Assessing the risks of microplastic particles (MP) in the environment plays an important role in plans to reduce the impacts of plastics, now and in the future. Risk assessment requires further insight in the relationship between the sources, fate, transport and exposure to microplastics. These insights help to provide policy makers and stakeholders with adequate advice on mitigating microplastic pollution, prioritizing perspectives for action and monitoring the microplastic burden to the environment. Furthermore, it guides the scientific community to priority areas for follow up research regarding the most urgent gaps in our understanding of risks of MP. One reason to understand risk is to be able to reduce risk. This relates to risks of the particles themselves, but also those of plastic-associated chemicals and/or pathogens. Here, modelling can be an important tool to answer future questions about the most effective approach to plastic pollution. This in the context of realizing a non-toxic environment, green chemistry, combating antibiotic resistance and the transition to a circular economy. Given this background and the urgency that it entails, the main objective of this PhD project is to develop and validate a suite of transport-fate models for microplastics encompassing different spatial scales.