Microfiber Emissions from Functionalized Textiles

Microfiber Emissions from Functionalized Textiles: History

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Subjects: Green & Sustainable Science & Technology

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Increasing textile waste collection and reuse can overall reduce the amount of landfills and possibly reduce microfiber emissions. Used textiles can be reused into industrial rags, furniture decorations, purses, backpacks, advertising textiles, and more to extend their lives.

toxic chemicals
textile functionalization’s
microfibers

1. Introduction

The most common and resilient modification to our Earth’s surface area is the debris of fiber fragments [1]. Since plastic was first manufactured in mass quantities in the 1950s, the demand for artificial polymers and plastics has rapidly increased, and the global production of these materials in 2021 was 391 million metric tons (MMT) [2]. Furthermore, this number is anticipated to increase to 589 MMT by 2050 [3]. As a result of their enormous production and consumption rates, plastic particles including micro and macroplastics have begun to accumulate in Earth’s atmosphere, Mount Everest [4], on coastlines, on the most distant islands, and in the deep sea [5].

In the 1970s, microplastic pollution in the marine environment was discovered for the first time. Spherules, disks, and pellets were found floating on the surface of the Sargasso Sea [6], along the coasts of New England [7], in the surface waters of the Atlantic Ocean, and in the surface waters of the Pacific Ocean, respectively [8,9]. The phrase “microplastics” refers to fragments of plastic that are smaller than 5 mm in size. Microplastics are further divided into two categories, primary and secondary microplastics; this information has been clearly discussed in many recent articles [10,11,12,13,14,15,16]. Microplastics can stem from a range of resources consisting of synthetic textiles, tires, roadway markings, aquatic coverings, personal care/cosmetic products, and crafted plastic pellets, as well as from the gradual fragmentation of bigger plastics over time [17]; among these sources, the domestic washing of garments has the highest potential for the generation of microplastics [18,19,20,21,22,23,24] (Figure 1). In addition to petroleum-based plastic fibers, man-made cellulose fibers (e.g., viscose rayon) have also been detected in different environmental matrices of deep-sea sediment and macroinvertebrate fishes, thus increasing the interest of the scientific community in this kind of plastic pollution, which is usually underestimated [25,26,27]. Microfibers are similar to microplastics in terms of their size; they also measure less than 5 mm in diameter. However, their composition is not exclusively restricted to plastic. Fibers that originate from natural sources (e.g., cotton, wool, silk, and hemp) and plastic microfibers that originate from synthetic materials such as polyamide (PA), polyester, polypropylene, polyacrylonitrile (PAN), and polyethylene pose significant threats to the internal organs of the organisms that ingest them. Microfibers of natural origin typically exhibit biodegradability in the atmosphere. However, the functionalization of textiles can impede the biodegradation process, additionally, these materials are harmful to aquatic organisms.

Figure 1. Main sources of microfibers in the aquatic environment from domestic washing, textile industries, and garment waste/landfills.

Throughout its production process, the textile industry employs significant quantities of various chemicals [28]. Most of the polymeric additives that have been found in coastal environments are considered endocrine disruptors [29,30,31,32]. The manufacturing of fibers involves the addition of a large number of additives, the purpose of which is to enhance the fibers’ processability and functionality; a list of additives is provided in Table 1. For example, UV stabilizers in the form of benzotriazoles and benzothiazoles are frequently found in the effluent of municipal wastewater [33,34]. Titanium dioxide is widely used in synthetic fibers as a delustering agent to diminish the luster and transparency of yarns [35,36,37]. Diisobutyl phthalate is a plasticizer used in textile production that is reprotoxic, endocrine-disruptive, and toxic to aquatic life. To improve the flexibility and durability of textiles, phthalates are often added to polyvinylchloride (PVC)-based coatings [38,39]. To make flame-retardant textiles, hexafluorotitanate salts [40], TiO₂ nanoparticles (NPs) [41,42] and brominated and phthalate compounds are commonly used in textile production, and these have shown reproductive and developmental toxicities [43,44]. Often, formaldehyde-based resins are added to improve the crease recovery properties of cellulose-based materials [45], and polyfluoroalkyl substances are added to improve the water repellency of textiles [46]. When it comes to natural fibers like cotton, it is possible to find hazardous pesticide residues that have been used during cultivation or applied for preservation purposes during storage [47]. Triclosan, which is extensively used in the garment industry as a fungicide, has been linked to endocrine disruption [48]. Furthermore, the process of coloring entails the utilization of dyes sourced from diverse chemical classes, predominantly comprising heavy metals that are commonly acknowledged as detrimental.

Table 1. Typical additives are used in man-made fiber production.

Type	Function	Examples
Processing Aids	Antioxidant	Hindered phenols, hindered amines, and phosphites
	Hydrolysis Stabilizer	Carbodiimide
	Nucleating Agent	Talcum powder, boron nitride, and organic phosphate salts
	Lubricant	Stearates and low-molecular-weight wax
	Polymer Processing Aid	Fluoropolymers
	Surfactant	Stearates and polyethylene glycols (PEGs)
Enhancing Additives	Plasticizer	Tributyl citrate and acetyl tributyl citrate
	Chain Extender	Difunctional acid derivatives, anhydrides, and epoxides
	UV Stabilizer	Hindered amine light stabilizers (HALS), titanium dioxide (TiO₂), zinc oxide (ZnO), and carbon black
	Flame Retardant	Phosphorous derivatives, halogen derivatives, and HALS
	Thermal Protection	Zirconia
Functional Additives	Colorant	Pigments, dyes, and carbon black
	Delustering	TiO₂, ZnO, mica, and optical brightening agents
	Antistatic	Carbon black, carbon nanotubes, graphene, and ZnO
	Antimicrobial	TiO₂, ZnO, nano-sized metal particles (Ag⁺, Cu²⁺, Zn²⁺), plant extracts, and phenol
	Water/Oil Repellent	Silicone and fluorine compounds

When textile microfibers are dumped into the ocean, they undergo photo- and biodegradation in addition to physical aging processes [49]. This ultimately results in the production of plastic debris at the micro- and nanoscale [50,51]. Polymer degradation is also regarded as a key source of dissolved organic carbon (DOC) release [52], as this DOC contains oligomers with varying degrees of oxidation [53] and various polymer additives (i.e., for man-made polymers) such as processing additives, enhancing additives, and functional additives [54].

Figure 2 illustrates how numerous routes of exposure might lead to microfibers accumulating in the human body. The textile industry is responsible for the invisible pollution that is created by textile microfibers, which have been detected in marine sediments and organisms [16]. This review covers some environmental routes (water, air, and soil) of microfiber contamination into the food web, describes their effects on human health, and presents new and relevant studies on their occurrence, fate, and behavior. This review paper reveals that the microfibers emitted from textiles are not biodegradable and that the functionalization of cellulose-based textile materials significantly influences their biodegradability. It is possible that these microfibers, which are produced from textiles that include a variety of dyes, hazardous compounds, and nanomaterials, could pose a variety of health threats to both human beings and other living organisms that are discussed in this work.

Figure 2. Schematic representation of exposure to microfibers through three routes: ingestion, inhalation, and dermal contact. Additionally presented are potential health risks of microfibers for human health via the food chain and dietary exposure.

2. Textile Functionalization as the Source of Microfiber Toxicity

The coloration and finishing process is one of the important and value-adding processes in the textile production chain (Figure 3). Typically, synthetic dyes and chemicals are functionalized with textile materials to improve some of their properties. [55]. Additionally, chrome or mordant dyes and metal complex dyes are utilized to achieve bright and dark colors. Most dyes contain heavy metals, including lead (Pb), arsenic (As), chromium (Cr), nickel (Ni), copper (Cu), cadmium (Cd), mercury (Hg), and zinc (Zn) (Table 2) [55,56,57]. Generally, heavy metals with a density of greater than 5 mg/cm³ are considered to have a high density. These heavy metals are non-biodegradable and difficult to clean up due to their complicated chemical makeup [58]. Consequently, the microfibers released from these textile materials contain heavy metals, which have carcinogenic, toxic, and nonbiodegradable effects that, in turn, cause enormous environmental problems [59,60,61]. Additionally, the metals are coated on the surface of the fibers to produce conductive textiles for electromagnetic shielding applications [62,63,64,65]. These heavy metals are notorious for their toxicity and negative effects on human health, as well as their impact on the environment. Additionally, the existence of organic additives, inorganic additives, and traces of monomers, metals, or other chemicals that can be discharged is a source of pollution that is more hazardous to human health than the released microfibers themselves [66,67]. The various chemicals used in the textile production chain are well described in Figure 4.

Figure 3. Textile production chain (i.e., linear chain).

The purpose of the scouring step in the pre-treatment process is to make a textile material highly and uniformly absorbent, and it is carried out in alkaline conditions. Scouring removes practically all contaminants, except for natural pigments, that can be removed by either oxidizing or reducing conditions. However, the industry largely uses H₂O₂, in which atomic oxygen, superoxide anions, and hydroxyl ions perform the bleaching action in a process also known as the oxidation of natural color [68].

Figure 4. Various chemicals are used in the textile production chain.

Table 2. Main use of heavy metals as additives in polymer products and their effects on human health.

Heavy Metals	Additives	Type of Polymers	Effects on Human Health	References
Antimony (Sb)	Flame retardants and biocides	Polyester cotton or polyester wool fabric	Metal-estrogenic effects and breast cancer	[69,70,71]
Aluminum (Al)	Stabilizers, inorganic pigments, and flame retardants	Polyester cotton or polyester wool fabric	Metal-estrogenic effects and breast cancer	[69,70,71,72]
Zinc (Zn)	Heat stabilizers, flame retardants, anti-slip agents, and inorganic pigments	Polyvinyl chloride (PVC), polyethylene (PE), and polypropylene (PP)	-	[71,72]
Bromine (Br)	Flame retardants	Polybutylene terephthalate (PBT), PE, polystyrene (PS), and PP	Apoptosis and genotoxicity	[71]
Arsenic (As)	Biocides	PVC, low-density polyethylene (LDPE), and polyesters	Congenital disabilities; lung, skin, liver, bladder, and kidney carcinogenic effects; gastrointestinal damage; and death	[71,72,73]
Lead (Pb)	Heat stabilizers, UV stabilizers, and inorganic pigments	PVC and all types of plastics in which red pigments are used	Anemia (less Hb), hypertension, miscarriages, disruption of nervous systems, brain damage, infertility, oxidative stress, and cell damage	[71,72,73,74,75]
Titanium (Ti)	UV stabilizers and inorganic pigments	PVC	Cytotoxicity on human epithelial lung and colon cells	[71,72,73,76,77]
Chrome (Cr)	Dyes for silk and metal complexes	PVC, PE, and PP	Allergic reactions to the body; nasal septum ulcer; severe cardiovascular, respiratory, hematological, gastrointestinal, renal, hepatic, and neurological effects; and possibly death.	[78]

3. Implication of Microfiber Contamination on Human Health

There are multiple ways in which microfibers can enter the body of a human being, including ingestion [14,136], inhalation [137], and skin contact [138], as is well-described in Figure 2. Each of these ways of being exposed is in some way connected to a certain environment and the chemical–physical features of that environment. One of the most significant sources of airborne microfibers is the textile production chain, which includes spinning, weaving, processing, landfilling, waste incineration, and the drying of clothing after washing [18,139] (Figure 2).

Since inhalation is one of the primary methods through which humans are exposed to microfibers, the released microfibers that contain many additives, such as nanomaterials and other chemicals such as perfluoroalkyl derivatives and formaldehyde, pose significant risks to human health. Although no research has been published on this topic, some studies have investigated the effects of polystyrene nanoparticles (PS-NPs) on human lung epithelial [140,141,142,143,144]. PS-NPs may directly interfere with membrane transporter activity in A549 cells, affecting xenobiotic and endogenous substrate disposition.

The microfibers emitted from functionalized textiles that have toxic properties might adversely affect fish and other aquatic life [145], which has the potential to create serious problems [146,147]. These microfibers have raised concerns since they have the potential to impact animal populations, which are essential for maintaining ecosystems [148,149], and the animal populations that provide vital ecosystem services might be harmed by reactions with these microfibers [150]. It is recognized that foodstuffs are the main sources of microfibers for humans (Figure 2) since most food, such as table salt [151,152], drinking water [153,154,155,156], beer [157,158], fruits/vegetables [159,160], and canned fish [161], is contaminated with microfibers. A recent study [162] demonstrated the presence of micro and nanoplastics in a variety of foods, including apples and carrots, which were shown to have the highest levels of contamination. Additionally, the authors observed microfibers in carrots (1.51 µm) and lettuce (2.52 µm), which had the largest amount [162]. Overall, 52,600–307,750 of microfibers were discovered in vegetable samples, whereas 72,175–130,500 were discovered in fruit samples [162]. In addition, Cauwenberghe and Janssen [136] found that the average consumer of shellfish in Europe consumes 11,000 microplastics per year. According to research [14], the average American diet and lifestyle result in the consumption of microfibers that is estimated to range between 39,000 and 52,000 particles per person. However, different age groups, genders, geographical conditions, and individual dietary habits and lifestyles all affect the amount of consumption. It is challenging to assess the actual threat that microfibers pose to human health based on the data that are currently available regarding the presence of microfibers in a wide variety of food sources and the corresponding findings of toxicity tests. More work needs to be performed to develop an analytical method that is both standardized and operational for identifying and quantifying microfibers, and more research needs to be conducted to investigate the potential effects that microfibers and associated chemical contaminants could have on human health [14,163].

In most cases, dermal contact with microfibers is related to exposure to monomers and additives, which are on a long list of endocrine disruptors. However, this route of exposure is regarded to be less significant [138,164,165]. For instance, research was conducted on the dermal uptake of substances in rainbow trout, showing evidence for the uptake of 1 μm latex spheres from the water in the surrounding environment, with particles localizing and remaining in the surface and sub-surface epidermal cells of the skin, as well as in phagocytes underlying the surface of the gills [164].

In addition, oxidative stress can be caused in human epithelial cells when they are exposed to microplastics and nanoplastics [166]. The term “persorption” refers to the mechanical kneading of solid particles (with a diameter of up to 130 μm) in the gastrointestinal tract, where they pass through gaps in the single-layer epithelium at the villus tips and into the circulatory system. This process is thought to be a possible route of uptake in the digestive tract [167,168].

Recent research conducted by Nur et al. [169] resulted in the development of a probabilistic lifetime exposure model for the purpose of determining the amount of microplastics consumed by children and adults. This model considers microplastics consumed through inhalation, eight different food types, intestinal absorption, biliary excretion, and plastic-associated chemical exposure through a physiological-based pharmacokinetic submodel. Based on biphasic, reversible, and size-specific sorption kinetics, the chemical absorption results of the food and ingested microplastic of all nine intake media revealed that the contribution of microplastics to overall chemical intake was negligible. Considering the need for future research, discussions regarding the currently unknown contributions of different types of foods should be held. We will likely trust the results of the aforementioned studies for the time being, as it may take some time for microplastics to reach humans due to the complexity of the food system, but the probability of ingestion is growing as microplastic production and consumption continue to rise.

Potentially harmful consequences of microplastics on human health [137,139], including inflammation and subsequent genotoxicity [170], have been identified. Similar to other non-biological micro- and nanoparticles, inhaled microplastics can translocate into the pulmonary epithelium through diffusion, direct cellular penetration, or active cellular absorption [171]. Interstitial fibrosis and granulomatous lesions were observed in the lungs of employees who work in the plastic industry, and these issues were attributed to acrylic, polyester, and nylon dust [137,139,170]. Microfiber absorption via inhalation has been compared to that via ingestion (via the food web) in the published literature [172]. Human microfiber ingestion is rather low compared with exposure levels, with studies finding that microfibers are breathed in between 3 and 15 times more than they are ingested [173,174]. Numerous toxicological investigations of ingested microfibers have been published in the scientific literature. Most of this research employed polystyrene particles as a benchmark material for more sophisticated microfibers, and only a few studies concerned polyethylene [174,175,176,177,178,179]. In addition, the dose, dose rate, and period of exposure employed in the trials all had significant impacts on the harmful consequences. Most studies showed toxicological effects on parameters such as oxidative stress [180,181,182,183,184,185], inflammation [185,186,187,188,189,190,191], mitochondrial dysfunction [192,193,194,195], lysosomal dysfunction [196,197], and genotoxicity [198,199,200]. Figure 11 illustrates the main toxicological effects found in cell cultures.

Figure 11. Toxicological effects of polystyrene microparticles on cell cultures: oxidative stress, apoptosis, inflammation, mitochondrial and lysosomal dysfunction, and genotoxicity, (Reprinted from [174] with Creative Commons Attribution License (CC BY)).

Arif et al. [201] collected the stools of human fishermen living in the coastal area of Surabaya, Indonesia. They found that more than 50% of the studied samples included a microfiber concentration ranging from 3.33 to 13.99 µg per gram of stool, and most of them were high-density polyethylene (HDPE). Additionally, Philipp et al. [144] studied microfibers in human stools, and they observed PP and PET with a size range of 50–500 μm and a concentration of 2 particles per gram of stool. Additionally, a median of 20 microfibers with size range from 50 to 500 μm per 10 g of human stool was observed by Yan et al. [190].

Ragusa et al. [202] found microfibers in human placentas. The particles were found in the placentas of four healthy women who had normal pregnancies and births. Microfibers were detected on both the fetal and maternal sides of the placenta and in the membrane within which the fetus developed. Unfortunately, we do not know how microfibers reach the bloodstream or if they come from the respiratory or the gastrointestinal systems. In particular, five microfibers were found on the fetal side, four were found on the maternal side, and three were found in the chorioamnionitis membranes, indicating that once inside the human body, these microfibers can reach placenta tissues at all levels. It is noteworthy that small portions of placentas (~23 g with respect to a total weight of ~600 g) were analyzed, letting us hypothesize that the number of microfibers within an entire placenta is much higher.

As these findings show, it is important to continue looking for microfibers in human fluids, and additional research should be conducted to determine how microfibers interact with and make their way into the human body. The contamination of samples by airborne microfibers is an important aspect of the microfiber detection process that needs to be considered. Therefore, a significant amount of focus needs to be paid to the treatment of samples to prevent the incorrect identification of microfibers in human samples, particularly for particles of less than 10 mm in size, and to increase the total number of samples that are gathered. In addition, there is an immediate need for more research that is conducted on a transnational and interdisciplinary scale and focuses on the toxicology of these particles to fully understand the effects that these particles have in the long term on humans and to assist health organizations in developing prevention guidelines.

This entry is adapted from the peer-reviewed paper 10.3390/toxics11050406

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