Microplastics in wastewater treatment plants: Detection, occurrence and removal

Evaluation of the available strategies to control the emission of microplastics into the aquatic environment

No effective strategy has been found so far to control the emission of microplastics. The purpose of this article is to review the available control strategies, as well as barriers to developing them. Based on the estimations in the available literature, decomposition of larger plastics, clothes washing and tire abrasion play an essential part in the total emission rate of microplastics into the ocean. Nonetheless, there is no corresponding information regarding the soil, and more information is needed to prioritize the emission sources of microplastics more preciously. Generally, there have been two approaches for the management of the microplastic issues, including the substitution of non-plastic materials for plastic ones in products such as personal care products, and microplastic removal from wastewater. The former is in its infancy and has commenced only in a few developed countries. Existing wastewater treatment plants (WWTPs) as the other approach can transfer a significant portion of the microplastics into the sludge. The result is that the final destination of these microplastics can be the soil. Since there is little information on how serious the impact of microplastics is on the soil as compared with water, the currently used WWTPs cannot be considered as a final remedy. Furthermore, there has been not been any specifically designed techniques to remove microplastics from wastewater efficiently and economically.

Microplastic contamination in salt pans and commercial salts - A baseline study on the salt pans of Marakkanam and Parangipettai, Tamil Nadu, India

We studied the abundance of microplastics from commercial table salts and table salts from salt pans at Marakkanam and Parangipettai, Tamil Nadu, India. Microplastic abundance in the salts collected from salt pans had a range of 3.67 ± 1.54 to 21.33 ± 1.53 nos./10 g of salt which were higher than the microplastics retrieved from the commercial salts which ranged from 4.67 ± 1.15 to 16.33 ± 1.53 nos./10 g of salt. All the microplastics retrieved were fibers which were secondary in origin. Black, red, blue, green, white, brown, and colorless microplastics were observed in the samples. FT-IR results showed that 4 types of polymers, namely, Nylon, Polypropylene (PP), Low Density Polyethylene (LDPE), and Polyethylene Terephthalate (PET) were present in the samples. Domestic and municipal wastewater discharges into the estuaries may contribute to microplastics in the table salts. Our study proves that table salts (processed and unprocessed) are prone to microplastic contamination.

Enhancing Microplastics Removal from Wastewater Using Electro-Coagulation and Granule-Activated Carbon with Thermal Regeneration

Discharge from sewage treatment plants (STPs) is a significant pathway of entry for microplastics (MPs) to the environment. Therefore, STPs should be considered as an important barrier to the distribution and circulation of MPs in the aquatic environment. In this study, the fate and material-specific properties of MPs were investigated in an STP-equipped and granule-activated carbon (GAC) tower with a thermal regeneration system. This system functioned with a tertiary treatment unit. The GAC with thermal regeneration removed 92.8% of MPs and was useful for removing MPs with a specific gravity less than that of water and with a size of 20–50 µm, which had negligible removal in the conventional STP process. In addition, a lab-scale electric-coagulation experiment was conducted to examine its potential utility as a pretreatment process for further enhancing the removal efficiency of MPs by GAC. After 30 min of electro-coagulation using aluminum electrodes, 90% of MPs were converted into separable flocs by centrifugation. These flocs may be effectively removed by GAC or other tertiary treatment steps. This study demonstrates that GAC with thermal regeneration is a tertiary process that can efficiently prohibit the release of MPs from STPs and circulation of MPs in the natural environment.

In Situ Identification and Spatial Mapping of Microplastic Standards in Paramecia by Secondary-Ion Mass Spectrometry Imaging

Microplastics (MPs) are universally present in the ecosystem and pose great threats to the environment and living organisms. Research studies have shown that small MPs (<50 μm in diameter) are especially toxic and account for more than half of all MPs collected in the Atlantic Ocean. Nevertheless, current methods for the detection and analysis of MPs are incapable of achieving rapid and in situ analysis of small MPs in the biota to ultimately enable the study of their biological effects. In this work, we report a method that allows rapid in situ identification and spatial mapping of small MPs directly from paramecia with high accuracy by acquiring chemical composition information using secondary-ion mass spectrometry (SIMS) imaging. Specifically, six types of common MPs (polymethyl methacrylate, polyvinyl chloride, polypropylene, polyethylene terephthalate, polyglycidyl methacrylate, and polyamide 6) with a diameter of 1-50 μm were simultaneously imaged with high chemical specificity at a spatial resolution of 700 nm. In situ spatial mapping of a group of MPs ingested by paramecia was performed using SIMS fragments specific to the plastic composition with no sample pretreatment, revealing the aggregation of MPs in paramecia after ingestion. Compared with existing methods, one additional advantage of the developed method is that the MPs and the organism can be analyzed in the same experimental workflow to record their fingerprint spectra, acquiring biochemical information to evaluate MP fate, toxicity, and the MP-biota interaction.

Occurrence, fate and removal of microplastics as heavy metal vector in natural wastewater treatment wetland system

Microplastics pollution in aquatic ecosystems is of great concern; however, systemic investigations are still lacking in freshwater wetland systems used for wastewater treatment. The present study discusses such freshwater wetland system in Eastern India to understand its microplastics transport mechanism, heavy metals association and microplastics removal efficiency. Microplastics (63 µm - 5 mm) were heavily found in surface water and sediments of treatment ponds (7.87 to 20.39 items/L and 2124.84 to 6886.76 items/kg) and associated wastewater canals (30.46 to 137.72 items/L and 1108.78 to 34612.87 items/kg). A high content of toxic metals (As, Cd, Cr, Cu, Ni, Pb and Zn) were found on the microplastics with polyethylene terephthalate and polyethylene as major plastics types which were also found in fishes and macroinvertebrates of treatment ponds. Machine learning algorithm revealed a close association between microplastics content in fishes and surface water, indicating risk associated with floating microplastics to the aquatic biota. The study also revealed that microplastics were acting as heavy metals vector and potentially causing fish contamination. Surface water microplastics removing efficiency of the treatment ponds was estimated to be 53%. The study bespeaks about transport of microplastics through wastewater canals and their retention in treatment ponds emphasizing sustainability maintenance of natural wastewater treatment systems especially considering microplastics contamination to the aquatic biota of freshwater wetland systems.

Study of a stream in Argentina with a high concentration of microplastics: Preliminary analysis of the methodology

This study presents for the first time results about the microplastic concentration and their origin in a stream of the Pampas region in Argentina, receiving wastewater of an intermediate city. The most appropriate procedure to analyze and quantify the microplastics in the studied system is the use of an oxidative digestion process using a 30% H₂O₂ solution to eliminate the organic matter in the samples. A high quantity of MPs, on the order of millions of microplastics per m³ of water, was estimated in the Langueyú stream. 56% of the microplastics correspond to fibers with diameters between 10 and 15 μm and lengths less than 500 μm, while 44% are fragments with sizes of tens of micrometers. Raman microspectroscopy was used to identify the type of fibers. The characteristics of the microplastic fibers released in a wash load test are comparable with those observed in the Langueyú stream, in particular, the average sizes and the distribution of the diameters of the MPFs are similar. The processes in the sewage treatment plant, prior to their discharge in the stream, would affect the color of the fibers and their length.

Optical Monitoring of Microplastics Filtrated from Wastewater Sludge and Suspended in Ethanol

The abundance of microplastics (MPs) in the atmosphere, on land, and especially in water bodies is well acknowledged. In this study, we establish an optical method based on three different techniques, namely, specular reflection to probe the medium, transmission spectroscopy measurements for the detection and identification, and a speckle pattern for monitoring the sedimentation of MPs filtrated from wastewater sludge and suspended in ethanol. We used first Raman measurements to estimate the presence and types of different MPs in wastewater sludge samples. We also used microscopy to identify the shapes of the main MPs. This allowed us to create a teaching set of samples to be characterized with our optical method. With the developed method, we clearly show that MPs from common plastics, such as polypropylene (PP), polyethylene terephthalate (PET), polystyrene (PS), and polyethylene (PE), are present in wastewater sludge and can be identified. Additionally, the results also indicate that the density of the plastics, which influences the sedimentation, is an essential parameter to consider in optical detection of microplastics in complex natural environments. All of the methods are in good agreement, thus validating the optics-based solution.

Sampling, pre-treatment, and identification methods of microplastics in sewage sludge and their effects in agricultural soils: a review

Microplastics are widely detected in wastewater treatment plants. They can remove microplastics from wastewaters with a high yield, but it means that microplastics are transferred and accumulated to sewage sludge. Lately, increasing attention has been paid to microplastics in raw and treated wastewaters. However, studies about quantification and identification of microplastics in sewage sludge are very scarce and need to be further investigated. Since the sludge-based microplastics are newly studied and are a challenging matrix due to high organic content, there is limited knowledge of sampling, pre-treatment methods, identification techniques, and expression units. Besides, treated sewage sludge is mostly used for soil amendment to improve soil fertility and it gives economic advantages. This situation creates a pathway for microplastics entering the soil environment with unknown consequences. To the best of our knowledge, microplastics have a large specific surface area, small size, and hydrophobicity which makes it a good adsorbent for other pollutants. Therefore, the combined effect of microplastics with adsorbed pollutants such as heavy metals, antibiotics, and persistent organic pollutants could give serious harm to soil safety and soil organisms. Herein, new developments in the methods for sampling, pre-treatment, and identification techniques of microplastics in sewage sludge were reviewed. Then, the abundance of microplastics, major polymer types, and shapes in sewage sludge were examined. Finally, the effects and ecological risks of microplastic pollution as a result of agricultural usage of sewage sludge in the soil environment have been summarized. Also, the main points for future research were highlighted.

Removal of Microplastics from Waters through Agglomeration-Fixation Using Organosilanes—Effects of Polymer Types, Water Composition and Temperature

Due to the fact, that microplastics are a global environmental problem, new ways for their removal from water, soil and air need to be developed. New materials in combination with easy to implement technologies for microplastic removal come into the focus of scientific studies and engineering, especially for application in water resources. In our comparative case study, the effects of water composition and temperature on the agglomeration-fixation reaction of microplastics using organosilanes were examined. We compared biologically treated municipal wastewater, seawater and demineralized water at temperatures ranging from 7.5–40 °C. Temperature variations and tested water compositions showed no negative effect on microplastic removal. The residues of the organosilanes remaining in the water after the fixation process were monitored using ICP-OES and DOC measurements. Only one of the organosilanes tested showed no dissolved residues in the waters. Microplastic encompasses a multitude of different types of polymers with different properties and surface chemistries. Therefore, we compared the efficiency of the process for polyethylene, polypropylene, polyamide, polyester, and polyvinylchloride as examples of common polymer types with different chemical compositions. A strong effect of the polarity of microplastics and organosilanes on removal efficiency was observed. The organic groups of organosilanes can be chemically adapted to different polymer types.

Isotope ratio mass spectrometry and spectroscopic techniques for microplastics characterization

Micro- and nano-scale plastic particles in the environment result from their direct release and degradation of larger plastic debris. Relative to macro-sized plastics, these small particles are of special concern due to their potential impact on marine, freshwater, and terrestrial systems. While microplastic (MP) pollution has been widely studied in geographic regions globally, many questions remain about its origins. It is assumed that urban environments are the main contributors but systematic studies are lacking. The absence of standard methods to characterize and quantify MPs and smaller particles in environmental and biological matrices has hindered progress in understanding their geographic origins and sources, distribution, and impact. Hence, the development and standardization of methods is needed to establish the potential environmental and human health risks. In this study, we investigated stable carbon isotope ratio mass spectrometry (IRMS), attenuated total reflectance - Fourier transform infrared (ATR-FTIR) spectroscopy, and micro-Raman spectroscopy (μ-Raman) as complementary techniques for characterization of common plastics. Plastic items selected for comparative analysis included food packaging, containers, straws, and polymer pellets. The ability of IRMS to distinguish weathered samples was also investigated using the simulated weathering conditions of ultraviolet (UV) light and heat. Our IRMS results show a difference between the δ13C values for plant-derived and petroleum-based polymers. We also found differences between plastic items composed of the same polymer but from different countries, and between some recycled and nonrecycled plastics. Furthermore, increasing δ13C values were observed after exposure to UV light. The results of the three techniques, and their advantages and limitations, are discussed.

Total coliform and Escherichia coli in microplastic biofilms grown in wastewater and inactivation by peracetic acid

Microplastics (MP) have been proposed as a vector for pathogenic microorganisms in the freshwater environment. The objectives of this study were (a) to compare the fecal indicator growth in biofilms on MP and material control microparticles incubated in different wastewater fractions and (b) to compare MP biofilm, natural microparticle biofilm, and planktonic cell susceptibility to disinfection by peracetic acid (PAA). Biofilms were grown on high-density polyethylene, low-density polyethylene, polypropylene MP, or wood chips (as a material control) and incubated in either wastewater influent or pre-disinfection secondary effluent. Reactors were disinfected with PAA, biofilms were dislodged, and total coliform and Escherichia coli were cultivated. Fecal indicators were quantifiable in both MP and wood biofilms incubated in the wastewater influent but only on the wood biofilms incubated in secondary wastewater effluent. More total coliform grew in the wood biofilms than MP biofilms, and the biofilms grown on MP and woodchips were more resistant to disinfection than planktonic bacteria. Thus, it may be possible to refer to the disinfection literature for fecal indicators in biofilm on other particles to predict behavior on MP. Treatments that remove particles in general would help reduce the potential for fecal indicator bypass of disinfection. PRACTITIONER POINTS: MP biofilm had lower concentrations of fecal indicators than wood biofilm Biofilm on MP was not more resistant to disinfection than wood biofilm Biofilms, regardless of substrate, were more resistant to disinfection than planktonic organisms.

Abundance and characteristics of microplastics in municipal wastewater treatment plant effluent: a case study of Guangzhou, China

Wastewater treatment plants (WWTPs) have been proposed as significant sources of microplastics (MPs) in freshwater and estuarine environments. WWTPs, even those with high removal efficiencies, release millions of MPs per plant daily. China is the largest plastic producer worldwide, but only a few studies of MP pollution from WWTPs have been carried out in China. In this work, we present a comprehensive report concerning the MPs in effluent from six WWTPs in Guangzhou, which is the third largest city in China. The six WWTPs employ different treatment processes and serve different populations and types of factories. The average abundance of MPs in the effluents of all six WWTPs was 1.719 ± 1.035 MP/L. Fiber was the most common type of MP in the effluent, accounting for 39.48 ± 6.37% of all MPs. Fourier transform infrared spectroscopy confirmed that 35.7% of the particles were plastics, including polyethylene terephthalate (31.9%), polypropylene (26.6%), and polyethylene (9.7%). The results showed that advanced or tertiary treatment technologies could substantially remove MPs and that the size of the population served was positively associated with the abundance of MPs. The number of textile factories was a key factor contributing to the total release of MPs. In addition, the MP shapes and polymer compositions showed that the occurrence of MP types is regional, varies regionally, and is related to the types of factories in the vicinity. More studies on the effects of specific industries are suggested in order to improve the management of wastewater discharge and reduce MPs presence in the natural environment.

Biochar produced from the co-pyrolysis of sewage sludge and waste tires for cadmium and tetracycline adsorption from water

Application of sewage sludge biochar as an adsorbent for pollutant removal has obtained special attention due to their low cost and surface functionality. In this research, sludge-tire composite biochar (STB) was successfully prepared through co-pyrolysis at 300, 500 and 700 °C, respectively. Cadmium (Cd) and tetracycline (TC) were selected as the target pollutant. The results indicated that STB has the highest surface area (49.71 m²/g), more inorganic minerals (Kaolinite) as well as relatively stable physicochemical properties with 10% tire particles (TP) at 700 °C. The adsorption results indicated that the pseudo-second-order equation and Langmuir isotherm model could better describe the adsorption of Cd²⁺ and TC by STB. The maximum adsorption capacity of Cd²⁺ and TC was 50.25 mg/g and 90.09 mg/g, respectively. The main mechanism of the adsorption process of STB for Cd mainly involves anion binding adsorption and ion exchange. The main mechanism of the adsorption process of STB for TC mainly involves complexation and cation exchange. The present study could set a scientific foundation for further research on the recycle of sewage sludge and tires.

A probabilistic risk assessment of microplastics in soil ecosystems

Plastics have a variety of applications due to their versatility, relative cost, and strength-to-weight ratio, and resistance to degradation. As a result, plastic waste can be found in all corners of the Earth. A class of plastic contaminants that have received increasing attention in terms of their potential impact on ecosystems is microplastics (≤5 mm). The greatest attention to date has been on their potential effect in marine ecosystems. However, a growing number of studies are examining their potential impact on soil ecosystems. The data reported in the literature on the environmentally-relevant concentrations of microplastics in soils and the concentration of microplastics that causes an adverse effect in soil biota were used to perform a probabilistic risk assessment of microplastics to soil biota. An environmental exposure distribution was constructed from the concentrations of microplastics reported in soil in the literature. Species sensitivity distributions were constructed using concentration of microplastics in soil that had no adverse effect on soil species (NOEC) or the lowest concentrations that had an adverse effect on soil species (LOEC) reported in the literature. The 95th centile of the environmental exposure distribution (8147 microplastic particles per gram of soil) was greater than 22 and 28% of the species sensitivity distribution constructed using NOECs and LOECs, respectively. The assessment concluded that environmentally relevant concentrations of microplastics reported in the literature could pose a considerable risk to soil biota. It is also important to note that due to the continued production of large quantities of plastic and the persistence of microplastics in the environment, environmentally-relevant concentrations of microplastics in soil are likely to only rise.

Fate and effects of microplastics in wastewater treatment processes

Microplastics (MPs) have garnered growing attention of researchers, as they are proved to be hazardous to the environment and humans. Wastewater treatment plants (WWTPs) are deemed as an important releasing source of MPs to the environment, and thus it is of significance to study the behavior of MPs in WWTPs. In this review, the fate of MPs in WWTPs and their effects on different wastewater treatment processes have been comprehensively discussed. Studies have shown that the secondary treatment is the most efficient process to remove MPs from wastewaters with a removal rate around 98%. The presence of MPs can increase reagent addition dosage, inhibit nitrogen conversion rate, and cause membrane fouling in wastewater treatment processes. Besides, the influences of MPs on activated sludge mainly exert on nitrification and denitrification processes, sludge digestion, and microbial communities. However, it is worth noting that different methods have been employed to determine the concentrations of MPs in WWTPs. As a result, the removal performance on MPs in WWTPs is difficult to be accurately assessed. Moreover, complicated interaction among MPs and other environmental pollutants may expand the impacts of MPs on wastewater treatment processes, which still remains insufficiently investigated. Therefore, this review has also proposed some knowledge gaps existing in present MP studies in WWTPs, and would provide reference to alleviate the adverse effects of MPs for future research.

The entering of polyethylene terephthalate microplastics into biological wastewater treatment system affects aerobic sludge digestion differently from their direct entering into sludge treatment system

The entering of the widespread polyethylene terephthalate (PET) microplastics into biological wastewater treatment system results in their retention in sewage sludge, which inevitably enters the sludge treatment system. However, all previous studies regarding the impact of microplastics on sludge treatment system were conducted by directly adding microplastics to system and focusing on anaerobic sludge digestion, although PET microplastics commonly enter into the biological wastewater treatment system first before sludge being subsequently treated. The potential impact of the microplastics on waste activated sludge (WAS) aerobic digestion is also completely missing. Therefore, herein the influences of PET microplastics with different entry paths on WAS aerobic digestion as well as the key mechanisms involved was firstly explored. Experimental results demonstrated that compared to the control test, the entering of PET microplastics to biological wastewater treatment system inhibited WAS aerobic digestion by 10.9 ± 0.1% through the decreased hydrolysis, although WAS solubilization during aerobic digestion was improved due to the change of generated WAS characteristics. In contrast, when PET microplastics was directly added to the sludge aerobic digester, there was little impact on solubilization, while the hydrolysis were inhibited seriously, thereby suppressing WAS aerobic digestion more severely by 28.9 ± 0.1%. Further investigation revealed that PET microplastics reduced the populations of key bacteria (e.g., Saprospiraceae, Chitinophagaceae and Xanthomonadaceae) involved in aerobic digestion via induced oxidative stress or/and releasing toxic chemical. This study provided a more accurate approach to assessing the real situation regarding the influences of PET microplastics on aerobic sludge digestion.

Removal of micron-scale microplastic particles from different waters with efficient tool of surface-functionalized microbubbles

Microplastic (MP) contamination in water has garnered significantly global concerns. The MP removal particularly challenges when the particle size decreases to several microns and other contaminants co-exist. This study used the coagulative colloidal gas aphrons (CCGAs) to simultaneously remove the micron-scale MP particles (~5 µm in diameter) and dissolved organic matter (DOM). Carboxyl-modified poly-(methyl methacrylate) (PMMA) and unsurface-coated polystyrene (PS) were chosen as target MPs. Over 94% of PS particles and almost 100% of color were simultaneously removed with lower CCGA consumption than the scenarios with either contaminant in water. The PMMA removal was not as high as the PS removal since the HA polyanions could compete with the negatively-charged PMMA for CCGAs. High salinity reduced the removal of HA by changing its interfacial behaviors without impacting the MP separation. In river water or influent of wastewater treatment plant, the MP particles were almost completely eliminated whereas the DOM (tyrosine-like or tryptophan-like) was partially removed. The fluorescence quenching titration revealed that CCGAs preferably captured the free DOM and the DOM-coated MP particles through complexation interaction. The study denoted that the CCGA system could be a robust tool for efficiently and synergistically removing micron-scale MPs and DOM from different water matrixes.

Revisiting Microplastics in Landfill Leachate: Unnoticed Tiny Microplastics and Their Fate in Treatment Works

Due to the environmental risks caused by microplastics, understanding the sources and characteristics of microplastics and cutting off their routes into the environment are crucial. However, so far, studies on microplastics in the landfill leachate system (a major pathway of microplastics into the environment) are still limited, especially for tiny particles <50 µm that might have higher risks to the environment. This study investigated the microplastics in landfill leachate and in leachate treatment works, with a size detection limit down to 10 µm. The results showed that the microplastics particle and mass concentrations in the untreated leachate were 235.4 ± 17.1 item/L and 11.4 ± 0.8 µg/L, respectively, with tiny particles (<50 µm) accounting for over 50%. Overall, 27 polymeric materials were detected in leachate samples, with polyethylene and polypropylene being the most abundant in the untreated leachate. The neutral buoyancy of microplastics (average density: 0.94 g/cm³), together with irregular shapes, suggested they may be difficult to be removed by sedimentation. Further exploring the fate of microplastics in leachate treatment works showed that the membrane treatment effectively reduced microplastics loading to 0.14% for particle and 0.01% for mass, but the average particle density rose. The differences in polymeric materials distribution at different sampling locations and the presence of membrane-related polymer in membrane treatment effluent suggested tiny microplastics could be generated and released from membrane systems. Moreover, this study discovered that the sludge dewatering liquor could contain a high amount of microplastics, and the estimated particle loading was about 3.6 times higher than that in dewatered sludge. This suggested a new approach to microplastics mitigation through separating microplastics from the sludge dewatering liquor before its recirculation.

Microplastics in African ecosystems: Current knowledge, abundance, associated contaminants, techniques, and research needs

Despite Africa ranking top in mismanaged plastic waste, there is insufficient data on the extent of microplastics and its interaction with other contaminants in its ecosystems. Microplastics pollution has been documented globally, however, specific data from the continent is crucial for accurate risk assessment and to drive policies. We critically reviewed 56 articles from 1987 to 2020 and provide an overview of the current knowledge of the abundance and distribution of microplastics and associated contaminants in African aquatic systems and organisms. Most of the studies were carried out in the marine environment and there is currently no available data on the abundance of microplastic pollution in the African terrestrial environment. We show that across all studies, 5-100% of all sampled aquatic organisms contained microplastics. Concerning high levels of microplastics were reported in fish from Egypt compared to other parts of Africa and the world. Across all persistent organic pollutants sampled in microplastics, hopanes and phthalates were present at high concentrations while sodium and zinc were high relative to other trace metals reported. The most frequently occurring plastics were polyethylene followed by polypropylene and polystyrene. We found that most of the studies relied on visual inspection (52%) > FTIR (38%) > Raman spectroscopy (5%) > Scanning electron microscopy (3%) > Differential scanning calorimetry (2%) for identifying microplastics. Major gaps in sampling and identification techniques which may have overestimated or underestimated the current levels were identified. We discuss other research priorities and recommend solutions to address these issues associated with microplastic pollution in Africa.

Do membrane filtration systems in drinking water treatment plants release nano/microplastics?

Drinking water treatment plants (DWTPs) are thought to be able to remove many micropollutants including nanoplastics (NPs) and microplastics (MPs). However, few studies have focused on the water treatment process itself producing NPs and/or MPs. This paper discussed the possibility of releasing NPs and MPs from organic membranes in drinking water treatment plants. The effects of physical cleaning, chemical agents, mechanical stress, aging, and wear on the possibility of membrane breach during long-term use were analyzed. Further analysis based on membrane aging mechanisms and material properties revealed that the membrane filtration systems could release NPs/MPs to drinking water supply networks. Although the toxicity of membrane materials to human body needs further study, the action that should be taken to treat the release of NPs/MPs in DWTPs cannot be ignored: (1) in-depth study of the generation and release mechanisms of NPs/MPs; (2) reconsideration of membrane life cycle design; (3) determination of NPs/MPs concentration limits in drinking water through toxicity assessment; (4) accelerating development of biomembrane and inorganic membrane materials; and (5) unification of NPs/MPs sampling and testing standard. Accordingly, more research needs to be conducted to investigate the release of NPs and/or MPs from DWTPs.

Effect of microplastic particle size to the nutrients removal in activated sludge system

Microplastics as emerging environmental pollutants, its effect to the bioprocess of water and wastewater treatment has aroused concern. This study investigated the effects of microplastic polystyrene (PS) particle size to the activated sludge nutrient removal process. The ammonia, nitrite, nitrate and phosphorus removal under various PS particle size during nitrification and denitrification process was tested. The results indicated that with PS particle size 150-300 μm, the ammonia oxidation during nitrification process was inhibited to 71%, 92%, and 80% as compared with the blank reactor, for PS concentration at 0.01 g/L, 0.05 g/L and 0.10 g/L, respectively. The nitrite accumulation during nitrification process was also high at PS particle size 150-300 μm and concentration no less than 0.05 g/L. The nitrate reduction during the denitrification process was all inhibited to 69%-94% as compared with the blank, except for reactor No.4. The phosphate removal during nitrification process was not affected by the existence of microplastics PS, the average removal rate was over 80% after 2 h and over 95% after 3 h, respectively. The microplastics particle size plays important role in affecting the activated sludge nutrient removal process.

Environmental prevalence, fate, impacts, and mitigation of microplastics-a critical review on present understanding and future research scope

Microplastics are considered to be ubiquitous and widespread emerging contaminants. They are persistent in the nature and pose considerable harm to the environment. Their omnipresence is documented in almost all aquatic habitats, several atmospheric and terrestrial environments, and also in human consumables. The objective of this review is to provide an overview of the environmental prevalence of the microplastics in all environmental compartments, and their possible adverse impacts. It also presents review of the studies conducted in India and the epitome of potential mitigation measures. The need and direction of future research are highlighted. The review will help in determining the exposure levels, environmental consequences, and risk estimations, and will guide the researchers and policymakers.

A review of microplastic distribution in sediment profiles

The growing use of plastic and their indiscriminate disposal into the environment has resulted in the accumulation of huge quantities of microplastic (MP) in the marine environment. Several studies have investigated the pathways of MPs reaching marine environments and a few have begun looking at their inventories in sediment profiles. Recent estimates suggest between 70 and 90% of the MP particles are accumulated into sediment profiles. This paper reviews MPs in sediment cores, and the methods used for chronological reconstruction to provide evidence to link the plastic usage and MP inventories over time. In one example, a ²¹⁰Pb dated sediment core from Kuwait Bay revealed 0.1 MPs g^-1 of sediment deposited in approximately 1951 and 0.5 MPs g^-1 in sediment from 2009 indicating a progressively increasing presence in recent sediments. The review also highlights the issue of very large spatio-temporal variation in MP concentrations, indicating the limitation of a snapshot study especially when dealing with the surface sediments; and it demonstrates the relevance of using sediment cores for a better assessment of MP input and inventories in the marine environment. It is proposed that MP sediment data should be reported as N m^-2 year^-1 or g m^-2 year^-1, and cores preferably dated using ²¹⁰Pb, and supported by at least one other stratigraphic marker to enhance the usefulness of these datasets, since ²¹⁰Pb can reliably date sediments as old as 100 years, a time-span which extends well beyond the time plastic production began. The anomalies in data processing and reporting in terms of number per kg of sediment or per cm²/m² should be addressed essentially by adopting a standardized protocol.

Effects of microplastic exposure on the blood biochemical parameters in the pond turtle (Emys orbicularis)

The accumulation of microplastics (MPs) is a growing problem in aquatic ecosystems. Despite increased research on MPs in the last decade, their potential threat to freshwater ecosystems remains an open question. In the present study, the negative impacts of MPs were investigated on blood biochemical parameters in the European pond turtle (Emys orbicularis). Pond turtles were distributed into three experimental groups (n = 9 for each group) and were fed diets containing 250, 500, and 1000 mg MPs (PE100 polyethylene) per kg of food for 30 days, and a control group fed with a standard uncontaminated diet. The results indicated that exposure to 500 and 1000 mg kg^-1 MPs caused a significant increase in the activities of alanine and aspartate aminotransferases, and in the levels of cholesterol, glucose, creatinine, urea, and calcium (Ca⁺²) compared with the control group. On the contrary, the activity of gamma-glutamyl transferase and the levels of total protein, albumin, total immunoglobulins, and phosphorus were significantly reduced in E. orbicularis exposed to 500 and 1000 mg kg^-1 MPs when compared with the controls. In all the MP-exposed groups, the activity of lactate dehydrogenase and globulin and magnesium (Mg⁺²) levels were significantly reduced; while creatine phosphokinase and alkaline phosphatase activities were increased with respect to the control turtles. A significant decrease in triglyceride levels was reported in E. orbicularis exposed to 1000 mg kg^-1 MPs. MPs intake induced notable alterations in blood biochemical parameters of E. orbicularis. These results suggest that changes in the blood biochemical parameters could be an appropriate bio-indicator to evidence the existence of tissue damage in E. orbicularis.

Distribution and removal characteristics of microplastics in different processes of the leachate treatment system

Microplastics (MPs) in environments are widely concerned in recent years due to the widely occurrence and potential risk to environments. With a large amount of plastic waste discarded into the landfills, leachate generated from landfills was found to be an important pollution source of MPs. However, the removal efficiency and characteristics of MPs in leachate treatment system were not clear. In this study, the concentration variation and the removal performance of MPs in leachate treatment system with the process of pretreatment + biotreatment + advanced treatment were investigated. The results showed that 58.33% of MPs were removed during the leachate treatment process. The Ultrafiltration had the highest efficiency of removing MPs, but the advanced treatment technologies (Nanofiltration and Reverse Osmosis) did not contribute to the removal of MPs. Furthermore, the removal performance of MPs in leachate treatment process was determined by MPs properties, such as size, shape and polymer type. The whole leachate treatment process had higher removal efficiencies for particle MPs compared to fiber MPs, and only 50% of fiber MPs were removed in biological treatment and advanced treatment. Ultrafiltration had better removal effect on microplastics with the size of less than 1 mm, and MPs less than 0.5 mm were almost removed by advanced treatment but accumulated in the sludge with the abundance of 0.893 ± 0.252 items/g. The results showed that a considerable amount of MPs (10⁶ items/day) discharged with the effluent (3200 t/d), and most removed MPs from leachate accumulated in sludge, which would cause potential risk to the environments.

Sedimentary microplastic concentrations from the Romanian Danube River to the Black Sea

A multitude of recent studies have detailed microplastic concentrations in aquatic and terrestrial environments, although questions remain over their ultimate fate. At present, few studies have detailed microplastic characteristics and abundance along a freshwater-marine interface, and considerable uncertainties remain over the modelled contribution of terrestrial and riverine microplastic to the world's oceans. In this article, for the first time, we detail sedimentary microplastic concentrations along a River-Sea transect from the lower reaches of a major continental river, the River Danube, through the Danube Delta, the Black Sea coast to the Romanian and Bulgarian inner shelf of the Black Sea. Our results indicate that isolated areas of the Danube Delta are still relatively pristine, with few microplastic particles in some of the sediments sampled.

Microplastics pollution in mangrove ecosystems: A critical review of current knowledge and future directions

Over the last decade, microplastics (MPs, plastic particles <5 mm) as emerging contaminants have received a great deal of international attention, not only because of their continuous accumulation in both marine and terrestrial environment, but also due to their serious threats posed to the environment. Voluminous studies regarding sources, distribution characterization, and fate of MPs in the different environmental compartments (e.g., marine, freshwater, wastewater, and soil) have been reported since 2004, whereas MPs pollution in unique marine ecosystems (e.g., coastal mangrove habitat) receives little scientific attention. Mangrove ecosystem, an important buffer between the land and the sea, has been identified as a potential sink of MPs caused by both marine and land-based activities. Moreover, the source and distribution characteristics of MPs in this ecosystem are significantly different from other coastal habitats, mainly owing to its unique features of high productivity and biomass. With the impetus to provide a more integrated view of MPs pollution in mangrove habitats, a literature review was conducted based on the existing studies related to this topic. This is the first review to present the current state of MPs pollution in mangrove ecosystems, specially including (i) the possible sources of MPs in mangrove areas and their pathways entering into this habitat; (ii) MPs pollution in the different mangrove compartments (including surface seawater, sediments, and biotas); and (iii) factors influencing MPs distribution in mangrove areas. Toward that end, the research gaps are proposed to guide for future research priorities.

A review of microplastics aggregation in aquatic environment: Influence factors, analytical methods, and environmental implications

A large amount of plastic waste released into natural waters and their demonstrated toxicity have made the transformation of microplastics (MPs; < 5 mm) and nanoplastics (NPs; < 100 nm) an emerging environmental concern. Aggregation is one of the most important environmental behaviors of MPs, especially in aquatic environments, which determines the mobility, distribution and bioavailability of MPs. In this paper, the sources and inputs of MPs in aquatic environments were first summarized followed by the analytical methods for investigating MP aggregation, including the sampling, visualization, and quantification procedures of MP' particle sizes. We critically evaluated the sampling methods that still remains a methodological gap. Identification and quantification of MPs were mostly carried out by visual, spectroscopic and spectrometric techniques, and modeling analysis. Important factors affecting MP aggregation in natural waters and environmental implications of the aggregation process were also reviewed. Finally, recommendations for future research were discussed, including (1) conducting more field studies; (2) using MPs in laboratory works representing those in the environment; and (3) standardizing methods of identification and quantification. The review gives a comprehensive overview of current knowledge for MP aggregation in natural waters, identifies knowledge gaps, and provides suggestions for future research.

Degradation of common polymers in sewage sludge purification process developed for microplastic analysis

To enable and/or facilitate analysis of microplastics from environmental samples, a purification process is required to reduce the organic matter content. The development of such process has as one main concern, besides achieving efficient organic matter reduction, the preservation of the microplastics. In this study, a three-step method for sewage sludge purification was proposed employing sodium dodecyl sulfate and hydrogen peroxide. The effects of the purification method on seven polymers (LLDPE, HDPE, PP, PS, PET, PA66 and SBR) were evaluated in terms of mass change, surface characteristics, mechanical properties, thermal properties and functional groups change. It was also assessed how the polymers were affected by the purification chemicals without the presence of sewage sludge. The purification process led to changes in all tested plastics, but in different intensities. LLDPE, HDPE, PP, PS and PET did not suffer considerable degradation. PET was more affected by hydrolysis than oxidation. On the other hand, the integrities of PA66 and SBR were noticeably affected. The effects of the purification process were considered to be due to the plasticizer behavior of water and oxidation on PA66 and loss of filler and oxidation on SBR. For both polymers there was a reduction on the tensile strength of around 50-60% after the purification, indicating they could be prone to fragmentate into smaller pieces along the process. After purification, PA66 also started to decompose at a temperature around 10 °C lower comparing to virgin samples. Except for SBR, the presence of sewage sludge and its oxidation was more harmful to the polymers than the purification chemicals without the presence of sewage sludge. This study serves as an evaluation of the effects of the purification process on the degradation of microplastics and a methodology for such assessment when designing a purification process.

Treatment of microplastics in water by anodic oxidation: A case study for polystyrene

Water pollution by microplastics (MPs) is a contemporary issue which has recently gained lots of attentions. Despite this, very limited studies were conducted on the degradation of MPs. In this paper, we reported the treatment of synthetic mono-dispersed suspension of MPs by using electrooxidation (EO) process. MPs synthetic solution was prepared with distilled water and a commercial polystyrene solution containing a surfactant. In addition to anode material, different operating parameters were investigated such as current intensity, anode surface, electrolyte type, electrolyte concentration, and reaction time. The obtained results revealed that the EO process can degrade 58 ± 21% of MPs in 1 h. Analysis of the operating parameters showed that the current intensity, anode material, electrolyte type, and electrolyte concentration substantially affected the MPs removal efficiency, whereas anode surface area had a negligible effect. In addition, dynamic light scattering analysis was performed to evaluate the size distribution of MPs during the degradation. The combination of dynamic light scattering, scanning electron microscopy, total organic carbon, and Fourier-transform infrared spectroscopy results suggested that the MPs did not break into smaller particles and they degrade directly into gaseous products. This work demonstrated that EO is a promising process for degradation of MPs in water without production of any wastes or by-products.

Microplastic distributions in a domestic wastewater treatment plant: Removal efficiency, seasonal variation and influence of sampling technique

Wastewater treatment plants (WWTPs) serve as an important route of microplastics (MPs) to the environment. Therefore, more effective MPs sampling and detection methodologies, as well as a better understanding of their influence on MPs occurrence and distributions in WWTP effluents, are needed for better removal and control. In this work, the efficiency of a municipal WWTP to remove MPs was assessed by collecting samples from raw to tertiary effluent during a 12-month sampling campaign (season-based) using different sampling methods (containers, 24-h composite and large grab samples). MPs retrieved from different treatment units within the WWTP were identified and quantified using plastic/non-plastic staining followed by optical microscopy, SEM and μ-Raman microscopy. Overall, the mean removal efficiency of MPs in the WWTP was 97%, with most MPs removed by the secondary stage and a mean effluent concentration of 1.97 MPs L^-1 after sand filtration. The relative abundance of particles was lower than fibers in treated effluent compared with the raw wastewater, with MP fibers constituting 74% of the total MPs in raw wastewater and 91% in treated effluent. Taking seasonal variations into account is important as total MPs concentration in the effluent was notably higher in winter compared with the other seasons. Increasing the sampled volume using large samples or 24-h composite samples significantly reduced the variability between replicates. However, MPs concentration post the tertiary stage was significantly lower using morning sampling (9 am) by large grab sampling method (1.2 MPs L^-1) compared to 24-h composite sampling (3.2 MPs L^-1) possibly due to intra-daily changes. Using a finer mesh size (0.45 μm) to capture MPs beyond the size range typically studied (≥20 μm) effectively doubled the number of MPs detected in the tertiary effluent and highlights the importance of standardizing sampling procedures.

Pervasive distribution of polyester fibres in the Arctic Ocean is driven by Atlantic inputs

Microplastics are increasingly recognized as ubiquitous global contaminants, but questions linger regarding their source, transport and fate. We document the widespread distribution of microplastics in near-surface seawater from 71 stations across the European and North American Arctic - including the North Pole. We also characterize samples to a depth of 1,015 m in the Beaufort Sea. Particle abundance correlated with longitude, with almost three times more particles in the eastern Arctic compared to the west. Polyester comprised 73% of total synthetic fibres, with an east-to-west shift in infra-red signatures pointing to a potential weathering of fibres away from source. Here we suggest that relatively fresh polyester fibres are delivered to the eastern Arctic Ocean, via Atlantic Ocean inputs and/or atmospheric transport from the South. This raises further questions about the global reach of textile fibres in domestic wastewater, with our findings pointing to their widespread distribution in this remote region of the world.

Influence of biodegradable polybutylene succinate and non-biodegradable polyvinyl chloride microplastics on anammox sludge: Performance evaluation, suppression effect and metagenomic analysis

Microplastics (MPs) has been widely detected in wastewater treatment plants. However, there is a lack of research on its influence on anaerobic ammonia oxidation (anammox) process. Therefore, the effects of polybutylene succinate (PBS) and polyvinyl chloride (PVC) MPs on the nitrogen removal performance, microbial community and metabolites of anammox sludge were investigated. Results showed that PBS and PVC MPs reduced the nitrite removal efficiency of the anammox sludge, and PVC1 (0.1 g/L PVC) group was the most significant at 19.2 %. Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) spectra showed that PBS2 (0.5 g/L PBS) group increased the polysaccharide content in the anammox sludge. This may be because of the byproduct, which was produce during the biodegradation of PBS MPs, and decrease the agglomeration capacity of sludge, so as to increase the mass transfer. PBS2 group reduced the relative abundance of Methanosaeta (10.18 %) and the methane modules, and stimulated the anammox bacteria Ca. Brocadia (1.17 %) and the relative nitrogen metabolism modules. PVC2 group reduced the relative abundance of Ca. Brocadia (3.02 %), while was enriched Methanosaeta (2.1 %). Non-biodegradable PVC MPs was more harmful to anammox sludge, which would draw attention to the entry of PVC MPs into the anammox system.

The difference of aggregation mechanism between microplastics and nanoplastics: Role of Brownian motion and structural layer force

In recent years, microplastics (MPs) and nanoplastics (NPs) have attracted worldwide attention because of the potential risks they pose to aquatic environments, but there are few studies on the difference of aggregation mechanism between MPs and NPs. In this study, 100 nm and 1 μm polystyrene plastics were selected as models to explore the aggregation mechanism of MPs/NPs under different aquatic environments. The influence of ion species and concentrations on the aggregation behaviors and kinetics were systematically investigated to predict the effects of water quality on the occurrence form of MPs and NPs based on DLVO theory and revised modified Smoluchowski theory. Results showed concentration, valence and hydrated ability of cations jointly affected the aggregation behavior of NPs. The critical coagulation concentration ratio of cations were consistent with Schulze-Hardy rules. But the different aggregation rate coefficients of same valent cations were ascribed to the structural layer force. Anion species played a role in the reaction-controlled regime by producing hydrogen ions to neutralize negative charges on NPs surfaces. Due to the strong Brownian motion and structural layer force, NPs would be stable in freshwater but preferentially aggregated when transport through brackish water, estuaries, eutrophication and high hardness areas and sea water, forming the accumulation hot spots of NPs in the sediment. While for MPs, physical process controlled the aggregation mechanism of them, leading to high stability in natural water and eventually transporting into marine environments. This study provided a theoretical foundation for assessing the transport, distribution, fate and ecological risks of MPs and NPs in realistic aquatic environments.

Microplastic's story

The problem of microplastic pollution is now the order of the day in front of everyone's eyes affecting the environment and the health of leaving creature. This work aims to retrace the history of microplastics in a critical way through a substantial bibliographic collection, defining the points still unresolved and those that can be resolved. Presence of marine litter in different environments is reviewed on a global scale, focusing in particular on micro and macro plastics definition, classification and characterization techniques.

A review of the removal of microplastics in global wastewater treatment plants: Characteristics and mechanisms

Wastewater treatment plants (WWTPs) are considered to be the main sources of microplastic contaminants in the aquatic environment, and an in-depth understanding of the behavior of microplastics among the critical treatment technologies in WWTPs is urgently needed. In this paper, the characteristics and removal of microplastics in 38 WWTPs in 11 countries worldwide were reviewed. The abundance of microplastics in the influent, effluent, and sludge was compared. Then, based on existing data, the removal efficiency of microplastics in critical treatment technologies were compared by quantitative analysis. Particularly, detailed mechanisms of critical treatment technologies including primary settling treatment with flocculation, bioreactor system, advanced oxidation and membrane filtration were discussed. Thereafter, the abundance load and ecological hazard of the microplastics discharged from WWTPs into the aquatic and soil environments were summarized. The abundance of microplastics in the influent ranged from 0.28 particles L^-1 to 3.14 × 10⁴ particles L^-1, while that in the effluent ranged from 0.01 particles L^-1 to 2.97 × 10² particles L^-1. The microplastic abundance in the sludge within the range of 4.40 × 10³-2.40 × 10⁵ particles kg^-1. In addition, there are still 5.00 × 10⁵-1.39 × 10¹⁰ microplastic particles discharged into the aquatic environment each day Moreover, among the critical treatment technologies, the quantitative analysis revealed that filter-based treatment technologies exhibited the best microplastics removal efficiency. Fibers and microplastics with large particle sizes (0.5-5 mm) were easily separated by primary settling. Polyethene and small-particle size microplastics (<0.5 mm) were easily trapped by bacteria in the activated sludge of bioreactor system. The negative impact of microplastics from wastewater treatment plant was worthy of attention. Moreover, unknown transformation products of microplastics and their corresponding toxicity need in-depth research.

An audit of microplastic abundance throughout three Australian wastewater treatment plants

Wastewater treatment plants (WWTPs) have been identified as an important pathway of microplastics to the environment. Most studies have focused on wastewater effluent, but generally only a small fraction of microplastics entering WWTPs are present in treated effluent. Instead, the majority of microplastics are expected to be retained in the sludge. To our knowledge, there is limited information on microplastics in sludge/biosolids from Australian WWTPs, despite 75% of biosolids produced in Australia being used for agriculture. This study evaluated the abundance of microplastics throughout the treatment trains of three WWTPs in Australia. The fate of microplastics >25 μm during treatment and their release to the environment was evaluated using an audit approach. The highest microplastic concentrations were detected in the influent, with fibres the dominant form of microplastic found. The screening and grit removal process preceding primary treatment removed 69-79% of microplastics, with these microplastics transported to landfill. Only 0.2-1.8% of the total microplastics in the influent were present in the final effluent, while 8-16% were retained in biosolids. This equates to between 22.1 × 10⁶ to 133 × 10⁶ microplastic particles per day released in effluent, between 864 × 10⁶ to 1020 × 10⁶ microplastic particles per day in biosolids, and between 4100 × 10⁶ to 9100 × 10⁶ microplastic particles per day transported to landfill. This study shows for the first time that most microplastics are retained during the initial screening and grit removal process with the load of microplastics going to landfill an order of magnitude greater than that in biosolids. Landfills may thus be an important sink (and potential future source) of microplastics from wastewater.

Role of Structural Morphology of Commodity Polymers in Microplastics and Nanoplastics Formation: Fragmentation, Effects and Associated Toxicity in the Aquatic Environment

With the continued growth in plastic production, its ubiquitous use and insufficient waste management and disposal, the increased levels of plastics in the environment have led to growing ecological concerns. The breakdown of these plastic macromolecules to smaller micro and nanosized particles and their detection in the aerial, aquatic, marine and terrestrial environments has been reviewed extensively, especially for thermoplastics. However, the formation of micro and nanoplastics has typically been explained as a physical abrasion process, largely overlooking the underlying chemical structure-morphology correlations to the degradation mechanisms of the plastics. This is particularly true for the common commodity thermosets. This review focuses on the degradation pathways for the most widely produced commodity thermoplastics and thermosets into microplastics (MP)s and nanoplastics (NP)s, as well as their behaviour and associated toxicity. Special emphasis is placed on NPs, which are associated with greater risks for toxicity compared to MPs, due to their higher surface area to volume ratios. This review also assesses the current state of standardized detection and quantification methods as well as comprehensive regulations for these fragments in the aquatic environment.

Microplastics in real wastewater treatment schemes: Comparative assessment and relevant inhibition effects on anaerobic processes

The occurrence, fate and removal of microplastics (MPs) in a wastewater treatment plant (WWTP) in Central Italy were investigated together with their potential adverse effects on anaerobic processes. In the influent of the WWTP, 3.6 MPs^.L^-1 were detected that mostly comprised polyester fibers and particles in the shape of films, ranging 0.1-0.5 mm and made of polyethylene and polypropylene (PP). The full-scale conventional activated sludge scheme removed 86% of MPs, with the main reduction in the primary and secondary settling. MPs particles bigger than 1 mm were not detected in the final effluent and some loss of polymers types were observed. In comparison, the pilot-scale upflow granular anaerobic sludge blanket (UASB) + anaerobic membrane bioreactor (AnMBR) configuration achieved 94% MPs removal with the abatement of 87% of fibers and 100% of particles. The results highlighted an accumulation phenomenon of MPs in the sludge and suggested the need to further investigate the effects of MPs on anaerobic processes. Accordingly, PP-MPs at concentrations from 5 PP-MPs^.gTS^-1 to 50 PP-MPs^.gTS^-1 were spiked in the pilot-scale UASB reactor that was fed with real municipal wastewater, where up to 58% decrease in methanogenic activity was observed at the exposure of 50 PP-MPs^.gTS^-1. To the best of our knowledge, the presented results are the first to report of PP-MPs inhibition on anaerobic processes.

Magnetically steerable iron oxides-manganese dioxide core-shell micromotors for organic and microplastic removals

Because of micro/nanoscale manipulation and task-performing capability, micro/nanomotors (MNMs) have attracted lots of research interests for potential applications in biomedical and environmental applications. Owing to the low-cost, good motion behavior, and environmental friendliness, various low-cost metal oxides based MNMs become promising alternatives to the precious metal based MNMs, in particular for environmental remediation applications. Hereby, we demonstrate the facile and scalable fabrication of two types of bubble-propelled iron oxides-MnO₂ core-shell micromotors (Fe₃O₄-MnO₂ and Fe₂O₃-MnO₂) for pollutant removal. The Fe₂O₃-MnO₂ micromotor exhibits efficient removals of both aqueous organics and suspended microplastics via the synergy of catalytic degradation, surface adsorption, and adsorptive bubbles separations mechanisms. The adsorptive bubbles separation achieved more than 10% removal of the suspended microplastics from the polluted water in 2 h. We clarified the major contributions of different remediation mechanisms in pollutants removals, and the findings may be beneficial to a wide range of environmental applications of MNMs.

Microplastics could be a threat to plants in terrestrial systems directly or indirectly

Microplastics (MPs) are an emerging threat to ecosystem functioning and biota. The major sources of MPs are terrestrial and agricultural lands. But their fate, concentration in the terrestrial environment, and effects on soil and biota are poorly understood. There is a growing body of concern about the adverse effects of MPs on soil-dwelling organisms such as microbes in mycorrhizae and earthworms that mediate essential ecosystem services. Environmental concentrations and effects of MPs are considered to increase with increasing trend of its global production. MPs in the soil could directly impact plants through blocking the seed pore, limiting the uptake of water and nutrient through roots, aggregation, and accumulation in the root, shoot, and leaves. However, MPs can also indirectly impact plants by affecting soil physicochemical characteristics, soil-dwelling microbes, and fauna. An affected soil could impact plant community structure and perhaps primary production. In this article, we have assessed the potential direct and indirect impacts of MPs on plants. We have discussed both the positive and negative impacts of MPs on plants in terrestrial systems based on currently available limited literature on this topic and our hypothetical understandings. We have summarized the most current progress in this regard highlighting the future directions on microplastic research in terrestrial systems.

Release of Plastics to Australian Land from Biosolids End-Use

Plastics are contaminants of emerging concern that can enter the environment from multiple sources, including via land application of treated sewage sludge (biosolids). Biosolids samples collected from 82 wastewater treatment plants (WWTPs) across Australia and covering 34% of the population during census week in 2016 were quantitatively analyzed to estimate the release of seven common plastics. Quantitative analysis was performed by pressurized liquid extraction followed by double-shot microfurnace pyrolysis coupled to gas chromatography mass spectrometry. Ninety nine percent of the samples contained plastics (Σ₆plastics) at concentrations of between 0.4 and 23.5 mg/g dry weight (median; 10.4 mg/g dry weight), while polycarbonate was not detected in any sample. Per-capita mass loads of plastics (Σ₆plastics) released were between 8 and 877 g/person/year across all investigated WWTPs. Polyethylene was the predominant plastic detected, contributing to 69% of Σ₆plastics. Based on the concentrations measured, it was projected that around 4700 metric tons (Mt) of plastics are released into the Australian environment through biosolids end-use each year, equating to approximately 200 g/person/year, which represents 0.13% of total plastics use in Australia. Of this, 3700 Mt of plastics are released to agricultural lands and 140 Mt to landscape topsoil. Our results provide a first quantitative per-capita mass loads and emission estimate of plastic types through biosolids end-use.

Review of current trends, advances and analytical challenges for microplastics contamination in Latin America

Microplastics accumulation is an emerging environmental issue and a threat to marine life and human health. There is a growing number of investigations on the abundance and distribution of microplastics in different water bodies and biota worldwide, with relatively few studies conducted in Latin America, however, the current knowledge of microplastics sources, occurrence, transport, fate and potential impacts remains largely unexplored. This review presents the current trends and advances of microplastics on a lesser known region of the world by compiling the research performed to date in different environmental compartments. The sampling techniques and methods for microplastics extraction in the existing literature data are also summarized. Among 78 published studies reviewed, 34% of studies were from Brazil and 46% of studies have mainly focused on biota. The main findings showed that microplastics are not negligible across Latin America significantly varying in their distribution, with the prevalence of fibers comprising 62% of the total. Polyethylene, polypropylene, polyethylene terephthalate and polystyrene have been identified as the most common polymer types, accounting for 80% of the total. Limited studies and lack of standardized methodologies render difficulties to establish fundamental information on microplastics abundance and types in most countries of this region. Therefore, this review will primarily serve as a baseline when evaluating the environmental relevance of microplastics in Latin America and would stimulate discussions focusing on this topic, calling for more research in future.

Influence of polyether sulfone microplastics and bisphenol A on anaerobic granular sludge: Performance evaluation and microbial community characterization

The retention of polyether sulfone (PES) and bisphenol A (BPA) in wastewater has received extensive attention. The effects of PES and BPA on the removal of organic matter by anaerobic granular sludge were investigated. We also analyzed the changes in the electron transport system and the effects on the composition of extracellular polymeric substances (EPS), as well as alternations of the microbial community in the anaerobic granular sludge. In the experimental groups which received BPA, the removal of the chemical oxygen demand (COD) were significantly suppressed, which an average removal efficiency of less than 65%, 30% lower than that of the control group. In the loosely-bound EPS (LB-EPS) excitation-emission matrix (EEM) spectra, the absorption peak of tryptophan disappeared when the BPA pollutants was added, which it was present in the control group without added pollutants. The addition of PES and BPA also affected protease, acetate kinase, and coenzyme F₄₂₀ activities in the anaerobic granular sludge. Especially, the coenzyme F₄₂₀ reduced from 0.0045 to 0.0017 μmol/L in the presence of PES and BPA. The relative abundance of Spirochaetes decreased in the presence of PES and BPA, while the relative abundance of Bacteroidetes increased from 12.98% to 22.87%. At the genus level, in the presence of PES and BPA, the relative abundance of Acinetobacter increased from 2.20% to 9.64% and Hydrogenophaga decreased sharply from 15.58% to 0.12%.

Plastic litter pollution along sandy beaches in the Caribbean and Pacific coast of Colombia

Plastic pollution is a global problem that poses a threat to coastal and marine ecosystems and human livelihoods and requires effective solutions adaptable to local conditions. In Colombia, the knowledge about marine plastic pollution is still limited and the development of effective strategies for managing marine and coastal environments is crucial. Therefore, plastic pollution was assessed on 43 Colombian sandy beaches on the Caribbean and Pacific coasts. Amounts of macroplastic ranged from 35 ± 15 to 81 ± 23 items 100 m^-1, being product's packaging the most common. Microplastic densities ranged from 3 to 1387 items m^-2. The highest microplastic concentrations were found on the beaches from Caribbean cities and in rural areas of Pacific municipalities. Fragments and polyethylene were the most commonly observed shape and polymer categories, respectively. Tourism and poor waste management practices are the primary plastic sources on the studied beaches. Plastic litter on Colombian beaches are a problem that requires prevention, mitigation, and control actions to help conserve this ecosystem.

Synergistic effects of water temperature, microplastics and ammonium as second and third order stressors on Daphnia magna

Daphnids, including the water flea Daphnia magna, can be exploited for wastewater treatment purposes, given that they are filter feeder organisms that are able to remove suspended particles from water. The presence of pollutants, such as microplastics and chemicals, might be considered stressors and modify the behaviour and survival of D. magna individuals. The impact of the cumulative pollutants that regulate the fate of living organisms has yet to be fully determined. Here we present the effect of double and triple combinations of stressors on the behaviour of D. magna. The impact of water temperature, ammonium and polystyrene microplastics on the filtration capacity and survival of D. magna is studied. Water temperatures of 15 °C, 20 °C and 25 °C, microplastic-to-food ratios of 25% and 75%, and ammonium concentrations of 10 and 30 mg N-NH₄⁺ L^-1 are tested after making dual and triple combinations of the parameters. A synergistic effect between water temperature and ammonium is normally observed but not in the case of the lower values of ammonium concentration and temperature. The combination of three stressors (water temperature, microplastics and ammonium) is also found to be synergistic, producing the greatest impact on D. magna filtration capacity and reducing their survival. In comparison with the effect of the two stressor conditions, the combination of the three stressors caused a reduction of between 13.1% and 91.7% in the t_50% time (the time required for a 50% reduction in the D. magna filtration capacity) and a reduction of between 4.8% and 54.5% in TD50 (the time for 50% mortality).

Investigation and fate of microplastics in wastewater and sludge filter cake from a wastewater treatment plant in China

Microplastics (MPs) have been widely detected in wastewater treatment plants (WWTPs) due to their small particle size, wide distribution, and difficulty in removal. Previous studies, however, mostly focused on MPs in wastewater, thereby neglecting sludge. To comprehensively understand the changes of MPs in WWTPs, we investigated the quantity and characteristics of MPs in wastewater and sludge of a WWTP in Harbin, a typical inland city in China, and calculated the MPs removal rate. The results showed that there were 126.0 ± 14.0 particles/L MPs in the influent and 30.6 ± 7.8 particles/L in the effluent, about 75.7% MPs were removed and transferred to the sludge during this WWTP. The abundance of MPs in dewatered sludge and sludge filter cake was 36.3 ± 5.7 and 46.3 ± 6.2 particles/g (dry sludge), the sludge disposal scale of this WWTP can reach 1300 tons/day, which was equivalent to about 7.74 × 10¹² microplastic particles accumulated in sludge per year. These sludges were used as fertilizers in the soil, which will cause secondary pollution of MPs. Raman spectroscopic analysis showed that about 89.5% of particles were plastic polymers, such as polyesters, polyamide (PA), polyethylene terephthalate (PET) and polyethylene (PE), which suggested that MPs may be derived from laundry and personal care products. Therefore, we recommend that more work should be devoted to how to control the release of MPs at the source and the reuse of sludge after treatment by WWTPs.

Influence of synthetic wastewater on entrapped air on the isotactic and atactic polypropylene microplastic surfaces

The municipal wastewater collection system is recognized as an initial point of interaction between microplastics (MPs) and the urban wastewater matrix. The raw wastewater contains a wide variety of organic and inorganic substances including chemicals and heavy metals. However, the fate of MPs in urban sewer systems is not yet well understood. In this work two types of virgin polypropylene (PP) samples, isotactic (iPP) and atactic (aPP), were exposed to two synthetic wastewater solutions in order to study their effects on the physical properties of the hydrophobic polymer surfaces. Particular attention was paid to the pollution adhesion at the air-liquid-solid interfaces of the surface air pockets entrapped on the polymer surfaces. The first wastewater solution consists of mixed fat, oil and grease (FOG) - surfactant and another which is an exclusively contained wastewater surfactant. The interaction experiment over a period of 10 min between the polymer's air pocket and solutions indicated that the size of the bubble in the mixed FOG-surfactant solution increased more pronouncedly for iPP (%152) in contrast to aPP (%31) and was also compared with the greater surface roughness of the polymers. The size variation of the spherical cap on the immersed polymer surfaces were measured between 17 µm and 85 µm using image processing techniques while the data was analyzed by the Young-Laplace equation. The corresponding technical surface roughness of the polymers, the surface tension of the liquids and their air/water contact angle on the flat polymer surfaces were also measured. The results of this study indicated that surface air pockets influence the adsorption capacity of MPs and thus their buoyancy and contamination potential.

Microplastics in wastewater treatment plants of Wuhan, Central China: Abundance, removal, and potential source in household wastewater

Wastewater treatment plants (WWTPs) are identified as an important source of microplastics (MPs) released into the aquatic environments. The purpose of this study is to compare the abundance and removal of MPs of two WWTPs located in Wuhan City, China, and to evaluate the characteristics of MPs in household wastewater. The results showed that the abundance of MPs in the wastewater of two WWTPs has decreased sharply from 23.3 to 7.9 n L^-1 and 80.5 to 30.3 n L^-1 with corresponding removal rates of 66.1 and 62.7%, respectively. The fiber, fragment, and microbead present in the three sources of household wastewater (toothpaste, facial cleanser and laundry wastewater) and WWTPs have similarity in shape, and further the main component of MPs in household wastewater and WWTPs is polyvinyl chloride, as is evident from Raman spectrum analysis. Each use of 1 g facial cleanser can release about 1000 MPs, which is higher than that of toothpaste; however, microbeads are only found in the frosting cleanser. An interesting finding is that toothpaste contained fewer amounts of MPs than expected; hence, we observed absence of microbeads in toothpaste. However, over 150,000 fibers are released while washing an average washing of 1 kg of clothing. It has further been estimated that the daily discharge of MPs from household wastewater to WWTPs in China is 9.1 × 10¹⁰. Thus, the results indicate that the MPs in household wastewater mainly contribute to the MPs in wastewater of WWTP, therefore, the use of MPs in the personal care products should be banned or alternatives of primary MPs use in these products must be developed.