- Tiny plastic particles detected in some of the most remote parts showing up in ice cores drilled in the Arctic, in protected wilderness areas in the Western US, and on high mountains in the European Alps.
Researchers have long assumed that minute particles were being transported long distances through the atmosphere before raining down or falling out of the atmosphere as dust. Reports C&EN.
A modelling study published this week supports the evidence for the idea, modelling how microplastics from vehicle tires and brake pads hitch an atmospheric ride from urban streets to remote regions and the world’s oceans (Nat. Commun. 2020, DOI: 10.1038/s41467-020-17201-9).
The Research Findings
The past studies suggest waterways as the only route for microplastic movement but the pathway could not explain how it reached many remote regions, says Timothy Hoellein, an ecologist at Loyola University Chicago, not involved in the atmospheric modelling research.
His team has found microplastics in remote rivers within Yellowstone National Park in Montana, where “there’s nobody around,” he says. Atmospheric transport seemed like the only way microplastics could reach those rivers.
To model how microplastics move by air, atmospheric chemist Nikolaos Evangeliou and his team at the Norwegian Institute for Air Research focused on one source of microplastics: roadways.
Traffic-microplastics were produced when friction between the road and tires or between brake pads causes bits of plastic to break off or volatilise and are a relatively minor source of these pollutants, Evangeliou says.
Evangeliou and his colleagues focused on traffic microplastics because they knew they could quantify them relatively well, he says.
The Research Modelling
The team estimated traffic microplastic emissions around the world using greenhouse gas emissions data, which correlate with traffic intensity; lifetime weight loss of returned tires; and other information.
They then fed the estimate into atmospheric transport models for particulates. They developed these models to study the movement of fine aerosols that have implications for human health and the climate; with small modifications, they can predict the movement of plastic microparticles, too.
In a nutshell, the study suggests that atmospheric transport can move plastic microparticles from densely populated areas to distant places, including the Arctic.
The team estimates that each year; the atmosphere transports 140 metric kilotons (kt) of traffic-produced particles into the world’s oceans—equivalent to the amount delivered by rivers—and 86.1 kt to the world’s ice and snow cover.
Evangeliou says the deposition of microplastics on the world’s already vulnerable snow and ice formations is particularly concerning. Since they are dark, these particles may absorb sunlight and speed up melting, he says.
Finding the Emission Sources
The study is a step in pinpointing the sources of the microplastics at the study sites which otherwise was difficult, says Hoellein. Janice Brahney, a bio-geochemist at Utah State University, agrees. The work takes “first steps to figure out what are the major emission point sources into the atmosphere.” The next step is to validate modelling studies with field measurements, Brahney says. Brahney’s working on it.
Last month, her group published the results of a survey of microplastic pollution in protected wilderness areas in the western US (Nat. Commun. 2020, DOI: 10.1038/s41467-020-17201-9).
She had set out to study patterns of dust deposition, but when she realised how much of the dust was actually microplastics, she pivoted: In her study, about 98% of soil samples from US protected areas contained microplastic pollutants. She used models from the US National Oceanic and Atmospheric Administration to trace where those particles originated in the region. “As an air mass moves through an urban centre, it picks up plastic,” she says. She’s now working on a study that will link observational data and global atmospheric models.
While ecologists try to find out the effects of microplastics on ecosystems, atmospheric chemists want to know more about their geophysical effects, which have been little studied.
Some atmospheric aerosols serve as condensation sites that seed rain and snow formation, and some can affect regional temperatures by absorbing or reflecting sunlight. Researchers want to know whether microplastics behave similarly. Evangeliou says he’s now studying whether and how atmospheric microplastics affect the climate.
Both Brahney’s and Evangeliou’s studies raise more questions than scientists hold answers to, Brahney says. “It’s scary how little we know,” she says.
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Source: C&EN
