In 2017, Janice Brahney was examining dust that had blown across the wilderness of the Western United States to determine its nutrient composition. She slid her samples under a microscope, expecting to see the usual quartz and feldspar grains, pollen and random bug parts.

Instead, what leaped from the lens were candy-colored shards and spherules – blue, pink and red plastics mixed with the dust like foul confetti.

“I was really taken aback when I saw this,” said Brahney, an assistant professor of biogeochemistry at Utah State University. “I had no idea that our pollution had extended to that level.”

Sensing a potential discovery, Brahney, along with fellow researchers, started monitoring dust deposits in nearly a dozen protected areas in the West – places we tend to think of as relatively pristine, like Joshua Tree National Park, Rocky Mountain National Park and the Grand Canyon.

At each location, they found microplastics blown in on the breeze. In a study released Friday in the journal Science, they reveal just how much plastic is landing on protected areas in the West: more than 1,000 tons each year, equal to 123 to 300 million pulverized plastic water bottles.

Not many hikers huffing up a mountain trail would realize they might be breathing in components of what used to be somebody’s snazzy nylon pants. Minuscule plastic particles – microplastics, made from artificial-clothing fibers, broken-down consumer products, beads used in medical and industry applications and other sources are practically undetectable to the naked eye.

But they’re ubiquitous now, thanks to a world that generates hundreds of millions of tons of plastic every year.

“We are producing something that doesn’t go away, and just because we can’t see it doesn’t mean it’s not there,” Brahney said.

The study found microplastic particle sizes that ranged between 4 and 188 microns, which are as small as one-tenth the width of a human hair. On the upper end, the researchers found particles twice the size of fine beach sand. Some of the smaller particles can, if ingested, become lodged in human lungs.

We’ve known for decades that plastics litter the oceans, accumulating in floating garbage patches, piling up like landfills in deep-sea trenches and eaten by the tiniest organisms in the marine food chain.

But it hasn’t been until recently that scientists realized it was flying above our heads, similar to how dust particles are picked up by the wind. One of the first studies on this phenomenon came out in 2015 – through the precise mechanisms of uptake and deposition, and, more importantly, their consequences, are still poorly understood.

The discovery of airborne plastic dusting cities and agricultural areas as well as more-remote locations have alarmed the research community that studies such contamination. “Atmospheric transport means our wilderness areas – and thus our safety net of ecosystems, insects, and animals not affected by farming – are not safe,” Steve Allen, a plastics researcher at Scotland’s University of Strathclyde, said via email.

“The effects of microplastic on these areas is still being researched, but it is known that even the physical act of eating it can block the digestive tract of small creatures like worms. That is not even counting the mutagenic, carcinogenic and endocrine-disrupting chemicals that plastic carries,” Allen said.

Brahney’s work sheds new light on the atmospheric plastic cycle, revealing the role that cities play as generation tanks, how storms can fling plastics many miles away, and vast ribbons of lightweight plastic whizzing across vast distances on the power of large-scale atmospheric circulation like the jet stream.

This research “has shown that it is not a simple process of source to deposition and that it is influenced by the bigger atmospheric processes,” said Allen, who in 2019 released a study of microplastic deposition in the French Pyrenees.

“This opens up a lot of new questions on the mechanisms and factors influencing this transport. It is exciting and very worrying.”

So what’s behind the great aerial migration of plastic?

To find out, Brahney used a publicly available computer model from the National Oceanic and Atmospheric Administration (NOAA) called HYSPLIT that reconstructs the source regions of a particular air mass.

“You can give it a point in space and say, ‘Tell me for the previous 48 hours where that air mass came from, and it gives you this nice spatial output of (its) trajectory,'” she said.

The detective work pointed one of several fingers at cities. The highest deposition rates of “plastic rain” the researchers found was in Rocky Mountain National Park, less than 50 miles from Denver and Fort Collins. Colo.

That cities influence the drift of microplastic makes sense, as they’re where most people and plastic sources are located. Human activity can release plastic into the air in a variety of ways, from spraying industrial paints and coatings that contain microbeads to running clothes dryers that belch out fibers to driving on tires that degrade into nasty black dust.

Thunderstorms might not just bring rain and lightning, but also torrents of microplastics after they pass over urban centers and erodible soils. “We were able to show that a storm track and the energy from a storm can pick up a lot of plastics from a city and deposit it somewhere remotely,” Brahney said.

The National Park Service, for its part, recognized the potential hazards that come with so much microplastics raining down within its protected areas.

“The NPS is concerned about the deposition of microplastics in parks and wilderness areas. The recent study further contributes to the large body of evidence that microplastics are everywhere, including remote and high elevation areas,” Kristi Morris, a physical scientist in the air resources division of the National Park Service, said via email.

“Further studies are needed to understand some key mechanisms that enable microplastics to be emitted and transported over large distances and to better understand the effects that microplastics have on park ecosystems and biota,” Morris stated.

“(An) important question to me is: How much microplastic is in the atmosphere in comparison with other natural particles, and does this actually have the potential to affect weather patterns?” Melanie Bergmann, a marine ecologist who studies microplastic at Germany’s Alfred-Wegener-Institute, said via email.

“Particles can act as nuclei for condensation. This depends of course on the particle load and sizes, but it is a question to tackle in my opinion.”

Even without cities and storms, plastic fallout seems to always be persistent, billowing and falling like invisible, non-digestible snow. This constant deluge of plastic is typically made up of smaller, lighter particles like fibers, which can travel vast distances under the influence of high-level winds like the jet stream.

“I think we can identify (if) it’s coming from far away and it’s within the size range that can move across continents,” Brahney said. “Given the amount of plastics we’ve put into the world, there’s no reason to think it hasn’t been moving around the globe.”

That means the flake of ethylene-acrylic copolymer now landing imperceptibly on your nose could’ve originated from, say, somewhere in Morocco. Or perhaps Fiji, as it has been shown that microplastic can erupt from the surface of the ocean in a process called bubble-burst ejection.

Short of installing giant HEPA filters from the North to South Pole, can anything be done to stop the circulation of airborne plastic? One obvious solution is to reduce our plastic production, which continues at a rampant pace. A consumer movement has taken hold worldwide to eliminate the use of plastic straws, for example, but this goes only so far.

The goal of cutting plastic use is increasingly at odds with oil companies looking for new profit sources that are turning increasingly to plastics.

“This is important in an era of a shale-gas fracking boom, which is closely linked with the production of polyethylene, the most common plastic produced,” Bergmann said.

“Building of new (plastic-making) infrastructure is on the way with $180 billion of investments, rather than reductions.”

In the meantime, we can contemplate the implications of inhaling particles of plastic of a size known to be small enough to be a source of potential harm to human bodies. However, a lack of studies means the effects on people are a mystery.

“The human health effect of breathing this material is almost unknown, in spite of the first study on human lungs being back in 1998,” Allen said. “Simple logic tells us this cannot be good for us. It is hard to imagine a sentence starting with: ‘The health benefits of breathing airborne microplastic …'”

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