Scientists in Germany are raising the alarm after finding a significant amount of microplastics in snow samples in the Alps and the Arctic — two of the most pristine locations on Earth.

In a study published in the journal Science Advances last week, the researchers said their findings point to a troubling possibility: that plastics aren’t just polluting our lands and clogging our waterways, but befouling the air around us as well.

“I was really astonished concerning the high concentrations” of microplastics found in Arctic snow, study co-author Gunnar Gerdts told the Los Angeles Times. Microplastics are tiny fragments of plastic that often originate from larger debris that have degraded over time. Gerdts’ team said it found up to 14,400 microplastic particles per liter of melted Arctic snow ― a staggering amount for a remote region where few humans reside.

“We found a lot of microplastics, like record concentrations,” Gerdts said of the Arctic snow, “and the question arose: From where does the microplastic originate?”

There are just two possibilities, he noted: “from the water or from the air.”

While it’s known that microplastics and other plastic debris is transported by ocean currents, scientists have become increasingly convinced that small plastic fragments are also being carried through winds and precipitation.

Earlier research conducted in Tehran, Iran, and Dongguan, China, found evidence of microplastics in the cities’ atmospheric fallout. A 2015 study in France found that microplastic concentration in urban dust increased fivefold after it rained, suggesting that rain and other precipitation could play a role in transporting the pollutant to the Earth’s surface. And just last week, researchers from the United States Geological Survey said they’d found evidence that it was “raining plastic” over the Rocky Mountains.

To assess the validity of this precipitation theory, the German researchers analyzed snow samples from a variety of locations including urban areas in Europe, as well as the remote Swiss Alps and ice floes in the Arctic.

“The scientists were careful to sample only snow on the surface because they wanted to see how much microplastic was brought there by fresh precipitation,” the Times reported.

The team concluded that precipitation did indeed appear to have transported the pollutant ― and, in the case of the Alps and the Arctic, over vast distances.

“The large concentrations of [microplastics or MPs] and microfibers in snow highlight the importance of the atmosphere as a source of airborne MPs and microfibers,” the study said. “Through this pathway, MPs likely find their way into soil and aquatic environments and therefore also into food chains.”