Many studies have been carried out about microplastics (tiny pieces of plastic usually measuring less than 5mm) being found within the world’s oceans and rivers. However, researchers from Technische Universität Darmstadt (TU Darmstadt), in Germany, have discovered that they are also accumulating in our forests.
The research, published in August 2025 in Nature, aimed to close the knowledge gap of how microplastics occurred in forest ecosystems.
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Geoscientists gathered samples containing soil, fallen leaves and throughfall deposition (the materials, such as water, water and pollutants, that pass through the canopy to the forest floor) from four different sites in a managed forest area east of the city of Darmstadt, in south-west Germany.
The team also created a model to estimate how much microplastic has entered forests from the atmosphere since the 1950s – when plastic became cheaper to produce and began to be used in commercial packaging on a large scale.
This would help them assess how much of the total pollution stored in forest soils can be traced back to airborne sources.
A cascade of microplastics
After analysing the samples, the scientists concluded that atmospheric deposition was a major source of microplastics in the soil, first landing on the upper leaves of the canopy.
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“The microplastics from the atmosphere initially settle on the leaves of the tree crowns, which scientists refer to as the ‘comb-out effect’,” explains lead author Collin J. Weber, from the Institute of Applied Geosciences at TU Darmstadt.
“Then, in deciduous forests, the particles are transported to the forest soil by rain or the autumn leaf fall, for example.”
Once microplastics settle on leaves, they stick to the waxy coating of their surface (which minimises the leaf’s moisture loss and protects it against UV radiation).
When the leaves decompose on the top layer of soil, the microplastics move deeper within the soil.
The team didn’t find any significant differences in particle sizes and aspect ratios in forest throughfall deposition and soils, which supported their assumption that microplastics enter forest soils through atmospheric deposition (where precipitation transports substances from the atmosphere to land or water), or leaf litter fall.
“We conclude that forests are good indicators of atmospheric microplastic pollution and that a high concentration of microplastics in forest soils indicates a high diffuse input – as opposed to direct input such as from fertilisers in agriculture – of particles from the air into these ecosystems,” explains Weber.
The researchers claim that it is the first study to demonstrate how forests can become contaminated by microplastics, and to connect that with the theory of particles travelling through the air.
Read the full study, titled Forest soils accumulate microplastics through atmospheric deposition.
Top image: looking up into a tree canopy. Credit: thianchai sitthikongsak/Getty Images
