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How microplastic gets to the Arctic

An interdisciplinary research team from the University of Vienna and the Max-Planck Institute for Dynamics and Self-Organisation in Göttingen, Germany, has established in an ongoing study that the shape of microplastic particles contributes decisively to their transport properties. They combined laboratory experiments with model simulations of the global distribution of microplastic particles and concluded that fibres with a length of up to 1.5 millimetres can, because of their shape, reach very distant places of the Earth such as the Arctic.
 

 

Microplastic particles have been found in some of the most remote corners of our planet. When they are found at places well away from civilisation such as Arctic glaciers, it is assumed that the microplastic gets there through the air, in other words by atmospheric transport. However, the enormous range of the particles cannot be explained with the present transport models, says Daria Tatsii from the Institute for Meteorology and Geophysics at the University of Vienna, who is the lead author of the study published in the magazine Environmental Science & Technology. For microplastic particles, a much closer range of distribution is predicted according to existing knowledge. Even taking into account factors such as strong winds and turbulence that keep individual particles up in the air, or even electrical forces that could increase the transport distances for microplastic, it is not enough, says the research team, to explain the huge spread of microplastic particles. Another possibility examined in this project is the influence of the particle shape. In the transport calculation models used so far, it has generally been assumed, according to the study, that the particles are spherical. The actual form of microplastic particles is, however, often nowhere near spherical.
 
To begin with, the scientists determined by experiment how quickly microplastic fibres and spherical microplastic particles of different lengths and sizes drop to the ground from the atmosphere. With the help of a high-precision 3D printer, they produced fibres with an exactly defined shape and length. Subsequently, they introduced them individually into a chamber filled with air and measured how quickly they fell to ground. They then used their measurements in a model that describes the process of falling to ground of fibre-shaped particles, and implemented this in a global atmospheric transport model to calculate the microplastic distribution. The resultant differences between the transport of fibres and spherical particles surprised the research team: Fibres with a length of up to 1.5 millimetres could reach the most distant places on the Earth. According to calculations by the scientists, spherical particles rapidly fall to ground out of the atmosphere, whereas microplastic fibres with a length of up to 100 micrometres stay moving around so slowly in the atmosphere that they could also rise up very high. A second set of simulations had also shown that the deposition of spherical particles was concentrated very much on densely populated source regions, whereas fibres became deposited globally. The study thus shows that the shape of the microplastic is an important factor for the global distribution in the environment, and that microplastic in the atmosphere can be transported to almost any point on the globe and is very possibly also present in the stratosphere. Furthermore, the research team suspects that microplastic particles such as from plastic films and particles with a non-uniform surface structure could have even greater transport potential in the atmosphere than that of the microplastic fibres studied by them. In order to research the influence of microplastic on the atmosphere or also the processes of cloud formation and the stratospheric ozone, the research team considers further studies to be urgently needed.
 
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