From source to mouth: an integrated assessment of microplastics in the Sinos River, Southern Brazil, using SEM-EDS analysis and atmospheric modeling

Plastic waste is one of the main causes of the deterioration of freshwater ecosystems. Once in the environment, microplastics (MPs) have harmful effects on living organisms and pose risks to human health. This study used an integrated approach to assess the presence of microplastics in surface water and sediment samples from three sites along the Sinos River in the State of Rio Grande do Sul, Brazil. Scanning Electron Microscopy (SEM) and Energy-Dispersive Spectroscopy (EDS) were employed for characterization, and a Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model was proposed to understand atmospheric influences. Microplastics were found in all samples and sites, including the river's source. Fibers were predominant, and particle sizes ranged from 67 µm to 4.2 mm. A total of 109 particles were recovered from the water samples (12±4 L-1 particles), and 21 from the sediment samples (2±2 100 g-1 particles). SEM analysis revealed surface cracking, and EDS confirmed the prevalence of carbon and oxygen in the particles. Based on the atmospheric model, the trajectories of air masses prior to sampling at the highest site demonstrate that MPs can be transported from other locations. Our study reports microplastic contamination in Caraá for the first time, provides insights for future studies on the atmospheric transport and deposition of microplastics in countryside regions, and highlights the urgent need to include these pollutants in environmental quality assessments of this important hydrographic basin.