Microplastics and nanoplastics — long known to pollute oceans, rivers, and agricultural land — are now confirmed to be accumulating in forest ecosystems, with airborne deposition identified as the dominant contamination pathway.
That is according to geoscientists Dr Collin J. Weber and Moritz Bigalke from TU Darmstadt, whose study in Communications Earth & Environment is the first to directly link atmospheric plastic transport to long-term storage in forest soils.
Plastic particles settle first on canopy leaves before being carried to the forest floor by rain or autumn leaf fall — a process the team calls the “comb-out effect.”
“The microplastics from the atmosphere initially settle on the leaves of the tree crowns,” said Dr Weber. “Then, in deciduous forests, the particles are transported to the forest soil by rain or the autumn leaf fall, for example.”
Arriving on the forest floor, the particles do not remain near the surface. Leaf decomposition traps and buries them progressively deeper, with the highest concentrations found in the upper layers of fresh litter — though significant amounts were detected well underground, driven by organic matter breakdown and the activity of soil organisms.
Working across four forest sites east of Darmstadt, the team applied a newly refined analytical technique to measure microplastic concentrations in soil, fallen leaves, and atmospheric deposition, with spectroscopic methods used to chemically analyse each sample. Atmospheric inputs were also modelled back to the 1950s, quantifying the duration of this accumulation.
“Our results indicate that microplastics in forest soils originate primarily from atmospheric deposition and from litterfall. Other sources have only a minor influence,” Weber said. “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 of particles from the air into these ecosystems.”
Forests already face mounting pressure from climate change, drought, and shifting fire patterns. Weber said the findings add another layer of risk — and raise direct questions about human exposure, given that particles at concentrations sufficient to contaminate remote forest soils are also moving through the air people breathe.
“Forests are already threatened by climate change, and our findings suggest that microplastics could now pose an additional threat to forest ecosystems,” he said.
Published in Communications Earth & Environment, the full study is available at DOI: 10.1038/s43247-025-02712-4.
