Descripción: **Motivation** Scientists have risen concerns about the accumulation of plastics in the environment since the early 1970s. Plastics, especially when they are small, have a toxic effect on marine biota. Studies have estimated that nearly 25% of the total mismanaged plastic waste ends in oceans while 75% ends in soils. However, neither soils nor oceans are permanent plastic sinks. Nowadays, the scientific community proposes that plastics cycle in the environment; that they move through different ecosystems in a way that resembles geochemical cycles. The problem, in its broadest dimension, is that this plastic cycle gets feed as time passes by our increasing plastic production and demand. In other words, the amount of plastic traveling through the environment increases every year, worsening the problem. Soils house almost 75% of all mismanaged plastic waste. However, the incidence of plastic pollution is not equal across different land uses. Arable lands, especially soils used for crop production, have the highest incidence of plastic pollution. They are the most exposed to the entry of plastics. The use of plastic covers to increase crop yield and organic fertilizers, such as wastewater sludge, introduce plastics to arable lands at constant rates. It is not easy to address this problem, as the use of plastic covers and sludge-based fertilizers cannot be replaced in the near future. Fortunately, in the case of soils the toxicity of plastics is not that relevant as it is the risk of microplastics liking out to other ecosystems. Hence, if we understand the process by which microplastics are transported out of agricultural fields we can set maximum load rates to avoid environmental liabilities without affecting crop yield by limiting agricultural supplies. **Goal** This project will unveil the effects of surface roughness (soil texture and aggregation), and water availability on the transport of microplastics out of agricultural fields a diffuse source of microplastic pollution. The project aims to contribute to our understanding of how soil conditions and irrigation management promote or limits the transport of microplastics by runoff. **Novelty** This proposal stands out from previous research efforts as it addresses three unresolved research gaps. First, studies so far have addressed only subsurface transport of microplastics in soils. Scientists have neglected surface transport, although evidence suggests that this might be the dominant transport process. Second, to date, estimations of plastic loads from land to water have assumed that microplastic discharge follows sediment discharge, but this has not been tested. Third, evidence suggests that irrigation technology might influence the rate at which microplastics migrate out of agricultural fields. However, no study has purposely tested this hypothesis. **Methods** We will run a series of three experiments using simulated rain and soil flumes to (a) characterize microplastic discharge and verify if it follows sediment discharge; (b) quantify the effect of surface roughness on the transport of microplastics by excess water; (c) size the effect of microplastic shape and composition on the ease of runoff transport, and; (d) estimate microplastic runoff transport by different irrigation technologies. We will build a rainfall simulator and fill soil flumes with soil and plastics of different shapes (fiber, pellet, and films) and compositions (high density plastics -PVC and PET- and low density plastics -PE and PP-). Then, and according to the particular design of each experiment, we will test different texture classes and aggregate stability (experiment 1), slopes and rainfall intensity (experiment 2), and irrigation technology (experiment 3), over the discharge of microplastics out of the flumes. We will quantify the temporal discharge of microplastics and sediments in the runoff water, and evaluate the dynamics of microplastic discharge based on their composition and shape. It is our best intention that the acquired knowledge will help to set maximum loads and prevent microplastic diffuse pollution.
