Microplastics — tiny fragments of plastic less than a millimeter across — are now firmly embedded in one of the least disturbed ecosystems in Europe: forests. A new study by researchers at the Technical University of Darmstadt finds that forest soils in central Germany are accumulating significant amounts of these particles, largely through the simple act of filtering the air.
The study focused on four forest sites east of Darmstadt, in the state of Hesse. Each site represented a different stand: mature beech trees about 70 years old, a 50-year-old oak and beech mix, and two pine-dominated stands with beech or ash trees around 60 years old. These managed forests grow on soils typical of the region — Cambisols and Dystric Cambisols — making them representative of temperate European woodland.
Forests as Plastic Filters
The research shows that forests act as natural sieves for airborne pollution. Just as tree canopies are known to trap metals and chemical residues, they now appear to be capturing airborne plastic. Rainwater washing through the canopy, known as “throughfall,” delivers much of this material to the forest floor, where it mixes with falling leaves and slowly works its way deeper into the soil.
Microplastic concentrations in these soils were striking. Across the four study sites, the average levels reached more than 4,000 particles per kilogram of soil. The most contaminated layers were not the fresh leaf litter but the more decomposed organic horizons, followed by the mineral soil beneath. Over time, particles are transported downward by natural litter turnover processes.
A Long History of Accumulation
By comparing today’s concentrations with known plastic production trends, the researchers estimated that forest soils have been quietly accumulating microplastics since around 1950, when mass plastic manufacturing began in Europe. In fact, the current levels in these German forest soils are comparable to those found in urban soils — an unsettling benchmark given the remoteness of the sites.
This means forests are not just passive backdrops to the plastic age; they are long-term sinks, steadily absorbing the fallout of airborne plastic pollution.
Why It Matters
Soils are the foundation of forest health. The presence of plastics in the very horizons where nutrients cycle raises questions about subtle but consequential impacts: how microplastics might alter soil chemistry, disrupt microbial communities, or interfere with carbon and nitrogen flows that underpin forest productivity.
The Darmstadt study underscores a broader message: atmospheric deposition is not only delivering greenhouse gases and pollutants but also plastics to ecosystems previously assumed to be relatively pristine. The cumulative effect, building up invisibly over decades, may prove as significant as the better-known agricultural and urban sources of soil contamination.
Source
Forest soils accumulate microplastics through atmospheric deposition, Commun Earth Environ 6, 702 (2025), 2025-08-26
Boˆreal 