Visible light photocatalytic degradation of polypropylene microplastics in a continuous water flow system

Insights into Anthropogenic Micro- and Nanoplastic Accumulation in Drinking Water Sources and Their Potential Effects on Human Health

Anthropogenic microplastics (MPs) and nanoplastics (NPs) are ubiquitous pollutants found in aquatic, food, soil and air environments. Recently, drinking water for human consumption has been considered a significant pathway for ingestion of such plastic pollutants. Most of the analytical methods developed for detection and identification of MPs have been established for particles with sizes > 10 μm, but new analytical approaches are required to identify NPs below 1 μm. This review aims to evaluate the most recent information on the release of MPs and NPs in water sources intended for human consumption, specifically tap water and commercial bottled water. The potential effects on human health of dermal exposure, inhalation, and ingestion of these particles were examined. Emerging technologies used to remove MPs and/or NPs from drinking water sources and their advantages and limitations were also assessed. The main findings showed that the MPs with sizes > 10 μm were completely removed from drinking water treatment plants (DWTPs). The smallest NP identified using pyrolysis-gas chromatography-mass spectrometry (Pyr-GC/MS) had a diameter of 58 nm. Contamination with MPs/NPs can occur during the distribution of tap water to consumers, as well as when opening and closing screw caps of bottled water or when using recycled plastic or glass bottles for drinking water. In conclusion, this comprehensive study emphasizes the importance of a unified approach to detect MPs and NPs in drinking water, as well as raising the awareness of regulators, policymakers and the public about the impact of these pollutants, which pose a human health risk.

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.

Photodegradation of Microplastics by ZnO Nanoparticles with Resulting Cellular and Subcellular Responses

Both zinc oxide nanoparticles (ZnO NPs) and microplastics (MPs) were extracted from one commercial sunscreen, while other ingredients were removed based on the "like dissolves like" principle. MPs were further extracted by acidic digestion of ZnO NPs using HCl and characterized as spherical particles of approximately 5 μm with layered sheets in an irregular shape on the surface. Although MPs were stable in the presence of simulated sunlight and water after 12 h of exposure, ZnO NPs promoted the photooxidation by producing hydroxyl radicals, with a 2.5-fold increase in the carbonyl index of the degree of surface oxidation. As a result of surface oxidation, spherical MPs were more soluble in water and fragmented to irregular shapes with sharp edges. We then compared the cytotoxicity of primary MPs and secondary MPs (25-200 mg/L) to the HaCaT cell line based on viability loss and subcellular damages. The cellular uptake of MPs transformed by ZnO NPs was enhanced by over 20%, and MPs caused higher cytotoxicity compared with the pristine ones, as evidenced by a 46% lower cell viability, 220% higher lysosomal accumulation, 69% higher cellular reactive oxygen species, 27% more mitochondrial loss, and 72% higher mitochondrial superoxide at 200 mg/L. Our study for the first time explored the activation of MPs by ZnO NPs derived from commercial products and revealed the high cytotoxicity caused by secondary MPs, providing new evidence on the effects of secondary MPs on human health.

Microplastic remediation technologies in water and wastewater treatment processes: Current status and future perspectives

Microplastics (MPs) are a type of contaminants produced during the use and disposal of plastic products, which are ubiquitous in our lives. With the high specific surface area and strong hydrophobicity, MPs can adsorb various hazardous microorganisms and chemical contaminants from the environment, causing irreversible damage to our humans. It is reported that the MPs have been detected in infant feces and human blood. Therefore, the presence of MPs has posed a significant threat to human health. It is critically essential to develop efficient, scalable and environmentally-friendly methods to remove MPs. Herein, recent advances in the MPs remediation technologies in water and wastewater treatment processes are overviewed. Several approaches, including membrane filtration, adsorption, chemically induced coagulation-flocculation-sedimentation, bioremediation, and advanced oxidation processes are systematically documented. The characteristics, mechanisms, advantages, and disadvantages of these methods are well discussed and highlighted. Finally, the current challenges and future trends of these methods are proposed, with the aim of facilitating the remediation of MPs in water and wastewater treatment processes in a more efficient, scalable, and environmentally-friendly way.

Microplastic sources, formation, toxicity and remediation: a review

Microplastic pollution is becoming a major issue for human health due to the recent discovery of microplastics in most ecosystems. Here, we review the sources, formation, occurrence, toxicity and remediation methods of microplastics. We distinguish ocean-based and land-based sources of microplastics. Microplastics have been found in biological samples such as faeces, sputum, saliva, blood and placenta. Cancer, intestinal, pulmonary, cardiovascular, infectious and inflammatory diseases are induced or mediated by microplastics. Microplastic exposure during pregnancy and maternal period is also discussed. Remediation methods include coagulation, membrane bioreactors, sand filtration, adsorption, photocatalytic degradation, electrocoagulation and magnetic separation. Control strategies comprise reducing plastic usage, behavioural change, and using biodegradable plastics. Global plastic production has risen dramatically over the past 70 years to reach 359 million tonnes. China is the world's top producer, contributing 17.5% to global production, while Turkey generates the most plastic waste in the Mediterranean region, at 144 tonnes per day. Microplastics comprise 75% of marine waste, with land-based sources responsible for 80-90% of pollution, while ocean-based sources account for only 10-20%. Microplastics induce toxic effects on humans and animals, such as cytotoxicity, immune response, oxidative stress, barrier attributes, and genotoxicity, even at minimal dosages of 10 μg/mL. Ingestion of microplastics by marine animals results in alterations in gastrointestinal tract physiology, immune system depression, oxidative stress, cytotoxicity, differential gene expression, and growth inhibition. Furthermore, bioaccumulation of microplastics in the tissues of aquatic organisms can have adverse effects on the aquatic ecosystem, with potential transmission of microplastics to humans and birds. Changing individual behaviours and governmental actions, such as implementing bans, taxes, or pricing on plastic carrier bags, has significantly reduced plastic consumption to 8-85% in various countries worldwide. The microplastic minimisation approach follows an upside-down pyramid, starting with prevention, followed by reducing, reusing, recycling, recovering, and ending with disposal as the least preferable option.

Post-pandemic micro/nanoplastic pollution: Toward a sustainable management

The global health crisis caused by the COVID-19 pandemic has resulted in massive plastic pollution from the use of personal protection equipment (PPE), with polypropylene (PP) being a major component. Owing to the weathering of exposed PPEs, such contamination causes microplastic (MP) and nanoplastic (NP) pollution and is extremely likely to act as a vector for the transportation of COVID-19 from one area to another. Thus, a post-pandemic scenario can forecast with certainty that a significant amount of plastic garbage combined with MP/NP formation has an adverse effect on the ecosystem. Therefore, updating traditional waste management practices, such as landfilling and incineration, is essential for making plastic waste management sustainable to avert this looming catastrophe. This study investigates the post-pandemic scenario of MP/NP pollution and provides an outlook on an integrated approach to the recycling of PP-based plastic wastes. The recovery of crude oil, solid char, hydrocarbon gases, and construction materials by approximately 75, 33, 55, and 2 %, respectively, could be achieved in an environmentally friendly and cost-effective manner. Furthermore, the development of biodegradable and self-sanitizing smart PPEs has been identified as a promising alternative for drastically reducing plastic pollution.

A high-throughput expression and screening platform for applications-driven PETase engineering

The environmental consequences of plastic waste have impacted all kingdoms of life in terrestrial and aquatic ecosystems. However, as the burden of plastic pollution has increased, microbes have evolved to utilize anthropogenic polymers as nutrient sources. Of depolymerase enzymes, the best characterized is PETase, which hydrolyzes aromatic polyesters. PETase engineering has made impressive progress in recent years; however, further optimization of engineered PETase toward industrial application has been limited by lower throughput techniques used in protein purification and activity detection. Here, we address these deficiencies through development of a higher-throughput PETase engineering platform. Secretory expression via YebF tagging eliminates lysis and purification steps, facilitating production of large mutant libraries. Fluorescent detection of degradation products permits rapid screening of depolymerase activity in microplates as opposed to serial chromatographic methods. This approach enabled development of more stable PETase, semi-rational (SR) PETase variant containing previously unpublished mutations. SR-PETase releases 1.9-fold more degradation products and has up to 7.4-fold higher activity than wild-type PETase over 10 days at 40°C. These methods can be adapted to a variety of chemical environments, enabling screening of PETase mutants in applications-relevant conditions. Overall, this work promises to facilitate advancements in PETase engineering toward industrial depolymerization of plastic waste.

Mechanism and characterization of microplastic aging process: A review

With the increasing production of petroleum-based plastics, the problem of environmental pollution caused by plastics has aroused widespread concern. Microplastics, which are formed by the fragmentation of macro plastics, are bio-accumulate easily due to their small size and slow degradation under natural conditions. The aging of plastics is an inevitable process for their degradation and enhancement of adsorption performance toward pollutants due to a series of changes in their physiochemical properties, which significantly increase the toxicity and harm of plastics. Therefore, studies should focus on the aging process of microplastics through reasonable characterization methods to promote the aging process and prevent white pollution. This review summarizes the latest progress in natural aging process and characterization methods to determine the natural aging mechanism of microplastics. In addition, recent advances in the artificial aging of microplastic pollutants are reviewed. The degradation status and by-products of biodegradable plastics in the natural environment and whether they can truly solve the plastic pollution problem have been discussed. Findings from the literature pointed out that the aging process of microplastics lacks professional and exclusive characterization methods, which include qualitative and quantitative analyses. To lessen the toxicity of microplastics in the environment, future research directions have been suggested based on existing problems in the current research. This review could provide a systematic reference for in-depth exploration of the aging mechanism and behavior of microplastics in natural and artificial systems.

Bioremediation of microplastics in freshwater environments: A systematic review of biofilm culture, degradation mechanisms, and analytical methods

Microplastics, defined as particles <5 mm in diameter, are emerging environmental pollutants that pose a threat to ecosystems and human health. Biofilm degradation of microplastics may be an ecologically friendly approach. This review systematically summarises the factors affecting biofilm degradation of microplastics and proposes feasible methods to improve the efficiency of microplastic biofilm degradation. Environmentally insensitive microorganisms were screened, optimized, and commercially cultured to facilitate the practical application of this technology. For strain screening, technology should focus on microorganisms/strains that can modify the hydrophobicity of microplastics, degrade the crystalline zone of microplastics, and metabolise additives in microplastics. The biodegradation mechanism is also described; microorganisms secreting extracellular oxidases and hydrolases are key factors for degradation. Measuring the changes in molecular weight distribution (MWD) enables better analysis of the biodegradation behaviour of microplastics. Biofilm degradation of microplastics has relatively few applications because of its low efficiency; however, enrichment of microplastics in freshwater environments and wastewater treatment plant tailwater is currently the most effective method for treating microplastics with biofilms.

Plastic waste management for sustainable environment: techniques and approaches

Excessive exploitation, negligence, non-degradable nature, and physical and chemical properties of plastic waste have resulted in a massive pollution load into the environment. Consequently, plastic entres the food chain and can cause serious health issues in aquatic animals and humans. The present review summarizes currently reported techniques and approaches for the removal of plastic waste. Many techniques, such as adsorption, coagulation, photocatalysis, and microbial degradation, and approaches like reduction, reuse and recycling are potentially in trend and differ from each other in their efficiency and interaction mechanism. Moreover, substantial advantages and challenges associated with these techniques and approaches are highlighted to develop an understanding of the selection of possible ways for a sustainable future. Nevertheless, in addition to the reduction of plastic waste from the ecosystem, many alternative opportunities have also been explored to cash plastic waste. These fields include the synthesis of adsorbents for the removal of pollutants from aqueous and gaseous stream, their utility in clothing, waste to energy and fuel and in construction (road making). Substantial evidence can be observed in the reduction of plastic pollution from various ecosystems. In addition, it is important to develop an understanding of factors that need to be emphasized while considering alternative approaches and opportunities to cash plastic waste (like adsorbent, clothing, waste to energy and fuel). The thrust of this review is to provide readers with a comprehensive overview of the development status of techniques and approaches to overcome the global issue of plastic pollution and the outlook on the exploitation of this waste as resources.

Insight into the photodegradation and universal interactive products of 2,2',4,4'-tetrabromodiphenyl ether on three microplastics

The transformation process of contaminants on microplastics (MPs) exposed to sunlight has attracted increasing attention. However, the interactions between them are typically disregarded; therefore, this work investigated the photodegradation of 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) on three MPs (polystyrene (PS), polypropylene (PP) and polyethylene (PE)) and the interactions between these two. The inhibition of aged PS on the elimination of BDE-47 was due to light shielding, while aged PP and PE increased the degradation rate. More hydroxyl radicals (HO•) was detected in the PS system, which resulted in the higher degradation rate of BDE-47 on PS. A total of 33 different products were identified and four reaction pathways were presented, and the reaction mechanisms mainly included debromination, hydroxylation, carbon-oxygen-bond breaking and interactive reactions. The Ecological Structure Activity Relationship (ECOSAR) and Toxicity Estimation Software Tool (TEST) programs were used to evaluate the toxicity of reaction products, and the results indicated that even though BDE-47 was the most toxic, the interaction products were still toxic or harmful to aquatic organisms. This study provides significant information on the photodegradation of contaminants on common microplastics and their interaction, which cannot be ignored.

Microplastics distribution and microbial community characteristics of farmland soil under different mulch methods

The widespread use of plastic film in agricultural production has resulted in the accumulation of large amounts of residual plastic film in the soil, and most of the plastic residuals eventually break up into microplastics (MPs). However, the effects of different film mulching methods on the soil ecosystems are largely unexplored. Therefore, we investigated the MPs distribution and the physicochemical properties and microbial community structure in the farmland soil tillage layer covered with different mulching method of film. The results indicate that the film mulching method had no significant effect on the soil pH and organic matter content, however, the respiration intensity of the soil covered with mulching film (MF) (60.11-84.99 μg/g) and shed film (SF) (56.10-65.68 μg/g) was significantly higher than that covered with shed film & mulching film (SMF) (17.25-39.16 μg/g). The MPs abundance in the soil covered with MF (1367 particles/kg soil) was significantly higher than that covered with SF (800 particles/kg soil) and slightly higher than that with SMF (1000 particles/kg soil). The small-sized (0-0.5 mm) MPs abundance was increased with the tillage layer depth (0-20 cm), while the large-sized (1-5 mm) MPs abundance was the opposite. In addition, in the soil covered with agricultural film, the dominant phylum and genera of the bacteria were Proteobacteria (relative abundance was 64.06 %) and Pseudomonas (13.16 %), respectively. In the soil without agricultural film application as a control treatment, the diversity of the soil bacterial community was higher than that in the soil covered with agricultural film, and the relative abundances of the top 10 genera were all less than 5 %. Overall, this study provides essential information for understanding the effects of different film mulching methods on the agricultural systems. Overall, this study provides essential information for understanding the effects of different film mulching methods on the distribution of MPs and the biogeochemical properties of farmland soils.

Photocatalytic solid-phase degradation of polyethylene with fluoride-doped titania under low consumption ultraviolet radiation

Photodegradation of plastic in solid-phase requires the polymer to be composited with an efficient photocatalyst. We report herein the successful synthesis and characterization of fluoride-doped-TiO₂ and its applicability, for the first time, on solid-phase photodegradation of polyethylene films. Nearly half weight loss of polyethylene, containing only 2% of the photocatalyst, is eliminated after three weeks of ultraviolet A radiation using a low consumption light emitting diode lamp, defeating previously reported data. The half-life time of the plastic was around 3 weeks, highlighting the viability of this process for real applications. Results were compared to raw PE and PE composite with well-known TiO₂, resulting in, respectively, 0 and 26% of weight loss. The degradation process was monitored by optical microscopy, scanning electron microscopy, X-ray diffraction, thermogravimetric analysis, Fourier transform infrared and X-ray photoelectron spectroscopy, which revealed the formation of plastic cracks, loss of polyethylene crystallinity and thus stability, the oxidation of C-H bonds and the oxidized state of the surface compounds during photodegradation. The obtained results open a path for the future production of cleaner and self-photodegradable plastics, where the photocatalyst would be introduced in all the manufactured plastics, making possible the quicker photodegradation of the plastics that end up on the environment and the plastics reaching wastewater treatment plants.

Dielectric barrier discharge plasma for the remediation of microplastic-contaminated soil from landfill

The huge amount of plastic waste accumulated in landfills has caused serious microplastic (MP) pollution to the soil environment, which has become an urgent issue in recent years. It is challenging to deal with the non-biodegradable MP pollutants in actual soil from landfills. In this study, a coaxial dielectric barrier discharge (DBD) system was proposed to remediate actual MP-contaminated landfill soil due to its strong oxidation capacity. The influence of carrier gas type, applied voltage, and air flow rate was investigated, and the possible degradation pathways of MP pollutants were suggested. Results showed the landfill soil samples contained four common MP pollutants, including polyethylene (PE), polypropylene (PP), polystyrene (PS), and polyvinyl chloride (PVC) with sizes ranging from 50 to 1500 μm. The MP pollutants in the soil were rapidly removed under the action of reactive oxygen species (ROS) generated by DBD plasma. Under the air flow rate of 1500 mL min^-1, the maximum remediation efficiency represented by mass loss reached 96.5% after 30 min treatment. Compared with nitrogen, when air was used as the carrier gas, the remediation efficiency increased from 41.4% to 81.6%. The increased applied voltage from 17.5 to 24.1 kV could also promote the removal of MP contaminants. Sufficient air supply was conducive to thorough removal. However, when the air flow rate reached 1500 mL min^-1 and continued to rise, the final remediation efficiency would be reduced due to the shortened residence time of ROS. The DBD plasma treatment proposed in this study showed high energy efficiency (19.03 mg kJ^-1) and remediation performance (96.5%). The results are instructive for solving MP pollution in the soil environment.

Microplastic contamination in the freshwater shrimp Macrobrachium amazonicum in Itacoatiara, Amazonas, Brazil

The present study analyzed the presence of microplastics (MPs) in the shrimp Macrobrachium amazonicum, which is an economically important food that is consumed in several regions of the Brazilian Amazon. A total of 600 specimens of M. amazonicum were captured at two sampling sites (urban and rural area). A total of 2597 MP particles were recorded in the shrimps, with a significant difference between the two sites. The presence of MPs in the body parts also differed significantly. No significant difference was found between MPs abundance and sex of the shrimps. The size of the MPs did not differ significantly between the collection sites and between the body parts. Dark blue fiber-type MPs were the most abundant. A positive correlation was observed between the abundance of MPs and the total weight of shrimps. Raman spectroscopy identified the dark blue fibers as polypropylene and the FTIR technique identified the light blue fragments as nylon. The results indicate that the presence of MPs in the M. amazonicum shrimp is associated with the capture sites near the urban area and is present in the diet of the Amazonian population that regularly consumes this crustacean in traditional dishes.

Insights into the removal of microplastics and microfibres by Advanced Oxidation Processes

Water treatment plants' effluents are hotspots of microplastics (MPs) and microfibres (MFs) released into the aquatic environment because they were not designed to capture these particles. Special attention should be given to MFs, since they mainly come from laundry and are related to one of the main MP shapes detected in water and wastewater treatment plants. In this sense, Advanced Oxidation Processes (AOPs) could be a feasible solution for tackling MP and MF pollution, however, it is still premature to extract conclusions due to the limited number of studies on the degradation of these particles (specifically MFs) using AOPs. This review addresses the impacts of AOPs on MPs/MFs, focusing on their degradation efficiency, toxicity, and sustainability of the processes, among other aspects. The review points out that polyamide MFs can achieve mass loss >90% by photocatalytic system using TiO₂. Also, the low oxidation of MPs (<30 %) by conventional Fenton process affects mainly the surface of the MPs. However, other Fenton-based processes can provide better removal of some types of MPs, mainly using temperatures >100 °C, reaction time ≥ 5 h, and initial pH ≤ 3, achieving MP weight loss up to 96 %. Despite these results, better operating conditions are still required for AOPs since the ones reported so far are not feasible for full-scale application. Additionally, ozonation in treatment plants has increased the fragmentation of MPs (including MFs), leading to a new generation of MPs. More attention is needed on toxicity effects of intermediates and methods of analysis employed for the analysis of MPs/MFs in wastewater effluent should be standardized so that studies can be compared effectively. Future research should focus on the sustainability of the AOP for MP removal in water treatment (power consumption, chemicals consumed and operational costs) for a better understanding of full-scale applicability of AOP adapted to MP treatment.

Magnetically boosted 1D photoactive microswarm for COVID-19 face mask disruption

The recent COVID-19 pandemic has resulted in the massive discard of pandemic-related plastic wastes, causing serious ecological harm and a high societal burden. Most single-use face masks are made of synthetic plastics, thus their careless disposal poses a direct threat to wildlife as well as potential ecotoxicological effects in the form of microplastics. Here, we introduce a 1D magnetic photoactive microswarm capable of actively navigating, adhering to, and accelerating the degradation of the polypropylene microfiber of COVID-19 face masks. 1D microrobots comprise an anisotropic magnetic core (Fe3O4) and photocatalytic shell (Bi2O3/Ag), which enable wireless magnetic maneuvering and visible-light photocatalysis. The actuation of a programmed rotating magnetic field triggers a fish schooling-like 1D microswarm that allows active interfacial interactions with the microfiber network. The follow-up light illumination accelerates the disruption of the polypropylene microfiber through the photo-oxidative process as corroborated by morphological, compositional, and structural analyses. The active magnetic photocatalyst microswarm suggests an intriguing microrobotic solution to treat various plastic wastes and other environmental pollutants.

Recent approaches and advanced wastewater treatment technologies for mitigating emerging microplastics contamination - A critical review

Microplastics have been identified as an emerging pollutant due to their irrefutable prevalence in air, soil, and particularly, the aquatic ecosystem. Wastewater treatment plants (WWTPs) are seen as the last line of defense which creates a barrier between microplastics and the environment. These microplastics are discharged in large quantities into aquatic bodies due to their insufficient containment during water treatment. As a result, WWTPs are regarded as point sources of microplastics release into the environment. Assessing the prevalence and behavior of microplastics in WWTPs is therefore critical for their control. The removal efficiency of microplastics was 65 %, 0.2-14 %, and 0.2-2 % after the successful primary, secondary and tertiary treatment phases in WWTPs. In this review, other than conventional treatment methods, advanced treatment methods have also been discussed. For the removal of microplastics in the size range 20-190 μm, advanced treatment methods like membrane bioreactors, rapid sand filtration, electrocoagulation and photocatalytic degradation was found to be effective and these methods helps in increasing the removal efficiency to >99 %. Bioremediation based approaches has found that sea grasses, lugworm and blue mussels has the ability to mitigate microplastics by acting as a natural trap to the microplastics pollutants and could act as candidate species for possible incorporation in WWTPs. Also, there is a need for controlling the use and unchecked release of microplastics into the environment through laws and regulations.

A discussion of microplastics in soil and risks for ecosystems and food chains

Microplastics are among the major contaminations in terrestrial and marine environments worldwide. These persistent organic contaminants composed of tiny particles are of concern due to their potential hazards to ecosystem and human health. Microplastics accumulates in the ocean and in terrestrial ecosystems, exerting effects on living organisms including microbiomes, fish and plants. While the accumulation and fate of microplastics in marine ecosystems is thoroughly studied, the distribution and biological effects in terrestrial soil call for more research. Here, we review the sources of microplastics and its effects on soil physical and chemical properties, including water holding capacity, bulk density, pH value as well as the potential effects to microorganisms and animals. In addition, we discuss the effects of microplastics in combination with other toxic environmental contaminants including heavy metals and antibiotics on plant growth and physiology, as well as human health and possible degradation and remediation methods. This reflect is an urgent need for monitoring projects that assess the toxicity of microplastics in soil and plants in various soil environments. The prospect of these future research activities should prioritize microplastics in agro-ecosystems, focusing on microbial degradation for remediation purposes of microplastics in the environment.

Heavy Metal Removal from Aqueous Effluents by TiO2 and ZnO Nanomaterials

The presence of heavy metals in wastewater, such as Ni, Pb, Cd, V, Cr, and Cu, is a serious environmental problem. This kind of inorganic pollutant is not biodegradable for several years, and its harmful effect is cumulative. Recently, semiconductor nanomaterials based on metal oxides have gained interest due to their efficiency in the removal of heavy metals from contaminated water, by inducing photocatalytic ion reduction when they absorb light of the appropriate wavelength. The most commonly applied semiconductor oxides for these purposes are titanium oxide (TiO2), zinc oxide (ZnO), and binary nanomaterials composed of both types of oxides. The main purpose of this work is to critically analyse the existent literature concerning this topic focusing specially in the most important factors affecting the adsorption or photocatalytic capacities of this type of nanomaterials. In particular, photocatalytic activity is altered by various factors, such as proportion of polymorphs, synthesis method, surface area, concentration of defects and particle size, among others. After a survey of the actual literature, it was found that, although these metal oxides have low absorption capacity for visible light, it is possible to obtain an acceptable heavy metal reduction performance by sensitization with dyes, doping with metallic or nonmetallic atoms, introduction of defects, or the coupling of two or more semiconductors.

Microplastics Derived from Food Packaging Waste-Their Origin and Health Risks

Plastics are commonly used for packaging in the food industry. The most popular thermoplastic materials that have found such applications are polyethylene (PE), polypropylene (PP), poly(ethylene terephthalate) (PET), and polystyrene (PS). Unfortunately, most plastic packaging is disposable. As a consequence, significant amounts of waste are generated, entering the environment, and undergoing degradation processes. They can occur under the influence of mechanical forces, temperature, light, chemical, and biological factors. These factors can present synergistic or antagonistic effects. As a result of their action, microplastics are formed, which can undergo further fragmentation and decomposition into small-molecule compounds. During the degradation process, various additives used at the plastics' processing stage can also be released. Both microplastics and additives can negatively affect human and animal health. Determination of the negative consequences of microplastics on the environment and health is not possible without knowing the course of degradation processes of packaging waste and their products. In this article, we present the sources of microplastics, the causes and places of their formation, the transport of such particles, the degradation of plastics most often used in the production of packaging for food storage, the factors affecting the said process, and its effects.

Plastic waste in sandy beaches and surface water in Thanh Hoa, Vietnam: abundance, characterization, and sources

The occurrence and characterization of marine debris on beaches bring opportunities to track back the anthropogenic activities around shorelines as well as aid in waste management and control. In this study, the three largest beaches in Thanh Hoa (Vietnam) were examined for plastic waste, including macroplastics (≥ 5 mm) on sandy beaches and microplastics (MPs) (< 5 mm) in surface water. Among 3803 items collected on the beaches, plastic waste accounted for more than 98%. The majority of the plastic wastes found on these beaches were derived from fishing boats and food preservation foam packaging. The FT-IR data indicated that the macroplastics comprised 77% polystyrene, 17% polypropylene, and 6% high-density polyethylene, while MPs discovered in surface water included other forms of plastics such as polyethylene- acrylate, styrene/butadiene rubber gasket, ethylene/propylene copolymer, and zein purified. FT-IR data demonstrated that MPs might also be originated from automobile tire wear, the air, and skincare products, besides being degraded from macroplastics. The highest abundance of MPs was 44.1 items/m³ at Hai Tien beach, while the lowest was 15.5 items/m³ at Sam Son beach. The results showed that fragment form was the most frequent MP shape, accounting for 61.4 ± 14.3% of total MPs. MPs with a diameter smaller than 500 μm accounted for 70.2 ± 7.6% of all MPs. According to our research, MPs were transformed, transported, and accumulated due to anthropogenic activities and environmental processes. This study provided a comprehensive knowledge of plastic waste, essential in devising long-term development strategies in these locations.

A critical review of microplastic degradation and material flow analysis towards a circular economy

The resilience and low cost of plastics has made their usage ubiquitous, but is also the cause of their prevalence and longevity as waste. Plastic pollution has become a great concern to the health and wellbeing of ecosystems around the world; microplastics are a particular threat, due to their high mobility, ease of ingestion by wildlife, and ability to adsorb and carry toxic contaminants. Material flow analysis has been widely applied to examine stocks and flows of materials in other industries, and has more recently been applied to plastics to examine areas where waste can reach the environment. However, while much research has gone into the environmental fate of microplastics, degradation strategies have been a lesser focus, and material flow analysis of microplastics has suffered from lack of data. Furthermore, the variety of plastics, their additives, and any contaminants pose a significant challenge in degrading (and not merely fragmenting) microplastic particles. This review discusses the current degradation strategies and solutions for dealing with existing and newly-generated microplastic waste along with examining the status of microplastics-based material flow analysis, which are critical for evaluating the possibility of incorporating microplastic waste into a circular economy. The degradation strategies are critically examined, identifying challenges and current trends, as well as important considerations that are frequently under-reported. An emphasis is placed on identifying missing data or information in both material flow analysis and degradation methods that could prove crucial in improving understanding of microplastic flows, as well as optimizing degradation strategies and minimizing any negative environmental impact.

Current status of microplastics and nanoplastics removal methods: Summary, comparison and prospect

In modern society, plastics also play an indispensable role in people's lives due to their various excellent properties. However, when these plastic products are discarded after being used, after being subjected to external influences, they will continue to be worn, damaged and degraded into micro- and nano-scale plastics, which are microplastics and nanoplastics (M/NPs). Although people's attention has been paid to M/NPs at present, the focus is still mainly on the detection and hazard of M/NPs, and how to remove M/NPs is relatively less popular. This review was written in order to draw the attention of more researchers to remove M/NPs. This review first briefly introduces the research background of M/NPs, and also shows the main analytical methods currently used for qualitative and quantitative M/NPs. Then, most of the current literature on the removal of M/NPs was collected, and they were classified, summarized, and introduced according to the classification of physical, physicochemical, and biological methods. The advantages and disadvantages of various methods are summarized, and they are also compared, which can help more researchers choose the appropriate method for research. In addition, the application scenarios of these methods are briefly introduced. Finally, some future research directions are proposed for the current research status of M/NPs removal. It is hoped that this will further promote the development on the method of removing M/NPs.

Microplastics: Occurrences, treatment methods, regulations and foreseen environmental impacts

Microplastics are a silent threat that represent a high degree of danger to the environment in its different ecosystems and of course will also have an important impact on the health of living organisms. It is evident the need to have effective treatments for their treatment, however this is not a simple task, this as a result of the behavior of microplastics in wastewater treatment plants due to their different types and nature, their long molecular chain, reactivity against water, size, shape and the functional groups they carry. Wastewater treatment plants are at the circumference of the release of these wastes into the environment. They often act as a source of many contaminations, which makes this problem more complex. Challenges such as detection in the current scenario using the latest analytical techniques impede the correct understanding of the problem. Due to microplastics, treatment plants have operational and process stability problems. This review paper will present the in-depth situation of occurrence of microplastics, their detection, conventional and advanced treatment methods as well as implementation of legislations worldwide in a comprehensive manner. It has been observed that no innovative or new technologies have emerged to treat microplastics. Therefore, in this article, technologies targeting wastewater treatment plants are critically analyzed. This will help to understand their fate, but also to develop state-of-the-art technologies or combinations of them for the selective treatment of microplastics. The pros and cons of the treatment methods adopted and the knowledge gaps in legislation regarding their implementation are also comprehensively analyzed. This critical work will offer the development of new strategies to restrict microplastics.

Developments in advanced oxidation processes for removal of microplastics from aqueous matrices

Continuous incorporation of microplastics (MPs) and their fragmented residues into the ecosystem has sparked significant scientific apprehensions about persistence, a multitude of sources, and toxicity impacts on human health and aquatic entities. Overcoming this multifaceted hazard necessitates the development of novel techniques with robust efficiencies to eliminate microplastics from the environmental compartments. Coagulation, flocculation, and membrane filtration are non-destructive techniques but necessitate extra steps for microplastic degradation, whereas biological means have been confirmed less efficient (less than 15% degradation). Recent reports have emphasized advanced oxidation processes (AOPs) as practical treatment alternatives, representing superior catalytic efficacy for microplastic degradation (≈30-95%). Nevertheless, additional investigations should be carried out to evaluate the performance of AOPs in degrading microplastics under real environmental matrices. Moreover, the detection of transformed metabolites, degradation mechanistic insights, and toxicity bioassays are required to substantiate AOP assumption as feasible remediation substitutes. This review focuses on the source, occurrence, discharge, transportation, and associated paramount health risks of microplastics. Advanced oxidation processes-assisted removal of microplastics from the aqueous matrices is thoroughly vetted with up-to-date findings. Factors affecting the degradation of MPs have been discussed in detail. In addition to the generalized mechanistic insights into photocatalytic degradation, the risk assessment of aging intermediates is also comprehended. Finally, the review was concluded by emphasizing current research gaps and incoming research tendencies to provide guidelines for efficiently addressing microplastic pollution.

Prospects of TiO2-based photocatalytic degradation of microplastic leachates related disposable facemask, a major COVID-19 waste

COVID-19 is one of the serious catastrophes that have a substantial influence on human health and the environment. Diverse preventive actions were implemented globally to limit its spread and transmission. Personnel protective equipment (PPE) was an important part of these control approaches. But unfortunately, these types of PPE mainly comprise plastics, which sparked challenges in the management of plastic waste. Disposable face masks (DFM) are one of the efficient strategies used across the world to ward off disease transmission. DFMs can contribute to micro and nano plastic pollution as the plastic present in the mask may degrade when exposed to certain environmental conditions. Microplastics (MPs) can enter the food chain and devastate human health. Recognizing the possible environmental risks associated with the inappropriate disposal of masks, it is crucial to avert it from becoming the next plastic crisis. To address this environmental threat, titanium dioxide (TiO2)-based photocatalytic degradation (PCD) of MPs is one of the promising approaches. TiO2-based photocatalysts exhibit excellent plastic degradation potential due to their outstanding photocatalytic ability, cost efficiency, chemical, and thermal stability. In this review, we have discussed the reports on COVID-19 waste generation, the limitation of current waste management techniques, and the environmental impact of MPs leachates from DFMs. Mainly, the prominence of TiO2 in the PCD and the applications of TiO2-based photocatalysts in MPs degradation are the prime highlights of this review. Additionally, various synthesis methods to enhance the photocatalytic performance of TiO2 and the mechanism of PCD are also discussed. Furthermore, current challenges and the future research perspective on the improvement of this approach have been proposed.

Surfactant-sodium dodecyl sulfate enhanced degradation of polystyrene microplastics with an energy-saving electrochemical advanced oxidation process (EAOP) strategy

Microplastics have been identified as a kind of emerging pollutant with potential ecological risks, and it is an urgent endeavor to find proper technologies for their remediation. Electrochemical advanced oxidation process (EAOP) technology has exhibited robust performance in the removal of various refractory organic pollutants. In this study, we explored a new remediation strategy for polystyrene microplastics (PS MPs), introducing sodium dodecyl sulfate (SDS) to enhance its degradation performance in boron-doped diamond (BDD) anode adopted EAOP. At first, we investigated the degradation behaviors of SDS in the BDD electrolysis. According to the SDS half-life under various current densities, the SDS addition strategy into EAOP is proposed; that is, supplement SDS to 500 mg/L at every half-life during electrolysis except the last cycle. Results indicated that SDS addition greatly enhanced MPs degradation rate in 72 h of EAOP, about 1.35-2.29 times higher than that in BDD electrolysis alone. The SDS assisted EAOP also led to more obvious changes in the particle size, morphology, and functional groups of the MPs. After treatment, a variety of alkyl-cleavage and oxidation products were identified, which attributed to the strong attack of oxidants (i.e., persulfate) on the MPs. The enhanced persulfate generation and oxidants adsorption on MPs can explain the enhancement effect in the EAOP strategy. Cost analysis results showed the surfactant only accounts for < 0.05% of the total operating costs in the SDS assisted EAOP. In general, the current study provided new insight into the effective way to improve the EAOP efficiency of microplastics.

Removal of nanoplastics in water treatment processes: A review

Nanoplastics are drawing a significant attention as a result of their propensity to spread across the environment and pose a threat to all organisms. The presence of nanoplastics in water is given attention nowadays as the transit of nanoplastics occurs through the aquatic ecosphere besides terrestrial mobility. The principal removal procedures for macro-and micro-plastic particles are effective, but nanoparticles escape from the treatment, increasing in the water and significantly influencing the society. This critical review is aimed to bestow the removal technologies of nanoplastics from aquatic ecosystems, with a focus on the treatment of freshwater, drinking water, and wastewater, as well as the importance of transit and its impact on health concerns. Still, there exists a gap in providing a collective knowledge on the methods available for nanoplastics removal. Hence, this review offered various nanoplastic removal technologies (microorganism-based degradation, membrane separation with a reactor, and photocatalysis) that could be the practical/effective measures along with the traditional procedures (filtration, coagulation, centrifugation, flocculation, and gravity settling). From the analyses of different treatment systems, the effectiveness of nanoplastics removal depends on various factors, source, size, and type of nanoplastics apart from the treatment method adopted. Combined removal methods, filtration with coagulation offer great scope for the removal of nanoplastics from drinking water with >99 % efficiency. The collected data could serve as base-line information for future research and development in water nanoplastics cleanup.

Mitigation of microfibers release from disposable masks - An analysis of structural properties

The use of disposable face masks increased rapidly among the general public to control the COVID-19 spread. Eventually, it increased the disposal of masks and their associated impacts on environmental pollution. Hence, this study aims to analyze the impact of nonwoven fabric structural parameters and weathering on the microfiber release characteristics. Spunbond polypropylene nonwoven with four different weights and meltblown nonwoven with two different weights were used in this study to analyze microfiber release at dry, and wet conditions to simulate improper disposal in the environment. Exposure to sunlight significantly increases the microfiber release from 35 to 50% for spunbond fabric and 56-89% for meltblown fabric. Weathering in sunlight structurally affected the tensile properties of the polypropylene fibers due to photodegradation. The study showed that each mask can produce 1.5 × 102 and 3.45 × 101 mg of microfiber/mask respectively in dry and wet states. In the case of structural parameters, a higher GSM (grams per square meter), abrasion resistance, bursting strength, and thickness showed a positive correlation with microfiber release in both fabrics. Significantly a higher microfiber release was reported with meltblown fabric than the spunbond for a given GSM. The presence of finer fibers and more fibers per unit area in meltblown fabric was noted as the main cause. Nonwoven fabric GSM and the number of fibers in a specific area showed a higher influence on microfiber release. Based on the mask consumption reported in the literature, India alone can produce around 4.27 × 102 tons of microfibers/week as an average of dry and wet conditions. The study suggests that the proper selection of physical parameters can significantly reduce the microfiber fiber release at all stages.

Advanced oxidation processes for the elimination of microplastics from aqueous systems: Assessment of efficiency, perspectives and limitations

Microplastics act as a vector of heavy metals, organic pollutants, pathogens and resistance genes in the environment further aggravate the pollution of plastics. The conventional wastewater/water treatment processes can physically capture and remove most of microplastics, but the success rates varies. How to quickly remove a large amount of microplastics from aqueous system is a key research topic at present. Recently, advanced oxidation processes (AOPs) as a green elimination strategy has attracted attention because of its effective elimination, strong destruction and safety. The molecular chain of microplastics can be gradually degraded into small molecular organics until H₂O and CO₂ by strong oxidizing free radical produced by AOPs. Unfortunately, problematically, the elimination of microplastics in aqueous system by AOPs is recently carried out on a laboratory scale. The application and implementation of this strategy are restricted by long reaction time, low liquid phase degradation efficiency and the formation of nanoplastics. Generally, the technology is still in its infancy, and most studies are carried out under laboratory conditions. The degradation of microplastics in aqueous system also needs appropriate conditions, but it is not always feasible under field conditions in AOPs. Although AOPs can be used as a green degradation technology to eliminate microplastics in aqueous systems in theory, it still needs to be furtherly explored in practical application. Consequently, before AOPs as a green elimination strategy is successfully applied to the effective remove microplastics, more in-depth research is still required, such as the setting from single condition to complex environment, the transfer from laboratory scale to field scale, and systematic toxicity evaluation of corresponding products.

Tracking microplastics biodegradation through CO2 emission: Role of photoaging and mineral addition

Once microplastics (MPs) enter the terrestrial ecosystem, they may affect the assessment of soil carbon storage and the fluxes of greenhouse gases. This study showed microbial incubation diminished the size and dissolved organic carbon (DOC) content of MPs and introduced more oxygen-containing functional groups to MPs potentially through microbial colonization. The aged MPs generally showed higher carbon mineralization ratio (0.010-0.876 %) than the pristine MPs (0.007-0.189 %), which was supported by their higher enzyme activities and DOC content. Interestingly, four model minerals increased the DOC release and CO₂ emission from MPs by altering MPs physicochemical properties and shaping the habitat for microbial growth. The higher enzyme activities in mineral artificial soils, except for montmorillonite, served as a potential valid explanation for their higher mineralization. The high CO₂ emission but low enzyme activity in montmorillonite artificial soil was due to most DOC being already mineralized. Aging and minerals altered the microflora and enhanced the expression of some C metabolism- and N-related functional genes, which supplemented the cause of higher CO₂ and N₂O emissions from the corresponding artificial soils. Overall, the increased biomineralization of MPs carbon by minerals was divergent from the protective role of minerals on soil organic carbon.

Microplastics in aquatic systems, a comprehensive review: origination, accumulation, impact, and removal technologies

Although the discovery of plastic in the last century has brought enormous benefits to daily activities, it must be said that its use produces countless environmental problems that are difficult to solve. The indiscriminate use and the increase in industrial production of cleaning, cosmetic, packaging, fertilizer, automotive, construction and pharmaceutical products have introduced tons of plastics and microplastics into the environment. The latter are of greatest concern due to their size and their omnipresence in the various environmental sectors. Today, they represent a contaminant of increasing ecotoxicological interest especially in aquatic environments due to their high stability and diffusion. In this regard, this critical review aims to describe the different sources of microplastics, emphasizing their effects in aquatic ecosystems and the danger to the health of living beings, while examining, at the same time, those few modelling studies conducted to estimate the future impact of plastic towards the marine ecosystem. Furthermore, this review summarizes the latest scientific advances related to removal techniques, evaluating their advantages and disadvantages. The final purpose is to highlight the great environmental problem that we are going to face in the coming decades, and the need to develop appropriate strategies to invert the current scenario as well as better performing removal techniques to minimize the environmental impacts of microplastics.

Rapid surface degradation of co-axially arranged polypropylene globules by nanoporous carbonized TiO2 assisted with UV-C

The degradation of plastics, especially polypropylene (PP), is difficult since it is the most hydrophobic polymer. Photocatalytic degradation of PP films has been reported to be one of the most efficient degradation techniques. However, it is still insignificant to employ it in field applications. In this study, TiO₂ nanoparticles supported on amorphous carbon with nanoporosity (TiO₂@NC) are used as a photocatalyst to degrade macro-sized co-axially oriented PP globules under the influence of UV-C irradiation. Surface characterization such as SEM, ATR-FTIR, and XPS of the PP globules was performed. The SEM images distinctly showed the surface degradation phenomenon. Interestingly, the ATR-FTIR spectra demonstrated a significant rise in the band intensity in the -OH radical region and fairly in the CO region as well, with the increase in the photocatalytic time. Surprisingly, in the XPS spectra, the intensity of C-1s spectra kept on falling, and the intensity of O-1s spectra kept on rising with the increase in the photocatalytic time. The higher surface area due to nanoporosity of TiO₂@NC enhanced the photocatalytic degradation of PP globules than previously reported studies. TiO₂@NC seems to be a potential catalyst for the degradation of different types of polymers.

Recent advances in the breakdown of microplastics: strategies and future prospectives

Microplastics pollution is becoming a major environmental issue, and exposure to microplastics has been associated with numerous adverse results to both the ecological system and humans. This work summarized the state-of-the-art developments in the breakdown of microplastics, including natural weathering, catalysts-assisted breakdown and biodegradation. Characterization techniques for microplastic breakdown involve scanning electron microscopy, Fourier infrared spectroscopy, X-ray photoelectron spectroscopy, etc. Bioavailability and adsorption capacity of microplastics may change after they are broken down, therefore leading to variety in microplastics toxicity. Further prospectives for should be focused on the determination and toxicity evaluation of microplastics breakdown products, as well as unraveling uncultivable microplastics degraders via cultivation-independent approaches. This work benefits researchers interested in environmental studies, particularly the removal of microplastics from environmental matrix.

Removal of microplastics and nanoplastics from urban waters: Separation and degradation

The omnipresent micro/nanoplastics (MPs/NPs) in urban waters arouse great public concern. To build a MP/NP-free urban water system, enormous efforts have been made to meet this goal via separating and degrading MPs/NPs in urban waters. Herein, we comprehensively review the recent developments in the separation and degradation of MPs/NPs in urban waters. Efficient MP/NP separation techniques, such as adsorption, coagulation/flocculation, flotation, filtration, and magnetic separation are first summarized. The influence of functional materials/reagents, properties of MPs/NPs, and aquatic chemistry on the separation efficiency is analyzed. Then, MP/NP degradation methods, including electrochemical degradation, advanced oxidation processes (AOPs), photodegradation, photocatalytic degradation, and biological degradation are detailed. Also, the effects of critical functional materials/organisms and operational parameters on degradation performance are discussed. At last, the current challenges and prospects in the separation, degradation, and further upcycling of MPs/NPs in urban waters are outlined. This review will potentially guide the development of next-generation technologies for MP/NP pollution control in urban waters.

Immobilized enzyme/microorganism complexes for degradation of microplastics: A review of recent advances, feasibility and future prospects

Environmental prevalence of microplastics has prompted the development of novel methods for their removal, one of which involves immobilization of microplastics-degrading enzymes. Various materials including nanomaterials have been studied for this purpose but there is currently a lack of review to present these studies in an organized manner to highlight the advances and feasibility. This article reviewed more than 100 peer-reviewed scholarly papers to elucidate the latest advances in the novel application of immobilized enzyme/microorganism complexes for microplastics degradation, its feasibility and future prospects. This review shows that metal nanoparticle-enzyme complexes improve biodegradation of microplastics in most studies through creating photogenerated radicals to facilitate polymer oxidation, accelerating growth of bacterial consortia for biodegradation, anchoring enzymes and improving their stability, and absorbing water for hydrolysis. In a study, the antimicrobial property of nanoparticles retarded the growth of microorganisms, hence biodegradation. Carbon particle-enzyme complexes enable enzymes to be immobilized on carbon-based support or matrix through covalent bonding, adsorption, entrapment, encapsulation, and a combination of the mechanisms, facilitated by formation of cross-links between enzymes. These complexes were shown to improve microplastics-degrading efficiency and recyclability of enzymes. Other emerging nanoparticles and/or enzymatic technologies are fusion of enzymes with hydrophobins, polymer binding module, peptide and novel nanoparticles. Nonetheless, the enzymes in the complexes present a limiting factor due to limited understanding of the degradation mechanisms. Besides, there is a lack of studies on the degradation of polypropylene and polyvinyl chloride. Genetic bioengineering and metagenomics could provide breakthrough in this area. This review highlights the optimism of using immobilized enzymes/microorganisms to increase the efficiency of microplastics degradation but optimization of enzymatic or microbial activities and synthesis of immobilized enzymes/microorganisms are crucial to overcome the barriers to their wide application.

Effect of land use on microplastic pollution in a major boundary waterway: The Arvand River

The occurrence of microplastics (MPs) was investigated in the Arvand River (Iran). The Arvand River (200 Km) is a major water body that flows through land with diverse use and it meets the Persian Gulf. This study constitutes the first assessment of MP pollution (prevalence and physico-chemical characteristics) in the Arvand river, both in the sediment and in the water. MP monitoring has been carried out in 24 stations located along the river. The MP pollution found ranged between 1 and 291 items·L^-1 and 70 to 15,620 items·kg^-1 (dw), in water and sediment, respectively. The majority of MPs were fibres, black/grey and yellow/orange in colour, and mainly 250-500 μm and >1000 μm in size. Polyethylene terephthalate (PET), polypropylene (PP), nylon (NYL), high-density polyethylene (HDPE), and polystyrene (PS) were found in sediment samples. All these polymers, except HDPE, were also identified in the water samples. PET and PP were dominant in the water samples; whereas PET and PS were the most abundant in the sediments. The vicinity of urban wastewater effluents could be behind MP pollution in both water and sediments. Significant differences (p < 0.05) of MP concentrations were affected by different land uses when comparing MP levels in undisturbed natural area with urban areas. A strong correlation between MP fibres and fragments found with PCA biplots revealed their similar distribution in water. In the sediment samples, fibre and fragment MP particles were significantly correlated with colloidal particles (e.g., clay and organic matter) suggesting a relevant role of colloidal particles in the aquatic ecosystem of the Arvand River in transporting MPs. This study contributes to the better understanding of the presence of MP in major rivers, which are systems that have been scarcely investigated for this type of pollution, and it can inform interventions to reduce MP inputs to the river and sea.

Photon-induced redox chemistry on pyrite promotes photoaging of polystyrene microplastics

The mineral particles in sediment could affect polystyrene microplastics (PS-MPs) prosperity through physical and chemical interactions. Pyrite with semiconducting properties is the most abundant metal sulfide mineral in the sediments of lake and river mouths. The widespread sunlight and the coexistence of PS-MPs and pyrite in lake or river water due to frequently water fluctuation is a typical photoaging environment for PS-MPs. The oxidation of reactive oxygen species (ROS) generated from pyrite would degrade the PS-MPs in theory. However, researches about photoaging of PS-MPs mediated by pyrite are paucity. Here, we investigated the photoaging process of PS-MPs affected by pyrite under simulated light condition. Remarkably, surface morphology of PS-MPs mediated by pyrite was broken. And the oxygen-containing functional group of PS-MPs increased, as revealed by Fourier Transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and contact angle test. 2D-COS analysis showed photoaging of PS-MPs with pyrite happened in the following order: C-H > C=C > C=O > C-O > OH. The photoaging of PS-MPs and transformation of intermediate were accelerated by ROS (O₂·^-, ·OH and ¹O₂) generated from pyrite. The free ·OH may play a major role in the promotion. Because the interfacial ROS reactions on pyrite surface were limited due to the electrostatic repulsion between pyrite and PS-MPs. The study explored photoaging behavior of PS-MPs accelerated by pyrite, which could be helpful for understanding photon-induced redox chemistry on PS-MPs via widespread sulfide metal minerals on earth's surface and providing further information to assess potential risks of PS-MPs.

Zinc oxide nanoparticles dissolution and toxicity enhancement by polystyrene microplastics under sunlight irradiation

Zinc oxide nanoparticles (ZnO NPs) dissolution is a critical process for the transformation and toxicity of ZnO NPs in aquatic environments. However, the effect of microplastics (MPs) on dissolution and toxicity of ZnO NPs under sunlight irradiation is still lacking. Herein, the dramatic increase in sunlight-induced ZnO NPs dissolution by polystyrene (PS) MPs was proven, which was attributed to the increase in h⁺-dependent and proton-dependent ZnO NPs dissolution by PS MPs, yielding ¹O₂ generation inhibition and acid release, respectively. The sizes, functional groups and aging status of PS MPs and pH were characteristic ZnO NPs dissolution through modifying ¹O₂, •OH and O₂^•- generation and acid release. Furthermore, the ZnO NPs dissolution affected by PS MPs also occurred in three realistic water samples, which were mainly governed by dissolved organic matter (DOM) and CO₃^2-, rather than Cl^- or SO₄^2-. The PS MPs (1 μg/mL) dramatically altered the Zn²⁺:ZnO ratio in ZnO NPs suspension after 96 h of sunlight irradiation and presented vehicle effects on Zn²⁺, which in turn significantly increased the ion-related toxicity of ZnO NPs to Daphnia magna. Based on the PS MPs enhanced dissolution and toxicity of ZnO NPs, the effects of PS MPs on the environmental risk assessment of ZnO NPs should be seriously considered in freshwater environments under sunlight irradiation.

Mechanically durable anti-bacteria non-fluorinated superhydrophobic sponge for highly efficient and fast microplastic and oil removal

Microplastics (MPs) pollution evolves into a global environmental problem to be solved urgently. Although many studies are exploring ways to remove MPs from water environment, most of them are lack of selectivity and low efficiency. Herein, considering the fascinating absorption selectivity of superwetting materials, a robust magnetic-responsive superhydrophobic and superoleophilic sponge was firstly used to quickly eliminate MPs from water with very high efficiency. The functional sponge was fabricated by a non-fluorinated coating technique that consisted of polydimethylsiloxane (PDMS) grafted Fe₃O₄ particle, PDMS grafted halloysite nanotubes, and PDMS binder. The coated sponge achieved excellent mechanically durable and chemically stable superhydrophobicity that resisted a series of severe treatments. It was unquestionable to show very fast oil absorption. What's more, it especially showed very high adsorption capacity (24.3-48.2 mg/g) and could quickly adsorb almost 100% MPs (polypropylene, polyvinyl chloride, and polyethylene) from aqueous suspensions. Moreover, the removal rates remained almost 100% for these MPs after 50 cycles. Besides, the coated sponge had excellent salt tolerance and antibacterial activity to Escherichia coli (E. coli) (99.91%) and Staphylococcus aureus (S. aureus) (90.46%). The adsorption mechanism of the coating was discussed from the perspectives of molecular structure, electronic effect, steric hindrance, and size-scale effect. The absorption driving force mainly derived from the intra-particle diffusion under capillary attraction, whilst slight electrostatic interaction, hydrogen bond interaction, and σ-p (or p-p) conjugation between PDMS and MPs. This functional sponge was destined to be a new strategy in the removal of MPs and other solid pollutants, especially in the high-salinity and rich-microorganism water environment.

Nanomaterials for microplastic remediation from aquatic environment: Why nano matters?

The contamination of microplastics in aquatic environment is regarded as a serious threat to ecosystem especially to aquatic environment. Microplastic pollution associated problems including their bioaccumulation and ecological risks have become a major concern of the public and scientific community. The removal of microplastics from their discharge points is an effective way to mitigate the adverse effects of microplastic pollution, hence has been the central of the research in this realm. Presently, most of the commonly used water or wastewater treatment technologies are capable of removing microplastic to certain extent, although they are not intentionally installed for this reason. Nevertheless, recognizing the adverse effects posed by microplastic pollution, more efforts are still desired to enhance the current microplastic removal technologies. With their structural multifunctionalities and flexibility, nanomaterials have been increasingly used for water and wastewater treatment to improve the treatment efficiency. Particularly, the unique features of nanomaterials have been harnessed in synthesizing high performance adsorbent and photocatalyst for microplastic removal from aqueous environment. This review looks into the potentials of nanomaterials in offering constructive solutions to resolve the bottlenecks and enhance the efficiencies of the existing materials used for microplastic removal. The current efforts and research direction of which studies can dedicate to improve microplastic removal from water environment with the augmentation of nanomaterial-enabled strategies are discussed. The progresses made to date have witnessed the benefits of harnessing the structural and dimensional advantages of nanomaterials to enhance the efficiency of existing microplastic treatment processes to achieve a more sustainable microplastic cleanup.