Is the Paraiba do Sul River colourful? Prevalence of microplastics in freshwater, south-eastern Brazil

Context. Plastic pollution can be even more problematic to the environment when this material is fragmented into small pieces forming microplastics (MPs). Aims. The objectives of the present study were to investigate the abundance, morphotypes, predominant polymers, and colour of MPs on surface waters, and compare the effect of the hydrologic cycle on the abundance and richness of MP categories along a stretch of the Paraiba do Sul River basin, the water system of which flows through the most populous area in Brazil. Methods. Samples were taken from the superficial layer of the water column in high-water and low-water periods 2021, using bottles and plankton net. Key results. In total, 15 categories of MP were determined and 290 plastic particles were collected in both periods. A greater abundance of MPs was found during the high-water period than in the low-water period, considering both sampling methods. Conclusions. The MPs in the surface waters of the Paraiba do Sul River are significantly influenced by the rainfall regime.