In one of the first studies of its kind, University of Bern researchers have discovered an estimated 53 tonnes of microplastics in the floodplain soils of Swiss nature reserves.

Their findings, published in the journal Environmental Science and TechnologyExternal link, concern plastic pieces under 5 millimetres (0.20 inches) in diameter.

While plastic pollution in the ocean and freshwater bodies is a well-known phenomenon, the extent of the problem in soils is still not clear. To gather their data, researchers at the university’s Institute of Geography had to develop a novel method using microscopy for identifying and measuring the tiny particles in 29 floodplain soils from across Switzerland.

"Although the sites are located in nature reserves, microplastics were found in 90% of the soils," said co-author Moritz Bigalke in a University of Bern press releaseExternal link on Friday.

Most of the contamination was found near larger pieces of plastic, which suggests that the microplastics were produced by the physical breakdown of larger waste. But some microplastics were found isolated in the soil of more remote and mountainous regions, suggesting they may have been carried there by the wind.

One connection was clear: “The more people living in a specific area, the more contaminated the soil”, the press release said.

Co-author Michael Scheurer called the findings “alarming” because there is evidence that soil microplastics can harm or even kill earthworms – organisms that play a key role in soil fertility.

The researchers conclude that further research is needed, especially the concentrations of microplastics in agricultural soils and their potential impact on the food chain.

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