Micro- and Nanoplastics Produced from Textile Finishes: A Review

Abstract

The problem of increasing plastic pollution has emerged as a significant societal issue. Plastics can originate from various sources, and there is growing concern among researchers to study and investigate this new category of pollution. The plastic waste is found at the macro, micro, and nanoscale, and its study has had great significance according to the perspective of posing hazardous impacts on living organisms. Given the high demand for functional textiles, the textile industries are supporting the coating of different polymeric based finishes on the surface of textile products. The plastic debris emitted from these coated finishes are in the ranges of nanometric scale, so-called polymeric nanoplastics (PNPs). With the new terminology, polymeric nanoplastics (PNPs) released from textile finishes or coatings are being increasingly mentioned, and the term fibrous microplastics (FMPs) can be seen as outdated. This study is based on an intensive review of a very novel category of debris plastics (PNPs) mostly produced from textile finishes or coatings. In fact, FMPs and PNPs released from synthetic textiles and textiles coated with plastic-based finishes during washing activities are considered to be a major cause that contributes to the current overall load of microplastics (MPs) in the environment. A link between the concentration of NPs from textile fibers and NPs from textile polymeric-based coatings in freshwater and sediments within a particular local setting and the extent of activities of the textile industry has been demonstrated. Invested efforts have been paid to consider and concentrate on plastic pollution (nanoplastics from textile polymeric coatings). We also summarize existing methodologies to elucidate the identification and proactive quantification of nanoplastics shed from the textile polymeric coatings. To this end, more than 40 studies have been done to identify the physical, chemical, and mechanical parameters and to characterize nanoplastics.

Introduction

Microplastic pollution (MPs) pollution is a significant issue of concern with environmental challenges of the present 21st century. The subject refers to the release, emergence, and accumulation of plastic based fine particles and their adverse risks to both the environment and human health.¹ The general definition of microplastics (MPs) can be termed as the tiny plastic particles having sizes (length wise and diameter) in the range from 1 μm to 5 mm.² While the finest plastic debris with a size smaller than 1 μm is classified as nanoplastics (NPs).³ The plastic fibrils and coatings (micro-/nanosized debris) sheds off textile fabrics during its whole life span (from production until disposal) due to various kinds of mechanical and physical actions.⁴ In addition, during washing on the industrial scale and domestic laundering, these plastic components also diffuse to wastewater and emerge into the environment.⁵ Based on a report, a single piece garment such as a T-shirt made of 100% polyester can release over (401 ± 17 to 437 ± 35 mg per kg of washed fabric), 4,000,000 microfibers during a single washing cycle.⁶ The domestic and industrial washing of textiles is a significant source of MPs in wastewater, comprising up to 62% of all MPs found in aquatic ecosystems.⁷ The textile industry plays a pivotal function in adding MPs and also releasing polymeric coated natural microfilaments (MFs), such as the coating of polymeric finishes over cotton or wool, etc. The emissions of polyester microfibers have been reported in four scientific papers.⁸ They observed the quantity of fibers that are released from various polyester garments. In addition, microplastics derived from chemically treated materials or from polymeric coatings may pose as a vector for toxic chemical pollutants.⁹ Multiple research works have been performed to analyze the mitigating effect of several kinds of polymeric based finishes over the fiber’s fragments/filaments. The chemical treatment has been used to induce different functionalities in textiles. Generally, the common functional finishes used for textile coatings are antistatic agents, plasticizers, flame retardants, stabilizers, lubricants, antioxidants, and slip agents.¹⁰ Each of these finishes plays a unique and vital function not only in delivering but also in increasing the various types of functional properties of textiles, including flame retardancy, hydrophobicity, softness, hardness, antimicrobial ability, antistatic charge dissipation, etc.; for example, plasticizers including phthalic esters (PAEs) are widely utilized to improve the durability, flexibility, and stretchability of synthetic fabrics.¹¹ Phenolics, arylamines, and organophosphates are usually used as antioxidants.¹⁰ Such antioxidants not only give protection to natural cotton fabrics but also guarantee the safety and excellence of the end use of cotton fabric for hygienic purposes. However, the hazardous effects of these finishes on human health and on the aquatic environment are still a topic of current research and study because of their changing physical and chemical characteristics.¹²

As mentioned in the aforementioned section, a huge scientific literature is present on the release of MPs in wastewater from textile fibers. However, on the other side, the release of MPs or NPs from textile finishes or coatings into wastewater still has fewer research studies. Moreover, we did not find any review reports on the durability of these polymeric textile finishes and their impact on the release of micro-/nanoplastics in the environment. This study was preliminary: to consider and concentrate on plastic pollution (nanoplastics from textile polymeric coatings). Subsections of the review elaborate on the existing methodologies to elucidate the identification and proactive quantification of nanoplastics shed from textile polymeric coatings. Hence, the present comprehensive review explores two basic objectives; first, to understand the concept of using different polymeric based finishings on the surface of fibers to produce functional textiles, and second, to have a better understanding about the terminology and the polymeric nanoplastics (PNPs) released from textile finishes or coatings. Additionally, the further sections allowed us to preliminarily investigate the various methods to investigate the production of nanodebris from textile polymeric finishes, their recovery from textile effluent, their separation, centrifugation, and filtration, and various techniques of characterizations. Furthermore, present efforts and future remarks have been included to improve the situation of microplastics hazards. Moreover, the review also highlighted the current efforts and future strategies to tackle microplastic pollution.

Textile Fibrous Microplastics and Their Release

In recent years, the attention of researchers has been drawn toward the term “fibrous microplastics” (FMPs), a novel category of microplastics famous for their unique behaviors such as specific dimensions, flexibility in shapes, important sources of release, and availability in the environment. Normally the fibers are categorized into two main classes. Natural fibers can be obtained by both natural as well as plant sources (e.g., cotton, hemp, flax, or other cellulosic fibers), from animals (e.g., silk or wool i-e made of proteins), or inorganic-based (e.g., asbestos, which is composed of silicate minerals).¹³ Alternatively, synthetic fibers can be categorized as both inorganic (such as carbon, glass, or metal fibers) and organic variations derived from polymers. Man-made organic fibers (see Figure 1) typically fall into two categories: fibers resulting from the alteration of natural polymers and fibers produced from synthetic polymers. Additionally, synthetic fibers encompass a diverse range of materials synthesized from synthetic polymers, e.g., polyester (PES), PP, polyacrylic (PAN), and polyamide (PA). At this stage, synthetic fibers can be categorized into two groups: those created from petrochemical polymers (e.g., PA, PP, PES) and those resulting from the chemically altered natural polymers (e.g., cellulose acetate). Biopolymer-based (or biodegradable) fibers, such as PLA, must also be recognized as a source of FMPs. Due to their emerging status and their position as a specialized material group, they are not foreseen to have a substantial impact on the current FMP levels in the environment. However, this scenario could evolve in the future.

Figure 1.

Classification of fibers. Redrawn with permission from ref (15). Copyright [2021], [MDPI].

According to this definition, microparticles originating from synthetic textiles¹³ are made up of for example PA, PLA, PES, and cellulose acetate can be classified as MPs. On the other hand, microparticles released from cellulosic and regenerated cellulosic fabrics are not categorized as MPs. Many available studies do not steadily distinguish among regenerated, natural, and synthetic fibers when describing detected fibrous microparticles. This absence of distinction can potentially lead to inaccurate assessments of fibrous microparticles (FMPs) release and their environmental concentration. In this review article, we mention the term “FMPs” to specifically refer to synthetic fibrous microparticles characterized by lengths ranging from 0.1 μm to 15 mm and a length-to-diameter ratio exceeding 3. FMPs released from synthetic textiles are frequently treated as secondary MPs, and PNPs refer to nanoplastics called polymeric nanoplastics (the plastic debris emitted from these coated finishing lies in the range of the nanometric scale).¹⁴

Fibrous microplastics (FMPs) have been extensively discovered in huge quantities in urban settings including indoor environments¹⁶ and wastewater treatment plants (WWTPs).¹⁷ Moreover, they are prevalent in various natural environmental domains, including freshwater sources,^16,18 oceans,^19,20 soils,²¹ and air,^22,23 as well as remote ice and polar regions.²³ In fact, the key origin that contributes extremely to the production of fibrous microplastics is textile washing. Washing synthetic textiles has been identified as a primary origin of microplastics (MPs) and polymeric nanoplastics (PNPs) in wastewater treatment plant (WWTP) effluents.²⁴ It has been approximated that textile washing accounts for a minimum of 70% of the fibers entering WWTPs subsequently finding their way into the environment.²⁵ Numerous research studies have been conducted to determine the quantities of nanoplastics that are shed during the washing of these textiles. They have also explored the various factors involved in the whole process that could influence FMP and PNP release, ultimately resulting in direct discharge through WWTPs.²⁶

Some studies focused on assessing the release of fibers during textile washing have revealed a wide variation in the mass of shed FMPs and PNPs. The fibers examined in these washing experiments generally fell within the size range of 20–5000 μm, considering measurement and mesh sizes. Although there were cases of FMP release rates as low as zero, the majority of observed values for FMPs present in the washing effluent from the initial wash varied from 0.0012% to 0.042% by weight. On average, an individual consumes almost 5.5 kg of new textiles every year, while generating about 5.0 kg of household laundry per week (as per the studies involving laundry practices in Germany).^27,28

Consequently, it is possible to estimate the annual fiber release for every 100,000 individuals. These estimates range from 50.6 to 1180 kg of FMPs. When considering the German population, this results in a total FMP release of 42 to 979 tons per year, which aligns with the emission range reported by UBA, namely, 80 to 400 tons in Germany. Additionally, the suggested laundry rate of 5.0 kg per week per person, calculated based on an average of 3.3 kg per wash for Germany²⁷ is comparable to the estimate for Europe as a whole (3.7 kg per wash). Therefore, this estimate can also be applied to many other European countries. A projected annual on release of FMP for “fast fashion” to represent a potential “worst-case” scenario was also evaluated.

The study was involved by using three separate front-loading washing machines. Only washes were made in simple tap water without the use of any detergent or conditioner. Their final finding indicated that each wash of a garment can release more than 1900 fibers. In a study Dubais and Libezeit²⁹ observed that fibers discharged from polyester garments ranged from 0.033 to 0.039% w/w each washing. Nevertheless, these studies failed to provide detailed information on their selected methods and technical conditions. Furthermore, according to a recent study by Setala et al.,³⁰ on pure polyester fabrics, they used two types of polyester fabrics, one quite new and a second mechanically aged polyester cloth. The mechanically worn-out polyester garments released fibers masses exceeding 0.3% by weight of the unwashed garment mass throughout all treatments. The experiments in these three studies were conducted without the use of detergent.³¹ In a set of ten gentle and successive washes of polyester fleece textiles, it was discovered that fiber emissions initially decreased and eventually reached a stable level. Under the specific washing conditions considered, the inclusion of different types of liquid detergents and fabric softener did not have a notable impact on the level of fiber emissions.^32,33 Cotton fibers have a more diversified chemical composition than synthetic fibers, with functional groups such as hydroxyl and carboxyl present. Consequently, natural and synthetic fibers, in their capacity as sorbents and carriers, could potentially play distinct but significant roles in determining the environmental destiny of hydrophobic compounds. Recent studies have made significant progress in identifying the sources and pathways of microplastics in the environment.³⁴ Among the significant channels is wastewater treatment plants, which are affected by the load of washing garments and personal care goods.³⁵ Polyester and cotton are the most common textile fibers, along with a demand of 46 and 24 million tons, respectively, on an annual basis. A research study was carried out to observe the emissions of polyester and cotton fibers during machine washing of selected new and unused fabrics. The quantities of liberated polyester and cotton microfibers were determined using gravimetric and microscopic analysis of samples obtained from five consecutive wash cycles. Concentrations were expressed in terms of both mass and number of fibers per textile mass and surface area. Moreover, the study calculated the annual emissions of microplastics from household sources. They claimed that during the cleaning task, five partners take an action in cooperation: which are nominated as detergent, textile material, water, stain, and washing machine. Here, water not only acts as a substrate for transferring mechanical and thermal energies but also helps in cleaning and washing purposes. Various physiochemical processes and parameters involve the textiles washing procedure. The most important factors that affect washing procedures include mechanics, time of washing, temperature, and chemistry of the chemicals.³⁶ Their combine actions are responsible for an adequate washing effect.³⁷

In a recent study a freshly prepared single jersey PES knitted fleece fabric was subjected a number of washing cycles.³⁸ The physical appearance of the fabric was analyzed after each wash. The reduction in fibrous assembly over the fabric structure was analyzed. The visual detection found a significant difference between the sample after the first wash and after the 10 cycles. The results of microscopic analysis are shown in Figure 2.

Figure 2.

(a) Microscopic images of (b) microplastics removed from the surface of PES fleece fabric after washing and drying [results related to present research obtained from a lab report, at TUL].³⁸

Moreover, the data were interpreted statistically. A comparison of release of the microplastics during different drying cycles and release of microplastics during different washing cycles was done, and results are shown in Figure 3(a). It was noticed that the release of microplastics is more during the drying procedure as compared to the washing. The reason is that in wet conditions the fibers may remain entangled with each other due to different cohesive forces and weak hydrogen bonding. These forces may not be retained during the drying process and in turn the loosely held fibers are released sharply in the environment. The household washing machine is effective in washings as it reduces the washing time by severe mechanical agitation (action).³⁹ According to results of advance research numerals of microfibers released from polyester and cotton fabrics, after the first washing cycle it differs from 2.1 × 10⁵ to 1.3 × 10⁷ and a huge number of fibers are released from cotton fabrics. In fact, the results showed that the annual release of microfibers in Finland was approximated to be 154,000 kg (PES) and 411,000 kg (cotton). Synthetic waste discharge from washing machines contains release fibers which carry wastewater with the sewage system and are accumulated and float in them shown in Figure 3(b).³⁷

Figure 3.

(a) Release of microplastics during washing and drying [results related to the present research obtained from a lab report, at TUL]. (b) The microfibers shedding mode. Reprinted with permission from ref (37). Copyright [2022], [MDPI].

Need for and Functions of Polymeric Finishes on Textile Surfaces

The most common functional finishes include water repellents, antimicrobials, flame retardants, softeners, crease recovery, and UV protecting. Also some important effects are obtained through different coating agents such as antistatic agents, antioxidants, plasticizers, lubricants, stabilizing agents, and slip agents.⁴⁰ These polymeric finish coatings based on polymers such as polyamide, polypropylene (PP), polystyrene (PS), polyethylene (PE), polyvinyl chloride (PVC), polyethylene terephthalate (PET), and microplastics can also originate from less common plastics like polycarbonate. Such polymers make a layer on the surface of fibers in order to protect them against various physical and mechanical actions. However, these polymeric layers can be released in the form of micro-/nanosized debris along with the fragments of fibers because of the abrasion caused by wear and washing activities. Table 1 contains the different functional finishes based on different polymers.

Table 1. Different Textile Polymeric Functional Finishes.

Sr. no.	functional name of finish	performed function	polymer used	ref
1	Water repellent finishes	Hydrophobic barrier repelling water	Polytetrafluoroethylene (PTFE)	(41)
2	Flame retardant finishes	Reduce the flammability	Phosphorus-containing polymers	(42)
3	Antistatic finishes	Reduce the buildup of static electricity	Conductive polymers	(43)
4	Antimicrobial finishes	Inhibit the growth of bacteria, fungi, odor control	polypyrrole, polythiophene, polyaniline	(44)
5	Abrasion-resistant finishes	Improve their resistance to abrasion and extend the lifespan applications	Polyurethane, epoxy	(45)
6	Softening finishes	Softening finishes improve tear strength; abrasion and wrinkle resistance; stretch recovery and avoid shrinkage reduction	Silicone polymers, polyethylene emulsions, cationic polymers	(46)
7	Antipilling finishes	Reduce friction between fibers, minimizing pilling	Acrylic polymers, quaternary ammonium compounds	(47)
8	wrinkle-resistant finishes	Reduce the need for ironing, which helps them retain their shape	Polydimethylsiloxane, polyvinyl acetate (PVA)	(48)
9	Moisture management finishes	Suitable for activewear and outdoor clothing	Polyethylene glycol (PEG)	(48)
10	UV-Protective Finishes	Absorb or reflect harmful ultraviolet (UV) radiation, helping to prevent sunburn and skin damage	Acrylics, polyurethanes, epoxies	(49)

Several research works elaborated the mitigating effect of various finishing treatments over fiber segments. The chemical treatments can minimize the release of protruding fibers by developing the strong interaction and linkage to the surface of the textile. A variety of resins such as acrylic resin, polyurethane resin, and silicon emulsion were used on different synthetic fibers by the process of padding on an exhaust finish machine.^50,51 Similarly, another study described the effect of softness in fabric due to silicon emulsion than in the pure PET fabric, but the pilling tendency was worse. The washing testing revealed that silicon emulsion coated fabric released significantly less fiber pieces than other treatments. The main reason for this reduction is the decreased friction between the fabric and the detergent when using the silicon finish, which results in a softer surface on the PET fabric.⁵² Acrylic resins exhibit noble pilling resistance out of the carefully chosen auxiliaries along with the fabrics (PP, PET, PAN, and PA), and this kind of pattern was seen in both woven and knitted fibers fragments release which was reduced by De Falco⁵³ on a PA fabric through an easy pectin-based treatment. Other research was conducted where grafting of the PEC-GMA emulsion on PA fabric was done. In their research, Maior et al.⁵⁴ effectively explained the chemical interaction between PEC-GMA.⁵⁴ As per the ISO 105-C06:2010 standard test method, PEC-GMA-PA and pristine-PA fabrics were subjected to a wash for almost 45 min at 40 °C using a commercially available detergent (Ariel). The results showed that the pristine-PA fabric released 0.359 g of fibers fragments per kg of wash, with a length of 12 ± 222 μm and a mean diameter of 18 ± 3 μm. On the other hand, PEC-GMA-PA effectively reduces the presence of fiber fragments, with varying mean lengths of about 550 ± 384 μm, diameter of 16 ± 4 μm, and 0.058 g fiber fragments per kg of fabric. Then the analyzed reduction in fibers was almost 90%, which is a significant difference. A number of studies are available on the coating of biodecomposable polymers such as polylactic acid and poly(butylene succinate-co-butylene adipate) (PBSA), which have been applied to the polyamide (PA) fabric using the electrofluidodynamic (EFD) coating method.⁵⁵ A uniform surface coating is more effective against mechanical actions and may avoid the release of polymeric coating, as it creates a consistent surface layer that shields it from chemical and mechanical reactions, even during a severe laundering process. Following washing, pristine PA fabric may release an estimated 0.35 g/kg of fiber fragments. On the other hand, it was found that the final PA fabric containing PLA and PBSA released 63.4% and 76.8% fewer fiber fragments upon the PA fabric, respectively. Moreover, 15–20% of the mechanical qualities are lost during the severe washing and polishing process.⁵⁴ Furthermore, PLA offers greater endurance than PBSA coatings and is durable for at least five washing cycles. Figure 4 shows some common polymeric finishes to achieve functional properties of textile.

Figure 4.

Structural design of the most common types of textile polymeric finishes. Reproduced with permission from ref (52). Copyright [2021], [Elsevier].

The subsequent sections of this review aim to briefly describe the existing available studies and data related to PNPs released from textile coatings or finishes. The focus was particularly on laundry in order to know the amount of polymeric nanoplastics (PNPs) released from textiles during washing, the retaining and emission capacity of PNPs in various steps of the treatment process, the biological degradation of released PNPs, and the analytics of these PNPs and proactive measuring, separation, and characterization methodologies.

Production of Polymeric Microplastics (PMPs) and Polymeric Nanoplastics (PNPs) from Different Textile Finishes

In wet textile, the micro- and nanoplastics can originate from various sources, including different polymeric finishes and materials used in various applications. Fabrics often undergo various polymeric treatments and finishes, including coatings and laminates, to enhance their properties. Over time, during each washing cycle, these polymeric finishes can degrade, leading to the release of microplastic to nanoplastics into the environment. In fact, two types of plastic waste will be produced from textiles in this case: (1) nanoplastics released from polymeric coatings and (2) the segments of synthetic fibers bonded with polymeric coatings. Microplastics can be released from textile coatings.⁵⁵ The release of FMPs, PMPs, and PNPs occurs during textile washing, with synthetic textiles being a major source. The amount of PMPs released can vary depending on factors such as fabric structure, washing conditions, and external factors like friction.⁵⁶ Smart coating textiles, which utilize microcapsules for controlled release of active substances, can also contribute to the release of microplastics. Synthetic fibers including polyester and polyamide, commonly used coating materials in textiles, have the ability to release microplastics.

A wide range of polymeric coatings, finishes, and materials may be involved to produce the PMPs pollution. Eroding and release of micro-/nanoplastics continuously occurred during the entire lifespan of polymeric coated textiles, including cleaning and washing, during their production or disposal. Thus, the fibers and coatings of plastic could get into the environment through wind accumulation, landfill leaching, and wastewater treatment (WWT) plant discharges.⁵⁷ The following schematic illustration contains a pictorial view of a life cycle assessment considering monitoring, management, and mitigation techniques concerning the release of polymeric-coated fibers into the environment and their sustainability. Figure 5 shows a schematic diagram of PMPs or polymeric (PNPs) released from different polymeric substrates and their release and transport pathways to the environment.⁵⁸

Figure 5.

An overview of polymeric microplastics (PMPs) or polymeric (PNPs) released from different source materials and products and their emissions and transport pathways to the environment. Redrawn with permission from ref (58). Copyright [2022], [Elsevier].

The washing of synthetic textiles, which already contain polymeric coatings over their surfaces materials, has gained public attention and environmental concern with respect to PMP release. In reality, mechanical stirring and abrasion can be driven by the release of polymeric plastic coatings from synthetic fibers during the washing process. The International Union for Conservation of Nature (IUCN) proposed in 2017 that fibers produced during the laundering of synthetic textiles are the largest contributor of global micro- and nanoplastics into the oceans, representing 35% of the total.⁵⁹ The Fraunhofer UMSICHT Institute conducted an analysis of 74 environmentally important microplastic sources and estimated that FMPs originating from synthetic textile laundry activity ranked 10th in the list of top 10 FMP sources (with an approximate emission of 76.8 g per year).⁶⁰ However, the estimates were based on various assumptions and were incomplete or difficult to compare with analytical data. Despite the various methodologies, criteria, and measurement scales used, as well as the potential limitations in source ranking, synthetic textile washing has been identified as a significant contributor to FMPs, PMPs, and PNPs in the environment.⁶¹ In fact, these synthetic textile laundry activities that have been marked as an important source of FMPs also contain polymeric finishes in the environment.^35,62

Synthetic fibers, such as PET, PA and PU, commonly used coating materials in textiles, have the potential to release microplastics. These polymers introduce multifunctional properties such as water repellence, durability, breathability, wind proofing, softness and hand feel, abrasion resistance, UV resistance, elasticity, and stretch recovery. Besides being an exclusive application in clothing and home fabric, PET knitted fabric also acts as a raw material or as a base fabric for the functional coating of polyurethane synthetic leather (PU leather). A research study conducted by Shi et al. described the pattern of photodegradation of polyurethane coating over PET base fabrics. The main focus was to demonstrate the potential for chain scission and physical and chemical changes (such as surface morphology, crystallinity, and molecular weight). The production of MPFs and MPPs was distinguished. When compared with pure PET-P (layer of polyester finish over polyester fabric), PET-U (layer of polyurethane over the polyester fabric) followed the same but time-taking pattern in many properties and debris release rates as the time for photoaging was extended. Moreover, after almost 360 h of illumination, the generated NPs (including MPs and NPs) rose significantly to 9.3232 × 10⁷ MPs/g, and the amount of released NPs reached about 2.70 × 10¹¹ NPs/g from PET-U. The researchers used UV stimulus light to intensify the discharge of MPFs. After their interaction with UV irradiation, a huge amount of MPFs were split away from the textile substrate. Initially, both PET fabrics released a few fragments in the irradiation process. After that they showed much higher NPs including FMPs release, particularly after 240 h of the irradiation process (Figure 6). The production of NPs including FMPs from PET-U increased slowly during the initial 180 h of UV light exposure to continue the aging process. The average number of NPs rose to 4.97 × 10⁷ NPs/g after 360 h of irradiation. However, the number of NPs that were released from PET-P was 6.32 × 10⁷ NPs/g after 360 h of light aging. The same trend was also observed in the case of length and diameter. Greater length and big diameters were observed against PET fabric without coating.⁶³

Figure 6.

Release and assessment of polymeric fibers (a) with respect to weight (gram), (b) with respect to length (μm), and (c) with respect to diameter (μm). Reprinted with permission from ref (64). Copyright [2023], [ACS].

PE is the most commonly used to achieve hydrophobic surfaces. However, the presence of NPs generated from PE coatings on textiles can have potential health risks and may impact nutrient digestion and absorption.⁶⁴ A research study was carried out to find empirical evidence for indicating the release of polyethylene-based additives at the oceanic water surface as compared to the deep seawater, where the main plastic constituents were estimated to pass through, before entering the sediment layer. Another study deeply analyzed the release of plastic debris from soft polyvinyl chloride (PVC) plastic coatings and polyethylene (PE) in marine water. The polymeric debris was observed in the sample collected from natural surfaces and deep marine water, and was subjected to darkness at about 13 °C (Mediterranean deep seawater temperature) for almost 30 days. Based on their experiments, the researchers claimed the presence of PE coating is the most common polymer in the marine ecosystem.⁶⁵ Moreover, an additional research investigated the yield of nanosized plastic debris, resealed from low-density PE. The resultant yield contained PE nanometer sized plastic particles at number densities >10¹² L^–1 when subjected to several washes in water. The amount of released particles was based on the function of the initial temperature of water (ranging from high temperature vs ambient) against each of the tested substrates. The average diameter of obtained plastic particles was observed in the range of 30 to 80 nm, although very with few particles were found <200 nm.⁶⁶ Polytetrafluoroethylene (PTFE), a class of engineering thermoplastics that contain fluorine atoms in their chemical structure, is mostly used as a heat resistant and thermal barrier in firefighter clothes applications. Some well-known examples of fluorocarbon plastics (fluoropolymers) coatings over the textile and their released are well described.⁶⁷ Mondal et al. performed hydrophobic fluorocarbon based coating over the cotton fabric surface. He claimed fluoropolymers have good resistance to chemical attacking variety of functional coatings.⁶⁸ The PTFE coating on textiles has also been studied to increase the mechanical performance of fibers. Andrzej et al. explored the effect of washing on the mechanical characteristics of two specific PTFE-coated, glass threads woven fabrics. The tensile strength reduction, occurring when submerged, ranged from 5% to 16%, which mainly depends upon the type of coated woven fabric and the orientation of the weft or warp.⁶⁹ Moreover, a single scratch over the Teflon coating may generate around 9100 micro or nano plastics.⁷⁰ The most critical condition accounts, when the coating is breached during washing, and it generates approximately 2.3 million neoplastic particles debris.⁷¹ Nag et al. documented a research methodology for the degradation of poly tetrafluoro ethylene (PTFE) coatings in water. The effluent was subjected the high-resolution mass spectrometry. During the mechanical action and wear/tear process spectrometry detects around 53 mg of the polymeric nano fragments of fluorocarbons.⁷² Moreover, they claimed the reduction in strength (due to release of PTFE coating) of textile fibres and also a noticeable adverse effects of nano-plastics on human health and also the environment. The stress strain curves of glass fibers composed fabrics coated with PTFE, tested in different directions (warp and weft wise) before and after washing are shown in Figure 7.

Figure 7.

Stress–strain curves, S type fabric: (a) before washing and (b) after washing. Reprinted with permission from ref (70). Copyright [2022], [MDPI].

Another well-known polymer is melamine, indeed a type of plastic, but it is more accurately described as a thermosetting plastic resin rather than a traditional thermoplastic. It has unique physical properties such as durability, heat resistance, and flame retardancy, which make it a demanding material to produce functional textiles. Nile Red shows the slow release of the tiny plastic contents of about 176 particles/L (p/L) with the higher production (261 p/L) from polystyrene and melamine coatings. Researchers conducted a spectroscopic analysis on a much larger data set of polystyrene/melamine coated materials.⁷² Furthermore, they also observed the effect of surface roughness of plastic particles on the obtained spectra. Additionally, they also carried out photoluminescence excitation (PLE) spectroscopy in order to monitor the optimum excitation wavelength for the coated materials.⁷³ Higher microplastic production took place in a “hot” environment (192 p/L) relative to “cold” treatment (90 p/L). Another study claimed that repeated washing of a melamine coated bowl showed microplastic production was an order of magnitude greater after washing 100 times (394 p/L) relative to a bowl washed once (18 p/L).

Nanoplastics (NPs) impurities in rivers and lakes are of predominant environmental significance, as pure water systems deliver NPs from land to sea. An analysis showed NPs in the Taipu River, where there is an extremely advanced fabric industry in the Yangtze River Delta, China. Studies showed an extensive presence of NPs pieces with concentrations of 0.65–6.07 items/L and 0.30–3.63 items/L in the top and lower water surface. Translucent fibers 100–500 μm size with crucial NPs structures were investigated.⁷⁴ PET is considered 71.4% and 59.73% of the total FMPs and NPs recognized in top and lower water surfaces individually. These PET polymers were essentially exhibited in “fibrous” shapes, further showing the main sources of fabric wastewater. On the other hand, polyvinyl acetate (PVAC), utilized as textile film and resin matrix, was essentially represented as a fabric coating to form functional nonwoven fabrics. Despite threat analysis showing a low to average threat of NPs in the Taipu River, the wastewater from textile production seems to possess an excessive graywater footprint enhancing the threat of MPs contaminant from the polymeric coated fabric life cycle production. The research also helped to filled the gap between the data obtained from field and policymaking concerning NP management generating knowledge about cleaner textile manufacturing.⁷⁴ The dimethyl dihydroxy ethylene urea (DMDHEU) polymer was primarily used among various types of polymers, while it is frequently used in the industry because of its cost effectiveness and having excellent wrinkle recovery characteristics.¹⁷ This is normally applied over the fabric structure in combination with fixapret ECO. The Fixapret is a well-known modified cross-linker based on methanol, DEG, and DMDHEU. In fact this modified cross-linker has a huge advantage because of its low levels of formaldehyde contents.⁷⁵ A study was conducted to analyze the length and width of cotton fibers modified with different types of polymeric functional finishes. The manufactured single jersey knitted fabric was composed up of 100% cotton (pretreated scoured and bleached).⁷⁶ The finishes were applied through the Pad-Dry-Cure method with an applied pressure of 40 psi, during a time interval of 0.7 m/min, and applied 1 dip and 1 nip, and dried at 121 °C for 90 s. Subsequently, the finished applied textiles were cured at 171 °C for 45 s and postcured at 177 °C for 60 s.

Separation, Quantification, and Characterization

Prior to the explanation of characterization, it is crucial to have an understanding of the methods for separating and quantifying micro- and nanoplastics. The obtained MPs/NPs that are extracted from the aqueous phase are analyzed through vacuum filtration,⁷⁶ centrifugation,⁷⁷ and density separation⁷⁸ methods. These MPs/NPs are also quantified through optical spectroscopy, Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), nuclear magnetic resonance (NMR) spectroscopy, and stereo-microscopy. Moreover, most of the time, microscopy is coupled with Fourier transform infrared spectroscopy (micro-FTIR), with near infrared (NIR), or coupled SEM with NMR. In the same way SEM is also coupled with other spectroscopy techniques and energy dispersive X-ray spectroscopy (EDS). Among all the techniques listed above, the most important and key analysis technique for plastic particles is Fourier transform infrared (FTIR) spectroscopy, thanks to its nondestructive testing and option of repeatability.⁷⁹ Micro-FTIR can identify MPs smaller than 20 μm, which is a limitation of FTIR.⁸⁰ Moreover, the micro-FTIR technique has the potential to detect MPs that are much smaller such as 20 μm, which cannot be analyzed with conventional FTIR.⁸⁰

Various techniques like filtration, density separation, and selective extraction are used to isolate microplastics from environmental samples, making them easier to analyze. Advanced imaging techniques, coupled with machine learning algorithms, are used to automate microplastic detection and classification. This can significantly speed up the analysis process. Spectrofluorimetry is used for the detection of microplastics, as certain microplastics emit fluorescence when exposed to specific light wavelengths.⁸¹ Hydrodynamic filtration is another technique used for the detection of microplastics, a technique that relies on the flow characteristics of microplastics, sorting them based on their size and buoyancy, effectively separating them from other particles.⁸² In the context of biological samples, ingestion and biomarkers were used for the detection of microplastics to determine whether organisms have ingested microplastics.⁸³ In fact, textile wastewater from industrial activities, such as the textile manufacturing industry, can also contribute to the release of microplastics into rivers and lakes.⁸⁴ The presence of microplastics in textile wastewater highlights the need for cleaner production practices in the textile industry to reduce the environmental impact. Some results of a recent study³⁸ are summarized here. A single jersey pure PES knitted fleece fabric from 100% PES fiber (fineness 0.08 tex) having number of columns: 11.5 and number of rows: 17.5 (total planar weight 240 g/m²) was taken and subjected a number of washing cycles. The SEM image of the cross-sectional view of this fabric is shown in Figure 8(a). Microplastics were extracted from wastewater obtained after washing by filtering and after drying. A special type of sieve was selected for this purpose. The fibrous sieve with a mean pore size of 25 μm was used, with sett 145/130 and pore size 25/30 as shown in Figure 8(b).

Figure 8.

(a) The SEM images of a cross-sectional view of a single-sided knit fabric, (b) fibrous sieve-fabric PAD filter UHELON, sett 145/130, pore size 25/30 [results related to the present research obtained from a lab report, at TUL].³⁸

Moreover, the washing machine, barrel collecting water after washing, and filtration of wastewater through PAD filter are shown in Figure 9(a). The collected sample after filtration and drying was subjected to SEM and EDX analysis. The microfibrils are below the range of 50 μm. The EDX analysis showed some other traces of elements because of the impurities shown in Figure 9(b).

Figure 9.

(a) Setup for washing. (b) SEM and EDX analysis of microfibrils [results related to the present research obtained from a lab report, at TUL].³⁸

To analyze the release of microplastics, an abrasive action of domestic laundering of textiles or clothes are mostly done estimated by AATCC TM 212 (Fiber Fragment Release During Home Laundering),⁸⁵ ISO 4484-2:2023 (global measurement system for microplastics in the textile sector) and as well as European and international testing standards currently under development (International Organization for Standardization 2022).^86,87 While the possible standards to quantify the release of nanoplastics coatings are British Standards Institution (2010) Textiles - tests for color fastness. Part C06: Color fastness to domestic and commercial laundering, American Association of Textile Chemists and Colorists (2013) Color fastness to laundering: accelerated (No. TM61-2013). Textiles - Tests for color fastness to washing (ISO 105).⁸⁸⁻⁹⁰ Carlos et al. identify the released FMPs during washing by using microscopye. Figure 10(a) shows the textile substrate, machine model, and view of FMPs. Napper et al.⁵ washed the garment samples in a Whirlpool WWDC6400 washing machine. The total number of fibers shed from the wastewater outflow as a result during the laundry process was measured. For this purpose, a nylon cell microSieve (Fisher Scientific) with a pore size of 25 μm was fixed to one of the ends of the drain hose. After completing a washing cycle, the cell microSieve was removed and the fibers were collected. Because of the possibility of detergent or conditioner buildup on the collected fibers, they washed the collected fibers with 2 L of water and filtered them again using Whatman No. 4 filter paper and dried at a temperature of 30 °C to a constant weight. After the drying of obtained fibrous assembly, they were weighted by using a Cubis precision balance (Sartorius). During the weighing process, the following four parameters were considered. At first, fabric type (contained a fixed factor with three subsequent levels, 100% acrylic, 100% polyester, and a blend of 65% polyester/35% cotton); second, temperature kept during washing (contained subsequent two levels, washed at 30 and 40 °C); third parameter was selected detergent (fixed factor, 3 levels; washed in the absence of detergent, 20 mL of biodetergent (containing enzymes), and 20 mL of nonbio detergent is present); lastly, conditioner (with two levels: 20 mL of conditioner present or absent). The obtained design of the experiments provided 36 treatments in all. Fourier transform infrared spectroscopy confirmed that the fibers were the material type listed on the garment. The loss of fibers during the initial four washes was recorded (Figure 10(b)), but was not included in the data analysis.⁵

Figure 10.

(a) The released fibrous residues from textile substrate. (a) Structure of the textile surface (b) fibrils coming up from the yarn surface, (c) washing machine model, (d) fibrous residues (FMP), (e) microscopic view of the fibers. Reprinted with permission from ref (91). Copyright [2023], [ELSEVIER]. (b) Fiber loss from three fabrics (acrylic, polyester, and polyester-cotton blend) over the first 5 washes. Data from the fifth wash were used in the analysis (n = 4, ± SD). Reprinted with permission from ref (5). Copyright [2016], [Elsevier].

Yang et al. tried to identify the nanoplastic fragmentation of synthetic fibers during washing. Abrasion and washing experiments were performed on polyester textile. Different sizes and shapes were identified through a combination of techniques including scanning transmission X-ray microspectroscopy (STXM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and nanoparticle tracking analysis (NTA). The claimed average size of the diameter was 173–188 nm with varying length ranges 20 nm to 160 μm. Moreover, the amount of released nanofibrils was almost 3.3 × 10¹¹ nanoplastic particles.²⁶ Some advanced separation techniques are also based on the atomic force microscopy (AFM) technique. Researchers performed the pore-scale column test to separate the microplastics. The plastic debris was separated on the governing mechanisms for their nanoscale interfacial and adhesive forces by using colloidal-atomic force microscopy (C-AFM). The information regarding the location, magnitude, and occurrence of interfacial/adhesive forces was analyzed.^91,92

The majority of the studies discussed so far comprise an extensive investigation of MP in any kind of shape, i.e., spheres and films, and they focus on the assessment of fibers.⁹³ Another employed methodology comprises the retrieval of settled dust particles from vehicles or horizontal flat surfaces in classrooms,⁹⁴ the direct filtration of air assisted by a device, such as an air-pump, an ambient filter sampler,⁹³ and a total suspended particle sampler.⁹⁵ The actual height of the air filtration device used to collect MPs/FFs will influence the type and concentration of the collected particles and is recorded in each investigation. Because other methods are currently time-consuming and costly, fluorescence staining techniques are becoming popular for the rapid detection and quantification of NPs.⁹⁶ Various ways to quantify the number of released NPs have been proposed in the published literature. The gravimetric method, in which an analytical balance or a device, i.e., microbalance, is often utilized to measure the filter mass gain, is the most common method. Data can be provided in simple quantities such as milligrams or can be expressed as the weight percentage they represent, compared to the initial weight of the sample.⁹⁷ Another method is to compute the mass using a mathematical formula that focuses the number of fibers released, the average fiber diameter or volume, and the polymer’s average density.⁹⁸ In addition, a different method was used to calculate the MPs mass recovered based on a color assessment. The color measurement varies depending on fiber concentration and plastic present on them. The color of the recovered laundry wastewater was then analyzed to quantify the number of fragmented fibers in the solution.⁹⁹ All three methodologies demand imaging of the recovered fibers containing polymers with a microscope or image analysis equipment prior to analysis with graphical software. The manual method involves manually counting of fibers and drawing on fibers to trace their shape and length. Devices for these procedures include a light microscope,¹⁰⁰ stereo-microscope,¹⁰¹ digital cameras,¹⁰² scanning electron microscope,⁹⁸ and dynamic image analysis.¹⁰³ Measurements are achieved through graphic analytical software such as ImageJ.⁹⁸ A study was conducted on the photodegradation of polyester base fabrics with a polyurethane coating. The photodegradation of polyester base fabrics with polyurethane coating formed the nano- and microplastics. Manual counting of NPs and MPs released was performed under a microscope (NOVEL, N-300M) with a magnification of 40×. All fibers on the gridded filtration membrane were quantified, and after that the exact amount was obtained by scaling up according to the volume taken initially before filtering. In a research project, researchers investigated the aqueous leachates of NPS. They examined the inorganic elements released in the leachate after exposing it to UV light for 360 h using inductively coupled plasma-optical emission spectroscopy (ICP-OES, iCAP7400, Thermo Fisher Scientific, USA). The total organic carbon (TOC) in the leachates was calculated with a TOC analyzer (Vario TOC, Elementar Germany), and the total dissolved nitrogen (TDN) contents were estimated through the persulfate oxidation method.¹⁰⁴ The common method of quantification of nano- and microplastics is also based on their weight. In fact, plastics mostly quantified as a filter; at first, they weighed them with a microbalance (Mettler Toledo XP56) before and after the filtration of contaminated water samples (containing nano- or microplastics). The temperature and relative humidity of the weighing room were adjusted accordingly. The electrostatic charges of filters were eliminated by using a U-shaped ionizing electrode (PRX U27, HAUG GmbH, Germany). All weighings were analyzed two times and their mean values calculated. A study revealed that the microplastic fibers were analyzed under an optical stereoscopic microscope (Nikon SMZ-1B, magnification ×35). Overall, 13 or 14 grids were calculated which indicates almost 10 to 11% of the total effective area (14.2 cm²) of filters, respectively. The fibers were not evenly distributed above the effective area of filters, as they were highly concentrated in the middle as compared to the edges of the filter. The grids were selected diagonally along a single line to ensure the complete distance from the center of the filter.¹⁰⁵

The characterization process is the most important factor in assessing physical, chemical, mechanical, and other parameters of microplastics. Various instruments, including laser diffraction analyzers and particle counters, are employed for size distribution determination. As demonstrated by studies from Abbasi et al., microscopic techniques such as light microscopy, fluorescence microscopy (for the determination of microplastic), and scanning electron microscopy (for the determination of nanoplastic) aid in particle identification. Researchers utilized techniques like Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy for detailed analysis.²² Park et al. used elemental analysis, FTIR, and X-ray diffraction to examine the nanoplastics coated fabrics. Elemental analysis (carbon, hydrogen, and nitrogen) and FTIR are used to characterize synthetic fibers coated with polymeric finishes.¹⁰⁶ Scanning electron microscopy (SEM) is used to examine the effect of finishes and biodegradation on fiber morphology. The separation based on physical parameters such as weight, length and diameter have been performed by many researchers.^107,108 In a recent study Sola et al. quantify the microplastics based on physical parameters (weight, length, and diameter). The microplastics were shed during the washing of textile fabrics, and water was filtered through a filter paper. The weight of the filter paper was determined by using a precision balance. The mass of microplastics in parts per million was obtained by applying the following equation.

1

where ppm is the mass of the collected microplastics per mass of textile in mg/kg, Mm is the mass of the collected microplastics during washing and drying in mg, and Mkg is the mass of test specimens in kg.

The microplastics were spread over the filter paper and analyzed under a digital microscope (having a magnetification power 40×). Subsequently, ImageJ software (NIH, National Institutes of Health, Bethesda, Maryland, MD, USA) was used to give the exact measurements of lengths and diameters.¹⁰⁹ The majority of the literature analyzing NPs and MPs after washing prioritizes IR spectroscopy and infrared spectroscopy as the primary methods for determining MP and FF (PerkinElmer, model 2021). FTIR is a technique that creates the infrared spectrum of a material absorption or emission, and it is also useful for detecting material contaminants such as additives and organic or biological coatings adhered to the surface of the particles.¹¹⁰ This technique can also include microscopy to produce images that represent both spatial and spectral data, which is known as Raman imaging or simply mapping. This technique involves the gathering of spectra at a scanning position array as a spectrum matrix. The signal-to-noise ratio of any sample can be considerably improved by averaging spectral signals over the scanned part from the mapped images in contrast with the single-point Raman measurements of a single spectrum. Results from infrared spectra of materials can be compared with spectral libraries or databases of polymers and textile polymers for identification (PerkinElmer, 2021). FTIR and micro-FTIR techniques are extensively used in the literature to analyze FF obtained after washing and contamination on samples.^5,111 Filter compliance with the FT-IR analysis mode and particle size can be found in PerkinElmer, 2021, where a thorough evaluation of the filter type was performed to obtain tissue results of optimal MP characterization.

Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) were also used to evaluate the thermal properties of the fabric produced by X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF SIMS) and were also used to characterize the tissue surface. The surface hydrophilicity was analyzed by the measurement technique termed the water contact angle (WCA). Subsequently, the water absorption capacity was assessed by using the standard test method in accordance with AATCC TM 79-2014 (AATCC, 2017). Rola et al. stated that distinctive and separate melting peaks are necessarily required for the purpose of quantification and identification of microplastics through the use of thermogravimetric analysis along with analysis-differential scanning calorimetry (TGA-DSC). However, some other techniques based on TGA including coupled mass spectrometry (TGA-MS), Fourier transform infrared spectroscopy (TGA-FTIR), and thermal extraction desorption-gas chromatography–mass spectrometry (TED-GC-MS) mainly rely on the existence of at least one product of thermal degradation which could work as an indicator in the quantification and identification procedure.¹¹²

Some studies are involved in the use of a combination of characterization techniques to quantify and analyze the nano- or microplastics. As described under a microscope (NOVEL, N-300M) magnification of about 40×, manual counting of MPFs was carried out. After quantification of the fibers on a gridded filtration membrane, the overall quantity was measured by scaling up in accordance with the total volume that was taken before filtering. The released MPFs number was calculated according to the original weight of the PET part to assess and compare the degradation ability of two fabrics. Field emission scanning electron microscopy (FESEM; Quanta FEG 250, FEI, USA) was used to study the lengths and diameters of MPFs, and after that they were analyzed by ImageJ software19 based on FESEM images. The surface structural alterations before and after irradiation of released MPFs were calculated with the help of an in situ Micro-ATR/FTIR system (Bruker HYPERION 2000, Ettlingen, Germany). About 5 mL of collected suspensions was taken to examine them in an optical particle shape and size analyzer (Occhio 500 NanoXY, Belgium). The testing range of the analyzer was between 0.8 and 300 μm.

Some studies involve determining the type of plastic by a glass-transition temperature (T_g) by using a technique called differential scanning calorimetry (DSC, Q-2000). For this the heating and cooling are performed with a temperature range of 25–100 °C with a fixed rate of heating condition (10 °C/min) under an inert nitrogen environment. A research study was conducted to detect and characterize the NPs with a combination of ATR equipped with high-resolution scanning electron microscopy (HR-SEM) and EDX, also the combination of series of equipment ATR-FTIR-SEM-EDX. They all were used to characterize the raw and treated plastics with individual simulated weathering procedures, surface chemistry, surface morphology, composition, and PSD respectively. Another, composite characterization example contains HR-SEM (ZEISS, Gemini SEM 300, Germany) high vacuum mode and with an acceleration voltage of 3 kV. This testing unit used to examine surface morphologies of raw and treated plastics. Before HR-SEM imaging, all of the samples were sputter-coated (Quorum-150TS plus; UK) with chromium for almost 5 min. For elemental analysis of probe-sonicated plastics, EDX was used with a silicon drift detector-x-act from Quanta 200 FEG Environmental SEM. Microflow imaging (PSD-MFI5200, CL, USA) was used to quantify particle sizes and concentrations, where in situ images of suspended particles in a flowing matrix were captured with a digital camera equipped with an illumination and magnification system. By using a Zeta-sizer system (Malvern Instruments, UK), zeta potentials (determining surface charge) of each sample were recorded twice at about 25 °C. An X’PERT system was used to measure XRD patterns of each sample to determine their crystallinity.

Throughout the previous years, manufacture and use of plastics have gained much importance, but there have been no significant measures to reuse, recycle, or implement pollution control strategies which ultimately left a linear plastic economy. The toxicity of nanoplastics is important to consider because it is estimated to be more in quantity than microplastics in the environment. These nanoplastics are new and evolving contaminants of the environment, but their presence in the environment and potable water still requires study as there is no suitable quantitative analytical technique for them. In a study, Elvis et al. created a pretreatment technique that works by combining hydrogen peroxide digestion and Amicon Stirred Cell ultrafiltration (at 100 kDa, approximately 10 nm) with consequent detection by pyrolysis gas chromatography–mass spectrometry (Pyr-GC/MS). Following this methodology, the researchers were able to identify and quantify nine selected types of nanoplastics such as polyethylene (PE), poly(methyl methacrylate) (PMMA), poly(ethylene terephthalate) (PET), polyvinyl chloride (PVC), polycarbonate (PC), nylon-66, polystyrene (PS), and nylon-6 present in environment and potable water samples. A majority of the nanoplastics were detected at about 0.04 to 1.17 μg/L. Only PC was below the detection limit which was <0.44 μg/L. This analytical technique presents a precise solution not only to identify and quantify the nanoplastics but also for its monitoring. Moreover, it helped in the understanding of this category of pollution and devised a good approach for future research and investigation.¹¹³

In 2020, Jimenez-Lamana et al. devised a method for the detection and quantification of nanoplastics (NPTs) at environmentally relevant concentrations. The technique was based on conjugating nanoplastics along with the functionalized metal (Au) containing NPs. The method’s selectivity was accomplished by coupling the negatively charged carboxylate groups which is found at the nanoplastics surface with a positively charged gelatin fixed to the counting of separate nanoplastic particles, which ultimately leads to their precise quantification (<5% error). In order to develop an experiment, polystyrene particle models with certain controlled surface functionalization representing nanoplastics that were formed during degradation activity of plastic debris were utilized. A similar methodology was adopted for assessing nanoplastics of about 1 μm in tap, drinking, and river waters. The smallest detectable and quantifiable size depended on the degree of functionalization and the available labeling surface.¹¹⁴

In an investigation on nanoplastics (NPLs), Huber et al. studied various batch methods such as tunable resistive pulse sensing (TRPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), dynamic light scattering (DLS), and nanoparticle tracking analysis (NTA), along with separation techniques including centrifugal liquid sedimentation (CLS) and field-flow fractionation (FFF)-multiangle light scattering (MALS) combined with pyrolysis gas chromatography mass spectrometry (pyGC-MS) or Raman microspectroscopy (RM) for nanoplastics size, shape, and chemical constituent analysis and quantification. For experiments, a set of different test particles were used to find the applicability and limitations of considered techniques. These particles were taken in sets of four such as (i) polydisperse polyethylene (PE), (ii) (doped) polystyrene (PS) NPLs, (iii) titanium dioxide, and (iv) iron oxide nanoparticles (spherical and elongated). Hence, the combination technique, including FFF coupled to MALS and RM, can present data on physical and chemical characteristics. Moreover, the pyGC-MS analysis of FFF fractions can be utilized for the (semi) quantification and identification of polymeric particles.¹¹⁵

The present quantification methodologies only work on the detection of millimeter to micrometer sized plastic particles; however, plastic may be found at a much smaller, nanometer sized scale. A study conducted by Molenaar et al. combined sensitive fluorescence video microscopy, Nile Red staining of plastic particles, and single particle tracking (SPT) to count and quantify nanoplastics. By following this strategy, they indicated that particles with a diameter of 45 nm can be quantified, and the mixing ratio of different sized particles can be achieved. Moreover, the particle concentration as low as 2 × 10⁶ per mL can also be obtained. The researchers confirmed that this technique is efficient in quantification of size and concentration of nanoplastics that is mostly released from medical and consumer plastics in the environment.¹¹⁶

The system worked with Cu Kα radiation between 10° and 90° at a scan rate of 2° per minute. To get a specific surface area (SSA), measurements from Brunauer–Emmett–Teller (BET) were used on a Quantachrome Autosorb LX4, Austria, with krypton (Kr) as the analysis adsorptive. The lengths and diameter of MPFs were measured by using ImageJ software, in which MPFs (n > 50) were chosen on a random basis from corresponding FESEM images. By employing micro-FTIR (μ-FTIR) mapping, their identified structures of released MPFs were analyzed in order to obtain the cartography of C=O, −OH, and −CH₂ groups, which are characteristic peaks of PET polymers. In addition, field emission scanning electron microscope-energy equipped with an energy dispersive spectrometer (FESEM-EDS; Quanta FEG 250, FEI-Oxford Aztec X MaxN 80) was utilized to verify if the released nanoparticles were NPs.¹¹⁷ Moreover, Table 2 shows the common methods applied for the detection and separation of nanoplastics.

Table 2. Common Methods Applied for the Detection and Separation of Nanoplastics.

technique	categories	refs
Microscopy	Transmission electron microscopy	(118)
	Scanning electron microscopy	(79)
	Optical microscopy	(118)
	Stereo-microscopy	(119)
	Atomic force microscopy	(120)
Spectroscopy	Fourier transform infrared (FTIR) spectroscopy	(121)
	Nuclear magnetic resonance (NMR) spectroscopy	(122)
	Energy dispersive X-ray spectroscopy (EDS)	(123)
	Raman spectroscopy	(124)
Light scattering method	Dynamic light scattering (DLS)	(125)
	Spectrofluorimetry	(81)
Filtration techniques	Vacuum filtration	(76)
	Hydrodynamic filtration	(82)
Biomarkers and biosensors	Enzyme linked immunosorbent assays (ELISA)	(126)
	Surface plasmon resonance (SPR)	(127)
Centrifugation	Ultracentrifugation	(77)
	Density gradient centrifugation	(126)
Density separation	Differential sedimentation	(78)
	Field flow fractionation (FFF)	(128)
Chromatography	Liquid chromatography	(129)
	Pyrolysis gas chromatography	(129)
	Capillary electrophoresis (CE)	(130)

Future Remarks

The present review has focused on the release of polymeric microplastic fibers and polymeric coatings from the textile surfaces during washing. It covers the category of different types of synthetic fibers coated with various kinds of finishes and their release from the textile surfaces. The plastic waste found at macro-, micro-, and nanoscale has had major consequences from the perspective of significant and toxic impacts on living organisms. While increasing the awareness and growing concern about the release of nanoplastics and their adverse effects on the ecosystem (especially on the health of livings), there is need to pay more attention to the debris of plastic pollution from textiles (in fibrous form or functional coatings).¹³¹ Periyasamy et al. carried out an intensive study related to exponential growth in the number of publications on the topic related to release of microplastics during the last ten years as shown in Figure 11.¹³²

Figure 11.

Scientific research publications related to the present topic that have been published in the past decades. Reprinted with permission from ref (132). Copyright [2022], [Elsevier].

Annually, the average textile consumption is estimated to be 25 kg/person in Europe, and people wash their garments on a daily basis with automatic washers. Additionally, more literature is required to identify the ecological effects on living things. Finally, there is also a need for standardized research methods of measuring and quantifying nanoplastic pollution. In fact, at present, there is no such universal technique or methodology for measuring the release of nanoplastics from textile fibrous finishes. Previously, the release of synthetic plastic fibers fragments containing nanoplastic coatings during washing ranges from 100 to 300 mg for kg of washed fabric was estimated.⁶² Aside from that, there is need to do more work on aims to improve our understanding of micro- and nanoplastics released from textiles (fibers, fibrils, and polymeric coatings). In brief, there is need to study more textile-based sources which release micro- and nanoplastics, their quantification methods, and their effects on the environment (including air and water) and health. Additionally, the use of biodegradable polymer textile finishes (ecofriendly) should be used as an alternative to polymeric finishes. Various biopolymers like protein based material including collagen and cascin are used for flame retardancy,¹³³ and chitosan, cellulose, and poly(lactic acid), ca. are being explored for applications in textile processes.¹³³ These biopolymers offer benefits, such as antibacterial properties, UV protection, and enhanced wettability. For instance, chitosan coatings on fabrics have shown antibacterial activity against both Gram-positive and Gram-negative bacterial.¹³⁴ To achieve the future goals, a short-routed pathway can be simplified as shown in Figure 12.

Figure 12.

A pathway to prevent the release of micro- and nanofibers from finished textiles in the environment throughout the whole life cycle.

There is also a need for more research to find the release of fiber fragments per kg of garments after each washing cycle and only by washing the dirty dresses almost 6 kg twice a month, and estimate the release of nanocoatings in mg/year. Comprehensive research should also be conducted on textile functional polymeric based finishes and their categories. The size and densities of textile-based finishes should be measured in industrially contaminated water. In short, extensive research work is necessary in devising effective solutions to deal with the problem of pollution caused by nanoplastic coatings. Several actions including awareness about the list of functional polymeric finishes, their binding tendency with fabric surfaces, and harmful effects should be taken into account.

Conclusion

Plastic pollution originates from synthetic textiles taking into account only as FMPs, or micropills. With the invention of new technologies, a new term polymeric microplastics starts to be considered as a new part of textiles. However, the present perspective concerns plastic waste present at the macro-, micro-, and nanoscale and about functional textiles coatings (which lie in the ranges of the nanometric scale, so-called PNPs). Starting from a concise summary related to the main categories of all fibers, the concept of synthetic plastic based fibers were discussed. Gradually, a focus on the release or shedding of fibers from textile structures was elaborated. In the modern era of smart and innovative textiles, not a single garment is fabricated without functional finishes. Almost 50% of these finishes contain thermoplastic coatings. The invested efforts have been paid to consider and concentrate on plastic pollution (nanoplastics from textile polymeric coatings). Hence further sections of review deeply assess the importance of plastic finishes, their binding patterns, importance, and functionalities they provide (during service). Knowledge concerning important functional polymers, chemical coatings, and resins and their impact as a functionality enhancer such as flame retardancy, hydrophobicity, antipathogenic, etc. were intensively discussed. As previously described in the aforementioned section of our review that textile-based micro-/nanopollution gains a synergic effect by the combination of plastic fibers having plastic coatings over them. Hence, our findings suggest that there must be more findings, studies, and novel ways to identify these nanoplastics especially those released from synthetic textile coatings. In addition, the authors tried well to summarize existing methodologies to elucidate the identification and proactive quantification of nanoplastics shed from textile polymeric coatings. In fact, more than 40 studies involve identifying the physical, chemical, and mechanical parameters and characterizing nanoplastics. To this end, a crucial understanding about the methods for separating and quantifying micro- and nanoplastics and their characterization techniques is described. Furthermore, the nanoplastics released into wastewater from textile laundry has toxic effects on human health such as crossing biological barriers and transfering across generations. Moreover, the biointerface of nanoplastics facilitates the entry into eukaryotic cells, which include both active and passive targeting mechanisms. In addition, the impact of nanoplastics on intracellular target organelles (such as endoplasmic reticulum, lysosome, mitochondria, etc.) is investigated in order to assess the response of specific organelles toward the toxicity of these nanoplastics. Such studies highlight the factor of exposure to these nanoplastics and their significant biological impacts.¹³⁵

Glossary

Abbreviations

MPs

Microplastics

NPs

Nanoplastics

PNPs

Polymeric Nanoplastics

FMPs

Fibrous Microplastics

FTIR

Fourier Transform Infrared Spectroscopy

ToMEx

Toxicity of Microplastics Explorer

PAEs

Phthalic Esters

PES

Polyester

PA

Polyamide

PAA

Polyacrylic Acid

PLA

Polylactic Acid

WWTP

Wastewater Treatment Plant

PE

Polyethylene

PP

Polypropylene

PS

Polystyrene

PET

Polyethylene Terephthalate

PVC

Polyvinyl Chloride

PTFE

Polytetrafluoroethylene

PVA

Polyvinyl Acetate

PEG

Polyethylene Glycol

PAN

Peroxyacetyl Nitrate

GMA

Glycidyl Methacrylate

PBSA

Poly-Butylene Succinate-co-butylene Adipate

EFD

Electrofluidodynamic

PMPs

Polymeric Microplastics

IUCN

International Union for Conservation of Nature

PU

Polyurethane

PLE

Photoluminescence Excitation

PVAC

Polyvinyl Acetate

DMDHEU

Dimethylol Dihydroxy Ethylene Urea

NIR

Near Infrared

SEM

Scanning Electron Microscopy

EDS

Energy Dispersive X-ray Spectroscopy

TOC

Total Organic Carbon

NMR

Nuclear Magnetic Resonance

TDN

Total Dissolved Nitrogen

XRD

X-ray Diffraction

TGA

Thermogravimetric Analysis

DSC

Differential Scanning Calorimetry

XPS

X-ray Photoelectron Spectroscopy

ToF-SIMS

Time-of-flight Secondary Ion Mass Spectrometry

HR-SEM

High-resolution Scanning Electron Microscopy

BET

Brunauer–Emmett–Teller

The authors declare no competing financial interest.