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Airborne microplastics are depositing in forests
Researchers at TU Darmstadt have found that microplastics and nanoplastics are not confined to oceans, rivers, or agricultural soils — they also accumulate in forest ecosystems. The study, published in Nature Communications Earth & Environment, shows that the dominant pathway for plastic particles into forests is atmospheric deposition: airborne particles settle onto tree crowns, move to the forest floor via rain and leaf drop, and become trapped in leaf litter and soil.
Lead author Dr Collin J. Weber (Institute of Applied Geosciences, TU Darmstadt) describes the initial capture mechanism as the 'comb-out effect', where particles suspended in the air adhere to leaves and needles in the canopy. In deciduous stands especially, this canopy deposition is followed by litterfall and precipitation that transfer particles to the ground. Once on the forest floor, partially decomposed leaf litter acts as a primary reservoir for microplastics; however, the researchers also observed significant quantities deeper in the soil profile, transported downward by decomposition processes and soil fauna activity.
Microplastics and nanoplastics not only pollute oceans, rivers, and fields, but also forests.
This discovery reframes forests as active sinks for atmospheric plastic pollution and highlights the role of terrestrial ecosystems in the global redistribution of microplastics. The finding is relevant to environmental monitoring, ecosystem risk assessment, and public health considerations related to airborne particulates.
Sampling strategy, analytical advances and modeling
To quantify atmospheric inputs and storage, the research team collected coordinated samples of soil, leaf litter, and atmospheric deposition at four forest sites east of Darmstadt, Germany. They applied a newly refined analytical workflow tailored to detect and quantify microplastics on leaf surfaces and in soils. Spectroscopic methods were used to chemically identify polymer types and to distinguish plastic particles from natural organic and mineral matter.
The research team developed a customized method for analyzing microplastics on leaf surfaces.
In addition to laboratory analysis, the team developed a retrospective atmospheric-input model that estimates microplastic deposition to these forests since the 1950s. Combining measured concentrations with modeled historical inputs allowed the authors to assess how atmospheric deposition has contributed to the cumulative storage of plastics in forest soils. Results indicate that atmospheric deposition and subsequent litterfall are the primary sources of forest soil microplastics, while direct inputs (for example, from fertilizers or local point sources) play a comparatively minor role in the studied sites.
Key discoveries, ecological implications and future directions
Key discoveries from the study include the pronounced accumulation of microplastics in partially decomposed leaf litter layers and the downward transport of particles into mineral soil horizons. Because forests are spatially extensive and often remote from obvious terrestrial sources of plastic, their contamination points to widespread, long-range atmospheric transport of microplastic particles. This has implications for ecosystem function: microplastics in the litter layer could interfere with decomposition, soil structure, water infiltration, and the activity of invertebrates and microbes that mediate nutrient cycling.
The authors stress that forests, already stressed by climate change, may face an additional, previously underappreciated stressor in the form of microplastic pollution. The study further raises questions about human exposure pathways, as airborne microplastics that travel to forests are also part of the same atmospheric pool affecting populated areas.
Expert Insight
Dr. Elena Ramos, environmental chemist and science communicator, comments: 'Linking canopy deposition to soil storage provides a missing piece in understanding terrestrial microplastic budgets. The use of targeted spectroscopic methods is essential to reliably separate polymer particles from organic debris. Future studies should expand sampling across biome types and climates to map regional differences in atmospheric inputs and ecological response.'
Research and technology needs
To build on these findings, researchers recommend standardized protocols for sampling and analysis, expanded geographic surveys, and experiments to determine biological and chemical effects of microplastics in soil and litter. Advances in spectroscopy, imaging, and modeling of atmospheric transport will sharpen estimates of sources, residence times, and potential risks.
Conclusion
The TU Darmstadt study demonstrates that forests act as receivers of airborne microplastic pollution: particles settle on leaves, move to the forest floor through rain and litterfall, and accumulate in leaf litter and soils. Atmospheric deposition emerges as the principal pathway, making forests useful indicators of diffuse air-borne microplastic contamination. These findings broaden the geographical and ecological scope of plastic pollution and underscore the need for wider monitoring, improved analytical methods, and research into ecological and human-health implications of atmospheric microplastics.
Source: scitechdaily
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