Distribution of microplastics in water and sediment of Negro River and Peñol-Guatapé Reservoir, Colombia

The generation of microplastics (MPs, ≤5 mm) has become a pollution problem in rivers worldwide. Plastic debris can be transported through the water or trapped in the sediment in different proportions between rivers and reservoirs. The purpose of this study was to analyse the spatial and temporal pattern of contamination by MPs in water and sediment in the Negro River and Peñol-Guatapé Resevoir. Two samplings at 5 sites were conducted: 1 in the transition from the dry to rainy season and 1 in the rainy season. Three replicates of each sample (water, sediment) were taken, including physicochemical parameters. The density in water ranged from 350 to 789 MPs/m³, and in sediment from 8 to 194 MPs/kg. The primary forms of MPs were small blue and colourless fibres. The type of polymer corresponding to each plastic particle was identified using Fourier transform infrared spectroscopy. The polymers identified were polyvinyl chloride, polyethylene, polystyrene, polypropylene, polypyrrole, and poly (1-vinylpyrrolidone-co-2-dim ethyl aminoethyl methacrylate), and evidence of MP contamination in water and sediment was found at all sites. A seasonal effect was observed in the concentration of MPs. The incremental distribution along the river continuum suggests a significant drag and resuspension effect favoured by high flows, which reduced retention in the reservoir. This work provides a reference for understanding the dynamics of MP pollution in tropical Andean reservoirs.