Transport of marine microplastic particles: why is it so difficult to predict?
Marine microplastic particles (MPs,<5 mm) exhibit wide ranges of densities,sizes, and shapes, so that the entire MPs“ensemble”at every time instant can be character-ized by continuous distributions of these parameters. Accordingly, this community ofparticles demonstrates distributions of dynamical properties, such as sinking or risingvelocity, critical shear stress, and the re-suspension threshold. Moreover, all the MPs’properties vary significantly with the time spent in marine environment and withparticular conditions experienced by the particle on its journey. A brief review of thepresent-day numerical efforts towards prediction of MPs transport shows the prevalenceof the Lagrangian particle tracking approach, especially for floating litter. In a broadercontext, the present practice of MPs transport modelling follows the“selective”strategy(e.g., only a certain sub-class of MPs, or specific processes, are considered, sometimes in onlyone- or two-dimensional setting). The heterogeneous nature of MPs, their enormous longevityand movability in marine environment, and the wide spectrum of the involved environ-mental processes suggest further integration (or coupling) of different models in future, aswell as application of other types of models (ensemble modeling, chaos theory approaches,machine learning, etc.) to the problems of MPs transport and fate in the marine environment.Key words:microplastics, transport, modelling.