Resumen:
The growing concern with microplastic (MP) pollution in coastal and estuarine ecosystems has driven advances in environmental geosciences, particularly in understanding their transport, accumulation, and degradation dynamics. Within this context, the thesis entitled “Photodegradation of Microplastics in Mangrove and Beach Sediments in Todos os Santos Bay, Bahia – Brazil”, developed by Claudinéia de Souza Souza in the Graduate Program in Geochemistry: Petroleum and Environment (POSPETRO/UFBA), under the supervision of Prof. Dr. Joil José Celino and co-supervision of Prof. Dr. Márcio de Jesus Silva, investigates the mechanisms of MP degradation in contrasting sedimentary environments of Todos os Santos Bay (TSB), one of the largest tropical estuaries in Brazil and subject to intense anthropogenic pressures. The research is structured into three complementary chapters. The first analyzes the spatial distribution and potential sources of MPs in beach and mangrove sediments of TSB, considering abundance, morphology, color, and elemental composition. The results reveal significant differences between the ecosystems, associated with factors such as grain size, organic matter content, and hydrodynamics. In the second chapter, a multivariate statistical analysis integrates physicochemical sediment parameters (pH, total organic carbon, and total nitrogen) with MP behavior, allowing for discussion of their environmental persistence, interactions with the sediment matrix, and potential ecotoxicological implications. The third chapter constitutes the innovative axis of the thesis: the experimental assessment of photodegradation processes (photolysis and heterogeneous photocatalysis with TiO₂) applied to cosmetic plastic microspheres. Through gravimetric, spectroscopic (FTIR), and morphological (SEM/EDS) analyses, the feasibility and limitations of these degradation strategies are demonstrated, as well as their possible applications in remediation technologies. By integrating field data, geochemical analyses, and laboratory experiments, this work makes a substantive contribution to advancing environmental geochemistry in the study of plastic pollution, providing scientific support for public policies, technological development, and conservation of tropical coastal ecosystems. In addition to providing unprecedented data on TSB, the research expands the understanding of MP degradation processes, establishing itself as a reference for future investigations in Brazil and other tropical estuaries.
