New Zealand's air contains over 3 million plastic bottles worth of microplastics: study

Researchers have long known that pesky microplastics that plague water and land ecosystems have perforated air as well. What they didn't know was just how much of it is present in the atmosphere.

Earlier studies conducted in major global cities like London, Paris and Hamburg had revealed that airborne microplastics in one square metre of air numbered in the hundreds. However, a recent study on New Zealand-based Auckland's microplastic pollution levels indicates that the previous numbers are a gross underestimation of how dire the situation is.

Led by researchers from the University of Auckland, the 2020 study estimates that 74 metric tons of microplastics are dropping out of the atmosphere into the city annually. This is equivalent to over 3 million plastic bottles falling from the sky!

The mean number of airborne microplastics detected in a square metre in a day was 4,885. When compared to London (771 as per a study published in 2020), Hamburg (275 as per a study from 2019) and Paris (110 as reported in 2016), this is a huge number.

The vast difference in these estimates can be attributed to the fact that this new study used sophisticated chemical methods to find and analyse particles as small as 0.01 of a millimetre.

Furthermore, given just how tiny these particles are, it raises concerns regarding how much of it people might be inhaling and accumulating in their bodies.
Winds carrying microplastics
Experts have figured that waves breaking in the Hauraki Gulf may play a key role in Auckland's problem by transmitting water-borne microplastics into the air.

That effect seemed to be at play when researchers recorded increased microplastic numbers after winds from the gulf picked up speed, likely leading to bigger waves and more transmission.

"The production of airborne microplastics from breaking waves could be a key part of the global transport of microplastics. And it could help explain how some microplastics get into the atmosphere and are carried to remote places, like here in New Zealand," said Dr Joel Rindelaub of the School of Chemical Sciences at Waipapa Taumata Rau, University of Auckland.

Meanwhile, the particle sizes changed with wind direction. When winds passed over the Auckland city centre, the microplastics downwind were larger, indicating the plastics had gone through less environmental ageing and came from a closer source.

Polyethylene was the major substance detected, followed by polycarbonate and polyethylene terephthalate. Polycarbonate is used in electrical and electronic applications, while the other two are used in packaging material. All three of them are also used in the construction industry.

"The smaller the size ranges we looked at, the more microplastics we saw," Rindelaub says. "This is notable because the smallest sizes are the most toxicologically relevant."

The experiment was carried out over nine weeks during September, October and November 2020. Researchers think that future work needs to quantify exactly how much plastic we are breathing in, as it's becoming increasingly clear that this is an important route of exposure.

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