As plastics in our oceans break down into smaller and smaller parts without chemically decomposing, the resulting microplastics become a serious environmental problem. A new study at the Weizmann Institute of Science reveals a worrying aspect of microplastics – defined as particles smaller than 5 mm. They are carried into the atmosphere and carried by the wind to distant parts of the ocean, including those that appear clear. The analysis reveals that such tiny fragments can remain in the air for hours or days, spreading the potential to harm the marine environment and climb into the food chain affecting human health.
“A handful of studies have found microplastics in the atmosphere just above the water near the shore,” says Dr. Miri Trainic, in groups of prof. Ilana Korena from the Institute for the Department of Planet and Planet in collaboration with prof. Yinon Rudich of the same department and prof. Assaf Vardi from the Institute of Plant and Environmental Sciences. “But we were surprised to find a non-trivial amount above the seemingly pristine water.”
Koren and Vardi have been collaborating for years on studies designed to understand the connection between the ocean and the air. Although the way the oceans absorb materials from the atmosphere has been well studied, the opposite process – aerosolization, in which volatile constituents, viruses, algae fragments and other particles from seawater are introduced into the atmosphere – has been much less explored.
As part of this ongoing effort, aerosol samples were collected for study in Weizmann Laboratories during the operation of the 2016 research ship Tara, a schooner that brings together several international research teams to study the effects of climate change, primarily on marine biodiversity. Weizmann’s team placed the entrance of its measuring equipment on top of one of Tara’s masts (to avoid all aerosols generated by the schooner itself), and dr. J. Michel Flores of the Koren Group joined the mission to strive for collection as the schooner sailed the North Atlantic Ocean.
Identifying and quantifying the microplastic parts trapped in their aerosol samples was far from easy, as the particles proved to be difficult to extract under a microscope. In order to understand exactly what plastic enters the atmosphere, the team conducted Raman spectroscopy measurements with the help of Dr. Idda Pinkas from the Institute for Chemical Research to determine their chemical composition and size. The researchers found high levels of common plastics in their samples – polystyrene, polyethylene, polypropylene and more. Then, by calculating the shape and mass of microplastic particles, along with average wind directions and speeds above the ocean, the team showed that the source of this microplastic was most likely plastic bags and other plastic waste dumped near the coast and headed into the ocean hundreds of miles away.
Checking the seawater below the sample site showed the same type of plastic as in the aerosol, supporting the idea that microplastics enter the atmosphere through bubbles on the ocean surface or are lifted by winds and transported by air currents to distant parts of the ocean.
“Once the microplastic is in the atmosphere, it dries and is exposed to UV light and atmospheric components with which it chemically communicates,” says Tranic. “This means that particles that fall back into the ocean are likely to be even more harmful or toxic than before for any marine life that swallows them.”
“On top of that,” adds Vardi, “some of this plastic is becoming a scaffold for bacterial growth for all types of marine bacteria, so plastic in the air can offer free rides to some species, including pathogenic bacteria that are harmful to marine life and humans.”
“The actual amount of microplastics in ocean aerosols is almost certainly higher than that shown by our measurements, because our setup failed to detect those particles smaller than a few micrometers,” says Tranic. “For example, in addition to plastic that breaks down into even smaller pieces, there are nanoparticles that are added to cosmetics and that are easily washed into the ocean or formed in the ocean by the fragmentation of microplastics.”
Size, in the case of plastic particles, is important, not just because they can more easily stay in the air for long periods of time. When they do land on the water, they are more likely to be eaten by an equally small marine life, which, of course, cannot digest them. Thus, each of these particles can harm the marine organism or break through to the food chain and enter our bodies.
“And last but not least, like all aerosols, microplastics become part of large planetary cycles – for example, carbon and oxygen – in interaction with other parts of the atmosphere,” says Koren. “Because they are both lightweight and durable, we will see more microplastics being transported in the air as plastics that are already polluting our oceans disintegrate – even if we don’t add further plastics to our waterways.” he adds.