The project “Microplastic in fresh water systems” (MicBin) is part of the initiative Plastics in the Environment funded by the Federal Ministry of Education and Research (BMBF) and runs over a period of 3.5 years (2017-2021). Within MicBin the work package of the University of Augsburg focuses on measuring and modelling the microplastic fluxes via soil erosion from arable land into inland waters.

Therefore, repeatedly series of irrigation experiments are carried out on arable land. The irrigated plots were previously loaded with a defined amount of microplastic (HDPE 50-100 μm, 250-300 μm). The surface runoff and eroded sediment gets analyzed on degraded PE particles. This is intended to determine the potential transport of the microplastic particles via soil erosion. The main issue is to find out whether microplastic preferentially is washed out via surface runoff because of low density. Alternatively, whether a binding to soil particles or soil aggregates takes place, reducing the output. In addition to basic research about the behavior of microplastic in soils, the experiments are used to derive model parameters for erosion modeling. The SPEROS-C model was partly developed by the working group and will be used to generate simulations of the microplastic output of small selected catchments of tributaries of the river Danube. By the modeling of microplastic transport a quantification of uncertainties will be necessary. Because so far, all estimations about plastic in soils are based primarily on a very poor data knowledge.

According to current researches, soils could represent a huge sink for plastics. Especially agricultural soils are burdened by microplastic. The extent of this burden is not yet quantifiable. This is partly due to the varied and poorly defined sources on the one hand (fertilization with sewage sludge and compost, input by tire abrasion, atmospheric deposition, use of plastic in agriculture such as films in special cultures etc.). On the other hand, the limited knowledge about the behavior and the remain of plastic in soil. The detection of microplastics in soils is extremely difficult, since individual (micro-) particles and not uniformly distributed dissolved substances must be detected. Compared to water samples, the separation of the microplastic from the solid matrix is a special challenge.