The presence of microplastics (MP) in open environments has drawn the attention of decision makers and the scientific community to understand the potential risks. The risk assessment of MP in the aquatic environment needs the understanding of large-scale dispersal of MP. While field data continues to be gathered, its extent remains insufficient at both temporal and spatial scales. To expand the knowledge of MP dispersal, modelling tools are essential. In this study, the numerical modelling tool openTELEMAC is used to implement the Population Balance Equation (PBE) method applied to the size distribution of the MP coupled to a (horizontally) two-dimensional (2D) depth-averaged hydrodynamic model. With the help of PBE, the dynamic evolution of the particle size distribution is tracked. The transport of MP in the aquatic environment is influenced by the presence of sediments whose mass or volume fraction outnumber the MP by several orders of magnitude. Therefore, the sediment transport model is coupled to the hydrodynamic model, to capture the influences of the sediment classes mud and sand on the transport behaviour of the MP. In addition, the TOMAWAC wave model is coupled as well for a better representation of coastal dynamics.