Raining Plastics In The American West

Jun 13, 2020

Microscope image of microplastics in particulate samples. 500 pm.
Credit Janice Brahney / Utah State University

A new study from researchers at Utah State University finds tiny pieces of plastic are being transported atmospherically and deposited on western public lands in astounding annual quantities.

“This study was a total accident. We were intending to try to understand the dust transport of nutrients to remote ecosystems. Seeing plastic in the samples to begin with was very surprising. I was also surprised at the deposition rate. We calculated over 1000 tons of deposition per year to Western protected areas, which is only 6% of the total, contiguous US. And that number just seems enormous considering this is something we can't see," said Dr. Janice Brahney, an assistant professor in the Watershed Sciences Department at Utah State University.

To ensure she and her team weren’t overestimating, Brahney said they used two independent methods to calculate the rates microplastics were deposited—a visual count and FT-IR microscopy, which identifies the chemistry of the dust particles.

Brahney said there are a couple key findings from this study, for people to know.

“So, you know, one is that the atmosphere is accumulating our garbage and transporting it around the world. And I think that this notion that we're recognizing that plastics, most plastic types don't decompose," Brahney said. "They just degrade into small enough pieces where they can be transported in the air.”

She said localized, rainy events, especially over urban centers, deposited larger plastic particles, but less in number. Dry deposition particles were much smaller. This means high-elevation, atmospheric transport processes can move the dust-sized microplastics across continents.

“We don't have a very complete understanding of how plastics are moving through the air around the Earth," Brahney said. "It’s certainly worthwhile to try to understand the global movement of plastics because it would be really important for us to understand what the major sources are and where the major sinks are. So, you know, do we see a latitudinal difference? Where should we expect to see the greatest deposition rate?”