Abstract

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 Biob & iacute;o River, one of the most important rivers in Chile, to the ocean. MPs were collected from superficial water throughout the entire Biob & iacute;o 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 (similar to 20 times average) in microplastic concentration (particles/day) in winter (7 x 10(5)-1x10(8)) compared to summer (4 x 10(3)-7x10(5)). 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 similar to 40-50 % retention of microplastic in the midstream of the Biob & iacute;o River. Furthermore, a preliminary evaluation using the OpenDrift model, indicated that particles coming from the Biob & iacute;o River were mainly stranded on the Gulf of Arauco coast (approximate to 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.