Kuakata beach, known as Daughter of Sea in Bangladesh, has drawn a growing number of tourists from all over the world, leading to the higher use of single plastic products. This study was a first attempt to describe the occurrence, spatial distribution, and ecological risk of microplastics (MPs) in Kuakata beach sediments. A total of 24 surface sediment samples were collected from the intertidal zone of the beach, and MPs were extracted using the density separation method and a stereomicroscope. Fourier transform infrared (FTIR) spectroscopy was used for qualitative and quantitative identification. The results revealed that the average MPs in the beach sediment were 232 ± 52 items kg^–1 dry weight, which was much higher than many other sandy beaches throughout the world. Analyses of variance showed a significant (p < 0.01) difference among the mean abundance of MPs in sampling points. Fibers were dominated in every sampling point with an average of 123 ± 27 item kg^–1. Most of the MPs observed were colored (60%), and the rest were transparent (40%). It was found that the size range of 1–5 mm MPs constituted over half (55%) of total MPs covering an average value of 127 ± 34 items kg^–1. Three polymer types were identified in the sediment samples through FTIR analysis which followed the decreasing order of polyethylene terephthalate > polyethylene > polypropylene. Correlation analysis showed a positive relationship between the abundance of MPs and the finer grain size of sediment (p = 0.055; r = 0.7), indicating grain size-controlled the density of MPs. The pollution load index was assessed to estimate the ecological risk and found that the beach sediment of Kuakata belonged to the risk category I of the pollution index. This investigation provided preliminary information on MPs pollution in the marine ecosystem that the policymakers can use to take appropriate management approaches.

Microplastics (MPs) ingestion by fish signifies a worldwide threat to human health but limited research has examined their existence within the consumable portions (muscle) of fish. Thus, this study was undertaken to unveil the prevalence, characterization, and contamination extent of MPs across various body tissues, including the muscle of the king mackerel (S. guttatus) from the lower Meghna estuary in Bangladesh—a pioneering investigation in this region. In our analysis, we identified a total of 487 MPs, with an average abundance of 48.7 ± 20.3 MPs/individual. These MPs were distributed across different tissues, with respective concentrations of 0.84 ± 0.45 items/g in the digestive tract, 2.56 ± 0.73 items/g in the gills, and 0.3 ± 1.72 items/g in the muscle tissue. The observed variations among these tissue types were statistically significant (p < 0.05). Moreover, a significant positive correlation indicated that fish with higher weight had higher MPs in their gills and DT (digestive tract). The majority were <0.5 mm in size (97.74%) and exhibited a fiber-like shape (97.74%), with a notable prevalence of transparent (25.87%) and a pink coloration (27.92%). Remarkably, the majority of MPs were discovered within the size range of <0.5–1 mm (100%), particularly in the muscle tissue, signifying a substantial transfer of MPs into the human diet. Besides, we discovered only three polymer types of microplastics which could be attributed to the extensive use of food packaging, plastic containers, wrapping plastics, residential garbage, and plastic pipes that end up in the aquatic environment via river discharges. The contamination factor (CF) values of fish muscle (5.75) and the digestive tract (5.50) indicated that these fish organs were considerably contaminated (3 < CF < 6) with MPs. The pollution index of MPs (PLI > 1) indicated a high contamination level for MPs pollution of S. guttatus in the lower Meghna River estuary.

Trace-element or heavy-metal pollution has emerged as a serious concern in terms of both environmental and human health issues. This study measured six trace and toxic heavy metals (Pb, Cd, Cr, Ni, Cu, and Zn) in four marine fish and shrimp species to assess their accumulation levels and evaluate the risks to human health. The mean concentrations of the metals in fish and shrimp species (Labeo bata, Sillaginopsis panijus, Platycepalus fuscus, and Penaeus monodon) followed the decreasing order of Zn (40.8 ± 9.7 μg/g) > Cu (17.8 ± 7.1 μg/g) > Pb (6.2 ± 1.8 μg/g) > Ni (0.4 ± 0.3 μg/g) > Cd (0.06 ± 0.02 μg/g > Cr (below detection level). Among the metals, only Pb in finfish and Pb, Cu, and Zn in shrimp samples exceeded the national recommended limits, representing possible risks to consumers. The mean metal concentrations in the studied fish/shrimp species followed the descending order of P. monodon > S. panijus > P. fuscus > L. bata, which implies that bottom dwellers and omnivores had higher levels of metals. However, the estimated daily intake (EDI) concentrations of Zn and Cu for the studied species were lower than the RDA (Recommended Daily Allowance). In addition, the Target Hazard Quotient (THQ) and hazard index (HI or TTHQ) values for all species were < 1, indicating that consumers might not experience carcinogenic health risks. A strong significant (p < 0.05) correlation between Cu and Pb (r = 0.623) and Zn and Cu (r = −0.871) indicated they were from the same source of origin. Cluster analysis (CA) and principal component analysis (PCA) demonstrated possible anthropogenic sources of toxic metals in the study area, specifically industrial wastes and agricultural chemicals.

Heavy metal accumulation in aquaculture farms has become a major problem due to the widespread use of artificial feed to enhance fish productivity. To estimate the contamination level and identify metal sources, we investigated the amounts of seven heavy metals (Cu, Zn, Pb, Cd, Cr, Ni, and Mn) in the surface water of commercial fresh water aquaculture farms in a south Asian tropical coastal area. Atomic absorption spectrometry (AAS) was used to analyze 36 water samples from 12 commercial fish farms. The results demonstrated that the range of three heavy metals were detected in a decreasing order of Mn (0.0574–0.4100 mg.L⁻¹) > Zn (0.0125–0.3250 mg.L⁻¹) > Cu (0.0275–0.085 mg.L⁻¹). In all samples, the remaining four heavy metals (Pb, Cd, Cr, and Ni) were below the detectable level (BDL). Except for Mn, the amounts of the metals examined were below WHO and USEPA guideline values. According to the findings, the levels were found to be safe for drinking, agriculture production, and aquaculture. There was no significant correlation (p > 0.05) between heavy metal concentrations and water quality parameters, indicating that pollution came from diverse sources and that no single factor was controlling their levels. Furthermore, Analysis of Variance (ANOVA) revealed no significant differences in the mean metal values among the fish farms (p > 0.05). Multivariate analyses (CA and PCA) demonstrated the association and sources of metal in the study area. Although metal levels were not beyond the threshold limit, it is recommended that suitable measures and continuous monitoring should be undertaken to reduce heavy metal pollution in aquaculture farms and prevent water quality degradation.

As an intermediary connection between primary producers and higher trophic levels, zooplankton are an important component of the aquatic food chain, contributing significantly to aquatic biological productivity. This study describes the zooplankton diversity and community structure, as well as their relationships with ecological factors, in homestead ponds of a coastal district along the northern Bay of Bengal region. Significant differences (p < 0.05) were detected in the mean values of temperature, pH, DO, TDS, transparency, and phosphates from the ponds during December 2020, but no significant differences were found in the nitrate levels. However, no significant variances in the ecological parameters between months were found due to the study taking place in the same season. Sixteen zooplankton species, representing four groups, were found in the study area, with the highest mean abundance of 301.19 ± 40.55 ind./L recorded in February 2021 and the lowest of 293.02 ± 21.13 ind./L recorded in December 2020. The diversity (H’), evenness (e), richness (J), and dominance (D) ranged from 2.49 to 2.12, from 0.93 to 0.84, from 2.05 to 1.56, and from 0.13 to 0.09, respectively. Based on the SIMPER analysis, Diaptomus gracilis and Brachionus calyciflorus were found to be significant contributors (>10%) to the zooplankton community structure in different months. The ANOSIM results revealed that 10 species of zooplankton were significant contributors based on their average dissimilarity. The canonical correspondence analysis (CCA) identified that pH, transparency, nitrates, and phosphates have a significant impact on the abundance of zooplankton species in the homestead ponds in the study area.