How Rivers Export Plastic: Insights from Three Contrasting Global Systems

Abstract

Rivers are key pathways for transporting plastic pollution to the ocean, yet global estimates of riverine plastic export remain highly uncertain due to catchment diversity and the complexity of transport processes. To better understand dynamics at the river–ocean interface, we analyzed a comparative dataset from three rivers in the Caribbean, Southern Africa, and Southeast Asia, each characterized by distinct hydrometeorological and tidal regimes. We tracked 196 GPS drifters and monitored surface transport using forty-one cameras deployed across six river locations over multiple seasons. These observations informed simulations of three years of plastic transport (2020–2022). We find that rivers flush 50% of their floating plastics downstream within only 7–12% of the time. Annual average mass fluxes for the three rivers were 34–98% lower than previously reported by global models. Our results highlight that rivers act as long-term sinks for plastic pollution, and that estuarine transport is more limited than often assumed. This study provides critical observational and modelling insights to refine river‑to‑ocean plastic flux estimates and emphasizes the heterogeneity of emission dynamics across diverse river systems.