>b/b<: Typology and Distribution Approach in Coastal and Estuarine Ecosystems

The extensive Atlantic coast of Brazil, especially in the South and Southeast regions, concentrates densely populated urban areas and faces significant environmental pollution challenges. With large freshwater reserves and several rivers flowing into the ocean, there is a continuous input of pollutants, including microplastics (MP), which have become an increasingly prominent concern. However, many studies still focus on biota, beaches, and the ability of MP to adsorb contaminants, leaving gaps regarding their presence in sediments and surface waters. This PhD Thesis aimed to quantify and char acterize MP (300 μm 5 mm) in sediments and surface waters of marine and estuarine systems along the South and Southeast coasts of Brazil. Sampling was conducted in four regions: (i) the coastal area between Rio Grande do Sul and Santa Catarina (2019); (ii) the SantosSão Vicente Estuary (SP, 2022); (iii) the Tramandaí and Mampituba rivers (RS, 2023); and (iv) Paranaguá Bay (PR, 2023). Water samples were collected using a Manta net (300 μm), and sediments with multicore (MUC) and Van Veen samplers. Processing included sieving, organic matter digestion, density separation, filtration, and polymer identification by FTIR. In total, 49 samples were analyzed (20 water and 29 sediment), resulting in 1,980 particles, of which 62% were identified. Most unidentified particles consisted of fine fibers below the FTIR detection limit. Overall, MP were more abundant in surface waters than in sediments, being detected in 98% of samples. In coastal areas, concentrations ranged from 6.5 to <33.9 MPm-3 in water and from non-detected to 85.8 MPKg-1 in sediments. In estuaries, they ranged from 0.52 to 39.8 MPm-3 in water and from 28.6 to 772.2 MPKg-1 in sediments. The Tramandaí River (RS) and Paranaguá Bay (PR) showed the highest concentrations, exceeding those recorded in the Santos Estuary (SP), even though the latter is the most an thropized. MP were detected in 69% of sediment samples and in 100% of water samples. Identified particles included fragments, fibers, films, pellets, and tangles. In water, PP, LDPE, EPDM, PMMA, PVC, POM, PS, and PET were the most prominent; whereas in sediments, LDPE, EPDM, PET, and PP were most common. These polymers are widely used and frequently reported in marine pollution studies. Statistical analyses integrated with cli matological data indicated that environmental factors such as meteorolog ical conditions, oceanographic dynamics, and continental inputs influence MPdistribution. In estuaries, population density showed a relationship with observed concentrations, although in the Santos Estuary this correlation was unclear due to the limited number of stations. The results expand knowl edge about MP in southernsoutheastern Brazil and reinforce the urgency of mitigation actions, integrated public policies, and continuous monitoring. Aligned with the Decade of Ocean Science (20212030) and ODS 6, 13, and 14, this work contributes to the conservation of marine ecosystems and the protection of the populations that depend on them