Aerosol samples above the ocean reveal microplastics spread by the wind
Recent studies have shown just how far plastic pollution can travel when it is broken down into tiny fragments, with these so-called microplastics turning up everywhere from the Arctic to the Antarctic, and in human stool all around the world. A new study has highlighted a key link in this chain, demonstrating how microplastics can be swept across the surface of the seas by winds that carry them upward into the atmosphere, and far into remote parts of the ocean.
Microplastics are defined as tiny pieces measuring less than 5 mm in size, and recently, we’ve started to learn how ultra fine particles can become airborne and transported via the atmosphere. From there, they can be blown into the untouched corners of the French Pyrenees, or washed out of the atmosphere by Arctic snowfall.
Scientists at Israel’s Weizmann Institute of Science were studying aerosolization, where things like algal fragments, viruses and other particles are swept from the seawater up into the atmosphere. As part of this, the team collected aerosol samples from the top of a mast on a research vessel throughout a 2016 expedition, and used Raman spectroscopy to analyze the contents.
This revealed high concentrations of common plastics such as polystyrene, polyethylene and polypropylene, most likely coming from plastic bags and other plastic waste discarded near the shoreline hundreds of kilometers away. The team arrived at this conclusion after calculating the shape and mass of the particles, along with the average wind speeds and directions over the ocean.
“A handful of studies have found microplastics in the atmosphere right above the water near shorelines,” says study author Dr. Miri Trainic.“But we were surprised to find a non-trivial amount above seemingly pristine water.”
The water appeared pristine from above, but peering beneath the surface the researchers found the same types of plastics at the same sites as the aerosols. They say this adds weight to the idea that ocean microplastics may reach these remote parts of the ocean by bubbling to the surface and entering the atmosphere, where they may undergo harmful chemical changes before falling back down to the water.
“Once microplastics are in the atmosphere, they dry out, and they are exposed to UV light and atmospheric components with which they interact chemically,” says 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.”
The researchers point out that the microplastic problem won’t be going away anytime soon.
“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,” says study author Prof. 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 research was published in Nature.
Source: Weizmann Institute of Science