It’s been well-documented that rivers and runoff wash huge amounts of this pollution into the sea, but just as much plastic is likely hitching a ride to the ocean by another means: the wind.
The amount of microplastics deposited from the air into the world’s oceans is likely comparable to what flows in from rivers, a new study found. The report provides new insight into a major pathway that is spreading this pollution around the globe.
Carried on the wind, significant amounts of these airborne particles are even reaching the Arctic, where they could be contributing to ice melting, according to the findings published Tuesday in the journal Nature Communications.
Though initial studies have not found that microplastics pose a threat to human health, the authors cautioned that much more research is needed to understand the full scope of the problem and its impacts on ecosystems.
“A few things are well-known, like the amount [of microplastics] lost from clothes in a washing machine,” said Andreas Stohl, a professor of general meteorology at the University of Vienna and one of the co-authors of this study. “But our uncertainty ranges are really large and much, much more work is needed to compare different sources to each other.”
Roadways are a major source of microplastics
To model how microplastics move through the air, the team of researchers focused their attention on a relatively well-known source: our roadways.
The wear and tear of tires and brake pads leave behind huge amounts of these tiny pieces of plastic. Previous studies have found that tire abrasion is one of the most significant sources globally of microplastics in aquatic ecosystems, and is responsible for an estimated 30 percent of all the microplastic particles in our oceans.
It’s also one of the few sources of microplastics that researchers can estimate global emissions for.
“We know relatively accurately how much plastic is used in a tire and we know relatively well how much of a tire is worn down during its lifetime,” said Stohl. “There’s also good information on road traffic, so we could do distribute this globally.”
The researchers used two different models to calculate how much they are producing in different regions of the world.
The most particles are emitted in the eastern United States, northern Europe, major Chinese cities and dense parts of the Middle East and Latin America, they found. Globally, the researchers estimated that more than 3 million tons of microplastics are produced from tire and brake wear.
After estimating how much of these plastics are being generated around the world, the researchers next used a dispersion model to determine where the particles go next.
They found that larger particles — those roughly one-fifth the diameter of a human hair — can float in the air for between five and 11 days, but are typically deposited near the place they were produced.
Smaller particles, however, can drift on the wind for much longer and often do travel great distances, according to Nikolaos Evangeliou, a senior researcher at the Norwegian Institute for Air Research and another co-author of this study.
Of these smaller tire plastics, roughly 57% land in the ocean, making them a major contributor of ocean microplastics.
Microplastics could be connected to Arctic ice melt
But not all airborne microplastics make it to the ocean.
Significant amounts of these tiny particles, the study found, also land on snow and ice surfaces, including in the Arctic.
Since the mid-1990s, the Arctic has warmed at a rate more than twice the global average. The region’s sea ice cover is also shrinking, and Greenland’s massive ice sheet experienced near-record melting in 2019.
Previous studies have found that dark soot particles that land on snow and ice can darken the surface, increasing the amount of heat energy absorbed by the ice and in turn, accelerating melting.
And as dark microplastic particles land in the Arctic, they too could be contributing to melting, the researchers said.
The scientists cautioned, however, that the effects of these deposits on the ice need to be studied further.
“Given the large uncertainties and that we have only considered one kind of microplastics, there are probably more plastics in the Arctic than we know right now,” Stohl said. “This is not the main driver of Arctic melting, but it’s probably a small additional contribution of warmth.”