Spatio-temporal dynamics of microplastic contamination in tropical freshwater fish

Abstract

Plastic production and consumption have increased steadily over recent decades, contributing to the accumulation of debris in the environment, among which microplastics are now widely detected. Although research on microplastic contamination has expanded rapidly, freshwater ecosystems, particularly in tropical regions, remain comparatively understudied, and long-term perspectives are still rare. This thesis advances the understanding of microplastic contamination in tropical freshwater environments by addressing spatial and temporal dimensions. First, a literature review synthesizes the current state of research on microplastics in tropical freshwaters, identifying major advances and gaps across regions, ecosystems, and organism groups. Second, microplastic ingestion by fish is evaluated across different freshwater environments within a river basin, including lotic and lentic ecosystems, highlighting the role of hydrological context and the complexity of contamination patterns. Finally, long-term trends in microplastic ingestion by fish are assessed over a 24-year period across regions with contrasting land-use contexts, representing the first analysis of this kind for tropical freshwater fish. Overall, the results show that lentic environments can act as important accumulation zones, exposing organisms to higher contamination levels, and that temporal trends in fish contamination are not uniform but depend on regional environmental context. In addition, water turbidity influences microplastic ingestion in visual foragers. This thesis also highlights the importance of long-term ecological monitoring and biological archives as essential tools for reconstructing past contamination and advancing knowledge on plastic pollution.