Rivers as Conduits: A Comprehensive Model of Microplastic Fate and Transport

The surge in plastic production and its widespread usage in modern society have escalated the generation of plastic waste, resulting in the prevalent presence of microplastics (MP) in various ecosystems. Their stability and resistance to degradation promotes their persistence and accumulation in the environment, posing significant threats to ecological and human health. River systems acting as connection pathways between lands and oceans, play an important role in controlling the movement of MP. Therefore, understanding which are the main transport mechanisms that control the fate of MP in fluvial settings remains an important challenge. To this end, we developed a process-based model that solves the advection-dispersion-reaction equation (ADRE)  to predict how the amount of MP changes along the river network. The model considers MP inputs from anthropogenic sources and characterizes the transport and removal mechanisms (i.e. sedimentation, burial, resuspension, and bank removal) according to the different hydro-geomorphological conditions of the reaches that compose the fluvial network. The capability of the model to capture observed concentrations of MP was tested by using available literature data. Comparison between observed and modeled concentration of MP confirm the robustness of the proposed tool  and its versatility to dynamically represent the MP transport-removal processes. Model results  can be helpful to understand and address the challenges posed by MP pollution in riverine systems.