Some 74 metric tons of microplastics dropped out of the atmosphere onto the New Zealand city of Auckland in 2020, according to a study published this week in Environmental Science & Technology — the equivalent of 3 million plastic bottles.
The peer-reviewed study is the first to calculate the total mass of microplastics in a city’s air, and its findings suggest researchers may be dramatically undercounting the global prevalence of airborne microplastics.
To conduct the study, scientists from the University of Auckland collected microplastics falling on a rooftop of their downtown campus as well as on a residential garden in a city suburb. Almost all of the microplastics were too small to be seen by the naked eye; scientists identified the particles by applying a colored dye that emitted light under certain conditions. A heat treatment was also used for analysis.
“The smaller the size ranges we looked at, the more microplastics we saw,” Joel Rindelaub, the study’s lead author and a chemical scientist at the University of Auckland, said in a press release. “This is notable because the smallest sizes are the most toxicologically relevant.”
Microplastics’ smallest particles are more likely to be inhaled, and can potentially enter cells, cross the blood-brain barrier and even build up in organs such as the liver and brain, the authors warned. “Future work needs to quantify exactly how much plastic we are breathing in,” Rindelaub said. “It’s becoming more and more clear that this is an important route of exposure.”
In one square meter in one day, the Auckland study found that the average number of airborne plastics was 4,885 in 2020. That compares with 771 in a 2020 study in London, 275 in a 2019 study in Hamburg and 110 in a 2016 study in Paris. The discrepancy is largely because of the Auckland study’s inclusion of smaller size ranges, which were not part of previous research.
Since mass production began in the 1950s, humans have generated more than 8.3 billion metric tons of plastic, 79% of which ended up in landfills or dumped in the wild. Microplastics are generated from commercial product development and the breakdown of larger plastics. Once they enter the natural environment, they can pollute soil, kill wildlife and find their way into the food chain.
In Auckland, polyethylene — often used in packaging materials — was the most-detected substance, followed by polycarbonate, a type of plastic typically used in electrical and electronic applications. The study also noted a relationship between ocean plastic pollution, airborne microplastics in Auckland and more aggressive winds from the Hauraki Gulf of New Zealand’s North Island.
“The production of airborne microplastics from breaking waves could be a key part of the global transport of microplastics,” Rindelaub said. “And it could help explain how some microplastics get into the atmosphere and are carried to remote places, like here in New Zealand.”