Researchers said they found microplastic particles raining down on a secluded spot in the Pyrenees, 75 miles from the nearest city.

The study in the journal Nature Geoscience suggests that microplastics — long known as a source of water pollution — may also travel by air, spreading their ill effects far from population centers.

Deonie Allen, a lead researcher, said the five-month study was "the first step toward looking at microplastics as an airborne pollutant."

Researcher Steve Allen said they were surprised by the results. "It was astounding: 11,400 pieces of microplastic per square meter per month, on average," he said.

Microplastics can come from everyday items like plastic bottles or disposable contact lenses that break down over time. The fragments in the study were 10 to 300 microns across, with most about 50 microns, Allen said. For comparison, a human hair is about 70 microns wide.

"These are invisible atmospheric pollutants," Deonie Allen said.