On the ZIRKONthe Zittau Institute for Process Development, Circular Economy, Surface Technology and Natural Materials Research at Zittau/Görlitz University of Applied Sciences, a group of young researchers has been conducting research into microplastics since 2020. Under the title "Development of methods for the detection, elimination and immobilization of microplastics in soils, compost and plants", five young researchers are working on this highly controversial topic under the project management of Prof. Jens Weber following the initiation of the project by Prof. Jürgen I. Schoenherr.

The pollution of the environment by plastic, its abrasion and degradation products, is constantly increasing. We are all familiar with the images of "plastic waste islands" in the sea, beaches full of garbage and dead animals with plastic in their stomachs. But what about the fraction that is invisible to us - microplastics?

The presence of microplastics, i.e. particles between 0.1 µm and 5 mm in size, in marine and limnic waters is well known. However, there is another area that requires increased attention: microplastics in soil. The detection and quantification of the microplastic fraction in soil remains a challenge. The aim of the project is to contribute to the development of methods for the detection, characterization and elimination or immobilization of microplastics in soil. In addition, strategies for avoiding (micro)plastics are to be developed by analyzing the material flows. Microplastics enter the environment primarily through tire abrasion, "littering" ("disposal" of plastic waste in the environment) and applications in agriculture (e.g. mulch films, sewage sludge) and their degradation in the environment.

Extensive monitoring was carried out during the project to identify pollution hotspots. For this purpose, sediments from Saxon reservoirs were examined for their contamination, as well as various soils on roadsides and in fields.

Methods for elimination

Furthermore, various methods for eliminating microplastics from soils and compost are being investigated for their effectiveness.  The greatest challenge here is the complexity, i.e.  the high variance in properties, of a plastic-soil mixture. The tests showed that sand-plastic mixtures can be separated very well using various methods, such as density separation or electro-separation. For the application, this would mean that microplastics can be removed almost residue-free from sands or sediments that are used industrially or occur naturally with appropriate pre-treatment. For more complex soils or compost, however, current methods are less effective and further research is required.

In order to evaluate the effects of the quantity and composition of plastic in the soil and on plants, experiments were carried out with (crop) plants. For this purpose, different plant species were grown in the greenhouse and in the climate chamber on defined soil mixtures with the addition of different (micro)plastics in order to investigate the influence of microplastics in the soil on plant growth and yield. The focus of the experiments was on the effects on root growth, the transport of microplastics through roots and the long-term effects of microplastics on biomass production.

Another focus of the project is the optimization of analytical methods, for example, the materials from the planting trials were examined with regard to microplastic input, various methods were tested and suitable methods were continuously optimized during the project period.

Transport processes and behavior of microplastics

As part of a doctoral thesis (in cooperation with the TU Bergakademie Freiberg), the transport processes of microplastics in the soil are being investigated, with the behavior of microplastics in the saturated soil matrix being researched in column experiments. Initial results indicate that the transport distance of microplastic particles increases with decreasing diameter. Small fragmented microplastic particles, whose morphology is rather one-dimensional, were more susceptible to fragmentation within the soil columns, which promoted migration. Spherical microplastic particles remain in their initial position without fragmenting, while fibrous microplastic particles become entangled in the soil matrix. The degradation of microplastics into fragments appears to play an important role in promoting particle movement. The occurrence and infiltration of microplastics into a saturated soil matrix suggests a possible input into groundwater.

Column experiments were used to simulate a realistic model of the soil matrix. This is used to create a prediction model for the behavior and displacement of microplastics.

The research project thus combines the expertise of various disciplines and specialist areas to tackle a global problem and investigate possible solutions.

The results of this project were presented and discussed in public workshops throughout the duration of the project. International speakers also enriched these events with their expert contributions in the various specialist areas.