Microplastics in forests are building up as tiny plastic particles fall from the air, settle onto tree canopies, and then move into forest soils over time, according to new research from TU Darmstadt. The study says most of the microplastics found in forest soils come from atmospheric deposition rather than nearby direct pollution sources. That means forests are not isolated from plastic contamination, even when they are far from obvious local sources of waste.
The findings add forests to the growing list of environments affected by microplastics and nanoplastics, which were already widely known for contaminating oceans, rivers, and farmland. Researchers described this as a largely overlooked form of environmental pollution because the pathway into forests had not been studied in depth before. They said the work directly links forest contamination to particles carried through the atmosphere.
How Plastic Reaches Forest Soil
According to the research team, airborne microplastics first collect on leaves in the upper canopy, a process lead author Dr. Collin J. Weber called the “comb-out effect.” In deciduous forests, rain and autumn leaf fall then move those particles from the tree crowns to the ground. Earth.com also reported that the particles can be carried by wind before landing in forest canopies, underscoring the role of the atmosphere in spreading plastic pollution.
Once the material reaches the forest floor, natural processes help keep it there. The breakdown of fallen leaves plays a key role in trapping and storing microplastics in the soil, turning leaf litter into an important part of the accumulation process. Researchers found the highest concentrations in the top layer of leaf litter, where decomposition has only just started. They also detected significant amounts deeper underground, showing that the particles do not stay only at the surface.
The study says this movement into lower soil layers is linked to both decaying organic material and biological activity from organisms that break down leaves and redistribute particles. Earth.com similarly said soil organisms and natural movement gradually push the particles deeper underground over time. Together, those processes help explain how plastics can become embedded in forest soils rather than remaining only in fresh leaf litter.
What Scientists Measured
To examine how the buildup happens, the team collected samples from four forest sites east of Darmstadt in Germany. They analyzed soil, fallen leaves, and atmospheric deposition using a newly developed method combined with spectroscopic techniques. The researchers also built a model to estimate how much microplastic has entered forests from the atmosphere since the 1950s.
That model helped the team assess how much of the plastic stored in forest soils can be traced back to airborne sources. According to Weber, the results indicate that atmospheric deposition and leaves falling to the ground, known as litterfall, are the main origins of microplastics in forest soils. He said other sources appear to have only a minor influence.
Why Forests Matter
The researchers said forests can serve as indicators of atmospheric microplastic pollution because high concentrations in forest soils point to strong diffuse input from the air. Weber contrasted that with direct input, such as fertilizers used in agriculture, which the study says plays a smaller role in these forest sites. In that sense, forests may act as long-term record keepers of what is falling out of the atmosphere.
The study also says the findings provide a basis for evaluating the environmental risks of microplastics in both air and soil. Weber said forests are already threatened by climate change and that microplastics may now pose an added threat to forest ecosystems. The researchers added that the results may also matter for human health because they show how microplastics travel through the atmosphere globally and may be present in the air people breathe.
Publication Note
ScienceDaily and Mirage News both said the research was published in Nature Communications Earth & Environment. Earth.com, however, said the research is published in Communications Earth. All three sources identified TU Darmstadt and Dr. Collin J. Weber as central to the study and its findings on airborne microplastics in forests.
