As plastic litter in the oceans breaks up into smaller bits without breaking down chemically, the resulting microplastics become a serious threat to marine life.

Now we know that microplastics spread farther across the ocean than originally thought.

According to new study at the Weizmann Institute of Science in Israel, microplastic particles smaller than 5 millimeters are swept up and carried on the wind to far-flung parts of the ocean. The minuscule fragments can stay airborne for hours or days before landing back in the water.

“A handful of studies have found microplastics in the atmosphere right above the water near shorelines,” says Miri Trainic, a researcher in the groups of Prof. Ilan Koren, of the institute’s Earth and Planetary Sciences Department, and Prof. Assaf Vardi of the Plant and Environmental Sciences Department. “But we were surprised to find a non-trivial amount above seemingly pristine water.”

Koren, Vardi and Prof. Yinon Rudich of the Earth and Planetary Sciences Department have been collaborating for years on studies about the interface between ocean and air. One of these processes is aerosolization, in which viruses, algal fragments and other particles are swept from seawater into the atmosphere.

As part of this ongoing effort, aerosol samples were collected from the North Atlantic Ocean for study in the Weizmann labs during the 2016 run of the Tara research schooner.

With the help of Weizmann chemist Iddo Pinkas, the researchers detected high levels of common plastics – polystyrene, polyethylene, polypropylene and more – in their samples.

Calculating the shape and mass of the microplastic particles, along with the average wind directions and speeds over the oceans, the team showed that the source of these microplastics was most likely plastic bags and other plastic waste discarded near the shore hundreds of kilometers away.

“On top of that,” added Vardi, “some of these plastics become scaffolds for bacterial growth for all kinds of marine bacteria, so airborne plastic could be offering a free ride to some species, including pathogenic bacteria that are harmful to marine life and humans.”

Trainic said that when microplastics are airborne, they dry out and interact chemically with UV light and other atmospheric components. “That means the particles that fall back into the ocean are likely to be even more harmful or toxic than before to any marine life that ingests them.”

When microplastics land on the water’s surface, they are ingested by small marine animals and can work their way up the food chain to human beings.

“Like all aerosols, microplastics become part of the large planetary cycles – for example, carbon and oxygen – as they interact with other parts of the atmosphere,” said Koren.

“Because they are lightweight and long-lived, we will be seeing more microplastics transported in the air as the plastics that are already polluting our oceans break up – even if we do not add any further plastics to our waterways.”