Microplastics Fell With the Snow at Every Sierra Nevada Site Scientists Sampled

Microplastic particles turned up in freshly fallen snow at every Sierra Nevada site that a University of California, Riverside team sampled, the remote backcountry included, over six months of monitoring published Oct. 27, 2026, in Environmental Science & Technology.

Aleksandra Karapetrova, an environmental toxicologist at UC Riverside, and colleagues measured the particles, tiny fragments and fibers of plastic, in freshly fallen snow, in the snowpack and in dry fallout between storms. The paper reports plastic deposition rates in what they call a critical water resource, introduces faster infrared methods for identifying the particles, with fibers singled out, and gives a basis for long-term monitoring of plastic in the air.

Average concentrations in fresh snow ran 11.8 to 37.5 particles per liter at the remote sites, significantly less, the authors report, than the 68.3 to 92.9 particles per liter at the one site they describe as affected by human activity. Average bulk deposition rates were estimated at 267 to 3190 particles per square meter per day at the remote sites, against 3242 to 7480 at the affected site.

Back-trajectory modeling of the air arriving at the sites pointed to upwind regions that were mostly agricultural and suburban, while activity close to a site can also affect how much plastic its snow carries.

Karapetrova reached one collection site by chairlift and skied to the rest, according to a statement released by UC Riverside. "But no matter how far out the site, I always found microplastics there," she said.