Shape matters: Transport of microplastics to the polar regions
Why are microplastics found in the polar regions almost exclusively in fiber shape? The latest experiments and simulations seem to have found an answer to this question: Fibers can be transported significantly further in the atmosphere than particles with a different shape.
Not all microplastics are the same. Depending on their shape, size and polymer type, the particles, which can be up to five millimeters in size, behave completely differently in the environment. An Austrian-German research team experimented with different particle shapes and used simulations to discover that fibers travel much greater distances in the atmosphere than spheres.
The team reported in Environmental Science & Technology at the beginning of January that, according to the simulations, a total of up to 2.4 tons of microfibres are deposited in the high Arctic (north of 75° North) each year, while spheres of the same volume do not reach the region at all. This would explain why so many fibrous microplastic particles are observed in remote places such as Arctic or Antarctic glaciers and ice sheets.
The interdisciplinary research team from the University of Vienna and the Max Planck Institute for Dynamics and Self-Organization in Göttingen first conducted laboratory experiments to determine how quickly microplastic fibres settle in the atmosphere.
“Surprisingly, there is almost no data in the literature on the dynamics of microplastic fibers as they settle in air,” Dr. Mohsen Bagheri, scientist at the Max Planck Institute for Dynamics and Self-Organization in Göttingen and co-author of the study, said in a university press release. “This lack of data is largely due to the challenges of conducting controlled and repeatable experiments on such small particles in air. With advances in submicron-resolution 3D printing and the development of a novel experimental setup that allows tracking of individual microplastics in air, we were able to fill this knowledge gap and improve existing models in this study.”
In model simulations, they released 10,000 particles per day into the atmosphere at five different locations (northern Italy, north-west Russia, Shanghai, Svalbard and the south-west Pacific) over a period of one year. Based on these simulations, the researchers calculated the average distance travelled and how long the particles stayed in the atmosphere.
Their results show clear differences for spherical particles and fibers. While fibers with a length of 1.5 millimeters can stay in the atmosphere much longer and reach the most remote places on Earth in the model, spheres of the same mass travel comparatively short distances in the air and settle much closer to the respective regional plastic sources. For example, fibers released into the atmosphere in Italy can reach northern Europe and, in small quantities, the Arctic.
“With the novel laboratory experiments and modelling analysis, we certainly reduce uncertainties about the atmospheric transport of fibers and can finally explain via modelling why microplastics reach very remote regions of the planet,” Daria Tatsii from the Institute of Meteorology and Geophysics at the University of Vienna, first author of the study, explained. “An important result of the study is that our analysis is applicable not only to microplastics, but also to any other particles such as volcanic ash, mineral dust, pollen, etc.”
Furthermore, the study has shown that microplastic fibers can reach much greater heights in the atmosphere than previously assumed. “This could have implications for cloud processes and even for stratospheric ozone, since it seems possible that microplastic fibers are abundant in the upper troposphere and might even reach the stratosphere,” Professor Andreas Stohl said, Head of the Institute of Meteorology and Geophysics at the University of Vienna and senior author of the study. “For instance, we cannot rule out that chlorine contained in these particles is harmful to the ozone layer.”
In his view, however, it is too early to sound the alarm: “However, right now we do not even know how much plastic, and in which sizes and shapes, is emitted to the atmosphere, and we also do not know what happens to it under the extreme conditions of the upper troposphere and stratosphere. We are lacking very basic data. But given the dramatic increase in global plastic production, we have to be watchful,” Prof. Stohl said.
Julia Hager, PolarJournal
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