Microplastics and nanoplastics are widely known to contaminate oceans, rivers, and agricultural land. New research shows they also accumulate in forests. Geoscientists from the Technical University of Darmstadt reported this discovery in a study, Nature Communication Earth and Environmenthighlighted a form of environmental pollution that has been largely overlooked.
This study reveals that forests are not only affected by local sources of pollution. Instead, most microplastics arrive through the air and gradually accumulate in forest soil. The researchers say these tiny plastic particles first land on leaves in the upper canopy.
“Microplastics in the atmosphere first attach to leaves in the tree canopy, which scientists call the ‘comb-out effect,'” explains lead author Colin J. Weber, Ph.D., of the Institute of Applied Geosciences at Darmstadt University of Technology. “Then, in deciduous forests, the particles are carried into the forest soil by things like rain and fall leaf litter.”
How plastic particles move into soil
Once on the forest floor, natural processes take over. Decomposition of fallen leaves plays an important role in capturing and accumulating microplastics in the soil. The researchers found that concentrations were highest in the top layer of fallen leaves, where they have just begun to decompose. However, significant amounts were also detected deep underground.
This transfer to the subsoil is associated not only with the decomposition of organic matter, but also with biological activities such as leaf decomposition and organisms that help redistribute particles.
Measuring microplastics in soil, leaves, and air
To better understand how microplastics accumulate, the researchers collected samples from four forest locations east of Darmstadt, Germany. They analyzed soil, leaf litter, and atmospheric deposition (the transport of materials from the Earth’s atmosphere to the surface) using newly developed methods combined with spectroscopic techniques.
Scientists also created a model to estimate how much microplastic from the atmosphere has entered forests since the 1950s. This helped assess how much of the total pollution accumulated in forest soils can be traced back to airborne sources.
Forests as indicators of plastic pollution in the atmosphere
“Our results show that microplastics in forest soils come primarily from atmospheric deposition and fallen leaves on the ground, known as leaf litter, while other sources have a small contribution,” Weber explains. “We conclude that forests are a good indicator of atmospheric microplastic pollution, and that high concentrations of microplastics in forest soils indicate a high diffusive input of particles from the atmosphere into these ecosystems, as opposed to direct inputs, such as from agricultural fertilizers.”
New environment and potential health concerns
This study clearly shows how forests become contaminated with microplastics, and for the first time directly links that pollution to airborne particles. Until now, this pathway has not been thoroughly studied.
This finding provides an important basis for assessing the environmental risks of microplastics in both air and soil. “Forests are already under threat from climate change, but our findings suggest that microplastics may pose an additional threat to forest ecosystems,” Weber said. The results could also have implications for human health, as they highlight how microplastics move around the world in the atmosphere and can even be present in the air we breathe.
