In the forests of central Germany, scientists have discovered that trees and soils are quietly collecting large amounts of airborne microplastics. The study provides a clear picture of how plastic pollution travels through the air and ends up in terrestrial ecosystems.
Published in Communications Earth & Environment, the research found that forest soils contained between 120 and more than 13,000 microplastic particles per kilogram – levels similar to those found in urban soils and much higher than in farmland or wetlands. In some areas there were nearly a million microplastic particles per square metre.
Lead author Dr. Collin J. Weber from the Institute of Applied Geosciences at TU Darmstadt, said: ‘Our results indicate that microplastics in forest soils originate primarily from atmospheric deposition and from leaves falling to the ground, known as litterfall. Other sources, on the other hand, have only a minor influence.
‘We conclude that forests are good indicators of atmospheric microplastic pollution and that a high concentration of microplastics in forest soils indicates a high diffuse input – as opposed to direct input such as from fertilisers in agriculture – of particles from the air into these ecosystems.’
To track the movement of microplastics, the team used funnels to catch particles falling through tree canopies. On average, 9.1 microplastic particles landed per square metre each day, most smaller than 250 micrometres. The plastics were mainly polypropylene and polyethylene, the types commonly used in packaging, textiles and other everyday products.
The study found that these particles don’t just stay in the leaf litter. Over time, natural decomposition and soil processes move them deeper into the ground, where they can remain for decades or longer. Researchers estimate that the microplastics now in forest soils could have been building up since the 1950s, when global plastic production began to rise rapidly.
This research has important implications. Unlike farmland, which can receive plastics directly from fertilisers or mulches, forests are remote and largely free from local sources of plastic. This makes them excellent ‘natural monitors’ of diffuse pollution carried through the atmosphere.
Ultimately, the findings show that microplastics are not simply an ocean or urban issue. They are transported through the atmosphere like other airborne pollutants, settling in forests, accumulating in soils and entering terrestrial food webs. The forest filter effect, long recognised for trapping heavy metals and organic contaminants, now appears to operate for synthetic polymers as well.
The full research can be read here.
Photo: Kat Closon
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