Aging assessment of microplastics (LDPE, PET and uPVC) under urban environment stressors

Effects of erythromycin on biofilm formation and resistance mutation of Escherichia coli on pristine and UV-aged polystyrene microplastics

Microplastics (MPs) and antibiotics co-occur widely in the environment and pose combined risk to microbial communities. The present study investigated the effects of erythromycin on biofilm formation and resistance mutation of a model bacterium, E. coli, on the surface of pristine and UV-aged polystyrene (PS) MPs sized 1-2 mm. The properties of UV-aged PS were significantly altered compared to pristine PS, with notable increases in specific surface area, carbonyl index, hydrophilicity, and hydroxyl radical content. Importantly, the adsorption capacity of UV-aged PS towards erythromycin was approximately 8-fold higher than that of pristine PS. Biofilms colonizing on UV-aged PS had a greater cell count (5.6 × 108 CFU mg-1) and a higher frequency of resistance mutation (1.0 × 10-7) than those on pristine PS (1.4 × 108 CFU mg-1 and 1.4 × 10-8, respectively). Moreover, erythromycin at 0.1 and 1.0 mg L-1 significantly (p < 0.05) promoted the formation and resistance mutation of biofilm on both pristine and UV-aged PS. DNA sequencing results confirmed that the biofilm resistance was attributed to point mutations in rpoB segment of the bacterial genome. qPCR results demonstrated that both UV aging and erythromycin repressed the expression levels of a global regulator rpoS in biofilm bacteria, as well as two DNA mismatch repair genes mutS and uvrD, which was likely to contribute to increased resistance mutation frequency.

Modifying luteolin's algicidal effect on Microcystis by virgin and diversely-aged polystyrene microplastics: Unveiling novel mechanisms through microalgal adaptive strategies

Luteolin has shown great potential in inhibiting Microcystis-dominated cyanobacterial blooms (MCBs). However, widespread microplastics (MPs) in natural aquatic systems can serve as substrates for cyanobacterial growth, potentially impacting their resistance to external stress and might interfere with luteolin's algicidal effect. This study investigated the impact of virgin and diversely-aged polystyrene microplastics (PS-MPs) on the inhibitory effect of luteolin involving Microcystis growth and microcystins (MCs) content in water. Moreover, the underlying mechanism was also revealed by jointly analyzing the SEM images, oxidative stress, exopolymeric substances (EPSs) content and functional gene expression. Result suggested that 0.5, 5 and 50 mg/L virgin and diversely-aged PS-MPs almost reduced growth inhibition ratio and oxidative damage of Microcysits by both doses of luteolin by stimulating EPSs secretion and inducing cell self-aggregate or hetero-aggregate with PS-MPs. Compared to virgin PS-MPs, photo-aged PS-MPs possessed rougher flaky surfaces, and hydrothermal-aging cracks the MPs internally, which were more conducive to interacting and hetero-aggregating with cells, and exhibiting more significant protective effects to Microcystis. However, MPs further reduced MCs content in water, possibly attributed to their adsorption effect on MCs, compared to luteolin stress alone. Such toxic hetero-aggregate formed by MCs, MPs, and Microcystis cells are more likely to be consumed, thus entering the food chain and triggering toxic bioaccumulation, posing greater eco-risks. This is the first study to clarify the impact and mechanisms of virgin and diversely-aged MPs on allelopathic algicidal effects from the perspective of microalgal inherent detoxifying abilities and self-protective strategies.

Photoaged polystyrene nanoplastics exposure results in reproductive toxicity due to oxidative damage in Caenorhabditis elegans

The increase of plastic production together with the incipient reuse/recycling system has resulted in massive discards into the environment. This has facilitated the formation of micro- and nanoplastics (MNPs) which poses major risk for environmental health. Although some studies have investigated the effects of pristine MNPs on reproductive health, the effects of weathered MNPs have been poorly investigated. Here we show in Caenorhabditis elegans that exposure to photoaged polystyrene nanoplastics (PSNP-UV) results in worse reproductive performance than pristine PSNP (i.e., embryonic/larval lethality plus a decrease in the brood size, accompanied by a high number of unfertilized eggs), besides it affects size and locomotion behavior. Those effects were potentially generated by reactive products formed during UV-irradiation, since we found higher levels of reactive oxygen species and increased expression of GST-4 in worms exposed to PSNP-UV. Those results are supported by physical-chemical characterization analyses which indicate significant formation of oxidative degradation products from PSNP under UV-C irradiation. Our study also demonstrates that PSNP accumulate predominantly in the gastrointestinal tract of C. elegans (with no accumulation in the gonads), being completely eliminated at 96 h post-exposure. We complemented the toxicological analysis of PSNP/PSNP-UV by showing that the activation of the stress response via DAF-16 is dependent of the nanoplastics accumulation. Our data suggest that exposure to the wild PSNP, i.e., polystyrene nanoplastics more similar to those actually found in the environment, results in more important reprotoxic effects. This is associated with the presence of degradation products formed during UV-C irradiation and their interaction with biological targets.

An insight decipher on photocatalytic degradation of microplastics: Mechanism, limitations, and future outlook

Plastic material manufacturing and buildup over the past 50 years has significantly increased pollution levels. Microplastics (MPs) and non-biodegradable residual plastic films have become the two most pressing environmental issues among the numerous types of plastic pollution. These tiny plastic flakes enter water systems from a variety of sources, contaminating the water. Since MPs can be consumed by people and aquatic species and eventually make their way into the food chain, their presence in the environment poses a serious concern. Traditional technologies can remove MPs to some extent, but their functional groups, stable covalent bonds, and hydrophobic nature make them difficult to eliminate completely. The urgent need to develop a sustainable solution to the worldwide contamination caused by MPs has led to the exploration of various techniques. Advanced oxidation processes (AOPs) such as photo-catalytic oxidation, photo-degradation, and electrochemical oxidation have been investigated. Among these, photocatalysis stands out as the most promising method for degrading MPs. Photocatalysis is an environmentally friendly process that utilizes light energy to facilitate a chemical reaction, breaking down MPs into carbon dioxide and water-soluble hydrocarbons under aqueous conditions. In photocatalysis, semiconductors act as photocatalysts by absorbing energy from a light source, becoming excited, and generating reactive oxygen species (ROS). These ROS, including hydroxyl radicals (•OH) and superoxide ions ( [Formula: see text] ), play a crucial role in the degradation of MPs. This extensive review provides a detailed exploration of the mechanisms and processes underlying the photocatalytic removal of MPs, emphasizing its potential as an efficient and environmentally friendly approach to address the issue of plastic pollution.

Microplastic generation from field-collected plastic gauze: Unveiling the aging processes

Accumulation of plastic debris in the environment is a matter of global concern. As plastic ages, it generates microplastic (MP) particles with high mobility. Understanding how MPs are generated is crucial to controlling this emerging contaminant. In this study, we utilized high-density polyethylene (HDPE) plastic gauze, collected from urban settings, as a representative example of plastic waste. The plastic gauze was subjected to various aging conditions, including freeze-thaw cycling, mechanical abrasion, and UV irradiation. Following aging, the plastic gauze was rinsed with water, and the number of generated MPs were quantified. It was found that aged plastic gauze generated up to 334 million MP particles per m2 (> 10 µm) during rinsing, a number two orders of magnitude higher than unaged plastic. Fragmentation occurred in two dimensions for bulk MPs of all morphotypes. However, specific aging approaches (i.e., mechanical abrasion and UV irradiation) generated spheres and fibers via pseudo-3D fragmentation. Additionally, changes in molecular weight, size distribution, and surface oxidation characteristics unveiled a complex pattern (i.e., irregular changes with exposure time). This complexity underscores the intricate nature of plastic debris aging processes in the environment.

Generation of environmentally persistent free radicals on photoaged tire wear particles and their neurotoxic effects on neurotransmission in Caenorhabditis elegans

Tire wear particles (TWP) are a prevalent form of microplastics (MPs) extensively distributed in the environment, raising concerns about their environmental behaviors and risks. However, knowledge regarding the properties and toxicity of these particles at environmentally relevant concentrations, specifically regarding the role of environmentally persistent free radicals (EPFRs) generated during TWP photoaging, remains limited. In this study, the evolution of EPFRs on TWP under different photoaging times and their adverse effects on Caenorhabditis elegans were systematically investigated. The photoaging process primarily resulted in the formation of EPFRs and reactive oxygen species (O2•-, ⋅OH, and 1O2), altering the physicochemical properties of TWP. The exposure of nematodes to 100 μg/L of TWP-50 (TWP with a photoaging time of 50 d) led to a significant decrease in locomotory behaviors (e.g., head thrashes, body bends, and wavelength) and neurotransmitter contents (e.g., dopamine, glutamate, and serotonin). Similarly, the expression of neurotransmission-related genes was reduced in nematodes exposed to TWP-50. Furthermore, the addition of free-radical inhibitors significantly suppressed TWP-induced neurotoxicity. Notably, correlation analysis revealed a significantly negative correlation between EPFRs levels and the locomotory behaviors and neurotransmitter contents of nematodes. Thus, it was concluded that EPFRs on photoaged TWP induce neurotoxicity by affecting neurotransmission. These findings elucidate the toxicity effects and mechanisms of EPFRs, emphasizing the importance of considering their contributions when evaluating the environmental risks associated with TWP.

Photoaged microplastics enhanced the antibiotic resistance dissemination in WWTPs by altering the adsorption behavior of antibiotic resistance plasmids

Growing concerns have raised about the microplastic eco-coronas in the ultraviolet (UV) disinfection wastewater, which accelerated the pollution of antibiotic resistance genes (ARGs) in the aquatic environment. As the hotspot of gene exchange, microplastics (MPs), especially for the UV-aged MPs, could alter the spread of ARGs in the eco-coronas and affect the resistance of the environment through adsorbing antibiotic resistant plasmids (ARPs). However, the relationship between the MP adsorption for ARPs and ARG spreading characteristics in MP eco-corona remain unclear. Herein, this study explored the distribution of ARGs in the MP eco-corona through in situ investigations of the discharged wastewater, and the adsorption behaviors of MPs for ARPs by in vitro adsorption experiments and in silico calculations. Results showed that the adsorption capacity of MPs for ARPs was enhanced by 42.7-48.0 % and the adsorption behavior changed from monolayer to multilayer adsorption after UV-aging. It was related to the increased surface roughness and oxygen-containing functional groups of MPs under UV treatment. Moreover, the abundance of ARGs in MP eco-corona of UV-treated wastewater was 1.33-1.55 folds higher than that without UV treatment, promoting the proliferation of drug resistance. DFT and DLVO theoretical calculations indicated that the MP-ARP interactions were dominated by electrostatic physical adsorption, endowing the aged MPs with low potential oxygen-containing groups to increase the electrostatic interaction with ARPs. Besides, due to the desorption of ARPs on MPs driven by the electrostatic repulsion, the bioavailability of ARGs in the MP eco-coronas was increased with pH and decreased with salinity after the wastewater discharge. Overall, this study advanced the understanding of the adsorption behavior of MPs for ARPs and provided inspirations for the evaluation of the resistance spread in the aquatic environment mediated by MP eco-coronas.

New insights into the size-independent bioactive potential of pristine and UV-B aged polyethylene microplastics

The present study investigates the morphological, physicochemical, and structural changes occurred by the UV-B aging process of low-density polyethylene microplastics (LDPE MPs), as well as the bioactive potential of both pristine and UVaged MPs towards healthy peripheral blood lymphocytes. Specifically, LDPE MPs (100-180 μm) prepared by mechanical milling of LDPE pellets, were UV-B irradiated for 120 days (wavelength 280 nm; temperature 25 °C; relative humidity 50 %) and further examined for alterations in their particle size and surface, their functional groups, thermal stability, and crystallinity (by means of SEM, FTIR spectroscopy, XRD patterns, and TGA measurements, respectively). In parallel, isolated human peripheral blood lymphocytes were treated with different concentrations (25-500 μg mL-1) of either pristine or aged MPs (UVfree and UV120d LDPE MPs) for assessing the cytogenotoxic (by means of trypan blue exclusion test and the cytokinesis-block micronucleus assay using cytochalasin-B) and oxidative effects (using the DCFH-DA staining) in both cases. According to the results, UVfree and UV120d-LDPE MPs, with a size ranging from 100 to 180 μm, can differentially promote cytogenotoxic and oxidative alterations in human lymphocytes. In fact, UVfree LDPE MPs not being able to be internalized by cells due to their size, could indirectly promote the onset of mild oxidative and cytogenotoxic damage in human peripheral lymphocytes, via a dose-dependent but size-independent manner. The latter is more profound in case of the irregular-shaped UV120d-LDPE MPs, bearing improved dispersibility and sharp edges (by means of cracks and holes), as well as oxygen-containing and carbonyl groups. To our knowledge, the present findings provide new data regarding the bioactive behavior of pristine and UV-B aged LDPE MPs, at least in the in vitro biological model tested, thus giving new evidence for their size-independent and/or indirect mode of action.

The characteristics and influencing factors of farmland soil microplastic in Hetao Irrigation District, China

Microplastic pollution, a major global concern, has garnered increasing attention in agricultural ecosystem research. China's Hetao Irrigation District, vital for grain production in the Yellow River Basin, lacks sufficient research on microplastic pollution of agricultural soils. This study, based on a detailed background investigation and testing of 47 samples, is the first to elucidate the characteristics and potential influencing factors of microplastics in the Hetao Irrigation District. The abundance of microplastics in the farmland soil ranged from 1810 to 86331 items/kg, with 90% measuring below 180 µm and mainly in film and fragment forms. Predominant polymers were polyethylene (PE, 43.0%) and polyamide (PA, 27.8%). Key pollution influencers were identified as agricultural inputs, with low-density polyethylene (LDPE) being the most extensively used plastic type. The carbonyl index and hydroxyl indices of the detected LDPE microplastics ranged from 0.041 to 0.96 and 0.092 to 1.20, respectively. The study highlights the significance of mulching management and agronomic practices in shaping microplastic characteristics. Potential pollution sources include agricultural inputs, irrigation equipment, domestic waste, and tire wear. Proposed effective strategies include responsible plastic use, robust waste management, and irrigation system upgrades, establishing a foundation for future ecological risk assessments and effective management approaches in the Hetao Irrigation District. ENVIRONMENTAL IMPLICATION: The harmful substances studied in this paper are microplastics, which are widely distributed in the environment and have potential ecological risks. This study is the first to investigate the characteristics of microplastics in farmland soil within the Hetao Irrigation Area, a region that is of critical importance to agricultural production in the Yellow River Basin of China. The study provides comprehensive insights into the factors influencing the characteristics of microplastics and speculates on their sources. These findings offer a novel perspective on the assessment of microplastic contamination in the area and provide valuable recommendations for prevention and control measures.

Analysis and identification of degradation products in gas, particle, and liquid phases of polypropylene and polyethyleneterephthalate microplastics aging through non-thermal plasma simulation

Plastic aging can cause alterations in the physical and chemical characteristics of plastics, as well as their behavior in the environment. Due to the extremely slow natural aging process, laboratory simulated aging methods have to be used. In this study, non-thermal plasma (NTP) was adopted to investigate the aging process of polypropylene (PP) and polyethylene terephthalate (PET) microplastics. Various analytical instruments, including proton transfer reaction mass spectrometry and single-particle aerosol mass spectrometry, were employed to examine and identify the organic constituents of the gas, liquid, and particle phase degradation products, as well as to monitor the degradation process. The results showed that after 90 min of aging, both PP and PET surfaces showed yellowing, and the carbonyl index of PP increased while that of PET decreased, with an increase in crystallinity. The organic components of reaction products, such as ketones, esters, acids, and alcohols, increased with longer aging times. Gas products mainly contain aromatic hydrocarbons, while particles from aged PET contain compounds with benzene rings and metal elements. Liquid products from aged PP show a significant presence of branched alkanes. Based on this analysis, degradation mechanisms of PP and PET by NTP were proposed. This investigation represents the initial systematically exploration of the release of organic substances during the degradation of microplastics mediated by NTP. It provides significant insights into the detrimental organic compounds emitted during this process, thereby offering valuable information for understanding the environmental and human health implications of natural microplastic degradation. Furthermore, it addressed the requirements for increased attention to the potential environmental risks associated with these harmful components.

Interfacial interactions of polyethylene terephthalate microplastics and malachite green, tetracycline in aqueous environments

Polyethylene terephthalate microplastics (PET-MPs) are one of pivotal nondegradable emerging pollutant. Here the variation of the surface physicochemical characteristics of PET-MPs with UV irradiation aging and the adsorption behaviors of PET-MPs in malachite green (MG), tetracycline (TC) solution and the effect of coexisting Cu(II) were comparatively investigated. The yellowing, weakened hydrophobicity, and increased surface negative charge, crystallinity degree and oxygen-containing functional groups were manifested specifically by the aged PET-MPs. Different from the single system, the hydrophobic interaction and metal ion bridging complexation dominated the adsorption of MG and TC, respectively, in the binary solution. While in the ternary solution, cationic ion competition of Cu(II) with MG decreased its capture, and the formation of PET-Cu(II)-TC ternary complexes promoted TC adsorption. Moreover, PET-MPs could serve as an efficient vector for MG and TC in MG/TC/Cu(II) ternary system, indicating PET-MPs tend to carry more varieties in the complex environment, that may increase the environmental risk of PET-MPs.

The adsorption and its mechanism of venlafaxine by original and aged polypropylene microplastic and the changes of joint toxicity

Conjugation with the increment of consumption of polypropylene (PP) masks and antidepressants during pandemic, PP microplastics (MPs) and Venlafaxine (VEN) widely co-existed in surface waters. However, their environmental fate and the combined toxicity were unclear. Hence, we investigated the adsorption behaviors, and associated mechanisms of PP MPs for VEN. The impact factors including pH, salinity, and MPs aging were estimated. The results indicated PP MPs could adsorb amount of VEN within 24 h. The pseudo second-order kinetic model (R2 = 0.97) and Dubinin-Radushkevich model (R2 = 0.89) fitted well with the adsorption capacity of PP MPs for VEN, implying that chemical adsorption accompanied by electrostatic interaction might be the predominant mode for the interactions between PP MPs and VEN. Meanwhile, the adsorption capacity of PP MPs declined from pH of 2.5-4.5 and then increased from 4.5 to 9.5. The increased salinity (5-35 ppt) significantly suppressed the adsorption capacity. Aging by sunlight and UV triggered the formation of new functional group (carbonyl) on MPs, and then enhanced the adsorption capacity for VEN. Gaussian Model analysis further evidenced the electrostatic adsorption occurring in PP MPs and VEN. The combined exposure to PP MPs and VEN showed significantly antagonistic toxicity on Daphnia magna. The adsorption of VEN by PP MPs mitigated the lethal effects and behavioral function impairment posed by VEN on animals, implying the potential protective effects on zooplankton by PP MPs. This study for the first time provides perspective for assessing the environmental fate of MPs and antidepressants in aquatic system.

UV Irradiation of Polyethylene Terephthalate and Polypropylene and Detection of Formed Microplastic Particles Down to 1 μm

The degradation of plastics upon UVC irradiation in aqueous solution and the formation of microplastic (MP) particles were investigated. Polypropylene (PP) and recycled and virgin polyethylene terephthalate (PET) were irradiated with a UV lamp emitting light at 254 nm. Irradiation was performed for 15 and 30 min, respectively, at an intensity of about 0.3 W cm-2 . The formation of MP was studied by Raman spectroscopy. The results showed that MP particles were formed after irradiation and that their number was significantly higher in the recycled PET than in the virgin material. The number of PP MP formed was lower compared to PET and was not significantly different after 15 and 30 min. In addition, ethanol was used as an alternative solvent to investigate how its chemical properties and interactions with UVC irradiation affect the degradation of PET and PP plastics. The use of ethanol and recycled PET resulted in a lower number of MP particles at both irradiation times. When ethanol was used after 30 min of irradiation, significantly more PP MP formed. The different chemical structures of PET and PP combined with the different solvent properties of water and ethanol contribute to the differences in their susceptibility to UVC degradation.

Natural aging and adsorption/desorption behaviors of polyethylene mulch films: Roles of film types and exposure patterns

Polyethylene (PE) mulch films are an important source of microplastics (MPs) in agricultural soils, which may further affect the bioavailability of coexisting pollutants. In this study, white (WM), black (BM), and silver-black (SM) PE mulch films were aged on the soil surface and under soil burial to simulate the two exposure patterns of abandoned mulch films in the field. Results indicated that the soil-surface exposure induced more pronounced aging characteristics, and WM seemed the most susceptible. Serious surface deterioration by aging led to a drastic decrease in the tensile properties of the films, suggesting the tendency to fragment. Oxygen-containing functional groups were generated on the film surfaces, with oxygen/carbon ratios increasing by up to 29 times, which contributed to the prominent increase in Pb adsorption on the film-derived MPs. Additionally, the film surface became more hydrophobic when exposed to the soil surface but more hydrophilic in the soil-burial exposure, which was in agreement with the change in triclosan adsorption, i.e., promotion and suppression, respectively. Aging generally decreased the desorption potential of the adsorbed pollutants in simulated gastrointestinal solutions due to increased interactions. By comparison, exposure patterns were revealed to be the critical factor for these changes, regardless of film types.

Photo-oxidation of Micro- and Nanoplastics: Physical, Chemical, and Biological Effects in Environments

Micro- and nanoplastics (MNPs) are attracting increasing attention due to their persistence and potential ecological risks. This review critically summarizes the effects of photo-oxidation on the physical, chemical, and biological behaviors of MNPs in aquatic and terrestrial environments. The core of this paper explores how photo-oxidation-induced surface property changes in MNPs affect their adsorption toward contaminants, the stability and mobility of MNPs in water and porous media, as well as the transport of pollutants such as organic pollutants (OPs) and heavy metals (HMs). It then reviews the photochemical processes of MNPs with coexisting constituents, highlighting critical factors affecting the photo-oxidation of MNPs, and the contribution of MNPs to the phototransformation of other contaminants. The distinct biological effects and mechanism of aged MNPs are pointed out, in terms of the toxicity to aquatic organisms, biofilm formation, planktonic microbial growth, and soil and sediment microbial community and function. Furthermore, the research gaps and perspectives are put forward, regarding the underlying interaction mechanisms of MNPs with coexisting natural constituents and pollutants under photo-oxidation conditions, the combined effects of photo-oxidation and natural constituents on the fate of MNPs, and the microbiological effect of photoaged MNPs, especially the biotransformation of pollutants.

Leaching of heavy metals from polyester microplastic fibers and the potential risks in simulated real-world scenarios

Heavy metals have been incorporated as additives into synthetic textiles to enhance their functional properties. However, these fibers are susceptible to shedding due to mechanical wear, and the release of heavy metals from microplastic fibers (MFs) remains largely uncharacterized. Therefore, this study sought to quantify the levels of heavy metals in textiles, evaluate their leaching capabilities under various scenarios, and ultimately assess the potential health risks associated with MFs ingestion. First, we determined the metal content in eight commonly used polyester textiles. Subsequently, we estimated the metal leaching capacities of specific MFs sourced from carpets, curtains, sweaters, and scarves in freshwater, human saliva, human lung fluid, and fish gastric fluid at distinct time intervals. The results indicated that carpets contained the highest amount of total metals, with a concentration of 218 ± 8 mg/kg. Ultraviolet weathering, coupled with longer exposure durations, led to surface coarsening of MFs, which may be the primary reason for the enhanced leaching of metals in freshwater. Furthermore, our findings revealed that carbonyl index was unsuitable for characterizing aging because polyester inherently contains carbonyl groups. Instead, the O/C ratio emerged as a more suitable indicator. The leached concentrations and percentages of metals from MFs exhibited the following order in biofluids: Sb>Mn>Cr and Cr>Mn>Pb in biofluids, respectively. Finally, the estimated daily intake of metals was significantly below the tolerable thresholds (0.0014-0.14 mg/kg/d for fish and 0.0036-1.0 mg/kg/d for humans), indicating a negligible risk of heavy metal exposure through MFs for both fish and humans. ENVIRONMENTAL IMPLICATION: In recent years, the ecological risks posed by heavy metal contaminants loaded onto microplastic fibers have become an increasing concern. Therefore, our study sought to characterize the accumulation of heavy metals on plastic fabrics and the potential for these loaded heavy metals to be released when microplastic fibers originating from these fabrics enter freshwater environments and interact with organisms. This vector-like behavior underscores the importance of investigating the ecological hazards associated with microplastic fibers carrying contaminants in both environmental and organismal contexts.

Soils in distress: The impacts and ecological risks of (micro)plastic pollution in the terrestrial environment

Plastics have revolutionised human industries, thanks to their versatility and durability. However, their extensive use, coupled with inadequate waste disposal, has resulted in plastic becoming ubiquitous in every environmental compartment, posing potential risks to the economy, human health and the environment. Additionally, under natural conditions, plastic waste breaks down into microplastics (MPs<5 mm). The increasing quantity of MPs exerts a significant burden on the soil environment, particularly in agroecosystems, presenting a new stressor for soil-dwelling organisms. In this review, we delve into the effects of MP pollution on soil ecosystems, with a specific attention to (a) MP transport to soils, (b) potential changes of MPs under environmental conditions, (c) and their interaction with the physical, chemical and biological components of the soil. We aim to shed light on the alterations in the distribution, activity, physiology and growth of soil flora, fauna and microorganisms in response to MPs, offering an ecotoxicological perspective for environmental risk assessment of plastics. The effects of MPs are strongly influenced by their intrinsic traits, including polymer type, shape, size and abundance. By exploring the multifaceted interactions between MPs and the soil environment, we provide critical insights into the consequences of plastic contamination. Despite the growing body of research, there remain substantial knowledge gaps regarding the long-term impact of MPs on the soil. Our work underscores the importance of continued research efforts and the adoption of standardised approaches to address plastic pollution and ensure a sustainable future for our planet.

Determination of key factors affecting biofilm formation on the aged Poly(ethylene terephthalate) during anaerobic digestion

Biofilm formation on plastic surface is a growing concern because it can alter the plastic surface properties and exacerbate the ecological risk. Identifying key factors that affecting biofilm formation is critical for effective pollution control. In this study, the poly (ethylene terephthalate) (PET) was aged in water and air conditions with UV irradiation, then incubated in the digestate of food waste anaerobic digestion to allow biofilm formation. Surface analysis techniques, including scanning electron microscopy (SEM), atomic force microscopy (AFM), and Fourier-transform infrared spectroscopy with attenuated total reflection (FTIR-ATR), were utilized to investigated the changes in the topography, roughness, hydrophily, and functional groups change of the PET surface during the aging process. Confocal laser scanning microscopy (CLSM) was used to determine the distribution of microorganisms on the PET surface after incubation in the digestate. This study focused on understanding the interactions between the PET surface and biofilm to identify critical surface factors that affect biofilm formation. Results showed that the four months aging process decreased the contact angle of the PET surface from 96.92° to 76.08° and 68.97° in water and air conditions, respectively, corresponding to an increase of 44% and 70% in the surface energy. Additionally, aging in air conditions led to a rougher surface compared to water conditions. The arithmetic roughness average (Ra) of the PET-Water was 11.0 nm, comparable to that of the pristine PET, while the value of PET-Air was much higher (43.9 nm). The results further indicated that biofilm formation during anaerobic digestion was more sensitive to roughness than hydrophily. The PET surface aged in air conditions provided a more suitable environment for microbial reproduction, leading to the aggradation of living cells.

The molecular level degradation state of drift plastics in the Sea of Japan coastline

Polyethylene (PE) and polyethylene terephthalate (PET) are among the most abundant plastics polluting the oceans. However, their environmental fate depends on how they have been weathered. Due to its unique geography, the Sea of Japan is a pollution hotspot where plastics accumulate. In this study, the structures of plastics, having drifted into the Sea of Japan coastline environment, were analyzed with a particular focus on examining polymer crystallization and carbonyl formation; two factors which influence microplastic formation and the adsorption of contaminants onto plastic surfaces. PE in the coastal environment did not show evidence of crystallization, although carbonyl formation did increase. By contrast, PET bottles were shown to not be uniform in structure, with unaged bottles being less crystalline in the neck component compared to the body. Because of this difference, in environmental PET bottles, it was the bottle neck that showed increases in crystallization and carbonyl group formation.

Accessing the intrinsic factors of carbonyl index of microplastics: Physical and spectral properties, baseline correction, calculation methods, and their interdependence

Carbonyl index (CI) is a measure of the degradation status of microplastics. While many studies address environmental factors of microplastic degradation, intrinsic factors like physical properties, spectral properties, baseline correction, and CI calculation methods are less explored. This research focused on these aspects using surface seawater samples. We found that color and shape have limited dependence on particle size or signal-to-noise ratio (SNR). Baseline correction can significantly alter CI values, with the direction of the shift depending on the methods used. Additionally, most CI values before and after baseline correction and those calculated using different methods tend to be strongly correlated. Using the selected CI calculation methods, we found that CI values varied significantly by shape and color. CI's relation to the similarity between the sample and its pristine form suggests an alternative degradation measure. Our findings emphasize the need for standardized CI calculation methods.

Leveraging deep learning for automatic recognition of microplastics (MPs) via focal plane array (FPA) micro-FT-IR imaging

The fast and accurate identification of MPs in environmental samples is essential for the understanding of the fate and transport of MPs in ecosystems. The recognition of MPs in environmental samples by spectral classification using conventional library search routines can be challenging due to the presence of additives, surface modification, and adsorbed contaminants. Further, the thickness of MPs also impacts the shape of spectra when FTIR spectra are collected in transmission mode. To overcome these challenges, PlasticNet, a deep learning convolutional neural network architecture, was developed for enhanced MP recognition. Once trained with 8000 + spectra of virgin plastic, PlasticNet successfully classified 11 types of common plastic with accuracy higher than 95%. The errors in identification as indicated by a confusion matrix were found to be caused by edge effects, molecular similarity of plastics, and the contamination of standards. When PlasticNet was trained with spectra of virgin plastic it showed good performance (92%+) in recognizing spectra that had increased complexity due to the presence of additives and weathering. The re-training of PlasticNet with more complex spectra further enhanced the model's capability to recognize complex spectra. PlasticNet was also able to successfully identify MPs despite variations in spectra caused by variations in MP thickness. When compared with the performance of the library search in identifying MPs in the same complex dataset collected from an environmental sample, PlasticNet achieved comparable performance in identifying PP MPs, but a 17.3% improvement. PlasticNet has the potential to become a standard approach for rapid and accurate automatic recognition of MPs in environmental samples analyzed by FPA FT-IR imaging.

UV Light Causes Structural Changes in Microplastics Exposed in Bio-Solids

Bio-solids (biological sludge) from wastewater treatment plants are a significant source of the emission of microplastics (MPs) into the environment. Weakening the structure of MPs before they enter the environment may accelerate their degradation and reduce the environmental exposure time. Therefore, we studied the effect of UV-A and UV-C, applied at 70 °C, on three types of MPs, polypropylene (PP), polyethylene (PE), and polyethylene terephthalate (PET), that are commonly found in sewage sludge, using three shapes (fibers, lines, granules). The MPs were exposed to UV radiation in bio-solid suspensions, and to air and water as control. The structural changes in and degradation of the MPs were investigated using Attenuated Total Reflectance-Fourier Transform Infrared Spectrometry (ATR-FTIR) and surface morphology was performed with SEM analysis. UV exposure led to the emergence of carbonyl and hydroxyl groups in all of the PP samples. In PE and PET, these groups were formed only in the bio-solid suspensions. The presence of carbonyl and hydroxyl groups increased with an increasing exposure time. Overall, UV radiation had the greatest impact on the MPs in the bio-solids suspension. Due to the surface-to-volume ratio of the tested samples, which influences the degradation rate, the fibers were more degraded than the other two plastic shapes. UV-A was slightly more effective at degrading the MPs than UV-C. These findings show that ultraviolet radiation in combination with an elevated temperature affects the structure of polymers in wastewater bio-solids, which can accelerate their degradation.

Microplastic contamination in Indian rural and urban lacustrine ecosystems

This study investigates the microplastics (MPs) pollution of the lacustrine ecosystems of Tamil Nadu, South India. It examines the seasonal distribution, characteristics and morphology of MPs and assesses the risk posed by MPs pollution. MPs abundance in the 39 rural and urban lakes studied varies from 16 ± 2.69 to 118.17 ± 22.17 items/L (water) and 19.50 ± 4.75 to 156.23 ± 36.41 items/kg (sediment). The water and sediment of urban lakes show average MPs abundances of 88.06 items/L and 115.24 items/kg respectively, while the rural lakes exhibit average MPs abundances of 42.98 items/L and 53.29 items/kg. The results demonstrate that study areas with more residential and urban centers with higher population density and larger discharge of sewage have greater MP abundance. Urban zones have greater MP diversity integrated index (MPDII = 0.73) than rural zones (MPDII = 0.59). Fibres are the dominant group and polyethylene and polypropylene are the most commonly found polymers, possibly gaining entry through land-based plastic litter and urban activities in this region. The weathering index values, 50 % of MPs exhibit high degree of oxidation (WI >0.31) with an age of >10 years. SEM-EDAX results reveal that the weathered MPs from urban lakes have a wider variety of metal elements (Al, Cr, Mn, Co, Ni, Cu, Zn, As, Sr, Hg, Pb and Cd) than those from rural lakes (Na, Cl, Si, Mg, Al, Cu). Though PLI shows low risk (<10) in terms of abundance, PHI reflects pollution status III (10-100) and IV (100-1000) in rural areas and IV and V (>1000) in urban areas based on the toxicity score of the polymer. Ecological risk assessment shows minor risks (<150) at present. The assessment indicates the risk posed by the MPs to the lakes studied and emphasizes the necessity for best MP management practices in future.

Coagulation studies on photodegraded and photocatalytically degraded polystyrene microplastics using polyaluminium chloride

Microplastics are ubiquitous persistent emerging contaminants, and its presence has been detected even in the most pristine and fragile ecosystems. Advanced oxidation processes are one of the novel degradation technologies used for the elimination of microplastics from the environment. In this study, the effect of ultraviolet C (UV-C, 253.7 nm) and ultraviolet A (UV-A, 365 nm) irradiations on polystyrene (PS) microplastic properties in the presence and absence of titanium dioxide were studied along with their coagulation performances using polyaluminium chloride (PAC). The effects of solar irradiation on the chemical properties of microplastics in aqueous and dry conditions were also investigated. PS microplastics (1.5 g) in three size ranges, 300-150 μm, 150-75 μm, and <75 μm were used during this experiment. After 45 days of irradiation, samples showed discolouration, brittleness, and loss of hydrophobicity. Images obtained from scanning electron microscope revealed smoothening and melting of PS surfaces upon UV exposure. Attenuated total reflectance- Fourier transform infrared spectroscopy and X-ray photon spectroscopy of photoaged samples revealed chemical alterations, bond cleavage and formation of oxygenated functional groups on microplastic surfaces. PAC coagulation of samples before and after UV irradiation showed drastic differences in removal efficiencies, with UV-C irradiated microplastics exhibiting maximum efficiency. Large sized and photocatalytically degraded microplastics showed better removal efficiencies than small sized particles. The 300-150 μm sized PS microplastic, degraded photo catalytically under UV-C irradiation showed approximately 99 % removal efficiency, while PS < 75 μm photodegraded under UV-A irradiation showed only 74.2 % removal efficiency.

Differences in microplastic degradation in the atmosphere and coastal water environment from two island nations: Japan and New Zealand

Microplastics are subject to environmental forces that can change polymer organization on a molecular scale. However, it is not clear to what extent these changes occur in the environment and whether microplastics in the atmospheric and water environment differ. Here we identify structural differences between microplastics in the atmosphere and water environment from Japan and New Zealand, representing two archipelagos differing in their proximity to nearby countries and highly populated areas. We first highlight the propensity for smaller microplastics to arrive via air masses from the Asian continent to the Japan Sea coastal area, while New Zealand received larger, locally derived microplastics. Analyses of polyethylene in the Japanese atmosphere indicate that microplastics transported to the Japanese coastal areas were more crystalline than polyethylene particles in the water, suggesting that the plastics arriving by air were relatively more aged and brittle. By contrast, polypropylene particles in New Zealand waters were more degraded than the microplastic particles in the air. Due to the lack of abundance, both polyethylene and polypropylene could not be analyzed for both countries. Nevertheless, these findings show the structural variation in microplastics between environments in markedly different real-world locations, with implications for the toxic potential of these particles.

Challenges of Raman spectra to estimate carbonyl index of microplastics: A case study with environmental samples from sea surface

This study investigates the feasibility of using the carbonyl index (CI) derived from Raman spectra as an indicator of plastic degradation and its relationship with the CI calculated from Fourier transform infrared (FTIR) spectra, using microplastic samples of polyethylene (PE) from surface seawater. Multiple methods were used to calculate the CI values of FTIR spectra, while proposed methods were used to calculate the corresponding CI values of Raman spectra. Some significant relations between FTIR CI and Raman CI were observed. However, small R2 values suggest weak functional relationships, which can be attributed to the low signal-to-noise ratio (SNR) of Raman spectra. These results highlight the challenges of establishing a functional relationship between FTIR CI and Raman CI, including challenges such as the uniformity of Raman spectra, determining optimal Raman measurement parameters, selecting appropriate peaks for Raman CI calculation, deciding on spectral processing methods, and addressing the interdependence of these issues.

Predicting adsorption capacity of pharmaceuticals and personal care products on long-term aged microplastics using machine learning

We investigated the adsorption mechanism of 66 coexisting pharmaceuticals and personal care products (PPCPs) on microplastics treated with potassium persulfate, potassium hydroxide, and Fenton reagent for 54, 110, and 500 days. The total adsorption capacity (q_e) of 66 PPCPs on 15 original microplastics was 171.8 - 1043.7 μg/g, far below that of 177 long-term aged microplastics (7114.0 - 13,114.4 μg/g). Around 69.8% of q_e was primarily influenced by the total energy, energy of the highest occupied molecular orbital, and energy gap of PPCPs, calculated using the B3LYP/6-31 G* level. Furthermore, 111 aged microplastics exhibited similar total q_e values. Additionally, we developed predictive models based on attenuated total reflectance Fourier transform infrared spectroscopy to predict the individual and total q_e on 192 microplastics. These models, including the maximal information coefficient and gradient boosting decision tree regression, exhibited high accuracy with R_training² values of 0.9772 and 0.9661, respectively, and p-values below 0.001. Spectroscopic analysis and machine learning models highlighted surface functional group alterations and the importance of the 1528-1700 cm^-1 spectral region and carbon skeleton in the adsorption process. In summary, our findings contribute to understanding the adsorption of PPCPs on microplastics, particularly in the context of long-term aging effects.

Low environmental impact remediation of microplastics: Visible-light photocatalytic degradation of PET microplastics using bio-inspired C,N-TiO2/SiO2 photocatalysts

Microplastics (MPs) are plastic particles with sizes between 1 μm and 5 mm with a ubiquitous presence in aquatic ecosystems. MPs harm marine life and can cause severe health problems for humans. Advanced oxidation processes (AOPs) that involve the in-situ generation of highly oxidant hydroxyl radicals can be an alternative to fight MPs pollution. Of all the AOPs, photocatalysis has been proven a clean technology to overcome microplastic pollution. This work proposes novel C,N-TiO₂/SiO₂ photocatalysts with proper visible-active properties to degrade polyethylene terephthalate (PET) MPs. Photocatalysis was performed in an aqueous medium and at room temperature, evaluating the influence of two pH values (pH 6 and 8). The results demonstrated that the degradation of the PET MPs by C,N-TiO₂/SiO₂ semiconductors is possible, achieving mass losses between 9.35 and 16.22 %.

Photo-aging promotes the inhibitory effect of polystyrene microplastics on microbial reductive dechlorination of a polychlorinated biphenyl mixture (Aroclor 1260)

Polychlorinated biphenyls (PCBs) and microplastics (MPs) commonly co-exist in various environments. MPs inevitably start aging once they enter environment. In this study, the effect of photo-aged polystyrene MPs on microbial PCB dechlorination was investigated. After a UV aging treatment, the proportion of oxygen-containing groups in MPs increased. Photo-aging promoted the inhibitory effect of MPs on microbial reductive dechlorination of PCBs, mainly attributed to the inhibition of meta-chlorine removal. The inhibitory effects on hydrogenase and adenosine triphosphatase activity by MPs increased with increasing aging degree, which may be attributed to electron transfer chain inhibition. PERMANOVA showed significant differences in microbial community structure between culturing systems with and without MPs (p < 0.05). Co-occurrence network showed a simpler structure and higher proportion of negative correlation in the presence of MPs, especially for biofilms, resulting in increased potential for competition among bacteria. MP addition altered microbial community diversity, structure, interactions, and assembly processes, which was more deterministic in biofilms than in suspension cultures, especially regarding the bins of Dehalococcoides. This study sheds light on the microbial reductive dechlorination metabolisms and mechanisms where PCBs and MPs co-exist and provides theoretical guidance for in situ application of PCB bioremediation technology.

Gaseous products generated from polyethylene and polyethylene terephthalate during ultraviolet irradiation: Mechanism, pathway and toxicological analyses

The generation of various degradation products from microplastics (MPs) has been confirmed under ultraviolet (UV) irradiation. The gaseous products, primarily volatile organic compounds (VOCs), are usually overlooked, leading to potential unknown risks to humans and the environment. In this study, the generation of VOCs from polyethylene (PE) and polyethylene terephthalate (PET) under UV-A (365 nm) and UV-C (254 nm) irradiation in water matrixes were compared. More than 50 different VOCs were identified. For PE, UV-A-derived VOCs mainly included alkenes and alkanes. On this basis, UV-C-derived VOCs included various oxygen-containing organics, such as alcohols, aldehydes, ketones, carboxylic acid and even lactones. For PET, both UV-A and UV-C irradiation induced the generation of alkenes, alkanes, esters, phenols, etc., and the differences between these two reactions were insignificant. Toxicological prioritization prediction revealed that these VOCs have diverse toxicological profiles. The VOCs with the highest potential toxicity were dimethyl phthalate (CAS: 131-11-3) from PE and 4-acetylbenzoate (3609-53-8) from PET. Furthermore, some alkane and alcohol products also presented high potential toxicity. The quantitative results indicated that the yield of these toxic VOCs from PE could reach 10² μg g^-1 under UV-C treatment. The degradation mechanisms of MPs included direct scission by UV irradiation and indirect oxidation induced by diverse activated radicals. The former mechanism was dominant in UV-A degradation, while UV-C included both mechanisms. Both mechanisms contributed to the generation of VOCs. Generally, MPs-derived VOCs can be released from water to the air after UV irradiation, posing a potential risk to ecosystems and human beings, especially for UV-C disinfection indoors in water treatments.

New sight of microplastics aging: Reducing agents promote rapid aging of microplastics under anoxic conditions

The aging of microplastics (MPs) occurs extensively in the environment, and understanding the aging mechanisms of MPs is essential to study the properties, fate and environmental impact of MPs. We proposed a creative hypothesis that polyethylene terephthalate (PET) can be aged by reducing reactions with reducing agents. Simulation experiments based on the principle of reduction of carbonyl by NaBH₄ were conducted to test the correctness of this hypothesis. The results showed that after 7 days of experiments, physical damage and chemical transformation occurred in the PET-MPs. The particle size of MPs was reduced by 34.95-55.93 %, and the C/O ratio was increased by 2.97-24.14 %. The changing order of surface functional groups (CO > C-O > C-H > C-C) was obtained. The occurrence of reductive aging and electron transfer of MPs was further supported by electrochemical characterization experiments. These results together reveal the reductive aging mechanism of PET-MPs: CO is firstly reduced to C-O by BH₄^- attack, and then further reduced to ·R. The resulting ·R recombines to form new C-H and C-C. This study is beneficial to deepen the understanding of the chemical aging of MPs, and can provide a theoretical basis for further research on the reactivity of oxygenated MPs with reducing agents.

Temperature-Dependent Molecular Evolution of Biochar-Derived Dissolved Black Carbon and Its Interaction Mechanism with Polyvinyl Chloride Microplastics

Biochar-derived dissolved black carbon (DBC) molecules are dependent on the BC formation temperature and affect the fate of emerging contaminants in waters, such as polyvinyl chloride microplastic (MP_PVC). However, the temperature-dependent evolution and MP_PVC-interaction of DBC molecules remain unclear. Herein, we propose a novel DBC-MP_PVC interaction mechanism by systematically interpreting heterogeneous correlations, sequential responses, and synergistic relationships of thousands of molecules and their linking functional groups. Two-dimensional correlation spectroscopy was proposed to combine Fourier transform-ion cyclotron resonance mass spectrometry and spectroscopic datasets. Increased temperature caused diverse DBC molecules and fluorophores, accompanied by molecular transformation from saturation/reduction to unsaturation/oxidation with high carbon oxidation states, especially for molecules with acidic functional groups. The temperature response of DBC molecules detected via negative-/positive-ion electrospray ionization sequentially occurred in unsaturated hydrocarbons → lignin-like → condensed aromatic → lipid-/aliphatic-/peptide-like → tannin-like → carbohydrate-like molecules. DBC molecular changes induced by temperature and MP_PVC interaction were closely coordinated, with lignin-like molecules contributing the most to the interaction. Functional groups in DBC molecules with m/z < 500 showed a sequential MP_PVC-interaction response of phenol/aromatic ether C-O, alkene C═C/amide C═O → polysaccharides C-O → alcohol/ether/carbohydrate C-O groups. These findings help to elucidate the critical role of DBCs in MP environmental behaviors.

Identification of microplastics using a convolutional neural network based on micro-Raman spectroscopy

Microplastics (MPs) pose a threat to human and environmental health, and have emerged as a global environmental issue. Because MPs are small and complex, methods of quickly and reliably classifying and identifying them are either lacking or in the early stages of development. In this study, micro-Raman spectroscopy and a convolutional neural network (CNN) were combined to establish identification models for 10 MP references and three environmental samples. In addition, an interaction network was established based on pair-wise correlations of Raman bands to determine the influence of environmental stress on MPs. The CNN model achieved average classification accuracies of 96.43% and 95.6% for the 10 MP references and the three environmental samples, respectively. For MPs exposed to environmental stressors, an interaction network can provide highly sensitive, information-dense, and universally applicable signatures for characterizing the environmental processes affecting MP spectra. The results of this study can help establish efficient and automatic analysis for accurate identification of MPs as well as an intuitive exhibition of spectral changes on environmental exposure.

An optimized acidic digestion for the isolation of microplastics from biota-rich samples and cellulose acetate matrices

Plastic pollution is a growing concern. To analyze plastics in environmental samples, plastics need to be isolated. We present an acidic/oxidative method optimized to preserve plastics while digesting synthetic cellulose acetate and a range of organics encountered in environmental samples. Cellulose acetate was chosen for optimization as it can be purchased as a reference material, can co-occur with plastics in environmental samples and, if it can be completely digested, is a potential filter material for the collection of nano- and micro-plastics from natural waters. Other forms of particulate organic matter (POM) were chosen to provide a range of chemistries that might alter digestion efficiency and due to the interest in the community of isolating plastics from samples where these organics occur. For instance, microalgal POM occurs in lake and ocean waters, riverine POM in rivers, and inclusion of tuna provides a test for the suitability of the method for isolating plastics from animal tissues. The method is a one-pot overnight (16-18 h) digestion in 5 M nitric acid with 0.3 M sodium persulfate heated to 80 °C. The method provides quantitative removal of cellulose acetate (exceeding detection limits), near quantitative removal of microalgal POM and Albacore tuna tissue (>99%), but only 86% of urban river POM, all while retaining >99% by mass of C-C bonded polymers polyethylene, polypropylene, and polystyrene and >96% by mass of polyethylene terephthalate. Fourier transform infrared spectroscopy (FT-IR) and %-C content analysis confirmed plastic polymer stability during digestion. However, some additives in appear susceptible to digestion with FT-IR results indicating the loss of N,N'-ethylenebis(stearamide) from polyethylene. This method provides a simpler and more effective method than many in the literature. We present recommendations for the application of this method, as well as limitations and areas for future improvement.

Characteristics and behaviors of microplastics undergoing photoaging and Advanced Oxidation Processes (AOPs) initiated aging

The fact that 94% of microplastics (MPs) ubiquitous in the environment are subject to natural weathering makes the aging study currently a research hotspot. This review summarized the physicochemical characteristics of MPs undergoing natural and artificial aging and evaluated current analytical methods used in aging studies. Besides, the differences in photoaging and aging induced by advanced oxidation processes (AOPs) were discussed, leading to a conclusion that AOPs composed of oxidant and ultraviolet (UV) irradiation can better facilitate the alteration of MPs compared to UV irradiation alone. In addition, the environmental behavior of aged MPs was outlined and their adsorption properties for organics and metals were highlighted as a result of combined effects of hydrophobic, π-π, diffusion, and hydrogen bond interaction. Furthermore, the mechanisms of photoaging and AOPs-initiated aging were analyzed, mainly the role of reactive oxygen species (ROS) and environmentally persistent free radicals (EPFRs). Finally, the applications of two-dimensional correlation spectroscopy (2D-COS) and three-dimensional fluorescence spectra using excitation emission matrix-parallel factor analysis (EEM-PARAFAC) were discussed for the aging process analysis. This overview plays an important role in explaining the aging characteristics of MPs and provides a theoretical foundation for further investigations into their toxicity and removal.

The generation of environmentally persistent free radicals on photoaged microbeads from cosmetics enhances the toxicity via oxidative stress

Microbeads used in personal care products have been one of the important sources of microplastics (MPs), and little has been reported on their environmental behaviors and health risks. The characteristics of environmentally persistent free radicals (EPFRs) and the toxicity assessment of MPs (environmentally relevant concentrations) from cosmetics during photoaging remains largely unknown. In this study, the formation of EPFRs on polyethylene (PE) microbeads from facial scrubs under light irradiation and their toxicity were investigated using C. elegans as a model organism. The results suggested that light irradiation induced the generation of EPFRs, which accelerates the aging process and alters the physicochemical properties of PE microbeads. Acute exposure to PE (1 mg/L) at photoaged times of 45-60 d significantly decreased the physiological indicators (e.g., head thrashes, body bends, and brood size). The oxidative stress response and stress-related gene expression were also enhanced in nematodes. The addition of N-acetyl-l-cysteine induced significant inhibition of toxicity and oxidative stress in nematodes exposed to 45-60 d of photoaged PE. The Pearson correlation results showed that the concentration of EPFRs was significantly correlated with physiological indicators, oxidative stress, and related-genes expression in nematodes. The data confirmed that the generation of EPFRs combined with heavy metals and organics contributed to toxicity induced by photoaged PE, and oxidative stress might be involved in regulating adverse effects in C. elegans. The study provides new insight into the potential risks of microbeads released into the environment during photoaging. The findings also highlight the necessity for considering the role of EPFRs formation in evaluating the impacts of microbeads.

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

Microplastics (MPs) are ubiquitous in the environment, of which 94 % undergo the aging process. Accelerated aging induced by advanced oxidation processes (AOPs) is significant in explaining the formation pathway of secondary MPs and enables possible mineralization. In this study, ozonation coupled with hydrogen peroxide (O₃/H₂O₂), a type of AOPs, was applied for the aging of MPs (polyethylene, PE). Physiochemical properties of aged PE MPs were analyzed through scanning electron microscope, Fourier-transform infrared spectroscopy-attenuated total reflection, and X-ray photoelectron spectroscopy. The mechanism regarding the contribution of reactive oxygen species (•OH) was determined using chemical probe (p-chlorobenzoic acid) and quencher (tert-butanol). Possible transformation pathways were modeled via two-dimensional correlation spectroscopy. Mineralization of MPs, associated with aging was also studied, with the percentage of PE degradation determined by mass loss. Our results confirmed that ozonation promoted fragmentation of PE, with 20 mM H₂O₂ facilitating the production of •OH. The growth of oxygen-containing functional groups on the surface of PE was consistent with the alteration of the oxygen-to‑carbon atom ratio, revealing the formation of CO, CO, and C-O-C. The enhanced adsorption property of aged PE for triclosan was due to the increased specific surface area and negative charges on the surface. Moreover, the percentage of PE degradation was higher at lower concentrations, and the mass loss reached 32.56 % at a PE concentration of 0.05 g/L after 8-h ozonation. These results contribute to revealing the long-term aging behavior of MPs and providing significant guidance for employing AOPs to achieve efficient removal.

Ageing characteristics and microplastic release behavior from rainwater facilities under ROS oxidation

Reactive oxygen species (ROS) are ubiquitous in the natural environment that are generated by chemical or biochemical processes. Plastic rainwater facilities, as an important part of modern rainwater systems, are inevitably deteriorated by ROS. As a consequence, microplastics will be released. However, information on how ROS affect the ageing characteristics of plastic rainwater facilities and the subsequent microplastic release behavior is still insufficient. To address this knowledge gap, Fenton reagents were used to simulate the reactive oxygen species (ROS) induced ageing process of three typical plastic rainwater components (rainwater pipe, made of polyvinyl chloride; modular storage tank, made of polypropylene; inspection well, made of high-density polyethylene) and the subsequent microplastic release behavior. After 6 days of Fenton ageing, an increase in sharpness, holes, and fractures on the rainwater facilities' surface was observed by scanning electron microscope (SEM). The functional group changes on the rainwater facilities' surface were analyzed by Fourier transform infrared spectrometer (FTIR) and two-dimensional correlation spectroscopy (2D-COS) and compared with the results of X-ray photoelectron spectroscopy (XPS). During the ageing process, oxygen-containing functional groups were generated and the carbon chains were broken, which promoted peeling and the release of microplastics. The amount of released microplastics (ranging from 158 to 6617 items/g facility) varied with the type of rainwater facilities, and the order was modular storage tank > inspection well > rainwater pipe. The release amount increased with ageing time, and a significant linear relationship was observed (r² > 0.91). The particle size of the released microplastics ranged from 2 to 1362 μm, among which 10-30 μm particles accounted for the largest proportion (62.7 %). The release amount increased exponentially with decreasing particle size (r² > 0.71). This study indicates that large amounts of microplastics could be released from plastic rainwater components during ROS-induced ageing.

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.

Assessment of relationship between aging and contaminant-carryover for different filter layer of surgical mask under urban environmental stressors

Abundant disposable surgical masks (SMs) remain in the environment and continue to age under urban environmental stressors. This study aimed to investigate the aging characteristics of SMs and the effect of different aged layers of SMs on phenanthrene (PHE), tylosin (TYL), and sulfamethazine (SMT) under two different urban environmental stressors (UV and ozone). The results show that UV exposure causes more severe aging of the SM layers than ozone. The middle layer, made of melt-brown fabric, has displayed the highest degree of aging due to its smaller diameter and mechanical strength. The two-dimensional correlation spectroscopy (2D-COS) analysis reveals the different aging sequences of functional groups and three layers in aged SMs under the two urban environmental stressors. Whether the SMs are aged or not, the adsorptions of three organic pollutants on SMs are positively correlated with the octanol-water partition coefficient. Furthermore, except for the dominant hydrophobic interaction, aged SMs can promote the adsorption of three organic pollutants by accessory interactions (hydrogen bonding and partition), depending on their structures. These findings highlight the environmental effects of new microplastic (MP) sources and coexisting pollutants under the influence of COVID-19, which is helpful in accurately evaluating the biological toxicity of SMs.

In situ degradation of low-density polyethylene film in irrigation maize field: Thickness-dependent effect

Thickness of low-density polyethylene (LDPE) film might determine its mechanical strength, clean production and soil health. Yet, this issue is little understood. In situ aging effects were evaluated in LDPE films with the thickness of 0.006 mm, 0.008 mm, 0.010 mm and 0.015 mm in maize field. The data showed that maximum tensile force (TFmax), maximum tensile strength (TSmax) and elongation at break (EAB) were massively lowered with increasing thickness after aging. The greatest and lowest reduction magnitude of EAB was 27.6 % and 11.2 % in 0.006 mm and 0.015 mm films respectively. Also, the melting point (Tm) and crystallinity (Xc) under Differential Scanning Calorimeter (DSC) tended to decline with the increasing thickness. Moreover, the peak intensity of crystalline regions tended to transfer and concentrate on the amorphous regions, and such tendency became more pronounced in the thin films. Interestingly, there existed a pronounced distinct thickness-dependent effects on soil bulk density (SBD) and soil water-stable aggregate proportion. Thick plastic film mulching increased SBD but reduced the proportion of macroaggregates (mainly referred to 0.015 mm and 0.010 mm). In addition, thick film mulching slightly reduced the levels of soil organic carbon (SOC) and total nitrogen (TN), but significantly promoted the contents of soil labile C and N. Particularly, it significantly promoted above- & under-ground biomass of maize across two growing seasons (p < 0.05). To sum up, thickening LDPE film may act as a promising solution to improve LDPE film residue recycling, while benefiting for higher productivity. However, thick film mulching may cause a certain adverse impact on soil structure, and further investigations would be needed in the future.

Impact of coastal wastewater treatment plants on microplastic pollution in surface seawater and ecological risk assessment

This study aims to understand the influence of wastewater treatment plant discharge on the microplastic status in the surface seawater of Istanbul. For this purpose, for the first time, the distribution, composition, and ecological risk of microplastics at nine sampling stations on the southern coast of Istanbul, Marmara, were investigated at monthly intervals over a one-year period. The results showed that the microplastic abundance ranged from 0 to over 1000 particles per liter. Fibers were the dominant form at all stations. Microplastics 249-100 μm were the dominant size, and transparency was the color most found at all stations. Polyethylene and ethylene-vinyl acetate were the major types of microplastics, accounting for 50% overall. The pollution load index revealed that over 70% of sampling stations were at hazard level I. However, the hazardous index was categorized as level III with a value of 662.3 due to the presence of the most hazardous polymer named polyurethane. Further investigations into the risk assessment of MP can reveal crucial knowledge for understanding the microplastic cycle.

UV and chemical aging alter the adsorption behavior of microplastics for tetracycline

This study evaluates the "vector" effects of different microplastics (MPs) on coexisting pollutants. The adsorption of tetracycline was studied on biodegradable plastics poly(butylene adipate-co-terephthalate) (PBAT) and non-biodegradable plastics polystyrene (PS), polypropylene (PP), and polyethylene (PE) after UV aging and chemical aging. The physicochemical properties of PBAT changed more obviously after UV radiation and chemical aging comparing to PS, PP and PE. Pores and cracks appear on the surface of aged PBAT. The crystallinity increased from 29.2% to 52.62%. In adsorption experiments, pristine and aged PBAT had strong vector effects on the adsorption of tetracycline than PS, PP and PE. The adsorption capacity of tetracycline on PBAT was increased from 0.7980 mg g^-1 to 1.2669 mg g^-1 after chemical aging. The adsorption mechanism indicated that electrostatic interactions and hydrogen bonds contribute to the adsorption process. In addition, for the adsorption of tetracycline on PS, π-π interaction was the main cause, and the adsorption mechanism was not considerably changed by aging. In conclusion, this study demonstrates that biodegradable plastics have substantial vector effect on coexisting pollutants at the end of their life cycle, this contributes to assessment of the risk from microplastic pollution.

Abiotic Long-Term Simulation of Microplastic Weathering Pathways under Different Aqueous Conditions

Microplastics (MPs) are one of the most abundant and widespread anthropogenic pollutants worldwide. In addition to the global spread and threats of plastic to native species by carrying toxic substances, its slow degradation rate and resulting long retention time in the environment constitute a problem that is still poorly understood. In this study, five of the most manufactured plastic types were weathered under simulated beach conditions for 18 months in freshwater, brackish water, and seawater. Those included polyethylene (PE), polypropylene (PP), polystyrene (PS), polyethylene terephthalate (PET), and polyvinyl chloride (PVC). PP was the first polymer type that fragmented after 9 months of weathering and influenced the pH of the surrounding water. Molecular surface changes were detected for all polymers, just after the first week. Hydroxyl bonds were one of the first groups incorporated into the polymers, weakening 2-3 weeks later. Carbonyl groups were also measured early, but with significantly different developments with time between the polymer types. Differences in degradation rates were proven between the water media, with the fastest degradation in seawater compared to brackish water and freshwater for PE and PP. These results are consistent with previous findings on MPs aged under environmental conditions and provide initial long-term observations of MP degradation pathways under simulated environmental conditions. These findings are valuable for assessing the fate and hazards of MPs in aquatic systems.

Physicochemical and biological ageing processes of (micro)plastics in the environment: a multi-tiered study on polyethylene

Pollution by plastic and microplastic impacts the environment globally. Knowledge on the ageing mechanisms of plastics in natural settings is needed to understand their environmental fate and their reactivity in the ecosystems. Accordingly, the study of ageing processes is gaining focus in the context of the environmental sciences. However, laboratory-based experimental research has typically assessed individual ageing processes, limiting environmental applicability. In this study, we propose a multi-tiered approach to study the environmental ageing of polyethylene plastic fragments focusing on the combined assessment of physical and biological processes in sequence. The ageing protocol included ultraviolet irradiation in air and in a range of water solutions, followed by a biofouling test. Changes in surface characteristics were assessed by Fourier transform infrared spectroscopy, scanning electron microscopy, and water contact angle. UV radiation both in air and water caused a significant increase in the density of oxidized groups (i.e., hydroxyl and carbonyl) on the plastic surface, whereby water solution chemistry influenced the process both by modulating surface oxidation and morphology. Biofouling, too, was a strong determinant of surface alterations, regardless of the prior irradiation treatments. All biofouled samples present (i) specific infrared bands of new surface functional groups (e.g., amides and polysaccharides), (ii) a further increase in hydroxyl and carbonyl groups, (iii) the diffuse presence of algal biofilm on the plastic surface, and (iv) a significant decrease in surface hydrophobicity. This suggests that biological-driven alterations are not affected by the level of physicochemical ageing and may represent, in real settings, the main driver of alteration of both weathered and pristine plastics. This work highlights the potentially pivotal role of biofouling as the main process of plastic ageing, providing useful technical insights for future experimental works. These results also confirm that a multi-tiered laboratory approach permits a realistic simulation of plastic environmental ageing in controlled conditions.

Can aged microplastics be transport vectors for organic micropollutants? - Sorption and phytotoxicity tests

Microplastics have been investigated over the last decade as potential transport vectors for other pollutants. However, the specific role of plastic aging, in which plastics change their characteristics over time when exposed to environmental agents, has been overlooked. Therefore, sorption experiments were herein conducted using virgin and aged (by ozone treatment or rooftop weathering) microplastic particles of LDPE - low-density polyethylene, PET - poly(ethylene terephthalate), or uPVC - unplasticized poly(vinyl chloride). The organic micropollutants (OMPs) selected as sorbates comprise a diversified group of priority substances and contaminants of emerging concern, including pharmaceutical substances (florfenicol, trimethoprim, diclofenac, tramadol, citalopram, venlafaxine) and pesticides (alachlor, clofibric acid, diuron, pentachlorophenol), analyzed at trace concentrations (each ≤100 μg L^-1). Sorption kinetics and equilibrium isotherms were obtained, as well as the confirmation that the aging degree of microplastics plays a major role in their sorption capacities. The results show an increased sorption of several OMPs on aged microplastics when compared to pristine samples, i.e. the sorption capacity increasing from one or two sorbed substances (maximum 3 μg g^-1 per sorbate) up to nine after aging (maximum 10 μg g^-1 per sorbate). The extent of sorption depends on the OMP, polymer and the effectiveness of the aging treatment. The modifications (e.g. in the chemical structure) between virgin and aged microplastics were linked to the increased sorption capacity of certain OMPs, allowing to better understand the different affinities observed. Additionally, phytotoxicity tests were performed to evaluate the mobility of the OMPs sorbed on the microplastics and the potential effects (on germination and early growth) of the combo on two species of plants (Lepidium sativum and Sinapis alba). These tests suggest low or no phytotoxicity effect under the conditions tested but indicate a need for further research on the behavior of microplastics on soil-plant systems.

Composition identification and UV-C irradiation growth inhibition effect of green shading on the greenhouse cover

Greenhouse cover pollution with green shading composed of dust, microalgae and bacteria is a severe problem in tropical areas. The shading results in lower greenhouse indoor light intensity reducing the yield and quality of protected horticulture crops. However, few studies have focused on environmentally efficient ways to remove green shading to increase greenhouse production. In this study, five purified microalgae were isolated from the green shading of three greenhouse roofs and were identified using morphological and molecular assessments. The effects of Ultraviolet-C irradiation (UV-C, 254 nm) at doses of 100, 200 and 300 mJ cm^-2 on the growth of GLY-1 microalgae were investigated. The results indicated that five purified microalgae all appeared to belong to the genus of Jaagichlorella. The purified microalgae cell density and chlorophyll content decreased respectively by 26.89-74.44 % and 42.02-77.31 % at 1-3 d after UV-C treatment with doses ranging from 100 to 300 mJ cm^-2. The inhibition of the growth rate of microalgae was significantly positively correlated with the UV-C irradiation dose and significantly negatively correlated with treatment time. In summary, UV-C irradiation treatment at 300 mJ cm^-2 and 3 d could substantially inhibit microalgae growth in green shading on greenhouse covers. UV-C irradiation could be an effective method for solving the problem of greenhouse cover pollution with microalgae.

A comparative study on the distribution behavior of microplastics through FT-IR analysis on different land uses in agricultural soils

Plastic materials have been variously exposed to arable land for decades through soil mulching, plastic housing, and sewage sludge composting. Their mechanical abrasion and biochemical degradation induce the proliferation of myriad microplastics that can further be broken into smaller nano-sized pieces that can be further accumulated in living organisms (including soil invertebrates, fruits, and vegetables); they can also be widely dispersed in neighboring environments. Despite the intensive use of plastics in agriculture, little is known about their origin of occurrence and environmental fate, especially with a size below 100 μm. Therefore, in this study, microplastics with a size in the range of 20-2,000 μm were investigated in soil samples obtained from three different conditions of land uses: tilled with plastic mulch, bare ground (i.e., uncultivated land), and in between the greenhouses of the farmland D located in Namyangju-si, Gyeonggi-do, Republic of Korea. They were primarily identified using Fourier transform infrared (FT-IR) spectroscopy coupled with a microscope. Prior to performing the analysis, microplastic extraction from the soil samples was validated using standardized high-density polyethylene (HDPE) microplastics of various sizes ranging from 20 to 500 μm. As a result, the number of microplastics was estimated to be (241 ± 52), (195 ± 37), and (306 ± 56) particles per kg of dry soil in tillage, bare ground, and in between greenhouses, respectively. They consist of polyethylene (PE), polypropylene (PP), and poly(ethylene terephthalate) (PET), which are the basic constituents of commonly used agricultural products. The particle size distribution depends on the type of plastic, the time elapsed since their usage, and the degree and duration of environmental exposure; the plastic particle sizes were smaller in tillage and around the greenhouses since agricultural films have been weathered for a long time, whereas those with relatively large sizes were found in the uncultivated.

Insights into the degradation of microplastics by Fenton oxidation: From surface modification to mineralization

This work aims at evaluating the fate of microplastics (MPs) along Fenton oxidation. For such goal, realistic MPs (150-250 μm) of five representative polymer types (PET, PE, PVC, PP and EPS) were obtained from commercial plastic products by cryogenic milling. Experiments (7.5 h) were performed under relatively severe operating conditions: T = 80 °C; pH₀ = 3; [H₂O₂]₀ = 1000 mgL^-1 (15 doses, 1 every 0.5 h); [Fe³⁺]₀ = 10 mgL^-1 (5 doses, 1 every 1.5 h). Slight MPs weight losses (∼10%) were achieved after Fenton oxidation regardless the MP nature. Nevertheless, oxidation yield clearly increased with decreasing the particle size given their higher exposed surface area (up to 20% weight loss with 20-50 μm EPS MPs). Clearly, MPs suffered important changes in their surface due to the introduction of oxygenated groups, which made them more acidic and hydrophilic. Furthermore, MPs progressively reduced their size. In fact, they can be completely oxidized to CO₂, as demonstrated in the oxidation of PS nanoplastics (140 nm), where 70% mineralization was achieved. The nature of the plastic particles had a relevant impact on its overall oxidation, being more prone to be oxidized those polymers which contain aromatic rings in their structures (EPS and PET) compared to those formed by alkane chains (PE, PP and PVC). In the latter, the presence of substituents also reduced their oxidation potential. Remarkably, possible leachates released along reaction were more quickly oxidized than the MPs/NPs, so it can be assumed that these dissolved compounds would be completely removed once the solid particles are eliminated. Notably, the leachates obtained upon MPs oxidation were more biodegradable than the released from the fresh solids. All this knowledge is crucial for the understanding of MPs oxidation by the Fenton process and opens the door for the design and optimization of this technology either for water treatment or for analytical purposes (MPs isolation).

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.