Suspended sediments open the way to microplastic sedimentation in shallow aquatic systems

Plastic particles represent an emerging contaminant in aquatic ecosystems, causing a global environmental crisis. Seas and oceans represent the final receptors for the macro- and microplastics (MPs) entering in the freshwater environment. Many studies have focused on the quantification of plastic debris in the marine environment [1] and on their residence time in rivers [2]. The end of water courses can also be a buffer for MPs. Shallow water environments (e.g., floodplains and wetlands) represent areas where MP can accumulate [3]. They are totally or partially enclosed areas with low energy zones and stagnant water, with low flow velocities and low channel slopes enhancing MP accumulation. Currents, flooding events and turbulence produced by wind promotes the presence of suspended sediments [4] that are expected to be transported alongside with MP particles. However, to date, the knowledge of the transport of MP in such transitional environments is limited, and the retention mechanism of MP and the time scales of MP processes remain unknown as well as the interaction with suspended sediment particles. In addition, the contribution of floodplains, wetlands, lagoons, intertidal zones, saltmarshes, and generally shallow water areas, is rarely taken into account within the MPs mass balance models. In this work we investigated the transport of a particle laden (MP and sediment) plume in a simulated shallow water system under a unidirectional flow. Three of the most common MP will be considered under study, PA fragments, PVC fragments and PET fibers. The interaction between sediment particles and MP will be studied through flume experiments with different sediment and MP concentrations in order to obtain the sedimentation rates of the different MP considered along the system.