An experimental flume study on the retention of Microplastic Fibers and Irregular Microplastics

Pore-scale microplastics (< 10 μm) are emerging contaminants whose behavior and fate in aquatic environments remain poorly understood. While the properties of spherical microplastics (SMPs) in fluvial systems have been studied, those of irregularly shaped microplastics (IMPs) and microplastic fibers (MPFs) remain poorly understood. We investigated how the transport and retention of IMPs and MPFs differ from those of SMPs. We compared the transport dynamics of 8 µm diameter IMPs and MPFs, with diameters ranging from 5 to 10 μm and lengths of 60–250 μm, with reference SMPs of diameters 1, 3, and 10 μm, by continuously monitoring microplastic concentrations in surface water and streambed sediments. Our results demonstrate how particle shape and sediment-particle ratio affect the transport and retention of microplastics in fluvial systems. These differences will have significant implications for the ecological impact and long-term fate of different MPs, including the duration of exposure to benthic organisms and the burial of MPs in deeper sediment layers due to river sedimentation cycles.