Determination of microplastics in municipal wastewater treatment plant effluents and sludge using micro-Raman spectroscopy
0 Abstract
Microplastics (MPs) increase global awareness due to their ubiquity, high concentration levels, and devastating effects on the aquatic environment. Wastewater treatment plants (WWTPs) are recognized as a significant source of microplastics in aquatic and terrestrial environments, particularly for plastics used in personal care products and textile fibers from the clothing industry. The focus of the present study was the determination of MP in wastewater and sewage sludge samples of WWTP of Ioannina city, according to their shape, size, concentration, and polymer type. A wet peroxide oxidation (WPO) method using 30% H2O2 and 0.05 M ferrous (II) solution was applied to the water effluent, while an enzymatic digestion method combined with WPO was employed to eliminate the organic matter and extract MPs from sludge samples. Micro-Raman spectroscopy coupled with appropriate software was applied to detect and quantify the microplastic particles. The outcomes from this study showed that the most representative shape of MP in effluent wastewater and sludge was fragments (66.7% and 75%, respectively), followed by fibers, spheres, and films. Polyamide (PA), p-acrylic acid (PAA), and p-acrylamide-co-p-acrylic acid (PAM-co-PAA) were the most abundant polymers (100% frequency of detection), followed by p-vinyl chloride (PVC), p-butyl methacrylate (PBMA), p-ethylene (PE), p-styrene (PS), p-propylene (PP), p-vinyl alcohol (PVA), and p-vinyl butyral (PVB) (20%-80% frequency of detection). The mean concentration of MPs in five sampling campaigns was 5.8 ± 0.6 particles/L in secondary WWTP effluents and 33.3 ± 8 particles/g in sludge. This study focused on monitoring campaign, in order to better understand the occurrence, impact, and risks associated with MPs on WWTPs.
Keywords
INTRODUCTION
Plastic particles ranging in size from 0.001 to 5 mm, so-called microplastics (MPs), have been used extensively during the last decades, while biotic and abiotic degradation of plastic debris also resulted in their formation in significant amounts. In compliance with the Commission Delegated Decision (EU, 2024/1441), “microplastic” is defined as a small unobtrusive particle that is solid, insoluble in water and composed partly or wholly of synthetic polymers or chemically modified natural polymers[1]. Based on the hazard model adopted from the Globally Harmonized System of Classification and Labelling of Chemicals (GHS) by the United Nations, the majority of plastic polymer types are considered hazardous substances[2]. The comprehensive presence of microplastics on a global scale has raised worldwide concerns affecting any environmental parts[3]. In 2023, European plastics production reached 54 Mt., and by 2050, 12,000 Mt. of plastic waste will have been dumped or released into the environment[4].
Depending on their origin, MPs can be divided into two groups: primary MPs that are used in different products such as personal and cosmetic products and originate from the release of small particles in the environment during personal and industrial use, manufacture, and transportation[5]; secondary MPs result from fragmentation of larger particles due to various processes such as chemical/mechanical degradation, hydrolysis, photodegradation, biodegradation, and other mechanisms[6,7]. MPs are also classified according to the form, size, and composition of the polymer[8].
Wastewater treatment plants (WWTPs) represent the final stage of the man-made water system, receiving microplastic pollutants from a variety of sources, including household and industrial activities[9,10]. In this sense, WWTPs are recognized as one of the largest sinks of microplastics and are not always able to efficiently remove microplastics during treatment, resulting in their release into the environment[11]. Since then, MPs have been deemed emerging pollutants demonstrating significant effects on biota and humans. Conventional WWTPs have been evidenced to reduce 60%-80% of MPs from the water phase, resulting in their transfer to the sludge phase. This sludge can be landfilled or used as agricultural biosolids after treatment. For example, Talvitie et al.[12] reported that around 80% of both plastic and non-plastic microplastics are distributed in dried sludge, while Vollertsen and Hansen[13] estimated that around 75% of microplastics are present in the sludge phase.
Polyamide (PA) (~ 53%), polyethylene (PE) (~ 17%), polyester (PES) (~ 90%), polypropylene (PP), polyethylene terephthalate (PET), and polystyrene (PS) are among the most common polymer types present in wastewater and sludge[14,15]. These polymers are discharged into wastewater due to human activities and have applications in various products such as packaging, textiles, and consumer goods. Specifically, PET is a type of polyester originating from clothing and textiles, PA is a polymer used in textiles and fishing gears, and PE is used in facial or body cleansing products, wrapping film, and water bottles[16-18]. The concentration of MPs in wastewater has been studied widely. In contrast, research on sludge is relatively scarce[19]. For instance, high MP concentrations in sewage sludge are observed in Germany (Sleeze) from 74 to 495 particles/g and in China from 74 to 240 particles/g due to its large population size, with fragments being the most abundant form (55%)[20]. In one of Italy’s largest WWTPs (Northern Italy, built in the 2000s), the number of detected MPs in effluent wastewater was 0.4 ± 0.1 MPs/L, and 113 ± 57 MPs/g in sludge dry weight, mainly polyesters (35%) and polyamide (17%)[21]. Another study from the city of Cadiz (Spain) reported the presence of MPs from 16.40 ± 7.85 MPs/L to 131.35 ± 95.36 MPs/L in urban and industrial WWTP effluents, respectively[22]. Furthermore, the study carried out by Mason et al.[23] in 17 wastewater treatment plants in the United States presented an average of 0.05 MP/L in the final effluent, and the majority of them were determined as fibers (59%) followed by fragments (33%), while the size of 57% of MPs ranged between 0.125 mm and 0.355 mm. Finally, there is considerable variation in measuring MPs in sludge samples from other research works that have established the presence of MP in both primary and secondary sludge between 0.2 and 238 particles/g[7,18,24,25].
It has also recently been announced that MPs are considered “vectors” for absorbing and transferring toxic compounds in the environment, including pharmaceuticals, organochlorine pesticides, persistent organic pollutants (POPs), polybrominated diphenyl ethers, heavy metals, polychlorinated biphenyls, and polycyclic aromatic hydrocarbons[26-28]. This is because MPs have a lipophilic nature, small size, a large specific surface area, and surface charges, thus providing numerous sites for interactions with chemicals and micropollutants, such as Van-der Walls forces, hydrogen bonding, ionic, electrostatic, aromatic-aromatic and π-π interactions, leading to an additional risk for the environment[8,16,29].
Therefore, to better understand the contribution of MPs to the environment, there is an immediate need for further research into the potential risks associated with MPs in WWTP effluents and sludge. According to the Codex Alimentarius in 2011[30], exposure assessment, hazard characterization, and risk identification are the steps involved in the risk assessment of MPs. A hazard classification model for 55 thermoplastic and duroplastic polymers, based on the EU regulation (EC: European Commission) No. 1272/2008[31] and Labelling (CLP: Classification, Labelling and Packaging) regulation on hazard classes and categories of chemicals which pose a risk to the environment and human health, has been developed by Lithner et al. (2011)[2].
In literature, there are five main approaches for collecting microplastics based on their operating principles. These include static mechanical method through mesh filters (used in this study)[32], dynamic mechanical behavior[33], fluid dynamics[34], chemical approaches that involve the separation of microplastics with chemical agents, microorganisms, or solid adsorbents[35,36] and magnetic technology (e.g., magnets, electromagnets)[37]. As reported by Spreafico et al.[38], the static mechanical approach has the most numerous patents, as seen in the recent publication trends. This method can collect microplastics ranging from 10 μm to 1000 μm. Furthermore, various extraction procedures have been developed to effectively quantify and characterize MPs in complex environmental matrices. Based on the sample matrix, the main extraction methods are categorized as follows: density separation using hypersaline solutions (e.g., NaCl, NaI, ZnCl2, NaBr, CaCl2, KI)[39], elutriation using gas or liquid to distinguish particles[40], pressurized liquid extraction[41], magnetic separation (e.g., Fe-Nanoparticles)[42], electrostatic separation[43], and oil-extraction protocols (e.g., castor oil, canola oil, mineral oil)[44,45]. Several studies have also reported pre-extraction steps, including sieving to separate larger visible particles and filtration to isolate the solid phase from the liquid phase[46]. Finally, to improve the extraction of microplastics, it is crucial to apply methods for removing organic matter, either after or prior to the separation techniques, which include acidic/or alkaline digestion, as well as oxidative and enzymatic digestion[17].
Up next, methods used to determine MPs range from visual observation via a dissection microscope over pyrolysis-gas chromatography-mass spectrometry (pyr-GC-MS)[47] to Fourier-transform infrared spectroscopy (FT-IR) and microscopy-Raman spectroscopy[18,48,49]. The carbon-based polymers of MP can be easily distinguished from other organic or inorganic particles using FTIR spectroscopy, and specific types of MP polymers can be identified using a library of spectra[50]. Compared with FTIR spectroscopy, micro- Raman spectroscopy serves as an alternative non-destructive technique for MP analysis and offers better spectral resolution (down to 1 μm compared to 10-20 μm for FTIR), broader spectral coverage, higher sensitivity to non-polar functionalities, less water intervention, and tighter spectral bandwidths[51-55]. Another advantage of using micro-Raman spectroscopy is that it can separate and give detailed information about the additive compounds (colorants, plasticizers, fillers, etc.) present in MP particles, compared to FTIR spectroscopy, which presents low identification percentages when MPs are covered with other materials[56]. However, sample pre-treatment, including sample digestion and separation from the contaminated matrices, is required prior to Raman and other spectroscopic detection methods for complex environmental or biological matrices where it is hard to recognize different shapes, sizes, and polymer types[52,57].
Therefore, the present study focuses on the application of methods to accurately identify and quantify microplastics in wastewater effluents and sewage sludge and provides a detailed investigation of microplastic concentration and characteristics (shape, size, and polymer type) across a typical WWTP in Ioannina, Greece. A simple and precise method including digestion of organic matter and density separation was validated for its efficacy in extracting microplastics from complex matrices. As far as we know, this study is the first of its kind to successfully apply micro-Raman spectroscopy combined with Particle FinderTM software based on mapping approaches for MP identification and visualization in complex environmental matrices such as sludge. The study finally targets the assessment of the associated risk of MPs occurrence in wastewater and sludge.
METHODS
Chemicals and materials
Hydrogen peroxide (H2O2) stock solution (30%), PS-NPs water suspension (2% solids content w/v), methanol, formic acid, phosphate-buffered saline (PBS, pH = 7), lipase obtained from Candida rugosa, protease from Bacillus licheniformis, and cellulase originated from Aspergillus niger were obtained from Sigma-Aldrich (Darmstadt, Germany). A purification system from Evoqua Water Technologies was used to provide ultrapure water. Iron (II) sulfate heptahydrate (FeSO4. 7H2O) was from Merck (Darmstadt, Germany), while ZnCl2 of high purity (> 98%) was provided from ChemLab (Zedelgem, Belgium). Macroporous silicon membranes of 5 and 2.5 μm pore diameter were obtained from smart Membranes [Halle (Saale), Germany].
Sample collection
Wastewater effluents and sludge samples were collected from the WWTP in Ioannina, Northwestern Greece. The WWTP serves a population of approximately 100,000 residents and handles mainly household and industrial effluents with an average flow of 17,600 m3/day. The system consists of a primary treatment stage equipped with a ventilated tank for the removal of grit and a sedimentation tank, a biological treatment stage (secondary treatment) consisting of an anaerobic stage and an aerobic decomposition stage, and finally a disinfection stage (tertiary treatment) by chlorination. The treated water outflow is discharged into the Kalamas River. The activated sludge process is employed with approximately 60% sludge reuse and an average solids retention time (SRT) of 11 days. More information about the main activities in the facility zone, and the capacity and function of WWTP can be found in the latest publications[58,59]. Wastewater effluent samples of 40 L were collected in five different sampling periods in dry weather from March to July 2024 at the beginning of each month through short-time pump sampling, sieved through stainless steel screens with sizes of 1000, 500, 250, 125, 63, and 25 μm and then covered with aluminum foil for further analysis. Grab secondary sludge samples of 2 kg were also collected during the same period, stored in glass bottles, and kept frozen in the dark at -20 °C. The sludge samples were then lyophilized and homogenized. They were stored at 4 °C until analysis.
Sample processing
Wastewater samples
The wastewater effluents were processed through oxidative digestion according to previously reported and validated methods[22,60-64]. Briefly, the contents of the mesh sieves (25-63, 63-125 and 250-500 μm) were washed into a 500 mL beaker using deionized water, while the particles in the mesh screens of 500-1000 and > 1000 μm were washed with water, collected by hand using metal tweezers and stored in Eppendorf tubes for analysis. 10 mL of a freshly prepared FeSO4 solution (0.05 M) was added to the beakers containing the washed particles (150-200 mL water). Subsequently, 20 mL of hydrogen peroxide solution (30%) was added and mixed intensively to oxidize the organic matter. Next, the beakers were heated to 55 °C on a hotplate for 5 h, covered with aluminum foil while stirring continuously (600 rpm) and visually checked every hour. If necessary, a further 10 mL of hydrogen peroxide was added to the beakers until no solid particles could be seen. The solution obtained was cooled to room temperature, transferred to a 50 mL centrifuge tube and centrifuged at 4000 rpm for 10 min [Supplementary Figure 1]. Afterward, the supernatant proceeded to a density separation step using 30 mL of ZnCl2 2M solution (density 3.1 g.cm-3), stirred for 30 min and settled overnight. The buoyant particles were then filtered on a silicon membrane filter of 2.5 μm pore diameter and rinsed with ultrapure water. All tools and bottles were rinsed with water and methanol to prevent sample contamination throughout the treatment process.
Sewage sludge samples
The sludge samples were processed according to the methodology described elsewhere[25,65-69] with some modifications, including enzymatic digestion, oxidative digestion, floatation, and filtration. In brief, 5 g of the lyophilized sludge sample was transferred to 500 mL glass beakers, 10 mL of ultrapure water was added to each beaker and magnetic stirred for 10 minutes until the sample was well mixed with water. Enzymatic digestion was carried out using enzymes that have been reported to be effective in the removal of organic matter from sewage sludge for the extraction of MP[68]. So, a mixture of three enzymes (0.3 g lipase from Candida rugosa, 1.95 mL protease from Bacillus licheniformis, and 0.375 g cellulase from Aspergillus niger) was added to the sludge samples, incubated at 50 °C with continuously stirring for 96 h while a buffer solution (PBS) was added to achieve optimal pH for enzymes [Figure 1]. At the end of enzymatic digestion, an oxidative post-treatment followed using 20 mL H2O2 (30% v/v) under heating to 50 °C and stirring for 24 h. Digested samples in beakers were transferred to 50 mL centrifuge tubes, beakers rinsed with ultrapure water, and density separation proceeded as described above in the wastewater sample preparation section. Finally, the buoyant particles were then filtered on a silicon membrane filter of 5 μm pore diameter and rinsed with ultrapure water.
Figure 1. The optimized protocol used for the elimination of organic matter from sludge. PBS: phosphate-buffered saline.
Method validation
PS has an intermediate density (1.05 g/mL) that covers a wide range of densities of the most known detected MPs in WWTPs while it is also one of the MPs commonly detected in WWTPs, and the availability of its standard suspension makes it appropriate for optimization experiments of the digestion process. In addition, previous studies[70] have also used PS for the optimization of different digestion methods in sludge. Thus, to validate the sample extraction methodology, an appropriate amount of PS-NPs suspension in water (2% solids content w/v) was spiked in 200 mL of tertiary treated wastewater effluent and 5 g dry sludge in a glass beaker, in order to generate an initial loading of 300 PS particles. Furthermore, 1 g of PVC particles [density (1.4 g/mL)] with a size range of 125-250 μm were also spiked in wastewater effluents and 0.1 g of PVC particles in 2 g of sludge. The samples were processed according to the methodology described above for wastewater and sludge, respectively. All MPs were counted using micro-Raman spectroscopy using the software Particle FinderTM. A total of 230 particles of the PS microbeads were recovered from wastewater samples, achieving 76.7% recovery, and 216 particles of PS were recovered from the sludge sample, achieving 72% recovery, which we deemed acceptable. PVC particles have been recovered in high yield, with extraction efficiencies ranging from 96% for effluents to 86.2% for sludge.
Identification, quantification and characterization of the extracted MPs
All suspect microplastics have been counted and classified as follows: shape (namely fiber, fragment, film, and sphere), size (perimeter and diameter), and volume. MP abundance was expressed as the median number of MP items per liter or per gram (a) at each sampling and (b) for all samplings and (c) as the frequency of detection of each microplastic in wastewater effluents and sludge samples.
The larger particles (500-1000 and > 1000 μm) were manually picked from the mesh screens, dried, weighted, and identified using attenuated total reflectance (ATR) - FTIR spectrophotometer (Shimadzu IR Spirit, Kyoto, Japan). FTIR spectra were recorded in transmittance mode, with 2 cm-1 resolution and 45 concurrent scans in the 4000 to 400 cm-1 region. The sample spectrum was compared to that of the library and the level of certainty was set up to > 70%.
For the determination of smaller MPs, a multi-modal Raman microscope, Labram SoleilTM (Horiba Scientific, Lyon, France), was used. The instrument is standardly equipped with two gratings (600 nm and 1800 nm) by default, a multiple channel detector and the LabSpec6 Spectroscopy suite software. Raman spectra were collected at variable magnifications of 5× and 50× using a laser with a wavelength of 532 nm and a power of 1.9-3 mW in the range of 1000-3800 cm-1. The integrating time was 50-200 s (usually 200 s), and the number of cumulations was 3-10 times (usually 6). Then, the Particle FinderTM software was applied to wastewater and sludge samples, enabling automated particle location, analyzing important particle parameters, like size and volume, and later chemical characterization using Raman spectra. Recorded spectra were baseline corrected to improve spectra quality and match the recorded spectra with the KnowItAllTM library database reference with > 70% identification. Particle FinderTM is ideal for use in environmental applications, analyzing microplastics where the number of particles is large and tracking by hand and tagging each particle would be time-consuming.
The surface morphology of representative MPs was determined using a Field Emission Scanning Electron Microscopy (Thermo Fisher Pharos Phenom, Waltham, MA, USA), run under high vacuum (0.1 Pa) with the acceleration voltage set at 15 kV, using a 20:80 ratio of backscatter and secondary electron detection. Each sample was coated with a 5 nm layer of chromium before analysis, while the chemical composition of the surface of the MPs was investigated by EDS analysis.
Risk assessment of microplastics
Microplastic risk assessment was calculated according to the methodologies used in literature[2,71-73]. Based on the abundance and polymer composition of MPs, the pollution loading index (PLI) method and polymer hazard index (HI) method were used to assess the MP pollution risk in the WWTP[73,74]. To make this assessment, the hazard scores of plastic polymers were adopted from Lithner et al[2]. The above protocol is beneficial for assessing both the combined effect of several pollutants and the environmental impact of particular contaminants in a specific location. The pollution load index for each sampling (PLIi) was used to quantify the overall pollution level of microplastics in wastewater and sludge. The following equations illustrate the assessment model:
where Ci is the abundance of microplastics at sampling i, Co is the minimum abundance value for all samplings, and CFi represents the pollution coefficient of MPs. The PLIi was calculated as the root of the CFi, while the pollution load index (PLI) denotes the nth root of the multiplication of all PLIi in samples. PLI < 10 indicates hazard category I, PLI 10-20 represents hazard category II, and PLI 20-30 and PLI > 30 show hazard category III and IV, respectively[75]. In order to assess a comprehensive indication of the risk posed by various microplastic polymers, Hakanson[76] suggested the idea of pollution risk index (PRI) that combines the PLI of microplastics and the hazard index (HI) of microplastic pollution according to the Equations (4-7).
where HIi is the hazard index of microplastic pollution at sampling i, Pn is the mass fraction of different microplastic polymer types at sampling i, Sn is the hazard score for microplastic polymers [Supplementary Table 1], HI is the hazard index of microplastic pollution of the WWTP for all samplings, PRIi is the pollution risk index of microplastics at sampling i, and PRI is the pollution risk index of the overall samplings of the WWTP. The risk categories of MPs hazard index and pollution risk index are represented in Supplementary Table 2.
RESULTS AND DISCUSSION
Occurrence of microplastics in wastewaters
The methodology used in this study successfully identified small MPs present in wastewater effluent samples. MPs were classified into six different particle sizes from 25 to > 1000 μm. The size distributions of MPs of wastewater effluent samples collected during different sampling periods are shown in Figure 2. The sizes of 25-63, 63-125, and 125-250 μm were the common sizes of MPs in all wastewater samplings, ranging from 5.8% to 37.3%, 18.6% to 55%, and 10.7% to 41.1%, respectively. It is noted that larger MPs (> 1000 μm) decreased during wastewater treatment steps and became smaller particles due to fragmentation[77]. Therefore, larger particles (> 1000 μm) in this study were between 5.5% and 10.4% in all wastewater samplings. The percentage variation of sizes 250-500 μm and 500-1000 μm are similar and varied from 5.5% to 12.6% and from 1.1% to 8.8%, respectively. The findings of this study were similar to those previously reported in other countries, i.e., MP particles at WWTPs were mainly in the range of 62.5-200 μm[64,78-80]. Furthermore, the size distribution in this study is also in agreement with a study that used micro-Raman spectroscopy for MP analysis in WWTP from Germany and found that 95% of all detected particles were in the 10 < dp < 30 μm and 30 < dp < 100 μm size classes[48].
Figure 2. The distribution percentage (%) of the sizes of the MPs in each sampling campaign. MPs: Microplastics.
The MP concentration (number of MPs per liter) according to the sieving sizes and across samplings is illustrated in Figure 3A and 3B, respectively. According to Figure 3A, the mesh screen sizes of 25-63, 63-125, and 125-250 μm presented the highest average MP concentration, i.e., 1.60 ± 1.3 particles/L, 1.76 ± 1.2 particles/L, and 1.31 ± 0.4 particles/L, respectively, while reduced average MP concentration from 0.19 to 0.50 particles/L was observed for larger particles from 250 to > 1000 μm size. The highest MP concentration count 9.05 ± 1.5 particles/L was found in the 4th sampling event and the lowest MP concentration 3.95 ± 0.56 particles/L in the 2nd sampling event. An average concentration of 5.8 ± 0.6 particles/L was detected in all samplings in the WWTP of Ioannina city. The reported MP concentrations in WWTP effluents in other studies ranged from 0.006 particles/L to 9 particles/L, which are in agreement with the concentration of MPs found in this study[10,12,61,81,82].
Figure 3. (A) MPs concentration (number of particles/liter) for all samplings according to their size and (B) MPs concentration (number of particles/liter) of all sieve sizes for each wastewater sampling. MPs: Microplastics.
The MPs could be in the form of fiber, fragment, film, and sphere. The fragments occupied a significant proportion, representing 67 ± 12.9% of all the particles in all samplings, followed by fibers and spheres (15 ± 5.9% and 12.7 ± 5.3%, respectively) among all the wastewater samplings, while films occupied relatively the smallest proportion at 5.5 ± 5% [Figure 4].
Figure 4. The distribution percentage (%) of the shapes of the MPs of all sizes (25 - > 1000 μm) in all samplings. MPs: Microplastics.
A total of 1,575 particles were detected in this study in wastewater effluents, and 1,076 particles were confirmed to be MPs, representing 68.3% using micro-Raman spectroscopy combined with Particle FinderTM software. The Raman spectroscopy revealed 22 different polymers in all samplings. The dominant microplastics in wastewater effluents, as shown in Figure 5, were p-acrylic acid (PAA) (48.3 ± 2.1%), followed by p-acrylamide (PAM) (13 ± 6.5%), p-vinyl-chloride (9.9 ± 6.2%), p-acrylamide-co-p-acrylic acid (9.6 ± 8.1%), p-butyl methacrylate (8.6 ± 8.5%), and p-ethylene oxide (8 ± 0.1%). Other types of MPs, such as PE, PS, PP, EVA, PVA, p-vinyl stearate (PVS), p-vinyl acetate (PVAc), etc., contributed with little proportion ranging from 0.6% to 5.3%. Polyamide, p-acrylic acid, p-acetylene, and PAM-co-PAA were the most abundant polymers (100% frequency of detection), followed by PVC, PBMA, PE, PS, PP, PVA, and PVB (20%-80% frequency of detection). An average of 102 ± 44 particles were detected as PAA, 16.6 ± 13.5 as PVC, 22 ± 2.5 as PAM-co-PAA, 13 ± 14 as PBMA, 8.6 ± 12.4 as PA, 8.6 ± 11.9 as PE, and < 5 ± 1.9 as the other polymer types. As illustrated in Figure 6, at the smallest size range 25-63 μm, PAA was the dominant polymer type with 53.9%, followed by the co-polymer PAM-co-PAA (17.4%) and PVC (10%). A similar pattern was observed for the other sieve sizes ranging from 63 to 500 μm, while for larger particles 500-1000 μm and > 1000 μm, the most abundant polymer types were PA (21.2%, 38.5%), EVA (30.3%, 35.4%), and p-acetylene (9.1%, 6.2%), respectively. The other polymer types, such as PP, PE, PS, p-acetylene, etc., ranged between 0.3 and 9.4% on sieves with mesh widths of 25 - > 1000 μm. According to the size of MPs, PAA particles have a mean diameter of 94 μm and an average perimeter of 532 μm, PVC particles 375 μm and 1312 μm, respectively, PA 187.5 μm and 961 μm, respectively, while PAM-co-PAA particles 44 μm average diameter and 410 μm average perimeter. Finally, as shown in Figure 7, the majority of PAA detected particles are in the form of fragments (46.7%) and spheres (23.1%). They probably originated from the fragmentation of synthetic textile materials into small pieces in a variety of ways, such as the secondary MP[83]. This is quite different from recent studies, which found that fibers are the dominant form of microplastics, followed by fragments[23,64,84-86]. The differences can be related to random natural variations among the samplings and the studied WWTP. Furthermore, the majority of observed PE and PP particles had spherical morphology (40% and 55.5%, respectively) matching microbeads from personal care products[87]. In the WWTP effluents examined by other researchers[48,82,88,89], PA, PAA, PVC, and polyesters predominated, which is also confirmed by the results of the present study. Comparable data for MP concentration, shape, size, and polymer type from other studies in different WWTPs across the world are presented in Table 1. The most abundant polymers in this study, p-acrylic acid, p-acrylamide, and p-acrylamide-co-acrylic acid, could originate from textiles, synthetic clothing, and medical devices[8], while the polymer type PVC has a wide range of uses and is usually employed in raincoats, seat covers, garden hoses, shoe soles, and shower curtains[18]. Detailed information about the uses of synthetic plastic particles detected in this study can be found in Supplementary Table 3.
Figure 5. The average percentage of polymer type of MPs of all sizes (25 - > 1000 μm) in wastewater effluent samplings. MPs: Microplastics.
Figure 6. The percentage of polymer type of MPs according to their size in wastewater effluent samplings. MPs: Microplastics.
Figure 7. The percentage of polymer type of MPs according to their shape in wastewater effluent samplings. MPs: Microplastics.
Reported MP concentration, shape, size, and polymer type in wastewater effluents and sludge from various WWTPs in different countries comparable with this study
| WWTP location | Predominant shapes | Predominant MP size | Predominant Polymer types | MP concentration Wastewater (MP L-1) | MP concentration Sludge (MP g-1) |
| Spain[22] | Fragments, fibers | 100-355 μm | PE, PP, PS, acrylate | - | 2.8-57.2 MP g-1 |
| Italy[21] | Fibers, films, fragments | 100-500 μm | Polyesters, PA, PE | 0.3 MP L-1 | 59.5 MP g-1 |
| United Kingdom[90] | Fragments | 25-178 μm | PE, PP, PET | 2-54 MP L-1 | 301-10,380 MP g-1 |
| Norway[24] | Beads, fragments | 50-125 μm | PE, PP, PET, PA | - | 6 MP g-1 |
| Australia[64] | Fragments, fibers | 38-125 μm | PA, PE, PP, PET | 2.8 MP L-1 | 7.9 MP g-1 |
| Denmark[88] | Fragments | 10-500 μm | Acrylates, PE, PP | 54 MP L-1 | - |
| Australia[61] | Fragments, fibers | 25 μm | PE, PP, PET | 19.6-30.3 MP L-1 0.18-0.96 MP L-1 | 15.9-56.5 MP g-1 |
| Germany[82] | Fibers | 50-100 μm | PE, PVA, PA, PS, PP | 1-9 MP L-1 | 1-24 MP g-1 |
| Germany[48] | Fibers | 30-100 μm | PET, PE, PP, PS | 3-5.9 MP L-1 | - |
| Changzhou, China[91] | Fragments, fibers | 100-500 μm | PET, PE, PP, PS, PE-PP | 3.6-13.6 MP L-1 | - |
| Finland[12] | Fibers, fragments | 20-100 μm | PE, PP, Polyester | 0.7-3.5 MP L-1 | 76.3 ± 4.3 MP g-1 |
| France[92] | Fragments, fibers | 20-80 μm, 80-200 μm | PS, PE, PAM | 2.84 MP L-1 | 16.13 ± 1.2 MP g-1 |
| Scotland[81] | Foams, fibers, films | > 500 μm | PAA, PA, PE, PS, Polyester | 0.25-15.7 MP L-1 | 7.8 ± 1.8 MP g-1 |
| Poland[93] | Fragments, fibers | 109-300 μm | - | 0.02-9.6 MP L-1 | 6.7-62.6 MP g-1 |
| This study | Fragments, fibers | 25-63 μm | PAA, PAM, PVC, PBMA, PE | 5.8 ± 0.6 MP L-1 | 33.3 ± 8 MP g-1 |
Representative Raman spectra profiles for different polymer types are presented in Figure 8. For instance, in the Raman fingerprint range, PE had three main peaks, namely the peaks corresponding to the CH2 twist at 1288 cm-1, the C-H bending mode at about 1432-1450 cm-1, and the C-H symmetric and antisymmetric stretching at 2870-2950 cm-1[94]. The spectral regions associated with PP include CH2 and CH3 symmetric and antisymmetric vibrational modes corresponding to 2800-3100, 1460, and 1378 cm-1 bands, as well as the region of 1155 cm-1 for [CH2CH(CH3)]n[54]. Furthermore, the band at 1300 cm-1 in p-acrylic acid is assigned to (-OH) bending vibrations, the sharp bands at 1694 and 1740 cm-1 correspond to C = O stretching, the peak at 1446 cm-1 at δ (CH2) and the band at 2900 cm-1 arise from C-H stretching modes[95]. A peak at 1600 cm−1 is assigned to the NH2 group of amides, the band at 1630 cm-1 corresponds to the stretching of the carbonyl (C = O) of acrylamide units in p-acrylic acid-co-acrylamide polymer, while the bands at 1433 and 1492 cm-1 are assigned to C-N stretching vibration of amides and the band at 1360 cm-1 is assigned to CH2 wagging vibration[96]. Moreover, adsorption experiments in the aqueous phase were conducted with pristine PS particles with emerging contaminants, as well as weathering of pristine PS under sunlight. More details are provided with supplementary information, and the recorded Raman spectra are provided in Supplementary Figures 2 and 3. Neither pollutant adsorption nor weathering resulted in identification matching levels lower than 70%. The ATR-FTIR detection technique was used to determine the composition of the polymer particles in the size ranges of 500-1000 and > 1000 μm. As shown in Figure 9, spectral regions associated with PA include -C=O at 1640 and 1712 cm-1 bands and -C-N-H absorption peaks at 1250 and 1550 cm-1 bands[97]. The FTIR spectrum of PS shows characteristic bands at 3000-3100 cm-1 corresponding to the C-H stretches due to the aromatic ring, peaks at 2924 and 2846 cm-1 are attributed to the symmetric and asymmetric stretched vibrations of CH2, while bands at 1602, 1490 and 1447 cm-1 correspond to the stretched vibration modes of the carbon-carbon bonds in the aromatic ring[98]. More examples of representative Raman and ATR-FTIR spectra for MPs detected in effluents and sludge are provided in the supplementary data [Supplementary Figures 4 and 5, respectively].
Figure 8. Representative Raman spectra of microplastics detected in wastewater effluents by micro-Raman spectroscopy.
Figure 9. Representative ATR-FTIR spectra of microplastics detected in wastewater samples (size range 500-1000 and > 1000 μm).
Scanning electron microscope (SEM) provides high-resolution images of a sample by directing an intense electron beam at the sample surface and can be used to analyze the weathering history of microplastics recovered from environmental compartments by examining the surface texture[99]. SEM combined with energy-dispersive X-ray spectroscopy (SEM-EDX) provides detailed information on microplastic elemental composition and inorganic additives[6]. Figure 10 shows the surface of the analyzed fibers and fragments, highlighting the effects of degradation processes. In fact, SEM micrographs of almost all the examined MPs presented surface cracking, fissures, pits, and roughness on the plastic particles. Furthermore, PA and PVC particles showed an irregular morphology with breaks and a rough surface with pores. De-la-Torre et al. (2022)[100], Hajji et al. (2021)[101] and Hajji et al. (2023)[9] reported similar surface characteristics upon the WWTP processes. In WWTPs, physical, chemical, and biological degradation processes took place in primary, secondary, and tertiary treatment steps. Hence, MPs are expected to be exposed to several stressors, such as surface abrasion from the mechanical mixing during the grit and grease removal stage, as well as the aeration of the activated sludge tank[102]. In addition, microorganisms can form biofilms on the surface of MPs or ingest MPs, eradicating them and causing modifications on their surface[8]. Finally, tertiary treatment processes such as filtration and chlorination may play a major role in the surface alteration of MPs[101].
Figure 10. SEM images of representative MPs recovered from wastewater, which were previously identified as (A) Polyamide (PA), (B) p-ethylene (PE), (C) p-styrene (PS), and (D) p-vinyl chloride (PVC). MPs: Microplastics; SEM: Scanning electron microscope.
It is revealed that carbon (C) and oxygen (O) are the most dominant constituents in the majority of the analyzed particles, according to the EDX elemental analysis of the selected MPs [Table 2]. In addition, small peaks of other elements, such as Na, N, Cl, K, Ca, P and S, are also present on the surface of analyzed MPs, originating from wastewater effluents and suspended solids in WWTPs. Moreover, these elements may originate either from additives, such as coloring agents and plasticizers used in plastics[103], or from the addition of various coagulants in the aeration tanks[104]. The O/C ratio is a significant index for the oxidation process on the surface of MPs in combination with the carbonyl (CI) and hydroxyl index (HI). The O/C ratio, CI, and HI indices were calculated according to literature[105,106] and are presented in Table 3. The results demonstrate a wide range of CI values, from 0.12 to 0.98, and O/C ratios ranging from 0.17 to 0.99, indicating moderate (CI values 0.15-0.3) and high levels of oxidation (CI > 0.31) and suggesting that non-aged and weathered MPs coexist in the samplings.
W% and A% of the elements detected on the surface of representative MPs recovered from wastewater
| Element | PA | PE | PS | PVC | ||||
| (%W) | (%A) | (%W) | (%A) | (%W) | (%A) | (%W) | (%A) | |
| Carbon | 37.01 | 42.67 | 35.54 | 40.98 | 28.33 | 36.37 | 69.63 | 80.50 |
| Nitrogen | 28.78 | 28.45 | 28.03 | 27.71 | 17.72 | 19.50 | n.d | n.d |
| Oxygen | 32.6 | 28.21 | 35.94 | 31.10 | 37.54 | 36.18 | 15.88 | 13.80 |
| Phosphorous | 1.0 | 0.45 | n.d | n.d | n.d | n.d | n.d | n.d |
| Potassium | 0.60 | 0.21 | n.d | n.d | 1.20 | 0.47 | n.d | n.d |
| Sulfur | n.d | n.d | 0.50 | 0.22 | 2.40 | 1.15 | n.d | n.d |
| Chlorine | n.d | n.d | n.d | n.d | 3.50 | 1.52 | 14.09 | 5.52 |
| Sodium | n.d | n.d | n.d | n.d | 3.20 | 2.15 | n.d | n.d |
| Calcium | n.d | n.d | n.d | n.d | 4.40 | 1.70 | n.d | n.d |
CI, HI, and O/C ratio of representative microplastics
| Polymer | CI/Reference | HI/Reference | O/C ratio/Reference |
| PE (> 1000 μm) | 0.96/0.016 | 1.02/0.007 | 0.76/0.007 |
| PE (63-125 μm) | 0.22/0.016 | 0.14/0.007 | - |
| PP (125-250 μm) | 0.24/0.018 | 0.21/0.015 | - |
| PS (> 1000 μm) | 0.98/0.026 | 0.95/0.017 | 0.99/0.025 |
| PVC (> 1000 μm) | 0.96/0.04 | 1.09/0.07 | 0.17/0.045 |
| PVC (250-500 μm) | 0.12/0.04 | 0.31/0.07 | - |
| PA (> 1000 μm) | 0.80/0.17 | 1.001/- | 0.88/0.17 |
Microplastics in sludge samples
A total of 1,091 particles were detected in this study in sludge samples, and 832 particles were confirmed to be MPs particles, representing 76.3%, using micro-Raman spectroscopy combined with Particle FinderTM software. The concentrations of microplastics detected in the sludge samples (n = 5) ranged from 20.4 to 40.2 particles/g dry weight with an average concentration of 33.3 ± 8 particles/g. The concentrations of microplastics detected are in a similar range to those found previously by other researchers[21,67,107-109], but lower than the reported average concentration from 37 to 286 particles/g dry weight in digested sludge from Finland[110], United States[111], United Kingdom[112,113], and Spain[86]. In sludge samples, the dominant MP types were p-styrene-co-butadiene (49.7%) and p-acrylic acid (39.8%), followed by ethylene-vinyl acetate (28.4%), p-acrylamide-co-acrylic acid (19.6%), and p-butyl methacrylate (19.6%) [Figure 11]. Polymer types such as PVA, PP, and PS were also determined in the samples, but at low percentages (6%-13%). p-acrylic acid was the most abundant polymer type (100% frequency of detection), followed by p-acrylamide-co-acrylic acid and p-butyl-methacrylate (60% frequency of detection) and PE, PS, PP, PVA, p-styrene-co-butadiene, PE-co-vinyl acetate, and PE-co-PAA (20%-40% frequency of detection). An average of 16.6 ± 15 particles/g detected as p-styrene-co-butadiene, 14.2 ± 11/g as PAA, 7.7 ± 5.7/g as PAM-co-PAA, 5.9 ± 1/g as PBMA, and < 5.8 ± 2/g as the other polymer types. The polymer composition of MPs in sludge presented some differences from that of effluent. More specifically, p-propylene occurrence increases in wastewater samples and decreases in sludge samples. This has occurred due to the fact that the density of PP (0.90 g/mL) is less than that of water. Furthermore, MPs that are denser than wastewater (PBMA: 1.07 g/mL, p-styrene-co-butadiene: 1.05 g/mL) are easily removed from wastewater by physical separation and settle to sludge[77,80]. This can be observed by the increased concentrations of the two polymer types in sludge compared to effluent samples. Moreover, it is also reported that one of the most common polymers found in sludge samples is rubber from car tires (such as butadiene rubber)[113]. This state is consistent with our study where the co-polymer, p-styrene-co-butadiene, was the most abundant polymer type found in sludge, also indicating the mixed character of the sewage system. Furthermore, inherent MPs were also classified according to their diameter and perimeter [Figure 12A and 12B], with an average size of 123.7 ± 58 μm diameter and 889.3 ± 651 μm perimeter. As shown in Figure 12, particles identified as p-styrene-co-butadiene and p-ethylene had the largest sizes, with average diameters of 166.7 ± 77.5 μm and 144.7 ± 0.5 μm, respectively. Xu and Bai (2022)[114] reported that more than 85% of MPs in sewage sludge had particle sizes below 500 μm, with 44.73% of MPs in the 100-200 μm range and 29.45% in the 200-500 μm range. This is also confirmed in the present study. P-styrene-co-butadiene particles have the largest average size of 166.7 ± 77.5 μm among all the polymer particles detected; therefore, they can be more easily precipitated in sludge. Finally, the fragments occupied again a significant proportion, representing 75 ± 5.6% of all the particles in all sludge samples, followed by films, fibers, and spheres (12.3 ± 4.7%, 6.9 ± 4.5%, and 5.9 ± 4.5%, respectively) [Figure 13A]. Most of the particles detected as PAA are in the form of fragments (41.5%) and spheres (24%), along with p-styrene-co-butadiene particles (fragments, 18.6% and spheres,14.7%) [Figure 13B]. The same conclusion was reached by previous research[27,62,78,79], and comparable data on MP shape, size, and polymer type can be found in Table 1.
Figure 11. The average percentage of MPs of all sizes in sludge samplings according to the polymer type. MPs: Microplastics.
Figure 12. (A) average contribution of each polymer type to the diameter of MPs and (B) average contribution of each polymer type to the perimeter of MPs extracted from sludge samples (n = 5). MPs: Microplastics.
Figure 13. (A) the distribution percentage (%) of the shapes of the MPs of all sizes in all samplings and (B) the percentage of polymer type of MPs according to their shape in sludge samples. MPs: Microplastics.
Risk assessment of microplastics at the WWTP
The PLI, HI, and PRI indices for wastewater and sludge samples were calculated and illustrated in Tables 4 and 5, respectively. All samplings (n = 5) had a PLI > 1, which indicates extended pollution by MPs in wastewater effluents as well as in sludge. For wastewater, the highest MP abundance was observed in the 4th sampling, as mentioned before, which correlated directly with the highest PLI value (1.51) for this sampling. In sludge samples, the PLI index for MPs ranged between 1.0 and 1.40. The overall pollution load index of all samplings was 1.14 for wastewater effluents and 1.47 for sludge, representing hazard category I, less than 10. For polymer hazard index, the 2nd sampling in wastewater effluents and the 4th sampling in sludge presented the greatest HI value (81.02 and 2441.1, respectively). Based on the various MP polymer types identified in different samplings, all wastewater effluent samples exhibited a low-medium hazard index (hazard category II) (HI = 44.5). Among the sludge samples, each five samplings exhibited hazard indices ranging from low to medium and to high (hazard category I, II, and III), but the overall polymeric hazard index of all samplings was 86.6, representing hazard category II (10-100, low-medium). The higher polymeric hazard scores of the toxic polymers detected in sludge samples, such as p-acrylic acid and p-styrene, are responsible for the high-risk characteristics even though their proportions were lower than those of other polymers. In contrast, a higher abundance of low-hazard polymers contributes to lower polymeric risk values[2,115]. Finally, the PRI index of the WWTP was calculated by combining PLI and HI values. For wastewater samples, the PRI for each sampling ranged from 21.2 to 81.0, representing the minor risk category, while the overall PRI of all sampling was 50.7, less than 150, representing hazard category I. For sludge substrate, PRI values showed a significant variability across the five sampling periods. The 2nd sludge sampling and 4th sampling showed PRI values of 1834.5 and 3076.4, respectively, and are in the “danger” risk category (IV), while the rest of the sludge samplings present minor risk category (0.6 to 104.9, hazard category I). Nevertheless, the overall pollution risk index for sludge in the WWTP presented a value of 109.1, less than < 150, and fell into the low risk category (hazard level I). As a result, the high MP abundance, HI values, and the presence of hazardous polymers were all correlated with elevated PRI values. Finally, the ecological risk associated with the presence of microplastics in the Kalamas River water body, where treated water effluents are discharged, was estimated based on dilution factors. The Kalamas River has an annual average flow of 54.2 m3/s in winter and 32 m3/s in summer[116]. The PLI values were greater than 1 in the two cases, indicating that the section of the river receiving the WWTP was polluted with microplastics. However, based on the abundance, polymer type, and toxicity of microplastics, HI and PRI values in both cases for all samplings were smaller than 10 and 150, respectively, indicating low risk (category I). To the best of our knowledge, this is the first study in Greece that provides important data and assesses the environmental risk of MPs in the WWTPs. Up to now, MP contamination in WWTP systems has not been part of the conventional environmental impact assessment. As the problem of MPs increases seriously, MP risk assessment will help to fully understand the status of MP pollutants, their migration pathways, and the potential harm to human health in order to improve both the aquatic and the terrestrial environment.
PLI, HI, and PRI indices of MPs in WW
| Samplings (Wastewater) | PLI | HI | PRI | Risk assessment of HI | Risk assessment of PRI |
| WW-1 | 1.09 | 51.8 | 57.0 | Low medium, (II) | Low, (I) |
| WW-2 | 1.0 | 81.0 | 81.0 | Low medium, (II) | Low, (I) |
| WW-3 | 1.07 | 43.5 | 46.8 | Low medium, (II) | Low, (I) |
| WW-4 | 1.51 | 13.9 | 21.2 | Low medium, (II) | Low, (I) |
| WW-5 | 1.07 | 68.3 | 73.4 | Low medium, (II) | Low, (I) |
PLI, HI, and PRI indices of MPs in SS
| Samplings (sewage sludge) | PLI | HI | PRI | Risk assessment of HI | Risk assessment of PRI |
| SS-1 | 1.28 | 35.8 | 45.9 | Low medium, (II) | Low, (I) |
| SS-2 | 1.40 | 1306.8 | 1834.5 | High, (III) | Very high, (IV) |
| SS-3 | 1.39 | 75.1 | 104.9 | Low medium, (II) | Low, (I) |
| SS-4 | 1.26 | 2441.1 | 3076.4 | High, (III) | Very high, (IV) |
| SS-5 | 1.0 | 0.60 | 0.60 | Low, (I) | Low, (I) |
CONCLUSIONS
The current study investigated MP pollution, a long-lasting problem, in the municipal WWTP of Ioannina, Greece. This study provides a comprehensive assessment of MP abundance and characteristics (morphotype, size, and polymer composition) in wastewater effluents as well as sewage sludge by utilizing an efficacious oxidative-enzymatic treatment protocol that reduces organic matter and extracts MPs efficiently from sludge and wastewater effluents. The mean concentration of MPs was 5.8 ± 0.6 particles/L in effluents and 33.3 ± 8 particles/g in sludge. Raman spectroscopy showed that the predominant shapes of MPs in sewage treatment wastewater and sludge were fragments, followed by fibers, spheres, and films. The microplastics mainly consisted of p-acrylic acid, polyamide, p-ethylene, and p-styrene-co-butadiene. Furthermore, this study provides data about the risk assessment of MPs in effluents and sludge from the WWTP. The assessment of the pollution load index of MPs in all samplings (WW and SS) indicated a low risk, categorized as hazard category I. The overall pollution risk index for all samplings (WW and SS) also showed a low risk, hazard level I, with the exception of high risk in some cases in sludge samplings 2 and 4. In conclusion, the present research work provides an in-depth knowledge of the occurrence and characteristics of MPs detected in the typical WWTP in Greece and also gives an assessment of the potential risks associated with the discharge of MPs into the environment.
DECLARATIONS
Acknowledgments
This research is co-financed by Greece and the European Union (European Social Fund- ESF) through the Operational Programme «Human Resources Development, Education and Lifelong Learning 2014-2020» in the context of the project “Chemistry and Technologies for Pollution Control and Environmental Protection (MIS 6004807).”
Authors’ contributions
Conception and design of the study and data analysis and interpretation: Miserli K, Konstantinou I
Data acquisition, validation, technical and material support: Miserli K
Writing - review and editing: Miserli K, Konstantinou I
Supervision, project administration: Konstantinou I
Availability of data and materials
The data presented in this study are available in this article and the associated Supplementary Material.
Conflicts of interest
Konstantinou I is an Editorial Board member of the journal Water Emerging Contaminants & Nanoplastics. Konstantinou I was not involved in any steps of editorial processing, notably including reviewer selection, manuscript handling, and decision making. The other authors declared that there are no conflicts of interest.
Ethical approval and consent to participate
Not applicable.
Consent for publication
Not applicable.
Copyright
© The Author(s) 2025.
Supplementary Materials
REFERENCES
1. Directive (EU) 2020/2184 of the European Parliament and of the Council by laying down a methodology to measure microplastics in water intended for human consumption. Available from http://data.europa.eu/eli/dir/2020/2184/oj [Last accessed on 12 Feb 2025]
2. Lithner, D.; Larsson, A.; Dave, G. Environmental and health hazard ranking and assessment of plastic polymers based on chemical composition. Sci. Total. Environ. 2011, 409, 3309-24.
3. Bayo, J.; López-Castellanos, J.; Olmos, S.; Rojo, D. Characterization and removal efficiencies of microplastics discharged from sewage treatment plants in Southeast Spain. Water. Res. 2023, 244, 120479.
4. Plastics Europe Deutschland & Messe Düsseldorf, Plastics - the Facts 2023. An analysis of European plastics production, demand and waste data. Available from https://plasticseurope.org/knowledge-hub/plastics-the-fast-facts-2023 [Last accessed on 12 Feb 2025].
5. Gonzalez GV, Dominguez Cortinas G, Hudson M, Shaw P, Williams ID. A Review of the origins of microplastics arriving at wastewater treatment plants. Detritus 2022. DOI: 10.31025/2611-4135/2022.15224.
6. Gao, Z.; Chen, L.; Cizdziel, J.; Huang, Y. Research progress on microplastics in wastewater treatment plants: A holistic review. J. Environ. Manage. 2023, 325, 116411.
7. Mesquita, D. P.; Quintelas, C.; Ferreira, E. C. Fate and occurrence of microplastics in wastewater treatment plants. Environ. Sci. :. Adv. 2023, 2, 1616-28.
8. Ali, I.; Ding, T.; Peng, C.; et al. Micro- and nanoplastics in wastewater treatment plants: Occurrence, removal, fate, impacts and remediation technologies – A critical review. Chemical. Engineering. Journal. 2021, 423, 130205.
9. Hajji, S.; Ben-Haddad, M.; Abelouah, M. R.; De-la-Torre, G. E.; Alla, A. A. Occurrence, characteristics, and removal of microplastics in wastewater treatment plants located on the Moroccan Atlantic: The case of Agadir metropolis. Sci. Total. Environ. 2023, 862, 160815.
10. Ou, H.; Zeng, E. Y. Occurrence and fate of microplastics in wastewater treatment plants. microplastic contamination in aquatic environments. Elsevier; 2018. pp. 317-38.
11. Mourgkogiannis, N.; Kalavrouziotis, I. K.; Karapanagioti, H. K. Questionnaire-based survey to managers of 101 wastewater treatment plants in Greece confirms their potential as plastic marine litter sources. Mar. Pollut. Bull. 2018, 133, 822-7.
12. Talvitie, J.; Mikola, A.; Setälä, O.; Heinonen, M.; Koistinen, A. How well is microlitter purified from wastewater? Water. Res. 2017, 109, 164-72.
13. Vollertsen, J., & Hansen, A. A. Microplastic in Danish wastewater: Sources, occurrences and fate. The Danish Environmental Protection Agency. 2017, Environmental Project Vol. 1906. Available from https://www.researchgate.net/publication/316966942_Microplastic_in_Danish_wastewater_Sources_occurrences_and_fate [Last accessed on 12 Feb 2025].
14. Talukdar, A.; Kundu, P.; Bhattacharya, S.; Dutta, N. Microplastic contamination in wastewater: Sources, distribution, detection and remediation through physical and chemical-biological methods. Sci. Total. Environ. 2024, 916, 170254.
15. Costa JP, Santos PSM, Duarte AC, Rocha-Santos T. (Nano)plastics in the environment - Sources, fates and effects. Sci. Total. Environ. 2016, 566-567, 15-26.
16. Gatidou, G.; Arvaniti, O. S.; Stasinakis, A. S. Review on the occurrence and fate of microplastics in Sewage Treatment Plants. J. Hazard. Mater. 2019, 367, 504-12.
17. Ainali, N. M.; Kalaronis, D.; Kontogiannis, A.; et al. Microplastics in the environment: Sampling, pretreatment, analysis and occurrence based on current and newly-exploited chromatographic approaches. Sci. Total. Environ. 2021, 794, 148725.
18. Hayany B, Rumpel C, Hafidi M, El Fels L. Occurrence, analysis of microplastics in sewage sludge and their fate during composting: A literature review. J. Environ. Manage. 2022, 317, 115364.
19. Kang, P.; Ji, B.; Zhao, Y.; Wei, T. How can we trace microplastics in wastewater treatment plants: A review of the current knowledge on their analysis approaches. Sci. Total. Environ. 2020, 745, 140943.
20. Rolsky, C.; Kelkar, V.; Driver, E.; Halden, R. U. Municipal sewage sludge as a source of microplastics in the environment. Current. Opinion. in. Environmental. Science. &. Health. 2020, 14, 16-22.
21. Magni, S.; Binelli, A.; Pittura, L.; et al. The fate of microplastics in an Italian Wastewater Treatment Plant. Sci. Total. Environ. 2019, 652, 602-10.
22. Franco, A.; Arellano, J.; Albendín, G.; Rodríguez-barroso, R.; Quiroga, J.; Coello, M. Microplastic pollution in wastewater treatment plants in the city of Cádiz: Abundance, removal efficiency and presence in receiving water body. Science. of. The. Total. Environment. 2021, 776, 145795.
23. Mason, S. A.; Garneau, D.; Sutton, R.; et al. Microplastic pollution is widely detected in US municipal wastewater treatment plant effluent. Environ. Pollut. 2016, 218, 1045-54.
24. Lusher, A.; Hurley, R.; Vogelsang, C. Mapping Microplastics in Sludge. Technical report; 2018. p.55.
25. Philipp, M.; Bucheli, T. D.; Kaegi, R. The use of surrogate standards as a QA/QC tool for routine analysis of microplastics in sewage sludge. Sci. Total. Environ. 2022, 835, 155485.
26. Wang, Q.; Zhang, Y.; Wangjin, X.; Wang, Y.; Meng, G.; Chen, Y. The adsorption behavior of metals in aqueous solution by microplastics effected by UV radiation. J. Environ. Sci. (China). 2020, 87, 272-80.
27. Zhang, X.; Chen, J.; Li, J. The removal of microplastics in the wastewater treatment process and their potential impact on anaerobic digestion due to pollutants association. Chemosphere 2020, 251, 126360.
28. Karapanagioti, H. K.; Endo, S.; Ogata, Y.; Takada, H. Diffuse pollution by persistent organic pollutants as measured in plastic pellets sampled from various beaches in Greece. Mar. Pollut. Bull. 2011, 62, 312-7.
29. Ma, B.; Xue, W.; Ding, Y.; Hu, C.; Liu, H.; Qu, J. Removal characteristics of microplastics by Fe-based coagulants during drinking water treatment. J. Environ. Sci. (China). 2019, 78, 267-75.
30. FAO and WHO. Standards Condex Alimentarius_Intenational food standards_ 2011. Available from: http://www.fao.org/fao-who-codexalimentarius/codex-texts/list-standards/en/. [Last accessed on 12 Dec 2025].
31. European Parliament and Council. Annex VI, table 3.1. Regulation (EC) No 1272/2008 of the European Parliament and of the Council of 16 December 2008 on classification, labelling and packaging of substances and mixtures, amending and repealing directives 67/548/EEC and 1999/45/EC, and amending Regulation (EC) No 1907/ 2006; 2008. Available from: http://data.europa.eu/eli/reg/2008/1272/oj [Last accessed on 12 Dec 2025].
32. Sun, J.; Dai, X.; Wang, Q.; van, L. M. C. M.; Ni, B. J. Microplastics in wastewater treatment plants: Detection, occurrence and removal. Water. Res. 2019, 152, 21-37.
33. Xu, G.; Liu, K.; Xu, B.; et al. Confined Microenvironments from Thermoresponsive Dendronized Polymers. Macromol. Rapid. Commun. 2020, 41, e2000325.
34. Stock, F.; B. Narayana VK, Scherer C, et al. Pitfalls and Limitations in Microplastic Analyses. In: Stock F, Reifferscheid G, Brennholt N, Kostianaia E, editors. Plastics in the Aquatic Environment - Part I. Cham: Springer International Publishing; 2022. pp. 13-42.
35. Hanif, M. A.; Ibrahim, N.; Dahalan, F. A.; Md, A. U. F.; Hasan, M.; Jalil, A. A. Microplastics and nanoplastics: Recent literature studies and patents on their removal from aqueous environment. Sci. Total. Environ. 2022, 810, 152115.
36. Siipola, V.; Pflugmacher, S.; Romar, H.; Wendling, L.; Koukkari, P. Low-Cost Biochar Adsorbents for Water Purification Including Microplastics Removal. Applied. Sciences. 2020, 10, 788.
37. Nomura, N.; Mishima, F.; Nishijima, S. Study of Micro-Plastics Separation From Sea Water With Electro-Magnetic Force. IEEE. Trans. Appl. Supercond. 2022, 32, 1-5.
38. Spreafico, C.; Russo, D. Investigating the evolution of the technologies for collecting microplastics. J. Environ. Manage. 2023, 326, 116710.
39. Debraj, D.; Lavanya, M. Microplastics everywhere: A review on existing methods of extraction. Sci. Total. Environ. 2023, 893, 164878.
40. Constant, M.; Billon, G.; Breton, N.; Alary, C. Extraction of microplastics from sediment matrices: Experimental comparative analysis. J. Hazard. Mater. 2021, 420, 126571.
41. Okoffo, E. D.; Ribeiro, F.; O'Brien, J. W.; et al. Identification and quantification of selected plastics in biosolids by pressurized liquid extraction combined with double-shot pyrolysis gas chromatography-mass spectrometry. Sci. Total. Environ. 2020, 715, 136924.
42. Rhein, F.; Scholl, F.; Nirschl, H. Magnetic seeded filtration for the separation of fine polymer particles from dilute suspensions: Microplastics. Chemical. Engineering. Science. 2019, 207, 1278-87.
43. Enders, K.; Tagg, A. S.; Labrenz, M. Evaluation of Electrostatic Separation of Microplastics From Mineral-Rich Environmental Samples. Front. Environ. Sci. 2020, 8, 112.
44. Scopetani, C.; Chelazzi, D.; Mikola, J.; et al. Olive oil-based method for the extraction, quantification and identification of microplastics in soil and compost samples. Sci. Total. Environ. 2020, 733, 139338.
45. Karlsson, T. M.; Vethaak, A. D.; Almroth, B. C.; et al. Screening for microplastics in sediment, water, marine invertebrates and fish: Method development and microplastic accumulation. Mar. Pollut. Bull. 2017, 122, 403-8.
46. Rani, M.; Ducoli, S.; Depero, L. E.; et al. A Complete Guide to Extraction Methods of Microplastics from Complex Environmental Matrices. Molecules 2023, 28, 5710.
47. Okoffo, E. D.; Rauert, C.; Thomas, K. V. Mass quantification of microplastic at wastewater treatment plants by pyrolysis-gas chromatography-mass spectrometry. Sci. Total. Environ. 2023, 856, 159251.
48. Wolff, S.; Kerpen, J.; Prediger, J.; Barkmann, L.; Müller, L. Determination of the microplastics emission in the effluent of a municipal waste water treatment plant using Raman microspectroscopy. Water. Res. X. 2019, 2, 100014.
49. Ivleva, N. P.; Wiesheu, A. C.; Niessner, R. Mikroplastik in aquatischen Ökosystemen. Angewandte. Chemie. 2017, 129, 1744-64.
50. Shim, W. J.; Hong, S. H.; Eo, S. E. Identification methods in microplastic analysis: a review. Anal. Methods. 2017, 9, 1384-91.
51. Araujo, C. F.; Nolasco, M. M.; Ribeiro, A. M. P.; Ribeiro-Claro, P. J. A. Identification of microplastics using Raman spectroscopy: Latest developments and future prospects. Water. Res. 2018, 142, 426-40.
52. Tian, M.; Morais, C. L. M.; Shen, H.; et al. Direct identification and visualisation of real-world contaminating microplastics using Raman spectral mapping with multivariate curve resolution-alternating least squares. J. Hazard. Mater. 2022, 422, 126892.
53. Sobhani, Z.; Zhang, X.; Gibson, C.; Naidu, R.; Megharaj, M.; Fang, C. Identification and visualisation of microplastics/nanoplastics by Raman imaging (i): Down to 100 nm. Water. Res. 2020, 174, 115658.
54. Chakraborty, I.; Banik, S.; Biswas, R.; Yamamoto, T.; Noothalapati, H.; Mazumder, N. Raman spectroscopy for microplastic detection in water sources: a systematic review. Int. J. Environ. Sci. Technol. 2023, 20, 10435-48.
55. Halvorson, R. A.; Vikesland, P. J. Surface-enhanced Raman spectroscopy (SERS) for environmental analyses. Environ. Sci. Technol. 2010, 44, 7749-55.
56. Nava, V.; Frezzotti, M. L.; Leoni, B. Raman Spectroscopy for the Analysis of Microplastics in Aquatic Systems. Appl. Spectrosc. 2021, 75, 1341-57.
57. Ouyang, W.; Zhang, Y.; Wang, L.; Barceló, D.; Wang, Y.; Lin, C. Seasonal relevance of agricultural diffuse pollutant with microplastic in the bay. J. Hazard. Mater. 2020, 396, 122602.
58. Miserli, K.; Athanasiou, V.; Boti, V.; Hela, D.; Konstantinou, I. Determination of PFAS in wastewaters and natural waters by solid phase extraction and UHPLC LTQ/Orbitrap MS for assessing occurrence and removals. Case. Studies. in. Chemical. and. Environmental. Engineering. 2023, 8, 100505.
59. Miserli, K.; Boti, V.; Konstantinou, I. Analysis of perfluorinated compounds in sewage sludge and hydrochar by UHPLC LTQ/Orbitrap MS and removal assessment during hydrothermal carbonization treatment. Sci. Total. Environ. 2024, 929, 172650.
60. Yang, L.; Li, K.; Cui, S.; Kang, Y.; An, L.; Lei, K. Removal of microplastics in municipal sewage from China's largest water reclamation plant. Water. Res. 2019, 155, 175-81.
61. Ziajahromi, S.; Neale, P. A.; Telles, S. I.; Chua, A.; Leusch, F. D. L. An audit of microplastic abundance throughout three Australian wastewater treatment plants. Chemosphere 2021, 263, 128294.
62. Üstün, G. E.; Bozdaş, K.; Can, T. Abundance and characteristics of microplastics in an urban wastewater treatment plant in Turkey. Environ. Pollut. 2022, 310, 119890.
63. Dyachenko, A.; Mitchell, J.; Arsem, N. Extraction and identification of microplastic particles from secondary wastewater treatment plant (WWTP) effluent. Anal. Methods. 2017, 9, 1412-8.
64. Raju, S.; Carbery, M.; Kuttykattil, A.; et al. Improved methodology to determine the fate and transport of microplastics in a secondary wastewater treatment plant. Water. Res. 2020, 173, 115549.
65. El, H. B.; El, F. L.; Quénéa, K.; et al. Microplastics from lagooning sludge to composts as revealed by fluorescent staining- image analysis, Raman spectroscopy and pyrolysis-GC/MS. J. Environ. Manage. 2020, 275, 111249.
66. Maw, M. M.; Boontanon, N.; Fujii, S.; Boontanon, S. K. Rapid and efficient removal of organic matter from sewage sludge for extraction of microplastics. Sci. Total. Environ. 2022, 853, 158642.
67. Ziajahromi, S.; Slynkova, N.; Dwyer, J.; et al. Comprehensive assessment of microplastics in Australian biosolids: Abundance, seasonal variation and potential transport to agroecosystems. Water. Res. 2024, 250, 121071.
68. Löder, M. G. J.; Imhof, H. K.; Ladehoff, M.; et al. Enzymatic Purification of Microplastics in Environmental Samples. Environ. Sci. Technol. 2017, 51, 14283-92.
69. Sakali, A.; Coello, D.; Haïlaf, A.; et al. A new protocol to assess the microplastics in sewage sludge. Journal. of. Water. Process. Engineering. 2021, 44, 102344.
70. Zhang, Z.; Liu, W.; Gao, Q.; et al. Microplastics extraction from wastewater treatment plants: Two-step digestion pre-treatment and application. Water. Res. 2023, 230, 119569.
71. Haque, A.; Holsen, T. M.; Baki, A. B. M. Distribution and risk assessment of microplastic pollution in a rural river system near a wastewater treatment plant, hydro-dam, and river confluence. Sci. Rep. 2024, 14, 6006.
72. Na, S. H.; Kim, M. J.; Kim, J.; et al. Fate and potential risks of microplastic fibers and fragments in water and wastewater treatment processes. J. Hazard. Mater. 2024, 463, 132938.
73. Xu, P.; Peng, G.; Su, L.; Gao, Y.; Gao, L.; Li, D. Microplastic risk assessment in surface waters: A case study in the Changjiang Estuary, China. Mar. Pollut. Bull. 2018, 133, 647-54.
74. Tomlinson, D. L.; Wilson, J. G.; Harris, C. R.; Jeffrey, D. W. Problems in the assessment of heavy-metal levels in estuaries and the formation of a pollution index. Helgolander. Meeresunters. 1980, 33, 566-75.
75. Koutsikos, N.; Koi, A. M.; Zeri, C.; Tsangaris, C.; Dimitriou, E.; Kalantzi, O. I. Exploring microplastic pollution in a Mediterranean river: The role of introduced species as bioindicators. Heliyon 2023, 9, e15069.
76. Hakanson, L. An ecological risk index for aquatic pollution control.a sedimentological approach. Water. Research. 1980, 14, 975-1001.
77. Yang, Z.; Li, S.; Ma, S.; et al. Characteristics and removal efficiency of microplastics in sewage treatment plant of Xi'an City, northwest China. Sci. Total. Environ. 2021, 771, 145377.
78. Dong, S.; Gao, P.; Li, B.; et al. Occurrence and migration of microplastics and plasticizers in different wastewater and sludge treatment units in municipal wastewater treatment plant. Front. Environ. Sci. Eng. 2022, 16, 1577.
79. Lv, X.; Dong, Q.; Zuo, Z.; Liu, Y.; Huang, X.; Wu, W. Microplastics in a municipal wastewater treatment plant: Fate, dynamic distribution, removal efficiencies, and control strategies. Journal. of. Cleaner. Production. 2019, 225, 579-86.
80. Carr, S. A.; Liu, J.; Tesoro, A. G. Transport and fate of microplastic particles in wastewater treatment plants. Water. Res. 2016, 91, 174-82.
81. Murphy, F.; Ewins, C.; Carbonnier, F.; Quinn, B. Wastewater Treatment Works (WwTW) as a Source of Microplastics in the Aquatic Environment. Environ. Sci. Technol. 2016, 50, 5800-8.
82. Mintenig, S. M.; Int-Veen, I.; Löder, M. G. J.; Primpke, S.; Gerdts, G. Identification of microplastic in effluents of waste water treatment plants using focal plane array-based micro-Fourier-transform infrared imaging. Water. Res. 2017, 108, 365-72.
83. Hidalgo-Ruz, V.; Gutow, L.; Thompson, R. C.; Thiel, M. Microplastics in the marine environment: a review of the methods used for identification and quantification. Environ. Sci. Technol. 2012, 46, 3060-75.
84. Blair, R. M.; Waldron, S.; Gauchotte-Lindsay, C. Average daily flow of microplastics through a tertiary wastewater treatment plant over a ten-month period. Water. Res. 2019, 163, 114909.
85. Conley, K.; Clum, A.; Deepe, J.; Lane, H.; Beckingham, B. Wastewater treatment plants as a source of microplastics to an urban estuary: Removal efficiencies and loading per capita over one year. Water. Res. X. 2019, 3, 100030.
86. Edo, C.; González-Pleiter, M.; Leganés, F.; Fernández-Piñas, F.; Rosal, R. Fate of microplastics in wastewater treatment plants and their environmental dispersion with effluent and sludge. Environ. Pollut. 2020, 259, 113837.
87. Ziajahromi, S.; Neale, P. A.; Rintoul, L.; Leusch, F. D. Wastewater treatment plants as a pathway for microplastics: Development of a new approach to sample wastewater-based microplastics. Water. Res. 2017, 112, 93-9.
88. Simon, M.; van, A. N.; Vollertsen, J. Quantification of microplastic mass and removal rates at wastewater treatment plants applying Focal Plane Array (FPA)-based Fourier Transform Infrared (FT-IR) imaging. Water. Res. 2018, 142, 1-9.
89. Pirc, U.; Vidmar, M.; Mozer, A.; Kržan, A. Emissions of microplastic fibers from microfiber fleece during domestic washing. Environ. Sci. Pollut. Res. Int. 2016, 23, 22206-11.
90. Horton, A. A.; Cross, R. K.; Read, D. S.; et al. Semi-automated analysis of microplastics in complex wastewater samples. Environ. Pollut. 2021, 268, 115841.
91. Xu, X.; Jian, Y.; Xue, Y.; Hou, Q.; Wang, L. Microplastics in the wastewater treatment plants (WWTPs): Occurrence and removal. Chemosphere 2019, 235, 1089-96.
92. Kazour, M.; Terki, S.; Rabhi, K.; Jemaa, S.; Khalaf, G.; Amara, R. Sources of microplastics pollution in the marine environment: Importance of wastewater treatment plant and coastal landfill. Mar. Pollut. Bull. 2019, 146, 608-18.
93. Wiśniowska, E.; Moraczewska-majkut, K.; Nocoń, W. Efficiency of microplastics removal in selected wastewater treatment plants – preliminary studies. Desalination. and. Water. Treatment. 2018, 134, 316-23.
94. Tomba, J. P.; Mana, C. D.; Perez, C.; Desimone, P. M.; Galland, G. B. Microstructural characterization of semicrystalline copolymers by Raman spectroscopy. Polymer. Testing. 2016, 52, 71-8.
95. Todica, M.; Stefan, R.; Pop, C.; Olar, L. IR and Raman Investigation of Some Poly(acrylic) Acid Gels in Aqueous and Neutralized State. Acta. Phys. Pol. A. 2015, 128, 128-35.
96. Prouvé, E.; Drouin, B.; Chevallier, P.; Rémy, M.; Durrieu, M. C.; Laroche, G. Evaluating Poly(Acrylamide-co-Acrylic Acid) Hydrogels Stress Relaxation to Direct the Osteogenic Differentiation of Mesenchymal Stem Cells. Macromol. Biosci. 2021, 21, e2100069.
97. Asefnejad, A.; Khorasani, M. T.; Behnamghader, A.; Farsadzadeh, B.; Bonakdar, S. Manufacturing of biodegradable polyurethane scaffolds based on polycaprolactone using a phase separation method: physical properties and in vitro assay. Int. J. Nanomedicine. 2011, 6, 2375-84.
98. Fang, J.; Xuan, Y.; Li, Q. Preparation of polystyrene spheres in different particle sizes and assembly of the PS colloidal crystals. Sci. China. Technol. Sci. 2010, 53, 3088-93.
99. Turan N, Sari Erkan H, Onkal Engin G. Microplastics in wastewater treatment plants: Occurrence, fate and identification. Process. Safety. and. Environmental. Protection. 2021, 146, 77-84.
100. De-la-Torre, G. E.; Pizarro-Ortega, C. I.; Dioses-Salinas, D. C.; et al. Are we underestimating floating microplastic pollution? Mar. Pollut. Bull. 2022, 178, 113592.
101. Haji, S.; Ait, A. A.; Noureddine, S.; Ben, H. M.; Moukrim, A. Study of Physicochemical and Bacteriological Quality of Treated Wastewater by the New Aourir Plant (Southwestern of Morocco) Using Activated Sludge Technology in a Semi-Arid Region. J. Ecol. Eng. 2021, 22, 83-98.
102. Mahon, A. M.; O'Connell, B.; Healy, M. G.; et al. Microplastics in Sewage Sludge: Effects of Treatment. Environ. Sci. Technol. 2017, 51, 810-8.
103. Vetrimurugan, E.; Jonathan, M. P.; Sarkar, S. K.; et al. Occurrence, distribution and provenance of micro plastics: A large scale quantitative analysis of beach sediments from southeastern coast of South Africa. Sci. Total. Environ. 2020, 746, 141103.
104. Li, J.; Dagnew, M.; Ray, M. B. Effect of coagulation on microfibers in laundry wastewater. Environ. Res. 2022, 212, 113401.
105. Prata, J. C.; Reis, V.; Paço, A.; et al. Effects of spatial and seasonal factors on the characteristics and carbonyl index of (micro)plastics in a sandy beach in Aveiro, Portugal. Sci. Total. Environ. 2020, 709, 135892.
106. Dong, M.; Zhang, Q.; Xing, X.; Chen, W.; She, Z.; Luo, Z. Raman spectra and surface changes of microplastics weathered under natural environments. Sci. Total. Environ. 2020, 739, 139990.
107. Jiao, M.; Cao, S.; Ren, L.; Li, R. Analysis of composite microplastics in sediment using 3D Raman spectroscopy and imaging method. Journal. of. Hazardous. Materials. Advances. 2021, 3, 100016.
108. Jiang, F.; Wang, M.; Ding, J.; Cao, W.; Sun, C. Occurrence and Seasonal Variation of Microplastics in the Effluent from Wastewater Treatment Plants in Qingdao, China. JMSE. 2022, 10, 58.
109. Uogintė, I.; Pleskytė, S.; Pauraitė, J.; Lujanienė, G. Seasonal variation and complex analysis of microplastic distribution in different WWTP treatment stages in Lithuania. Environ. Monit. Assess. 2022, 194, 829.
110. Lares, M.; Ncibi, M. C.; Sillanpää, M.; Sillanpää, M. Intercomparison study on commonly used methods to determine microplastics in wastewater and sludge samples. Environ. Sci. Pollut. Res. Int. 2019, 26, 12109-22.
111. Beni N, Karimifard S, Gilley J, Messer T, Schmidt A, Bartelt-hunt S. Higher concentrations of microplastics in runoff from biosolid-amended croplands than manure-amended croplands. Commun. Earth. Environ. 2023, 4, 691.
112. Harley-Nyang, D.; Memon, F. A.; Jones, N.; Galloway, T. Investigation and analysis of microplastics in sewage sludge and biosolids: A case study from one wastewater treatment works in the UK. Sci. Total. Environ. 2022, 823, 153735.
113. Harley-Nyang, D.; Memon, F. A.; Osorio, B. A.; Galloway, T. Variation in microplastic concentration, characteristics and distribution in sewage sludge & biosolids around the world. Sci. Total. Environ. 2023, 891, 164068.
114. Xu, Z.; Bai, X. Microplastic Degradation in Sewage Sludge by Hydrothermal Carbonization: Efficiency and Mechanisms. Chemosphere 2022, 297, 134203.
115. Yuan, Z.; Nag, R.; Cummins, E. Ranking of potential hazards from microplastics polymers in the marine environment. J. Hazard. Mater. 2022, 429, 128399.
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Miserli, K.; Konstantinou, I. Determination of microplastics in municipal wastewater treatment plant effluents and sludge using micro-Raman spectroscopy. Water Emerg. Contam. Nanoplastics 2025, 4, 4. http://dx.doi.org/10.20517/wecn.2024.72
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