Sources, Transport, and Accumulation of Synthetic Microfiber Wastes in Aquatic and Terrestrial Environments

Abstract

The global proliferation of synthetic microfiber waste has emerged as a pressing environmental concern due to its widespread distribution in both aquatic and terrestrial ecosystems. Primary sources of synthetic microfibers include laundering of synthetic textiles, manufacturing, and plastic breakdown, with transport via wastewater, runoff, atmospheric deposition, and animal ingestion. This review highlights the sources of microfiber formation and accumulation, ranging from freshwater lakes and rivers to deep-sea sediments. The presence of microfibers in agricultural soils, urban dust, and even remote locations indicates atmospheric transportation and diverse accumulation patterns. Additionally, this review discusses the transportation of microfibers through various pathways and elaborates on various treatment technologies for microfiber removal and reduction. The potential human health impacts and mitigation solutions are also highlighted. Overall, this review aims to provide comprehensive knowledge of the sources, transport mechanisms, and accumulation patterns of synthetic microfibers, emphasizing their multifaceted environmental impact and the need for further research to develop effective solutions.

1. Introduction

The emergence of synthetic microfibers as a significant environmental pollutant stems primarily from their origin and physical characteristics. These tiny fibers, typically less than 5 mm long, are predominantly shed from synthetic textiles like polyester, nylon, and acrylic during washing, wearing, and manufacturing processes [1]. Despite being invisible to the naked eye, their accumulation in both aquatic and terrestrial ecosystems over recent decades has raised considerable environmental concerns. In contrast to other microplastics, which encompass a broader range of small plastic particles from various sources, microfibers stand out due to their textile origin. While microplastics include primary forms like microbeads from personal care products and industrial abrasives, as well as secondary particles resulting from the breakdown of larger plastic items through environmental processes [2,3], microfibers are primarily introduced into the environment through household laundry and wastewater systems. This specific pathway poses distinct challenges for water treatment and marine ecosystem health. The global increase in synthetic textile production, driven by economic growth, technological advancements, and changing consumer preferences, has significantly contributed to the release of microfibers into the environment [4,5]. Each wash cycle of synthetic garments releases thousands of these minute fibers, most of which evade filtration and ultimately enter rivers, lakes, and oceans, becoming pervasive forms of microplastic pollution [3]. Beyond textiles, microfibers are also generated during the production, use, and disposal of various synthetic products, further complicating efforts to mitigate their environmental impact. The transport pathways of synthetic microfibers are complex and extensive. They travel vast distances through wind and water currents, reaching remote deep-sea sediments, polar ice caps, and even becoming airborne in certain regions. These fibers have a propensity to bind with other pollutants and serve as vectors for toxic compounds. Due to their durability, synthetic microfibers persist in the environment for extended periods [4]. Moreover, their ingestion by a wide range of organisms—from microscopic plankton to large marine mammals—leads to physiological disturbances and the potential transfer of associated contaminants through the food web [5,6,7]. On land, synthetic microfibers are increasingly detected in agricultural soils, potentially due to the use of sewage sludge as fertilizer, as well as in terrestrial organisms. The long-term implications of microfiber accumulation in terrestrial ecosystems are still being investigated, with early indications suggesting adverse effects on soil properties and soil-dwelling organisms [8,9,10,11]. This review aims to comprehensively explore the sources, transport mechanisms, and accumulation patterns of synthetic microfibers in aquatic and terrestrial ecosystems. By synthesizing current knowledge, this review underscores the global scale of this environmental challenge, delineates its multidimensional impacts, discusses existing treatment technologies, and proposes strategies for mitigation. Addressing the pervasive issue of synthetic microfibers demands concerted efforts across industries, policymakers, and researchers to develop effective solutions that mitigate their environmental and health impacts.

2. Sources of Synthetic Microfibers

There are various sources of microfibers’ production and accumulation in aquatic and terrestrial environments, which are discussed below briefly (Figure 1 and Figure 2).

Table 1. Sources and properties of different microfibers (indicative).

Destination	Microfiber Types	Size Range (μm)	Shape	References
Tubifex worms	PET and acrylic microfibers	55–4100	Fibrous	[4]
Sediment	PP	<400	Spherical	[6]
Fish	PE, PP, and cellulose	1000–5000	Fibrous	[7]
Body scrubs	PE, WS, PAA, MC, silica, and pumice	12.3–273.4	Irregular, spherical, granular	[12]
Toothpaste	PE and CaCO3	<20	Irregular	[13]
Surface water	PP, PS, PVC, PET, and polyamide	100–5000	Fibrous	[14]
Facial scrubs	PE or LDPE, wax, Luwax, and PVC	85–186	Irregular, granular, spherical	[15]
Surface water	PE, PP, and PS	200	Fibrous	[16]
Wastewater treatment plant	PE, PP, acrylic, PS, and cellulose acetate	≤2500	Fibrous	[17]
Oyster	-	240–1000	Spherical	[18]
Shrimp P. australiensis	Polyamide, rayon, PP, and PE	-	Fibrous	[19]

shows the final destination and properties of different microfibers (MFs).

2.1. The Textile Industry and Washing Machines

The textile and fashion industry is a major contributor to synthetic microfiber pollution. Textiles contribute about 14% of plastic waste production by sector, the second-largest source of plastic pollution following packaging. Approximately 60 million tons of synthetic fibers is produced each year, with polyester being the most common. It was reported that approximately 700,000 microfibers (about 0.5 g in weight) could be discharged with laundry sewage for every cycle that the washing machine drum rotates. Globally, it is estimated that 500,000 tonnes of microfibers is released into the ocean because of domestic washing annually [20]. Synthetic fabrics like polyester, nylon, and acrylic are commonly used in clothing production. During the manufacturing process, as garments are cut, stitched, and finished, small synthetic fibers are released into the environment [12]. Additionally, when consumers wear and wash these synthetic garments, they shed microfibers. These microfibers, which are too small to be filtered by wastewater treatment plants, often find their way into water bodies, particularly through the drainage systems of homes [13]. One of the most prevalent sources of synthetic microfibers is household washing machines. When the synthetic clothing is laundered, especially in the form of fleece jackets, yoga pants, and athletic wear, thousands of tiny synthetic microfibers are released with each wash cycle [15,16,17,18]. Over time, the cumulative impact of countless washing machines worldwide contributes significantly to microfiber pollution. From raw materials to the end product, fiber losses occur at each step of the textile production processes, including spinning, weaving, dyeing, finishing, cutting, trimming, and sewing. For example, in different manufacturing processes, the cotton fiber loss rates for different end products are listed in Table 1, released by the Better Cotton Initiative (2022) through member survey responses in 2020 (Initiative 2020) [21]. Between 6 and 43% of fibers were lost during each process (Table 1). If the fiber loss rate is simply set at 30% from fiber to end product, about 70,000,000 tonnes of cotton was globally wasted in 2020 [22]. Assuming that the microfiber loss rate is 1% from fiber to end product during the production of home textiles and apparel, nearly 1.1 million metric tons of microfiber was lost, which is 2.2 × 10⁶ times the weight of the estimated fibers being released from domestic washing [12].

Source reducing microfibers is crucial for mitigating their environmental impact, the primary focus is on minimizing their release at the origin. This can be achieved through multiple strategies, such as improving the design and manufacturing of synthetic textiles to reduce fiber shedding. Innovations in fabric production, such as tighter weaves and the use of coatings, can significantly decrease microfibers’ release during washing. Additionally, implementing better washing machine filters and encouraging the use of liquid detergents, which are less abrasive than powder detergents, can help reduce microfiber discharge. Public awareness campaigns and education on proper garment care can further contribute to reducing microfiber pollution. By addressing the issue at its source, these measures collectively help prevent microfibers from entering waterways and, ultimately, the broader environment.

2.2. Plastic Products and Materials

In 2020, global plastic production reached approximately 367 million tons. A substantial portion of these plastics are used in products that degrade into microfibers over time [23]. This issue primarily arises from the widespread use of synthetic polymers in various everyday items, including clothing, packaging, and household goods. These microfibers make their way into wastewater systems and, eventually, into rivers, lakes, and oceans. Plastic packaging materials, such as disposable bottles and food containers, can degrade over time, shedding microplastic particles into the environment. Plastic packaging accounts for about 40% of global plastic production, equating to roughly 147 million tons annually. These materials contribute significantly to the overall microplastic burden as they degrade [24]. Similarly, the wear and tear of plastic products like car tires and construction materials contributes to the release of microplastics on roadways and urban areas, which can be washed into water bodies through stormwater runoff [25]. It is estimated that 1.5 million tons of tire wear particles is released into the environment each year globally. Used in construction and landscaping, geotextiles made from synthetic fibers can degrade and release microfibers. The global usage of geotextiles is projected to reach 7.9 billion square meters by 2025, contributing significantly to microfiber pollution [26]. These synthetic microfibers and microplastics pose significant environmental and health risks, as they are ingested by various organisms and can accumulate in the food chain, potentially exposing humans to toxic chemicals.

2.3. The Fishing Industry

The fishing industry contributes to approximately 10% of the global marine plastic pollution, including microfibers. One of the primary sources of these microfibers is the materials used in fishing gear and equipment. An estimated 640,000 tons of fishing gear, including nets and ropes, is lost or discarded in the oceans every year. These materials are predominantly made of synthetic fibers that degrade into microfibers over time [26]. Many fishing nets, lines, and other tools are constructed from synthetic polymers such as nylon and polyester, designed for their durability and longevity [27]. However, these materials are not biodegradable, and as they wear and degrade due to the harsh marine conditions, they shed tiny microfibers into the water. Studies have found that polypropylene ropes used in the fishing industry can release up to 20,000 microfibers per meter per use. In areas heavily influenced by fishing activities, marine sediments have been found to contain up to 200,000 microfibers per square meter [25]. These minuscule plastic particles are virtually invisible to the naked eye but are pervasive in the marine ecosystem [28]. They can be ingested by a wide range of marine organisms, from small zooplankton to larger fish and even whales, inadvertently introducing them into the food chain. Additionally, when fishing gear becomes lost or abandoned, often referred to as ‘ghost gear’, it continues to release microfibers into the water over time, compounding the problem. It is estimated that ghost gear can account for up to 70% of large plastic debris in certain ocean regions.

2.4. Landfills and Waste Sites

Landfills and waste sites significantly contribute to the dispersal of synthetic microfibers into the environment. This problem arises from the disposal of vast quantities of synthetic materials, such as clothing, household goods, and plastic products, which often contain microfibers [29]. When these items reach landfills, they undergo degradation and breakdown due to environmental factors and microbial activity, releasing microfibers into the surrounding soil and, in some cases, nearby water bodies through leachate [30]. Studies have found that landfill leachate can contain up to 250 microfibers per liter. In the U.S., landfills receive approximately 11 million tons of textile waste each year. Given that textiles can shed thousands of microfibers per garment, this represents a significant source of microfiber pollution [31]. This poses a risk to both terrestrial and aquatic ecosystems, as microfibers can migrate through groundwater and surface runoff.

2.5. Personal Care Products

Microfiber waste from personal care products, particularly those containing microplastics, contributes to environmental pollution. It is estimated that between 8000 and 16,000 tons of microplastics, including microbeads, is used in personal care products annually in the United States alone. Globally, approximately 30,000 to 80,000 tons of microplastics from personal care products enters the environment each year [30]. Many wet wipes contain synthetic fibers, which contribute to microfiber pollution. It is estimated that wet wipes contribute to around 1–2% of the microplastic pollution found in aquatic environments. Each wet wipe can release thousands of microfibers during use and disposal. A single wet wipe can shed up to 150,000 microfibers into wastewater systems. Microbeads used in facial scrubs are a significant source of microplastic pollution. One tube of facial scrub can contain as many as 300,000 microbeads. Toothpaste with microbeads can release microplastics into the environment. Each application of toothpaste can introduce up to 100,000 microbeads into wastewater systems [31].

Understanding the diverse sources of synthetic microfibers is critical for addressing the growing issue of microfiber pollution. Efforts to mitigate this problem should encompass both prevention at the source, such as improved textile manufacturing techniques and product design, and effective wastewater treatment and waste management strategies to capture and manage these tiny plastic particles before they can harm the environment.

3. Transport Mechanisms

A few points with extensive descriptions related to the transport of synthetic microfiber wastes in both aquatic and terrestrial environments are given below.

3.1. Waterborne Transport in Aquatic Environments

Synthetic microfibers released into water bodies, such as rivers and oceans, can be transported over long distances. The buoyant nature of microfibers allows them to remain suspended in the water column for extended periods. When released from washing machines, textiles, and other sources, these microfibers are carried away by the flow of water [32]. They can be transported downstream by river currents and tides, dispersing across vast areas. As these microfibers move with the water, they pose a significant risk to aquatic ecosystems [33,34]. They can be ingested by aquatic organisms, bioaccumulate in the food chain, and negatively impact the health of marine life (

Table 2. Effect of microfibers (MFs) on aquatic organisms.

Microfibers	Organism	Exposure Time	Concentration	Ecotoxicological Effects	References
PET	Daphnia magna	48 h	12–100 mg/L	Mortality rate increased	[27]
PES	Oryzias latipes	21 days	10,000 MFs/L	Embryo production increased	[28]
PET	Corbicula fluminea	48 h	100, 1000 MFs/L	Polyester fibers were taken up in the small size range	[33]
PET	Daphnia magna	48 h	100 mg/L	No acute effect on test organism	[34]
Polyester	Apostichopus japonicus	72 h	25, 40 MFs/mL	Coelomic fluid accumulation, lysozyme toxicity	[35]
PET	Homarus gammarus	5 days	1, 10, 25 MFs/mL	Survival rate decreased at 25 MFs/mL	[36]
PES	Palaemon pugio	96 h	45,000 MFs/L	No significant mortality rate	[37]
PET	Montastraea cavernosa	48 h	30 mg/L	MFs did not elicit a feeding response	[38]
PP	Danio rerio	24 h	20 mg/L	Intestine damaged by ingestion of microfibers	[39]
PP	Emerita analoga	71 days	3 MFs/L	Retention of egg clutches, embryonic development increased	[40]
PP	Nephrops norvegicus	8 months	5 MFs/per feeding	Reductions in blood protein and lipids, body mass reduced	[41]
Fibers, PET	Calanus helgolandicus	24 h	100 MFs/mL	Feeding reduction	[42]
Fibers	Mytilus edulis	48 h	2000 MFs/mL	Microfibers taken up in multiple organs	[43]
Fibers; PA	Gammarus fossarum	24 h	10–100,000 microbeads/ individual	Reduction in assimilation and wet weight gain	[44]

).

3.2. Transport in the Atmosphere

Airborne transport is a lesser-known yet notable contributor to the distribution of synthetic microfibers in the environment [35]. This phenomenon occurs when microfibers shed from various sources, such as clothing, textiles, and synthetic materials used in building construction, become airborne and are carried by wind currents [36]. In urban areas, these microfibers are released through activities like traffic and industrial processes, as well as during laundry and in indoor dust particles. Once airborne, these minuscule fibers can be transported over long distances, eventually settling into terrestrial and aquatic ecosystems. They may even be deposited into bodies of water, thus adding to the already pressing issue of waterborne microfiber pollution [37]. In addition to their role in soil and water contamination, airborne microfibers pose a potential health risk, as they can be inhaled and contribute to indoor air pollution, potentially carrying with them toxic chemicals [38,39].

3.3. Terrestrial Transport

The mechanism of terrestrial transport of microfibers involves several key processes that facilitate their movement and distribution across land environments. Initially, microfibers are shed from synthetic textiles through activities such as washing clothes, which releases fibers into wastewater. When wastewater treatment plants fail to capture all of the microfibers, the remaining fibers can enter the environment through the application of treated sludge as fertilizer on agricultural land [40,41]. Rainfall and irrigation further drive terrestrial transport by generating surface runoff that carries microfibers across the landscape, where they can infiltrate soils [42]. Within the soil, microfibers interact with soil particles and organic matter, which can trap and hold them, leading to their accumulation [43,44]. Additionally, wind can resuspend and redistribute microfibers deposited on surfaces, contributing to their spread. These mechanisms result in the integration of microfibers into terrestrial ecosystems, where they can affect soil health, interact with soil organisms, and potentially be taken up by plants, posing risks to the broader environment and food chain [45,46].

Table 3. Effects of microfibers on terrestrial organisms (indicative information).

Microfibers	Organism	Exposure Time	Concentration	Ecotoxicological Effects	References
Polyacrylic	Mucor fragilis, Fusarium sp.	42 days	0.4%	Water-stable aggregates were decreased with four specific strains	[8]
Acrylic and nylon mixture	Acrasis rosea, Lolium perenne	30 days	10 mg/kg (0.001%)	No negative impact on plant and earthworm biomass or worm mortality; germination rate decreased and chlorophyll a/b ratio altered	[47]
PES blanket	Enchytraeus crypticus	3 weeks	0.02, 0.06, 0.17, 0.5, 1.5% (various)	Soil exposure to long fibers significantly affected reproduction	[48]
Polyacrylic nitrile	Caenorhabditis elegans	24 h	0.001, 0.01, 0.1%	Toxicity of MFs on the organism increased after long-term wet–dry cycles in soil	[49]
PE cushion	Lumbricus terrestris	35 days	0.1, 1%	No mortality and no bioaccumulation, but alteration of mt and hsp70	[50]
PET	Achatina fulica	28 days	0.014, 0.14, 0.71 g/kg	No mortality and no growth inhibition	[51]

shows the effects of microfibers on terrestrial organisms.

4. Accumulation in the Environment

This section presents extensive descriptions related to the accumulation of synthetic microfiber wastes in both aquatic and terrestrial environments:

4.1. Sediment Accumulation in Aquatic Environments

One of the primary ways synthetic microfibers accumulate in aquatic environments is through sedimentation. As microfibers are released into water bodies, they can gradually settle to the bottom, accumulating in the sediments. The accumulation is influenced by the size, buoyancy, and density of the microfibers, as well as the water’s flow rate and turbulence [52]. Over time, these microfibers can amass in significant quantities within the sediment layers, particularly in areas with high input rates. This accumulation poses various ecological risks, as it can alter sediment characteristics, potentially smother benthic habitats, and become a source of contamination for bottom-dwelling organisms. In coastal areas, synthetic microfibers can accumulate along shorelines and beaches. They are often carried by ocean currents and waves, where they may become trapped in intertidal zones and accumulate in large quantities [53]. Accumulated microfibers can have aesthetic, ecological, and economic impacts on coastal communities, affecting both wildlife and tourism. Figure 2 shows the time taken for the degradation of various substances that are primary sources of microfibers.

4.2. Bioaccumulation in Aquatic Food Webs

Synthetic microfibers can accumulate in aquatic food webs as they are ingested by organisms at the base of the food chain, such as zooplankton and filter-feeding species [52]. These microfibers can then be transferred to higher trophic levels as predators consume contaminated prey. As microfibers move up the food web, they can reach fish and other marine species that are commonly consumed by humans. The potential for microfibers to bioaccumulate in aquatic organisms raises concerns about human health risks associated with the consumption of contaminated seafood [54]. Figure 3 shows the schematic of the sources of waste plastics and their transportation routes.

4.3. Resuspension and Re-Entry into the Water Column

In aquatic environments, accumulated microfibers in sediments can be resuspended and re-enter the water column during various events, such as storm surges, wave action, and dredging activities. When resuspended, these microfibers can once again become mobile and be transported downstream, potentially affecting distant areas [56,57,58]. The cycle of accumulation, deposition, and resuspension can make it challenging to manage and mitigate the presence of synthetic microfibers in aquatic ecosystems [59].

Understanding the mechanisms of accumulation of synthetic microfiber wastes in both aquatic and terrestrial environments is vital for addressing the issue. Effective mitigation strategies should focus on reducing the input of microfibers, enhancing waste management practices, and developing technologies to capture and remove microfibers from the environment, particularly in areas where accumulation is a significant concern.

5. Techniques for the Identification and Detection of Microplastics

Identification and detection of microplastics follow the sampling process and involve a complex procedure to confirm whether the separated particles are microplastics or false microplastics. Various techniques are employed for identification and chemical composition detection, including SEM-EDS, FTIR, NIR, Raman, and NMR spectroscopy [60,61,62]. SEM-EDS is a powerful microscope technique that provides information about the surface and additives present on microplastics. FTIR and Raman spectroscopy are among the best techniques for chemical characterization, offering accuracy without damaging the sample and producing spectra through the interaction of molecules with light [63]. FTIR analysis is suitable for particles up to 20 μm in size, while Raman spectroscopy can be applied to particles as small as 1 μm. Recently, NIR and NMR spectroscopy have also been used for the identification of microplastics [64,65,66]. NIR does not require pre-treatment and can detect particles up to 1 mm in size in environmental samples, while NMR analysis quantifies the amount of microplastics present in a sample.

Table 4. Techniques for identification and detection of microplastics.

Identification Methods	Benefits	Limitations	References
FTIR	Detection of small plastic particles (less than 20 µm) with µ-FTIR Non-destructive analysis of materials Short analysis time	Poor spatial resolution Not suitable for wet samples Difficult to detect MPs with irregular shape	[67]
Raman spectroscopy	Analysis of samples in solutions, gases, films, surfaces, solids, and single crystals is possible Detection of small MPs (1 µm) and NPs (<1 µm) Non-destructive analysis of materials	Requires extensive organic purification of the sample Possible fragments released by adhesive polymers Time-consuming and expensive	[68]
Atomic force microscopy	Three-dimensional images of the surface structure of the polymers No radiation damage to the sample	Damage caused by the interaction of the tip with the sample No prevention against outside factors like contaminations	[69]
Thermal analysis	Characterization of low-solubility MPs and additives	Destructive technique and complex data	[70]
Py-GC-MS	Polymer and mass of MPs are determined Additives and heavy metals adsorbed to MPs can be reported Rapid detection	Not applicable for high-concentration samples Sample destruction Data on the shape, size, and color of MPs are not available Limit of detection > 50 μm	[71]
Optical sensing	Simple Portable Sensor-based detection	Time-consuming Labor-intensive	[72]
Polarized light scattering	MPs’ size and concentration can be determined	Requires sophisticated equipment Inefficiency	[73]

represents different techniques for the identification and detection of microplastics.

6. Treatment Technologies

Wastewater treatment plants (WWTPs) are the primary recipients of MFs prior to their discharge into natural water bodies, and in most cases they escape the WWTPs. There are two broad categories for MF removal in WWTPs: conventional, and innovative. Conventional techniques include settling, filtration, adsorption, membrane bioreactors, coagulation, and flocculation [67,68]. In this section, some innovative technologies for MF treatment are discussed along with WWTPs. Some of these are scalable and are currently in use, while others are in further research and development phases.

6.1. Wastewater Treatment Plants (WWTPs)

The majority of MPs found in wastewater treatment plants come from urban activities (tire damage, paint shedding, plastic/textile industries) and domestic items (cosmetics, exfoliants, scrubbers, and textiles). The wastewater systems are designed to convey effluent water discharged from urban and domestic activities to wastewater treatment plants (WWTPs), aiming to eliminate pollutants prior to their discharge into various water bodies. Peller et al. [58] investigated a WWTP in Michigan, USA, reporting a phenomenal removal rate of 97% for MPs. The majority of removed MPs were sequestered from the sludge generated during wastewater treatment. Leslie et al. [59] reported that WWTP sludge contains an average of 650 MP particles per kilogram of wet sludge. The major concern with these remaining MPs in the sludge is due to their frequent reuse as a fertilizer, which reintroduces MPs into the environment. Dris et al. [60] found that smaller MFs (<800 µm) exhibited a higher likelihood of passing through WWTPs, constituting approximately 70% of MFs in the wastewater. Similarly, Fortin et al. [61] identified MFs ranging from 1 to 10 µm in size as the most prevalent in the water samples extracted post-WWTP. Hartline et al. [62] estimated that if a WWTP serving a population of 100,000 people achieved an MF removal rate of 98.4%, it would still release approximately 1 kg of MFs into water bodies daily. Correspondingly, Uddin et al. [63] reported that, globally, WWTP-treated water contributes to the annual release of 1.47 × 10¹⁵ MPs into oceans, while approximately 50% of global wastewater (especially in underdeveloped nations) remains untreated, resulting in the emission of approximately 3.85 × 10¹⁶ MPs annually. Henry et al. [64] underscored that MPs traversing WWTPs can absorb pathogens from wastewater, transporting them into natural environments.

Table 5. Treatment technologies for removal of microplastics.

Methods	MP Particle Removed	Efficiency (%)	Advantages	Challenges	References
Electrocoagulation	-	90 (pH 3–10) 99.24 (pH 7.5)	Does not rely on chemicals or microorganisms, energy-efficient	Operation time needs to be reduced	[74]
Al and Fe salt	<0.5 mm	45.34	Simple process, does not require additional set-up	Low efficiency	[75]
Wastewater treatment plant	100 μm	99	Conventional process, no additional cost	Not possible to remove MPs of size < 100 μm	[76]
Filtration with granular activated carbon	1–5 μm	56.8–60.9	Efficient to remove plastic particles in the nanoscale size range	Frequent clogging, more regeneration time	[77]
Algal masses	20 μm	94.5	No chemical, electrical, or mechanical operations	Efficiency will vary owing to physiological and environmental conditions	[78]
Membrane bioreactor (MBR)	250 μm	99.3	MBR process helped to retain moremicroplastics compared to the conventional activated sludge process	Not possible to remove MPs of size < 250 μm	[79]
Bioremediation (Ideonellasakaiensis 201-F6)	PET	-	PET could be degraded within 6 weeks	Identification of other microorganisms of the same type that could be more effective for these bioremediation processes is required	[80]
Bioremediation (EPS by Cyanothece sp.)	<300 μm	-	Hetero-aggregation capability at 1 and 10 mg/L of both nanoplastics and microplastics	-	[81]
Air flotation and nano-ferrofluid processes	PE 75 μm, PVC 150 μm, PES 300 μm	PE 85%, PVC 82%, PES 69%	-	Nanofluid particles were ineffective to remove NPs/MPs	[82]

shows different treatment technologies for the removal of microplastics.

Additionally, wastewater treatment plants (WWTPs) play a role in producing secondary MPs, which, upon partial degradation, can manifest as nanoparticles and nanofibers [76]. Conventional WWTP treatment processes, including sand filtration, ultraviolet disinfection, and biological processes, can induce further degradation of MPs into submicron particles, complicating detection and leading to the underestimation of MP emissions in prior studies [79]. The abundance of nanoplastics, estimated to be 1014 times higher than that of MPs due to their origin from fragmentation processes [81], necessitates additional research for a comprehensive understanding of the detrimental impacts of MPs on public health.

6.2. Electrochemical Oxidation

Electrochemical oxidation (EO) is emerging as a promising method for treating microfibers in wastewater, leveraging the principles of electrochemistry to degrade and remove these pollutants. In this process, an electric current is applied to electrodes submerged in the wastewater, generating reactive species such as hydroxyl radicals, which effectively oxidize and break down microfibers into smaller, less harmful molecules [65,66]. The advantages of EO include its ability to operate at ambient conditions, its relatively low energy consumption, and the minimal production of secondary pollutants. This method can be integrated with other treatment processes to enhance overall removal efficiency. As research advances, optimizing electrode materials and configurations aims to further improve the effectiveness and scalability of EO for microfiber removal, making it a viable solution for reducing microplastic pollution in treated effluents.

6.3. Photocatalytic Degradation

Photocatalytic degradation is a cutting-edge approach to treating microfibers in wastewater, utilizing light-activated catalysts to break down these persistent pollutants. Typically, this process involves the use of semiconductors like titanium dioxide (TiO₂), which, when exposed to ultraviolet (UV) light, generate reactive oxygen species (ROS) such as hydroxyl radicals. These ROS effectively degrade microfibers into smaller, non-toxic molecules [83]. The advantages of photocatalytic degradation include its ability to operate under mild conditions and its potential for complete mineralization of contaminants, minimizing secondary pollution. Research is focused on enhancing the efficiency of this method by developing novel photocatalysts, such as doped TiO₂ or composite materials, which can be activated by visible light and offer higher degradation rates [84]. Integrating photocatalytic degradation with conventional wastewater treatment processes could significantly reduce microfiber pollution, contributing to cleaner water bodies and a healthier environment.

6.4. Magnetic Separation

Magnetic separation is an innovative method for treating microfibers in wastewater, leveraging the unique properties of magnetic materials to isolate and remove these pollutants. This technique involves the use of magnetic nanoparticles or beads that are functionalized to bind specifically to microfibers. Once the microfibers are bound to the magnetic particles, an external magnetic field is applied to separate the complex from the wastewater. This method is highly efficient, allowing for the rapid and targeted removal of microfibers with minimal energy input and without the need for chemical additives [85,86]. Research is focused on optimizing the surface chemistry of magnetic particles to improve binding efficiency and selectivity for various types of microfibers. Magnetic separation can be easily integrated into existing wastewater treatment systems, offering a scalable and environmentally friendly solution to reduce microfiber pollution and enhance water quality.

6.5. Activated Carbon Filtration

Activated carbon filtration is a widely utilized method for treating microfibers in wastewater, capitalizing on the highly porous nature and large surface area of activated carbon to adsorb these pollutants effectively. During this process, wastewater passes through a bed of activated carbon, which captures microfibers through physical adsorption and chemical interactions. This technique is highly efficient in removing not only microfibers but also a wide range of organic and inorganic contaminants, contributing to overall water purification [87]. The effectiveness of activated carbon filtration can be enhanced by optimizing the particle size and surface properties of the carbon, as well as by combining it with other treatment methods like pre-filtration and coagulation to reduce the load of larger particles. Regeneration of spent activated carbon through thermal or chemical processes allows for sustainable reuse, making this method both cost-effective and environmentally friendly in managing microfiber pollution in wastewater treatment plants.

6.6. Dissolved Air Flotation (DAF)

Dissolved air flotation (DAF) is an effective method for treating microfibers in wastewater, utilizing air bubbles to separate these fine pollutants from the water. In the DAF process, air is dissolved in the wastewater under pressure and then released at atmospheric pressure in a flotation tank. The released air forms tiny bubbles that attach to microfibers and other suspended solids, causing them to float to the surface, where they can be skimmed off and removed. This technique is particularly advantageous for its ability to handle high loads of fine particles and its efficiency in clarifying water with minimal chemical additives. DAF systems can be optimized by adjusting parameters such as bubble size, air-to-solids ratio, and the addition of coagulants or flocculants to enhance microfiber aggregation and flotation. The integration of DAF in wastewater treatment plants offers a robust solution for reducing microfiber pollution, improving the quality of effluent, and protecting aquatic environments [88].

6.7. Electrocoagulation

Electrocoagulation is a promising technique for treating microfibers in wastewater, utilizing electrically induced coagulation to remove these contaminants. In this process, an electric current is applied to metal electrodes, typically aluminum or iron, which dissolve into the water, releasing metal ions. These ions react with the water to form hydroxides that act as coagulants, binding to microfibers and other suspended particles to form larger aggregates. These aggregates can then be easily separated from the water through sedimentation or flotation [89]. Electrocoagulation is advantageous due to its ability to simultaneously remove a wide range of pollutants, including microfibers, without the need for added chemicals. This method can be fine-tuned by adjusting the current density, electrode material, and operational parameters to maximize removal efficiency and minimize energy consumption [90]. Integrating electrocoagulation into existing wastewater treatment systems offers an effective and environmentally friendly approach to mitigating microfiber pollution and improving water quality.

6.8. Constructed Wetlands

Constructed wetlands have emerged as a promising solution for the removal of microfibers from wastewater. These engineered ecosystems mimic natural wetlands by utilizing vegetation, soil, and microbial processes to filter and degrade contaminants. The mechanism of microfiber removal in constructed wetlands involves a combination of physical, chemical, and biological processes. Firstly, as wastewater flows through the wetland, physical filtration occurs as microfibers become entangled in the dense network of plant roots and settle into the substrate. This root structure acts as a sieve, capturing microfibers from the water column. Sedimentation also plays a role, as the slower flow rates within the wetland allow heavier particles, including microfibers, to settle out of the water. Additionally, biofilm formation on plant roots and substrate surfaces promotes the adsorption of microfibers. Microbial degradation further aids in breaking down microfibers; specific bacteria and fungi in the wetland’s biofilm can metabolize organic components of microfibers, facilitating their decomposition. Through these synergistic processes, constructed wetlands provide an effective and sustainable approach to mitigating microfiber pollution. Sotiropoulou et al. [91] designed one vertical flow constructed wetland (VFCW), planting Zantedeschia aethiopica for the treatment of laundry wastewater. The average concentration of microfibers decreased from 71 ± 25 microparticles/L in the influent to 1 ± 1 microparticles/L in the effluent of the VFCW when an HLR of 63.7 mm/d was applied. Long et al. [92] investigated microfiber removal in a wastewater treatment plant and reported that constructed wetlands contributed to 26.59% of the total microfiber removal, with an overall removal efficiency of 72.38%.

7. Environmental and Health Impacts

Microfiber wastes, primarily in the form of synthetic polyester and nylon fibers, have infiltrated marine ecosystems worldwide. These minuscule particles pose a significant environmental threat by entering the food web. When marine organisms—such as zooplankton, filter-feeding invertebrates, and small fish—ingest microfibers, these particles can accumulate in their tissues. This not only harms individual organisms but disrupts marine ecosystems as a whole. Microfibers can alter the behavior, growth, and reproductive success of marine species, potentially leading to imbalances and population declines [46]. The physical presence of microfibers in the gastrointestinal tracts of marine organisms can lead to a range of adverse effects. These tiny plastic particles can obstruct the digestive system, causing blockages, damage to internal organs, and impaired nutrient absorption. Furthermore, microfibers can act as carriers for toxic chemicals that adhere to their surfaces [52]. In the marine environment, they can release these chemicals, potentially leading to toxicity and disrupting hormonal, metabolic, and reproductive processes in aquatic organisms. In the process of bioaccumulation and biomagnification, microfibers can reach the human diet as well. Microfiber wastes are not limited to aquatic environments. They can also accumulate in terrestrial ecosystems, particularly in soils. This accumulation can affect soil health, microbial communities, and the growth of plants [13]. Microfibers can alter the physical properties of soil, including its texture, porosity, and water-holding capacity. These changes can affect soil aeration and drainage, potentially leading to waterlogging or drought conditions for plants. Some microfibers, especially those made from synthetic materials, can leach harmful chemicals into the soil. These chemicals might include plastic additives, dyes, and other pollutants, which can alter the soil’s chemical composition and pH balance [93]. The presence of microfibers can disrupt soil aggregates, which are crucial for maintaining soil’s structure. Disrupted soil structure can lead to increased erosion and reduced soil stability. The introduction of microfibers can reduce microbial activity by creating a physical barrier that microbes cannot easily penetrate. This can decrease the decomposition rate of organic matter and the cycling of nutrients [94]. Changes in microbial communities might also affect the prevalence of soil pathogens. Some studies suggest that microfibers can create niches for pathogenic microbes, potentially increasing the incidence of plant diseases. Microfibers can physically impede roots’ growth and development. Roots may struggle to penetrate soils laden with microfibers, leading to stunted growth and poor plant health. Plants might absorb harmful chemicals leached from synthetic microfibers through their roots. This can lead to phytotoxicity, affecting plants’ growth and development [83].

While research on the direct health impacts of microfiber ingestion through contaminated seafood and inhalation of airborne microfibers is ongoing, there is growing concern about potential risks to human health (Figure 4). Ingested microfibers may release plastic-related chemicals into the human body, and while the long-term effects are not yet fully understood, they may lead to a range of health problems. Airborne microfibers may reach the respiratory system, potentially causing respiratory irritation and inflammation. Studies have also raised concerns about the potential for microfibers to act as carriers for harmful microorganisms, introducing pathogens into the human body. Microfiber pollution can have aesthetic and economic consequences. Accumulated microfibers on beaches and shorelines can deter tourists, impacting local economies and tourism-dependent communities. The unsightly presence of microfibers in the environment also diminishes the natural beauty of landscapes and can negatively affect people’s quality of life [95,96].

Addressing the environmental and health impacts of microfiber wastes is a complex and multifaceted challenge. Solutions involve reducing the release of microfibers from their sources, improving waste management practices, developing effective filtration and treatment technologies, and advancing our understanding of the long-term effects on both the environment and human health. Public awareness and policy initiatives are also essential for mitigating the detrimental effects of microfiber pollution and protecting both ecosystems and human well-being.

8. Mitigation and Solutions

This section presents descriptions related to the mitigation and solutions for addressing microfiber wastes:

• Textile manufacturing innovations: One of the primary strategies for mitigating microfiber pollution is the development and use of sustainable textiles. Designing and producing clothing made from natural fibers (cotton, hemp, and wool) or less-shedding synthetic materials can significantly reduce the release of microfibers during washing and use [97,98,99]. Additionally, treatments such as surface coatings can make fabrics more resistant to abrasion. Sustainable textile manufacturing should prioritize the use of biodegradable or low-impact materials and incorporate innovative design and production techniques that minimize microfiber shedding.
• Wastewater treatment enhancements: Enhancing wastewater treatment technologies is crucial in reducing the release of microfibers into the environment [92]. Advanced filtration technologies such as membrane bioreactors, magnetic separation, and advanced oxidation processes can improve microfiber capture [77,79,81]. Implementing bio-based flocculants can also help in aggregating microfibers for easier removal. These systems can be integrated into existing treatment plants to improve their efficiency in removing microfibers.
• Microfiber filtration: At the household level, the installation of microfiber filtration devices (PlanetCare filter, XFiltra, Filtrol, etc.) in washing machines is an emerging solution. These devices, often referred to as microfiber filters or laundry filters, capture microfibers released from clothing during the wash cycle [100]. By preventing the release of microfibers into wastewater, they represent a proactive approach to reducing microfiber pollution at its source.
• Public awareness and education: Public awareness campaigns and consumer education are essential for combating microfiber pollution. Individuals can take steps to reduce their contribution by washing synthetic garments less frequently, using cooler water temperatures, and using laundry bags specifically designed to capture microfibers. Being informed about the environmental impacts of microfibers and making sustainable choices when purchasing clothing can also make a significant difference [100].
• Regulatory and policy measures: Governments and regulatory bodies can play a vital role in addressing microfiber pollution by implementing and enforcing regulations that require manufacturers to develop more sustainable products and textiles. Legislation can set standards for microfiber shedding and encourage the adoption of best practices for reducing pollution at the source [101,102].
• Research and innovation: Continued research is essential for understanding the full extent of the problem and identifying effective mitigation strategies. Scientists and innovators are working to develop new materials and coatings that shed fewer microfibers and exploring the use of natural and biodegradable alternatives to synthetic textiles [103]. Innovations in textile recycling and circular economy models are also being explored to reduce waste and microfiber emissions.
• Circular economy and recycling: Promoting the recycling of textiles can reduce the need for virgin synthetic fibers and decrease microfiber pollution. Closed-loop recycling systems where textiles are collected, processed, and remade into new fabrics can help create a circular economy [104]. Encouraging manufacturers to establish take-back programs for old clothing can ensure textiles are recycled rather than discarded.

Mitigating microfiber pollution is a complex challenge that requires collaboration among governments, industry, scientists, and consumers. A combination of approaches, including the development of sustainable textiles, improved wastewater treatment, consumer education, and regulatory measures, is necessary to address this pressing environmental issue. By taking proactive steps at multiple levels of society, it is possible to reduce the release of microfibers into the environment and protect aquatic and terrestrial ecosystems from the harmful effects of microfiber pollution.

9. Conclusions

In conclusion, the sources, transport, and accumulation of synthetic microfiber wastes in both aquatic and terrestrial environments represent a multifaceted environmental challenge with far-reaching consequences. The origins of these microfibers are diverse, ranging from textile manufacturing and the fashion industry to plastic products, fishing gear, and urban runoff. Once released, microfibers can be transported over long distances through various pathways, affecting both marine and terrestrial ecosystems. Their accumulation in sediments, soils, and food webs has ecological repercussions, threatening the health of aquatic organisms, disrupting terrestrial ecosystems, and potentially impacting human health through the food chain. Addressing this issue requires a holistic approach, encompassing improved waste management, innovative textile production methods, enhanced filtration technologies, and greater public awareness. Only through collaborative efforts at the global, national, and individual levels can mitigation of the environmental and health risks associated with synthetic microfiber pollution be achieved. Reckless and excessive consumption of plastic products should be curbed and potentially even regulated by legislation, particularly in developed countries.