Hundreds of thousands of tonnes of microplastics that make their way to the ocean may be transported back to shore by sea breeze, new research has found.

Microplastic contamination around the planet is ubiquitous and found in nearly every corner of the planet. Previous studies have suggested that microplastics can be transported long distances in the atmosphere by wind and have been discovered in the Pyrenees mountains, raining in the Rocky Mountains, contained within Antarctic ice, and littered on the beaches of some of the world’s most remote islands. In 2018 alone, 359 million tons of plastic was manufactured globally – about 10 percent of which is believed to be transported to the ocean by way of pollution every year. Until now, it was thought that plastics that made their way into the ocean stayed here, moving along with currents before ultimately settling along the seabed.

“Where the oceanic plastics being ‘lost’ is relatively unknown and this research adds a small but important piece to the puzzle,” said study co-author Dr Deonie Allen in a statement.

“We don’t know a lot about the effect on humans but a growing number of studies are showing there is a potential danger from inhalation of microplastic particles.”

Researchers from the University of Strathclyde and Observatoire Midi-Pyrénées reviewed existing literature related to microplastics, finding that evidence suggests microplastics are making their way to “some of the most remote corners of the globe” though there has been “limited discussion” on how they got there. To determine what processes might be contributing to the global spread, the team then conducted a pilot study to analyze microplastics in sea spray along the Atlantic southwest coast of France. For one week, researchers employed a “cloud catcher” machine and pumped filters to capture water droplets, then analyzed them for microplastics. Different wind directions and speeds were tested, as well as conditions for various weather events like a storm or fog.

Researchers discovered the first evidence of microplastics being ejected by sea spray and released into the atmosphere before then being transported back onto land both by onshore and offshore winds. Collected microplastic samples were “dominated by sea spray,” and plastic fragments contained within measured as small as 5 micrometers and as large as 140 micrometers. Fog generated by surf produced the highest concentration of plastic at 19 particles per cubic meter of air.

The findings, which are described in PLOS ONE, indicate that microplastics may be released from the ocean into the atmosphere by “bubble burst ejection” and “wave action” – such as strong wind events or turbulent seas – and being transferred back ashore via sea spray.

“Sea breeze has traditionally been considered ‘clean air’ but this study shows surprising amounts of microplastic particles being carried by it. It appears that some plastic particles could be leaving the sea and entering the atmosphere along with sea salt, bacteria, viruses, and algae,” said Steve Allen, a Strathclyde PhD candidate.

“Bubble ejection of particles is a well-known phenomenon but we have now shown that microplastic is also being ejected from the sea. To date, there has been no consideration of the oceans as an atmospheric microplastic source.”

The researchers conclude that if microplastics can escape the ocean and “become entrained through ocean-atmospheric exchange,” then further research is necessary to better understand the implications of atmospheric microplastic transport.