In a new study from the Weizmann Institute of Science, researchers have discovered that microplastics are carried by the wind to remote parts of the ocean. The tiny plastic particles get swept up into the atmosphere where they can remain airborne for hours or days.
Through this process, microplastics have even more opportunity to invade the marine environment and work their way into the food chain.
“A handful of studies have found microplastics in the atmosphere right above the water near shorelines,” says Dr. Miri Trainic. “But we were surprised to find a non-trivial amount above seemingly pristine water.”
The Weizmann team has been working for years to understand the interface between ocean and air. Many studies have investigated how materials from the atmosphere are absorbed by the ocean, but few have been focused on the phenomenon which occurs in the opposite direction. In a process known as aerosolization, viruses, algal fragments, and other particles are swept up into the atmosphere from seawater.
During a 2016 expedition, the researchers collected aerosol samples over the North Atlantic Ocean. It was challenging to identify and quantify the microplastic bits trapped in the aerosol samples, so the team used an advanced method known as Raman spectroscopy.
The analysis revealed high levels of common plastics such as polystyrene, polyethylene, and polypropylene in the samples. By calculating the shape and mass of the microplastic particles, as well as the average wind direction and speed, the experts determined that the source of the microplastics was likely to be plastic bags and other waste that had been discarded near the shore and entered the ocean hundreds of kilometers away.
When the researchers checked the seawater beneath the sample sites, they found the same types of plastic that were found in the aerosol samples. This suggests that microplastics enter the atmosphere through bubbles on the ocean surface or are picked up by the wind before traveling 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,” said Dr. Trainic. “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.”
“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,” explained Professor Assaf Vardi.
According to Dr. Trainic, the real amount of microplastic in the ocean aerosols is almost certainly greater than what the measurements showed, because the tests were not designed to detect particles below a few micrometers in size. “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.”
Smaller plastic particles are not only likely to stay airborne for longer, but are also more likely to be consumed by small marine animals. This plastic cannot be digested, which means that every single particle has the potential to harm a marine organism or to work its way up the food chain to humans. “Last, but not least, 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 Professor Ilan Koren. “Because they are both 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.”
The study is published in the journal Communications Earth and Environment.
By Chrissy Sexton, Earth.com Staff Writer