Sequestration and export of microplastics in urban river sediments

[Display omitted] •Small-sized microplastics are preferentially deposited and retained during fluvial processes.•Microplastics in the riverbed accumulate in the dry season and are released in the rainy season.•Wider riverbeds are hotspots for microplastic sequestration in rivers.•Seasonal rainfall increased the export of microplastics in the riverbed by 34.86%. In rivers, riverbeds are considered to have dual properties as a short-term sink and a source of further mobilization for microplastics. To better understand the sources, storage, and fate of microplastics in river systems, this study quantified the formation of microplastic hotspots in riverbeds and seasonal variations in microplastic inventories in riverbeds, especially for small-sized microplastics (