Most of our plastic waste gets buried in landfills, incinerated or recycled -- but up to 18% ends up in the environment. Since plastic isn't easily decomposable it instead fragments into smaller and smaller pieces until the microplastics are small enough to be swept into the air.
"Akin to global biogeochemical cycles, plastics now spiral around the globe," said the study, led by researchers from Utah State University and Cornell University, and published in the journal Proceedings of the National Academy of Sciences.
That means much of the plastic that gets dumped in the sea and across the land is broken down and spat back out, posing potential risks for our ecosystems. And though there has been some progress with the creation of biodegradable polymers, the researchers warned microplastics "will continue to cycle through the earth's systems."
"We found a lot of legacy plastic pollution everywhere we looked; it travels in the atmosphere and it deposits all over the world," said lead author Janice Brahney in a news release from Cornell. "This plastic is not new from this year. It's from what we've already dumped into the environment over several decades."
The research team collected atmospheric microplastic data from the western United States from 2017 to 2019, and found an estimated 22,000 tons of microplastics are being deposited across the US each year.
In the US, the main way plastics get tossed into the air is through road traffic. Car tires, brakes and even road surfaces contain plastic, which can be worn down into microplastics that enter the atmosphere. The turbulence of cars on the road -- the motion of tires, the braking process, the exhaust they emit -- all help churn up plastic on the ground and send it skyward, according to the study.
This happens in the ocean, too, where large clusters of waste form entire plastic islands. They are broken down into plastic particles that sit on the top layer of the water, where they are tossed into the air by waves and wind.
There are several other ways microplastics enter the atmosphere, in large cities through the wind, and in farms through soil dust during agricultural processes.
Once they enter the atmosphere, plastics can stay airborne for up to six and a half days, according to the study. Within this time, "under the right conditions, plastics can be transported across the major oceans and between continents, either in one trip or by resuspension over the oceans," the study said.
The US, Europe, Middle East, India and Eastern Asia are hotspots for land-based plastic deposition, said the study. Meanwhile, ocean sources of airborne plastic are more prominent along the coasts, including the US' West Coast, the Mediterranean, and southern Australia. Dust and agriculture sources for microplastics are more prevalent in northern Africa and Eurasia, while microplastics from road traffic are major contributors in "heavily populated regions" worldwide.
Microplastics are everywhere -- they influence soil and plant production, are consumed by flora and fauna, and "act as vectors for contaminants," said the study. Though previous studies have not found that microplastics pose a threat to human health, this study's researchers warned they "may have negative and as yet unknown consequences for ecosystems and human health."
"The inhalation of particles can be irritating to lung tissue and lead to serious diseases, but whether plastics are more or less toxic than other aerosols is not yet well understood," said the study. It added that further research is also needed to understand the impact of different factors including population density and ocean circulation.
The researchers also called for better plastic waste management.
"Our relative ignorance of the consequences despite rapidly rising plastic concentrations in our environment highlights the importance of improving plastic waste management or, indeed, capturing ocean plastics and removing them from the system," the study said.
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April 13, 2021 at 11:10AM
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