Microplastics in Aquatic Ecosystems: A Global Review of Distribution, Ecotoxicological Impacts, and Human Health Risks

Abstract

Microplastics (MPs), defined as synthetic polymer particles less than 5 mm in diameter, are widely acknowledged as ubiquitous contaminants in aquatic ecosystems, including freshwater, marine, and polar environments. Global concern with MPs has significantly increased; nevertheless, much of the current knowledge remains fragmented and, at times, limited to specific regions or ecological compartments. This study emphasizes the necessity of a thorough synthesis by critically analyzing global microplastics’ dispersion patterns, ecological consequences, and associated human health concerns. A systematic approach was employed, integrating specific search terms and establishing inclusion and exclusion criteria across various scientific databases to obtain a representative collection of literature. The study covers important topics such as the classification of MPs, their distribution, environmental impacts, and interactions with other pollutants, including heavy metals, pharmaceuticals and endocrine-disrupting chemicals. Particular emphasis is placed on comparing ecosystem-specific vulnerabilities, such as those found in tropical wetlands, marine gyres, and polar systems. The review examines potential human exposure pathways, via contaminated seafood, water, and air, while also compiling new information about cellular and physiological damage, including oxidative stress, inflammation, hormone disruption, and possible genetic effects. This investigation highlights the value of collaborative monitoring, the adoption of biodegradable alternatives, policy development, and interdisciplinary research by integrating knowledge from ecology and public health. The primary objective is to advance ecosystem-specific mitigation techniques and promote evidence-based policy development in addressing this intricate environmental issue.

1. Introduction

In recent decades, the global production and use of plastics have escalated, propelled by their affordability, resilience, and adaptability across several sectors, including packaging, textiles, electronics, automotive, and healthcare [1,2,3]. Consequently, plastic waste has become one of the most enduring and widespread environmental contaminants. Microplastics (MPs), defined as plastic particles smaller than 5 mm, represent a particularly insidious hazard due to their diminutive size, mobility, and capacity to accumulate within living creatures and ecosystems [4,5]. Microplastics are classified into two types: primary microplastics, which are created for use in products like cosmetics and personal care items, and secondary microplastics, which are formed when larger plastic waste breaks down due to sunlight, wear and tear, and microorganisms [6,7].

Microplastics have been identified in nearly all environmental compartments, encompassing seas, freshwater systems, sediments, soils, and the atmosphere. The primary emphasis of study and policy has focused predominantly on marine habitats, especially ocean gyres and coastal areas where substantial plastic garbage accumulates [8]. Recent studies have demonstrated the widespread occurrence of MPs in freshwater systems, rivers, lakes, and wetlands, that serve as pathways for plastics transitioning from terrestrial to marine environments [9,10,11]. Wetlands and estuarine zones, owing to their hydrological intricacies and significance as biodiversity hotspots, are especially susceptible to MP pollution [12,13,14,15]. Additionally, the Arctic and Antarctic regions, which were once thought to be untouched, have shown measurable amounts of MPs in sea ice, snow, and the stomachs of local wildlife, raising concerns about how these pollutants are spread over long distances through the air and oceans [5,16,17,18].

Notwithstanding the growing global focus, existing research is still disjointed, frequently concentrating on geographic areas or types of ecosystems. There is a significant gap in understanding how MPs are spread, accumulated, and processed in different types of aquatic environments, such as freshwater, oceans, and polar areas [19,20,21,22]. Additionally, there are very few studies comparing how MPs affect different ecosystems and their potential risks to human health through accumulation in the food chain [4,23,24,25,26].

The ecological hazards presented by MPs are significant. These particles can infiltrate aquatic food webs via ingestion by plankton, benthic invertebrates, mollusks, and fish, frequently becoming trapped in digestive or respiratory systems [6,27,28,29]. Laboratory and field investigations have recorded physiological disturbances, such as oxidative stress, genotoxicity, inflammation, modified reproductive function, and behavioral deficits across several species [8,30,31,32]. In addition to causing physical harm, MPs can carry harmful substances from the environment, such as persistent organic pollutants (POPs), heavy metals, antibiotics, and chemicals that disrupt hormones, because these substances stick to the surfaces of the plastic particles due to their water-repelling nature [10,33,34,35,36]. The “Trojan Horse” effect amplifies toxicity and elevates the ecological footprint of MPs well beyond their chemical makeup alone [37,38,39].

The possibility of human exposure is equally concerning [40,41]. Microplastics have been identified in seafood, potable water, table salt, honey, beer, and ambient air [42,43,44]. Recent biomonitoring investigations have verified the existence of MPs in human blood, placentas, lung tissue, breast milk, and feces, indicating extensive internalization and systemic circulation [13,14,15]. Although evidence is still emerging, recent studies indicate that MPs may contribute to hormone disruption, neuroinflammation, cellular stress, and immune dysfunction in humans [14,15,33,45,46]. Susceptibility is more pronounced in developing nations, where inadequate waste management, elevated population density, and reliance on water resources exacerbate environmental exposure and health hazards [3,47,48].

Bangladesh exemplifies the intersection between ecological sensitivity and human-induced strain. The country is especially vulnerable to plastic pollution due to its extensive wetland systems, estuaries, and low-lying river networks [12]. Research has recorded the occurrence of MPs in fish markets, freshwater fish species, estuary sediments, and drinking water sources. However, systematic research is still scarce, and policy frameworks sometimes lack enforcement mechanisms or standard monitoring techniques [3,12].

The routes by which MPs infiltrate aquatic ecosystems are complex [49]. Urban runoff, stormwater drainage, untreated sewage, industrial discharge, atmospheric deposition, and agricultural runoff collectively facilitate the pervasive dissemination of MPs [50,51,52,53]. Upon introduction, MPs have intricate transport dynamics affected by particle size, shape, density, and hydrological conditions [54,55,56,57]. Low-density polymers, such as polyethylene (PE) and polypropylene (PP), typically float and are prevalent in surface waters, but denser materials such as polyvinyl chloride (PVC) and polyethylene terephthalate (PET) accumulate in sediments [58,59,60]. Moreover, biofouling can modify buoyancy, resulting in the vertical redistribution of particles within the water column. Biological processes, such as ingestion by zooplankton, excretion in fecal pellets, and predation, further influence their mobility and fate [61,62,63,64].

The effects of MPs within ecosystems are significantly influenced by context [65]. Microplastics in tropical wetlands can disrupt sediment microbial populations, diminish water quality, and impair fish larval development [66]. In Arctic locations, MPs coupled with ice may disrupt plankton dynamics, resulting in cascading impacts on food webs dominated by cold-adapted organisms. Similar impacts occur on coral reefs, estuaries, and mangroves, which show diminished biodiversity, disrupted nutrient cycling, and poor susceptibility to climate change stressors [67,68,69,70,71,72,73,74,75,76,77].

Although there is increasing evidence of ecological and health repercussions, MP pollution continues to be inadequately managed on a global scale [78,79,80]. In 2022, the United Nations Environment Assembly (UNEA) adopted a resolution to establish a legally binding instrument against plastic pollution; however, its scope and enforceability are still ambiguous [81,82]. Such governance challenges are further mirrored at local scales, where small-scale fishers and coastal communities face systemic vulnerabilities often exacerbated by limited water, sanitation, and hygiene (WASH) access and weak institutional support [83,84]. Concurrently, national policies exhibit significant variability. Certain nations have enacted prohibitions on single-use plastics or microbeads in cosmetics, but others have established extended producer responsibility (EPR) frameworks and imposed plastic fees. Nonetheless, the efficacy of these efforts is variable, especially in areas without adequate infrastructure or monitoring mechanisms [85,86,87,88,89,90].

A primary problem in tackling MPs contamination is the absence of standardized methods for sampling, classification, and toxicity evaluation [91,92,93,94]. Variations in mesh sizes, detection thresholds, and chemical analysis methodologies impede comparability among experiments [95,96]. Furthermore, there is a paucity of long-term ecological and epidemiological studies, resulting in considerable ambiguity about chronic exposure and intergenerational impacts. Establishing standardized protocols, interdisciplinary collaborations, and data sharing platforms is crucial for addressing these constraints [97,98,99].

Considering these challenges and information deficiencies, a thorough, cross-ecosystem evaluation is both opportune and important. This work aims to bring together different research areas by thoroughly reviewing current studies on MP pollution in aquatic environments, including freshwater wetlands, ocean gyres, and polar regions. The study also focuses on identifying the principal sources and categories of MPs reported worldwide; analyzing their spatial and trophic distribution across various ecological zones; synthesizing data on ecotoxicological impacts across significant aquatic taxa; assessing human exposure risks via ingestion and inhalation pathways; and delineating mitigation strategies and policy interventions tailored to regional contexts.

This review enhances the comprehension of microplastics’ behavior across environmental gradients and their effects on both ecological and human systems. It underscores the pressing necessity for policy consistency, public awareness, and scientific innovation to alleviate the enduring effects of MP contamination.

2. Materials and Methods

2.1. Strategy for Literature Review

A detailed review of existing research was carried out using the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) method to provide a complete summary of MP pollution in aquatic environments. The review concentrated on peer-reviewed papers published from 2000 to 2025, with particular emphasis on recent developments from 2017 to 2025 to reflect current trends. The databases examined comprised Web of Science, Scopus, PubMed, Google Scholar, and ScienceDirect. Search strings were meticulously constructed using Boolean operators (AND, OR) and various pertinent keywords, including microplastics, aquatic ecosystems, wetlands, freshwater, marine, polar regions, toxicity, bioaccumulation, and human health risks. The investigation yielded a diverse array of interdisciplinary research relevant to environmental science, toxicology, ecology, and public health.

2.2. Inclusion and Exclusion Criteria

The selection process for qualifying articles was governed by established inclusion and exclusion criteria to ensure scientific rigor and relevance. Studies were included if they were published in English, peer-reviewed, and provided original data on MPs, their toxic effects, or health risks in aquatic environments such as rivers, wetlands, oceans, and polar areas. We excluded studies that lacked primary data, such as editorials, letters, theoretical works, or articles focused solely on terrestrial MP contamination. Further exclusions were applied to obsolete research that failed to provide innovative insights or did not meet methodological quality standards. This twofold screening method improved the validity of the evidence base used for synthesis.

2.3. Study Selection Process

A preliminary set of 3226 entries was identified via the integrated database search. After removing duplicates and evaluating titles and abstracts for pertinence, 1032 retained were retained. A comprehensive examination resulted in the appraisal of 427 publications for eligibility. After the final screening phase, 119 papers fulfilled all requirements and were incorporated into the synthesis. The study selection and screening procedure is depicted in a PRISMA flow diagram (Figure 1), which delineates the phases of identification, screening, eligibility evaluation, and final inclusion. Each screening phase was independently evaluated by two team members to reduce bias and ensure consistency.

2.4. Data Extraction and Categorization

For each selected article, comprehensive data extraction was conducted using a standardized template. The extracted variables included MP polymer types (e.g., PE or PP), particle morphology (including fibers, pieces, or beads), size distribution, sampling location, and ecosystem classification. Additionally, information was gathered about the living organisms studied (such as fish, plankton, and mollusks), their trophic levels, and health effects, such as oxidative stress, hormone disruption, and inflammation. Data on interactions between MPs and co-contaminants, such as heavy metals, pharmaceuticals, or POPs, were also recorded where relevant. Research was evaluated for its ability to clarify human exposure pathways, such as ingestion of seafood, drinking water consumption, and inhalation of airborne particulates. Results were consolidated to enable comparative analysis across various environmental sectors and geographical regions.

2.5. Quality Control and Verification

The entire extraction procedure was independently validated by two co-authors to verify methodological accuracy and data reliability. Discrepancies in data interpretation or classification were resolved through discussion until consensus was achieved. Only studies utilizing proven detection methods, including Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, and pyrolysis gas chromatography-mass spectrometry (Py-GC-MS), were emphasized. These procedures guaranteed precise polymer identification and reduced the occurrence of false positives. Studies lacking methodological transparency or failing to use standardized detection procedures were omitted to ensure data quality throughout the review.

2.6. Strategy for Data Synthesis

Due to the variability in research methodologies, ecosystems examined, and analytical approaches employed in the included publications, a narrative synthesis approach was used rather than a quantitative meta-analysis. Thematic categorization enabled the identification of trends, regional patterns, ecosystem vulnerabilities, and interspecies toxicological responses. This qualitative comparison method facilitated a more refined understanding of MP pollution in aquatic systems, emphasizing both common results and context-dependent differences. This synthesis incorporated discussion of knowledge gaps, emerging pollutants, and mitigation techniques to provide an in-depth overview of MP research and its implications.

3. Results and Discussion

3.1. Global Status of Microplastics in Aquatic Ecosystems

Microplastic contamination has attained critical levels in certain aquatic ecosystems. Initially, studies on MPs focused on marine systems, particularly coastal areas and open oceans, where significant accumulation zones, such as the Great Pacific Garbage Patch, are well documented [100]. Recent data have increasingly demonstrated the existence of MPS in freshwater bodies, wetland habitats, high-altitude lakes, and polar regions [3]; Table 1. This broadened research focus has uncovered a significantly more widespread and intricate worldwide distribution than previously believed [7,101,102].

In freshwater systems such as rivers, lakes, wetlands, and estuaries, MPs generally derive from urban runoff, household sewage, industrial discharge, and the deterioration of improperly managed garbage along riverbanks [2,46,54,102]. Rivers including the Ganges, Yangtze, and Amazon are now considered significant channels for the transfer of terrestrial plastics to the oceans [3,100]. Low flow velocities and intricate hydrology in wetland ecosystems sequester MPS in sediment, making them hotspots of persistent pollution [12,18,56]. Recent research in subtropical and tropical wetlands has recorded the occurrence of MPs in fish, mollusks, and benthic invertebrates, with concentrations frequently surpassing those in neighboring river systems [12,18,73].

Marine ecosystems persist as the ultimate repository for plastic debris. Microplastics have been identified in the water column, surface waters, sediments, and deep-sea benthic environments. Fibers, pieces, and microbeads have been detected in several marine organisms, including plankton, bivalves, fish, seabirds, and marine mammals [18,103,104]. Studies in the Mediterranean Sea, South China Sea, Bay of Bengal, and North Atlantic show that the amount of MPs varies considerably due to ocean currents, proximity to the coast, and regional waste management practices [10,72,74,103].

The recent discovery of MPs in polar regions is particularly concerning. Research has identified MPs integrated into Arctic and Antarctic Sea ice, snow, and surface waters [105]. The principal sources are believed to encompass long-range atmospheric transport, marine commerce, fishing operations, and fragmented debris from lower latitudes conveyed by ocean currents [106]. Microplastics have been identified in zooplankton, Arctic cod, and seabirds inside the Arctic Ocean, prompting concerns regarding bioaccumulation and disruptions to food webs in these delicate ecosystems [107,108,109].

The concentration and dispersion of MPs are affected by several parameters, including polymer type, density, degradation rate, and environmental conditions such as salinity, temperature, and hydrodynamics [110,111,112,113,114]. Low-density polymers, including PE and PP, typically float and aggregate at the surface, but denser plastics such as PET and PVC subside into sediments. Furthermore, particle size and morphology influence transport and ingestion rates across trophic levels, with smaller particles being more easily internalized by aquatic species [115,116,117].

The global distribution of MPs exhibits notable discrepancies. Developed nations with superior waste management facilities typically show reduced concentrations in freshwater ecosystems but increased offshore pollution due to historical contamination [118]. Conversely, developing nations in Southeast Asia, Sub-Saharan Africa, and South America are characterized by insufficient waste disposal systems, which encounter significant inland and coastal pollution [73,114]. Regional climate, hydrological patterns, and socioeconomic factors further affect local MP concentrations and associated risks [17,18,81].

Notwithstanding the expanding corpus of research, a global consensus on standardized methodologies for MP sampling, categorization, and reporting remains elusive. Variations in sampling mesh sizes, extraction solvents, and analytical methodologies (e.g., FTIR versus Raman spectroscopy) complicate inter-study comparisons. The absence of methodological uniformity presents a considerable obstacle to charting global MP trends and formulating universal mitigation policies [73,117]. Microplastics are acknowledged as a pervasive contaminant impacting aquatic ecosystems globally, ranging from tropical wetlands and significant river systems to isolated Arctic regions and deep-sea basins [119,120,121,122,123]. The global situation of MPs indicates the extent of plastic production and mismanagement, as well as deficiencies in environmental governance, monitoring, and remediation efforts [73]. The subsequent sections explore ecosystem-specific effects, trophic transmission, ecotoxicology, and mechanisms of human exposure.

Table 1. Global distribution and observations of microplastics in aquatic ecosystems.

Ecosystem/Region	Key Observations	Source (2020–2025)
Freshwater (e.g., Yangtze River, Lake Victoria)	High MP load from urban runoff and sewage; concentrations range 100–3000 particles/m3; fibers dominant.	[3,100]
Wetlands (e.g., Sundarbans, Mekong Delta)	Sediment retention of MPs; high accumulation in benthic invertebrates; largely unregulated.	[10,11,12,77]
Marine (e.g., Mediterranean Sea, Bay of Bengal)	Surface and deep-sea MPs widely reported; trophic transfer observed in fish and seabirds.	[3,10,49]
Polar Regions (Arctic, Antarctic)	MPs detected in sea ice and Arctic cod; sources include long-range transport and shipping activity.	[18,107,121,122,123]
Freshwater (India—Ganges River)	Significant MP loads from urban runoff and industrial zones; 4000–13,000 particles/m3 recorded.	[79]
Freshwater (Russia—Volga River)	Moderate MP concentrations in populated areas; fibers and fragments dominant.	[119,124]
Freshwater (Europe—Rhine, Thames)	High variability depending on urbanization level; major input from wastewater and combined sewage overflows.	[66,74,102,125]
Freshwater (Brazil—Tietê River)	Informal settlements and poor waste management lead to elevated MP concentrations.	[126]

Table 1. Global distribution and observations of microplastics in aquatic ecosystems.

Ecosystem/Region	Key Observations	Source (2020–2025)
Freshwater (e.g., Yangtze River, Lake Victoria)	High MP load from urban runoff and sewage; concentrations range 100–3000 particles/m3; fibers dominant.	[3,100]
Wetlands (e.g., Sundarbans, Mekong Delta)	Sediment retention of MPs; high accumulation in benthic invertebrates; largely unregulated.	[10,11,12,77]
Marine (e.g., Mediterranean Sea, Bay of Bengal)	Surface and deep-sea MPs widely reported; trophic transfer observed in fish and seabirds.	[3,10,49]
Polar Regions (Arctic, Antarctic)	MPs detected in sea ice and Arctic cod; sources include long-range transport and shipping activity.	[18,107,121,122,123]
Freshwater (India—Ganges River)	Significant MP loads from urban runoff and industrial zones; 4000–13,000 particles/m3 recorded.	[79]
Freshwater (Russia—Volga River)	Moderate MP concentrations in populated areas; fibers and fragments dominant.	[119,124]
Freshwater (Europe—Rhine, Thames)	High variability depending on urbanization level; major input from wastewater and combined sewage overflows.	[66,74,102,125]
Freshwater (Brazil—Tietê River)	Informal settlements and poor waste management lead to elevated MP concentrations.	[126]

3.2. Origins and Categories of Microplastics in Aquatic Ecosystems

Microplastics arise from several sources and are generally categorized into two principal types: primary MPs and secondary MPs. Primary MPs are deliberately produced at small sizes and are frequently used in personal care items (e.g., exfoliants in facial scrubs), industrial abrasives, or biomedical applications. Microbeads and small plastic pellets (nurdles) often enter water systems through sewage, industrial waste, or accidental spills during transport and handling [55,73].

Larger pre-existing plastic debris in the environment decomposes to produce secondary MPs. These come from things like packaging materials, fishing gear, synthetic clothes, and agricultural films that break down over time because of things like sunlight, wear and tear, oxidation, and bacteria. In contrast to primary MPs, secondary MPs display significant variability in size, shape, and chemical composition, influenced by their source material and degradation processes [1,18,65].

The primary routes via which MPs infiltrate aquatic ecosystems encompass home and industrial wastewater discharge, urban runoff, stormwater drainage, landfill leachate, atmospheric deposition, and maritime operations. Major contributors in metropolitan areas include synthetic fibers from washing machines, tire wear particles from roadways, and microbeads in cosmetics. Agricultural runoff, open dumping, and aquaculture waste are significant sources in rural and coastal areas. Maritime transport, fishing operations, and offshore oil exploration intensify marine plastic pollution, whereas polar regions are contaminated with MPs by long-range atmospheric and oceanic transfer [5].

The varieties of MPs present in aquatic systems differ markedly according to local human activities, plastic consumption trends, and degradation circumstances. Prevalent polymer types included PE, PP, polystyrene (PS), PET, and PVC. Of these, PE and PP are the most widespread, largely because of their extensive use and low density, enabling them to float and disperse in surface waters [73]. In contrast, denser polymers such as PET and PVC typically accumulate in sediments and benthic strata. These plastics differ in how stable they are, how quickly they break down, and how well they can attract pollutants, which influences how long they last in the environment and their harmful effects on living things [8].

Regarding morphology, MPs are typically classified as fibers, pieces, films, pellets, spheres, or foam. Fibers, primarily derived from synthetic textiles and fishing nets, predominate in both freshwater and marine ecosystems. Fragments originate from the mechanical disintegration of hard plastics, whereas films are generally produced from plastic bags and wrappers [127]. Personal care goods or medicinal uses commonly include spheres or beads; however, their prominence has diminished in certain countries due to microbead prohibitions [10,87].

Recent investigations indicate that MP profiles differ among ecosystems. For example, river systems in Asia and Africa are primarily characterized by textile fibers and film-like MPs from informal waste disposal, whereas coastal areas frequently display greater quantities of pellets and pieces originating from fishing gear [73]. In polar regions, fibers and weathered pieces are predominant, perhaps due to extensive transit and reduced degradation rates at freezing temperatures [5,120].

A significant concern in MP pollution is the inadequate elimination of MPs by traditional wastewater treatment plants (WWTPs). Tertiary treatment techniques can eliminate a substantial number of bigger particles; nonetheless, numerous MPs, particularly those under 100 µm, evade filtration and are discharged into receiving waterways. Furthermore, the sludge produced during treatment, which contains significant quantities of MPs, is frequently used as fertilizer in agricultural fields, establishing a secondary route for environmental dissemination [16].

The capacity of MPs to serve as carriers for other pollutants further compounds their existence and durability. Because they repel water and have a large surface area compared to their size, MPs easily attract heavy metals, polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), antibiotics, and other harmful substances. This increases their risk to the environment and creates complex toxic effects when aquatic animals eat them [7].

3.3. Ecotoxicological Impacts of Microplastics on Aquatic Organisms

Microplastics are increasingly acknowledged as ecotoxic agents capable of disrupting physiological, behavioral, and metabolic processes in range of aquatic species. Their effects vary among different species and environments, depending on factors such as particle size, shape, type of plastic, concentration, and presence of other pollutants. Recent research has presented persuasive evidence of detrimental effects in both laboratory and field environments, highlighting growing concern regarding MPs as a burgeoning threat to aquatic biodiversity [6,7].

The consumption of MPs by aquatic organisms is now thoroughly documented across trophic levels, including zooplankton, benthic invertebrates, fish, amphibians, seabirds, and marine mammals (Figure 2). Microplastics can accumulate in the digestive tract of filter feeders and small invertebrates, impeding feeding and causing tissue damage. In mollusks and crustaceans, exposure to MPs has been associated with oxidative stress, lysosomal destabilization, immunological suppression, and reproductive toxicity [1,2,6,25]. The consequences are often concentration-dependent and influenced by the physical properties of the particles; for instance, fibers are more likely to entangle or clog feeding organs.

In fish, micro- and nanoplastics can cross epithelial barriers, accumulate in tissues such as the liver and brain, and induce a range of physiological and behavioral disturbances. Recent studies in zebrafish have demonstrated that exposure to environmentally relevant concentrations of these particles leads to suppressed locomotor activity, altered nervous system function, oxidative stress, and disruptions in normal metabolic and endocrine signaling pathways [116].

The occurrence of MPs in Arctic species further exemplifies their ecotoxicological impact. Arctic cod, zooplankton, and benthic amphipods from the Arctic Ocean have shown signs of eating MPs, which can impair energy transfer in the food chain and affect reproduction in cold-adapted species. In these areas, reduced metabolic rates and extended lifespans may enhance the bioaccumulation of MPs and related pollutants [5,18,121]. In wetland habitats critical for breeding and nursery grounds, the accumulation of MPs in juvenile amphibians and fish has been linked to slower growth, skeletal deformities, and increased mortality.

A significant problem regarding MP toxicity is their capacity to serve as vectors for additional harmful compounds. The hydrophobic surfaces of MPs quickly absorb various environmental contaminants, including heavy metals (e.g., cadmium, lead, mercury), POPs, and antibiotics. Upon consumption, these contaminants may be released within the organisms, leading to cumulative or synergistic harmful effects. The “Trojan Horse” effect has been demonstrated in several studies, suggesting that combined exposure to plastics and pollutants often causes severe health impacts than exposure to either alone. The metabolic pathways affected by MPs are diverse and organism-specific. Common effects include lipid peroxidation, altered antioxidant enzyme activity (such as superoxide dismutase and catalase), DNA damage, and hormone receptor disruption. These molecular-level impacts can result in broader consequences, including compromised reproduction, diminished immune response, developmental abnormalities, and increased mortality. Furthermore, prolonged exposure, even at minimal doses, has shown sublethal effects that jeopardize long-term population viability [1,6,11,16].

Although most toxicity studies have focused on individual organisms in controlled environments, recent research highlights the need to examine community- and ecosystem-level impacts. Mesocosm experiments and studies in polluted wetlands have shown shift in species composition, altered food web relationships, and the loss of keystone species due to ongoing exposure to microplastics. Such changes can diminish ecosystem services, decrease biodiversity, and weaken the resilience of aquatic systems to climate change and other stressors [7,25,65,73].

Despite accumulating evidence, important gaps persist in our understanding of long-term MP toxicity under ecologically relevant conditions. Most research remains short-term, limited to a narrow range of species, and performed under artificial exposure scenarios. More studies are needed to assess the chronic and transgenerational effects of microplastics on living organisms, as well as their interactions with other global challenges such as climate change, ocean acidification, and nutrient pollution.

3.4. Bioaccumulation, Trophic Transfer, and Disruption of Food Webs

Microplastics can accumulate in living organisms and move through the food chain in aquatic environments, raising concerns about ecosystem health and species diversity. Owing to their persistence, diminutive size, and potential to be mistaken for food, MPs are consumed by a diverse array of aquatic animals, including zooplankton, benthic invertebrates, fish, and apex predators (Table 2). When aquatic animals ingest MPs, these tiny particles can build up in their stomachs, tissues, or organs and be transferred to predators, disrupting the flow of energy and increasing the risk of physical and chemical harm [8,84,89].

In lower trophic levels, such as zooplankton and filter-feeding invertebrates, MPs are ingested through feeding mechanisms that do not discriminate by particle type. These organisms act as principal conduits for MPs in the aquatic food web. Research has shown that copepods and cladocerans accumulate PS and PE particles, which reduce their ability to feed and reproduce effectively [8]. Small fish feast upon these contaminated organisms, resulting in the trophic transmission of MPs. Laboratory studies have confirmed this process by analyzing contents of fish stomachs and tissues, often linking ingestion to inflammation and metabolic disturbances.

As MPs ascend the trophic levels, bioaccumulation frequently intensifies in predatory fish, seabirds, and marine mammals. In fish, MPs can traverse the intestinal barrier and accumulate in hepatic and brain tissues, causing histopathological damage and oxidative stress. Research from the Mediterranean Sea, Bay of Bengal, and Arctic fjords has identified MPs in commercially important species such as anchovies, salmon, and cod, indicating possible transfer to humans through seafood consumption [5,10,18,108,109,110,111,112,113]. Recent studies have also documented the presence of MPs in polar animals, including Antarctic krill, Arctic cod, and seabirds, as well as in snow and sea ice layers, illustrating long-range atmospheric and oceanic transport processes [115,120,121,122,123,125].

Top predators, such as seabirds and marine mammals, consume MPs either indirectly via contaminated prey or directly by ingesting plastic fragments misidentified as food. Fulmars, for example, have been found with substantial amounts of plastic waste in their stomachs, resulting in gastrointestinal blockage, starvation, and reduced reproductive success. Marine mammals, including seals, polar bears, and several crustacean species, have also been documented to ingest MPs, which can potentially lead to chronic inflammation and modification of gut microbiota [128].

Table 2. Ecotoxicological effects of microplastics in aquatic organisms.

Ecosystem	Organism Group	Observed Effects	Reference (2022–2025)
Freshwater	Zooplankton (e.g., copepods, cladocerans)	Reduced feeding rate, gut blockage, impaired reproduction, oxidative stress	[7,8]
Estuarine	Mollusks (e.g., mussels, oysters)	Tissue damage, lysosomal destabilization, reduced filtration efficiency, inflammation	[1,6]
Estuarine	Crustaceans (e.g., crabs, shrimp)	Enzymatic imbalance, growth inhibition, oxidative damage, reproductive delay	[6,23]
Marine	Fish (e.g., zebrafish, anchovy, cod)	Neurobehavioral changes, endocrine disruption, liver inflammation, bioaccumulation	[9,10]
Marine	Seabirds (e.g., fulmars)	Gastrointestinal obstruction, malnutrition, reduced reproductive success	[5,128]
Polar	Marine mammals (e.g., seals, polar bears)	Immune modulation, microbiome disturbance, accumulation in gut tissues	[5,128]

Table 2. Ecotoxicological effects of microplastics in aquatic organisms.

Ecosystem	Organism Group	Observed Effects	Reference (2022–2025)
Freshwater	Zooplankton (e.g., copepods, cladocerans)	Reduced feeding rate, gut blockage, impaired reproduction, oxidative stress	[7,8]
Estuarine	Mollusks (e.g., mussels, oysters)	Tissue damage, lysosomal destabilization, reduced filtration efficiency, inflammation	[1,6]
Estuarine	Crustaceans (e.g., crabs, shrimp)	Enzymatic imbalance, growth inhibition, oxidative damage, reproductive delay	[6,23]
Marine	Fish (e.g., zebrafish, anchovy, cod)	Neurobehavioral changes, endocrine disruption, liver inflammation, bioaccumulation	[9,10]
Marine	Seabirds (e.g., fulmars)	Gastrointestinal obstruction, malnutrition, reduced reproductive success	[5,128]
Polar	Marine mammals (e.g., seals, polar bears)	Immune modulation, microbiome disturbance, accumulation in gut tissues	[5,128]

The disturbance of food webs due to MP pollution extends beyond individual health impacts. Prolonged exposure may result in alterations to species interactions, predator–prey relationships, and the efficiency of energy transfer. For example, when MPs reduce prey fitness or alter predator feeding behavior, such modifications can lead to shifts in population structures and even the collapse of localized food webs. Wetland and estuarine systems, which support diverse and interconnected communities, are especially susceptible to such disturbances [65,73].

In Arctic ecosystems, where energy flow depends on seasonal growth and simple food chains, the movement of MPs presents unique risks. Arctic cod, a crucial prey species for seabirds and marine mammals, have exhibited high rates of MP ingestion, potentially subjecting higher predators to prolonged, sub-lethal impacts in harsh environmental conditions. The slower metabolism and longer lifespans of polar species can result in greater accumulation of harmful substances and delayed elimination, exacerbating environmental effects [5,109,113,128].

The chemical load associated with MPs exacerbates the ecological ramifications of bioaccumulation and trophic transmission. Chemicals that adhere to MPs, such as POPs, PAHs, and antibiotics, can be released in the digestive system, causing internal exposure. The combination of physical and chemical stressors can disrupt hormone function, immune response, and DNA integrity in affected species [6,16,59].

While many laboratory studies have validated trophic transfer in controlled environments, there is less field research measuring its occurrence in natural ecosystems. Diversity in species’ diets, habitats, and MP availability complicates generalizations. Moreover, long-term ecological data are scarce, especially regarding cumulative effects, sub-lethal thresholds, and population-level consequences. Future research must include studies addressing multiple generations and entire ecosystems to understand how changes in the food webs caused by MPs affect biodiversity, resilience, and ecosystem services [7,65,73].

3.5. Human Exposure and Health Impacts

Human exposure to MPs has emerged as a pressing public health issue owing to their pervasive prevalence in the environment and increasing identification in food, water, and biological tissues. What was once thought to be solely an environmental issue is now recognized as a potential threat to human health, especially since recent studies show that MPs can enter human body through ingestion, inhalation, or dermal contact and exert biological effects [14,15,22].

The principal mode of exposure is ingestion of contaminated food and drink. Microplastics have been found in various types of shellfish, such as mussels, oysters, prawns, and finfish, which are often eaten whole or with their internal organs intact, increasing the likelihood of human ingestion [11,73]. Filter-feeding species, such as bivalves, acquire MPs from their environment, which are then transmitted to humans. Research indicates particle concentrations between 0.36 and 0.89 per gram in mussels available in markets in Europe and Asia [10,108]. Furthermore, commercial salt, bottled water, and drinking water sources have been identified to contain MPs at varying concentrations, frequently surpassing 100 particles per liter in bottled products [31,32].

Inhalation also constitutes a significant exposure route, especially in urban settings and enclosed spaces. Airborne synthetic fibers released from apparel, furnishings, and construction materials can potentially be absorbed into the respiratory system. Recent research has shown MP fibers in human lung tissues and bronchoalveolar lavage samples, substantiating internal exposure by inhalation [13,93]. The long-term health effects of inhaling in MPs are still being investigated, but early findings link ongoing inhalation to issues such as respiratory discomfort, inflammation, and exacerbation of lung diseases [13,14,20].

Dermal exposure is typically regarded as a minor route; however, it may be significant in occupational environments or with extended contact with contaminated water, such as during swimming or when handling wastewater sludge. Despite the relatively effective barrier provided by human skin, tiny particles and additives included in MPs may penetrate compromised or sensitive skin under specific circumstances [16,36].

The toxicological impacts of MPs on humans are still under investigation; however, initial studies indicate considerable health risks. Microplastics can provoke oxidative stress, inflammation, immunological dysregulation, and endocrine disruption at the cellular level. Laboratory investigations using human cell lines have revealed diminished cell viability, mitochondrial impairment, and heightened generation of reactive oxygen species (ROS) following MP exposure [9,14,30]. Inflammatory responses and DNA damage have also been reported, raising concerns over potential carcinogenic implications from prolonged exposure [30].

In addition to their physical presence, MPs frequently serve as conduits for other harmful compounds, such as heavy metals, antibiotics, and POPs. Adsorbed pollutants may desorb within the gastrointestinal or respiratory systems upon entry, increasing internal exposure. For instance, MPs contaminated with bisphenol A (BPA) and phthalates have been linked to endocrine disruption and reproductive damage in animal studies [16,22]. The possibility of synergistic toxicity arising from both the plastic particle and its chemical constituents is a significant concern in toxicological evaluations.

Biomonitoring investigations have verified the presence of MPs in human biological specimens, such as blood, feces, placentas, breast milk, and lung tissue [15,33,34,92,93]. Detection of MPs in placental tissue and newborn waste indicates that exposure may occur before birth, raising concerns about developmental harm and effects on future generations [15,41]. These findings have necessitated urgent epidemiological research to determine causal relationships between MP exposure and human health effects.

Geographic and socioeconomic differences may aggravate health risks. Populations in low- and middle-income countries (LMICs) have disproportionate exposure due to insufficient waste management, dependence on contaminated food sources, and restricted access to clean water. The informal recycling sector, open dumping, and unregulated incineration of plastic waste facilitate both direct and indirect exposure pathways in these areas [22,48].

Despite increasing concerns, a worldwide consensus on safe exposure levels or regulatory thresholds for MPs in food and water remains absent. The World Health Organization (WHO) has recognized this data deficiency and advocated for standardized detection methodologies and enhanced toxicological research to guide risk assessment frameworks [36,48]. Meanwhile, preventative measures are advocated, such as minimizing plastic consumption, improving water treatment facilities, and endorsing biodegradable alternatives [14].

3.6. Knowledge Gaps, Policy Obstacles, and Research Trajectories

Despite increasing awareness and a burgeoning body of research, substantial knowledge gaps remain in our understanding of MP pollution, especially within aquatic ecosystems. These limitations impede the development of effective mitigation strategies and robust policy frameworks, particularly given the increasing ecological and human health threats [33,51]. A significant challenge is the absence of standard procedures for the detection, quantification, and classification of MPs across various environmental matrices [21]. Differences in sample collection methods, filter sizes, digestion protocols, and polymers identification techniques (such as FTIR and Raman spectroscopy) make it difficult to compare results across studies [34,68,70]. The lack of globally recognized thresholds for MP concentrations in water, sediment, or biota hampers environmental assessments and risk evaluations.

Another major deficiency is the lack of long-term, ecosystem-scale research. Most available data originate from brief laboratory experiments or isolated field observations. There is insufficient research on chronic exposure, delayed effects, and transgenerational impacts, especially in non-model organisms [7,8]. Furthermore, trophic interactions and food web responses are inadequately understood, particularly in vulnerable ecosystems such as wetlands and polar environments [4,5]. Despite their biological significance and susceptibility to plastic deposition, these ecosystems are frequently overlooked [8].

Regulatory responses are often disjointed and reactive. Although several countries have enacted bans on plastic items (e.g., microbeads, single-use plastics), comprehensive legislative frameworks for MP surveillance and reduction are rare [48,50,86]. Current policies frequently focus on solid waste management while overlooking the pervasive and persistent nature of MPs in aquatic environments [73]. Furthermore, there is minimal coordination between environmental and health sectors, resulting in a fragmented approach to MPs from a One Health perspective [36].

A geographic mismatch also exists in research and policy development, with high-income countries dominating scientific publications and regulatory innovation [22,73]. Low- and middle-income countries, such as Bangladesh, are often characterized by inadequate waste management infrastructure and under-representation in global decision-making, despite facing heightened exposure risks. This disparity obstructs the development of internationally relevant mitigation strategies and contributes to regional environmental injustice [22,48,73].

From a public health perspective, there is an urgent need for epidemiological research to establish causal relationships between MP exposure and human disease. Although MPs have been identified in human blood, placenta, and lung tissue, the clinical significance of these findings remains ambiguous [40,41]. Risk assessment methods must consider both the physical harm from particles and the chemical harm from attached contaminants to properly evaluate health effects. In the absence of such models, regulatory bodies lack the empirical basis needed to establish exposure limits or formulate safety guidelines [36,99].

Interdisciplinary research and global collaboration are essential to bridge these gaps. Collaborative networks comprising ecologists, chemists, toxicologists, engineers, and policymakers can facilitate the development of standard monitoring techniques and novel solutions [55,63]. Such solutions may include biodegradable polymers, bio-based plastic alternatives, advanced wastewater treatment technologies, and circular economy strategies designed to reduce plastic influx into aquatic ecosystems [48].

The development of early warning indicators and predictive ecological models can help forecast the environmental and biological effects of MP contamination [55,63]. These tools would facilitate the prioritization of intervention areas, the evaluation of mitigation strategy effectiveness, and the incorporation of MP indicators into global sustainability frameworks, including the United Nations Sustainable Development Goals (SDGs) [48,73,95].

Future studies must address both the ecological and socioeconomic aspects of MP pollution to achieve meaningful progress. This includes integrating Indigenous knowledge systems, engaging stakeholders in co-designing interventions, and increasing public awareness through science communication and community-led monitoring. A comprehensive and inclusive approach is essential to address the complex challenges presented by MPs at local, national, and global levels.

4. Conclusions

Microplastics have become a ubiquitous contaminant in global aquatic ecosystems, impacting environmental health and presenting threats to human welfare. This study has consolidated recent research regarding the distribution, origins, and ecological effects of MPs in freshwater, wetland, marine, and polar ecosystems. It has examined bioaccumulation patterns, trophic transfer dynamics, and the overarching consequences for food web structure and ecosystem stability. Microplastics have been shown to interfere with physiological, metabolic, and reproductive functions in various aquatic species. Their progression through trophic levels, coupled with their capacity to accumulate and transfer toxic substances, amplifies their ecological impact. These effects extend to human populations via dietary exposure, inhalation, and perhaps prenatal transmission, as evidenced by recent biomonitoring studies. Nevertheless, the long-term health ramifications of MP exposure in humans remain inadequately comprehended.

Although apprehension is increasing, scientific and regulatory reactions to MP pollution continue to be fragmented. Significant gaps persist in the standardization of detection methodologies, understanding of chronic and multigenerational toxicity, and determination of safe exposure limits. These challenges are especially pronounced in low- and middle-income regions, where monitoring is inadequate and exposure risks are disproportionately high. Addressing the multifaceted challenges of MP contamination requires a unified global effort. This includes establishing standardized monitoring mechanisms, investing in multidisciplinary research, and implementing ecosystem-specific mitigation strategies. Policies must integrate ecological and public health considerations, promote sustainable alternatives, and foster equitable solutions across regions. An integrated approach is essential for the effective mitigation of environmental and health concerns posed by microplastics.