Microplastics Are 'Spiraling' the Globe Through the Atmosphere, Study Finds

From the deepest part of the ocean to the heights of Mount Everest, microplastics are everywhere. 

They are so pervasive they now "spiraling around the globe" through Earth’s atmosphere the same way chemicals like carbon or nitrogen do, according to a new study published in the Proceedings of the National Academy of Sciences this month.

“The amount of mismanaged plastics in the environment is growing at an incredible rate,” study co-author and Irving Porter Church Professor of Engineering at Cornell University’s Department of Earth and Atmospheric Sciences Natalie Mahowald tells Treehugger. “Like the carbon dioxide in the atmosphere, we are seeing an accumulation of microplastics.”

From Data to Models

To solve a problem, one must first understand it. The new study furthers this goal by being the second to model how microplastics cycle through the atmosphere and the first to do so while considering multiple sources. 

The research builds off of a data set published in Science last year of microplastic pollution found in protected areas in western United States. That study, led by assistant professor Janice Brahney of Utah State University’s Department of Watershed Sciences, examined microplastics deposited by both wind (dry conditions) and rain (wet conditions).

It found plastic that fell with rain was more likely to come from cities, soil, and water while wind-blown plastics were more likely to have traveled long distances. It further estimated microplastics were falling on protected areas in the south and central of the U.S. West at a rate of more than 1,000 metric tons per year.

That study, Brahney tells Treehugger, was the “driving force” behind this month’s paper, which Brahney also co-wrote. 

“Once we had an understanding of how much plastic was being deposited (wet or dry) and what the prospective source areas were, we wanted to see if we could use a model to constrain what landscape types were contributing most to atmospheric loads,” Brahney explains.

Brahney, Mahowald, and their team came up with five hypotheses for the sources of atmospheric plastics and then tested them based on the 2020 data set and a model. 

Understanding the Plastic Cycle

The plastic that ends up in the atmosphere is not being emitted directly from landfills and garbage cans, Utah State University researchers explained. Instead, waste breaks down over time and ends up in a variety of different locations that then feed it up into the air. It's what the researchers are calling "legacy plastic pollution."

The study identified three key sources of secondary plastics:

1. Roads: Roads were responsible for 84% of the plastics found in the western U.S. dataset. Plastics are likely broken up by vehicle traffic and sent into the air by the movement of tires.
2. The Ocean: The ocean was the source of 11% of the plastics found in the dataset. The 8 million metric tons of plastic that enter the world’s oceans every year are likely churned up and spit into the air by wind and wave action.
3. Agricultural Soil: Soil dust deposited 5% of the plastics in the data set. This is likely because microplastics that end up in wastewater elude most filter systems and end up in the soil when that water is included in fertilizers. 

Once launched, microplastics can last in the atmosphere from a couple of hours to a few days, Mahowald tells Treehugger. That’s enough time to cross a continent, she told Utah State University.

The study also modeled how the atmosphere moves plastics around the globe. It found plastics are most likely to be deposited over the Pacific Ocean and the Mediterranean Sea. However, continents receive more atmospheric plastics from the oceans than they deposit into them.

There are high concentrations of land-based plastics in the United States, Europe, the Middle East, India, and Eastern Asia, while ocean-based plastics are prominent along the U.S. Pacific coast, the Mediterranean, and southern Australia. Agricultural dust is a common plastic source in North Africa and Eurasia. 

More Questions than Answers 

While the study is an important first step, it is just the beginning of understanding the atmospheric plastic cycle. 

“As we really know almost nothing about microplastics this study really asks more questions than it answers, but we didn’t even know to ask the questions previously!” Mahowald tells Treehugger. 

One of those questions is exactly where the plastics sent up from roads, waves and dust come from originally. 

Another is what all these microplastics circulating in the atmosphere are doing to the environment and to us.

“Microplastics are not well understood, but we think they could impact human health and ecosystems,” Mahowald explains. “While in the atmosphere, they could serve as ice nuclei, reflect or absorb incoming or outgoing radiation, and change snow and ice albedo. They could also change atmospheric chemistry. We don’t understand them, and should study these possibilities more.”

Mahowald and Brahney’s study is not the first to show that microplastics are ending up in the air. University of Strathclyde researchers Steve Allen and Deonie Allen co-wrote a study last year finding that microplastics were transferring from the ocean to the atmosphere via the sea breeze. 

“There is no doubt that plastics are cycling through the atmosphere, in and out of the ocean and to and from the land,” they tell Treehugger in an email. “The real challenge is in finding out how much and where are the points we can try to stop it.”

They think the new study’s modeling did a “pretty good job” of tracking atmospheric plastics but thought it underestimated the sheer number of microplastics involved. They also noted it was based on a western U.S. data set and that microplastic levels needed to be documented across the globe in a variety of climates and terrains. 

But both research teams share a commitment to understanding microplastic pollution so that it can be prevented. 

“If we can stop the accumulation now when it is not so terrible, we can prevent the type of situation we are in with respect to climate, where drastic action has to take place to prevent bad outcomes,” Mahowald says.

And the stakes could be high. Steve Allen and Deonie Allen noted microplastics can absorb chemicals like DDT, PCBs, and heavy metals which could harm the creatures and ecosystems that encounter them. 

“Humans did not evolve to breathe plastic,” they wrote. “What it does to our bodies is an unknown, but logic suggests it is not good.”