Microplastic (MPs) pollution is a global concern that affects all environments. Rivers have been identified as a major transport route for MPs from land to oceans. In this context, we evaluated the MP contribution from the Biobío River, one of the most important rivers in Chile, to the ocean. MPs were collected from superficial water throughout the entire Biobío River basin (and its tributaries) during the summer and winter of 2022. The samples were physically (color, size, and shape) and chemically (polymeric composition) analyzed using a microscope, a Fourier-transform infrared (FTIR) spectrometer, and a micro-FTIR. Results showed evident seasonal variations, with a significant increase (∼20 times average) in microplastic concentration (particles/day) in winter (7 × 105-1x108) compared to summer (4 × 103-7x105). Fibers were the dominant morphology with polyethylene terephthalate (PET; 20-40 %) and polypropylene (PP; 20-50 %) as the most abundant polymers. The river downstream showed the highest sample particle diversity (e.g., size, color, and polymeric composition). The river's behavior suggests a main role as a "Reservoir", corresponding to ∼40-50 % retention of microplastic in the midstream of the Biobío River. Furthermore, a preliminary evaluation using the OpenDrift model, indicated that particles coming from the Biobío River were mainly stranded on the Gulf of Arauco coast (≈100 %), suggesting a potential accumulation zone. This study contributes crucial information to understanding the behavior of plastic pollution in freshwater courses and its likely impacts on the coastal environments.

Institute of Urban Environment Chinese Academy of Sciences China

Instituto Argentino de Oceanografía Departamento de Química Bahía Blanca Argentina

Masaryk University Faculty of Science Brno Czech Republic

Universidad Católica de la Santísima Concepción Concepción Chile

Universidad Católica de Temuco Facultad de Recursos Naturales Temuco Chile

Universidad de Concepción Environmental Science Faculty Centro EULA Chile

Universidad San Sebastián Facultad de Ingeniería Arquitectura y Diseño Concepción Chile

Universidad San Sebastián Facultad de Ingeniería Arquitectura y Diseño Concepción Chile; Masaryk University Faculty of Science Brno Czech Republic

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