Even at the Bottom of the World, the Ocean Is Belching Plastic

With its small population and remote location, New Zealand might hope to be sheltered from the world’s plastic pollution. But new research shows that’s far from the case. In a recent study published in Environmental Science and Technology, researchers report a mist of microplastics is constantly drifting across the country’s largest city.

“We don’t produce large amounts of plastics here in New Zealand,” said Joel Rindelaub, a research fellow at the University of Auckland in New Zealand who led the study. “But we did see large amounts of plastics falling out of the sky in Auckland.”

In 2020, Rindelaub and his colleagues installed two simple devices fashioned from glass bottles to capture plastic as it fell from the air—one in a suburban garden and the other on top of a six-story building in the heart of the city. They then used fluorescence microscopes to count the particles of plastic they collected in the contraption’s filter. The team was able to detect fragments as small as 10 microns (0.01 millimeter)—far smaller than previous studies could see.

“What got us to 10 microns,” said Rindelaub, “was mostly just the amount of time and effort that was devoted to this. A graduate student was working for months to scan the entire filter.”

The researchers counted almost 5,000 particles of plastic per square meter falling out of Auckland’s air every day. They then heated the microplastics and analyzed their breakdown at very high temperatures, which allowed them to figure out what kinds of plastics were present. Polyethylene and polycarbonate—plastics commonly used in packaging—were the most prevalent.

The team found that at least 74 metric tons (82 US tons) of plastic—the equivalent of 3 million plastic bottles—are falling on the city in a year.

Their results suggest that earlier studies conducted in London, Paris, Hamburg, and elsewhere have greatly underestimated the amount of microplastics in the world’s atmosphere. Ominously, the figures also hint that an even larger amount of smaller microplastics—smaller than 10 microns—remains undetected in Auckland’s air.

“The smaller the size ranges that we looked at, the greater the number of microplastics we saw,” said Rindelaub. “It actually increased exponentially, the smaller we got.”

Microplastics smaller than 10 microns may pose a severe risk to human health, as they can easily be inhaled. Nanosized particles (less than 0.1 micron) can enter the bloodstream and vital organs, including the brain. They may even be able to penetrate cells.

Plastic particles also attract chemical pollutants from the atmosphere and can therefore act as a vehicle for carcinogenic toxins such as DDT (dichlorodiphenyltrichloroethane) and PCBs (polychlorinated biphenyls) to enter the human body.

Plastic from the Sea

That Auckland’s atmosphere is full of plastic is far from surprising; microplastics are ubiquitous on planet Earth. They have even been found in Antarctica and in the Mariana Trench, the deepest place in the ocean.

“Basically, everywhere on the planet that scientists have looked,” said Rindelaub, “they’ve been able to find evidence of humanity’s synthetic existence.”

Studies have reported that 8.3 billion metric tons of plastic have been produced globally. Only 9% has been recycled, and 12% has been incinerated, with the rest finding its way into the environment. As much as 236,000 metric tons of plastic are floating on the surface of the ocean.

Indeed, much of the plastic detected by Rindelaub and his team in Auckland appeared to be coming not from the city itself, but from the surrounding sea.

Indeed, much of the plastic detected by Rindelaub and his team in Auckland appeared to be coming not from the city itself, but from the surrounding sea.

“When winds were coming off the Hauraki Gulf at about 15 to 20 meters per second, that’s when we saw the largest amount of microplastics,” said Rindelaub.

Only recently has the ocean’s role as a source for airborne microplastics been studied. In 2020, Steve Allen, from Dalhousie University, Halifax, Canada, and Deonie Allen, from Birmingham University, United Kingdom, and the University of Canterbury, New Zealand, found around 19 particles of plastic per cubic meter in sea mist coming off the Atlantic Ocean on a beach in France. The pair also discovered microplastics high in the snows of the French Pyrenees that could be traced back to the Mediterranean Sea and Atlantic Ocean.

The ocean, said Deonie Allen, is not the final resting place for plastic.

“There is no sink in the world for microplastic,” she said. “It will degrade over time, from macro- to micro- to nanoplastic. The smaller it gets, the easier it is for it to move.”

Ocean currents can carry plastic to every corner of the globe. In rough seas, said Allen, micro- and nanoplastics behave exactly like sea-salt aerosols and bacteria, which are expelled by the sea when air bubbles burst at the surface.

Once in the atmosphere, microplastics can be transported vast distances by wind. Plastics detected in the Auckland study could have come from anywhere in the world.

“What goes in the ocean in the Northern Hemisphere sooner or later gets [there].”

“Everyone thinks of New Zealand as quite a clean country,” said Steve Allen. “Unfortunately, it’s surrounded by water. What goes in the ocean in the Northern Hemisphere sooner or later gets [there].”

Though Deonie Allen and Steve Allen were not involved in the Auckland study, they were “not even vaguely surprised” at its findings or that the team was able to detect smaller particles than previous studies.

The science of measuring atmospheric microplastics, said Deonie Allen, is still in its infancy. There are several different methods being used around the world, each with its own strengths and weaknesses.

The approach the Auckland team used allowed them to gauge the masses of different kinds of plastics in the air, but it didn’t allow them to match plastic types to particle sizes, something Rindelaub says will be important for future research.

“You really need to know the sizes of those particles, and exactly what types of polymers they are, before it becomes useful,” he said. “What are we breathing? How much are we breathing? Those are extremely important for any sort of toxicological risk assessment. So that’s what we’re starting to climb toward.”

—Bill Morris, Science Writer

Citation: Morris, B. (2023), Even at the bottom of the world, the ocean is belching plastic, Eos, 104, https://doi.org/10.1029/2023EO230014. Published on 17 January 2023.
Text © 2023. The authors. CC BY-NC-ND 3.0
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