Microplastic Occurrences in Freshwater Fish of Bangladesh

Abstract

Over the years, there has been widespread detection of microplastics (MPs) in unacceptable concentrations, which has increased the susceptibility of our environment to emergent pollutants. Bangladesh has produced tremendous plastic over the past four decades due to its accelerated population growth, urbanization, and cost-effectiveness. This plastic undergoes a process of degradation, which gives rise to the problem of MPs. Although over the last 7 years, a significant number of MP studies have been conducted in Bangladesh, MP contamination in freshwater fish-related studies was first conducted in 2021. Comprehensive studies of MP contamination in freshwater fish have yet to be explored entirely in Bangladesh. However, MP contamination in freshwater fish has a devastating impact on the gut health, immunity, and increase in the risk of developing diseases. Hence, this book chapter seeks to provide an up-to-date account of MP contamination in Bangladesh’s freshwater fish by synthesizing prior research. Furthermore, this chapter will explore MPs origins, distribution patterns, destiny, and transit in freshwater fish populations. This study is significant because it contributes to the increasing knowledge regarding MP pollution in freshwater ecosystems, which is particularly crucial in regions such as Bangladesh, which rely significantly on freshwater resources.

1. Introduction

The contamination of aquatic species with microplastics (MPs) is becoming a concerning global issue. Due to the widespread usage of plastics, which has significantly increased the accumulation rate over the past few decades, large amounts of toxic and nonbiodegradable solid waste have been dispersed across the aquatic ecosystem. Biological, physical, and chemical processes break down the systematic cohesiveness of larger plastic traces, which then convert into microscopic particles [1, 2, 3]. MPs are minuscule plastic fragments that arise during the production of commercial products as well as the disintegration of bigger plastics. MPs are a pollutant that may be dangerous for both animal health and the environment. As the name suggests, microplastics are minuscule particles of plastic. They are officially classified as polymers with a diameter of less than five millimeters, or 0.2 inches—smaller than the typical pearl used in jewelry [4]. There are many sources of microplastics, such as bigger plastic waste that breaks down into ever-tinier fragments. Furthermore, little fragments of synthetic polyethylene plastic known as microbeads are used as exfoliants in certain toothpastes, cleansers, and other cosmetic items. These microscopic particles could endanger aquatic life since they are easily filtered out of water and end up in the ocean and Great Lakes [5]. The quantity of MP in freshwater environments has been the subject of relatively little investigation; yet the increasing number of studies that have been carried out provides compelling evidence for the presence of MP contamination in freshwater systems. It is necessary to have a deeper comprehension of the diverse range of primary (produced in tiny sizes) and secondary (obtained from the disintegration of other macro- and micro-plastic) MP sources in freshwater. The fact that MP particles can travel great distances from their source complicates the process of identifying their origin. If not taken into consideration, there is also a chance that distinct fate (such as biological uptake, photodegradation, biofouling, and settling) and transport processes could change the MP profile seen at a source in comparison to what might be seen at a sampling site, which could make fingerprinting techniques for source tracking more difficult [6]. Microplastic (MP) pollution has become a major global environmental concern because of its wide distribution, richness, and effects on ecosystems, in addition to posing health hazards to individuals. Around half of all plastics are made for single-use purposes; however, over 5 trillion plastic bags and 1 million plastic bottles are bought worldwide annually [7]. Global plastic output rose by almost 9% between 2016 and 2019; however, because of the COVID-19 epidemic, this rate significantly declined in 2021 (367 Mt.) [8]. On the other hand, disposable plastics (such as gloves, masks, syringes, goggles, sharps, and gowns) have increased dramatically as a result of the novel coronavirus disease (COVID-19) [9, 10]. The majority of these throwaway products are composed of plastic materials, such as nylon, polystyrene (PS), polypropylene (PP), and polyethylene (PE). Although MPs do not directly affect living things, their small size, sharp edges, and polymer composition make them poisonous over time [10]. With over 700 rivers and watercourses, including tributaries, Bangladesh boasts one of the greatest river networks in the world, with a total estimated length of 24,140 km [11]. Together with these vast aquatic habitats, Bangladesh boasts the third-highest aquatic fish biodiversity in Asia, behind China and India. There are about 800 species of fish in fresh, brackish, and marine waters, with about 475 of those species being found in marine habitats [12]. In the fiscal year 2017–2018, Bangladesh produced a total of 4.28 million metric tons of fish, making it one of the top fish-producing nations in the world [12]. Over 50% of animal protein comes from fish [13, 14]. MPs have the potential to be consumed by aquatic organisms due to their small size, motility, and extensive dispersion. Studies have shown that annelid, mollusk, crustacean, fish, bird, and mammal species that live in wild freshwater environments have been found to consume plastic [14, 15, 16, 17, 18, 19, 20].

The widespread occurrence of microplastics in aquatic settings has drawn attention from throughout the world in recent years. Freshwater habitats and the creatures that live there are seriously threatened by these tiny plastic particles, which are either produced as microbeads in personal care products or are the byproduct of bigger plastic trash breaking down. Bangladesh is especially susceptible to the introduction of microplastics into its freshwater bodies due to its vast network of rivers and lakes. Therefore, it is critical to comprehend the scope and consequences of microplastic pollution in freshwater fish in order to protect Bangladesh’s environment and public health. In the context of Bangladesh, this book chapter attempts to present a thorough summary of the current status of research on microplastic occurrences in freshwater fish. This study tried to investigate the origins, patterns of distribution, fate, and transit of microplastics on freshwater fish populations by combining previous research. This study is important because it adds to the increasing amount of knowledge about microplastic pollution in freshwater ecosystems, which is important, especially in areas like Bangladesh, where freshwater resources are heavily relied upon.

2. Types and sources of microplastics in freshwater ecosystems

2.1 Types of MPs

Plastic particles less than 5 mm (but rarely measured at less than 0.3 mm) are known as microplastics (MPs). Through human use, they become part of the ecosystem. Certain plastics are produced as MPs, but over time, exposure to water and sunlight can cause bigger plastic waste to break down into micro-sized particles. Because MPs have such a wide range in form and shape, it is challenging to quantify and distinguish MPs from natural particles. Microplastic contamination can be caused by beaded beauty products, synthetic clothes, plastic bags, polystyrene foam, and throwaway plastics. There are 13 varieties of MPs; the most prevalent ones are polystyrene, polypropylene, and polyethylene. MPs fall into three main categories: Synthetic fabrics are the source of microfibers, which are often the most prevalent kind of microplastics. These fibers shed after regular wear and machine washing of clothes, such as fleece coats. The majority of microfibers emitted into water have a size of 0.1–0.8 mm, when macroplastics physically crack, fragments result. Personal care products frequently contain microbeads [21]. The most prevalent microplastics, also known as synthetic polymers, that are discovered in marine environments are acrylic (AC), polyester (PES), polyethylene (PE), polypropylene (PP), polystyrene (PS), and polyamide (PA, which includes nylon) [22]. Atoms of carbon and hydrogen joined in polymer chains make up microplastic. Microplastics usually contain additional chemicals such as phthalates, polybrominated diphenyl ethers (PBDEs), and tetrabromobisphenol A (TBBPA), many of which leak out of the plastics after they are exposed to the environment.

There are two categories of microplastics: primary and secondary. Primary microplastics include plastic pellets (also called nurdles) used in industrial manufacturing, microbeads found in personal care items, and plastic fibers used in synthetic textiles (like nylon). One way that primary microplastics get into the environment is through product use, such as washing personal care products into wastewater systems from homes, accidental spills during manufacturing or transportation, or abrasion during washing (such as washing clothes made of synthetic textiles). When bigger plastics are subjected to weathering—that is, when they are exposed to things such as wave action, wind abrasion, and UV radiation from sunlight—secondary microplastics are created as a byproduct [23]. There are several sources of microplastics in drinking water, such as municipal water systems, numerous distribution water systems (such as tap water), and packaging materials (such as plastic bottles, plastic-lined cartons, and glass) [24]. Mineral water packaged in glass, plastic, or lined containers is thought to be a potential cause of microplastic contamination in drinking water. According to Cox et al. [25], people who follow recommendations and drink bottled water may consume up to 90,000 microplastic particles annually. The two chief sources of plastic particles that contribute to the presence of microplastics (MPs) in the environment are the primary source and the secondary source. But pinpointing the precise source of MPs found in the environment is difficult, if not impossible. Plastic pellets, paint, washing wastewater, sewage sludge, artificial turf, rubber roads in cities, plastic running tracks in schools, and tire wear on vehicles are the main sources of environmental microplastics (MPs). Secondary sources, on the other hand, include large-scale plastic wastes from farming, fishing, and other sources, as well as city trash, such as plastic bottles and bags. Because of the quick rise in the number of cars on the planet, tire wear on automobiles is thought to be one of the most significant sources of environmental microplastic among these. Studies on the existence of rubber particles in the environment are, however, extremely rare. Although big plastic wastes require hundreds of years to decompose into MPs in the natural environment, secondary sources of MPs are thought to currently account for the majority of MPs in the environment [26].

2.2 Sources of MPs

2.2.1 Primary sources of MPs

Personal care products: MPs converted into microbeads are small. Microbeads can replace synthetic pigments in personal care products for washing, whitening, and exfoliating. Thermoplastic microbeads include polyethylene (PE), polypropylene (PP), polystyrene (PS), and polytetrafluoroethylene (PTFE), while thermoset materials include polyurethane (PU), polyethylene terephthalate (PET), and polymethyl methacrylate. Microplastic beads are 93% polyethylene. Microplastic beads are found in facial cleansers, toothpaste, sunscreen, shower gel, and hair dye. Due to their small size, insolubility in water, and gradual disintegration, microbeads enter the sewer network with washing wastewater. Current sewage treatment technology cannot remove plastic microbeads. Microbeads enter the environment via sewage sludge, which is commonly utilized in agriculture [26].

Plastic pellets: Plastic pellets are used to make plastic products. Plastic pellets are stored, transported, and processed using semifinished products. Styrene, vinyl chloride, ethylene, and propylene are made from petroleum and coal, the main basic materials for plastic. Thermosets and thermoplastic polymers exist. Recycling plants and polymer factories make these pellets [27].

Vehicle tires: Although a precise amount of microplastic contamination is still unknown, brake pads and tire wear are additional sources. Despite the common misconception that tires are made entirely of natural rubber, a tire’s natural rubber percentage can occasionally be as low as 20%; the remaining elements, such as plastics, are synthetic. Approximately 0.5 million metric tons (MMT) of microplastics are produced annually in the European Union as a result of car tire wear. This estimate’s straightforward extrapolation to the world’s car fleet reveals an annual microplastic release of about 2.5 million tons, or 4% of the weight of all tires on the road worldwide [28].

City dust: The term “city dust” describes a broad spectrum of urban-based microplastic sources; the most common and well-studied sources of city dust include artificial grass, building paints, and industrial abrasives. In contact sports, artificial turf is frequently utilized as a way to cushion hits and shield athletes from harm. The majority of microplastics from artificial turf originate from the polymeric infill, which can be inadvertently removed by athletes or during maintenance, even if the artificial grass fibers eventually break down into microfibers [28].

Paint: Most paint contains pigments, fillers, solvents, and minor amounts of useful ingredients. Based on their usage, paints can be architectural, automotive, aircraft, and marine, or natural resin, phenolic, alkyd, amino, nitro, epoxy, chlorinated rubber, acrylic, polyurethane, organic silicone, and silicone. According to studies, applying a paint layer to a surface can create microscopic plastic particles that can be released into the environment through abrasion, aging, and erosion. Thus, painting is a major source of environmental microplastic. Architectural coatings, marine coatings, automobile coatings, and road-marking paint can release environmental microplastic [29].

Agricultural uses for primary microplastics: A wide range of polymer-based agricultural products, including mulches for controlling temperature and moisture, silage and fumigation films, and anti-bird and weed protection, may contain microplastics. Although the amount of microplastics in these polymers is unclear, if their contribution to microplastic pollution is measured, they may rank among the main sources [28].

Washing wastewater: Household laundry wastewater and washing plant wastewater release enormous volumes of plastic microfibers into the environment from textile shedding. Importantly, washing releases polyester and polyamide synthetic fibers. Each piece of clothing may discharge about 1900 microfibers to wastewater treatment plants during washing. Sewage treatment plants cannot remove MPs. Plastic microfibers released during laundry washing enter the environment with effluent or sludge. Plastic microfibers in soil, rivers, and oceans make up most MPs, according to studies [26].

Plastic running tracks from schools: The 1968 Mexican Olympics introduced polyurethane running tracks. Plastics included EPDM and waste tire rubber as extras. Plastic running tracks usually have a hybrid or permeable surface layer. Hot and wet locations have permeable plastic running tracks and hybrid ones that are weatherproof and waterproof. Previous investigations found hazardous chemicals in some plastic running tracks. MPs might loosen from the track by wind and moisture with aging. Assessment criteria that affect MP release from plastic running tracks are unknown, making MP emissions estimates problematic [26]. Figure 1 shows the primary sources of microplastics.

Figure 1.

Primary sources of microplastics.

2.2.2 Secondary sources of microplastics

Secondary microplastics come from improperly disposed of bigger plastic particles. Physical, biological, and chemical processes include light irradiation aging, biological crushing, and mechanical grinding to degrade plastic structures into MPs.

Plastic bottles: Bottles are PET, PE, or PP. After heating or mixing plastic with an organic solvent, these bottles are made in a blow, extrusion, or injection mold. Beverages, pickles, honey, dried fruit, edible oils, and agricultural veterinary medicines use plastic bottles. Some locations offer clean drinking water in plastic bags and bottles. For convenience, sanitation, cost, and transparency, most people buy mineral water or other drinks in plastic bottles. One million plastic bottles are sold worldwide per minute [7].

Disposable plastic tableware: Making disposable plastic tableware involves thermoplastic molding resin or other materials. Plastic lunch boxes, plates, saucers, straws, knives, forks, spoons, cups, bowls, and cans are not food storage. Plastic tableware is cheap, lightweight, waterproof, and durable, making it popular globally. Plastic tableware is mostly PP, PE, PS, etc. Packaging such as foam cups, instant noodle boxes, and rapid food boxes employ polystyrene foam. If improperly disposed of, plastic tableware can leak MPs into sewers, soil, oceans, etc. Tableware may pollute 269,000 tons of streams and oceans worldwide [26, 30].

Plastic packaging: Plastic wraps shipping, storage, and distribution items. Such packaging comprises boxes, bags, films, etc. Plastic packaging with comparable or better design is replacing glass, metal, and paper due to its low cost, oxygen/moisture barrier, biological inertness, and lightness. The world generates 39.7% plastic and 25% packaging. Food, paper towels, and clothing are plastic-packaged. All around us are PE, PP, and PS packaging microplastics [26].

Fishing wastes: Plastic fishing waste includes buoys, crates, rods, tanks, nets, lines, and wires. The global discard of commercial fishing equipment is 0.13–135,000 tons. Polystyrene foam marine plastic litters China’s Shandong Coast and Mongolia’s Hofsgar Lake. The rapid rise of the aquaculture business, which uses many Styrofoam floating devices, and the vast quantity of abandoned fishing nets and foam pontoons lost to the sea owing to natural wear and biological decay are the main sources of such rubbish ocean plastics have surged because aquaculture abandoned massive feed garbage sacks. As fishing fleets employ more plastic nets, replenishing has destroyed many ocean nets. Fishing nets and ropes are made from LDPE, PA, and PP monofilament. Transparency and diameter vary. After entering the ecosystem, fishing nets and ropes shed fibers. Shipments accidentally spill significant amounts of plastic into the ocean. MPs predominate in fishing waste foams [31, 32].

Farming film: Agricultural plastic sheeting creates microplastics. A thin sheet of polyvinyl chloride, polyethylene, and other compounds is blow-molded agricultural mulch. Agriculture uses 3.4% of global plastic. The early 1950s saw plastic mulch films in agriculture. Films that enhance soil temperature and minimize pollutants boost agricultural yield and income, ensuring food security. Its high consumption and short lifespan make plastic mulch film recovery difficult, recycling efficiency low, and MP release into the soil simple. PE, LDPE, and LLDPE agricultural film microplastic are abundant [7]. Figure 2 shows the secondary sources of microplastics.

Figure 2.

Secondary sources of microplastics.

3. Fate and transport of microplastics in freshwater ecosystems

Due to plastic usage, microplastics have entered waterways, especially around industrial and urban areas. Urban transit lines, rainfall, agricultural runoff, and wastewater discharge pollute distant water sources. Microplastics’ size, shape, chemical makeup, and organic processes such as weathering and biofouling affect their distribution and fate in freshwater. When microplastics enter aquatic systems, settle in sediments, or are consumed by aquatic species, trophic transfer and bioaccumulation threaten the entire food chain [33]. Treatment plants only catch a portion of industrial and domestic wastewater microplastics, thus some escape. Microplastic discharge is high due to limited treatment capacity, especially in low-income countries. Microplastics and synthetic fibers in sewage sludge fertilizer pollute soil [34]. Microplastics from farms can pollute streams through runoff, rainfall, and flooding. Microplastics can spread widely in surface water, the water column, and benthic sediment after they reach aquatic systems because of their diverse forms [35]. Where rivers flow through cities and towns that absorb plastics industry effluent, freshwater microplastic pollution is strongly linked to terrestrial environments. Plastic waste in upstream watersheds is positively connected with river plastic [36]. Littering, overflow, wastewater discharge, and rainwater discharge produce plastic contamination in rivers [37, 38]. Farms are substantial terrestrial sources of microplastics due to plastic films, fertilizers, and irrigation that pollute soil [39]. Sewage sludge, used as fertilizer, contains synthetic fibers and microplastics that increase terrestrial microplastic pollution. Rainfall and irrigation runoff carry microplastics from soil to rivers and surface waterways [40, 41]. Low recovery rates from broad agricultural mulch film use contribute to plastic pollution. Microplastics from crop-irrigating wastewater build up in soil and enter waters. Microplastics travel differently through soil, and microbeads and bacteria interact differently. Microplastics are spread by transportation and sedimentation; hence, air deposition is a source in freshwater [42, 43].

Microplastics’ destiny in freshwater relies on their size, shape, density, chemical composition, ambient circumstances, and creature interactions. Microplastics may sink into sediment or persist in the water column for long durations. Microplastics might stay in sediment or be resuspended. Aquatic species can ingest microplastics, infiltrating food webs and causing ecological damage. Mechanical and chemical processes may fragment microplastics, increasing their prevalence and potential consequences in freshwater ecosystems. Urban runoff, wastewater treatment plant effluents, atmospheric deposition, and recreational activities can introduce microplastics into freshwater habitats. Microplastics in freshwater systems can settle in sediment, be swallowed by aquatic creatures, or be transmitted downstream to other water bodies. Microplastic transport and fate in freshwater ecosystems depend on flow, sedimentation, and biological interactions. Microplastics enter the environment through terrestrial ecosystems and wastewater infrastructure since most plastic comes from land. The main ways primary microplastics enter the environment are:

• Road runoff: Since most micropollution is created outside, roadside runoff is a key microplastic carrier [28].

• Wastewater treatment plants (WWTPs): WWTPs treat wastewater. Some pollution is treated by wastewater. Tertiary WWTPs catch over 90% of microplastics in effluent sludge. Even with microplastic retention of >90%, the volume of wastewater handled allows many microplastics to bypass filtration [28].

• Marine activities: Shipping, fishing, and tourism directly release microplastics into the ocean [28].

• Wind transfer: City dust and other microplastics can be carried by wind. Microplastics can travel vast distances and pollute air, food, and beverages. In metropolitan environments, 355 particles/m²/day are deposited [28].

4. Distribution and accumulation of microplastics (MPs) in freshwater fish of Bangladesh

Over the years, microplastics (MPs) have been detected in air, water, and soil environmental compartments. Although MPs in urban drive systems are widely distributed, MPs in freshwater fish-related studies are still limited in Bangladesh. However, based on the existing research of MPs in freshwater fish of Bangladesh, this section divided Bangladesh into four regions: Dhaka, northern, southwestern, and southeastern regions.

4.1 Distribution and accumulation of microplastics (MPs) in freshwater fish of Dhaka regions

Dhaka, the capital of Bangladesh, is surrounded by five big rivers along with many small canals and lakes. According to the existing research, the fish of the Turag, Balu, and Buriganga Rivers and Dhanmondi, Gulshan, and Hatir Jheel Lake in Dhaka have come to light of investigation [44, 45, 46, 47, 48]. The first study of MPs in freshwater fish in Bangladesh was conducted in 2021 based on the Turag and Balu Rivers [44]. In this study, Parvin et al. [44] collected 48 fish representing 18 taxa from these rivers, where most fish (73.30%) are contaminated with MPs. Three fish samples of Heteropneustes fossilis (stinging catfish), Notopterus notopterus (bronze featherback), and Mystus cavasius (Gangetic mystus) did not show any MP contamination [44]. After this study, Khan et al. [45] collected 46 fish belonging to 12 different fish species from the Turag River and identified that MPs contaminated 89.31% of the fish. This finding is 1.21 times greater than the previous study of the Turag River [44]. On the other hand, Khan et al. [46] and Mercy et al. [48] found that 100 and 93.30% of fish in the Turag River and various lakes of Dhaka are contaminated by MP, respectively. However, similar rates of MP contamination were observed in the Brazos River basin, USA (45–75%), and Prairie Creek, Canada (73.5%) [49, 50]. In 2021, 107 MPs were detected in the freshwater fish samples of the Turag River [44], whereas 106 MPs were found in 2023 with an average value of 2.30 [45]. Moreover, Haque et al. [47] collected 11 fish species from the Buriganga River and found 3.60 times more MPs than the Turag River [45]. Hence, this state indicates the increasing trend of MP contamination in freshwater fish in the Dhaka region of Bangladesh.

Parvin et al. [44] found that the concentrations of MPs in the Turag and Balu River varied from 9 to 0.50 MPs/individual, where Mystus vittatus (Striped dwarf catfish) showed the highest concentration, Puntius sophore (Barb) and Eutropiichthys vacha (River Catfish) exhibited the lowest concentration. The hierarchy of the concentration of MPs in fish samples of the Turag and Balu Rivers was: M. vittatus > C. reba > N. meni > C. carpio > A. grammepomus > A. testudineus > O. mossambiscus > C. calbasu > L. rohita > M. armatus > O. bimaculatus > L. bata > P. sophore > E. vacha [44]. On the other hand, Khan et al. [46] found that the fish samples of C. striata had the highest concentration (3.8 ± 1.30) of MPs, followed by A. testudineus (3.4 ± 1.14) and Puntius sophore (2.40 ± 0.54) in the Turag River. Moreover, according to Khan et al. [45], L. calbasu and A. bengalensis contained the highest and lowest amounts of MPs, respectively. Moreover, the hierarchy of MP contamination of fish samples was L. calbasu (20%) > W. attu (14%) > H. fossilis (12%) > M. vittatus (11%) > C. brofuscus (10%) > N. notopterus (7%) > C. reba (6%) > P. vittatus (5%), Nandus nandus (5%) > O. pabda (4%) > C. striata (3%), and A. bengalensis (3%). Unlike the Turag River studies, Haque et al. [47] observed many MPs in P. sophore (3.82 MPs/g) fish samples. Moreover, the findings of this study revealed that the C. reba fish samples had the highest concentration of MPs (5.34 MPs/g). This was followed by the P. sophore (3.82 MPs/g) > A. microlepis (3.67 MPs/g) > X. cancila (2.90 MPs/g) >M. armatus (2.39 MPs/g) > O. bimaculatus (1.87 MPs/g) > E. vacha (1.70 MPs/g) > A. cobojius (1.63 MPs/g) > H. plecostomas (1.30 MPs/g) > L. calbasu (0.99 MPs/g) > H. fossilis (0.65 MPs/g), which shows a rapid fluctuation of concentration. Many MPs have also been detected in the fish samples of various lakes in Dhaka city, such as Dhanmondi Lake, Gulshan Lake, and Hatir Jheel Lake [48]. The hierarchy concentration of MPs in Dhanmondi Lake was O. mossambicus (8.20) > Chitala (5.30) > C. marulius (3.50) > C. punctuate (1.50), > C. catla (1.10). On the other hand, it was C. catla (5.70) > C. striata (3.60) > P. pangasius (2.10) for Gulshan and Hatir Jheel Lake. Furthermore, in Dhanmondi Lake, the GIT of O. mossambicus exhibited the highest concentration of MPs at 4.88 g, while C. marulius displayed the lowest quantity at 0.31 g [48]. However, the highest concentration of MPs in Hatir Jheel Lake was found in the GIT of C. catla (1.40 g) [48]. However, it has been noteworthy that the fish samples of lake water contained slightly more MPs than river water. This may happen because the river has a big flowing water body and a large area that can reduce the concentration of pollutants. On the other hand, lakes are confined to a small area and have no water flow, making them more vulnerable to pollutants. However, the above MPs in freshwater fish-related studies have been carried out at different times with different fishes. Due to this, the level of MP contamination in a particular fish based on various rivers is still unknown.

The shape of MPs in Turag River was found to be fiber, fragments, foam, and filament. For example, Parvin et al. [44] found that the shapes of MPs from the Turag River were fiber (75%), fragments (19%), foam (5%), and filament (1%). Moreover, Khan et al. [45] observed fibers (43%), followed by fragments (41%), films (12%), and foams (4%). Haque et al. [47] found similar results in the Buriganga River. This investigation showed that the fiber, fragment, foam, film, and pellet distribution patterns were 36.68, 26.07, 17.19, 10.60, and 9.46%, respectively. The abundant shape of fiber indicates that the textile industry could be the primary source of MP contamination in the aquatic bodies of the Dhaka region of Bangladesh. However, like these studies, the prevalence of fibers was also observed in the various fish samples globally [51, 52]. However, Parvin et al. [44] found that 36, 29, and 35% of MPs were in the range of <500 μm, (500 μm–1 mm), and (1–5) mm, respectively, in Turag River. On the other hand, Khan et al. [46] observed that 56–71% of MPs were in the size of <0.5 mm. Like the Turag River, 42.38% of MPs in the Buriganga River were in <0.5 mm, whereas 31.13% were in (0.5–1) mm, and 26.49% were in the range of (1–5) mm. Moreover, Mercy et al. [48] also observed similar results with 28.88% (<100 μm), 14.29% (101–200) μm, 11.49% (201–400) μm, 5.90% (401–600) μm, 8.39% (601–800) μm, 10.56% (801–1000) μm, and 20.50% >1000 μm. The various sizes of MPs in Dhaka regions, Bangladesh, indicate both primary and secondary sources of MP pollution. However, various MPs of various colors were observed in the fish samples of the Turag, Balu, and Buriganga Rivers. For example, Parvin et al. [44] found that transparent (43%), blue (15%), and red (13%) were the most abundant colors of MPs in Turag and Balu River fish samples. Similar to this study, Khan et al. [45] observed transparent (43%), red (28%), and white (20%) in the Turag River. However, Khan et al. [46] found that the most dominant MPs’ colors in Turag River fish samples were blue, red, green, black, and purple. Haque et al. [47] also observed similar results with blue (30.40%), pink (10.90%), red (7.30%), and white (5.70%) in the Buriganga River. However, Mercy et al. [48] found that transparent (32.92%), black (19.25%), white (11.80%), and blue (10.56%) were the most abundant colors of MPs in the various lakes of Dhaka (Gulshan, Hatir Jheel, and Dhanmondi) which is similar to the studies by Parvin et al. [44] and Khan et al. [45]. However, the various colors of MP indicate the rapid use of textile products, plastic bags, bottles, and shopping bags. The occurrence of MPs in freshwater fish in Bangladesh is demonstrated in Figure 3.

Figure 3.

The occurrence of MPs in freshwater fish in Bangladesh.

Parvin et al. [44] investigated that the chemical composition of MPs was ethylene-vinyl acetate (EVA), high-density polyethylene (HDPE), and polypropylene (PP) in Turag and Balu River fish samples. On the other hand, Khan et al. [45] found that PS, PP, CA, PE, and PA were the identified polymer types in the fish samples of Turag River, whereas PS showed the highest concentration at 39%. The findings of this research are closely related to the Turag River study of Khan et al. [46], where PP (40%), PS (30%), and PS (30%) were the chemical composition of fish samples. The findings of this study are similar to the results of fish samples in Lucknow, India, and Michigan, USA [53, 54]. In the fish samples of the Buriganga River, the chemical composition of MPs was found to be HDPE (30%), ABS (20%), EVA (20%), PETE (10%), CA (10%), PS (5%), and nylon (5%), similar to the chemical composition of the Turag River. However, Mercy et al. [48] identified that PVC, LDPE, HDPE, PP, EVA, and PC were the chemical composition of fish samples in lakes of Dhaka, Bangladesh. These types of polymers are the potential sources of sealants, coatings, adhesives, packaging, pipes, car body components, wheel covers, enclosures, headgear for protection, manufactured footwear, expanded foams, sponges, molded items, floor mats, bottles, geomembranes, plastic bags, films, synthetic fibers, and textile products. Moreover, these polymers indicate the potential MPs transport from the land surface to the ocean through stormwater runoff to nearby rivers and then the ocean. It has been noteworthy that the demersal zone (1.87 ± 0.39 MPs/individual) showed more concentration of MPs than the benthopelagic zone (1.5 ± 0.26 MPs/individual) and pelagic zone (0.63 ± 0.18 MPs/individual) species in Turag River [45]. Moreover, Parvin et al. [44] observed that MP ingestion rates were higher in the demersal zone than in the benthopelagic and pelagic zones. The concentration of MPs was higher in the benthopelagic zone in the Buriganga River [47], which is different from the Turag River. This variation may happen due to the different fish species, pollutants, geographical locations, and migration nature of fish.

Lastly, according to the above research studies, it can be concluded that the concentration of MPs in fish has gradually increased in the aquatic bodies of Dhaka region, Bangladesh. The increasing trend of fragments indicates the rapid degradation process of MPs in environmental compartments. Moreover, MPs are being converted into nanoplastics.

4.2 Distribution and accumulation of microplastics (MPs) in freshwater fish of northern regions, Bangladesh

In the northern part of Bangladesh, Khan and Setu [55] first investigated the MP contamination in the fish species of the Jamuna River. In this investigation, 76% of the fish sample from the Jamuna River contained MPs contamination, with an average of 1.80 ± 1.65 per total fish. The samples of W. atto contained the highest concentration of MPs contamination (3.50 ± 1.93), followed by A. bengalensis (2.14 ± 1.21), L. calabash (2.12 ± 1.55), O. panda (1.00 ± 0.58), C. Garcia (1.00 ± 1.12), C. reba (1.00 ± 1.41), and A. coil (0.80 ± 1.30). This study’s results are very close to the Turag River’s MP contamination. Most of the MPs were found to be in fiber (70%), film (14%), line (10%), fragment (4%), and foam (2%). However, the distribution pattern of MPs in the Jamuna River differs from other Bangladesh studies. Black (27%), white (26%), blue (24%), red (17%), and green (6%) were found to be the most abundant colors of MPs in Jamuna River. However, like the Turag and Balu Rivers, the demersal zone contained more MPs than the benthopelagic and pelagic zones. On the other hand, the old Brahmaputra stream in north central Bangladesh contained much MP contamination [56]. In this river system, 58.93% of fish samples were detected, and M. armatus (eel) contained (10.31 ± 0.75) MPs. The predominant form of MPs identified was fiber (49.03%), with granules closely behind at 28.02%. Most of the MPs in this study showed less than 1 mm, and black was the most frequent color of MPs. Nearly 72% of MPs were smaller than 1 mm, and 50.97% were black. PE (59%) and polyamide (40%) were the chemical compositions of MPs. Sultana et al. [57] found that 43.60% of fish samples in the Padma River contained MPs contamination, where PS, PP, Polyamide-6, and PU were the chemical composition of MPs.

4.3 Distribution and accumulation of microplastics (MPs) in freshwater fish of southwestern regions, Bangladesh

Akter et al. [58] investigated the MPs contamination on the 17 fish of the southwestern region (Jessore, Narail, Khulna, Bagerhat, Satkhira). In this study, 142 MPs were found in the range of 0.14–3.43 MPs/fish, where the average concentration per fish was 1.13 ± 0.84. The hierarchy of the concentration of MPs in fish samples was as follows: C. punctata (3.43 ± 3.15) > P. paradiseus (2.29 ± 1.60) > G. chapra (1.86 ± 1.21) > S. bacaila (1.86 ± 1.46) > L. bata (1.71 ± 1.89) > C. soborna (1.43 ± 1.27) > P. ranga (1.14 ± 1.07) > X. cancila (1.00 ± 1.00) > M. cephalus (1.00 ± 1.53) > T. fasciata (0.86 ± 1.07) > P. sophore (0.57 ± 0.79), E. danrica (0.57 ± 0.79) > G. giuris (0.57 ± 0.53) > M. tengara (0.57 ± 0.79) > H. fossilis (0.43 ± 0.53) > M. armatus (0.43 ± 0.79) > A. mola (0.14 ± 0.38). This state is 7.69 times higher than the Persian Gulf, Iran, and 2.41 times lower than the Songkhla Lake, Thailand [59, 60]. Moreover, it is 7.96 times lower than the Turag River [44]. Black (60.60%), red (22.50%), blue (12%), and transparent and white (4.90%) were the most frequent colors of MPs, which is very similar to the results of Jamuna River, Dhanmondi Lake, Gulshan Lake, and Hatir Jheel Lake. Moreover, these frequent black MPs may potentially cause the degradation of other colored MPs in aquatic ecosystems. The distribution pattern of MPs was fiber (94.4%), fragment (3.5%), and film (2.1%), which is similar to the Turag River, Buriganga River, Brahmaputra River, Padma River, and various lakes of Dhaka (Dhanmondi, Gulshan, and Hatir Jheel). However, PE (73.08%), PP (21.15%), and PS (5.77%) were the most abundant types of microplastic polymers in this study.

4.4 Distribution and accumulation of microplastics (MPs) in freshwater fish of southeastern regions, Bangladesh

On the other hand, the Karnaphuli River, which is situated in the southeastern part of Bangladesh, showed a significant level of MPs contamination in fish [61]. In this study, the concentration of fish samples of S. phase, P. paradises, O. pama, and M. rosenbergii was (13.17 ± 0.76), (10.83 ± 0.81), (5.93 ± 0.62), and (9.33 ± 0.82) items, respectively. The highest concentration of MPs was detected in the GIT of S. phase, 8.29 ± 1.75, which is comparatively higher than the fish samples of another region of Bangladesh. Moreover, like other aquatic bodies of fish, fibers were found to be the most dominant types of MPs in the Karnaphuli River. Furthermore, PE and PET were the most dominant types of plastic polymers in this study. However, the pattern of MP contamination in the feeding zone was pelagic > demersal > benthic > benthopelagic, showing a different pattern from Turag, Buriganga, Jamuna, Brahmaputra, and southeastern part aquatic bodies. Siddique et al. [62] recently identified rapid MP contamination in O. niloticus fish samples from the Noakhali district. The range of MP contamination in O. niloticus fish samples was found to be (3–10) particles/fish GIT, where fibers (90.95%) were the most dominant shape of MP types. However, the most frequent types of MP colors were black (25.13%), blue (24.12%), and red (23.12%). In this study, PP, PE, PET, and PVC were the identified polymers, which are similar to the chemical composition of the Karnaphuli and Turag Rivers.

Table 1 states that a significant amount of MP contamination has occurred in the Dhaka, northern, north central, southwestern, and eastern regions over the past years. Moreover, heavy industrial zones, especially Dhaka and the southeastern (Chittagong district), have shown comparatively higher MP contamination than other areas. Specifically, Dhaka and Chittagong’s textile and shipbreaking industries, along with the rapid use of plastics (bottles, shopping bags, packets, agricultural activities), make these regions a sacred place for MPs. Notably, it has been stated that the feeding zones of fish are contaminated, and their distribution patterns vary from one river to another. Hence, there is no reason to think that slight MPs have been found in some fishes because the dynamism of pollutants, especially MPs, is much more capable of contaminating that fish heavily with time.

Location	Region	Fish samples	Abundance variation	Composition	Polymer types	References
Turag and Balu River	Dhaka	M. vittatus, C. reba, N. meni, C. carpio, A. grammepomus, A. testudineus, O. mossambiscus, C. calbasu, L. rohita, M. armatus, O. bimaculatus, L. bata, P. sophore, E. vacha.	(9–0.50) MPs/individual	Fiber (75%), fragments (19%), foam (5%), filament (1%)	HDPE, PP, PE, EVA	[44]
Turag River	Dhaka	L. calbasu, W. attu, H. fossilis, M. vittatus, C. brofuscus, N. notopterus, C. reba, P. vittatus, Nandus nandus, O. pabda, C. striata, A. bengalensis.	(20–3) MPs/individual	Fibers (43%), fragments (41%), films (12%), foams (4%)	PS, PP, CA, PE, PA	[45]
Turag River	Dhaka	P. sophore, A. testudineus, C. striata	(3.8 ± 1.30–2.40 ± 0.54) MPs/individual	Fiber (93%) followed by fragments, films, and foams.	PP, PS, PS	[46]
Buriganga River	Dhaka	C. reba, P. sophore, A. microlepis, X. cancila, M. armatus, O. bimaculatus, E. vacha, A. cobojius, H. plecostomas, L. calbasu, H. fossilis	(5.34–0.65) MPs/g	Fiber (36.68%), fragment (26.07%), foam (17.19%), film (10.60%), pellet (9.46%)	HDPE, ABS, EVA, PETE, CA, PS, nylon	[47]
Various lake (Dhanmondi, Gulshan, and Hatir Jheel)	Dhaka	O. mossambicus, Chitala, C. marulius, C. punctuate, C. catla, C. striata, P. pangasius	(8.20–1.10) MPs/individual	Fibers are most abundant	PVC, LDPE, HDPE, PP, EVA, PC	[48]
Jamuna River	Northern region	W. atto, A. bengalensis, L. calbasu, O. pabda, C. garua, C. reba, A. coila.	(3.50 ± 1.93–0.80 ± 1.30) MPs/individual	Fiber (70%), film (14%), line (10%), fragment (4%), foam (2%)	—	[55]
Old Brahmaputra stream	North central region	M. armatus (eel)	(10.31 ± 0.75) MPs/individual	Fiber (49.03%)	PE, polyamide	[56]
Freshwater aquatic bodies of Jessore, Narail, Khulna, Bagerhat, Satkhira	Southwestern	C. punctate, P. paradiseus, G. chapra, S. bacaila, L. bata, C. soborna, P. ranga, X. cancila, M. cephalus, T. fasciata, P. sophore, E. danrica, G. giuris, M. tengara, H. fossilis, M. armatus, A. mola	(3.43–0.14) MPs/individual	Fiber (94.4%), fragment (3.5%), film (2.1%)	PE, PP, PS	[58]
Karnaphuli River	Southeastern region	S. phasa, P. paradiseus, O. pama, and M. rosenbergii	(13.17–5.93) MPs/individual	Fibers are most frequent	PE, PET	[57]
Noakhali district aquatic bodies	Southeastern region	O. niloticus	(10–3) MPs/individual	Fiber (90.95%)	PE, PET, PVC	[62]

Table 1.

Distribution of microplastics (MPs) in freshwater fish in Bangladesh.

However, it has been observed that the MP contamination in the fish of the Bay of Bengal, Bangladesh, was in the range of 3.20–8.72 MPs/individuals [63]. Moreover, Ghosh et al. [64] investigated and found the concentration level of MPs (1–3.8)/individuals, whereas Siddique et al. [65] found (7–51) items/species. These studies indicated that MP contamination in fish in Bangladesh is comparatively higher in saline water than in freshwater. However, as these various types of fish are one of the most popular foods in Bangladesh, it is crucial to take the necessary steps and strategies to control this pollution.

4.5 Influencing factors of microplastics (MPs) in freshwater fish in Bangladesh

Over the years, microplastics (MPs) in freshwater fish of Bangladesh have been detected at significant levels. Hence, understanding the influencing factors of MPs in freshwater fish in Bangladesh is crucial to controlling MPs contamination. Since very few studies have been conducted on this issue, many influencing factors are yet to be explored. However, this section will discuss some influencing factors based on published papers.

4.5.1 Anthropogenic factors

Bangladesh is a land of textile and shipbreaking industries [47]. Moreover, rapid population growth, urbanization, and plastic industries make Dhaka and Chittagong and its surrounding aquatic bodies badly polluted with various pollution. As with other pollutants, a significant number of microplastics (MPs) have been detected in various freshwater fish of Bangladesh [44]. Mercy et al. [48] stated that textile fabrics, shopping and packaging bags, plastic bottles, and shipbreaking industrial wastes could be linked with these massive MPs contamination in freshwater fish. Moreover, Khan et al. [46] identified fishing gear, roping, clothing, and urban debris as responsible for MP contamination in fish. However, MPs’ various colors and fiber shapes indicated the various garments, dyeing, chemical companies, tanneries, paint, and paper-making industries. Furthermore, research has revealed that transparent MPs naturally float in potable water and aquatic bodies, where they are readily ingested by fish, thereby potentially increasing the rate of MPs ingestion [46, 58]. Unfortunately, because these kinds of industries are located near bodies of water, the repercussions for our biological systems are becoming increasingly severe. For example, the Turag and Buriganga Rivers have already shown massive MP contamination due to these factories. Hence, it is necessary to stop these industrial activities near aquatic bodies.

4.5.2 Fish feeds

Over the past decades, fish feed use has rapidly increased in Bangladesh [66]. However, impermissible limits of MPs have been detected in Bangladesh in the recent years [67, 66]. Siddique et al. [67] stated that 100% of Bangladesh fish feeds contain MPs with significant levels. In grower fish feed samples, the MPs concentration level was in the range of (2200–500) particles/kg, whereas it was (1650–600) particles/kg for starter fish samples and (1600–750) particles/kg for finisher fish feed samples. On the other hand, Muhib and Rahman [66] found the size of MPs in fish feeds was (14–4480) μm, with (550 ± 45.45–11,600 ± 56.10) MPs/kg of fish feed. Therefore, it can be concluded that fish feeds are one of the most potential sources of MPs in the aquatic body.

4.5.3 Physical structure of fish (length and weight)

According to several studies, concentrations of MPs in fish have a great relationship with fish length and weight [63, 68]. They explained that large fish have comparatively high food and energy demand, leading to a high chance of MP ingestion. However, Parvin et al. [44] found no correlation with them based on the Turag and Balu River study. On the other hand, other studies of Bangladesh focusing on the Turag, Buriganga, Brahmaputra, Jamuna, Karnaphuli, and southwestern region have found a significant level of correlation between MP concentration and fish length and weight [45, 47, 55, 61].

4.5.4 Feeding habits of fish and abundance of microplastics (MPs)

Fish feeding habits and the abundance of microplastics (MPs) have a significant correlation [69, 70]. Although it is critical to determine which feeding habits, such as omnivores, carnivores, and herbivores, are responsible for ingesting MPs with higher concentration, several studies in Bangladesh stated that MPs ingestion rate of omnivores is comparatively higher than the herbivorous and carnivorous [44, 55, 48, 47]. Notably, carnivorous fishes have potentially the highest risk of MP poisoning due to prey of various organisms such as crabs, insects, and smaller fish [46]. On the other hand, omnivorous fishes have the second potential risk of MP contamination as they take grit, silt, algae, and larvae [58]. Moreover, it has been found that demersal, benthopelagic, and pelagic feeding greatly influence the ingestion rate of MPs [55]. Demersal fishes that generally live and feed near the bottom of the water body have taken more MPs than the benthopelagic and pelagic fishes. This indicates that demersal fishes ingest high-density MPs accumulated in the river bed.

5. Impacts of microplastics (MPs) on freshwater fish and human health

The impacts of microplastics (MPs) on freshwater fish depend on the characteristics of MPs (density, concentration, size, shape, and polymer) and their interaction with the ecology of the species [71]. These effects vary from no effect to irreplaceable changes in fish species, such as mobility rate, feeding rates, gene expression, growth, development, physiology, and survival ability [72]. However, after entering the aquatic medium, MPs tend to move and behave depending on the density, size, and shape of the MPs. Low-density MPs float into the waterbody, whereas high-density MPs move toward sediment [72]. The accumulation of these high-density MPs depends on the water flow and the sediment’s nature [73]. These high-density polymers can quickly accumulate in sediment if these factors favor them. During this mobility period of MPs, fish can ingest various MPs. Moreover, fish unknowingly ingest colorful MPs because they think of them as prey [48]. After ingesting these MPs, fish are going through several detrimental issues. Firstly, ingesting MPs in massive amounts can create blockages in the gastrointestinal tract (GIT) of fish [71]. Moreover, the morphometrics and physicochemical properties of MPs can alter the digestive systems of fish. These MPs can also modify the internal temperature and pH of fish, producing harmful chemicals [61]. MPs of <10 μm can translocate the intestinal barrier of fish and enter fish blood [71]. Moreover, these nano-size MPs can move throughout the fish body. After that, these nano-size MPs significantly affect fish’s liver, muscles, and brains [70]. However, MP contamination at the tissue level depends on the MP ingesting rate of fish. The impacts of microplastics (MPs) on freshwater fish and human health are illustrated in Figure 4.

Figure 4.

The impacts of microplastics (MPs) on freshwater fish and human health.

A massive concentration of MPs in the GIT of fish can create tissue-level contamination that is more detrimental to fish species. Oxidative stress, historical damage, and alteration of blood chemistry of fish can occur due to this tissue level MPs contamination [48]. However, the human body can face several health issues due to consuming these fishes. According to several studies, it has been found that the human body has faced disruption of immunity, cytotoxicity, neurotoxicity, carcinogenicity, reproductive toxicity, oxidative stress, metabolism alteration, and translocation to distant tissues due to the consumption MP contamination fish during long periods [46]. Various birds and animals are also affected by consuming these contaminated fishes. Lastly, since the contamination of MPs has adversely affected over 700 aquatic species across the globe, it is critical to implement effective strategies to manage this global issue.

6. Mitigation strategies and future directions

The mitigation of microplastic contamination necessitates a comprehensive strategy that takes into account a variety of intrinsic elements. Plastics can enter wetlands, lakes, and rivers after being discharged into terrestrial settings [24]. Human settlements are often located close to these bodies of water because of their benefits, most notably water availability for various uses, such as irrigation, industrial processes, and potable consumption, as well as essential transportation networks [74]. Microplastics (MPs) are becoming more common in freshwater sources worldwide.

6.1 Available technologies for removal of MPs in freshwater

Controlling pollution in aquatic areas requires removing microplastics (MPs). Appropriate treatment technologies should be developed to prevent the entrance and circulation of microplastics in the environment based on a better understanding of the features of MP. Many technologies have been designed to remove MPs, such as membrane filtering, coagulation, adsorption, magnetic separation, and photodegradation [75, 76]. Table 2 shows the available technologies for removal of MPs from water [45].

Approaches	Technologies	Methods
Physical	Filtration	Utilizes barriers to physically remove MPs from water.
	Adsorption/magnetic separation	Utilizes barriers to physically remove MPs from water.
	Density separation	Separates MPs based on their density differences from water.
Chemical	Coagulation	Involves adding chemicals to water to clump MPs together for easier removal.
	Photocatalysis	Uses light-activated catalysts to degrade MPs into less harmful substances.
	Oxidation treatment	Applies oxidizing agents to break down MPs chemically.
Biological	Microbial degradation	Leverages microorganisms to biodegrade MPs.
	Bioreactors	Utilizes controlled environments to enhance microbial degradation of MPs.

Table 2.

Available technologies for removal of MPs from water [45].

Tang and Hadibarata [76] found that MPs reach freshwater through wastewater treatment plants, endangering aquatic life. Water treatment facilities can remove MP more efficiently with multi-stage treatment technologies, although only sometimes. Traditional wastewater treatment includes primary, secondary, and tertiary treatment for secondary effluent. After screening for large floating objects, silt settles in grit chambers. To aid sedimentation, primary clarifiers use flocculants and coagulants. Secondary treatment uses activated sludge to remove soluble organic compounds. Instead of secondary clarifiers, membrane bioreactors produce high-quality effluent. A2O systems remove phosphate and nitrogen in dedicated tanks. Tertiary treatment includes membrane methods like ultrafiltration, reverse osmosis, and activated carbon filtration. Ozone, chlorination-dichlorination, or UV irradiation disinfect before discharge. Primary, secondary, and tertiary WWTPs may remove 16.5 to 98.4%, 78.1% to 100%, and 87.3 to 99.9% of MPs, respectively [76].

6.2 Emerging freshwater MP removal technologies

Granule-activated carbon (GAC), heat regeneration, and electrocoagulation boost microplastic removal efficiency. Kim and Park [77] found that standard STPs cannot eliminate microplastics under 200 μm [77]. However, GAC treatment with thermal regeneration is more effective in removing microplastics between 20 and 50 μm. Electric coagulation may boost removal efficiency for 30 minutes. Electrocoagulation increases microplastic size and density, making it an effective microplastic removal method. Standard biological treatment, electrocoagulation, and GAC with thermal regeneration are promising methods for addressing emerging environmental concerns caused by micro-hazardous contaminants, such as microplastics.

6.3 Alternative methods

Businesses, municipalities, and communities must work together to solve microplastic contamination. This urgent approach stresses the importance of behavioral changes, production improvements, and consumer reassessment. Collaboration across industries can solve the global microplastic pollution problem and protect our ecosystem for future generations [78]. Eriksen et al. [79] proposed four ways to microplastic pollution: (a) source identification and quantification of MPs, emphasizing the need to identify MP sources to better customize interventions; (b) zero-scale waste strategies, emphasizing the importance of minimizing plastic waste at its source; (c) extended producer responsibility (EPR), calling for producers to be responsible for the entire life cycle of a product to promote sustainability; and (d) green engineering solutions. Three main areas should be prioritized: (1) preventive measures and national and international regulations; (2) remediation of microplastics in freshwater; and (3) public awareness and biodegradable plastic use. These strategies work together to reduce microplastics and protect the environment [78, 79].

Plastic waste-to-energy methods recover energy and solve recycling issues, including polymer sorting and new plastic competition. However, it maintains linear economics. Reformulating plastics into feedstocks requires energy to extract components for biofuels, including petrol (waste-to-energy), chemicals, lubricants, and carbon black. Pyrolysis and gasification can produce plastic waste fuels with similar physicochemical attributes and prices to petrol. This is especially true for catalyzed fuels. By adding carbon black to asphalt, byproducts can be valorized alongside fuel production. Alternatives include plastic waste-derived carbon nanotubes, which are cost-effective and reduce CO₂ emissions. Boats could use plastic marine garbage for onboard gasification [80].

6.4 Initiatives of different countries to regulate microplastics from aquatic body

Improved waste management, wastewater treatment, and novel design and development were used to combat plastic pollution. Bans, phasedowns, and limits on single-use plastics and industrial microbeads were also implemented. Microbeads in personal care products were also banned. Many nations and territories have banned plastic microbeads for industrial use and agreed to phase them out. The USA, Canada, and the UK banned plastic microbeads for industrial use in 2015, 2017, and 2018. Microbeads in rinse-off personal care products were banned in the US and UK. Meanwhile, the circular economy project promotes zero waste. UNEP has announced a global drive to eliminate primary plastic trash by 2022. Several EU legislations, such as the Water Framework Directive, attempt to protect all bodies of water. Emission restrictions and river basin regulations are used in this directive to improve water quality at a set time. The Common Fisheries Policy also reduces chemical and nutrient pollution in aquatic systems. Integrated Coastal Zone Management and the Marine Strategy Framework Directive were implemented to combat MP pollution. Life cycle economy and assessment were used to assess plastics’ design, production, use, and recycling. Sol-gel-induced agglomeration removes microplastics (MPs) from aquatic systems. Air purifiers remove microplastics (MPs) (>0.1 mm) to improve indoor air quality. Fungi may degrade microplastics (MPs) in soil. Further efforts are being made to reduce plastic pollution in terrestrial and marine habitats [81].

6.5 Future directions

The following is a list of critical research gaps and changes that are required:

• Bangladesh is situated along the banks of the 907 rivers. Regrettably, most research endeavors have been concentrated on the Turag, Buriganga, Jamuna, Brahmaputra, Karnaphuli, and Padma Rivers. Under these conditions, it is critical to comprehend the present MPs contamination affecting other species of river fish in Bangladesh. Furthermore, this research will aid in identifying unidentified influencing factors that elevate the level of MPs contamination.

• The presence and distribution of microplastics (MPs) in environmental compartments have been the subject of numerous scientific investigations; nevertheless, there is still a dearth of precise knowledge regarding the seasonal fluctuation in MP contamination in freshwater fish in Bangladesh. Therefore, future studies must concentrate on the seasonal fluctuations in the presence of microplastics (MPs) in freshwater fish in Bangladesh.

• Although the quantity and morphological features of MPs contamination in aquatic compartments have been the subject of numerous studies, a more comprehensive examination of MPs’ geographical and temporal distribution is still required. Furthermore, sediments serve as a storage site for microplastics (MPs) in water bodies and store essential data about human activities. Therefore, it is imperative to conduct vertical distribution research on microplastics (MPs) to evaluate their life cycle and the historical occurrence of MP pollution in a specific aquatic environment.

• The river possesses a substantial volume of water and a vast expanse, which has the potential to mitigate the accumulation of pollutants. Conversely, lakes are limited in size and lack water movement, rendering them more susceptible to pollution. Hence, it is crucial to discover the spatio-temporal distribution of MPs in lake water fish of Bangladesh.

• Future research should focus on creating a mathematical framework that can help us better understand where and how MPs are found in different parts of the environment.

• Few studies have been conducted on how MPs affect human health and aquatic ecosystems. Most of the research focused on the direct effects of MPs on human health and aquatic ecosystems. It is essential to comprehend the combined impacts of MPs and numerous harmful pollutants, such as POPs, chemical additives, and heavy metals, as MPs are adsorbed on these pollutants. Therefore, it is imperative to conduct further study to gain a more comprehensive understanding of the long-term presence of these contaminants in different environmental compartments and their possible ecotoxicological consequences. For a better understanding of the long-lasting effects of microplastics (MPs), it will be easier to figure out how dangerous they might be to aquatic environments and come up with good ways to reduce their effects.

• Research concentrating on techniques for remediating MPs remains limited. It is crucial to examine the role of microorganisms in eliminating MPs from aquatic compartments to advance the development of upgrading technologies. Furthermore, microplastic cleanup technologies must be used at appropriate sites to prevent pollution in various ecosystems and atmospheres.

• The focus of future research should be the development of hybrid remediation techniques that contribute to the attainment of sustainable development goals (SDGs) and enhanced efficacy.

• Even though numerous nations have adopted diverse legislative strategies to combat microplastic pollution, standardized legislative approaches remain limited. Therefore, implementing effective policy and management instruments may aid in mitigating the effects of MPs on environmental compartments.

7. Conclusions

There is a significant concern over the increasing prevalence of microplastic (MP) contamination in the global food supply, especially in freshwater fish. Moreover, although a rapid concentration of microplastics (MPs) has been detected in Bangladesh’s environmental compartments, MP contamination in freshwater fish-related studies is still limited. However, it has been found that the concentration of MP contamination in Turag River fish was 2.22–6.6 times higher in 2023 than in 2021. Moreover, the MPs contamination of Turag River fishes was 5.71–3.75, 1.93, and 5.83–21.42 times greater than the MPs contamination of Jamuna River, Old Brahmaputra River, and southwestern part aquatic bodies fishes. The fish of River Buriganga, Karnaphuli, Padma, various lakes of Dhaka city, and aquatic bodies of Noakhali district also showed a significant number of MP contamination. Dhaka’s river and lake fish showed rapid MP contamination due to the massive use of plastic products, textile and metal industries, and improper treatment systems. Notably, it has been identified that several factors, especially fish length, weight, feeding zone habit, and commercial fish feed, are leading to an increase in MP contamination in the aquatic bodies of fish. However, the interlinkage between the MP contamination level and seasonal variation should be studied. Moreover, as fish feed contains massive MPs, the Government should take necessary steps against fish feed maker factories. Moreover, as this contamination of MPs has a detrimental impact on human health and other wildlife, legislative activities, policies, and proper remediation techniques should be implemented immediately to control this contamination. Additionally, further research is essential to understand the long-term health effects of ingesting MPs, particularly bioaccumulation and potential toxicological impacts.

Conflict of interest

The authors declare that they have no conflict of interest.