Abstract
<jats:p>This chapter introduces environmental fate and transport models, emphasizing the challenges, advancements, and uncertainties in integrating specific processes relevant to micro- and nanoplastic (MNP) particles. Firstly, the different roles and aims of environmental fate models are discussed. Then, the two main modelling approaches employed for estimating MNP transport in the environment are introduced and discussed with selected examples: (1) process-based multimedia mass-balance models and (2) environmental transport models. Here we focus on balancing the needs for MNP-specific process descriptions to adequately capture the complexities of MNP fate and transport in the environment, with sufficient environmental realism to account for spatio-temporal differences in environmental drivers. Finally, data needs and challenges in model validation are discussed.</jats:p>