Tropical estuaries are highly productive yet increasingly threatened by natural and anthropogenic pressures, necessitating robust ecological assessments for sustainable management. This study assesses the spatio-seasonal distribution of macrobenthic assemblages and evaluates the ecological health of the Sangu River estuary based on their bioindicator potential. Sediment samples for macrobenthos analysis were collected during three seasons (pre-monsoon, monsoon, and post-monsoon) from nine stations across three estuarine zones influenced by sedimentation, aquaculture, and terrestrial runoff. We employed microbenthic diversity indices, multivariate analyses, the AZTI’s Marine Biotic Index (AMBI), and multivariate-AMBI (M-AMBI) to evaluate the ecological health status of the study area. Our study recorded 13 taxa, dominated by Nereididae (40.90%), Mysidae (14.29%), and Capitellidae (10.20%). Macrobenthos diversity (Shannon diversity) ranged from 0.80 to 1.22, and abundance showed negative correlations with salinity (r = −0.29) and silt (r = −0.22), and a positive correlation with dissolved oxygen (r = 0.29). Analysis of Similarities (ANOSIM) indicated that seasonal variation was the primary driver of community structure (p < 0.001). AMBI classified most stations as having good to moderate ecological status, while M-AMBI indicated moderate disturbance across seasons, with elevated proportions of opportunistic taxa (EG V: 14.4–32%) reflecting persistent anthropogenic stress. This study provides the first empirical ecological baseline for the Sangu River estuary and highlights the applicability of family-level AMBI assessments in data-limited tropical estuarine systems.

Microplastics (MPs) are widespread aquatic pollutants that can accumulate in fish, posing potential risks to food safety and human health. This study investigated MPs in ready-to-use fish powders (RUFPs) from Bangladesh and evaluated their reduction through primary processing. Three powder types—whole fish powder (WFP), eviscerated fish powder (EFP), and fish muscle powder (FMP), prepared from five small fish species: Anchovy (Coilia sp.), Fringescale sardine (Sardinella fimbriata), Ganges river sprat (Corica soborna), Indian river shad (Gudusia chapra), and Pool barb (Puntius sophore). A total of 157 MPs were detected in 13 RUFP samples, with concentrations of 0.4–3.4 (1.21 ± 0.77) MPs g-1 dry weight. Among WFPs, Fringescale sardine had the highest concentration, followed by Indian river shad, Pool barb, Anchovy, and Ganges river sprat. MPs decreased from WFP to EFP to FMP (0.8–2.6, 0.6–2.2, and 0.6–1.4 MPs g-1, respectively). On an extrapolated wet-weight basis, processing reduced MP loads by 46–52% after evisceration and 54–77% after muscle isolation relative to whole fish. Most MPs were fibers, blue in color, and 20–150 µm in size. ATR-FTIR identified synthetic polymers and cellulose derivatives. Overall, processing substantially reduced MP loads, indicating its potential to improve the safety of fish-based products.