Global plastic export by rivers: large differences in trends between microplastics and macroplastics

Plastic pollution in aquatic ecosystems has become a major concern due to the adverse consequences it poses to marine and human health. Rivers are a major source of inputs of plastic waste into seas. Modelling studies in the past have estimated plastic fluxes into seas for microplastics or macroplastics. However, sources of both macro- and microplastic exports by rivers to coastal waters and their past and future trends have hardly been addressed simultaneously in a spatially explicit way (e.g., sub-basins). This includes both point sources (sewage) for microplastics from car tyre wears, personal care products, household dust and laundry as well as diffuse sources (mismanaged solid waste) for macroplastics and their fragmentation to microplastics. This study aimed to analyse the past (2010-2020) and future (2020-2100) river export of macro- and microplastics using the MARINA-Plastics model using a scenario with the rapid urbanization and high economic development under high global warming in the existing MARINA-Plastics (Model to Assess River Inputs of pollutaNts to seAs for Plastics). The model results show that estimated that globally, the annual river export of macroplastics is modelled to decrease by only 7% whereas the river export of microplastics is modelled to increase by 144% between 2010 and 2020. The large increase for microplastics is associated with increasing trends in urbanization over the period of 2010-2020. In the future, globally, the annual river exports of macroplastics are projected to increase by 118% and microplastics are projected to decrease by 8% in 2100. The sub-basins of the Atlantic, Indian and Pacific Oceans will account for more than 85% of the total river export of plastics in the future. The large increase for macroplastics is related due to poor management of waste and poor collection rates. The hotspots for macroplastic pollution in coastal waters are modelled to shift from Europe and North America to Africa and Asia in the future. Our insights could inform the design of plastic reduction policies at the international level and support the achievement of Sustainable Development Goal 14 (clean marine waters).

All authors acknowledge the support of the Water Systems and Global Change Group of Wageningen University. I. Micella is supported by the European Union's Horizon 2020 research and innovation program under the Marie Sklodowska-Curie Grant Agreement No. 956623 (InventWater).