Microplastics (MPs) as hazardous contaminants has drawn the rapid attention of the general public due to their omnipresence and adverse impacts on ecosystems and human health. Despite this, understanding of MPs contamination levels in the estuarine ecosystems along the Bay of Bengal coast remains very limited. This research focused on the presence, spatial distribution, morpho-chemical characteristics and ecological implications of MPs in water and sediment from five key estuaries (Meghna, Karnaphuli, Matamuhuri, Bakkhali, and Naf rivers) within the Bengal delta. Out of the five estuaries, the Meghna exhibited the least amount of MPs in both surface water (150.00 ± 65.62 items/m³) and sediment (30.56 ± 9.34 items/kg). In contrast, the highest occurrence of MPs was recorded in Karnaphuli river water (350.00 ± 69.22 items/m³) and Matamuhuri river sediment (118.33 ± 26.81 items/kg). ANOVA indicated a statistically significant distinction (p < 0.01) among the examined estuaries. Most identified MPs were fibers and < 0.5 mm in size in both water and sediment samples. Transparent MPs were dominant in both water (42.28%) and sediment (45.22%). Besides violet, red, blue, pink and green colored MPs were also observed. Various polymer types, including PE, PP, PET, PS, Nylon, EVA, and ABS, were detected, with PE being the dominant one. Based on the polymer risk index (PHI), the estuaries were classified as hazard level V, signifying a severe level of MP contamination. However, the potential ecological hazardous index (PHI), potential ecological risk index (RI), and pollution load index (PLI) indicated moderate pollution levels. This study offers initial insights into the pollution caused by MPs in major estuaries of Bengal delta, which policymakers can utilize to implement suitable management strategies.

Understanding how coastal ecosystems mitigate pollution is essential due to their critical role in safeguarding environmental health, and supporting restoration efforts. This study, for the first time, evaluated the contamination levels and retention capacities of micro- and mesoplastics, and heavy metals across coastal habitats-specifically mangrove (MH), invasive Kikuyu grass (KH), and salt marsh cord grass (SH)-along a subtropical intertidal beach. Of the 120 sediment samples collected, 60 were analyzed for micro- and mesoplastics using wet peroxide oxidation and FTIR spectroscopy, while the remaining 60 were examined for heavy metal concentrations via ICP-MS. Results showed that KH habitats retained the highest plastics (153 ± 10.9 items/kg), followed by MH (112 ± 4.58 items/kg), SH (73.17 ± 6.81 items/kg), and NV (50.83 ± 10.87 items/kg) areas with significantly different retention in MH and KH habitats. Heavy metals followed a decreasing retention order of Mn > Zn > Cu > Cr > Pb > Ni > As > Cd > Hg. Significant difference was observed in Pb, Cr retention by an invasive Kikuyu grass (KH1) station, and Cu retention in two invasive Kikuyu grass stations (KH1 and KH3). However, in general no habitats were significantly different in retaining the metals. Principal Component Analysis and Canonical Correspondence Analysis revealed that micro- and mesoplastics were strongly associated with Zn, Cu, and Pb. KH habitats showed the highest retention efficiency, however, the associated toxicity risk increased with retention levels, indicating a higher risk in KH habitats compared to NV areas. The study highlighted Kikuyu grass habitats as both efficient pollutant sinks and potential ecological risk zones, emphasizing the need for targeted remediation to optimize retention while safeguarding ecosystem health.

The Fauzderhat coast of Chattogram (Bangladesh) is increasingly affected anthropogenic pressures, necessitating an understanding of its ecological conditions to inform effective ecosystem management. Despite this urgency, the local succession patterns and environmental impacts on macrobenthic communities remain poorly understood. This study examines the saltmarsh bed macrobenthos in Fauzderhat, documenting 81,724 individuals from 54 species. These include ten families and twenty-two species of annelids, ten and twelve species of arthropods, and ten and eleven species of mollusks, as well as six and nine species from different phyla. Seasonality showed significantly different patterns of changes, with the number of species and abundance peaking during the monsoon (53 species) and post-monsoon (21,969) conditions, respectively, and being lowest in the post-monsoon condition (39 species) and winter (18,265 individuals). Species richness, diversity, and evenness were significantly higher in monsoon and lower in post-monsoon conditions, with the differences being only significant in the former. Cluster analysis and line graphs indicated that average species abundance was lowest post-monsoon, increased through the winter and pre-monsoon conditions, then declined again during monsoon conditions. SIMPER analysis revealed the highest dissimilarity between pre-monsoon and post-monsoon conditions while winter and post-monsoon conditions showed the lowest dissimilarity of microbenthic assemblages. Correlation coefficients showed the macrobenthos were positively correlated with soil salinity, dissolved oxygen, and pH, while they were negatively correlated with sand, Inundation Period, and nutrients. CCA showed that monsoon conditions (higher water temperature, inundation period, and tidal height) created unfavorable environments for most species, except for several species. Conversely, winter favored species like M. oligobranchia. Post-monsoon nutrient levels increased stress, reducing species presence, while pre-monsoon conditions supported balanced diversity.

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.