Rivers as microplastic factories

Abstract Even in an ideal future where macroplastic emissions into rivers are entirely eliminated, plastic stored in river channels and floodplains, will be remobilized, and fragment into microplastics through its interaction with natural fluvial processes, such that riverine plastic emissions will continue for centuries As more time passes, rivers may cut new routes through plastic deposits, such as landfill sites, whilst deposits of plastic in the oceans will eventually become rocks, perhaps becoming uplifted as plastic mountain ranges, ready to start the cycle again. These processes can generate ongoing lulls and fluxes of secondary microplastics, prolonging threats to ecosystems and human health for millennia. In this perspective, we explore how understanding the way todays rivers move and deposit sediment—based on fluvial geomorphological knowledge—can help explain where and how plastic debris breaks down into microplastics, and how this insight can be used to better manage and reduce long-term plastic pollution in rivers.