Microplásticos em águas superficiais e sedimentos do rio Guaraguaçu: uma avaliação espaço-temporal

Abstract

The ubiquity of microplastics has become an increasing environmental concern. Microplastics are plastic particles smaller than 5 mm, originating from the fragmentation of larger debris or released directly into the environment. Despite the growing number of studies, significant knowledge gaps remain regarding their spatiotemporal distribution in river systems under estuarine influence, which limits environmental and risk assessments. In this context, this study aimed to analyze the occurrence, distribution, and physical and chemical characterization of microplastics in surface water and sediment of the Guaraguaçu River basin, located on the coast of Paraná, Brazil. Sampling was conducted during four campaigns throughout 2024 (March, June, September, and December) at 22 sites distributed across the basin. Surface water was collected using a trawl net, and sediment samples were obtained with a grab sampler. Processing included sieving, chemical digestion (when applicable), density separation, and filtration. Quantification and morphological characterization were performed under a stereomicroscope, while chemical identification was carried out using microscopy coupled with infrared (FTIR) and Raman spectroscopy. A total of 1,770 items classified as potential microplastics were recorded across the four campaigns (703 in March, 378 in June, 375 in September, and 314 in December), with marked variation between matrices: surface water predominated in June and December (323 vs. 55; 228 vs. 86), whereas sediment predominated in September (168 vs. 207). Spatial distribution indicated the occurrence of items even at upstream sites, suggesting that local hydrodynamics and tidal regimes influence redistribution and accumulation, in addition to gradients of anthropogenic pressure. Morphologically, a consistent pattern was observed, with fibers predominating in surface water and fragments in sediment; microbeads were detected in September and December campaigns but were not confirmed as polymers in chemical analyses. The most frequent colors included blue, black, and gray, consistent with diffuse sources associated with domestic effluents, artisanal fishing, and fragmentation of everyday plastic products. Chemical characterization confirmed polyester and polypropylene as the dominant polymers. In surface water, polyester (52.3%) and PP (38.6%) accounted for most identified polymers, while sediment was dominated by PP (50%), followed by PET (21.4%), PE, and polyester (14.3% each). Overall, the results demonstrate the widespread distribution of microplastics in the Guaraguaçu River basin and highlight the combined influence of polymer properties (density, shape) and hydrosedimentological dynamics (tides, deposition/resuspension) on transport and retention between compartments. These findings contribute to the understanding of microplastic environmental behavior in coastal rivers and provide support for monitoring actions and future risk assessments.