Photoaging process and mechanism of four commonly commercial microplastics

The silent invasion of microplastics polyvinyl chloride and polyethylene terephthalate: Potential impact on osteoporosis

BACKGROUND

The relationship between the environment and diseases is a crucial and complex topic that has garnered significant attention in recent years. In our study, we also follow the thread and explore the correlation between microplastics (MPs) and osteoporosis (OP).

METHODS AND RESULTS

We found that MPs were detected in the blood samples of nearly all participants. Moreover, It was compelling that PVC and PET emerged as the most common MP polymers in our study. A verification process was conducted comparing the clinical data with the results of MPs detection. This analysis revealed a significant exposure risk to MPs from sources such as bottled water, take-out containers. Through molecular biology techniques, we confirmed that MPs have a significant toxic effect on osteoblasts and associated with abnormal gene expression.

CONCLUSION

MPs may be considered to have a potential correlation with the progression of OP.

Photoaged polystyrene nanoplastics induce perturbation of glucose metabolism in HepG2 cells via oxidative stress

MICRO: & nano-plastics (MNPs) have been considered an emerging persistent pollutant in the environment. Most of the works focus on the potential toxicity of pristine, rather than photoaged, MNPs, let alone the underlying mechanisms of toxicity. To address this gap, we exposed human liver cancer cells (HepG2) to polystyrene nanoplastics (PS-NPs) with varying degrees of photodegradation, including pristine PS-NPs and photoaged PS-NPs irradiated with UV for 8 days (short-term) and 32 days (long-term).The surface characteristics of PS-NPs exhibited a significant alteration as characterized by SEM, FTIR, XPS, and Zetasizer. Exposure to PS-NPs affected cell viability, ion transport capacity and glucose metabolism, and also induced oxidative stress. Photoaged PS-NPs posed relatively higher impacts than pristine ones on HepG2 cells. Long-term photoaged PS-NPs induced the glucose metabolic disorders in a dose-dependent manner, while pristine and short-term photoaged PS-NPs induced the metabolic disorders only at high concentrations. The severe cellular metabolic toxicity of PS-NPs was attributed to the changes in physicochemical properties induced by UV irradiation, such as the production of oxygen-containing functional groups (hydroxyl, carboxyl, and carbonyl groups). Taken together, the long-term photoaged PS-NPs suppressed more than 10% of cell vitality compared to the pristine ones, and disrupted the glucose metabolism in HepG2 cells, particularly gene expression associated with glucose homeostasis.

Inorganic Additives Induce More Small-Sized Microplastics Releasing from Medical Face Masks

Although previous studies have extensively explored the release of microplastics from masks, the specific influence of inorganic additives on microplastic emissions has remained unidentified. Herein, we performed a comparative analysis of medical face masks (MFMs) with calcium carbonate (CaCO3) additives against those devoid of CaCO3 to understand their roles in microplastic release. Briefly, our investigation employed surface-enhanced Raman spectroscopy (SERS) to examine micro- and nanoplastic release, while the stereoscopic characterization of mixing states of additives in microplastic was accomplished through a simulated Raman scattering (SRS). We also pioneered a three-dimensional imaging (3D imaging) method for investigating the internal aging of plastic using SRS, which clearly revealed the link between inorganic additives inside polymers and photoaging. We found that inorganic additives substantially accelerate the photoaging of the plastic materials through multiple pathways and induce more small-sized microplastics. Follow-up radical quenching experiments confirmed carbonate radicals as the main cause of this phenomenon. Our research exposes the hazardous potential of inorganic additives in masks to amplify the emission of microplastics.

Aging of textile-based microfibers in both air and water environments

Textile-based microfibers (MFs) are a predominant source of global microplastics (MPs) pollution. Yet, less is known about the aging of textile-based MFs. This study explored the aging behavior of textile-based polyethylene terephthalate (PET) MFs with white (without pigment) and black (with carbon black as pigment) colors in both air and water environments. Ultraviolet (UV) and plasma aging were carried out to simulate the short- and long-term aging of MFs. Results indicated that white MFs exhibited more pronounced surface changes, formed more -OH bonds, and showed a higher increase in the oxygen-to-carbon(O/C) ratio than black MFs in both air and water environments. For example, in the air environment, the percentage increase of O/C for white MFs was 24.43 %, compared to 16.4 % for black MFs during plasma aging process. Further investigations were conducted to elucidate the mechanisms driving higher degree of aging of white MFs. It was verified that the carbon black in the black MFs could enhance their tensile strength and hardness, thereby countering the aging process. Furthermore, excitation-emission-matrix (EEM) analysis of dissolved organic matter (DOM) released from MFs, combined with the detection of reactive oxygen species (ROS) generated by MFs in the water environment, confirmed that carbon black functioned as an effective anti-aging additive. Its protective role, attributed to UV and plasma shielding and reactive radical-trapping mechanisms, led to higher aging degree in white MFs compared to black MFs. These findings provide insights into predicting the aging behaviors of textile-based MFs with different colors in air and water environments.

Photodegradation Controls of Potential Toxicity of Secondary Sunscreen-Derived Microplastics and Associated Leachates

The escalating environmental concern over secondary microplastics (SMPs) stems from their physicochemical evolution from primary microplastics (PMPs), yet the contribution of varying physicochemical transformations to the ultimate environmental risks remains unknown. In this study, a photomechanical degradation process was employed to convert the primary sunscreen-derived microplastics (SDMPs) into secondary SDMPs. While mechanical degradation caused physical fragmentation, photodegradation induced both physical and chemical alterations, introducing surface oxidation, chemical bond scission, and cross-linking to the secondary SDMPs. Employing a combination of alkaline digestion and pyrolysis GC-MS techniques, it was observed that both physical fragmentation and photooxidation led to heightened intracellular sequestration of MPs. Although the bioaccumulated SDMPs could be indicated by the enlarged lysosomes and fragmented mitochondria, toxicity of secondary SDMPs at the cellular level was primarily driven by chemical transformations post-photodegradation. A nontargeted analysis employing high-resolution mass spectrometry identified 46 plastic-associated compounds in the leachate, with photodegradation-induced chemical transformations playing a crucial role in the dissociation of hydrophobic additives and oxidative conversion of leached compounds. The toxicity of the leachate was exacerbated by photodegradation, with mitochondrial fragmentation serving as the primary subcellular biomarker, indicative of leachate toxicity. This study elucidates the pivotal role of photodegradation in augmenting the cytotoxicity of secondary SDMPs, shedding light on the intricate interplay between physicochemical transformations and environmental risks.

Polyethylene fragments in Argentinean horticultural soils: Environmental transformation to a composite material

Polyethylene macro, meso, and microplastics collected from horticultural soils in Moreno, Buenos Aires, Argentina, were studied to understand their physicochemical transformations after environmental exposure. These plastics contained mechanically stable compounds of Si (1.2-4.0 %), Al (0.91-1.5 %), and Fe (0.64-2.2 %), likely due to soil clay particles adhering to the plastic. The plastics' surfaces were oxidized, with high carbonyl (0.05-0.23) and hydroxyl (1.6-2.7) indices. Weathering led to thinner, rougher surfaces with increased contact angles due to the presence of clay and polar organic groups. Scanning electron microscopy (SEM) showed cracks and particles on the surfaces, while atomic force microscopy (AFM) revealed roughness increased from 0.44 nm in pristine polyethylene (p-PE) to 1.60 nm in weathered samples. Heavy metal sorption experiments showed that the weathered plastics absorbed significantly more Ni2+ and Pb2+ than unweathered PE (4.5 times for Ni2+ and 11 times for Pb2+). After removing clay with hydrofluoric acid, the plastics still retained the same amount of these metals, suggesting that the sorption occurred mainly on the modified plastic surface rather than the clay. Arsenate tests indicated that the plastics selectively absorbed cationic metals. This study also developed a simple ATR-FTIR method for quantifying silicate on polyethylene surfaces, contributing to an understanding of soil-derived particle interactions with plastic in agricultural settings.

Polypropylene microplastics triggered mouse kidney lipidome reprogramming combined with ROS stress as revealed by lipidomics and Raman biospectra

Microplastics intrigue kidney toxicity such as mitochondrial dysfunction and inflammation promotion. However, as an organ relying heavily on fatty acid oxidation, how microplastics influence kidney lipidomes remain unclear. Hence, we performed Raman spectra and multidimensional mass spectrometry-based shotgun lipidomics to decode kidney lipidomics landscape under polypropylene microplastics exposure. Kidney functions and cellular redox homeostasis were remarkably disturbed as revealed by levels of biochemical renal function markers, malonaldehyde, hydrogen peroxide and antioxidants. Ultrastructure alterations including the foot process fusion implied the kidney injury associated with lipidomic changes. Raman spectra successfully further confirmed the cellular change of reactive oxygen species and lipid disorders. Lipidomics showed that polypropylene microplastics caused abnormal lipidome and irregular exchange by remodeling triglycerides and phospholipids. Genes involved in lipid metabolism such as Fads1 and Elovl5 exhibited highly diversified expression profiles responding to polypropylene microplastics stress and possessed significant correlations with ROS indicators. These results explained ultrastructure alterations and aggravation of kidney injuries. Our work revealed polypropylene microplastics inducing lipidomic detriment in mouse kidney by Raman spectra and lipidomics firstly, elucidating the significances of lipidomic remodeling coupled with ROS stress in the kidney damages. The findings provided reliable evidence on the health risks of polypropylene microplastics in kidney.

Adsorption behavior of Cu(II) on UV-aged polyethylene terephthalate and polypropylene microplastics in aqueous solution

Plastics are widely used across various applications from packing to commercial products. Once discarded, they were subjected to environmental stresses, causing them to degrade into microplastics (MPs). These small, invisible pollutants pose a significant threat to aquatic ecosystems, gradually compromising the resilience and vitality of the natural environment. Moreover, MPs will act as carriers for other contaminants, for example, heavy metals (HMs). Although many studies have explored MPs and HMs independently, their combined behavior and interactions remain poorly understood. Understanding these interactions is increasingly important given rising pollution levels. MP formation and adsorption behavior are heavily influenced by factors such as UV aging, which remains unclear. In this study, both virgin and UV-aged MPs specifically PET and PP (the most widely used plastics globally) were examined in their interactions with copper (Cu2+) solutions. Surface analysis techniques such as FTIR, SEM, XRD, and AAS were employed to compare the virgin and UV-aged MPs. The results revealed that UV-aged MPs exhibited high adsorption capacities for HMs compared to virgin MPs, which can be attributed to increased pore volume and oxidative degradation. Adsorption capacity differences at various concentrations showed up to a 20% increase, with UV-aged PET MPs displaying capacities ranging from 0.6 to 3.54 mg/g. Similarly, UV-aged PP MPs showed a 15% increase in adsorption capacity ranging from 1.51 to 4.25 mg/g. The present study provided the significant evidence on the behavior of MPs adsorption and underscores the need for further research on the long-term environmental impacts of aged MPs and their interactions with pollutants.

Female zebrafish are more affected than males under polystyrene microplastics exposure

Microplastics are ubiquitous in freshwater and can be absorbed into fish skin and gills, accumulate in the gut, and be transported to other tissues, thus posing a risk to fish health. Further studies are needed, however, to investigate effects such as endocrine disruption and multi-tissue toxicity. In this study, zebrafish were exposed to polystyrene (PS) microplastics and health-related indicators were measured, including skin mucus, gut damage, oxidative stress, stable isotope composition and reproduction as well as an assessment of changes to metabolites using a metabolomics approach. Results showed that concentrations of PS microplastics were higher in gills than those in the gut. Minimal impact to immunoglobulin M level and lysozyme activity in mucus indicated, however, that microplastic toxicity primarily stemmed from ingestion rather than disruption of skin mucus immunity. Female zebrafish were more affected by PS microplastics. Gut microbiota dysbiosis was induced, especially in females. Significant alterations in pathways associated with lipid and energy metabolism were observed in the liver of female fish. PS microplastics also induced sex steroid hormone disorder and reduced female egg production, possibly linked to the alteration of gut microbiota and hepatic metabolism. Combined, these results highlight the gender-specific toxicity of PS microplastics to zebrafish health, potentially harming their population.

Microplastics in agricultural soil: Unveiling their role in shaping soil properties and driving greenhouse gas emissions

Microplastics (MPs) contamination is pervasive in agricultural soils, significantly influencing carbon and nitrogen biogeochemical cycles and altering greenhouse gas (GHG) fluxes. This review examines the sources, status, mechanisms, and ecological consequences of MPs pollution in agricultural soils, with a focus on how MPs modified soil physicochemical properties and microbial gene expression, ultimately impacting GHG emissions. MPs were found to reduce soil water retention, decreasing soil respiration and increasing emissions of CO2, CH₄, and N2O. They also enhanced soil aggregate stability and influenced soil organic carbon (SOC) sequestration, contributing further to GHG emissions. MPs-induced increases in soil pH were associated with suppressed CH₄ and N2O emissions, whereas the abundance of genes encoding enzymes for cellulose and lignin decomposition (e.g., abfA and mnp) stimulated enzyme activity, intensifying N2O release. Additionally, a reduced soil C/N ratio promoted denitrification processes. Changes in microbial communities, including increases in Actinomycetes and Proteobacteria, were observed, with a rise in genes associated with carbon cycling (abfA, manB, xylA) and nitrification-denitrification (nifH, amoA, nirS, nirK), further exacerbating CO2 and N2O emissions. This review provides valuable insights into the complex roles of MPs in GHG dynamics in agricultural soils, offering perspectives for improving environmental management strategies.

Mechanistic insights into the co-transport of microplastic degradation products in saturated porous media: The key role of microplastics-derived DOM

Microplastic-derived dissolved organic matter (MP-DOM) forms from the aging of microplastics (MPs), but the co-transport behavior of MP-DOM and aged MPs (AMPs) remains poorly understood. This study investigates the co-transport of AMPs and MP-DOM generated from original MPs (OMPs) over a wide range of environmentally relevant conditions. The transport of AMPs and MP-DOM changes as the degree of aging increases, specifically related to changes in their physicochemical characteristics. Results showed that the order of migration ability was MP-DOM > AMPs > OMPs under almost all tested conditions. The change of hydrophobicity of MP-DOM and AMPs, as well as small molecular weight of MP-DOM, was primarily responsible for this order. The role of MP-DOM as a degradation product in the co-transport process is notably significant under various environmental conditions because of its high mobility and organic carbon fraction within the system. Furthermore, it is important to note that MP-DOM affected the transport of MPs through a combination of positive and negative effects. Key mechanisms include electrostatic repulsion caused by protonation reactions triggered by the acidic pH of MP-DOM, steric hindrance, and competition for retention sites on media surfaces. This study contributes to a deeper understanding of the transformation and fate of MPs in complex environmental systems.

Molecular-level insights into the leachates released from ultraviolet-aged biodegradable and conventional commercial microplastics and their mechanism of toxicity toward Chlorella pyrenoidosa

Understanding the harmful effects of microplastics (MPs) and their derivatives is a priority in environmental study. However, the characteristics and toxic effects of leachates from MPs at the molecular-level remain unclear. Herein, two conventional commercial MPs [polystyrene (PS) and polyethylene (PE)] and two biodegradable commercial MPs [polylactic acid (PLA) and polybutylene adipate-co-terephthalate/PLA (PBAT/PLA)] were subjected to leaching under ultraviolet-irradiation, and their leachates were investigated. The results showed that the surface morphology of MPs increased in roughness after ultraviolet-irradiation treatment, especially for biodegradable MPs, meanwhile, the particle size of four MPs decreased in various degrees. The biodegradable MPs released several times more dissolved organic matter (DOM) and nano-plastic particles than conventional MPs. Fourier transform ion cyclotron resonance mass spectrometry revealed that lignin-like substances were the predominant component of MP-DOM, followed by protein- and tannin-like substances. The molecular composition and characteristics of the DOM varied significantly among MPs. Transcriptomic analysis showed that 737 and 1259 genes, respectively, were differentially expressed in Chlorella pyrenoidosa in PLA- and PBAT/PLA-MP leachate-treated groups compared with controls, more than in the PS (352) and PE (355) groups. These findings, verified by physiological and histopathological analyses, indicate that the leachates from the biodegradable MPs induced more damage to Chlorella pyrenoidosa than those from the conventional MPs. This is mainly attributed to far more DOM and nano-plastic particles containing in leachates of biodegradable MPs than these of conventional MPs. This study deepens our comprehension of the potential hazards of MP-leachates, and promotes the prudent use and disposal of plastic products.

Modeling the temporal evolution of plastic film microplastics in soil using a backpropagation neural network

Plastic films are a crucial aspect of agricultural production in China, as well as a key source of microplastics in farmland. However, research into the environmental behavior of microplastics derived from polyethylene (PE) and biodegradable plastic films such as polybutylene adipate-co-terephthalate (PBAT) is limited by inadequate knowledge of their evolution and fate in soil. Therefore, we conducted controlled soil incubation experiments using new and aged microplastics derived from prepared PE and PBAT plastic films to determine their temporal evolution characteristics in soil. The results indicated that PBAT microplastics exhibited more pronounced changes in abundance, size, and shape over time than PE microplastics. Notably, the magnitude and timing of changes in newly introduced PBAT microplastics were consistently delayed relative to those of aged microplastics. Specifically, the abundance of aged PBAT microplastics initially increased then decreased, whereas their size continuously decreased, ultimately reaching 21.9 % and 47.5 % of the initial values, respectively. Furthermore, we constructed a novel backpropagation neural network model based on our morphological and spectral data, which effectively identified the incubation duration of PE and PBAT microplastics, with recognition accuracies of 98.1 % and 84.6 %, respectively. These findings offer a novel perspective for assessing the environmental persistence and fate of plastic film microplastics.

Response of sedimentary microbial community and antibiotic resistance genes to aged Micro(Nano)plastics exposure under high hydrostatic pressure

Several studies reported that the presence of microplastics (MPs)/nanoplastics (NPs) in marine environments can alter microbial community and function. Yet, the impact of aged MPs/NPs on deep sea sedimentary ecosystems under high hydrostatic pressure remains insufficiently explored. Herein, the sedimentary microbial community composition, co-occurrence network, assembly, and transfer of antibiotic resistance genes (ARGs) in response to aged MPs/NPs were investigated. Compared with the control, NPs addition significantly reduced bacterial alpha diversity (p < 0.05), whereas MPs showed no significant impact (p > 0.05). Moreover, networks under NPs exhibited decreased complexity than that under MPs and the control, including edges, average degree, and the number of keystone. The assembly of the microbial community was primarily governed by stochastic processes, and aged MPs/NPs increased the importance of stochastic processes. Moreover, exposure to MPs/NPs for one month decreased the abundance of antibiotic resistance genes (ARGs) (from 94.8 to 36.2 TPM), while exposure for four months increased the abundance (from 40.6 to 88.1 TPM), and the shift of ARGs in sediment was driven by both functional modules and microbial community. This study is crucial for understanding the stress imposed by aged MPs/NPs on sedimentary ecosystems under high hydrostatic pressure.

Distinct exposure impact of non-degradable and biodegradable microplastics on freshwater microalgae (Chlorella pyrenoidosa): Implications for polylactic acid as a sustainable plastic alternative

Microplastics (MPs) are increasingly recognized as significant sources of harm to biota in various environments. However, the detrimental impacts of aged MPs with different structures and degradability remain poorly understood. In this study, aged MPs from polylactic acid (PLA), polyethylene (PE), and polystyrene (PS), representing biodegradable, aliphatic, and aromatic plastics, respectively, were prepared to examine their effects on microalgae (Chlorella pyrenoidosa). Structural and property analyses indicated the presence of aging and oxygen-containing functional groups on the surfaces of the MPs, which correlated with an increase in negative electrical charge (i.e., aged PLA > aged PE ≈ aged PS). Aged PLA MPs affected microalgae biomass, promoted protein synthesis, and elevated mild oxidative stress. In contrast, aged PE and PS MPs not only affected biomass, protein, and carbohydrate synthesis but also inhibited photosynthetic pigment production and activity, resulting in intracellular oxidative stress. Excitation-emission-matrix spectra analysis showed that PLA induced microalgae to secrete large amounts of humic acid-like extracellular polymers, whereas aged PE and aged PS groups contained only small amounts of them and proteins. This study addresses critical knowledge gaps in the toxicology of various aged MPs on microalgae and provides valuable insights into the potential of PLA as a sustainable alternative to conventional plastics in microalgae culture industry.

Unveiling the optical and molecular characteristics of aging microplastics derived dissolved organic matter transformed by UV/chlor(am)ine oxidation and its potential for disinfection byproducts formation

The investigations into the existence and behavior of microplastics (MPs) in water environment were widely conducted, while the characteristics of dissolved organic matter derived from MPs (MPs-DOM) during advanced oxidation have garnered comparatively little attention. In this study, Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) was employed along with multiple statistical analyses to gain a deeper understanding of the conversion of MPs-DOM in UV/chlor(am)ine advanced oxidation processes (AOPs). The diverse treatments exhibited varying degrees of augmentation in both aging and fragmentation of MPs with the order of UV/Cl2 > UV > UV/NH2Cl. The fragmentation degree of MPs upon two UV-based AOPs (UV-AOPs) was dependent on their monomer chemical structure. The highest TOC values of three MPs-DOM were observed after UV/Cl2 AOP and the lowest after UV/NH2Cl AOP. Polyvinyl chloride (PVC) displayed a greater release of MPs-DOM under varying leaching conditions. UV/Cl2 AOP favored the reaction with saturated MPs-DOM, while UV/NH₂Cl AOP reduced unsaturated MPs-DOM, alleviating disinfection byproducts (DBPs) formation after chlorination. The precursors generated by UV/Cl₂ AOP owned lower H/C, higher modified aromatic index (AImod), and lower molecular weight (MW) products after chlorination. PVC-DOM with fewer CH₂ groups was more reactive. -H₂O, +O and -CH₂ reactions dominated in PVC-DOM (CHO compounds), while -2H, +O, -CH₂ did in PVC-DOM (CHON compounds). The dominant chlorine addition/substitution reactions occurred in PVC-DOM treated by UV/Cl₂ AOP, identifying 195 Cl-DBPs with 220 precursor-product pairs. Mass difference analyses showed that +2H and +O reactions were the most frequent of the 24 reaction types.

Molecular properties of dissolved organic matter leached from microplastics during photoaging process

The occurrence of dissolved organic matter (DOM) derived from microplastics (MPs) and its effect on aquatic systems has attracted great interest recently. However, the photoaging effect on the molecular structure of MP-derived DOM (MP-DOM) remains unclear. This paper presents the characteristics of DOM leached from three commercial MPs, i.e., polyethylene (PE), polypropylene (PP) and polyethylene terephthalate (PET) under UV irradiation. With prolonged aging periods, the surface roughness and oxygen-containing groups on the surface of MPs increase as more DOM leachate is generated. Moreover, the dissolved organic carbon (DOC) content of the leached DOM from PET MPs varies from 0.52 mg/L to 2.25 mg/L, which is higher than PE and PP MPs, due to the larger increased surface reaction area and the cleavage of the benzene ring. According to the excitation-emission matrix and parallel factor analysis (EEM-PARAFAC), the plastic-derived protein/phenolic-like components (C1 and C3) in MP-DOM were changed into photo-induced humic-like components (C2), which were closely related to the intermediates during photo-oxidation. High-performance liquid chromatography-mass spectrometry (HPLC-MS) analysis further identified that the highest proportion of antioxidants (24.8 %∼34.6 %) was contained in MP-DOM. Plasticizers, intermediate additives, and antimicrobial agents were also detected in DOM leachate. Correlation analysis identified that the composition of leached DOM was positively correlated with the surface roughness, the carbonyl index (CI), and the chemical groups of MPs. Moreover, a partial least square structural equation model (PLS-SEM) analysis further verified that the change of morphology and the chemical structure of MPs could affect the DOM structures and fractions directly. This study provides an in-depth understanding of the composition of MP-derived DOM during the aging process, as well as a comprehensive environmental impact assessment of MPs.

Accumulation of nanoplastics by wheat seedling roots: Both passive and energy-consuming processes

Nanoplastics can transfer from the environment to plants and potentially harm organisms. However, the mechanisms on how crop root systems absorb and transport nanoplastics are still unclear. Here, original and fluorescent labeled polystyrene and polyvinyl chloride nanoparticles (PS-NPs, PVC-NPs; 30 nm; 10 mg L-1) were employed to study the distribution and internalization pathways in wheat seedling roots. In the study, nanoplastics accumulated more in the root tip and surface, with PVC-NPs more prevalent than PS-NPs. After being treated with inhibitors (Na3VO4, chlorpromazine and amiloride), the nanoplastics mean fluorescence intensities were reduced by 4.0-51.1 %. During the uptake, both passive and energy-consuming pathways occurred. For the energy-consuming uptake pathway, macropinocytosis contributed more to cytoplasm than clathrin-mediated endocytosis. H+ influx was observed during nanoplastic transport into the cytoplasm, and the reduction in plasma membrane ATPase activity led to a decrease in nanoplastic internalization. These results elucidate the pathways of nanoplastics absorption and transport in wheat roots, provide crucial evidence for assessing nanoplastics' ecological risks and support the development of technologies to block nanoplastics absorption by crop roots, ensuring agricultural and ecosystem safety.

Dynamics of plastic debris and its density change between river compartments in the Tuul River system, Mongolia

Plastic pollution in river environments has become an emerging global concern. However, the migration of plastic and changes in its properties between river compartments are less understood. This study demonstrates the plastic debris aging and the dynamics between floodplain, surface water, and sediment compartments of the Tuul River, Mongolia. Plastic occurrence is evaluated in terms of their abundance, size, shape, polymer type, and photodegradation in each compartment. Photodegradation stages were calculated using the carbonyl index (CI). Plastic abundance was 5.46 ± 3.53 items m-2 in the floodplain, 155 ± 100.7 items m-3 in the surface water, and 128.4 ± 76.3 items kg-1 in the sediment. Microplastics dominated in the size category in all compartments, while macro- and megaplastics were found only in the floodplain. Polyethylene and polypropylene dominated the surface water and sediment, while polystyrene was the predominant plastic in the floodplain. A positive correlation was found between the distributed polymer types in the surface water and sediment compartments. The similar composition in size and polymer type suggests vertical plastic migration from water to sediment. Although CI values showed that the plastic aging was significantly different between water and sediment (water, 0.61 ± 0.26, and sediment, 0.90 ± 0.68), the dominance of low-density plastics with high CI in the sediment suggests that the aged plastic density changed during the vertical transport in the river system.

Insights into the inhibitory effects of trichloroisocyanuric acid disinfectant on the phototransformation of polypropylene microplastics

The chemical components in the natural aquatic environment have the potential to be involved in phototransformation of microplastics (MPs). Little information is available regarding the mediation effects of artificially introduced chemicals on MP phototransformation, especially those used in aquaculture water that are vulnerable to human interference. Herein, this study investigated the phototransformation process and mechanism of polypropylene microplastic (PP MPs) in presence of trichloroisocyanuric acid (TCCA) disinfectant with unique properties unlike the conventional inorganic chlorine disinfectants. The results showed that the presence of TCCA inhibited the surface photooxidation of PP MPs. Analysis of PP MP surface and reaction filtrate indicated that the inhibitory effects were likely derived from TCCA derivatives and the weakening in promoting effect of polypropylene microplastic-derived dissolved organic matter (PP-DOM) as photolytic byproducts, with the more important role of free chlorine in initial period and that of other chlorine species (i.e., the adsorbed chloride ions (Cl-), newly formed carbon-chlorine (CCl) bonds, chlorinated cyanurates, and chlorinated products) in middle and later period. The study highlights for the first time the important role of chlorine species derived from TCCA in phototransformation process of co-existed PP MPs and proposes a previously unrecognized phototransformation pathway, which will provide a new understanding and knowledge for the environmental behavior of MPs in aquaculture environment.

Photoaging-induced variations in heteroaggregation of nanoplastics and suspended sediments in aquatic environments: A case study on nanopolystyrene

Photoaging of nanoplastics (NPs) and heteroaggregate with suspended sediments (SS) determines transport processes and ecological risks of NPs in aquatic environments. This study investigated the disruption of photoaging on the heteroaggregation behavior of polystyrene NPs (PSNPs) and SS in different valence electrolyte solutions and deduced the interaction mechanisms by integrating aggregation kinetics and molecular dynamics (MD) simulation. Increasing the electrolyte concentration significantly enhanced the heteroaggregation between PSNPs and SS, and the divalent electrolytes induced the heteroaggregation more efficiently. MD simulation at the molecular level revealed that PS and SS could spontaneously form clusters, and photoaged PS has a stronger potential to fold into a dense state with SS. Photoaging for 30 d retarded heteroaggregation due to the steric hindrance produced by the leached organic matter in NaCl solutions, and the critical coagulation concentration (CCC) increased by >85.44 %. Contrarily, photoaging caused more oxygen-containing functional groups produced on the surface of PSNPs through Ca2+ bridging promoting heteroaggregation and thus destabilizing in CaCl2 solutions, the CCC decreased by 23.53 % ∼ 35.29 %. These findings provide mechanistic insight into the environmental process of NPs and SS and are crucial for a comprehensive understanding of the environmental fate and transport of NPs in aquatic environments.

Insight into the dynamic transformation properties of microplastic-derived dissolved organic matter and its contribution to the formation of chlorination disinfection by-products

Microplastics (MPs) can cause adverse effects and pose potential threats to humans and the environment. In addition, dissolved organic matter leached from MPs (MP-DOM) is also a critical issue due to its ecotoxicity and potential to form disinfection by-products (DBPs) during the disinfection process of water treatment plants. However, limited information is available on the dynamic transformation of MP-DOM during UV irradiation and subsequent disinfection, which may further influence the formation of DBPs in MP-DOM. Herein, PSMPs-DOM were leached in aqueous solutions under UV irradiation and the samples were then chlorinated. PSMPs-DOM before and after chlorination were characterized by multiple spectral technologies and methods. With prolonged irradiation time, the aromaticity, molecular weight, humic-like substances and oxygen-containing functional groups of PSMPs-DOM increased, suggesting the continuous transformation of PSMPs-DOM. After chlorination, the aromaticity, molecular weight and humic-like substances of PSMPs-DOM decreased, among which the changes of C2 and oxygen-containing functional groups were more significant. Besides, the PSMPs-DOM formed under prolonged irradiation exhibited higher chlorine reactivity, owing to the more aromatic structures and unsaturated bonds. TCM, DCBM, DBCM and TBM were detected in all chlorinated PSMPs-DOM samples, while the PSMPs-DOM formed at the later stage of irradiation exhibited lower THMs formation potential. The correlation results showed that the conversion of humic-like substances in PSMPs-DOM affected the THMs formation potential, with photo-induced humic-like substance being a more dominant factor. This study provided more information on the relationship between the compositional transformation of MP-DOM and their potential to form DBPs, which may facilitate the assessment of potential toxicity associated with MPs-containing water, as well as the development of more effective water treatment methods.

Photo-aging of brominated epoxy microplastics in water under simulated solar irradiation

Microplastics have become an increasingly concerning pollutant in aquatic environments, and photodegradation is their main degradation pathway in water. Gaining insight into the transformation process of microplastics will enhance our understanding of their behavior and destiny in natural environments. This paper studied the aging process of BER microplastics in aquatic environments under simulated sunlight and investigated the changes in the physical and chemical properties of microplastics and the changes in the leachate. During the photodegradation process, BER-MPs underwent extensive oxidation and reduction in particle size, and the originally smooth surface developed numerous voids, accompanied by yellowing. Introduction of O atoms in the molecular chains increased their hydrophilicity, resulting in the polymer chains breaking away from the plastic particles and dissolving in water. Also, once BER was excited by light, environmentally persistent free radicals are produced on its surface. Moreover, the breaking of C-Br bonds occurred during the photodegradation process of BER-MPs, which suggested that tetrabromobisphenol A would be transformed during the photoaging process of BER even if it was covalently bound to BER.

The aging of microplastics exacerbates the damage to photosynthetic performance and bioenergy production in microalgae (Chlorella pyrenoidosa)

The toxicity of microplastics (MPs) on freshwater plants has been widely studied, yet the influence of aged MPs remains largely unexplored. Herein, we investigated the influence of polyvinyl chloride (PVC) MPs, both before and after aging, at different environmentally relevant concentrations on Chlorella pyrenoidosa, a freshwater microalgae species widely recognized as a valuable biomass resource. During a 96-h period, both virgin and aged MPs hindered the growth of C. pyrenoidosa. The maximum growth inhibition rates were 32.40 % for virgin PVC at 250 mg/L and 44.72 % for aged PVC at 100 mg/L, respectively. Microalgae intracellular materials, i.e., protein and carbohydrate contents, consistently decreased after MP exposure, with more pronounced inhibition observed with aged PVC. Meanwhile, the MP aging significantly promoted the nitrogen uptake of C. pyrenoidosa, i.e., 1693.45 ± 42.29 mg/L (p < 0.01), contributing to the production of humic acid-like substances. Additionally, aged PVC induced lower chlorophyll a and Fv/Fm when compared to virgin PVC, suggesting a more serious inhibition of the photosynthesis process of microalgae. The toxicity of MPs to C. pyrenoidosa was strongly associated with intercellular oxidative stress levels. The results indicate that MP aging exacerbates the damage to photosynthetic performance and bioenergy production in microalgae, providing critical insights into the toxicity analysis of micro(nano)plastics on freshwater plants.

Triclosan-loaded aged microplastics exacerbate oxidative stress and neurotoxicity in Xenopus tropicalis tadpoles via increased bioaccumulation

Microplastics and chlorine-containing triclosan (TCS) are widespread in aquatic environments and may pose health risks to organisms. However, studies on the combined toxicity of aged microplastics and TCS are limited. To investigate the toxic effects and potential mechanisms associated with co-exposure to TCS adsorbed on aged polyethylene microplastics (aPE-MPs) at environmentally relevant concentrations, a 7-day chronic exposure experiment was conducted using Xenopus tropicalis tadpoles. The results showed that the overall particle size of aPE-MPs decreased after 30 days of UV aging, whereas the increase in specific surface area improved the adsorption capacity of aPE-MPs for TCS, resulting in the bioaccumulation of TCS under dual-exposure conditions in the order of aPE-TCS > PE-TCS > TCS. Co-exposure to aPE-MPs and TCS exacerbated oxidative stress and neurotoxicity to a greater extent than a single exposure. Significant upregulation of pro-symptomatic factors (IL-β and IL-6) and antioxidant enzyme activities (SOD and CAT) indicated that the aPE-TCS combination caused more severe oxidative stress and inflammation. Molecular docking revealed the molecular mechanism of the direct interaction between TCS and SOD, CAT, and AChE proteins, which explains why aPE-MPs promote the bioaccumulation of TCS, causing increased toxicity upon combined exposure. These results emphasize the need to be aware of the combined toxicity caused by the increased ability of aged microplastics to carry contaminants.

Microplastic-derived dissolved organic matter: Generation, characterization, and environmental behaviors

Microplastics (MPs) represent a substantial and emerging class of pollutants distributed widely in various environments, sparking growing concerns about their environmental impact. In environmental systems, dissolved organic matter (DOM) is crucial in shaping the physical, chemical, and biological processes of pollutants while significantly contributing to the global carbon budget. Recent findings have revealed that microplastic-derived dissolved organic matter (MP-DOM) constitutes approximately 10 % of the DOM present on the ocean surface, drawing considerable attention. Hence, this study's primary objective is to explore, the generation, characterization, and environmental behaviors of MP-DOM. The formation and characteristics of MP-DOM are profoundly influenced by leaching conditions and types of MPs. This review delves into the mechanisms of the generation of MP-DOM and provides an overview of a wide array of analytical techniques, including ultraviolet-visible (UV-Vis) spectroscopy, fluorescence spectroscopy, Fourier transform infrared spectroscopy (FTIR), and mass spectroscopy, used to assess the MP-DOM characteristics. Furthermore, this review investigates the environmental behaviors of MP-DOM, including its impacts on organisms, photochemical processes, the formation of disinfection by-products (DBPs), adsorption behavior, and its interaction with natural DOM. Finally, the review outlines research challenges, perspectives for future MP-DOM research, and the associated environmental implications.

Behavioral impairments and disrupted mitochondrial energy metabolism induced by polypropylene microplastics in zebrafish larvae

Polypropylene microplastics (PP-MPs) are emerging pollutant commonly detected in various environmental matrices and organisms, while their adverse effects and mechanisms are not well known. Here, zebrafish embryos were exposed to environmentally relevant concentrations of PP-MPs (0.08-50 mg/L) from 2 h post-fertilization (hpf) until 120 hpf. The results showed that the body weight was increased at 2 mg/L, heart rate was reduced at 0.08 and 10 mg/L, and behaviors were impaired at 0.4, 10 or 50 mg/L. Subsequently, transcriptomic analysis in the 0.4 and 50 mg/L PP-MPs treatment groups indicated potential inhibition on the glycolysis/gluconeogenesis and oxidative phosphorylation pathways. These findings were validated through alterations in multiple biomarkers related to glucose metabolism. Moreover, abnormal mitochondrial ultrastructures were observed in the intestine and liver in 0.4 and 50 mg/L PP-MPs treatment groups, accompanied by significant decreases in the activities of four mitochondrial electron transport chain complexes and ATP contents. Oxidative stress was also induced, as indicated by significantly increased ROS levels and significant reduced activities of CAT and SOD and GSH contents. All the results suggested that environmentally relevant concentrations of PP-MPs could induce disrupted mitochondrial energy metabolism in zebrafish, which may be associated with the observed behavioral impairments. This study will provide novel insights into PP-MPs-induced adverse effects and highlight need for further research.

Aging behavior and leaching characteristics of microfibers in landfill leachate: Important role of surface mesh structure

Mesh-structured films formed by the post-processing of microfibers improves their permeability and dexterity, such as disposable masks. However, the aging behavior and potential risks of mesh-structured microfibers (MS-MFs) in landfill leachate remain poorly understood. Herein, the aging behavior and mechanisms of MS-MFs and ordinary polypropylene-films (PP-films) microplastics, as well as their leaching concerning dissolved organic matter (DOM) in landfill leachate were investigated. Results revealed that MS-MFs underwent more significant physicochemical changes than PP-films during the aging process in landfill leachate, due to their rich porous habitats. An important factor in the photoaging of MS-MFs was related to reactive oxygen species produced by DOM, and this process was promoted by photoelectrons under UV irradiation. Compared with PP-films, MS-MFs released more DOM and nano-plastics fragments into landfill leachate, altering the composition and molecular weight of DOM. Aged MS-MFs-DOM generated new components, and humus-like substances produced by photochemistry showed the largest increase. Correlation analysis revealed that leached DOM was positively correlated with oxygen-containing groups accumulated in aged MS-MFs. Overall, MS-MFs will bring higher environmental risks and become a new long-term source of DOM contaminants in landfill leachate. This study provides new insights into the impact of novel microfibers on landfill leachate carbon dynamics.

eDNA Adsorption onto Microplastics: Impacts of Water Chemistry and Polymer Physiochemical Properties

Adsorption of biomacromolecules onto polymer surfaces, including microplastics (MPs), occurs in multiple environmental compartments, forming an ecocorona. Environmental DNA (eDNA), genetic material shed from organisms, can adsorb onto MPs which can potentially either (1) promote long-range transport of antibiotic resistant genes or (2) serve to gain insights into the transport pathways and origins of MPs by analyzing DNA sequences on MPs. However, little is known about the capacity of MPs to adsorb eDNA or the factors that influence sorption, such as polymer and water chemistries. Here we investigated the adsorption of extracellular linear DNA onto a variety of model MP fragments composed of three of the most environmentally prevalent polymers (polyethylene, polyethylene terephthalate, and polystyrene) in their pristine and photochemically weathered states. Batch adsorption experiments in a variety of water chemistries were complemented with nonlinear modeling to quantify the rate and extent of eDNA sorption. Ionic strength was shown to strongly impact DNA adsorption by reducing or inhibiting electrostatic repulsion. Polyethylene terephthalate exhibited the highest adsorption capacity when normalizing for MP specific surface area, likely due to the presence of ester groups. Kinetics experiments showed fast adsorption (majority adsorbed under 30 min) before eventually reaching equilibrium after 1-2 h. Overall, we demonstrated that DNA quickly binds to MPs, with pseudo-first- and -second-order models describing adsorption kinetics and the Freundlich model describing adsorption isotherms most accurately. These insights into DNA sorption onto MPs show that there is potential for MPs to act as vectors for genetic material of interest, especially considering that particle-bound DNA typically persists longer in the environment than dissolved DNA.

Characterization of microplastic-derived dissolved organic matter in freshwater: Effects of light irradiation and polymer types

This study investigated the impacts of light irradiation and polymer types on the leaching behavior of dissolved organic matter (DOM) from microplastics (MPs) in freshwater. Polypropylene had the highest leaching capacity of DOM after photoaging, followed by polystyrene (PS), polyamide (PA) and polyethylene terephthalate (PET). While similarly low levels of DOM were observed in the remaining 5 MP suspensions under UV irradiation and in almost all MP suspensions (except PA) under darkness. These suggest that the photooxidation of some buoyant plastics may influence the carbon cycling of nature waters. Among 9 MP-derived leachates, PET leachates had the highest chromophoric DOM concentration and aromaticity, probably owing to the special benzene rings and carbonyl groups in PET structures and its fast degradation rate. Protein-like substances were the primary fluorescent DOM in MP suspensions (except PS), especially in darkness no other fluorescent substances were found. Considering the bio-labile properties of proteins together, MPs regardless of floating or suspended in an aquatic environment may have prevalent long-term effects on microbial activities. Besides, from monomers to hexamers with newly formed chemical bonds were identified in UV-irradiated MP suspensions. These results will contribute to a deep insight into the potential ecological effects related to MP degradation.

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.

Aging of polystyrene microplastics by UV/Sodium percarbonate oxidation: Organic release, mechanism, and disinfection by-product formation

The occurrence and transformation of microplastics (MPs) in environment has attracted considerable attention. However, the release characteristics of MP-derived dissolved organic matter (MP-DOM) under oxidation conditions and the effect of DOM on subsequent chlorination disinfection by-product (DBP) still lacks relevant information. This study focused on the conversion of polystyrene microplastics (PSMPs) in the advanced oxidation of ultraviolet-activated sodium percarbonate (UV/SPC-AOP) and the release characteristics of MP-DOM. The DBP formation potential of MP-DOM was also investigated. As a result, UV/SPC significantly enhanced the aging and fragmentation of PSMPs. Under UV irradiation, the fluorescence peak intensity and position of humus-like and protein-like components of MP-DOM were correlated with SPC concentration. The aging MP suspension was analyzed by gas chromatography-mass spectrometry (GC-MS), and various alkyl-cleavage and oxidation products were identified. Quenching experiments and electron paramagnetic resonance (EPR) detection confirmed that carbonate and hydroxyl radicals jointly dominated the conversion of PSMPs. The formation of DBP was related to the components of MP-DOM. Overall, these results help to understand the aging behavior of MPs in AOP. Moreover, MP-DOM released by MPs after AOP oxidation may be a precursor of DBPs, which deserved more attention.

Mulch-derived microplastic aging promotes phthalate esters and alters organic carbon fraction content in grassland and farmland soils

Agricultural plastic mulch is a major microplastics (MPs) source in terrestrial ecosystems. However, knowledge about the aging characteristics of mulch-derived MPs entering natural and agricultural soils and their effects on phthalate esters (PAEs) and organic carbon fractions is still limited. Black (contains black masterbatches) and white polyethylene (PE) and biodegradable (Bio, Poly propylene carbonate and Polybutylene adipate terephthalate synthetic material (PPC+PBAT)) mulch-derived MPs, at 0.3% (w/w) dose, were added to grassland and farmland soils for eight-week incubation. Microplastic (MP) aging degree was explored by quantifying the carbonyl index (CI). The soil PAEs and organic carbon fractions were also analyzed. After incubation, black and white PE-MP aged greater in farmland than in grassland. PAEs accumulated highest in PE-MP treatment (5.27-6.41 mg kg-1) followed by Bio-MP (1.88-2.38 mg kg-1). Soil organic carbon (SOC), particulate organic carbon (POC), and microbial biomass carbon (MBC) were reduced by 5.3%-8.2%, 31.8%-41.6%, and 39.7%-63.0%, dissolved organic carbon (DOC) was increased by 10.1%-27.6% in grassland containing MP compared to control. MPs' aging degree promoted PAEs content or altered nutrients, then regulated soil microbial biomass and extracellular enzyme activity directly or indirectly, ultimately affecting SOC. ENVIRONMENTAL IMPLICATION: Microplastics are persistent environmental pollutants that gradually undergo surface aging in response to extracellular enzymes secreted by microorganisms. As microplastics age, their surface roughness and functional groups change; thus, organochemical contaminants gradually leach out. Therefore, this study analyzed the aging of mulch film-derived microplastics under the action of diverse microorganisms in farmland and grassland soils and the effect on plasticizer and organic carbon fractions. The results proved that polyethylene microplastic aging degree was highest in farmland soil. Besides, biodegradable microplastic caused lower contamination of phthalate esters than polyethylene, but they affected soil carbon balance in grassland and farmland soils. STATEMENT OF ENVIRONMENTAL IMPLICATION: This study highlights that MPs affect organic carbon fractions by influencing the PAEs, available nutrients, and extracellular enzyme activity.

Seawater Accelerated the Aging of Polystyrene and Enhanced Its Toxic Effects on Caenorhabditis elegans

Microplastics (MPs) are emerging pollutants and pose a significant threat to marine ecosystems. Although previous studies have documented the mechanisms and toxic effects of aging MPs in various environments, the impact of the marine environment on MPs remains unclear. In the present study, the aging process of polystyrene (PS) in seawater was simulated and the changes in its physicochemical properties were investigated. Our results showed that the surface of the PS eroded in the seawater, which was accompanied by the release of aged MPs with a smaller size. In situ optical photothermal infrared microspectroscopy revealed that the mechanism of PS aging was related to the opening of the carbonyl group and breaking of the bond between carbon and benzene removal. To verify the toxic effects of aged PS, Caenorhabditis elegans was exposed to PS. Aged PS resulted in a greater reduction in locomotion, vitality, and reproduction than virgin PS. Mechanistically, aged PS led to oxidative stress, high glutathione s-transferase activity, and high total glutathione in worms. Together, our findings provided novel information regarding the accelerated aging of PS in seawater and the increased toxicity of aged PS, which could improve our understanding of MPs' ecotoxicity in the marine environment.

Occurrence, characteristics, and factors influencing the atmospheric microplastics around Jiaozhou Bay, the Yellow Sea

Atmospheric microplastics are attracting increasing attention as an emerging pollutant. However, research on its characteristics and influencing factors is insufficient. This study examines the characteristics and spatiotemporal distribution of atmospheric microplastics around Jiaozhou Bay, the Yellow Sea. The results showed that the dominant shapes of microplastic were fragments (61.9 %) and fibers (25.6 %), and the main types were polyethylene terephthalate (23.8 %), polyethylene (31.6 %) and cellulose (rayon, 34.9 %). The deposition rate of microplastic varied from 8.395 to 80.114 items·m-2·d-1, with a mean of 46.708 ± 21.316 items·m-2·d-1. The deposition rate was higher in the dry season than in the rainy season, indicating the influence of weather condition. The annual mass of atmospheric microplastics entering the bay was estimated to be 7.612 ± 3.474 tons. For the first time, this study reveals that atmospheric microplastics in Jiaozhou Bay change spatiotemporally due to monsoons, which pose a potential threat to marine ecosystems.

Toxicity of polyvinyl chloride microplastics on Brassica rapa

Microplastics (MPs) can pose high risk to living organisms due to their very small sizes. This study selected polyvinyl chloride MPs (PVC-MPs) which experienced up to 1000 h UV light radiation to investigate the influence of PVC-MPs on Brassica rapa growth. The outcomes showed the presence of PVC-MPs inhibited the plants' growth. The stem length, root length, fresh weight and dry weight of plants exposed to PVC-MPs after 30 days reduced by 45.9%, 35.2%, 26.1% and 5.2%, respectively. The chlorophyll, soluble sugar, malondialdehyde (MDA) and catalase (CAT) concentrations for plants exposed to PVC-MPs after 30 days increased by 25.9%, 135.7%, 88.7% and 47.1% respectively. It was also observed that PVC-MPs blocked the plants' leaf stomata and even entered plants' bodies. This might lead to PVC-MPs movement within the plants and influence plants' growth. The transcriptomic analysis results indicated that exposure to PVC-MPs up-regulated metabolic pathway of plant hormone signal transduction of the plants and down-regulated pathway network of ribosome. However, the research outcomes also showed that the PVC-MPs' locations in soil (located at the upper layers or at lower layers) and the UV light radiation time did not exert significantly different influences on inhibiting plants' growth. This can be attributed to PVC-MPs' small sizes and not much decomposition under light radiation. These imply that longer light radiation time and different particle sizes should be included into future research in order to further explore photodegraded MPs' toxicity effects on plants.

Increased bio-toxicity of leachates from polyvinyl chloride microplastics during the photo-aging process in the presence of dissolved organic matter

The pollution caused by microplastics (MPs) has gained global attention due to their potential risks to organisms and human health. The process of photo-aging, which plays a crucial role in the transformation of MPs in aquatic environments, has the potential to influence the ecological risk posed by these particles. Dissolved organic matter (DOM) is a prevalent photosensitizer in surface waters that has been shown to facilitate the transformation of various organic compounds by generating reactive oxygen species under light irradiation. The present study investigated the influence of humic acid (HA), a typical component of DOM, on the photo-aging process of polyvinyl chloride MPs (PVC-MPs), using Fourier transform infrared spectroscopy, as well as assessing the resulting ecological risk through bioassays. The results revealed that the presence of HA enhanced the photo-aging of PVC-MP. Moreover, the leachate exhibited higher acute and genetic toxicity under light irradiation when compared to dark conditions. Notably, the presence of HA significantly increased the toxicity of the leachate, emphasizing the need to consider the impact of DOM when assessing the ecological risk of MPs in surface waters. These findings contribute to a more comprehensive understanding of the potential risks associated with microplastic pollution in natural environments.

Toxicity of photoaged polyvinyl chloride microplastics to wheat seedling roots

Photoaging-prone and additive-rich polyvinyl chloride microplastics (PVC-MPs) are abundant in the terrestrial environment, However, current knowledge about the effects of PVC-MPs on terrestrial plants is lacking. Herein, we investigated the physicochemical toxicity mechanisms of photoaged PVC-MP components, i.e. leachate (L), leached PVC-particles (P), and unleached PVC-MPs (UAMP), to wheat seedling roots. 108-h photoaged components were more detrimental to root growth than unaged ones, with root length decline by 3.56%- 7.45%, indicating enhanced ecotoxicity. Notably, 108-h aged UAMP displayed more pronounced inhibition to root architecture, nutrient content and root activity, and more significant stimulation on antioxidant systems compared to 108-h aged L and P. The abovementioned phenomena suggested the presence of a synergistic effect between physical damage from P and chemical harm from L. Surface adsorption experiments demonstrated that the adsorption of photoaging induced smaller particles caused physical damage to root system. Exposure treatment suggested that there was appreciable environmental risk posed by photoaged PVC-MP-derived additives, e.g., Irgafos 168-ox and Irganox 1076. Based on principal component analysis (PCA), additives from leachate played a greater role in UAMP ecotoxicity. Therefore, PVC-MP-derived additives require more consideration and put forward an important new aspect for the impact assessment of PVC-MPs in the environment.