Microplastics have been found to be so light they can be carried on the wind and transported to far-flung parts of the ocean, including those that appear to be clear of the pollutant.
“A handful of studies have found microplastics in the atmosphere right above the water near shorelines,” said Dr Miri Trainic, researcher at the Weizmann Institute. “But we were surprised to find a non-trivial amount above seemingly pristine water.”
While the process through which oceans absorb materials from the atmosphere has been well studied, the opposite process (aerosolisation) – in which volatiles, viruses, algal fragments and other particles are swept from seawater into the atmosphere – has been investigated less thoroughly. As part of this effort, aerosol samples were collected for study in order to understand exactly what plastic was getting into the atmosphere.
The researchers detected high levels of common plastics – polystyrene, polyethylene, polypropylene and more – in their samples.
Then, 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 the plastic bags and other plastic waste that had been discarded near the shore and made its way into the ocean hundreds of kilometres away.
Checking the seawater beneath the sample sites showed the same type of plastic as in the aerosol, providing support for the idea that microplastics enter the atmosphere through bubbles on the ocean surface or are picked up by winds, and are transported on air currents to remote parts of the ocean.
“Once microplastics are in the atmosphere, they dry out, and they are exposed to UV light and atmospheric components with which they interact chemically,” Trainic said. “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.”
Vardi said: “On top of that, 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.”
“The real amount of microplastic in the ocean aerosols is almost certainly greater than what our measurements showed, because our setup was unable to detect those particles below a few micrometres in size,” Trainic added.
“For example, in addition to plastics that break down into even smaller pieces, there are the nanoparticles that are added to cosmetics and which are easily washed into the ocean, or are formed in the ocean through microplastic fragmentation.”
In the case of plastic particles, size does matter, not only because lighter ones may stay airborne for longer periods. When they land on the water’s surface, they are more likely to be eaten by small marine life, which cannot digest them. Thus, every one of these particles has the potential to harm a marine organism or to work its way up the food chain and into our bodies.