Multi-Type Microplastic Migration Model Driven by River Hydrodynamic Conditions

Microplastics have complex compositions and properties, and their migration in aquatic environments is unpredictable due to various influencing factors. This study investigates the forces on microplastics in river systems, determines hydrodynamic parameter thresholds for different microplastic types' movement state changes via hydraulic experiments, and proposes a novel migration model. This model accurately characterizes forces on diverse microplastics, effectively simulates their movement trajectories and fate in aquatic systems, and is validated by data from the Xianyou section of the Mulan River. Simulations show that in this section, microplastics below 0.5 mm account for 71.62% of the total, mainly fragmentary (29.7%) and fibrous (37.8%) types. PP migrates fastest as drift mass, while large-sized PS and PA below 0.5 mm are transported as suspended mass. PET, due to its high density, sinks to the riverbed. Fragmentary microplastics have the highest transport rate at the end section. The closer the pollution source is to the end section, the higher the number of light microplastics and the total transport rate. The total flux of microplastics from typical pollution sources in this section is 9.66×1011, with a total transport rate of 65.58%. The innovation of this paper is to introduce a multi-type microplastics migration model driven by river hydrodynamic conditions, aiming to clarify the complex migration mechanisms of microplastics in freshwater environments and provide new ideas and theoretical guidance for studying their transport laws in freshwater ecosystems.