Microplastics and nanoplastics have long been recognized as pollutants in oceans, rivers, and agricultural lands. Recent research has revealed that these particles also accumulate in forest ecosystems. Geoscientists from the Technical University of Darmstadt have published findings highlighting this little-studied form of environmental pollution.

Pathways of Microplastic Entry into Forests

The study showed that forests are contaminated not only by local sources. The majority of microplastics enter forests through the atmosphere and gradually settle into forest soils. Initially, the particles land on the leaves in the upper canopy, a process known as the "combing effect." In deciduous forests, these particles reach the soil together with rainfall or falling leaves.

Mechanisms of Accumulation in Soil

Once microplastics reach the forest floor, they become involved in natural processes. The decomposition of fallen leaves helps retain and accumulate these particles in the soil. The highest concentrations were found in the upper layer of the forest litter, where decomposition is just beginning, but significant amounts were also detected in deeper layers. The downward movement of particles is influenced not only by the breakdown of organic matter but also by biological activity, such as the actions of organisms that redistribute particles.

Methods of Measurement and Analysis

To study microplastic accumulation, the research team collected samples of soil, fallen leaves, and atmospheric deposits from four forest sites east of Darmstadt, Germany. The analysis was conducted using new methods combined with spectroscopic technologies. A model was also developed to estimate the atmospheric input of microplastics into forests since the 1950s, allowing researchers to determine the share of pollution linked to airborne sources.

Forests as Indicators of Atmospheric Pollution

The results indicate that most microplastics in forest soils come from atmospheric deposits and falling leaves. Other sources have only a minor impact. Forests are considered effective indicators of atmospheric microplastic pollution, and high concentrations of particles in the soil point to significant diffuse input from the air, as opposed to direct sources such as agricultural fertilizers.

Ecological and Potential Risks

For the first time, the study has provided detailed evidence of how forests are contaminated by microplastics and established a direct link between this process and airborne particles. The data obtained lay the groundwork for assessing the ecological risks of microplastics in both air and soil. Forests are already under threat from climate change, and microplastics may pose an additional danger to forest ecosystems. Furthermore, the findings emphasize that microplastics are spread globally through the atmosphere and can be present in the air humans breathe.