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<p>Agricultural soils play a key role as sink of microplastic (MP) coming from different sources, especially via the application of sewage sludge, compost, plastic mulch films, and tire ware. However, the effectiveness of this sink might be substantially reduced in areas subjected to water erosion. The aim of this study is to determine the transport behavior of MP during water erosion events on arable land. More specifically it is analyzed if MP is preferentially transported or behaves more conservative as attached to soil minerals and/or encapsulated in soil aggregates. A series of rainfall simulations were performed over 1.5 years on two plots at two test sites representing different intensively used soils (silty loam and loamy sand) in Southern Germany. The plots (4.5 m x 1.6 m) were spiked with microplastic (high density polyethylene) consisting of two different size fractions, fine MP (MP<sub>f</sub>, 53-100 μm) and coarse MP (MP<sub>c</sub>, 250-300 μm) incorporated into the topsoil (< 10 cm). The results clearly underline the selective nature of MP erosion leading to an enrichment ratio of MP in the eroded sediments of the loamy sand plot of 3.82 to 7.86, compared to an enrichment ratio from the silty loam plots of 1.41 to 5.29. Interestingly, there was no significant difference in enrichment ratios between MP<sub>f</sub> and MP<sub>c</sub>. Over time, an increasing connection between MP and soil particles could be observed. During the first rainfall simulation only 12% (MP<sub>c</sub>) and 34-49% (MP<sub>f</sub>) of the eroded plastic particles were connected to mineral particles or soil aggregates, while during the last simulation 1.5 years later about 31-47% (MP<sub>c</sub>) and 57-67% (MP<sub>f</sub>) of the eroded particles were bond to the soil matrix. Overall, our results indicate a strong dependency of the erosion transport behavior of MP depending on soil characteristics and time since application, while surprisingly we found little effect of MP size. </p>

<p><span lang="EN-US">Agricultural soils play a key role as sink of microplastic (MP) coming from different sources, especially via the application of sewage sludge, compost, the decay of plastic mulch, and tire ware particles along streets. However, the effectiveness of this sink might be substantially reduced in areas subjected to water erosion. The aim of this study is to determine the transport potential of MP during water erosion events on agricultural land. More specifically, we are interested if MP is preferentially transported or if it is attached or associated to soil minerals and aggregates leading to a more conservative transport behavior. The transport behavior is studied based on a series of plot rainfall simulations on a silty loam (16% sand, 59% silt, 25% clay; 1.3% OC) and a loamy sand soil (72% sand, 18% silt, 10% clay; 0.9% OC) located at experimental farms in Southern Germany. To simulate heavy rain on dry and wet soil a sequence of two simulations with a gap of 30 min was performed for 30 min each (rainfall intensity 60 mm/h) on each of the four plots (2 m x 5 m). The simulations are repeated in spring and autumn for two years. Before the beginning of the experiment all plots were prepared, adding fine (53-100 μm) and coarse (250-300 μm) microplastic (high density polyethylene) in a topsoil (< 10 cm) concentration of 10 g/m<sup>-2</sup> and 50 g m<sup>-2</sup>. The different soils show similar mean runoff rates for the dry run (2 l min<sup>-1</sup>), whereas the wet run produced slightly higher rates on the silty loam (5.5 l min<sup>-1</sup>) compared to the loamy sand soil (4 l min<sup>-1</sup>). In contrast, MP erosion and transport under the loamy sand was more selective, leading to MP enrichment for the first set of experiments of a factor of 3 to 20, compared to MP under silty loam with an enrichment factor of 0,4 to 0,8. The results from the first set of rainfall simulations clearly underlines the selective nature of MP erosion and transport leading to a disproportionate loss of MP from eroding sites into inland waters. The degree of MP enrichment in surface runoff is heavily depending on soil texture and especially moisture status at the beginning of an erosive rainfall event. Further investigations regarding more long-term MP enrichment effects depending on MP association to soil minerals and aggregates are under preparation. </span></p>

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