The need for research regarding the occurrence and effects of microplastic (MP) in the environment has become apparent by numerous studies. However, even though release rates into terrestrial environments are suggested to be 4-23 times higher than those into oceans (Horton et al., 2017, doi: 10.1016/j.scitotenv.2017.01.190), research about MP in soils is only just starting. The first studies reported that MP influenced soil physical properties. For example, it can be incorporated into soil aggregates (de Souza Machado et al., 2018, doi: 10.1021/acs.est.8b02212), or clog soil pores (Zhang et al., 2019, doi.org/10.1016/j.scitotenv.2019.03.149) possibly affecting soil hydraulic properties. In this study we aim at increasing the mechanistic understanding of the influence of MP particles on vertical water flow. We irrigated soil columns filled with simple substrates with and without the addition of MP particles (polystyrene, 0.1% or 0.5% of dry weight, homogeneously mixed). To compare the arrival times of the irrigation water, NaCl was used as tracer. The arrival times of the drainage and tracer fronts were characterized by the viscous flow approach (e.g. Bogner & Germann, 2019, doi:10.2136/vzj2018.09.0168). Furthermore, we analysed the drainage water for possible MP leaching out of the soil columns by fluorescence microscopy after staining with Nile Red (Konde et al., 2020, 10.1016/j.marpolbul.2020.111475). Preliminary results indicate that MP changed the infiltration time of irrigation water substantially.