“Plastics now spiral around the globe”
Microplastics can be thought of as litter that never, ever goes away. New research into this seemingly invisible pollution shows just how durable they can be as they go from land to sea to air and back again.
Every day, microplastics — often smaller than the head of a sewing needle — infiltrate our oceans, our seafood, and even our own bodies. Now, scientists say the problem is more extreme than previously realized.
In a study published Monday in the Proceedings of the National Academy of Science, researchers suggest atmospheric microplastics — bits of fibers and fragments in the air — can re-enter the atmosphere, even if they’ve already settled on land or water.
Three striking findings are:
- 84 percent of atmospheric microplastics in the western U.S originate from road dust.
- The greatest concentration of atmospheric microplastics is estimated to be over the ocean.
- While Antarctica contributes no microplastic emissions, it’s still polluted by microplastics.
What’s new — Co-author Natalie Mahowald is a Cornell University professor whose specialty is Earth and atmospheric science. While previous research shows microplastics can reach remote parts of Earth — far away from their origin — this study provides new and alarming data, Mahowald tells Inverse.
“Our paper suggests that not only are microplastics getting to remote regions, but they are being resuspended from the ocean, agricultural regions, or roads into the atmosphere,” Mahowald says.
Furthermore, Mahowald and colleagues found approximately 1 gigagram (Gg) of microplastic sits in the atmosphere over the western United States. For context, 1 gigagram equals 1,000,000 kilograms.
The study team found three sources that contribute to the pervasiveness of microplastics in the atmosphere above the western U.S.: roads, the ocean, and dust from agricultural production.
- The largest contributor to microplastics was roads (84 percent)
- The second-highest contributor was oceans (11 percent)
- The final and least contributing source was agricultural dust (5 percent)
On average, the study suggests particles linger in the atmosphere for different periods of time, ranging anywhere from an hour to 6.5 days. This depends on the size and source of the microplastic.
How they did it — To measure microplastic abundance, the team sourced information collected by data stations throughout the western United States for 14 months.
Armed with this data, the scientists modified atmospheric models to determine where atmospheric microplastics were coming from, their time spent in the atmosphere, and where they accumulated above Earth’s surface.
They also examined the size of microplastics, dividing them up by big, medium, and small particles (though they used the medium-sized particles as their baseline for reference).
They included only microparticles that were bigger than 4μm (micrometers), as smaller particles can be harder to track and measure. Four micrometers is 0.004 millimeters.
For comparison, the head of a sewing needle ranges from half a millimeter to 1 millimeter, so microparticles really can be quite tiny.
Finally, the scientists applied their model to a global context to understand the bigger impact of microplastics in the atmosphere.
Digging into the details — While previous research already found microplastics can enter Earth’s atmosphere, this data provides new insight into the range of sources contributing to the polluted spread.
“Our combination of model and data suggest that those microplastics may well come from not only road sources, but also agricultural dust and oceans,” Mahowald says.
Critically, roads may not specifically contribute to atmospheric microplastics. Instead, it’s more about plastic particles are being carried — through winds or other means — and being deposited on roads, including roads that are far from human cities.
Tires driving over these roads then break down plastic particles — which would otherwise be too big to ascend into the atmosphere — into finer microplastics, enabling them to be launched into the atmosphere.
However, we can’t discount the important role that oceans play in circulating microplastics, the study argues. “Most continents were net importers of plastics from the marine environment, underscoring the cumulative role of legacy pollution in the atmospheric burden of plastic,” the scientists write.
Why it matters — Ultimately, the team found microplastics could wind up far from their original dumping site. The research suggests the greatest concentration of atmospheric plastics is above the ocean, while Antarctica was found to have its own microplastic pollution — despite being so far from the actual creation of microplastics.
“The idea that microplastics are being resuspended means that all the unmanaged plastics we are accidentally dumping into the ocean or on land could be ending up in other remote regions,” Mahowald says.
Furthermore, Mahowald’s research suggests microplastic pollution is increasing. And while recent research found microplastics in the placenta of unborn children, we still don’t really know how microplastics affect health.
“Given these preliminary findings, the accumulation and transport of microplastics in the natural environment may have negative and as yet unknown consequences for ecosystems and human health,” the study team writes.
What’s next — The researchers write that their study “leads to more questions than it definitively answers.”
Some of these questions have to do with constraints in the data. The study relies on data from the western U.S, which means that there’s a high degree of uncertainty about the application of these findings on a global scale. As the study authors put it, “plastics now spiral the globe.”
For example, the authors suggest that plastic is used more in road materials in Europe and Asia than in the U.S. — which could alter the degree of plastics entering the atmosphere from roads. The researchers also hypothesize that Africa and Asia are the largest global source of plastic, so further studies are required on these continents specifically.
Different agricultural practices around the globe — such as greater use of plastic mulch in China’s agricultural fields — could lead to a bigger release of microplastics into the atmosphere in those regions. Meanwhile, coastal areas may face a greater atmospheric concentration of microplastics from ocean spray. Changing ocean currents could also affect the distribution of microplastics.
Ultimately, the team argues that our “relative ignorance” should spur us to improve plastic waste management and technologies that can capture and remove plastics from the ocean.
Abstract: Plastic pollution is one of the most pressing environmental and social issues of the 21st century. Recent work has highlighted the atmosphere's role in transporting microplastics to remote locations'S. Allen et al., Nat. Geosci.12, 339 (2019) and J. Brahney, M. Hallerud, E. Heim, M. Hahnenberger, S. Sukumaran,Science368, 1257–1260(2020)]. Here, we use in situ observations of microplastic deposition combined with an atmospheric transport model and optimal estimation techniques to test hypotheses of the most likely sources of atmospheric plastic. Results suggest that atmospheric microplastics in the western United States are primarily derived from secondary re-emission sources including roads (84%), the ocean (11%), and agricultural soil dust (5%). Using our best estimate of plastic sources and modeled transport pathways, most continents were net importers of plastics from the marine environment, underscoring the cumulative role of legacy pollution in the atmospheric burden of plastic. This effort uses high-resolution spatial and temporal deposition data along with several hypothesized emission sources to constrain atmospheric plastic. Akin to global biogeochemical cycles, plastics now spiral around the globe with distinct atmospheric, oceanic, cryospheric, and terrestrial residence times. Though advancements have been made in the manufacture of biodegradable polymers, our data sug-gest that extant nonbiodegradable polymers will continue to cycle through the earth’s systems. Due to limited observations and understanding of the source processes, there remain large uncertainties in the transport, deposition, and source attribution of microplastics. Thus, we prioritize future research directions for understanding the plastic cycle.