Three rivers to the test: Lessons for global plastic transport modelling

Rivers are key pathways for plastic pollution to the ocean, yet global river export models remain highly uncertain due to catchment diversity and the complexity of plastic transport. We examined the critical river-ocean interface using a comparative dataset from three rivers in the Caribbean, Southern Africa, and Southeast Asia with distinct hydrometeorological and tidal regimes. We traced 196 GPS drifters and monitored surface transport at six river locations using forty-one cameras over multiple seasons. Using these observations, we simulated three years of plastic transport (2020-2022). We show that rivers flush 50% of their plastics downstream within only 7-12% of the time. Annual average mass fluxes for the three rivers were 34-98% lower than earlier global model estimates. Our findings underline that rivers are long-term pollution sinks, and that estuaries have limited transport. We provide critical insights from observations and modelling to refine river-to-ocean plastic flux models and underscore the heterogeneity of emission dynamics across diverse river contexts.