Not all microplastics are the same
“The results of the study demonstrate that microplastics cannot be regarded as a homogeneous group of substances"
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Researchers led by Collaborative Research Centre (CRC) 1357 microplastics at the University of Bayreuth have overturned a common scientific assumption in a new study: microplastic particles do not all exhibit similar transport behaviour regardless of their shape. Instead, microplastics behave differently in aquatic environments depending on whether they occur as fragments or fibres. This insight reshapes our understanding of how strongly organisms are exposed to microplastics – an assessment that is crucial for evaluating the environmental risks posed by microplastic pollution.
The Bayreuth researchers examined the differing behaviour of microplastic fragments and fibres that commonly occur in nature, comparing them with spherical microplastic particles. These beads are typically used in scientific microplastics research. For this purpose, the team led by first author Marco La Capra, a doctoral researcher under the Chair of Hydrology at the University of Bayreuth and a member of CRC Microplastics, recreated natural river conditions in a controlled laboratory setting using a so-called flume. In this transparent channel filled with realistic sediment, water is pumped continuously through the flume, allowing flow velocities to be precisely adjusted.
“In our experimental setup, we investigated microplastics of different shapes under varying flow velocities and with different sediment bed compositions. This enabled us to replicate a wide range of fluvial habitats – from fast-flowing mountain streams to lowland rivers. Using our measuring instruments, we were able to capture the complex interactions between hydrodynamic forces, particle buoyancy and turbulence,” says La Capra.
“The study clearly shows that fibres – which account for a significant proportion of the microplastics found in aquatic environments – behave differently from other particle shapes, an aspect we are only beginning to understand,” explains Dr. Sven Frei from Wageningen University & Research in the Netherlands and an associated researcher at the Bayreuth Center of Ecology and Environmental Research (BayCEER) at the University of Bayreuth.
The results of the study show that particle surface characteristics also influence behaviour in and on the sediment. Spherical particles barely deposit in or on the sediment and are transported directly downstream by the water flow. Fragments, by contrast, penetrate the sediment, either settling more deeply or being flushed out more rapidly, depending on the sediment type. Fibres, however, tend to accumulate on the sediment surface and can become anchored there up to certain flow velocities. This means that during flood events, for example, a significantly increased release of microplastics from sediments may occur, indicating that environmental pollution forecasts need to be reassessed compared with previous assumptions based on laboratory studies.
“The results of the study demonstrate that microplastics cannot be regarded as a homogeneous group of substances. Instead, due to their extremely diverse properties and characteristics, they must always be examined on a case-by-case basis. This underlines both the complexity of the research field and the many open – yet urgent – questions, particularly with regard to risks for humans, nature and the environment,” emphasises Professor Dr. Christian Laforsch, Chair of Animal Ecology at the University of Bayreuth and spokesperson for CRC Microplastics.
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