UC Riverside study finds microplastics in fresh Sierra Nevada snow, a major freshwater source for northern Nevada

What the researchers found

A team of scientists from the University of California, Riverside found tiny plastic fibers in freshly fallen snow across the Sierra Nevada, including at remote locations, the Nevada Current reported. The team tested new snowfall at seven sites over six months. The study was published this month in the journal Environmental Science and Technology.

Aleksandra Karapetrov, an environmental toxicologist at UC Riverside, began the work after years of skiing on fresh snow in remote parts of the range and wondering how clean it really was. "It was surprising the consistency at which we found microplastics everywhere," she told the Nevada Current.

Remote and populated sites

Microplastics showed up at both remote and populated sites, but populated sites had roughly three times the average concentration, according to the Nevada Current. The most common types were plastics often used in clothing and packaging. Particles ranged in size from 1 micron, or one one-thousandth of a millimeter, to 5 millimeters.

Why it matters for Nevada

The Sierra Nevada snowpack supplies about 60% of freshwater in northern Nevada, the Nevada Current reported. The study did not determine how much plastic ultimately reaches drinking water. More on regional supplies is available in our water coverage.

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

What is known about health effects

Researchers have found that some chemicals used in plastics have documented health effects, including hormone disruption, inflammation and cellular damage, according to the Nevada Current. Those findings concern chemicals used in plastics, not a measured dose from snow.

How plastic ends up in snow

Researchers think microplastics get into the air when plastic products shed fibers or wear down into small fragments. Winds then carry those fibers, and through mechanisms that are not fully understood, they can travel long distances through the atmosphere. The study describes how snow pulls that airborne plastic down to the ground, far from where it was produced or used.

The scavenging effect

As snowflakes fall, they collect particles suspended in the air, a process called scavenging. That helps explain why the researchers measured substantially more plastic arriving with falling snow than during dry weather. "Snowflakes have such a big surface area," Karapetrov told the Nevada Current.

Longer dry periods were associated with higher concentrations of microplastics after storms. Karapetrov said that may reflect a buildup of particles in the atmosphere.

Measuring single storms

Karapetrov said what is new about the study is that it measures how much plastic is deposited during individual storms. That lets researchers connect their measurements to particular weather events. "We can calculate the rate of microplastics that were deposited in a storm," she said.

Where the plastic may come from

To look for possible sources, the team traced the air masses that brought in the storms they sampled. Most of that air passed over Fresno and Madera counties in California, suggesting the Central Valley may be one region contributing particles, the Nevada Current reported.

Karapetrov described both local transport from nearby towns within a 10 to 20 mile radius and regional transport over longer distances. Earlier research has found microplastics in snowpack across the West and around the world. Plastic pollution has been documented from the summit of Mount Everest to the depths of the oceans.

What to watch next

• How much of the plastic found in Sierra Nevada snow reaches drinking water, a question this study did not answer.
• Development of a standardized method to test for microplastics, which Karapetrov said does not yet exist.
• Research on what dose of microplastics may be safe to consume, since human health effects remain largely unknown.
• Further study of how microplastic fibers travel long distances through the atmosphere, which is not fully understood.