atmosphere when plastic products shed fibers or break down into small fragments, said Karapetrov. Those fibers and fragments are eventually blown by winds and then – through mechanisms which are not fully understood – transported long distances through the atmosphere.

Snowflakes then collect the tiny plastic particles suspended in the air through a process called scavenging, which are deposited on the ground as snowfall.

“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.

A majority of the storms tracked by the researchers (70%) traveled over the San Joaquin Valley in central California, suggesting the region may be contributing these particles. However, finding the exact origin of the microplastics would take further study, said Karapetrov.

“For the sizes of microplastics that we were detecting there was local transport, so coming from nearby towns within a 10 to 20 mile radius. There was also regional transport. Regional meaning, less than 50 miles,” Karapetrov said. 

The study also noted that researchers found larger concentrations of the smaller microplastics that can travel farther.

Researchers measured between 270 and 3,200 plastic particles per square meter per day at remote locations following snow storms. Areas with more human activity, including a ski area, accumulated as much as 7,500 plastic particles per square meter per day.

The University of California, Riverside study specifically examined how much microplastics are 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.”

Snowfall after prolonged dry periods had higher concentrations of microplastics following storms, possibly due to the accumulation of microplastics in the atmosphere, said Karapetrov.

“Storms that had longer dry periods seem to have trended towards having more microplastics in the snow,” Karapetrov said.

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

Microplastics research is still in its infancy, said Karapetrov. It’s still unclear how widespread microplastics in drinking water and snowpacks really are, and there’s no standardized method to test for them either. 

Some microplastics are so small they can’t be measured using current techniques, meaning microplastic pollution could be more prevalent than currently known, Karapetrov said.

“There’s only so many microplastics of a size range that they’re detecting. We don’t have methods to even measure nanoplastics yet that are verifiable. There’s limits to what we know for sure,” Karapetrov said.

The issue is likely widespread. Earlier research has detected microplastics in snowpack across the west and globally.

Limited research also makes it unclear how microplastic pollution in air and water impacts human health. Researchers have found that some chemicals used in plastics have documented health effects including hormone disruption, inflammation, and cellular damage.