Grand Canyon and Joshua Tree Are Being Showered With Microplastics From the Atmosphere, Scientists Discover

Researchers have estimated that more than 1,000 tons of microplastics—enough to make up to 300 million water bottles—are deposited by the wind and rain on National Parks and protected areas in the western United States every year.

The results, published in the journal Science, shed new light on the movement of microplastics around the globe, highlighting the important role of atmospheric transport, a process that has been previously overlooked by scientists.

The world produced nearly 350 million tons of plastic in 2017, according to research, and this figure is growing every year. A large proportion of the plastic that is manufactured accumulates in the environment as waste, eventually degrading into tiny microplastic particles that are now found in nearly every ecosystem on the planet, from the ocean depths to mountain tops.

But while microplastic pollution is ubiquitous, the processes that distribute the particles between marine, terrestrial and atmospheric environments around the planet—referred to as the "global plastic cycle"—remain poorly understood.

Scientists have long understood how airborne dust is transported around the world by winds. But it is only recently that studies have documented microplastics being transported long distances and to remote locations—such as the Arctic—by this dust, which falls to the ground during dry weather, or wet weather, via rain, snow or other forms of precipitation, in a process known as "deposition." The plastic fragments are so small and light that they can be picked up by winds.

In the latest study, Janice Brahney, from Utah State University and colleagues, analyzed the transport and accumulation of microplastics in eleven remote and protected areas across the western U.S., including the Grand Canyon and Joshua Tree National Park. She decided to investigate the issue after an accidental discovery.

"A few years ago I started a program to study phosphorus deposition in dust, the main objective was to characterize dust across space and time and determine how bioavailable dust nutrients were and what the impacts were to remote and sensitive ecosystems," she told Newsweek.

"Because I was very interested in what dusts were made of, I started to look at them under the microscope. In the beginning, I was very surprised to see so many colorful particles alongside the quartz grains and pieces of insects. After the shock settled, I realized there was much I could do with the samples and data I was generating. Because we were sampling at a high frequency and across space, we would be able to say something about where the plastics are coming from."

Grand Canyon
Visitors sit along the South Rim of Grand Canyon National Park, which has partially reopened on weekends amid the coronavirus pandemic, on May 25, 2020. Mario Tama/Getty Images

By comparing the size and shape of particles that fell during wet and dry weather, the researchers found that deposition rates averaged 132 plastics per square meter per day across the eleven areas, which amounts to more than 1,000 tons annually across all western U.S. protected areas if the figures are extrapolated.

In addition, they discovered that larger microplastics were deposited during wet weather, with these likely originating from nearby urban centers during localized storms. Meanwhile, microplastics deposited during dry weather tended to be smaller and had traveled further, having been transported long distances, just like airborne dust.

"I think one of the most important take-home messages [from the study] is that plastics aren't decomposing, only degrading into finer and finer pieces. Just because we can't see them, doesn't mean they aren't there," Brahney said. "It was initially surprising to me to see plastic in atmospheric deposition, but upon learning more about microplastics, it seems we should have anticipated this and it's likely been going on for some time."

"With our data, what we were able to show is that plastics that fall out in rain are more likely to be sourced from local sources, like a nearby city. Whereas plastics falling out of the sky during 'dry' periods appeared to be coming from much further away. We are only scratching the surface, and have a lot more to lean about the atmospheric limb of the plastic cycle," she said.

While the latest finding cast new light on the plastic cycle, there is still much we don't know about the implications of microplastics accumulating in sensitive ecosystems, as well as the impacts of this pollution on human health.

"With respect to [human health,] the size ranges we observed were the right size to be inhaled and could become deposited on lung tissue and upper airways. Some studies have shown this can lead to inflammatory response and lesions, while repeated exposure can have more serious consequences," Brahney said.

"With respect to ecosystems, there have been some studies in the marine environment that have shown implications for marine organisms, though there seem to be mixed results. Some studies have shown blockages in the intestinal tract with negative consequences. I am not aware of any studies with organisms in the terrestrial environment."

Brahney said there have been a handful of interesting studies that have shown that plastics can modify the thermal and other physical properties of soil. And in April of this year, a study was published in Global Change Biology indicating that plastics in the soil can have negative effects on plant production."

"I think it is an important study as we still know so little about microplastic pollution in the air. The interesting part to me is that it highlights the importance of dry deposition, which seems to convey more particles compared with rain," Melanie Bergmann from Alfred Wegener Institute Helmholtz-Centre for Polar and Marine Research, Germany, who was not involved in the latest paper, told Newsweek.

"This raises again the question of health implications for us and other air-breathing organisms, which we still dont know anything about. In addition it highlights once again that microplastics can travel vast distances before being deposited, especially the smallest particles. The article also highlights the implications that microplastic deposition might have on soil ecosystems. It could interfere with microbes and ecosystem services such as biogeochemical cycling. It also shows that we should include monitoring of microplastics as part of air pollution monitoring schemes," she said.

Steve Allen from the University of Strathclyde in Scotland also said that the study was an important piece of work that pushes forward our understanding of microplastics being transported in the atmosphere.

"Their use of wet and dry deposition—in rain or just falling from the sky—together with computer modeling has helped to point to sources really well. This confirms many of the assumptions we have all been using. Namely, that cities are a source for airborne microplastic and that means that we are all responsible for it. It is not just every piece of litter, but every piece of plastic in your yard is likely adding to atmospheric plastic pollution," Allen told Newsweek.

"Our wilderness areas are our safety net. These places, far from high pesticide use and urban pollution, should be safe for complex ecosystems to survive. But as Brahney's group has confirmed microplastics can travel there, then we have lost that safety net. Microplastics carry chemicals in addition to the chemicals in the plastic that they are made from. These are currently being studied and early results are suggesting that microplastics can have a serious effect on insects and animals in soil and water."

In an accompanying article, that was published in the journal Science alongside the latest study, Chelsea Rochman from the University of Toronto and Timothy Hoellein with Loyola University Chicago also praised the study,

"A key insight from the new work is that fundamental tools for studying global dust transport can be applied to microplastics. Like dust, most particles measured were within the size range typical of global transport," they wrote. "However, microplastics are less dense than soil and therefore might travel longer distances than natural dust particles."