Ozonation facilitates the aging and mineralization of polyethylene microplastics from water: Behavior, mechanisms, and pathways

In situ H2O2 production from self-sufficient heterogeneous Fenton reaction over Fe0/MoS2-x for potential environmental remediation applications

Fenton reaction technology has worked well in water and wastewater treatment; however it is often limited by such problems as continuous external supply of H2O2, slow Fe3+/Fe2+ cycle rate, high energy requirements, and maintenance of low pH during operation. Herein, a novel self-sufficient heterogeneous Fenton system based on Fe0/MoS2-x was designed, fabricated, and optimized to effectively address these problems. The combined presence of Fe0 and sulfur vacancies sites in MoS2-x played a pivotal role in the generation of H2O2via two-step single-electron reduction process without any energy consumption. The existence of dual active sites resulted in a considerable increase in the H2O2 yield (up to 0.6 mM/g/h) in a pH-neutral aqueous solution. Furthermore, the Fe3+/Fe2+ cycle rate was accelerated by Mo6+/Mo4+/Moδ+ sites. The factors collectively contributed to the impressive performance of the reaction in degrading complex pollutants (e.g., polyethylene, a model plastic matter) under pH-neutral conditions. In addition to its outstanding catalytic performance, Fe0/MoS2-x exhibited superior reusability and stability. Notably, the catalyst reactivity was well sustained in the presence of common competitive factors such as inorganic anions and dissolved organic pollutants, and for other polymer types. This study demonstrates that Fe0/MoS2-x with impressive self-sufficient Fenton reaction capacity has greater potentials for water and wastewater treatment.

Changes in electron distribution of aged microplastic and their environmental impacts in aquatic environments

Microplastics (MPs) are widespread environmental pollutants. This study primarily examines the changes in electro distribution of aged MPs in aquatic environments and their subsequent impact on the environment. Under the action of natural and artificial aging, the electron cloud arrangement of MPs will change, thus affecting the relevant properties of MPs. Among them, the free radicals formed by advanced oxidation technology will be enriched on the surface of MPs carrying benzene rings, and react with other pollutants (organic pollutants, heavy metals, etc.) adsorbed by MPs to form environmental persistent free radicals (EPFRs). The electron cloud density of MPs carrying EPFRs increases, and the reactivity will also increase. Additionally, the oxygen-containing functional groups on the surface of aged MPs enhance their selective adsorption, altering their environmental impact. MPs can serve as a source of free radicals in the environment, enhance the oxidation capacity of other substances in the environment, and even affect the expression of antibiotic resistance genes. In addition, MPs have a high mobility, which will have a greater negative impact in the environment. Additionally, the high mobility of MPs amplifies their negative environmental impact. This study examines the changes in electron distribution of aged MPs and highlights their effects on aquatic ecosystems, providing insights into pollution control, toxicity, and degradation mechanisms.

Exploring the co-occurrence of microplastics, DOM and DBPs inside PVC pipes undergoing chlorination by correlation analysis and unsupervised learning

Drinking water distribution systems face a multifaceted emerging concern, including in situ microplastic (MP) generation, chemical leaching from plastic pipes, and the formation of disinfection by-products (DBPs). This study investigated the co-release of MPs and chemical leachates from polyvinyl chloride (PVC) pipes exposed to different chlorine concentrations on a lab scale, as well as the subsequent formation of DBP. Results highlighted significant evidence of PVC-derived dissolved organic matter (PVC-DOM) and microplastic (PVC-MP) leaching at higher chlorine concentrations. However, at chlorine residuals of 1 ppm, natural organic matter (NOM) retained its importance, with minimal release of PVC-DOM and PVC-MP from plastic pipes. Correlation analysis highlights the critical role of DOM, including both NOM and PVC-DOM, as a key intermediary between MPs and DBPs. This is evidenced by the strongest observed correlations within the DOM group and its significant associations with both MPs and DBPs. Conversely, the limited direct connections between MPs and DBPs further underscore the importance of DOM as the key link between these two targets. Using unsupervised learning techniques, including clustering and dimensionality reduction, further elucidated the influence of DOM in controlling the data patterns, enabling robust interpretation of complex datasets, and providing valuable insights. This study contributes to advancing understanding of the co-occurrence and behaviors of MP, DOM, and DBP within drinking water distribution systems, as well as propelling the associated risk in this intricate scenario.

Application of FTIR two-dimensional correlation spectroscopy (2D-COS) analysis in characterizing environmental behaviors of microplastics: A systematic review

Microplastics (MPs) are ubiquitous in the environment, continuously undergo aging processes and release toxic chemical substances. Understanding the environmental behaviors of MPs is critical to accurately evaluate their long-term ecological risk. Generalized two-dimensional correlation spectroscopy (2D-COS) is a powerful tool for MPs studies, which can dig more comprehensive information hiding in the conventional one-dimensional spectra, such as infrared (IR) and Raman spectra. The recent applications of 2D-COS in analyzing the behaviors and fates of MPs in the environment, including their aging processes, and interactions with natural organic matter (NOM) or other chemical substances, were summarized systematically. The main requirements and limitations of current approaches for exploring these processes are discussed, and the corresponding strategies to address these limitations and drawbacks are proposed as well. Finally, new trends of 2D-COS are prospected for analyzing the properties and behaviors of MPs in both natural and artificial environmental processes.

A comprehensive review of microplastic aging: Laboratory simulations, physicochemical properties, adsorption mechanisms, and environmental impacts

As a new type of ecological environment problem, microplastic pollution is a severe challenge faced by the world, and its threat and potential risk to the ecosystem have become a hot research spot in the current environmental field. Microplastics (MPs) in the natural environment will experience aging effect, aging will change the physical and chemical properties of MPs and affect the adsorption behavior. Recently reported characterization techniques of MPs and laboratory simulation of aging are reviewed. The aging mechanism between MPs and different pollutants and the intervention mechanism of environmental factors (MPs, pollutants and water quality environment) were revealed. In addition, to further understand the potential ecological toxicity of MPs after aging, the release and harm of additives during aging, produce the environmentally persistent free radicals, and the mechanism of reactive oxygen species (ROS) removal of pollutants adsorbed on the surface of MPs were summarized. Future research efforts should focus more on bridging the disparity between laboratory aging simulations and natural environmental conditions to enhance the authenticity and ecological relevance of such studies. The ROS production mechanism of MPs provides a reference direction for removing pollutants adsorbed by aged MPs.

Recent advances in mechanistic insights into microplastics mitigation strategies via emerging advanced oxidation processes: Legislation, challenges, and future direction

Microplastics (MPs) pollution has emerged as a global environmental concern due to its detrimental impacts on ecosystems. Conventional wastewater/water treatment methods are inadequate for MPs removal due to their diminutive size ranging from micrometers to nanometers. Advanced oxidation processes (AOPs) have gained attention as a promising green strategy for the efficient and safe elimination of MPs from aqueous systems. In recent years, various AOPs, including direct photo-degradation, photocatalytic oxidation, electrochemical oxidation, sono-chemical oxidation, ozonation, as well as sulfate radicals-based AOPs (SR-AOPs), and the use of hybrid systems have all been extensively investigated for MP elimination. However, the molecular mechanisms of MP polymer chain scission by AOPs have not been thoroughly studied so far. In this review, we have attempted to provide a thorough overview of molecular mechanisms and highlighted recent advances in the degradation of commonly used MP by AOPs. The characteristics and limitations of each technique are thoroughly examined. Additionally, current policies and legislation on plastic pollution are discussed, emphasizing the need for regulatory frameworks to support effective MPs mitigation strategies. To advance the practical application of AOPs for MPs removal, future research direction should address the transition from controlled laboratory environments to complex field conditions, assess the sustainability of AOPs in terms of catalytic material design, selection of effective oxidants, power consumption, and operational costs. Given these challenges, recommendations for future research directions are proposed based on knowledge gaps in the reported literature. This review could offer a coherent summary of the molecular mechanisms involved in different MP elimination techniques, aiding in the advancement of more dependable AOPs technology with superior removal and degradation efficiency.

Insight into the removal of nanoplastics and microplastics by physical, chemical, and biological techniques

Plastic pollutants create health crises like physical damage to tissues, upset reproductive processes, altered behaviour, oxidative stress, neurological disorders, DNA damage, gene expression, and disrupt physiological functions, as the biosphere accumulates them inadvertently through the food web. Water resources have become the generic host of plastic wastes irrespective of their particle size, resulting in widespread distribution in aquatic environments. The pre-treatment step of the traditional water treatment process can easily remove coarse-sized plastic wastes. However, the fine plastic particles, with sizes ranging from nanometres to millimetres, are indifferent to the traditional water treatment. To address the escalating problems, the upgradation of different traditional physical, chemical, and biological remediation techniques offers a promising avenue for tackling tiny plastic particles from the water environment. Further, new techniques and hybrid incorporations to the existing water treatment techniques have been explored, specifically removing tiny plastic debris. A detailed understanding of the sources, fate, and impact of plastic wastes in the environment, as well as an evaluation of the above treatment techniques and their limitations and challenges, can only show the way for their upgradation, hybridization, and development of new techniques. This review paper provides a comprehensive overview of the current knowledge and techniques for the remediation of nanoplastics and microplastics.

Differences of microplastics and nanoplastics in urban waters: Environmental behaviors, hazards, and removal

Microplastics (MPs) and nanoplastics (NPs) are ubiquitous in the aquatic environment and have caused widespread concerns globally due to their potential hazards to humans. Especially, NPs have smaller sizes and higher penetrability, and therefore can penetrate the human barrier more easily and may pose potentially higher risks than MPs. Currently, most reviews have overlooked the differences between MPs and NPs and conflated them in the discussions. This review compared the differences in physicochemical properties and environmental behaviors of MPs and NPs. Commonly used techniques for removing MPs and NPs currently employed by wastewater treatment plants and drinking water treatment plants were summarized, and their weaknesses were analyzed. We further comprehensively reviewed the latest technological advances (e.g., emerging coagulants, new filters, novel membrane materials, photocatalysis, Fenton, ozone, and persulfate oxidation) for the separation and degradation of MPs and NPs. Microplastics are more easily removed than NPs through separation processes, while NPs are more easily degraded than MPs through advanced oxidation processes. The operational parameters, efficiency, and potential governing mechanisms of various technologies as well as their advantages and disadvantages were also analyzed in detail. Appropriate technology should be selected based on environmental conditions and plastic size and type. Finally, current challenges and prospects in the detection, toxicity assessment, and removal of MPs and NPs were proposed. This review intends to clarify the differences between MPs and NPs and provide guidance for removing MPs and NPs from urban water systems.

Negligible adsorption and toxicity of microplastic fibers in disinfected secondary effluents

Wastewater treatment plants play a crucial role in controlling the transport of pollutants to the environment and often discharge persistent contaminants such as synthetic microplastic fibers (MFs) to the ecosystem. In this study, we examined the fate and toxicity of polyethylene terephthalate (PET) MFs fabricated from commercial cloth in post-disinfection secondary effluents by employing conditions that closely mimic disinfection processes applied in wastewater treatment plants. Challenging conventional assumptions, this study illustrated that oxidative treatment by chlorination and ozonation incurred no significant modification to the surface morphology of the MFs. Additionally, experimental results demonstrated that both pristine and oxidized MFs have minimal adsorption potential towards contaminants of emerging concern in both effluents and alkaline water. The limited adsorption was attributed to the inert nature of MFs and low surface area to volume ratio. Slight adsorption was observed for sotalol, sulfamethoxazole, and thiabendazole in alkaline water, where the governing adsorption interactions were suggested to be hydrogen bonding and electrostatic forces. Acute exposure experiments on human cells revealed no immediate toxicity; however, the chronic and long-term consequences of the exposure should be further investigated. Overall, despite the concern associated with MFs pollution, this work demonstrates the overall indifference of MFs in WWTP (i.e., minor effects of disinfection on MFs surface properties and limited adsorption potential toward a mix of trace organic pollutants), which does not change their acute toxicity toward living forms.

Exploring the hidden environmental pollution of microplastics derived from bioplastics: A review

Bioplastics might be an ecofriendly alternative to traditional plastics. However, recent studies have emphasized that even bioplastics can end up becoming micro- and nano-plastics due to their degradation under ambient environmental conditions. Hence, there is an urgent need to assess the hidden environmental pollution caused by bioplastics. However, little is known about the evolutionary trends of bibliographic data, degradation pathways, formation, and toxicity of micro- and nano-scaled bioplastics originating from biodegradable polymers such as polylactic acid, polyhydroxyalkanoates, and starch-based plastics. Therefore, the prime objective of the current review was to investigate evolutionary trends and the latest advancements in the field of micro-bioplastic pollution. Additionally, it aims to confront the limitations of existing research on microplastic pollution derived from the degradation of bioplastic wastes, and to understand what is needed in future research. The literature survey revealed that research focusing on micro- and nano-bioplastics has begun since 2012. This review identifies novel insights into microbioplastics formation through diverse degradation pathways, including photo-oxidation, ozone-induced degradation, mechanochemical degradation, biodegradation, thermal, and catalytic degradation. Critical research gaps are identified, including defining optimal environmental conditions for complete degradation of diverse bioplastics, exploring micro- and nano-bioplastics formation in natural environments, investigating the global occurrence and distribution of these particles in diverse ecosystems, assessing toxic substances released during bioplastics degradation, and bridging the disparity between laboratory studies and real-world applications. By identifying new trends and knowledge gaps, this study lays the groundwork for future investigations and sustainable solutions in the realm of sustainable management of bioplastic wastes.

Leachate from municipal solid waste landfills: A neglected source of microplastics in the environment

Over the past decade or so, microplastics (MPs) have received increasing attention due to their ubiquity and potential risk to the environment. Waste plastics usually end up in landfills. These plastics in landfills undergo physical compression, chemical oxidation, and biological decomposition, breaking down into MPs. As a result, landfill leachate stores large amounts of MPs, which can negatively impact the surrounding soil and water environment. However, not enough attention has been given to the occurrence and removal of MPs in landfill leachate. This lack of knowledge has led to landfills being an underestimated source of microplastics. In order to fill this knowledge gap, this paper collects relevant literature on MPs in landfill leachate from domestic and international sources, systematically summarizes their presence within Asia and Europe, assesses the impacts of landfill leachate on MPs in the adjacent environment, and particularly discusses the possible ecotoxicological effects of MPs in leachate. We found high levels of MPs in the soil and water around informal landfills, and the MPs themselves and the toxic substances they carry can have toxic effects on organisms. In addition, this paper summarizes the potential impact of MPs on the biochemical treatment stage of leachate, finds that the effects of MPs on the biochemical treatment stage and membrane filtration are more significant, and proposes some novel processes for MPs removal from leachate. This analysis contributes to the removal of MPs from leachate. This study is the first comprehensive review of the occurrence, environmental impact, and removal of MPs in leachate from landfills in Asia and Europe. It offers a comprehensive theoretical reference for the field, providing invaluable insights.

Comparative study on physicochemical characteristics of atmospheric microplastics in winter in inland and coastal megacities: A case of Beijing and Shanghai, China

Atmospheric microplastics (MPs) have received global attention across various sectors of society due to their potential negative impacts. This study aims to understand the physicochemical characteristics of MPs in inland and coastal megacities for raising awareness about the urgent need to reduce plastic pollution. Laser Direct Infrared Imaging (LDIR) and Scanning Electron Microscopy (SEM) with Energy Dispersive X-ray Spectroscopy (EDX) techniques were employed to characterize atmospheric MPs in megacities (inland megacity Beijing and coastal megacity Shanghai) in China, focusing on their physicochemical characteristics, including compositional types, number concentration, morphology, size, possible sources, and potential health risks. The LDIR analysis identified sixteen different types of MPs present in the atmospheres of Beijing and Shanghai. The number concentration of atmospheric MPs in Beijing (3.0 items/m3) is 1.8 times that of Shanghai (1.7 items/m3). The study found that the variations in MP pollution between Beijing and Shanghai are influenced by the urban industrial structure and geographical location. Morphological analysis indicates that fragment MPs have the highest relative abundance in Beijing, while fibrous MPs dominate the atmosphere of Shanghai. Additionally, the study assessed the potential health risks of atmospheric MPs to urban residents. The results suggest that residents of Beijing face more severe health risks from atmospheric MPs compared to those in Shanghai. These findings underscore the urgency to address the issue of atmospheric MPs and provide crucial evidence for the formulation of relevant environmental and health policies.

Aging of plastics in aquatic environments: Pathways, environmental behavior, ecological impacts, analyses and quantifications

The ubiquity of plastics in our environment has brought about pressing concerns, with their aging processes, photo-oxidation, mechanical abrasion, and biodegradation, being at the forefront. Microplastics (MPs), whether originating from plastic degradation or direct anthropogenic sources, further complicate this landscape. This review delves into the intricate aging dynamics of plastics in aquatic environments under various influential factors. We discuss the physicochemical changes that occur in aged plastics and the release of oxidation products during their degradation. Particular attention is given to their evolving environmental interactions and the resulting ecotoxicological implications. A rigorous evaluation is also conducted for methodologies in the analysis and quantification of plastics aging, identifying their merits and limitations and suggesting potential avenues for future research. This comprehensive review is able to illuminate the complexities of plastics aging, charting a path for future research and aiding in the formulation of informed policy decisions.

Polystyrene microplastics accumulation in lab-scale vertical flow constructed wetlands: impacts and fate

Microplastics (MPs) are ubiquitous pollutants that significantly threaten organisms and ecosystems. Constructed wetlands (CWs), a nature-based treatment technology, can effectively remove MPs from wastewater. However, the responses of CWs when exposed to MPs remain unclear. In this study, lab-scale vertical flow constructed wetlands (VFCWs) were installed for receiving polystyrene (PS) MPs at concentrations of 100 μg/L and 1000 μg/L. The results showed that exposure to PS-MPs has no effects on COD and TP removal in VFCWs, but TN removal decreased by 3.69-5.37 %. Further investigation revealed that PS-MPs significantly impacted microbial communities and metabolic functions. The abundances of predominant nitrifiers (Nitrospira and Nitrosomonas) and denitrifiers (Nakamurella, Bradyrhizobium, and Bacillus) in VFCWs were significantly reduced, aligning with the responses of key enzymes. The presence of PS-MPs also decreased nitrogen removal by plant uptake, leading to decreased plant biomass and chlorophyll by 39.32-48.75 % and 5.92-32.19 %, respectively. Notably, > 90 % removal rates were observed for PS-MPs within VFCWs. In addition to PS-MPs interception by VFCWs substrate, the increase of released benzenes indicated that the PS-MPs biodegradation occurred. Such insights are vital for developing sustainable solutions to mitigate MPs' adverse effects on ecosystems.

Microfibers in anaerobic digestion: Effect of ozone pretreatment

Wastewater treatment plants receive significant microplastics, which are eventually discharged into the environment. Previous studies indicated that over 90% of microplastics, especially microfibers from laundry wastewater, are retained in primary sludge. The effect of microfibers from household laundry on anaerobic digestion has yet to be fully understood, which is the objective of the present study. The results in this study showed a positive correlation between methane production and the presence of microfibers. Compared to the control, the methane production increased by 2%, 27% and 43% with 20 mg/L, 100 mg/L and 1000 mg/L microfibers spiked into primary sludge, respectively. The present study suggests that microfibers at 20 mg/L insignificantly affected methane production in controlled anaerobic digestion. In contrast, ozone pretreatment of microfibers enhanced gas production by 12% in the same concentration level. Interestingly, ozone pretreatment at a higher concentration (100 mg/L-1000 mg/L) of microfibers did not affect methane production. SEM/EDX results imply that the ozone pretreatment has changed the surface characteristics of the microfibers, which provide more surface area for adsorption. The significant reduction of soluble phosphorus by 58% indicates that microfibers potentially act as a site for adsorption during anaerobic digestion. Overall, the presence of microfibers had a positive effect on anaerobic digestion. However, this work also indicated that the microfibers were not biodegraded during anaerobic digestion. Therefore, microfibers accumulate on biosolids, potentially affecting the final disposal of microfibers.

The influence of various microplastics on PBDEs contaminated soil remediation by nZVI and sulfide-nZVI: Impedance, electron-accepting/-donating capacity and aging

The microplastics (MPs) existed in the environment widely has resulted in novel thinking about in-situ remediation techniques, such as nano-zero-valent iron (nZVI) and sulfided nZVI (S-nZVI), which were often compromised by various environmental factors. In this study, three common MPs such as polyvinyl chloride (PVC), polystyrene (PS), and polypropylene (PP) in soil were found to inhibit the degradation rate of decabromodiphenyl ether (BDE209) by nZVI and S-nZVI to different degrees due to MPs inhibiting of electron transfer which is the main way to degrade BDE209. The inhibition strength was related to its impedance (Z) and electron-accepting (EAC)/-donating capacity (EDC). Based on the explanation of the inhibition mechanism, the reason for different aging degrees of nZVI and S-nZVI in different MPs was illustrated, especially in PVC systems. Furthermore, the aging of reacted MPs, functionalization and fragmentation in particular, indicated that they were involved in the degradation process. Moreover, this work provided new insights into the field application of nZVI-based materials for removing persistent organic pollutants (POPs).

Novel CuMgAlTi-LDH Photocatalyst for Efficient Degradation of Microplastics under Visible Light Irradiation

Microplastics (MPs) in the water system could easily enter the human body and pose a potential threat, so finding a green and effective solution remains a great challenge. At present, the advanced oxidation technology represented by photocatalysis has been proven to be effective in the removal of organic pollutants, making it a feasible method to solve the problem of MP pollution. In this study, the photocatalytic degradation of typical MP polystyrene (PS) and polyethylene (PE) by a new quaternary layered double hydroxide composite photomaterial CuMgAlTi-R400 was tested under visible light irradiation. After 300 h of visible light irradiation, the average particle size of PS decreased by 54.2% compared with the initial average particle size. The smaller the particle size, the higher the degradation efficiency. The degradation pathway and mechanism of MPs were also studied by GC-MS, which showed that PS and PE produced hydroxyl and carbonyl intermediates in the process of photodegradation. This study demonstrated a green, economical, and effective strategy for the control of MPs in water.