Microplastics in the Ecosystem: A Systematic Review of the Methods for Their Detection and Removal

. Currently, research on microplastics (MPs) has increased due to their rapid distribution throughout the world and their harmful efects on the ecosystem. However, a detailed description of their dispersion and the methods for both detection and removal has not been given. Te objective of this research is to carry out a bibliographic review that allows for a multidisciplinary analysis of microplastic contamination and current detection and removal methods. Te method used is PRISMA in which articles from reliable databases such as Scopus, Web of science, and Google Scholar were collected and analyzed to fnally provide details on the physical and chemical methods for detecting MPs, in addition to presenting the technologies for their removal. As a result of the analysis, critical information was obtained from the diferent studies on the impact of MPs on the ecosystem and the variation in detection and removal efciency according to the type of pretreatment and methods applied to the sample. It is concluded that this research is essential to understand the consequences that MPs have on the ecosystem and provide tools to evaluate and improve current technologies, mainly detection and removal.


Introduction
Te most frequently used polymers presently are polystyrene, nylon, polyurethane, polypropylene, and so on [1].Polymers accumulate in various environments and break down into microplastics as they are exposed to environmental stressors [2].Microplastics are primarily formed by the fragmentation of larger plastic items under various environmental factors, as well as fbers and particles from everyday objects such as clothing and personal care products [3].Microbial degradation can cause plastic to fragment into tiny pieces, which has led to extensive research into microplastics.Tese are defned as plastics with a diameter of less than 5 mm.Plastic's chemical properties, such as its hydrophobicity and its ability to attract other hydrophobic particles, also contribute to this issue [4].MPs found in urban wastewater typically originate from daily activities such as using toothpaste, cleaning products, and shower gels [5].Microplastics are tiny pieces of plastic that are harmful to the environment.Tey can come from a variety of sources, including the shedding of synthetic fbers from clothing during washing [6,7].Disposable face masks used to protect against COVID-19 are another source of microplastics [8].Te COVID-19 pandemic has caused a massive surge in the use of masks and gloves, estimated to be around 129 billion and 65 billion, respectively, per month globally.As a result, the amount of plastics being released into the environment, including the oceans, has signifcantly increased.Tis has led to a rapid increase in MP production, making it crucial to evaluate methods for quantifying, removing, and distinguishing microplastics to better understand the impact of MPs on the environment [9].
Several review articles on MPs have been published, with most focusing on a single method, such as the study by Rani

Origin and Distribution of Microplastic.
In recent years, the demand for plastics has increased globally which has translated into increased production of plastics, amounting to approximately 359 million tonnes per year.In addition, the COVID-19 pandemic in 2020 critically increased the production of plastic waste due to the use of face masks, face shields, and surgical gloves which were personal protective equipment (PPE) [14].Among the countries with the highest production of plastics, China is with a production of 30% of the total produced, followed by the countries belonging to the North American Free Trade Agreement (NAFTA) such as the United States, Canada, and Mexico, which together produce 18% of the total plastics, followed by the African continent with 7%, Latin America with 4%, and the 9 countries that make up the Commonwealth of Independent States (CIS) with 3% of the total production [15].Tese plastics due to poor recycling management end up being dumped in rivers and oceans; a global estimate estimates that this waste is between 1.15 and 241 million tonnes of plastic and that the majority of this material comes from Asian countries [16].
Te durability of these plastics has led to a signifcant accumulation of plastic waste that after some time due to physical or chemical degradation gives rise to MPs, there are also microplastics that are produced directly for the make-up industry, medicine, and others, and these MPs are distributed in diferent environments such as public roads, businesses, restaurants, and marine ecosystems such as rivers, oceans, and seas around the world [17,18].It has been observed that the distribution of MPs is majorly infuenced by either human activities or geographical conditions [19].Te reason behind this is the lightweight nature of MPs, which enables it to be carried to various locations through several means such as wind, water currents [20], precipitation, surface runof, infltration, and river transport.You can refer to Figure 2 for a visual representation of this phenomenon.Residues of MPs move extensively over large distances, evidenced by their occurrence in pristine and remote areas such as the poles [22], deep sea, and oceanic islands [23].

Type of Microplastics in the Environment.
MPs, or microplastics, can be divided into primary and secondary categories.Primary MPs are produced by companies themselves, mainly in the cosmetic and healthcare industry, to market them as additives [24].On the other hand, most MPs are of secondary origin.Tis is because plastic articles are often used in a disposable manner without considering that they can take over a hundred years to degrade in nature [25].Tis degradation can occur due to several factors such as ultraviolet radiation, biodegradation, physical erosion, or chemical oxidation.As a result, smaller plastic particles are released into the environment from items such as textile fbers, toys, and car tires [26].Tese particles, which have a diameter of less than 5 mm, are known as MPs.Secondary MPs are mostly moved to remote areas through tourism, to lakes and rivers through fshing, and to rivers, groundwater, and beaches through wastewater and urban runof, as well as to residential areas through urban transport [27].Table 1 shows the two main categories of MPs based on their origin and sources.
In Figure 3, the types of existing microplastics can be seen, including some captured in the depths of the sea that consisted mainly of colored pieces and the others in makeup microspheres that have already been prohibited in some countries such as England [38], which are the primary and secondary microplastics, respectively.

Secondary MPs
Fibers released during the production of textiles and clothing made of synthetic materials [28] Toys, rubber, kitchen utensils, electrical wires, and interior paint [29] Polyethylene (PE), polypropylene (PP), and polystyrene (PS) particles in cosmetic and medical products [30] Textile fbers originating from clothing due to daily use or washing processes and released from textile manufacturing plants [31] Cosmetic formulations often contain industrially produced microspheres and plastic particles [28] It arises during the consumption and design of plastic products (for example, when plastic bottles degrade) or when macroplastics decompose into MPs [32] Product of the industrial shot-blasting process using microplastics as an abrasive agent [31] Te marketing and use of disposable plastics, focus on straws and plastic bags [33] Synthetic grass (turf ) on the football pitch [34] Material obtained from fshing nets [35] Release of drilling fuids from oil and gas exploration activities, as well as in industrial abrasive processes [34] LDP (low-density polyethylene) sheeting is commonly used in agriculture to maintain soil moisture, control weeds, and regulate temperature, a process known as plastic sheeting [34] 4 International Journal of Ecology and supraglacial [43] wastes and eventually becoming widely distributed causing damage to biotic systems by entering the food chain through direct or indirect consumption, and indirect consumption occurs when food is consumed which transports the MP particles to places further away from their point of origin [44].
Te occurrence and accumulation of MPs occur worldwide, although the highest production of secondary MPs occurs in developing and emerging countries; among the main factors are the lack of recycling policies to raise awareness among the population and poor wastewater treatment management [45].Te occurrence of MPs on agricultural land occurs due to the use of crop fertilizers made from sludge from wastewater treatment plants, as industrial, textile, and domestic wastewater fows into these plants and transports MPs [46].In rivers, the main sources of MPs are the discharge of plastic waste directly into rivers, boil water discharges from urban areas, and surface runof [47].In aquaculture areas, the wear and tear of plastic materials that are part of working tools such as ropes, nets, cages, foam foats, and containers cause the appearance of MPs that pollute the waters of aquaculture ponds [48,49].In groundwater, MPs occur through leaching from the soil surface, percolation of wastewater through pores, and ground breaks.

Microplastic Toxicity.
Te toxicity of microplastics is related to the adhesion on their surface of pollutants and the release of phthalates, bisphenol A, and brominated fame retardants, the latter being used to enhance the properties of plastics which, when entering living organisms, have an impact on their health due to their intrinsic physical properties [50,51].In humans, the entry of MPs into the body can occur with primary and secondary MPs.Primary MPs can enter the body through the epidermis by the use of small plastic particles in cosmetics and orally employing some capsules and tablets that use MPs to enhance drug release [52].In secondary MPs, entry into the body can occur through airborne particles and textile fbers or the consumption of contaminated food, with indirect consumption being the main form of MP entry [53].Ingestion of MPs can occur through the consumption of fshery products [54] such as shellfsh [55], agricultural products such as fruits and vegetables [56], condiments such as basil [57] and cooking salt [58], and other industrial and packaged products such as bottled water due to inadequate water treatment or the constant reuse of bottles [59,60].
Te health efects that MPs can have on the human body are still being studied, and it is not yet fully understood which diseases they can cause.However, some of the possible health impacts of the presence of MPs are discussed below.Te presence of microplastics in the body can damage the intestinal epithelium, alter gene expression and hormone production, cause oxidative stress in the endocrine system, and contribute to skin conditions by entering through the capillary follicles [61].Te bronchioles may also be afected by the accumulation of MPs, as it can cause infammatory injury, oxidative stress, cytotoxicity, translocation [62], and neurotoxicity which is associated with the release of chemical additives such as plasticizers and brominated fame retardants from MPs that interfere with the functioning of the nervous system, in addition to MPs possibly altering reproductive function by afecting fertility and embryonic and transgenerational toxicity [63] (see Figure 4).

Microplastic Identifcation Approaches.
Te identifcation of MPs has now become a priority.However, it remains a challenge due to the intrinsic properties and varied physicochemical characteristics of MPs that make accurate recognition difcult [23].Tere are diferent methods to identify MPs, among which the physical method of visual inspection with the help of microscopes is not very accurate because MPs have a small size and a great variety of shapes, and in the samples, there is the presence of other materials that can generate confusion and an incorrect quantifcation; the use of this method is recommended when analyzing large plastic particles (>1 mm) [64].Another method is the chemical method which presents more precise results such as the use of vibrational techniques used in Fouriertransform infrared (FTIR) spectroscopy and Raman spectroscopy together with their microscopic variables (μFTIR or μRaman) for the identifcation of MPs based on the accessible references.Within the chemical method, we also have the technique of pyrolysis-gas chromatography/  [36,37].
International Journal of Ecology pyrolysis-mass spectrometry (Pyr-GC-MS), which combines two methodologies with pyrolysis [65].Another technique to consider for the identifcation of MPs is scanning electron microscopy (SEM) which provides high-resolution images using the area to be studied to reveal morphological details; this study is usually complemented by energy-dispersive Xray spectroscopy (EDS) which uses a high-energy electron beam to confrm the chemical composition of the particles, as each chemical element emits X-rays with specifc energies [66].Apart from traditional methods, various novel techniques have been developed for the detection of MPs.Tese techniques include thermogravimetry and diferential scanning calorimetry (TGA-DSC) which analyze the properties and thermal responses of polymers in the sample, thermal extraction, desorption, gas chromatography, and mass spectrometry (TED-GC-MS) among others [67].
Te integration of multiple methodologies can complement each other and help overcome the challenges associated with identifying microplastics [68] (see Figure 5).Table 2 shows a detailed overview of the primary analytical techniques used for the detection and quantifcation of MPs.Te table focuses on various pretreatment methods and concentration techniques and highlights the advantages and disadvantages of each method.

Physical Method
(i) Visual inspection method: MPs can be detected through visual inspection or by microscopy to quantify their presence in the samples being analyzed.Tis method relies on the fact that MPs have distinct physical characteristics that make them distinguishable from other particles [82].Te evaluation of microplastics (MPs) usually involves identifying their color and shape, which can be performed without a complex analysis.Tis method has several advantages, such as not requiring extensive training, expensive equipment, or toxic materials.However, it may lack precision, especially when analyzing particles smaller than 500 μm [83].Terefore, it is advisable to use this method for initial procedures or educational purposes only.It is worth noting that the margin of error can be as high as 70% due to the presence of contaminating particles in the sample that resemble MPs, making their distinction difcult [84].

Chemical Methods
(i) Pyr-GC/MS: At frst, high-temperature thermal decomposition of polymers is carried out through pyrolysis, resulting in smaller particles [69].Te temperature range for this process can vary between 500 and 800 °C.Te material obtained from pyrolysis can then be separated by using a gas chromatography column based on their retention time, which can vary according to their chemical and physical properties.Finally, mass spectrometry is used to compare the results of the samples with the library of spectra to identify microplastic particles [85].(ii) Fourier-transform infrared (FTIR): Fouriertransform infrared (FTIR) spectroscopy has three distinctive modes: transmittance, refectance, and attenuated total refection.Each mode is used to identify diferent aspects of the sample under test.In transmittance mode, the infrared spectrum is compared to identify the functional groups and chemical components present in the sample.Refectance mode is used when the sample is too opaque for transmittance mode, and the signal cannot be measured.Finally, attenuated total 6 International Journal of Ecology refection mode is used to provide a strong and easy-to-interpret signal [86].FTIR is an invaluable tool that enables us to identify microplastics by analyzing the vibrations of the chemical bonds in their polymers and also provides us with crucial information regarding the aging of the material by analyzing the carbonyl, hydroxyl, and carbon oxygen groups.Tis makes FTIR an essential resource for any study or research concerning the characterization of plastic materials [87].(iii) Raman spectroscopy (RS): Tis method is a powerful and noninvasive analytical technique that provides valuable information about complex molecular structures.It allows for the evaluation and identifcation of diferent types of materials without altering their integrity, as a high-energy laser with a specifc wavelength used as the output source [88].Tis makes it an important tool for analyzing polymers, as each polymer has its own unique Raman spectrum that can be used for identifcation and characterization purposes [89].
According to [90], this technique has been successfully utilized to quantify MPs with dimensions ranging from 20 μm to 50 nm even in low concentrations and complex environments.(iv) Attenuated total refection Fourier-transform infrared (FTIR-ATR): Tis technique is a relatively fast and nondestructive method that is primarily used for detecting the presence and characterization of MPs through molecular vibration analysis.
To achieve better detection time and precision, it is recommended to apply a pretreatment tailored to the specifc type of sample and analysis objective [91].It is worth noting that despite the advanced technology used for detecting MPs, the method still faces several challenges.One such challenge is detecting tiny particles that are embedded in various groupings or concealed by a biological coating [92].According to Aguirre's study [81], FTIR-ATR analysis revealed the presence of two primary types of polymers: polyester and polyethylene-vinyl acetate.Te correlation rate was found to be between 0.89 and 0.96 for these polymers, indicating their identifcation with high accuracy.(v) SEM-EDS: It is a highly efective analytical technique that combines scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) to identify and characterize microplastics (MPs).By using SEM to generate high-resolution images of the sample, this technique allows for the identifcation of the surface features and size of MPs, as well as other residues that may coincide in the sample.Tis information can be used to understand the degradation of MPs and to develop strategies for mitigating their harmful efects [75].EDS is capable of providing valuable information on the chemical composition of microplastics, allowing for the identifcation of their types.Tis is made possible through the use of X-rays emitted by each element present in the sample.In addition, SEM-EDS is a powerful tool that enables visualization of both morphological and compositional data of inorganic elements with a signifcant amount of carbon [93].(vi) Micro-Fourier-transform infrared (micro-FTIR): Infrared microscopy is a powerful technique that uses infrared radiation to analyze the molecular vibrations of chemical bonds.Tis approach allows for the identifcation and characterization of microscopic particles (MPs) in samples placed under observation, as each bond has its characteristic International Journal of Ecology 8 International Journal of Ecology band in the IR spectra.By using a qualitative method, this technique enables the identifcation of chemical components on a microscopic scale in various ecosystems, making it a valuable tool for scientifc research and analysis [94].Micro-FTIR is a highly precise technique for detecting microplastics (MPs) with dimensions less than 100 mm.However, there is a need for further development of the technique to enable its use in large-scale studies.(vii) Termogravimetry coupled to diferential scanning calorimetry (TGA-DSC): Tis technique utilizes thermal analysis and weight loss control in TGA or phase change in DSC to identify MPs.Tis approach facilitates the analysis of small samples and enables the identifcation of the thermal decomposition of parliamentarians [95].In both scenarios, there is a possibility of errors when attempting to distinguish between diferent types of polymers.Tis is particularly true when there are polymers with similar properties, causing them to overlap and making it difcult to diferentiate one from the other [96].Majewski [78] has successfully employed this technique in various environments including wastewater.Te study was able to accurately quantify PP and PE particles, but it proved challenging to distinguish other communes from MPs. (viii) Termal extraction desorption-gas chromatographymass spectrometry (TED-GC-MS): Te TED-GC-MS technique has proven to be a reliable method for analyzing large samples, with a weight of up to 100 mg, and accurately identifying the mass and type of MPs.Tis technique has the advantage of being both efcient and cost-efective as it does not require prior treatments that consume a lot of time and money.With these benefts, this method is a promising solution for identifying and analyzing MPs in various samples [97].TED-GC-MS analysis is a powerful tool for characterizing polymers by determining the relative proportions of diferent types of polymers present in various environments.Tis information is used to identify and distinguish between diferent types of polymers with a high degree of accuracy [80].

Emerging Techniques for the Removal of Microplastics.
Over the years, several techniques have been developed to eliminate particulate matter and contaminants from different environments.Tese techniques can be divided into physical, chemical, and biological methods, with each method having its own advantages and disadvantages based on the source of the particles to be removed.In this section, we will discuss the latest solutions in detail, including physical methods that use magnetic principles for water purifcation, such as the magnetic nanoparticle method [66].
Moreover, various chemical methods have been proposed in the literature, including electrocoagulation [100,101] and photocatalysis [102,103], which have shown promising results in diferent applications.In this section, the biological methods used for removing microplastics are explained, with a focus on bacteria and fungi.While these eukaryotic organisms have been little studied, researchers continue to investigate their potential to efciently remove microplastics.While this method may not be as efcient as others, ongoing research provides valuable information to enhance their efectiveness [104].Figure 6 provides visual representations of each of the techniques used, and Table 3 ofers expanded information to supplement the visuals.

Physical Methods of Removal. Physical removal
techniques are an efective means of separating contaminants from a mixture without altering their chemical composition.Tese techniques leverage the physical properties of components, such as particle size, density, and morphology, to efciently flter large amounts of pollutants.However, the efectiveness of these techniques may vary depending on the characteristics of the contamination source and the treatment method used [105].When it comes to removing suspended solids from liquids, the sedimentation technique is commonly employed, relying on gravity to perform separation.However, particle retention-based methods such as ultrafltration (UF) and rapid sand fltration (RSF) can also be used to remove MPs, with varying efciency depending on their unique physical characteristics [109].Last, the article highlights two additional methods: one that utilizes polyoxometalate magnetic absorbers and another that employs dissolved air fotation [68].
(i) Rapid sand fltration (RSF): Te method exclusively relies on physical mechanisms to flter MPs by utilizing two types of force: the intermolecular van der Waals force and external forces that generate mechanical deformation.Tis approach ensures efective fltration and removal of MPs from the system [134].RSF fltration involves the use of a sand layer that captures and retains solid particles.Tis system consists of a layer of coarse sand with a granular size ranging from 3 to 5 mm.Te water passes through this layer and then goes through quartz with particles ranging from 0.1 to 0.5 mm, which efectively captures and retains the MP particles [109].(ii) Dissolved air fotation (DAF): It is a highly efective method used for the purifcation of suspended particles, including MPs (particulate matter).Te process involves introducing air microbubbles into water, which come into contact with the suspended particles and form a layer of sludge that can be easily removed.However, the efectiveness of the removal of MPs (microplastics) depends on various factors such as temperature, mixing speed, and air saturation.By analyzing these variables, the treatment system can be optimized to achieve better results International Journal of Ecology [135].Te method is not only safe but also highly efective, as it eliminates the need for direct contact with toxic compounds.In addition, the DAF system is cost-efective due to its minimal maintenance requirements and energy-efcient operations [136].
(iii) Disc flter (DF): Te fltration system comprises a series of circular discs, which are perforated and stacked in an airtight container.Typically, the meshes are made with high-quality polypropylene, polyester, or polyamide, which allow water to pass through while retaining any contaminating particles.Te size of the pores ranges between 10 and 40 microns, making it highly efective in fltering out impurities.Numerous studies have proven the remarkable efciency of this fltration system in producing clean and safe water.According to the research conducted by [110], the DF method demonstrated a remarkable retention rate of 89.7% for the particles, efectively capturing a signifcant portion of MP particles from wastewater.Over time, the surface of the flter may gradually accumulate sediment, which can lead to a decrease in fltration efciency.To maintain optimal performance, it is recommended to periodically clean the flter by washing away any accumulated sludge using high-pressure counterfow or using sodium hypochlorite.Tis will help ensure that the flter continues to operate efectively and efciently [111].One key factor that impacts the efciency of particle removal in a disc flter is the mesh size.A larger mesh size can flter a greater amount of particles, making it an important consideration for optimal fltration [137].(iv) Ultrafltration (UF): UF technology is a costefective way to purify water and remove contaminants without relying on expensive equipment or additives.Recent studies, such as the one mentioned by [112], have demonstrated high efciency rates in the removal of MPs, ranging from 86% to 97.96%.Te efciency of UF depends on the size of pores, design, material, operating pressure, and maintenance carried out on the membrane used, since these factors intervene in the retention of MPs particles [138], facilitating their electrostatic interaction with each other and the membrane surface.Hence, the correct confguration of the system is of paramount importance [139].(v) Dynamic membrane (DM): Te DM method is designed to minimize the buildup of deposits in the primary membrane by utilizing a highly permeable mesh with tiny holes that are on the scale of micrometers or millimeters.Tis mesh aids in the formation of a sedimentary layer that functions as a secondary protective layer, thus reducing the pressure in the primary membrane [140].An innovative approach to improve fltration efciency involves using an additional membrane as a protective layer.Tis method is efective in fltering out remaining contaminant particles and MPs at a higher rate.Moreover, this system operates solely   International Journal of Ecology Water passing through the membrane forms a concentrated polarization layer, which negatively afects fltration efciency due to fouling [112,113] Dynamic membrane (DM) 99% Low resistance to fltration, low transmembrane pressure, ease of operation, and absence of chemical treatment Due to its oily nature, frequent cleaning is necessary to prevent excessive membrane fouling and sediment accumulation, which leads to high-energy consumption [99] Magnetic nanoparticle method <92% By removing organic, inorganic, microbial, and microplastic pollutants from water, the magnetic compound can be easily retrieved using a conventional magnet It causes fragmentation of more fragile particulate matter and requires fltration suitable only for small water volumes [103,114,115] Chemical methods of removal Coagulation/focculation 61% Suitable for removing small microparticles, operating under adjustable conditions, and utilizing simple mechanical mechanisms Chemicals must be added to the medium for small microplastics [116] Electrocoagulation >90% No risk of contamination, efective for small particle removal, cost-efcient, and fexible for automation while minimizing sludge Repeated replacement of sacrifcial anodes is necessary to prevent cathode passivation.In addition, this product is not suitable for use in areas without access to electricity [100] Micromotors 67% Water is utilized as a nontoxic source for the efective removal of suspended particles and microplastics, while sunlight is harnessed as a renewable energy resource It takes a chain of magnetic clusters to overcome obstacles and lacks selectivity [117,118] Microsubmarines 70% Sustainability is demonstrated through recycling and the elimination of oil and microplastic pollution Microsubmarines have limited transportation capacity, thus requiring the combination of multiple microsubmarines in order to achieve sufcient capacity [119,120] Biological methods of removal Oxidation ditches 97% Compared to other biological treatment methods, sludge generation is reduced and less energy is consumed during the process Tis method is highly efcient in smaller facilities but requires more space than traditional treatment plants [108,121] Anaerobic, anoxic, and aerobic (A 2 O) 72-98% High organic loads can be handled with minimal sludge production Te anaerobic treatment process requires sufcient time to become efective [104,122] International Journal of Ecology 99.9%It is capable of removing high levels of biological oxygen demand (BOD) and chemical oxygen demand (COD) from a variety of wastewater compositions One of the major issues is the inability to eliminate contaminants that are resistant to removal [123,124] Sequential batch reactor (SBR)

92.74% It ofers an afordable solution for achieving lower levels of efuent contaminants, allowing for easy expansion and simple operation with low capital costs
Efective aeration control is essential for optimal SBR efciency, and the presence of sand can hinder this process [125] Conventional activated sludge (CAS) 95-99.9%Te treatment is cost-efective, adaptable to various tributary concentrations, and resistant to changes Te tank's long residence times, large settling surface, and high-energy consumption result in costly sludge processing and disposal [98,126] Adsorption on green microalgae 94.5 Te cut surfaces show a strong ability to attract small microplastic particles, and the selection is based on the surface charge of these microplastics Nonreusable method, with microplastics that chemically adhere to the surface, potentially contaminating it [127,128] Fungal degradation 59% of the weight of the MPs Natural decomposition through enzymes produced by fungi Te removal of MPs takes a long period, as it only becomes signifcant after an incubation period of 280 days at a temperature of 25 °C [129,130] Bacterial degradation 20.4-97% Te application of bacteria is highly selective, reducing the likelihood of generating harmful byproducts.Furthermore, it consumes less energy and is more cost-efective than chemical procedures and applicable in a variety of contexts Sometimes, the elimination of contaminants is not complete, and the process can be prolonged.Furthermore, it can be difcult to identify the right group of bacteria for efcient removal of MPs [131][132][133] 12 International Journal of Ecology on gravitational force, eliminating the need for bombs [141].(vi) Magnetic nanoparticle method: Magnetic particle separation is a technique that enables the removal of MP fragments from water using magnetic particles.Tis makes it easier to treat large quantities of water, making it more advantageous than traditional fltration techniques.Magnetic particles, such as Fe nanoparticles, have a hydrophobic property, which makes it easy for them to adhere to their surface and facilitate their collection using magnetic methods [121].According to recent research, magnetic carbon nanotubes (M-CNTs) have proven to be effective in adsorbing various polymers such as polyethylene (PE), polyethylene terephthalate (PET), and polyamide (PA).Te tests carried out showed that the total removal of MPs was achieved in just 300 minutes using 5 g•L −1 of M-CNTs in a concentration of 5 g•L −1 of MPs [142].A noteworthy study on this method was conducted by [126].Tey utilized a superparamagnetic iron oxide core (Fe 2 O 3 , hematite) that was coated with silica (magPOM-SILPs) on the outer layer.Tis coating had a high afnity to interact with various contaminants such as organic and inorganic particles, germs, and MPs in aqueous solutions.Te technique facilitated their extraction using a permanent magnet, making it easier to separate them from the solution.
3.6.2.Chemical Methods of Removal.Conglomerates can be formed through chemical reactions that transform the MPs in the chemical method.Tis process can also be utilized to decompose or make the surface of MPs adherent, which helps in extracting them from water using flters or other procedures [116].When employing the chemical method, a common approach is to introduce certain chemicals that can interact with the polymer particles, leading to the formation of focs.Tis process facilitates the fltration of MPs, but it may generate waste or sludge that needs to be collected afterwards [106].Scientists are currently conducting studies to identify the optimal coagulants or parameters that need to be considered for efcient removal of MPs.Tese parameters include the type of coagulant, the appropriate dosage, and retention time [70].
(1) Coagulation/focculation: Electrocoagulation is an efective method for removing microplastics from aquatic environments due to the negative charge of MPs.In various studies, the use of iron salts (Fe 2 (SO 4 ) 3 .9H 2 O and FeCl 3 .6H 2 O) and aluminum salts (KAl(SO 4 ) 2 .12H 2 O, AlCl 3 .6H 2 O, and Al 2 (SO 4 ) 3 .18H 2 O) has been found to be efective in adhering to MPs.In addition, focculants are used to facilitate the formation of globules that can be easily precipitated to the base of the coagulation tank [143].Te process of removing MPs from water before releasing them into the environment is imperative in water treatment plants.Recent tests conducted by [144,145] have shown that coagulants containing aluminum and polyacrylamide are highly efective in removing MPs from water.(2) Electrocoagulation: Tis is a potential technique to remove MPs and has the advantage that it does not leave sludge residues like coagulation, since it uses electric current in the sacrifcial electrodes for the release of metal hydroxides, which precipitates MP particles, avoiding the use of chemical additives [146].Tese electrodes can be made of various materials, but the most used ones are aluminum and iron, which after the electrochemical reactions produce metal ions from the anode and hydroxide ions from the cathode.Te latter adhere to MPs, obtaining more voluminous conglomerates that can be fltered more easily [147].(3) Photocatalysis: Tis technique for removing MP particles involves the use of solar energy to activate photocatalysts.Tese photocatalysts speed up chemical reactions that degrade and decompose MP particles through oxidation.Te process of photocatalysis is cost-efective and does not have a negative impact on the ecosystem.Terefore, it is a promising technique for the removal of MPs [107].One of the materials used for photocatalysis in the removal of particulate matter is titanium dioxide (TiO 2 ).Most studies on MP removal use TiO 2 since it can absorb light, particularly ultraviolet light, and generate pairs of electrons and holes in its crystalline structure.Tis occurs due to the diference in energy between the conduction and valence regions when TiO 2 is continuously exposed to light.As a result, the surface temperature rises, leading to the removal of contaminating particles from water [148], Examples of this are the micromotor and the microrobot, which will be detailed as follows: Micromotor: Tese are materials capable of selfpropulsion through the conversion of energy into mechanical motion.Photocatalytic activity can play a role in this process, as in the case of a study by [149], where the micromotor was made of titanium dioxide (TiO 2 ) and utilized the photocatalysis of hydrogen peroxide (H 2 O 2 ) with visible light to move itself.In the absence of light, it used glucose oxidase (GOx) to continue moving.Te movement of the micromotor is a result of photochemical reactions that occur in water and H 2 O 2 due to electron holes [118].In a recent study conducted by [117], TiO 2 was used as a base material, in combination with other elements, to eliminate microplastics (MPs) from water.Te resulting material, called (Au@mag@TiO 2 , mag � Ni, Fe), exhibited excellent mobility when exposed to UV radiation and H 2 O 2 in water.When tested in river water, it demonstrated a 67% efciency in MP removal.
Microrobots: Tey are a recently developed technique for eliminating MPs, based on self-propulsion using light, which allows them to interact with their surroundings.To International Journal of Ecology achieve the best results in terms of micromotor speed, various semiconductors must be tested to identify those most sensitive to light [150].For example, the photocatalytic microrobot propelled by light, constructed with bismuth vanadate (BiVO 4 ) developed by [119], has the ability to move efciently in aquatic environments under visible light stimulation, adhere to the surface of diferent polymer structures such as polylactic acid (PLA), polycaprolactone (PCL), polyethylene terephthalate (PET), and polypropylene (PP), and decompose MPs into small organic molecules and oligomers.

Biological Methods of Removal.
Te biological approach utilizes microorganisms like bacteria and fungi to break down MPs and organic substances in wastewater through aerobic and anaerobic processes.Te research conducted by [151] suggests that aerobic processes are more efcient in degrading organic matter and MPs than anaerobic processes, which are primarily used for sludge stabilization.According to [152], after treatment, a total of 2.743 MP/kg (dw) are left in the sludge, indicating that microorganisms are capable of removing MPs when enzymatic activities occur [153].
(1) Oxidation ditches: Te oxidation ditch treatment method is based on the principle of activated sludge.It is used for treating wastewater and involves aerobic biological processes that occur in the oxidation channel.During these processes, organic substances and MPs present in water are decomposed [154].
Tere are four generations in this method.In the frst generation, oxidation ditches are used to combine oxygenation processes and gradual decantation of water intermittently.Te second generation involves the addition of a vertical aerator with microorganisms that transform nitrogen compounds into different elements through nitrifcation and denitrifcation.Bacteria are used to transform nitrates into gaseous nitrogen (N2).Te third generation achieves signifcant dephosphorization and denitrifcation, enabling the fourth generation to use a return system to improve MP removal efciency [108].Recent studies have demonstrated that this method is highly efcient, achieving a 97% removal rate of MPs [121].(2) Anaerobic, anoxic, and aerobic (A 2 O): Te technique includes three phases: the frst is anaerobic, which afects the organic load, followed by the anoxic phase, and fnally the aerobic phase.Denitrifcation takes place during these phases, which helps in reducing the amount of nitrates in water, capturing phosphorus, and oxidizing organic material [142].
Te study conducted by [126] demonstrated the efectiveness of this method in degrading microfbers, achieving a removal efciency of 98.3%.Furthermore, another study conducted by [155] found that the method was highly efcient in removing MPs from wastewater, with a removal efciency of 99.18%.Te presence of these pollutants in the sludge further supports the potential of this technique for wastewater treatment.(3) Membrane bioreactors (MBRs): To produce a highquality treated efuent, a technique that uses membranes and microorganisms in an aerobic environment is employed to remove MPs.Te process involves transferring the contaminated water to the bioreactor, which then flters MPs from the water fow through a membrane [156].Filtering membranes can be classifed as microfltration or ultrafltration depending on pore size.Most membranes have pores with a diameter of 0.1 micrometers, which easily retains MP particles and microorganisms [139].Tis technique efectively eliminates MPs, but avoiding membrane fouling is crucial [157].(4) Sequential batch reactor (SBR): It is a wastewater treatment system that is confgured to work sequentially, allowing treated water to pass through all treatment phases to remove contaminating residues and fragments of MPs [158].One of the main advantages of this system over conventional techniques is that it can perform the entire treatment in a single tank [159].Te SBR system has one inlet for wastewater and an aerator system that uses compressors with a stage for sludge renewal.Furthermore, it has an extraction mechanism to separate purifed water and regulation systems to program the operating sequence [160].(5) Conventional activated sludge (CAS): Te system is designed to treat wastewater by utilizing microorganisms that break down organic matter.Tis system is composed of two phases.In the frst phase, air is mixed with boiled water to facilitate the biodegradation of particulate matter by creating bioflms generated by microorganisms.In the second phase, decantation is performed to separate the biological sludge from the treated water, which effectively removes MPs [161].Tis technology efciently removes MPs with a 95 to 99.9% success rate, particularly from microfbers [126].(6) Role of microalgae in the degradation of microplastics: Tere are certain organisms, such as the green alga Scenedesmus dimorphus, the diatom Navicula pupula, and the blue-green alga Anabaena that can decompose microplastics through biodegradation processes.Both high-and low-density polyethylene can be decomposed by these organisms.
In fact, the degradation of low-density polyethylene (LDPE) has been noted to be particularly efcient [131].Microalgae degrade polymeric substrates on plastic surfaces in wastewater using ligninolytic enzymes and exopolysaccharides [162].(7) Fungal degradation of microplastics: Biodegrading plastics can be challenging due to their chemical and physical properties, which include a high molecular mass, hydrophobic nature, and low solubility.
14 International Journal of Ecology However, using flamentous fungi in bioremediation processes presents a viable solution to tackle this issue [129].Fungi possess the ability to trigger the creation of diferent chemical bonds in microplastics.
Tese bonds include functional groups like carboxyl, carbonyl, and ester.Fungi's flamentous structures, called hyphae, are widely distributed and can penetrate the surface of polymeric materials efectively.
As a result, they can establish connections and initiate the degradation process of plastics [163].Fungi belonging to the genus Aspergillus, such as Aspergillus niger, Aspergillus favus, and Aspergillus oryzae, are mainly used in biodegrading low-density polyethylene.Tis is because of their natural ability to be produced abundantly and grow extensively [164].(8) Bacterial degradation of microplastics: Most of the bacteria that are capable of decomposing plastic materials through enzymatic processes belong to Gram-negative bacilli.Specifcally, Pseudomonas bacteria have proven to be highly efective in biodegrading various plastics, including polyethylene variants of both natural and synthetic origins [165].
According to research conducted by [114], highimpact polystyrene emulsions containing nanometer-scale plastic particles showed a signifcant reduction in turbidity within four days of exposure to Bacillus spp.and Pseudomonas spp.strains.Te study observed a decrease of 94.0% and 97.0%, respectively.According to a study conducted by [133], polyethylene sheets of 30 μm and 40 μm thickness were exposed to various types of bacteria including Bacillus, Brevibacillus, Cellulosimicrobium, Lysinibacillus, Ochrobactrum, and Pseudomonas.Te study found that Bacillus cereus and Brevibacillus borstelensis had the highest biodegradation rates, with percentages of 35.7% and 20.4%, respectively.

Conclusions
Te lack of policies that raise awareness among the population about the management of plastic waste and the poor recycling of products, together with the environmental factors that degrade them and the cosmetic and medical industry, have generated an increase in the production of MPs, which are distributed in the most remote places because they are easily transported through the air, sewage, and food, afecting the fora and fauna of the places where they are deposited.Strategies to reduce the impact of MPs on the ecosystem have focused primarily on wastewater treatment plants because the channels through which water passes make it easier to control the detection and removal of MPs.Te technologies shown in this study for the detection and removal of MPs have limitations when applied, especially if applied individually, since efciency could be reduced.So, a solution will be to combine diferent techniques based on their advantages and disadvantages to improve efciency and their application in real situations, since if MP particles are too small or the water is too turbid, their identifcation or removal becomes more complex.Terefore, it is very important to focus on improving the detection and removal technologies of MPs, taking into account that in this study, with the aforementioned techniques, a higher concentration of MPs was detected in wastewater with concentrations that have reached up to 100 μm, and the technique with the best removal efciency has been membrane bioreactors with an efciency of 99.9%.

Figure 1 :Figure 2 :
Figure 1: PRISMA fowchart.Te fowchart presents the results and screening process of the original searches and the rerun of the searches.

Figure 4 :
Figure 4: Schematic illustration of exposure of MPs to human health.

Table 1 :
Proven origins of primary and secondary MPs.

Table 2 :
Table of microplastic detection methods.

Table 3 :
Methods applied in the removal of microplastics.