Abstract: Biofilms play a crucial role in regulating the behavior of microplastics (MPs) in aquatic environments, yet their dynamic mechanisms have often been overlooked in traditional models. We reviewed the formation mechanism of biofilm and its impact on the sedimentation behavior of MPs. Upon entering water, MPs are rapidly colonized by microorganisms, forming biofilm structures composed of extracellular polymeric substances (EPS) and microbial communities. This process is influenced by exposure time, environmental conditions, and the intrinsic properties of MPs. Biofilms significantly affect MPs sedimentation and vertical distribution by increasing their effective density, promoting aggregation, and altering surface properties, challenging the applicability of prediction models based solely on physical attributes. Microorganisms (particularly microalgae) and their EPS secretions are key factors driving sedimentation differences. We further summarized current research progress on biofilm-MPs interactions, their applications, and limitations. Future research should focus on the following areas. Mechanistically, we should develop multiscale models that integrate biofilm dynamics with hydraulic conditions. Methodologically, we should advance in-situ observation techniques to quantitatively characterize biofilm properties such as EPS composition and community function. From an application perspective, we should explore bioremediation strategies that use functional microorganisms, such as specific algae or bacteria, to control MPs sedimentation.

Key words: extracellular polymeric substance, microbial carrier, bioflocculation, heterogeneous aggregation, environmental fate