Primary Microplastics in the Ecosystem: Ecological Effects, Risks, and Comprehensive Perspectives on Toxicology and Detection Methods

Abstract

Recent discoveries of microplastics in cities, suburbs, and even remote locations, far from microplastic source regions, have raised the possibility of long-distance transmission of microplastics in many ecosystems. A little is known scientifically about the threat that it posed to the environment by microplastics. The problem’s apparent size necessitates the rapid development of reliable scientific advice regarding the ecological risks of microplastics. These concerns are brought on by the lack of consistent sample and identification techniques, as well as the limited physical analysis and understanding of microplastic pollution. This review provides insight regarding some unaddressed issues about the occurrence, fate, movement, and impact of microplastics, in general, with special emphasis on primary microplastics. The approaches taken in the earlier investigations have been analyzed and different recommendations for future research have been suggested.

Graphical Abstract

Keywords:

• Primary microplastics
• ecological risk
• identification techniques
• bioaccumulation
• microplastic toxicity

1. Introduction: general aspects of microplastics

Plastics, regarded as a miracle material, have freed humanity from the socioeconomic constraints brought on by a scarcity of natural resources. Globally, fossil fuel feedstock accounts for 97–99% of plastics while the remaining 1–3% are derived from bio (plant) based. In the last few decades, the amount of plastic manufactured annually around the world has dramatically expanded, rising from 2 million tonnes in 1950 – 381 million tonnes in 2015.¹ After 2000, more than 50% of the total amount of manufactured plastic was introduced into the market. It is anticipated that their production would rise, even more, hitting approximately 600 million tonnes in 2025 (Figure 1). About 42% of the plastic produced is consumed by the packaging business, with the construction and building sector using the remaining 19%. Numerous "essentials" in our daily lives, such as cling film, face masks, medical supplies, coffee mugs, and shopping bags are made of single-use plastic (SUP). The recent Covid-19 outbreak increased the usage of SUPs, particularly gloves, facemasks, and personal protective equipment (PPE) kits, which added 3.5% more to the world’s solid waste percentage. The US, India, and China are the largest producers of SUP, respectively.²

Figure 1. (a) Plastic production till 2025 and (b) primary plastic production by industrial sector, 2015.

Plastics are ubiquitous in the environment due to their high manufacturing rates and longevity. Initially, larger plastic trash drew the attention of scientists and the general public. Tiny plastic particles, however, were found in the marine environment as early as the 1970s.³ Microplastics (MPs) in the environment have gained more attention over the past several years and are now a prominent field of study. MPs are typically characterized as plastic particles that are less than 5 mm in size and have a wide range of shapes (including fibers, spheres, and fragments), sizes, colors, and compositions. Further, MPs can be categorized into primary and secondary regardless of their sizes. For application, for instance, in medical equipment and in personal care items like cosmetics and soaps, primary MPs are found in microscopic sizes (fibers, microbeads).⁴ Large plastic items, when in contact with the environment, physical, chemical, and biological factors cause the plastic to break down into tiny fragments, creating secondary MPs, including mulch breakage debris and tire-wear debris, among others. Terrestrial and aquatic ecosystems are found to contain enormous and diverse MPs. As MPs are difficult to degrade, they remain in the environment for a long time, which results in significant and harmful environmental pollution.⁵

This review addresses substantial knowledge gaps about the origin, destiny, migration, and effects of MPs, emphasising on primary MPs, which are becoming more widely acknowledged as a severe environmental threat. This study aims to provide a comprehensive understanding of the widespread presence of MPs in both terrestrial and aquatic ecosystems, their behavior, after entering the environment, as well as their potential negative effects on human and environmental health by integrating previous research findings. The goal of the review is to facilitate the development of evidence-based policies and interventions targeted at reducing the detrimental effects of MPs pollution by clarifying the sources, patterns of distribution, and ecological implications of primary MPs. Additionally, it offers guidelines for establishing effective risk management approaches for MPs by highlighting crucial areas for future research. This review seeks to give a thorough understanding of primary MPs and inspire the development of effective mitigation techniques, through a perspective, on which a relatively limited research is available.

2. Occurrence and distribution of MPs

Industrial, domestic and coastal activities are the prime anthropogenic actions that have resulted in the presence of these harmful plastic particles in the ecosystem (aquatic and terrestrial). In addition, the fragmentation of huge plastic garbage and residential runoff, comprising MPs fragments and microbeads (used in cosmetics and other consumer goods), are the major contributors to the entry of MPs into the aquatic ecosystem (Figure 2).⁶ The air-blasted resin pellets and powders that are released by the plastic manufacturing sectors also end up contaminating the aquatic environment. MPs pollution in the marine ecosystem is also caused by coastal activities like aqua tourism, marine industries, and fishing.⁷ MPs pollution in soils is mostly attributed to sewage irrigation, plastic trash, agricultural facilities (such as agricultural compost), surface runoff, fertilizer use and atmospheric deposition.⁸ In addition, MPs are produced during the stacking, disposal, or burning of plastic trash. Other sources of MPs in the environment include clothes, industrial dust emissions, housing infrastructure, and other daily life activities. MPs can be suspended and transported by air in the atmosphere since they are naturally low in weight.⁹ MPs temporal and spatial distribution across the soil, aquatic systems, and the atmosphere is controlled by the transit of those materials, as these can migrate between multiple ecological divisions. For instance, through human activity, wind erosion, and runoff, MPs in the soil can also be carried into neighboring environmental matrices including the water and air.¹⁰ Their movement within the soil is influenced by a number of aspects, including soil texture, cracking, biotic transport (soil biodiversity and soil community composition), and aggregation.¹¹

Figure 2. Occurrence and distribution of plastics into different environmental compartments.

The vertical transportation of MPs in the soil is facilitated by agricultural methods, soil fissures, root growth, and soil pores. Organisms have also been observed to be involved in the mobility and distribution of MPs in soil.⁸ Additionally, it’s possible for MPs in the soil to get into groundwater. Pollution from MPs in the environment may end up in the oceans and on land. Numerous elements, including wind direction, wind speed, particle density, and rain, have an impact on the transportation of MPs and their fallout or deposition in the atmosphere.¹² While some MPs settle through dry and wet deposition processes, others remain suspended in the atmosphere or eventually settle into aquatic and terrestrial ecosystems.¹³ Further, under intense and ongoing hydrodynamic events like waves, rainstorms, ocean currents, monsoons, and tides, the aquatic environment is a dynamic region, and thus, MPs can travel between the marine environment and the land.¹¹ The fundamental characteristics of MPs, such as shape, density, color and size, can have significant impact on their transportation.¹⁴

3. Classification and sources of MPs

MPs are classified into two main types based on their origin and manufacturing processes: primary and secondary. Primary MPs are intentionally manufactured particles, such as microbeads in cosmetics, resin pellets used in plastic production, and fibers from textiles. MPs in the micro-meter size are specifically manufactured for use in industrial abrasives for sandblasting, such as polyester or acrylic beads, plastic pre-production pellets (‘nurdles’), or personal care products like exfoliating agents in creams and cleansers comprising polyethylene ‘microbeads’. Primary MPs particles are most likely to reach wastewater treatment streams, after being washed down by industrial or domestic drainage systems. In spite of the capability of a few sewage treatment works to evacuate up to 99.9% the absolute number of particles entering the system may still permit a noteworthy number to bypass filtration frameworks, and be discharged into the freshwater environment with wastes.¹⁵

Secondary MPs are created as a consequence of the fragmentation of the macro and meso-plastic litter, resulting from the degradation and disintegration of larger plastic items, such as bottles, bags, and packaging materials owed to environmental factors like UV radiations, mechanical abrasion, and microbial activity.¹⁶ High temperatures and UV radiation can induce chemical changes in plastics, causing them to become brittle and therefore more prone to the fragmentation. Fragmentation allows greater surface area and particle count per unit mass. The contributing factors of fragmentation in marine waters are both wave action and sunlight. Plastic fragmentation is considered to occur readily on land, particularly at the soil surface, as a consequence of exposure to ultraviolet radiation from the sun, assisted also by temperature variations that are usually greater than those found in sea water. Despite the fact that microfibres are secondary particles, they will be released into the environment alongside primary MPs, via sewage effluents as well as sludge disposal. As a result, based on similar release routes, the fate and transfer of such fibers could be more closely linked with that of primary MPs. Understanding the distinction between the primary and the secondary sources is crucial for comprehensively assessing the impact of MPs on the environment and human health as depicted in Figure 3.

Figure 3. Primary and secondary sources of MPs in the environment.

3.1. Primary MPs

MPs particles are employed as exfoliants in some personal care product segments, such as hand cleaners, facial cleaners, and toothpastes.¹⁷ Polyolefin particles exhibiting a size of 74-420 μm and an amorphous frame, with no sharp edges were characterized as suitable for use as exfoliants in a US patent for skin cleaners containing plastic microparticles.¹⁸ Polyolefins used in them include polyethylene (PE), polypropylene (PP), and polystyrene (PS). Scrubs have been shown to contain PE microbeads in concentrations ranging from 0.4 to 10.6%, with sizes ranging from 40 to 1000 μm¹⁷. According to a Cosmetics Europe survey, PE accounted for 93% of the MPs used in skin cleaner products in these countries in 2012. MPs are also utilized in medical settings, such as in dental tooth polish and also as delivery systems for pharmaceutical active ingredients.¹⁹ MPs from medical and personal care products can be released into the environment post used via wastewater. MPs are also used in industrial abrasives used for air-blasting the paint off the metal surfaces and cleaning various types of engines, as well as drilling fluids for oil and gas exploration.²⁰ MPs made of poly allyl diglycol carbonate, acrylic, PS, melamine, and polyester (PES) are among the materials found in industrial abrasives.²¹ These may enter the environment if used in open systems or improperly disposed off. Another significant source of primary MPs is the raw material utilized to make plastic products (pre-production plastics), specifically plastic resin flakes or pellets and fluff or plastic powder that can enter the environment as a result of improper handlings, such as through run-off from processing plants or accidental loss during transit. Furthermore, degranulate generated during the recycling of plastic and remnants from plastic processing factories can eventually reach the aquatic or terrestrial ecosystems.

Glitter, a form of MPs, comprised of tiny, flat, shiny particles, is commonly used in household items, cosmetics, and arts and crafts. It is typically made of Mylar^TM, a type of polyester film known as BoPET (biaxially-oriented polyethylene terephthalate), which has a melting point of 260 °C and a real density of 1.38 g/cm^3,22 These particles are water-insoluble and often coated with metal to enhance the reflectivity. While plastic glitters come in a wide range of colors, shapes, and sizes; their environmental impact is a growing concern due to their potential to harm the ecosystems, as they can easily enter the environment and pose risks to life and human health. Though, some manufacturers have introduced biodegradable glitter alternatives made from plant-derived materials; despite this, the widespread use of plastic glitters continues, to raise the environmental and health concerns. Therefore, it is essential to address the ecological and health implications of glitter as a primary MPs, and to explore sustainable alternatives to mitigate its environmental impacts.²³

3.2. Secondary MPs

Secondary MPs are produced when bigger plastic materials break down into smaller pieces. The four human activities responsible for the plastic entery into the environment are thought to be general littering, the dumping of plastic waste, loss from poorly managed landfill sites, and waste collection.²⁴ Additionally, waste from the recycling facilities is lost due to wind contributes significantly toward the MP polluton.²⁵ A huge portion of the plastics, that is produced and used for packaging of goods, with a limited shelf life is habitually dumped in the landfills and is often covered periodically with soil or synthetic material to prevent the trash from being blown away. During natural calamities like strong seas, tsunamis, and hurricanes, substantial amounts of these plastic particles may be released into the ocean.²⁵ Another significant source of MPs found in the environment is low-density polyethylene (LDPE) films, which are employed in enormous quantities to raise soil temperature, protect crops, suppress weeds, and hold irrigation water in the soil (a process known as "plastic mulching"). The particles from these thin plastic foils could wind up in the soil if they crumble. Additionaly, a significant culprit of MPs release in the fibers released after washing PES blankets, fleeces, and shirts in home washing machines. During a single wash, the tested PES fleece released over 1900 fibers in total. Also, synthetic textile fibers are discharged into the air during routine use or tumble drying.²⁶ There are numerous other places from where MPs can enter the environment, such as car tyre abrasion and application of paints & protective coating. Abrasion from other plastic materials, such as household plastics, results in the release of MPs as well.²⁷ Material lost or discarded from fishing boats, aquaculture facilities, merchant ships, recreational boats, offshore oil or gas platforms, and during military operations are examples of ocean-based sources of marine litter. The dominant form in the environment is still unknown, but it is likely location-dependent; for example, the primary MPs may be more significant in areas close to wastewater discharge sources than secondary MPs, which may predominate in open waters. Table 1 provides the spatial and temporal pattern in the abundance of Primary MPs.

Table 1. Spatial and temporal pattern in the abundance of primary MPs.

S. No.	Country	Description	Ref.
1.	Mainland China	In 2015, one-sixth of the 737.29 Gg primary MPs waste from mainland China made its way out into the water. Tire dust and synthetic fiber accounted for the largest percentage of this trash, with 53.91 and 28.77% of the total, respectively.	^28
2.	Netherlands	In STP effluent, the total estimated concentrations of primary MPs from consumer items are 0.2, 2.7, and 66 µ/L in three different scenarios. The three product categories under consideration, namely paint and coatings, cleaning agents, and cosmetics and personal care items, are all significant contributors.	^29
3.	East Asia (marine medaka Oryzias melastigma.	Marine medaka embryos exposed to primary MPs experienced a variety of adverse outcomes, such as heart rate alterations, morphological irregularities, and various forms of deformity.	^30
4.	Sweden	Major kind of detected MPs are fibers and fragments: Influent MPs concentration 15MP L^-1 Effluent MPs concentration 8.3MP L^-1 and Daily MPs discharge 3.6 × 10^-4 MP d^-1^b	^31
5.	Finland (Baltic Sea)	Major kinds of detected MPs are synthetic particle and textile fiber: Influent MPs concentration 430, 180MP L^-1 Effluent MPs concentration 9, 5MP L^-1 and Daily MPs discharge 3.7 × 10^9 MP d^-1	^32
6.	Scotland (River Clyde, Glasgow)	Major type of detected MPs are fibers (polyamide, polyester, acrylic): Influent MPs concentration 16MP L^-1 Effluent MPs concentration 0.3MP L^-1 and Daily MPs discharge 6.5 × 10^7 MP d^-1	^33
7.	Germany (Lower Saxony)	Major type of detected MPs are fibers (polyethylene): Daily MPs discharge 4.2 × 10^4−1.2 × 10^7 MP d^-1	^34
8.	Australia (Sydney)	Major type of detected MPs are fibers (polyethylene): Influent MPs concentration 2MP L^-1 Effluent MPs concentration 0.3,0.2MP L^-1 and Daily MPs discharge 3.6 × 10^6−1 × 10^7 MP d^-1	^35
9.	Canada (Vancouver)	Major type of detected MPs are fibers and fragments: Influent MPs concentration 14MP L^-1 Effluent MPs concentration 1MP L^-1 and Daily MPs discharge 10.6 × 10^9−19.9 × 10^9 MP d^-1	^36
10.	Turkey (Seyhan and Yüreğir WWTP in Adana city)	Major type of detected MPs are fibers (polyester): Influent MPs concentration 4.8 × 10^6 MP per day; 2.0 × 10^6 MP per day Effluent MPs concentration 1.2 × 10^6 MP per day; 0.35 × 10^6 MP per day and Daily MPs discharge 2.2 × 10^5−1.5 × 10^6 MP d^-1	^37
11.	USA (Charleston Harbor, South Carolina)	Major type of detected MPs are fibers, microbeads: Daily MPs discharge 5 × 10^8−1 × 10^9 MP d^-1	^38
12.	China (WWTP located in Wuxi, Jiangsu Province, Eastern China)	Major type of detected MPs are fibers and fragments: Influent MPs concentration 4MP L^-1 Effluent MPs concentration 0.1, 0.1MP L^-1 and Daily MPs discharge 6.5 × 10^6−3.5 × 10^6 MP d^-1	^39
13.	Italy (Northern Italy)	Major type of detected MPs are fibers (polyamide and polyesters: Influent MPs concentration 3MP L^-1 Effluent MPs concentration 0.4MP L^-1 and Daily MPs discharge 10.6 × 10^8 MP d^-1	^40
14.	Netherlands (Dutch River Delta and Amsterdam Canals, Waste water treatment plant, North Sea Sediments and biota)	Major type of detected MPs are fibers: Influent MPs concentration 68–910MP L^-1 Effluent MPs concentration 52MP L^-1 and Daily MPs discharge 7.5 × 10^8−4.3 × 10^10 MP d^-1	^41
15.	Russia (Central WWTP of Vodokanal of St. Petersburg)	Major type of detected MPs are fibers, synthetic particles: Influent MPs concentration 467, 160MP L^-1 Effluent MPs concentration 16, 7MP L^-1	^42
16.	France (River Seine)	Major type of detected MPs are fibers: Influent MPs concentration 260–320MP L^-1 Effluent MPs concentration 14–50MP L^-1 and Daily MPs discharge 8.4 × 10^9 MP d^-1	^43
17.	South Korea (STF of M-city, Y-city, and S-city)	Major type of detected MPs are fibers and fragments: Influent MPs concentration 30, 17, 14MP L^-1 Effluent MPs concentration 0.4, 0.1, 0.3MP L^-1	^44
18.	Denmark (10 largest WWTP)	Major type of detected MPs are fibers and synthetic particles: Influent MPs concentration 7216MP L^-1 Effluent MPs concentration 54MP L^-1	^45
19.	Poland (Southern Poland)	Major type of detected MPs are fibers: Influent MPs concentration 19–552MP L^-1 Effluent MPs concentration 0.028–0.96MP L^-1	^46
20.	U.S. (Florida)	Prove that MPs have contaminated the tissues of intertidal marine predatory snails: 256 MPs were extracted from snails (n = 60), of which 93% were microfibers and 7% were microfragments. Furthermore, 67 MPs (8.375 MP/L) of which 97% were microfibers and 3% were microfragments were extracted from 8 L of seawater.	^47
21.	South Australia (Bellevue Heights, 5050)	MPs can be found in gardens as a result of using plastic landscaping fabrics in the mulch bed or by leaving plastic bubble wrap to be combined with mulches. They were initially quite huge, measuring more than 5 mm. However due to abrasion, weathering, or natural decay, MPs are freed from the garden after seven years.	^48
22.	Rome, Italy (Ospedale Fatebenefratelli Isola Tiberina)	Detection of MPs in human breastmilk Major type of detected MPs are nitrocellulose, polyethylene, polyvinyl chloride, polypropylene, chlorinated polyethylene, polyvinyl alcohol. Breastfeeding moms may expose their infants to toxins from beverages, foods and personal care products, which could have a harmful impact.	^49
23.	U.S.(Orontes River)	Major type of detected MPs are fibers and fragments: Influent MPs concentration 57.2MP L^-1 Effluent MPs concentration 2.1MP L^-1^a	^50

^a MP L^-1: Millions Particles per litre

^b MP d^-1: Million Particles per day

4. Characteristics of MPs

MPs pollution of the environment is now recognized as a risk to ecosystem and researchers have begun to address this field as an issue of importance in recent years, after recognizing the comparative lack of studies on MPs. The effects of MPs on soil ecosystems (both below and above ground) are almost unexplored. Furthermore, the effects of MPs on terrestrial systems vary depending on the type of MPs. It has been demonstrated that the physical and chemical characteristics of MPs influence their ability to bind pollutants.⁵¹

4.1. Physical properties of MPs

4.1.1. Size

The sampling and analytical techniques are frequently used to identify the sizes of micro/nano-plastics. While MPs come in a variety of sizes, the most prevalent range from 1 µm to 5 mm, nano-plastics (NPs) are approximately <100 nm in size.⁵² The research on MPs size has gradually shrunk to less than 2000 µm, due to the progress made in the qualitative and quantitative approaches for MPs. The presence of smaller MPs in the atmosphere warrants additional investigation, as evidenced by the abundance of fluorescent non-fibrous particles <20 µm and smaller fibers that were found in the total atmospheric deposition in downtown London.⁵³ These investigations demonstrated that MPs, which can be inhaled and consumed, make up a non-negligible portion of the atmospheric particulate matter. Additionally, the research suggests that inhaling MPs could be harmful to human health.

4.1.2. Shape

The most frequent morphologies in atmospheric MPs are fragmented and fibrous. In addition, there are other shapes such as spheres, flakes, and films. MPs have distinct physical characteristics depending on their shape. Fibers are typically very thin, flakes are typically thick and asymmetrical, and films are typically thin and flexible. Overall, the primary MPs morphology at the time of manufacture, surface deterioration and erosion processes, and residence time in the environment all affect the form of MPs in the atmosphere.⁵⁴

4.1.3. Color

One of the key aspects for the identification of plastic debris and potential contaminants during sample preparation is color. There have been reports of MPs/NPs in a variety of colors, including green, red, blue, orange, grey, yellow, white, brown, off-white, and tan. For the visual evaluation of MPs particles in the atmosphere, color is generally a helpful parameter. While low-density polyethylene (LDPE) has been given opaque colors, polypropylene has been clear and transparent. When reporting and interpreting results, it is important to take into account that MPs discoloration can happen during sample preparation (H₂O₂-oxidative digestion) and weathering.⁵⁵ Like natural foods, brightly colored NPs particles are frequently consumed by marine species. MPs in the colors black, blue, green, and red are primarily consumed by copepods, zooplankton, fish larvae, and euphausiid.⁵⁶

4.1.4. Crystallinity

Plastics density, permeability, and swelling characteristics are affected by the organized structural links known as crystallinity.⁵⁷ As MPs/NPs spend more time in their surroundings, their crystallinity changes. The polymer’s amorphous area breaking down encourages overall crystallinity and shrinks MPs/NPs size.¹¹ Crystallite materialization may change MPs/NPs from their counterparts and change their toxicity. It ultimately affects the surface area, particle shape, size, and chemical characteristics such as the adsorption of contaminants and additives, which in turn affects the ingestion rate.⁵⁸

4.1.5. Surface properties

Surface chemistry and surface area are the two main components of surface property. Particles in the nanoscale have a significant impact because MPs/NPs surface area grows as particle size decreases.⁵⁸ The deterioration of the plastic surface by photo- and oxidative processes results in the formation of new functional groups when OH radicals, O and N oxides, and other photo-generated radicals are interacted with.⁵⁹ Due to the disruption of the plastic’s surface area by these pathways—chemical leaching, creation of angular-shaped NPs from primary microbeads, and ingestion—microscopic particles are liberated.⁵⁷ Furthermore, because the microbial community uses the oxygenated binding sites, surface chemistry has a substantial impact on particle-biota interactions.⁶⁰

4.2. Chemical properties of MPs

MPs comprise additives (plasticizers, antioxidants), polymers, dyes, and pollutants that get adsorbed on the surface. When plastics are produced, utilized, and deteriorate, these chemicals are easily discharged into the environment.^61,62

4.2.1. Chemical additives

To increase the product’s efficiency, additives are added during the production of plastic to achieve the desired color, and transparency. These additions increase the polymer’s resistance to degradation by biological (bacteria and fungi), mechanical, physical (light radiation, ozone, and temperature) and electrical agents.⁶³ Additives include pigments, ultraviolet stabilizers, flame retardants, lubricants, and plasticizers as well as inert or reinforcing fillers. Additional ingredients include wood, clay or linen, graphite, cellulose pulp, glass fibers, jute, rock flour, cotton flakes and kaolin.⁶⁴ Low molecular weight additives embedded in the polymer matrix are brittle and can escape out into the neighboring water bodies (Polyethylene terephthalate (PET) oligomers from food trays and bottles; flame retardants from electronic items; nonylphenol from food contact materials; Lead (Pb) from un-plasticized PVC pipes; and Antimony (Sb) from PET water bottles).⁵⁹ The majority of MPs and NPs are additives and fundamental polymeric substances made from plastics and chemicals absorbed from the environment and are linked to plastic toxicity (i.e., monomers, plasticizers, solvents, additives-dyes, and catalysts).⁶⁰ These substances disturb the endocrine system, when ingested or inhaled, leading to metabolic diseases, hormonal imbalance, neuro-developmental abnormalities, reproductive issues and asthma. The impact of various additives in plastics on human health is given in Table 2.

Table 2. The impact of various additives in plastics on human health.^11,65,66

	Biocides	Stabilizers, antioxidants, and organic pigments	Plasticizers	Flame retardants
Additives	Heavy metals- Antimony, copper, mercury, arsenic, tin Butyltin trichloride Tetrabutyltin Arsenic trioxide	(TGIC) Triglycidylisocyanurate (TNPP) Tris-nonyl-phenyl phosphate (BHA) 2-t-butyl-4 hydroxyanisole Irganox 1010	(BBP) Butyl benzyl phthalate (MDA) Formaldehyde, 4,4′-methylenedianiline (DIHP) Diisoheptylphthalate (DCHP) Chlorinated paraffins, Dicyclohexyl phthalate	TCPP) Tris(2-chlorisopropyl)phosphate Boric acid (BDE 47) 2,2′,4,4′-Tetrabromodiphenyl ether Heavy metals—antimony, bromine, aluminum, zinc, bromine
Effect on human health	Breast cancer Metabolic and mental disorders Kidney disease Neuronal toxicity Cardiovascular disease	DNA methylation Miscarriages Hypertension Brain damage Anemia	Neuro-degenerative disorder Neuronal toxicity Metabolic and mental disorders Kidney disease	Genotoxicity DNA methylation Apoptosis Osteomalacia and bone fractures

4.2.2. Chemical structure

Higher sorption capacity may result from a chemical structure with a wide surface area or high porosity. For instance, PET had the highest sorption rate, while PE had the largest sorption capacity. The PE, with a higher sorption capacity, leads to more pollutant diffusion, due to its bigger surface area, wider space between polymer chains, and free volume.⁶⁷ As opposed to PE, PET has a smaller surface area and a glassy polymeric structure, which do not facilitate diffusion into the material and so have a faster sorption rate.

4.2.3. Chemical interactions

Pollutant affinity for MPs varies due to chemical interactions such as hydrogen bonding, electrostatic interaction, π–π interaction, hydrophobic interaction, or van der Waals force.⁶⁸ For example, because of the amide groups, hydrogen bonding between polyamide (PA) and antibiotics caused strong affinity.⁶⁹ The difference in the surface charges between amine-modified polystyrene (PS-NH₂) and carboxyl-functionalized polystyrene (PS-COOH), caused embryonic apoptosis, oxidative stress, cell death, and disruption of the cell membrane in the embryos of the sea urchin Paracentrotus lividus.

5. Bioaccumulation of MPs

5.1. Transfer mode of MPs in human body

MPs enter the human body through three main routes: ingestion, inhalation and skin contact (Figure 4).⁷⁰ Due to their prevalence in the water supplies and food chain, MPs are easily consumed.⁷¹ MPs are not able to penetrate the epidermal membrane being too thin, but they might still enter through hair follicles, wounds, or sweat glands. As they can easily enter the environment and pose risks to marine life and human health. The fact is that human body is exposed to MPs through all three channels, although environmental and seafood particles pose the highest danger of absolute exposure.

Figure 4. Three main routes by which plastic particles enter the body: Inhalation, ingestion, and skin contact.

5.1.1. Gastric exposure

Recent investigations on MPs exposure and toxicity have shown that ingesting plastic particles is the main way that people are exposed to.⁷² There are studies demonstrating that MPs are being consumed through food and drink, but there aren’t any explicitly examining the toxicity of NPs in individuals.⁷³ Human feces samples were initially examined, and the results revealed that plastic particles were being ejected, supporting the theory that people are consuming these particles through water and food. These observations, along with studies on ingested uptake in environmental models, unequivocally demonstrate that MPs and NPs consumption by humans will be pervasive.⁷⁴ It would be vital to investigate their pathway via the GI tract and identify whether these particles translocate across the gut epithelia or persist in the gut lumen. MPs ability to penetrate at the paracellular level is uncertain since the pores at the tight junction channels i.e., relevant have a maximum functional size of about 1.5 nm. It is possible that they will enter via lymphatic tissue, and it is more likely that they enter through endocytosis or phagocytosis and invade the Peyer’s patches’ microfold (M) cells.⁷⁵

5.1.2. Pulmonary exposure

Inhalation is the second most likely way for a human to come into contact with NPs. Indoor spaces have airborne plastic particles, mostly from synthetic textiles, which can cause occupational exposure or unintentional inhalation.⁷⁶ Exposure in outdoor areas may occur by inhaling contaminated aerosols from the ocean’s waves or airborne fertilizer particles from dry wastewater treatment processes. The lung’s alveolar surface area is substantial—about 150 m²—and its tissue barrier is very thin—less than 1 µm. Nanoparticles can distribute throughout the entire human body because this barrier is permeable enough to pass through and into the capillary blood system.⁷²

5.1.3. Dermal exposure

MPs/NPs are also commonly found in beauty and health products, especially in body and facial cleansers that are used directly on the skin.⁷⁷ Although there isn’t enough evidence to draw firm conclusions on the impacts of nanocarriers, skin penetration depends heavily on the size of the particles and the health of the skin. Only one study describes that the synthetic textile causes the penetration of nanoparticles on the epidermal barrier at a very minute quantity. The stratum corneum, the skin’s outermost layer, serves as a barrier to protect the skin from injury, microbial agents, and chemicals. Corneocytes comprise the stratum corneum, which is encased in lamellae of hydrophilic lipids which include long-chain free fatty acids, cholesterol, and ceramide. The skin could be exposed to plastic particles by contact with contaminated water or through the use of beauty and health products.⁷⁵ Plastic particles might enter the body through sweat glands, skin wounds, or hair follicles because MPs and NPs are hydrophobic, making it unlikely to pass through the stratum corneum and be absorbed.

5.2. Transfer in the bodies of animals (terrestrial and aquatic)

5.2.1. Terrestrial animals

MPs are ingested orally, where they enter the body, travel through the digestive system and is subsequently eliminated. However, a small number of MPs can persist for days in the intestine of organsms.⁷⁸ Cells can absorb MPs in the intestine through endocytotic processes.⁷⁹ MPs that enter the intestines have also been demonstrated to induce inflammation and mechanical damage. Because of this damage to the intestinal epithelium, MPs can easily spread to other tissues and organs of organisms or enter their bloodstream through intestinal capillaries. Recently, it was shown that NPs can permeate the mucosa and muscularis layers of the intestine, pass beyond the gut epithelium, and then be transferred into other organs (such as the liver) by blood circulation.⁸⁰ This was done using an ex vivo salmon (Salmo salmar) gut sac exposure system.⁸¹ Additionally, MPs can physically break up into smaller pieces as they go through the digestive system, which helps to facilitate their translocation.⁸² An inhalation investigation in maternal rats also revealed that 20 nm NPs translocated to the fetal liver, brain, heart, kidney, and lungs by intratracheal instillation in addition to placenta, heart, and spleen during gestation.⁸³

5.2.2. Aquatic animals

MPs in aquatic animals’ gill canals could be directly injected, translocated to the gastrointestinal tract, or intercepted and then conveyed to the capillaries via the gill filaments.⁸⁴ Exposure to MPs caused several types of damage to fish gills, such as the lifting of epithelial, inner opercular membrane swelling, and aneurysms in secondary lamellae. Another potential pathway for MPs entrance into animal bodies is through the epidermis. By adhering to animals’ damaged skin during the skin’s healing phase, MPs can infiltrate muscle tissue. According to certain reports, some plastic that was wrapped around sea turtles eventually grew into their muscles.⁸⁵

6. Fate of MPs

MPs appear to have no limits in the environment, and they are now pervasive throughout all ecosystems in the world (Figure 5). Plastic waste that has been released into the environment can be carried by the wind, swept from the land to surface waterways during rain, particularly with stormwater runoff, and transported in both freshwater and seawater. Large rivers are expected to transport a significant amount of micro- and macro-plastics into the oceans, although there aren’t many studies to support this hypothesis. Over 50% of the world’s population lives within 80 kilometers of the sea, thus, wind transport of macro-plastics to the oceans may be considerable. Very small MPs, which could be mobilized from open landfills, for example, may potentially be appropriate for airborne transport.

Figure 5. Plastic and plastic product lifecycle.

Depending on the density, plastics will either hover or submerge in water. Plastics having a density less than freshwater (about 1000 kg/m³) or seawater (about 1030 kg/m³) will be buoyant. The majority of consumer plastics, including PE, are buoyant in saltwater (Table 3). Plastics are typically colonized by a variety of species in aquatic environments. By increasing the density, this fouling can cause formerly buoyant objects to sink beneath the water’s surface. The density of a plastic object may decrease if it becomes fouled by other species, causing it to resurface in the water. The specific density of MPs may also vary due to erosion, and wind-driven mixing of the upper water layer may cause previously buoyant MPs to sink. Depending on ocean currents, local winds, and shoreline geography, plastics can be transported over great distances. Beaches and oceanic gyres become overrun with buoyant plastic trash, and benthonic debris which occurs on the sea floor in the region with little circulation. Because smaller particles at the water’s surface are less wind-exposed than larger ones, the mobility of MPs in surface waters may vary from that of macro-plastics.⁸⁷ Animals activity and aggregation of particles may also have an impact on the distribution of MPs. MPs can be covered by silt on beaches and in subtidal sediments, where they can be found at great depths. The movement of MPs throughout the terrestrial environment is still mostly unknown. It was established that the assimilation of micro- and macro-plastic particles into the soil is facilitated by terrestrial organisms like moles and earthworms. Plastic’s photo-oxidative degradation is somewhat effective on a beach surface, but very slowly for plastics buried in soil or beach silt, or deep ocean.⁸⁸

Table 3. Plastic material densities that are frequently observed in aquatic ecosystems.⁸⁶

Abbreviation	Structure	Plastic class	Density (kg/m^3)
PTFE		Polytetrafluoroethylene	2100–2300
PES		Polyester	1240–2300
–		Alkyd	1240–2100
PU		Polyurethane	1200
PC		Polycarbonate	1200–1220
PVC		Polyvinylchloride	1160–1580
PMMA		Polymethyl methacrylate (acrylic)	1090–1200
PS		Polystyrene	1040–1100
PA		Polyamide (nylon)	1020–1160
PET		Polyethylene terephthalate	960–1450
PP		Polypropylene	830–920
HDPE	–	High-density polyethylene	940–980
LDPE	–	Low-density polyethylene	890–930
EPS	–	Expanded polystyrene (Styrofoam)	10–40

7. Ecological risks of MPs

7.1. Effects of MPs on the aquatic ecosystem

Atmospheric MPs penetrate the aquatic ecosystems by both dry and wet deposition. Thus, atmospheric deposition is a significant cause of the occurrence of MPs in the aquatic environment. Due to their longevity, MPs are persistent in aquatic conditions. Some MPs, might sink to the ocean floor as a consequence of having a higher density than sea water, whereas other MPs that are less dense than seawater frequently float on the water. Organisms in freshwater and the ocean may consume MPs.

7.1.1. Effects on aquatic animals

Diverse aquatic organisms, including invertebrates, mammals, fish, shellfish, and fish, consume MPs that enter the aquatic ecosystem. Both active ingestion of seawater and passive ingestion of prey can expose mammals to MPs.⁸⁹ Because of the chemicals involved, MPs can have an impact on the gut microbiome of aquatic animals.⁹⁰ They may build up in the gastrointestinal tracts of aquatic animals, preventing them from ingesting and properly digesting food.⁹¹ Aquatic animals may become poisonous or even die as a result of this. Ingestion of modest dosages of MPs does not always result in the rapid death of organisms. MPs can have a major toxicological impact on fish, including the introduction of oxidative stress and inflammation in the gut. Non-aquatic animals like penguins and seagulls have been known to accidentally consume MPs that float on the water’s surface. The MPs wafting on the water are susceptible to intentional or unintentional feeding by zooplankton because they resemble their food in size and colour.⁹² Microfibres, mostly generated from synthetic textiles, seem to have a higher possibility than other fibers to infiltrate the food chain, as a consequence of ther size and shape. Ther size permit them to be promptly consumed by the aquatic organisms and are more susceptible to becoming entwined in large lumps inside the gut, instigating blockages.⁹³ In addition to having a deleterious impact on the flora and fauna directly, MPs can concentrate on living beings, reach the food chain, progress to various trophic levels, and potentially pose a risk to human health.

7.1.2. Effects on aquatic microorganisms

MPs increase the amount of inorganic and organic carbon in the aquatic environment, which increases microbial activity⁹⁴ and can cause additional CO₂ to be released into the aquatic environment resulting from changes in the CH₄ cycle. The MPs invasion altered the structure and composition of the bacterial communities and reduced the diversity and richness of the biofilm.⁹⁵ Food webs and carbon metabolism in aquatic environments are impacted by changes in the aquatic microbiome. Microorganisms prefer using MPs as novel substrates because of their buoyancy, hydrophobic surface, and capacity for long-distance transmission.⁹⁶ The colonization of pathogenic microbes on the surface of MPs may impact the transfer of deadly microbes into the aqueous environment.⁹⁷

7.1.3. Effects on hydrophytes

MPs that float on the water’s surface inhibit phytoplankton from absorbing light, which prohibits them from offering oxygen and food to aquatic organisms.⁹⁸ The architecture of phytoplankton communities can be drastically altered by high MPs concentrations.⁹⁹ Food webs and ecological processes in the aquatic environment will be impacted by the modifications to phytoplankton colonies. MPs also impair chlorella’s capacity for the process of photosynthesis through oxidative stress and physical deterioration.¹⁰⁰ Algae could become more prevalent in some areas of the phytoplankton habitat. Because they are generally denser than water, common MPs gravitate into aquatic habitats. Submerged plants will experience oxidative stress, antioxidant defenses, and chlorophyll fluorescence characteristics because of these MPs, which will result in decreased plant height.¹⁰¹ Plants submerged in water may be exposed to MPs through their leaves or roots.¹⁰² The presence of microfibrils in the cell wall provided evidence that MPs had penetrated the plant.

7.2. Effects of MPs on the terrestrial ecosystem

MPs are introduced into the terrestrial environment through littering and the dumping of sewer sludge to land. MPs have the capability to penetrate the terrestrial environment through atmospheric transport and deposition. Studies report that both dry and wet deposition are ways in which atmospheric MPs penetrate the terrestrial environment.¹⁰³ Tyre plastic may escape into the ground from the road.¹⁰⁴ MPs from the atmosphere that enter the terrestrial environment either linger in the soil for a long period or decay gradually. MPs build up significantly in the soil, potentially endangering terrestrial ecosystems.

7.2.1. Effects of MPs on the soil biophysical environment

The soil ecosystem is negatively impacted by MPs in a variety of ways depending on their type, size, and shape. Wearing clothing has also been shown to cause textiles to emit MPs into the air, which are then deposited in soil.¹⁰⁵ When textile waste is dumped as litter or thrown away in landfills, it can disintegrate and cause fibers to leak into the ground. Examples include single-use face masks, ropes, tarpaulins, and misplaced clothing.¹⁰⁶ It is believed that organisms like earthworms have the ability to move considerable quantities of MPs from the soil surface to greater depths.¹⁰⁵ MPs, which resemble soil particles in size and form, have less of an effect on the soil’s structure.¹⁰⁷ Since fibrous MPs have a very different form from soil non-linear particles, it is possible that they can coil around soil particles more effectively. MPs shapes have the power to change the biophysical characteristics of the soil. According to a study, MPs can alter the soil’s structure and impair its bulk density and water-holding capacity.¹⁰⁸ Types of MPs have an impact on how MPs and soil pore space interact. As opposed to PES beads, polyacrylic beads and PE fragments did not significantly lessen soil bulk density.

7.2.2. Effects of MPs on soil organisms

MPs pollution changes the soil’s physicochemical characteristics, which impacts soil hydrodynamics and microbiological activity.¹⁰⁹ Different soil microorganisms are affected by MPs in different ways. The microbial populations in the soil may unavoidably change as a result, having effects on the soil’s flora and fauna. MPs affect the composition of the microbial community in the soil. It was discovered that PE considerably altered the composition of bacterial communities and had an impact on their succession.¹¹⁰ By altering the soil environment, MPs have an impact on the evolution of soil microorganism.¹¹¹ MPs can provide nutrients and organic carbon to the soil, and bacteria that make use of this resource have a higher chance of surviving.

Moreover, MPs can be consumed by soil animals. Consumption of MPs may cause soil animals to receive insufficient nutrients, experience oxidative stress, and suffer intestine injury, which will impede their ability to develop and reproduce.¹¹² Lower concentrations of MPs had an impact on the mortality of soil animals in spite of the presence of tissue and immune system damage.⁸ Future studies are required to determine whether the immune system and histopathology can assist as possible indications of sensitivity to ingested MPs. The effects of MPs on soil creatures might vary, depending on their size and concentration. Through experimentation, it was discovered that the presence of MPs could have a considerable impact on the diversity and abundance of nematode and microarthropod communities.

The soil food chain may be affected by the way soil fauna reacts to the addition of MPs. The presence of MPs can drastically alter the soil fauna through extractable chemicals in MPs.¹¹³ MPs from the atmosphere may contaminate soil and have an impact on plant growth as well as on the leaves of the plants through dry and wet deposition. MPs present in the air can cling to leaf surfaces and even enter plants through stomata. Because of the morphology of the leaf stomata, the majority of the MPs that attached to and entered the leaf were found to be fibrous.¹¹⁴ Stomata in plant leaves take in NPs and send them downward to the roots. MPs foliar absorption may impact a plant’s ability to photosynthesis.¹¹⁵ Foliar MPs exposure can significantly slow growth by reducing the area of leaf, weight of dry crop and height of crop.¹¹⁶

7.3. Effects of MPs on the biogeochemical cycles of soil carbon and nitrogen

The carbon and nitrogen cycles, soil microorganisms, climate change, and greenhouse gases (GHGs) are all interconnected in significant ways. According to certain research, MPs deposited into the soil can change the makeup and operation of microbial communities, which in turn can influence the carbon and nitrogen cycles in the soil.¹¹⁷ According to a study, MPs additions can considerably increase CO₂ emissions from soil.⁵⁸ This might accelerate global warming and lead to additional severe environmental issues. The addition of MPs had no impact on soil nitrogen emissions, though. The size of MPs has an impact on the type of dissolved organic carbon in soil. According to a study, PVC hindered sediment nitrification and denitrification, while PUF and PLA encouraged it. The soil’s ability to hold nitrogen was diminished in MPs-treated soils, as MPs modify the porosity of the soil, which could further impact the nitrogen cycle.¹¹⁷ MPs could affect the carbon, nitrogen, and phosphorus-related genes and enzymes in soil bacteria, which in turn could affect the soil nutrient cycle.¹¹⁸

7.4. Effect on human health

As per studies, humans are primarily in continuous contact with environmental MPs through inhalation, ingestion, and skin contact.

7.4.1. Inhalation by respiration

Gravity causes MPs to settle in different parts of the human respiratory system. The body’s concentration of MPs can be decreased through the clearance mechanism. The clearance system may be slowed down by MPs particle toxicity brought on by cytotoxicity, excessive dust load, oxidative stress, and particulate matter translocation, thus impacting the overall human health.¹¹⁹ Because only MPs having sizes less than 10 µm can be ingested, an MPs size influences its respiratory potential. Since, MPs smaller than 10 µm were found both indoors and outdoors, they can also enter the human body though inhalation. Even though mucociliary clearance occurs for the majority of the coarse inhalable particles in the upper airway, some tiny particles can evade this system and settle deep inside the lungs.¹²⁰ As, fragments are mostly transmitted by air, 31 synthetic polymer particles and fibers, of which 87.5% fragmented and 12.5% were fibers, were found in the lung tissue of 13 of the 20 autopsies of the deceased, validating this theory. The upper respiratory tract retains the majority of the MPs that are inhaled. The duration and intensity of MPs exposure also have an impact on the impacts on human health. High levels of MPs in the environment could pose serious threats to people’s health.¹²¹ A mannequin could simulate inhaling 272 MPs within 24 h using a breathing thermal manikin.¹²⁰ When it comes to exposure to airborne MPs, young children are typically more at risk than adults.¹²² Low concentrations of atmospheric MPs typically expose the general public. However, practitioners who are exposed to high levels of MPs on the job, run the risk of developing occupational illnesses.¹²³ The size and form of MPs have a significant impact on cytotoxicity.. Lung cells exposed to MPs experienced significant morphological alterations and a reduction in cell growth.¹²⁴ Human lung epithelial cells’ internalization, cell viability, cell cycle, and apoptosis may be impacted by NPs.¹²⁵ It was shown that exposure to MPs caused inflammation, oxidative damage, and disruption of intercellular junctional proteins in normal human lung epithelial cells BEAS-2B.¹²⁶ Respiratory illnesses, both acute and chronic, may develop from this. Among other things, metals, possible PAH transporters, plastic additives, and airborne MPs were suspected of producing chemical toxicity.⁷⁵

The inflammatory potential of MPs with additives was often higher than that of MPs without additives.¹²³ Ultrafine particles (UFPs) may be inhaled and diffused from the lungs into the bloodstream, or they may be ingested after airway mucociliary clearance. These inhaled or ingested particles may continue to travel in the bloodstream and become harmful to other organs after translocation, including the liver, embryo, brain, etc.¹²¹

7.4.2. Oral ingestion

MPs are typically found in the food and water consumed by humans. Additionally, a lot of MPs are present in commonly used tap water, bottled drinks, and alcohol. In tests of tap water and various brands of bottled water from around the world, MPs particles were found.⁷³ 95% of MPs particles having size in the range of 6–100 µm, or 80% of MP particles with a size of 5–20 µm, were found in bottled water. Moreover, alcohol, salt, and shellfish all contain human-caused MPs pollution. Some MPs that reach the human digestive tract are expelled through feces¹²⁷ and some are still seen in human babies. The human body can develop abrasions, perforations, and even obstructions in the digestive tract as a result of MPs ingestion.¹²⁸ All plastic particles exhibited high resistance to artificial digestive juices, as demonstrated by the effects of artificial in vitro digestion on five types of MPs, and the primary stages of the human gastrointestinal tract do not break down particles.¹²⁹ PE could decrease cell functions and alter the composition of intestinal flora, which would be dangerous for human health, according to in vitro simulation studies on human cells Caco-2 and intestinal flora.¹³⁰ On the other hand, when PS of various sizes was utilized on Caco-2 cells, the particles did not harm or inflame the cells.¹³¹ MPs at the ambient level are unlikely to provide a severe health concern to humans when consumed orally. Epidemiological studies, in vivo animal experiments, and in vitro cell, culture techniques are used in the majority of current investigations on MPs in the human digestive system. MPs present in the human body can accrue in the digestive system or go to other organs e.g., liver, kidney, by oral consumption.¹³² Since MPs get decolorized in the digestive tract, the majority of MPs samples found in human digestion were clear laments.¹³³ It is thus far uncertain whether the MPs pigments stick around in people’s bodies and harm them.

7.4.3. Skin contact and dermal absorption

Pollutants in the form of particles have been linked to skin ageing. Particles from traffic can worsen wrinkles in the nasolabial creases and freckles on the cheeks and forehead. Nevertheless, tiny particulate matter is frequently viewed as a significant environmental hazard that leads to skin illnesses. Skin illnesses can develop and worsen as a result of various air pollution particulates that cause oxidative stress by releasing pro-inflammatory cytokines and reactive oxygen species (ROS). Further study in this area is required because there is no direct indication that atmospheric MPs can enter the skin.

8. Identification methods in MPs analysis

Monitoring of MPs in a range of biotic and abiotic environmental matrices can give fundamental scientific data on their pollution status, concentration hotspots, historical trends, and the fate and exposure of organisms. MPs monitoring studies demand accurate and comparable sampling and analytical techniques. In addition, proper qualitative and/or quantitative analytical procedures for MPs are needed for laboratory accumulation, toxicity, and weathering research. However, because MPs research is a recently reemerging topic, analytical methodologies for MPs are still in the early stages of development. MPs in environmental samples can be analyzed using extraction, isolation (or separation), identification, and quantification techniques (or classification).¹³⁴ Traditionally, preproduction resin pellets and other large MPs in the 1–5 mm size range have been identified by visual sorting with the naked eye.¹³⁵ However, in order to successfully perform an ecological risk assessment, quantification at the smallest scale is essential due to the ubiquitous environmental presence of MPs and their harmful biological consequences.

Researchers have been unable to create a uniform classification of MPs data due to the vast range of sizes of MPs and the complexity of their colors, shapes, and polymer kinds, which makes it more challenging to compare data. Using a single analytical technique, it is challenging to completely and accurately identify MPs of different sizes, shapes, and polymer types from complex environmental matrices. Therefore, it has become common practise to combine more than two analytical methodologies. MPs examination often involves two steps: physical evaluation of putative plastics (using a microscope, for example) and chemical characterization (using a spectrometer, for example) to confirm the presence of plastics. Each technique, as well as different combinations of them, has benefits and drawbacks.

8.1. Visual methods

Large MPs (1–5 mm) were commonly found on beaches and, to a lesser extent, in surface waters before the term "MPs" gained popularity. The size range of MPs is rather wide, hence sorting and identification was typically done side by side in a tray using forceps and the human eye. This visual method can be used to identify some small plastics, and colorful plastic pieces and pre-production resin pellets that vary in size from 2 to 5 mm and can be recognized by sight. There is a greater likelihood that small plastic particles will be missed by sorting in high strandline samples taken from beaches with high concentrations of interfering inorganic and organic materials, or in ambiguous plastics (approximately 1 mm in size) with colors similar to the interfering particles. However, for both specialists and nonprofessional volunteers who have undergone brief instruction, visual sorting and identification of big MPs offers an easy, straightforward, and quick procedure.¹³⁶

8.2. Stereo (or dissecting) microscopy

A popular method for identifying MPs with sizes in the hundreds of micron range is stereo- (or dissecting) microscopy (e.g., neuston net samples).¹³⁷ Microscopy-enhanced photos give objects’ surface textures and structural details in great detail, which is crucial for recognizing confusing, plastic-like particles. Although most particles in this size range can typically be identified by microscopy, it can be challenging to confidently identify plastics in sub-micron-sized particles (<100 µm) that lack a characteristic color or shape.¹³⁸ The microscopic detection of MPs on filter paper can be hampered by sediment samples whose light sediment particles are poorly separated by density. Microscopic inspection is further complicated by biogenic elements from silt and neuston net samples that have not been entirely removed by chemical digestion. According to numerous field monitoring studies, the majority of the MPs in water, sediment, and biota were made up of fibres.¹³⁹ However, by using only a microscope, it was challenging to distinguish between fibers that were synthetic (like polyester) and natural (like colored cotton).

8.3. Scanning electron microscopy (SEM)

Images of plastic-like particles can be seen at extremely high magnification and clarity using scanning electron microscopy (SEM). The separation of MPs from organic particles is made easier by high-resolution pictures of the surface roughness of the particles. The elemental makeup of the same object is revealed by additional investigation using energy-dispersive X-ray spectroscopy (EDS). Carbon-dominant plastics can be distinguished from inorganic particles by looking at the elemental makeup of the particles. The number of samples that can be processed using SEM-EDS is constrained by its cost and the time and effort required for sample preparation and analysis. Plastic colors cannot be utilized in SEM as identifiers. The technique is advised for additional elemental analysis and surface characterization of particular plastic particles.¹³⁹

In some instances, other cutting-edge microscopy methods have been utilized to identify plastic particles. In laboratory accumulation and toxicity investigations, polyethylene (PE) particles were successfully identified using polarized optical microscopy. Polarized light transmission can be affected by the crystal structure of plastics, and this transmission can then be measured.

8.4. Fourier transform infrared (FTIR) spectroscopy

A FTIR can be used for the identification to disclose the polymer composition as well as the abundance of MPs, which can assst in identifying identifying the source. The weathering status of MPs is also shown by the proportional content of oxygenated bonds (such as carbonyl groups) in the IR spectra. By using this technology, it is simple to identify carbon-based polymers, and the distinctive spectra produced by various bond compositions, which allow the plastics to be distinguished from other organic and inorganic particles. A reliable polymer spectrum library permits the identification of particular polymer types in addition to the confirmation of plastics. Micro-FTIR (m-FTIR) is used to conduct microscopic observation of micro-sized plastic-like particles before spectroscopic identification on a single platform by shifting between the object lens and IR probe, which is necessary for small MPs. FTIR measurement for MPs is accessible in transmission, reflectance, and attenuated total reflectance (ATR) modes.¹⁴⁰ The sample preparation step is not necessary for thick and opaque MPs in the reflectance and ATR modes, in contrast to the transmission mode. Additionally, the ATR mode creates stable spectra from uneven MPs surfaces, whereas the reflectance mode creates unstable spectra. Theoretically, it is possible to detect MPs as small as the ATR probe’s IR beam aperture (10 µm, for example). With the identification of plastic-like particles by microscopy and subsequent chemical confirmation by spectroscopy, m-ATR-FTIR now offers a promising way to identify MPs in environmental samples. However, it can be challenging to get distinct spectra for MPs with a maximum length of 50 µm, necessitating numerous attempts. Surface contact analysis is a type of measurement used in ATR-FTIR. MPs that are extremely worn or delicate may be damaged by the pressure from the ATR probe, and small plastic particles may be attracted to or pushed off the filter paper by electrostatic interaction with the probe tip. When used in contact analysis, remains of hard, sharp inorganic particles from sand samples can easily harm an ATR probe manufactured of germanium. By employing the IR spectra to identify each plastic-like particle, it is possible to limit the possibility of missing plastic particles and false-positive quantification of non-plastic particles. m-FTIR equipment is quite pricey. It takes a lot of time to use an ATR probe to identify each and every plastic-like particle. Samples may contain a large number of moderately or severely weathered MPs that are often formed of complicated and occasionally composite materials. Therefore, to acquire clear spectra and correctly interpret them, an expert operator is needed. A professional judgment based on a detailed examination of the spectrum is required when weathered plastics exhibit spectra of different polymers that have poor hitting potential in libraries. This may result in decisions that are made arbitrarily or based on statistical data and the criteria for meeting the percentage values. The human labor required in the FTIR process can be reduced by using pre-programmed, semi-automatic mapping without the requirement for microscopic pre-selection of particles for analysis.

It is uncommon to employ single FTIR mapping for routine examination of complicated field samples since it requires longer operating durations and only covers a small region for the chosen wavenumbers of certain polymer types. When compared to single beam mapping, the shortcomings of the focal plane array (FPA)-based reflectance imaging method could be approved. This method could provide information for the identification of MPs (150-250 µm) on larger surface areas, more quickly, and without sacrificing spatial resolution. Although FTIR operation time is greatly reduced by semi-automatic mapping technology, it still takes at least 9 h to scan a single filter paper. To enable frequent use of this approach in MPs analysis, other challenges must be resolved, that include the potential for plastics to be aggregated and the potential for plastics with irregular shapes to cause refractive errors in the reflectance mode. Therefore, after the analysis, each location and spectrum must now be manually validated. Smaller plastics (e.g., <100 µm) need additional identification due to the reflectance mode’s limits in producing clear spectra for tiny plastic particles. This needs more time for identification by ATR-FTIR or microscopy.

8.5. Raman spectroscopy

Micro-plastics have also been identified by using Raman spectroscopy. Each polymer has a distinct spectrum due to the molecular structure and atom composition that influence the backscattered light frequencies produced when a laser beam strikes an item. Raman analysis not only distinguishes between different types of plastics but also offers profiles of each sample’s polymer makeup, much like FTIR. Raman spectroscopy is analogous to the FTIR method when it comes to the nondestructive chemical analysis and microscopy combination, including the need for pricey equipment. In difficult MPs identification, the various reactions and spectra from FTIR and Raman spectroscopy can conflict with one another. Raman spectroscopy, which uses a narrower laser beam than FTIR, can identify MPs as small as a few millimeters in size. The advantage of Raman spectroscopy’s non-contact examination is that the MPs samples are preserved for potential future analysis. MPs in zooplankton samples can be found using confocal microscopy and Raman spectroscopy. Raman spectroscopy is sensitive to the addition and pigment compounds included in MPs, which makes it difficult to distinguish between different types of polymers.

8.6. SERS (surface-enhanced Raman spectroscopy)

SERS is a rapid, noninvasive spectroscopic analytical technique that uses distinct molecular vibrational fingerprints to identify analytes at the single-molecule level.¹⁴¹ Most molecules in a typical Raman scattering process produce weak Raman signals due to their relatively lower Raman scattering cross-section. Increasing the Raman signals to greater than or equal to the fifth order in SERS requires the use of plasmonic nanostructures composed of Ag, Au, Cu, and Al. The primary mechanism behind this amplification is the activation of localized surface plasmons, which came about as a result of incoming visible light interacting with noble metallic nanoparticles.¹⁴² Specifically, light that corresponds with the electron oscillation frequency produces a localized surface plasmon resonance, which increases the electrical field at the particle surface.¹⁴³ Instead of being uniformly distributed across the plasmonic nanostructure, the produced electromagnetic field is typically limited to sharp edges and tiny interparticle gaps, creating plasmonic "hotspots." Moreover, the elevated electromagnetic field intensifies both excitation and emitted radiation, leading to the notable increase in SERS signals that are independent of analyte type. This phenomenon, known as electromagnetic SERS enhancement, is one of the two established theories for SERS signal amplification.¹⁴¹ One of the challenges in SERS NPs detection might be optimizing the plasmonic hotspot for a strong SERS signal. It is commonly known that structures with sharp edges, are more effective at enhancing scattering strength. Therefore, employing optimally sized and shaped plasmonic nanoparticles to fabricate SERS substrates could be a great option.^144,145

When utilizing SERS, it is essential to choose an appropriate laser power level. It is well known that, depending on the intensity of the laser, the temperature surrounding a hot spot can rise to much greater temperatures than 200 °C. This temperature is greater than most common polymers’ glass transition temperature. To overcome these challenges, it is required to optimize the procedure by regulating the laser’s power, analyte types, and excitation wavelength.¹⁴⁴

8.7. AFM-IR

AFM-IR, or AFM with infrared spectroscopy, is a relatively new method in the sciences that examines events at the nanoscale. In AFM-IR, an AFM scans the surface of the material to provide an image with a high spatial resolution of as low as 50 nm, whereas infrared spectroscopy elucidates the mechanical and thermal properties of MPs. For the detection of PE, PET, and polycaprolactone with a particle size of less than 500 μm, this approach has shown noteworthy success. With spatial resolution below the traditional optical diffraction limits, it is utilized for compositional mapping and chemical analysis. With remarkable precision and detail, this approach provides physiochemical characteristics. It enables further MPs and NPs characterization, including hydrophobicity and conductivity. The technique requires a sample pre-processing step to make presumed MPs accessible to AFM.

8.8. Mass spectroscopy

Using mass spectrometry in conjunction with gas and liquid chromatography, one can analyze MPs by examining the distinct products that are produced during the pyrolyzed or hydrolyzed of MPs. These mass approaches have considerable potential for MPs identification and quantification, especially NPs, due to their outstanding sensitivity.

8.8.1. Inductively coupled plasma mass spectroscopy

The development of isotope tagging technology resulted in the invention of single particle inductively coupled plasma mass spectroscopy (ICP-MS), a novel mass spectrometry method for measuring MPs. This innovative method has made it feasible to measure the size and quantity of nanoparticles. For metal-based nanoparticles in environmental materials, this technique is often employed.¹⁴⁶ For instance, at a comparatively low detection limit of 8.4 × 10⁵ particles/L, ICP-MS has been used to evaluate the size and number concentration of the model Au-coated MPs (at submicrometer scale). Nevertheless, its utilization necessitated extensive sample preparation due to its reliance on an indirect evaluation of the Au coating.¹⁴⁷ It has been shown that ICP-MS can assess model MPs particle sizes and number concentrations by tracking 13 C during the process.¹⁴⁸

8.8.2. Pyrolysis gas chromatography–mass spectrometry (Pyr-GC–MS)

Mass spectrometry-based destructive analysis following the pyrolysis of suspected polymers is becoming more and more popular. This technique employs the thermal degradation of MPs in an inert atmosphere to reveal the structural composition of a macromolecule. Sample preparation for this approach is minimal, and direct injection is a possibility based on the environmental matrix. This method overcomes the problem of potential plastic underestimation because it is employed regardless of particle size and provides information on the mass of polymers in the samples.¹⁴⁹

When analyzing complex matrices, pretreatment procedures that include digestion or separation before injecting the material in the Pyr-GC-MS may be error-prone. As a result, the combination of pressurized liquid extraction (PLE) and other techniques has emerged as a potentially effective method to eradicate certain polymers (PVC, PMMA, PS, PE and PP) from intricate environmental samples. Because it can be difficult to prevent interference when working with environmental samples, double-shot pyrolysis in conjunction with PLE has also been employed.¹⁵⁰ In addition to polymer types, Pyr-GC-MS may identify plastic additives in samples from the first shot, when low-temperature thermally desorbs the interference. But the second shot contains the real polymer identification and quantification. It can provide an estimate of the mass of polymers in each sample rather than a particle count. Pyr-GC-MS, like other methods without optical interrogation, does not reveal the physical form of plastic waste.¹⁵¹

8.8.3. Liquid chromatography–tandem mass spectrometry (LC–MS/MS)

Minimal quantities of polymers can be detected using LC-MS/MS. This a versatile instrument used in medicine, pharmacology and the assessment of environmental exposures to minute heat-labile, nonvolatile chemicals. Polycarbonate, PET and nylon-based MPs were successfully identified and quantitatively analyzed in sewage sludge using LC-MS/MS.^152,153 This method can be detrimental since it necessitates the depolymerization of macromolecules before examination. The mass and quantity of monomers produced during depolymerization are disclosed by the detection method; however, the size, number, color, and shape of the MPs remain unknown. The method can also yield information about the size profile distribution when combined with size fractionation. Additionally, this method necessitates a substantial financial investment, knowledgeable operators, and meticulous sample preparation—which is usually vulnerable to experimental contamination.¹⁵⁴

8.8.4. Matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry

MALDI-TOF is a mass spectrometry technique that uses an ion source of MALDI and a detector of TOF as the mass analyzer. MPs investigations may examine this technique, which has been utilized since 1996 to detect whole bacterial cells without pretreatment. The device has proven to be effective in differentiating between different types of polymers. In conjunction with imaging techniques, it can also make it easier to examine the shape, size, color, and composition of MPs. More specifically, MALDI-TOF is a crucial tool for complex polymer characterization. Recently, PS and PET in complex biological materials have been identified and quantified using this mass spectrometric approach.¹⁵⁵ Perhaps one of the preferred analytical techniques is this one due to its wide mass range of detection.¹⁵⁶

8.9. Shrinking surface bubble deposition (SSBD)

The Shrinking Surface Bubble Deposition (SSBD) method is an innovative way to identify MPs in an array of environmental samples. The method concentrates the suspended particles in the water and deposits them on a substrate for observation and characterization by using plasmonic heating of mixed silver NPs with ambient water samples to produce a bubble through laser excitation. This method enables the direct visualization and identification of NPs in a range of water samples.¹⁵⁷

8.10. Flow cytometry

Flow cytometry is an extremely sensitive tool for detecting fluorescence signals and light scattering, which enables quick quantification of fluorescence-stained (NR, for example) MPs. It has been widely applied to the detection and analysis of MPs, such as molecules, cells, and microbes in liquid samples that are hydrodynamically concentrated into a stream so that they flow past incident light beams from one or more lasers one at a time. Sensitive photomultiplier tubes monitor parameters including light scatter and fluorescence, providing information about surface roughness/granularity (side scatter), size (forward scatter) and fluorescence from pigments or dye markers. A significant benefit of flow cytometry, aside from its sensitivity, is the elimination of human subjectivity because the method does not necessitate the visual interpretation of particles.^158,159

8.11. Thermal analysis

Recently, the thermo-analytical method—which gauges changes in polymer physical and chemical characteristics based on their thermal stability—was put to the test for identifying MPs. The technique of differential scanning calorimetry (DSC) can be used to examine the thermal characteristics of polymeric materials. Each plastic product has unique DSC characteristics; hence the approach needs reference materials to distinguish between different polymer kinds. DSC can be helpful in locating particular principal MPs for which reference materials are accessible, like polyethylene microbeads. Polyvinyl chloride (PVC), polyamide (PA), polyester (PES), polyethylene terephthalate (PET), and polyurethane (PU) could not be detected by thermogravimetry (TGA) in combination with DSC because their phase transition signals overlaps. TGA combined the benefits of a larger sample size with TGA compared to pyrolysis (pyro)-GC-MS and higher resolution with GC-MS compared to DSC when paired with solid-phase extraction (SPE), which was then coupled with thermal desorption gas chromatography mass spectrometry (TDS-GC-MS). The TGA-SPE-TDS-GC-MS approach was used to quantitatively identify PE injected into soil and mussel samples. A polypropylene (PP), polystyrene (PS), and polymer combination were also examined using this method.¹³⁹

Thermal analysis, however, is a destructive technique that precludes the further study of the MP sample. Although DSC analysis is quick and relatively easy, it is not always successful in distinguishing MPs from other polymer products in environmental samples. Chemical additives in MPs can be simultaneously analyzed using thermal analysis and GC-MS. Bulk samples, and single particles, can be examined using GC-MS and thermal analysis, which gives weighted (w/w) concentration data for MPs. The bulk analysis does not, however, offer data on the quantity, size, and shape of the MPs that were analyzed. Contrary to FTIR and Raman spectroscopy, this method demands a skilled operator as well as significantly more time and effort for operating the instrument and data analysis. These techniques would be helpful for screening analyses of bulk samples or further corresponding investigations of MPs that have not yet been thoroughly characterized by spectroscopy, but it seems too soon to employ them for routine analysis of MPs from environmental samples.

8.12. Material-supported MPs/NPs detection

8.12.1. Nanopipettes

MPs have grown in importance during the previous 20 years, and numerous research have examined MPs/NPs in environmental sample data. Scientists have conducted extensive research on this subject and have developed a range of innovative analytical techniques for their detection.^160–162 It has recently been reported that the analytical community has several potential uses for nanopipettes, which are made by heating glass capillaries during the pull-out process. Nanopipettes became popular as a means of developing chemical and biological sensors and conducting ion transport investigations at the nanoscale.^163,164

8.12.2. Microfluidic chips

To swiftly identify MPs in environmental samples, a unique analytical method still needs to be developed and optimised.^165–167 Micro-reservoirs leading to microfilters that are intended to capture all MPs particles in an ultra-compact region were used in the fabrication of the micro-optofluidic platform. To identify the type and nature of MPs present in this ultra-compact space, the researchers were able to successfully enable optical spectroscopy and imaging. Furthermore, passive size sorting was used to separate the MPs based on the size ranges in various reservoirs. The distributed sizes of the MPs samples were recovered using a reference technique that included flow cytometry; however, information regarding their chemical nature was lost in the process. In order to verify the possible use of this micro-optofluidic platform, model samples comprising standard MPs with varying sizes and chemical compositions were combined and effectively examined.¹⁶⁸

9. Global initiatives and control measures by international organisations, regional unions, and associations

Globally, there is increasing concern about regulating MPs and NPs, and several nations have responded to this concern by enacting different laws and regulations. An outline of a few of these policies is provided below (Table 4). In an effort to lessen the negative effects that MPs and NPs have on the environment and human health, these policies combine voluntary actions, regulatory strategies, and international cooperation. The efficacy of these interventions varies and frequently necessitates continual evaluation and accounting in response to novel scientific findings and technological advances.

Table 4. Different policy/strategies/initiatives adopted by the different national/international organisations, regional unions and associations.

National/International	Policy	Goals/ Initiatives	Measures	Ref.
European Union (EU)	EU Plastics Strategy	Make all plastic packaging recyclable by 2030, reduce plastic waste, promote circular economy practices.	Bans on certain single-use plastics, mandatory recycled content in products, extended producer responsibility schemes, and incentives for innovation in plastic recycling technologies.	^169
	REACH Regulation	Regulates chemicals and their safe use, including those that might contribute to MPs pollution.	Requires registration, evaluation, and restriction of substances, including additives in plastics that can degrade into MPs.	^170
	(MSFD) Marine Strategy Framework Directive	EU maritime waterways must reach Good Environmental Status (GES) by 2020.	Member states must develop marine strategies including measures to reduce marine litter, monitor MPs levels, and assess the effectiveness of policies.	^171
United States	Microbead-Free Waters Act of 2015	The production and distribution of rinse-off cosmetics with plastic microbeads are forbidden under federal legislation.		^172
	NOAA Marine Debris Program	Addresses marine debris through prevention, removal, research, and outreach.	Funding for research on MPs, educational campaigns, and partnerships with local organizations for cleanup efforts.	^173
Canada	Microbeads in Toiletries Regulations	Plastic microbeads in toiletries are prohibited nationwide from being developed, imported, or sold as of July 1, 2018.		^174
	Canada-wide Strategy on Zero Plastic Waste	Eliminate plastic waste and reduce plastic pollution	Enhancing extended producer responsibility, improving waste management systems, and supporting innovation in plastic alternatives.	^175
Japan	Act on Promotion of Resource Circulation for Plastics:	Comprehensive approach to plastic waste, promoting recycling and the use of biodegradable plastics	Encourages businesses to develop and use alternatives to traditional plastics and improve recycling infrastructure	^176
	Law for the Promotion of Marine Litter Processing	Targets reduction of marine litter including MPs	Provides funding for local governments to clean up marine litter and improve waste management practices	^177
Australia	National Waste Policy	Reduce waste and improve recycling by 2030	Phasing out problematic and unnecessary plastics by 2025, promoting product stewardship, and enhancing waste management infrastructure.	^178
China	Plastic Waste Management Policies	Limitations on microbeads in cosmetics and nationwide prohibitions on single-use plastics	Phased approach to banning and reducing single-use plastics, improving recycling rates, and promoting biodegradable alternatives	^179
	Action Plan for Zero-Waste Cities	Pilot initiative aimed at creating sustainable waste management practices	Focus on reducing plastic pollution, enhancing waste segregation and recycling, and promoting public awareness	^180
South Korea	Regulations on Microbeads	Ban on the manufacture, import, and sale of personal care products containing plastic microbeads, effective July 2017	–	^181
	Marine Litter Management Plan	National strategy to reduce marine litter, including MPs	Regular cleanup activities, public awareness campaigns, and partnerships with fishing and shipping industries to reduce litter	^182
International Initiatives	United Nations Environment Programme (UNEP)	Global initiatives to combat plastic pollution	The Clean Seas campaign, promoting policy changes, and supporting national and local initiatives to reduce plastic waste	^183
	International Convention for the Prevention of Pollution from Ships (MARPOL)	Includes regulations to prevent pollution from ships, addressing both operational and accidental discharges of plastics	Amendments to MARPOL Annex V prohibit the discharge of all plastics from ships	^184
	Global Partnership on Marine Litter (GPML)	A multi-stakeholder partnership to tackle marine litter	Facilitates international collaboration, shares best practices, and supports research and policy development to reduce marine litter, including MPs	^185

10. Recommendations for future research

The pollution of terrestrial and marine ecosystems by MPs is widespread worldwide. Research on a number of significant sources and release channels for MPs has been compiled in this review. Significant MPs loadings are anticipated across a wide range of environmental situations, which suggests a larger yearly discharge than the figure for the marine environment. After intensive literature survey it was found that there are various gaps in management of MPs which present numerous opportunities for future research. The distribution, movement, and destiny of MPs particles are predicted to be influenced by a variety of dynamic processes in terrestrial and freshwater systems because of their enormous complexity. A series of precise guidelines for further research have been identified by this review, as:

10.1. Harmonic progression of approaches and reporting, with improved quality assurance and control (QA/QC) techniques, to assure adequate data quality and enable accurateness between datasets

The vast range of methodological approaches used in the review for the investigations of the presence of MPs in terrestrial and marine ecosystems, including samples of biota, sediment and water is notable. This includes differences in the methods used for sampling, treating samples, using analytical procedures, and analyzing different particle size classes. Additionally, it is impossible to evaluate the quality of given data because many studies do not use a comparable set of QA/QC methods. Findings are frequently presented in a variety of ways, such as by using various measurement units or by publishing simply summary statistics that vary as well (such as minimum/maximum, mean, or median). The inability of diverse research to be compared is the pinnacle of this variability. In addition to providing useful baselines that can monitor the influence of remediation or reduction measures, collaboration of analytical techniques and investigating formats and the publication of data in appropriate repositories will aid in reducing ambiguity in a comprehensive, global overview of the condition of contamination.

10.2. An exhaustive analysis of the fate, sources, and effects of MPs in agricultural environments

The confluence of numerous MPs particle sources and release channels can be seen in agricultural contexts. Although the extent and relevance of this are mostly unclear, particles may also be linked to greater chemical loads from plastic additives (mostly for reducing the photodegradation of mulching films) or sorbed contaminants (such as from wastewater treatment plants). It is challenging to evaluate the relative contributions of various sources under pertinent environmental conditions or the accumulation of particles over time because agricultural settings are relatively uncontaminated and the destiny of particles in agricultural soils is still poorly understood. The effects of MPs contamination in agricultural ecosystems have only recently been the subject of a tiny amount of research. To get a comprehensive understanding of the dangers presented by MPs over spatial and temporal domains, more research is necessary. This is especially crucial considering the possibility that any adverse consequences could affect the security of the food supply and the health of the land.

10.3. Assessment of road-associated MPs particles (RAMP) as a source of MP to the environment

There are significant awareness gaps regarding environmental loadings, transportation from the road to various matrices, and persistence in gully-pots and water treatment systems for MPs particles associated with the road. In order to precisely estimate the amount of these road-associated microparticles released into the environment, including the contributions from various road-related sources, more investigation is urgently required. This is relevant in view of the recent attention received by these road-associated microparticles in a number of analyses of the worldwide major sources of MPs in the environment. Through the use of a novel and improved method for analyzing these microparticles in environmental samples, quantification should be possible.

10.4. Measures and technologies to separate particles within waste water treatment plant system or to reduce MPs emissions to wastewater

The role of wastewater systems, including their plants and combined sewer overflows, as a release channel for MP particles into both terrestrial and marine environments, was underlined in this research. In order to lessen the load on these plants and restrict releases from untreated discharges like combined sewer overflows, attempts should be made to minimize the amount of MPs particles entering wastewater at the source. A large portion of the wastewater produced worldwide is released untreated and is not connected to a WWTP. The environmental emission of MPs in so many nations would be constrained by improvements in wastewater treatment capacity worldwide. Many MPs forms have sewage sludge application on land recognized as a key release mechanism.

10.5. A Better perspective of the controls sustaining the preservation and transport of MPs particles in aquatic systems, including more accurate flux estimates to the marine environment

From their release to their final destination, MPs particles in freshwater systems are expected to travel over a complicated course. Several processes that obstruct downstream transit may be included in this. To establish thresholds and controls on MPs transport in freshwater environments, these dynamics need to be studied further. The bulk of particles is predicted to eventually end up in the marine environment, via fluvial systems. In order to incorporate the necessary complexity and pinpoint the effective constraints on MP’s release to the marine environment, estimates for this flow must be based on process-based research. As well as identifying zones of MPs build-up in freshwater systems, further research on the dynamics of MPs movement and spatial patterns of contamination can also highlight the places most at risk from potential contamination-related negative effects. This will aid in concentrating efforts to safeguard freshwater environments.

10.6. Further study of the occurrence of MPs in terrestrial and aquatic organisms, with an explicit focus on particle types such as RAMP

The impact of MPs pollution on ecosystems and human health has prompted extensive ecotoxicological studies. However, there is a lack of evidence regarding the uptake of MPs in actual field settings. To address this, a more comprehensive analysis of particle absorption in actual environmental conditions is essential to provide a contextual understanding of ecotoxicological investigations and to enhance risk assessments. Exposure to MPs is a critical factor in evaluating risk, and their presence in the environment can have detrimental consequences for both ecosystems and human health. Furthermore, existing studies have primarily focused on the impact of individual materials, with limited consideration for mixtures of biodegradable MPs and MPs at concentration ratios that reflect real environmental circumstances. It is imperative for future studies to incorporate such mixtures to better understand the combined effects and interactions of different types of MPs. Moreover, the concentration of MPs used in many experiments exceeds those found in the actual environment. Therefore, the concept of "environmentally relevant concentration" has become a significant consideration in toxicity experiments. Additionally, the duration of exposure is a crucial factor, as the continuous exposure to MPs in natural environmental conditions and the slower depuration process compared to other particles can significantly influence the outcomes of ecotoxicological studies.

10.7. Assessment of environment sinks for MPs particles at spatial and temporal scales

This analysis identified a number of potential locations that, in terrestrial and freshwater settings, could serve as transient, long-term, or even permanent sinks for MPs particles. Initial research has looked at the accumulation of some of these particles and their possible residence times. However, study is needed to determine the spatial and temporal scales on which these environments act as stores, as well as the possibility that they could later become sources of MPs contamination through reworking and remobilization. This is required to develop more appropriate and better-targeted remediation procedures rather than relying on quick solutions and acquire a better long-term perspective on environmental damage.

11. Comprehensive strategies for mitigating MPs pollution in textile lifecycles

11.1. The design and production pathway

One strategy for reducing microfibre shedding has been suggested: switching textile patterns to use more natural fibers. Besides this, the increased release of microfibres may be caused by the manufacturing procedures used to create synthetic fibers, yarns, textiles, and goods. Particularly, an essential component in the development of MPs is the use of abrasive friction during manufacture. Microfibre release while using a product could be decreased by employing alternate production techniques or textile construction techniques.

11.2. The use and caretaking pathway

The requirement that all washing machines have a specific microfiber filter by January 2025 was first introduced in France in 2020. Utilizing a washing machine filter can cut the emission of microfibres by as much as 80%. The release of microfibers is also impacted by the utilization of detergent and fabric softener. By designing non-aggressive, liquid detergents that are efficient at low temperatures and don’t rinse off textile finishes, some of which guard against fiber breaking, detergent producers can help reduce the shedding of microfibers. Powder detergents shouldn’t be used on synthetic fabrics because they create friction and break fibers.

11.3. Change in consumer behavior

According to numerous studies, the first few washes of new clothing are when microfibre releases are particularly high. This indicates that fast fashion, in which clothes are worn briefly before being replaced frequently, is responsible for a significant portion of microfibre releases. Therefore, modifications in consumer purchasing habits are required, as well as understanding of the effect that new apparel has on MPs pollution. More regenerative business models, which encourage less consumption and longer use, could allow such a transformation. Reused items typically shed fewer microfibres when washed than new ones, which has the added benefit of reducing both the quantity of new purchases and trash generation. Moreover, preparing an old article for reuse requires fewer resources than the production of a new similar one, thus providing a further environmental benefit.

11.4. The disposal and end-of life processing pathway

In addition to promoting textile reuse and recycling, which would decrease MPs emissions during production and use, textile waste collection and end-of-life treatment can also reduce secondary MPs contamination by preventing littering, improperly managed waste, and textiles being blown by the wind from open landfills. Due to improper disposal, the dumping of trash from open landfills, or the washing of synthetic clothing in untreated waste water, there is a risk that microfibres will spread.

11.5. Increasing knowledge and awareness

To promote research aimed at filling these information gaps on the release, spread, and effects of NPs and MPs, continued public and corporate support is required. To solve the complex difficulties related to various primary MPs contamination from textiles, intensive interdisciplinary collaboration across technical, behavioral, and regulatory measures is required.

12. Conclusions

Concern over MPs in the environment has recently come under fire for being a distraction from other problems endangering the health of the global environment. The impact of plastics on the environment is undoubtedly complex, and innovative approaches are needed to find answers. The fact is that, the outlaw or replacement of plastics is nearly imposible, because of their beneficial qualities and our growing reliance on them. The concern is that both their improper management and expansion into the natural environment are growing, as is their global utilization. Over time, these plastics will break down into MPs and NPs. The effects of these on toxicology or the ecosystem are not fully understood at this time. To comprehend how organic chemical partition coefficients to plastics are changed in the presence of sediment and soil, studies on the dynamic interactions between plastic particles, plasticizer additives, and environmental pollutants also need to be increased. In order to comprehend the mechanisms governing the bioaccumulation of plasticizers and co-transported compounds, studies of chemical dynamics within the guts of organisms are also required. Further investigation into MPs is required to determine their global distribution and potential human health exposure. This requires additional field sampling and the application of standardized analytical techniques.

Acknowledgment

The authors declare that no funds, grants, or other support were received during the preparation of this manuscript.

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Funding

The author(s) reported there is no funding associated with the work featured in this article.