A team of scientists at Freie Universität investigated the geological and biological effects of microscopic plastic particles on the soil and its microbes. Soil microorganisms play a central role in many biogeochemical cycles, such as the decomoposition of organic matter and the binding of carbon in soil. The research project provided the first experimental evidence that microplastics can functionally change the biophysical conditions of soil as well as the 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 prestigious 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 polluntion from microplastics in a previous study The new research provides experimental proof for the first time that plastic particles have biophysical effects on soil. In the experiments soil was contaminated with four different types of microplastics 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 basic 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 microplastics 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 microorganisms in the soil samples were thus forced to adapt to the new environmental conditions. Their activity showed signs of functional change.

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 microplastics pollution and responded to it,” explains Matthias Rillig.