Dangerous for soil? First experimental study on the influence of micro-plastics on soil & its micro-organisms

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Polyester fibers in soil. © Machado AAS

A team of scientists at Freie Universität investigated the physical and biological effects of micro-plastic particles on the soil and its microbes. Soil micro-organisms play a central role in many biogeochemical cycles, such as the decomposition of organic matter and the binding of carbon in soil. The research project provided the first experimental evidence that micro-plastics can change the biophysical conditions of soil as well as the functional activity of microbes. More studies are needed to show whether, and if so, how plastics – as anthropogenic, or human-induced – stressors have a long-term effect on the ecosystem of the Earth. The findings of this pioneering study were published in the latest issue of the journal Environmental Science & Technology.

Led by environmental scientist Dr. Anderson Abel de Souza Machado and biologist Prof. Dr. Matthias C. Rillig, the team had already pointed out the danger of pollution from micro-plastics in a previous study. The new research provides experimental evidence for the first time that plastic particles have biophysical effects on soil.

In the experiments soil was contaminated with four different types of micro-plastics in increasing concentrations. The scientists incubated these soil samples under natural conditions for five weeks in an experimental garden at Freie Universität. They then studied the soil and the activity of its microbes. The experiment showed that plastic particles, especially polyester fibers, exerted an influence on fundamental structural properties of the soil and its interaction with water. The soil bulk density (how tightly the soil particles were packed) and the interaction of those particles in forming aggregates were different when micro-plastics were present in the soil. Plastic particles increased or decreased the size of pore space in the soil and influenced how much water the soil could absorb. The micro-organisms in the soil samples were thus forced to change in response to the new environmental conditions. Their activity showed signs of functional change.

Graphical summary of the study results. Each contamination with different types of plastic fundamentally influences the soil and its functions – also as a habitat for microorganisms. (Image credit: Machado AAS, Environmental Science & Technology)

The authors point out that this is the first study of its kind. Therefore, it is not yet clear whether these changes will have a long-term negative impact on the soil and its ecosystems. “It might be too early to fully elaborate on the mechanism driving the microbial responses and to predict its consequences, but the fact is that microbes are perceiving the environmental change initiated by micro-plastics pollution and responded to it,” explains Matthias Rillig.