Researchers in France said this week that they found thousands and thousands of microplastic particles raining down on a secluded spot in the Pyrenees, 75 miles from the nearest city.

Their study, published 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 dense population centers.

Deonie Allen, one of the lead researchers, said the five-month study was “the first step toward looking at microplastics as an airborne pollutant.” Steve Allen, another researcher, called their findings “scary.”

“We kind of expected to find plastics there, but we certainly were not prepared for the numbers we found,” Mr. Allen said in an interview. “It was astounding: 11,400 pieces of microplastic per square meter per month, on average.”