When you stand on a beach and take in a great big gulp of fresh air, you’re actually breathing bacteria, viruses, and aerosolized salts. Those are all punted into the air when whales breach or waves crash or even when bubbles rise to the surface of the sea, ejecting material that gets caught up in sea breezes and fog banks. And as much as I hate to rain on your beach day, you can now add an omnipresent pollutant to that list of debris: microplastics.Microplastics are the ground-up remnants of plastic bottles and bags, or the synthetic fibers shed from your polyester clothing—technically anything smaller than 5 millimeters long—and of late scientists have been finding them everywhere, from the deep sea to the tallest mountains . And now, writing today in the journal PLOS ONE, researchers from Europe and South Africa demonstrate in the lab how popping bubbles can fling microplastics into the air; the same team also gathered microplastics from the air flowing over a French beach. The picture ain’t pretty: They found that up to 19 microplastic fragments float in a cubic meter of air. Even worse, they were measuring at the edge of relatively clean Atlantic waters—highly polluted seas like the Mediterranean are probably flinging far more particles onshore. Globally, the researchers calculate that 136,000 tons of microplastic could be blowing onshore each year.
Up until now, scientists had considered the ocean to be a kind of microplastic sink. When you wash your clothes, for instance, synthetic fibers flow in wastewater to a treatment plant, which only removes some of the microplastic before pumping the water out to sea. Plastic trash also flows into rivers and eventually out to sea, where it breaks into ever-smaller pieces over time. Ocean currents then transport the microplastic particles far and wide: Just last month, another group of researchers showed how microplastics flow into the deep sea , eventually settling in sediment and corrupting seafloor ecosystems.
And in the ocean the plastic bits stayed, researchers once thought. But this new work shows how something as minuscule as a bubble can burp microplastics into the atmosphere. Oceanic bubbles are quite complex; when one comes to the water’s surface, it brings both air and hitchhikers. “That bubble actually acts as like a sponge for tiny particles like sea salt, viruses, bacteria, and—potentially—plastics, as it comes up through the water column,” says University of Strathclyde microplastic researcher Deonie Allen, co-lead on the new research. “So the outside of that bubble is now sort of coated in particles.”
When the bubble surfaces, half of it protrudes above the water line, with the other half hidden beneath it. “On the top side out of the water, you've got a very thin layer of water, which when it bursts actually fragments, and that releases nano-sized materials,” says University of Strathclyde microplastic researcher Steve Allen, co-lead on the work. (The Allens are spouses.) “But when the ocean tries to fill the void left by the bottom half of the bubble, it comes in from all sides and produces the ejection, or the jet,” he continues.
In the lab, the Allens and their colleagues used a black light, or long-wave ultraviolet light, to watch this phenomenon in action, as their bubbles spewed fluorescent materials into the air. Scientists were already well aware that oceanic bubbles fling viruses, bacteria, and salts into the atmosphere, but in this experiment they’ve shown that microplastics come along for the ride as well.
And that’s not even the most violent transport method in the sea: All sorts of gunk is flung into the air when waves crash against the shore. It’s this particulate matter that makes its way into the atmosphere, attracting moisture to form fog.