Aging Significantly Affects Mobility and Contaminant-Mobilizing Ability of Nanoplastics in Saturated Loamy Sand

Insights into the effects of aging on the combined toxicity of polystyrene nanoplastics and chlordane against Caenorhabditis elegans

Nanoplastics are emerging contaminants that may co-exist with organochlorine pesticides and adversely affect invertebrates in the environment. However, the impact of environmental aging on the combined toxicity of nanoplastics and organochlorine pesticides remains unclear. This study investigated the effects of aging on the combined toxicity of polystyrene nanoplastics (PS NPs) and chlordane against Caenorhabditis elegans. The results showed that photo-aging altered the physicochemical properties of PS NPs and promoted the combined toxicity of PS NPs and chlordane to nematodes by reducing survival rate, body length and enhancing germline apoptosis. Additionally, combined exposure of nematodes to aged PS NPs and chlordane significantly increased reactive oxygen species production and intestinal permeability, suggesting that aging enhances combined toxicity through oxidative stress and intestinal damage. Moreover, aging increased chlordane contents in nematodes without promoting PS NPs accumulation, potentially leading to increased combined toxicity of PS NPs and chlordane. Notably, aging significantly increased the accumulation of PS NPs in the posterior intestine of the nematode during co-exposure, which may be responsible for the most sensitive and highest degree of change in germline apoptosis. These observations emphasize the significance of accounting for environmental aging as well as the accumulation and distribution of nanoplastics in organisms when assessing the combined effects of nanoplastics and coexisting pollutants.

Effects of polystyrene fragments on the transport of Pb2+ in saturated porous media: The role of microplastics characteristics and flow velocity

Microplastics (MPs) could interact with heavy metals via multiple mechanisms in subsurface environment. Understanding the effect of MPs on the fate of heavy metals is essential for the prediction of their ecological impacts. In this study, laboratory columns were conducted to investigate the effects of pristine/aged secondary polystyrene fragments of different sizes and dosages on the transport of Pb2+ in saturated porous media. MPs generally promoted Pb2+ mobility, and the promotion degree was greater with increasing MP size and dosage. The enhancement of Pb2+ mobility by naturally aged MPs was slightly weaker than that by pristine MPs. The sensitivity of Pb2+ mobility to MPs was correlated with the flow velocity, the promotion impact was more significant at larger flow velocity. The enhanced mobility of Pb2+ was mainly attributed to the decrease Pb2+sorption capacity of the media resulting from dilution effect, as well as alterations in pore structure and porosity caused by the high heterogeneity of MP fragments. Findings of this study indicated that the fate and transport of heavy metals are strongly influenced by the co-contamination with MPs. Evaluation of their cotransport in the subsurface is essential for accurately predicting their environmental risks.

Monitoring nanoplastic aging in situ by moth-eye mimic plasmonic substrates

Micro-nano plastics aging is crucial as it determines the environmental fate of each plastic particle, yet few studies involved in situ aging of nanoplastics. Herein, we utilized nanosphere lithography combined with goldnanorod assembly to prepare a moth-eye mimic plasmonic substrate featuring excellent SERS performance. The substrate was applied to in situ characterize the degradation process of PS nanoplastics during UV aging. Raman spectra evidence that the substrate is sensitive to superficial chemical changes of PS nanoplastics at initial stage during 24 h of continuous UV aging. The disruption of the benzene ring skeleton, the oxidation of the side chains of PS nanoplastics during UV aging, and the presence of oxidized methylene straight chains were identified. Practical applications in environmental sample revealed the chemical changes of PP, PS, and PE, which confirm the great potential of this SERS substrate for aging studies of nanoplastics.

Seasonal distribution of microplastics and associated ecological risks in a semi-arid freshwater ecosystem in India

Microplastics are persistent contaminants across all environmental matrices. However, there is a paucity of studies conducted in semi-arid aquatic environments. The present study investigated the seasonal variations in the distribution and characteristics of microplastics in water samples of Man Sagar Lake in northwestern India. The findings revealed that the average abundance of microplastics in samples was notably lower during the pre-monsoon season (42.93 ± 29.72 particles/L) compared to the post-monsoon season (70.54 ± 36.53 particles/L). A significant difference in microplastic abundance across different sampling locations was observed between the two seasons (F = 7.82, p < 0.0001). The majority of microplastics present in the samples during both seasons measured less than 500 μm in size, with fragments and fibers being the predominant shapes, and transparent being the most common-colored microplastic. The most abundant polymers detected were polyethylene, polypropylene, and polystyrene. Microplastic contamination factor (MCf) and Pollution Load Index (PLI >1) indicated a moderate to high level of microplastic contamination across all the sampling locations in both seasons. Furthermore, the potential ecological risk index (PERI) indicated that nearly 70 % of the lake area falls under the category of very high ecological risk in both seasons. Additionally, Spearman's correlation and PCA were employed to assess the interactions of microplastics with water quality parameters and potential source identification, respectively. The study's findings could help in developing region-specific remediation and prevention strategies by identifying high-risk areas and potential sources contributing to microplastic contamination.

Decreased particle size enhances the aging behavior of microplastics during sewage sludge composting: Physicochemical properties and cadmium loading

Although aerobic composting is capable of aging microplastics (MPs), the influence of size on MPs aging during composting and loading of cadmium (Cd) remains unclear. Therefore, we investigated variations in the physicochemical properties of polyethylene terephthalate microplastics (PET-MPs) with different sizes (1.0 -5.0, 0.2 -1.0, and 0.05 -0.2 mm) during composting and the concentration of Cd accumulated on the surface of different-sized aged PET-MPs. The results indicated that PET-MPs exhibited size-dependent as they aged during composting, with smaller sizes aging faster. After composting, the 0.05 -0.2 mm PET-MPs had the greatest increase in specific surface area (205.5 %), compared with the 1.0 -5.0 mm (18.7 %) and 0.2 -1.0 mm (95.6 %) PET-MPs. The greatest increase in the carbonyl index/oxygen-to-carbon atom ratio was also observed for the 0.05 -0.2 mm PET-MPs, which were 2.25 / 3.27 and 0.02 / 2.11 times higher than those of the 1.0 -5.0 mm and 0.2-1.0 mm PET-MPs, respectively. Similarly, size-dependent accumulation of Cd on the aged PET-MPs was also observed: 0.05-0.2 mm (5.37 mg/kg Cd) > 0.2 -1.0 mm (2.90 mg/kg Cd) > 1.0-5.0 mm (0.78 mg/kg Cd). These findings demonstrate that the aging behavior of polymer is closely related to their size, emphasizing the role of size in the fate and pollutant loading of polymer.

Nanoplastics enhance tebuconazole toxicity in lettuce by promoting its accumulation and disrupting phenylalanine metabolism: Importance of Trojan horse effect

Nanoplastics (NPs) are ubiquitous in agricultural environments and may exacerbate environmental risks of pesticides. This study investigates how NPs influence the toxicity of tebuconazole in lettuce. In a hydroponic model, NPs (10 and 50 mg/L) enhanced tebuconazole accumulation in roots and exacerbated its toxicity. To elucidate the underlying mechanisms, a combination of in vivo, in vitro, and in silico models was employed. The results indicated that NPs were taken up by roots through apoplast pathway, predominantly accumulating in roots (35.6-40.7 %) due to aggregation in root sap and adhesion to cell wall. Tebuconazole adsorbs onto NPs with a high adsorption capacity (123.7 mg/g), enabling NPs to serve as carriers that facilitate tebuconazole entry into roots. Once in the root sap, tebuconazole desorbed from NPs and accumulated in cell walls, leading to higher residue in the roots (7.19-9.85 mg/kg). Furthermore, tebuconazole bound to key proteins involved in auxin biosynthesis (e.g., YUC) and signaling (e.g., TIR), thereby inhibiting tryptophan-dependent auxin biosynthesis pathway and disrupting TIR1/AFB-mediated auxin signaling. Additionally, tebuconazole suppressed the phenylalanine pathway, reducing antioxidant secondary metabolites such as flavonols. When NPs are present, co-exposure intensified the inhibition of auxin and phenylalanine pathways, thereby amplifying the toxicity of tebuconazole, as evidenced by impaired plant phenotypes (e.g., biomass, root tips) and disrupted antioxidant systems. This study reveals threats posed by NPs and tebuconazole in agricultural systems and highlights the novel carrier effect of NPs in enhancing tebuconazole toxicity, emphasizing the urgent need to assess the fate and toxicity of NPs and coexisting pollutants.

Microplastics in Agricultural Soils: Sources, Fate, and Interactions with Other Contaminants

Microplastics (MPs) are recognized as emerging soil contaminants. However, the potential risks of MPs to agroecosystems have not been fully revealed, especially the compound toxic effects of MPs with co-existing organic or inorganic pollutants (OPs/IPs) in agricultural fields. In this study, we quantified the contributions of different agronomic practices to the sources of MPs in soil and highlighted the important influences of long-term tillage and fertilization on the migration and aging of MPs in agricultural fields. In addition, the antagonistic and synergistic interactions between MPs and OPs/IPs in soil were explored. We emphasized that the degree of adsorption of MPs and soil particles to OPs/IPs is a key determinant of the co-toxicity of those contaminants in soil. Finally, several directions for future research are proposed, and these knowledge gaps provide an important basis for understanding the contamination process of MPs in agricultural soils.

Micro-Sized Polymer Hydrogels as Model Microplastics: Interaction with Polycationic Toxins in Solution and Precipitate

The problem of polymer waste has reached a level that requires immediate solution. Microplastics (MP), potentially toxic polymer particles of 5 mm or less in size, are an important part of this problem. In the article, two types of micro-sized polymer particles are described, mimicking behavior of real MP. The first are soft anionic 570 nm microgels with a developed surface, which reproduce the structure of "aged" MP. The second are 380 nm microspheres with a solid polymer core and a thin outer anionic layer, which are taken as a model of the "initial" MP. Both types of anionic species electrostatically adsorb cationic polymers, toxic compounds, widely used in water treatment/purification, food industry, and cosmetics. The adsorption is accompanied by neutralization of the particle charge and aggregation of the species at mutual neutralization of the particles and polycation charges. Polycations pass from their complexes with microgels to free microgels, which results in dissolution of the aggregates and formation of homogeneous solutions, but the same polycations are not desorbed from microspheres when free microspheres are added, and the aggregates are preserved. No redistribution/dissolution is observed in the microgel-polycation-microsphere ternary systems. This picture reflects the different behavior of the aged and initial real MP when they are in contact with toxic polymer compounds. A possible mechanism for this difference is discussed. The results of the study clarify the details of the MP interaction with the environment and the role of MP in the spread of toxic components.

Enhanced Photoaging of Functionalized Nanoplastics by Cadmium Ions and Corresponding Diverse Transport Behaviors of Products in Porous Media: Mechanisms and Modeling

The photoaging of nanoplastics (NPs) mediated by heavy metals and the transport mechanisms of the products have been widely overlooked. This study demonstrated that cadmium ion (Cd(II)) mediation accelerated the photoaging of polystyrene NPs (carboxyl-modified CNPs, amino-modified ANPs, sulfonate, and amino comodified SANPs) by generating more •OH and 1O2, thereby altering their physicochemical properties and consequent transport behavior. Kinetic attachment models and Derjaguin-Landau-Verwey-Overbeek theory proved that the Cd(II)-mediated photoaging process had diverse effects on the transport and retention of surface-functionalized NPs in water-saturated sand media. In particular, Cd(II) mediation at 50 mg/L increased the hydroxyl and carboxyl groups on aged CNPs, facilitating their transport by 20.3% with reduced k2 (0.036 vs 0.021) and increased φmax (74.804 KBT vs 85.127 KBT) values. Conversely, enhanced aged ANP agglomerates driven by amino-carboxyl electrostatic attraction had ripening adsorption on additional heterogeneous surfaces of sand. The presence of reinforced fragments of aged ANPs deposited on sand led to remarkable detachment. Aged SANPs retained their original mobility after Cd(II) mediation due to negligible changes in surface groups, whereas their retention associated with a higher k1d (0.347 vs 0.183) became more reversible to be flushed out by water. This study provided insights for evaluating cocontamination risks in watersheds and surrounding soils.

Widening the Lens on Ultraviolet Absorbers: New Evidence from the Microenvironment of Agricultural Greenhouses and Workers' Risk Ranking Based on External Exposure and Internal Metabolic Processes

Greenhouses offer optimum growth conditions for plants and create a unique microenvironment for workers who work in them. Information about human exposure to UVAs particularly those employed in agricultural greenhouses remains unknown. In the present study, UVAs employed in agricultural greenhouses in North China were comprehensively analyzed and screened. The geometric mean concentration of ∑10UVAs in agricultural greenhouse plastic films (132 ng/g) was found significantly higher than that in the control films (27.1 ng/g) (p < 0.001), with UV-531 (35.9 ng/g) and UV-326 (24.9 ng/g) as the dominant components in used films, followed by that in soil and fine particles, indicating elevated levels of UVAs in agricultural greenhouses. Temperature was acquired as the main factor for the release of UVAs in agricultural greenhouses. Consistently, relatively high levels of UV-360 and UV-P were identified in the urine of greenhouse workers. The quantitative assessment of UVA exposure risks was conducted using Monte Carlo simulation, which identified soil contact as the main pathway, accounting for 88.22% of the total estimated exposure. Importantly, by integrating environmental exposure assessment, human ADME (absorption, distribution, metabolism, and excretion) parameters, and urinary biomonitoring data, UV-328 and UV-234 were identified as the highest-priority congeners for occupational health monitoring among greenhouse workers. The present study is the first to combine environmental exposure and metabolic behavior for the prioritization of UVA risks, emphasizing the urgent need for early intervention toward the health and safety of agricultural greenhouse workers.

Co-transport behavior of aged polymeric methyl methacrylate nanoplastics and florfenicol antibiotic in porous media: Effects of electrolyte, pH, and aging duration

This study investigates single and co-transport behavior of aged (14 and 30 days) poly(methyl methacrylate) nanoparticles (14dPMMANPs, 30dPMMANPs) and florfenicol (FF) in saturated porous media, under varying ionic strengths (IS) and pH values. The results indicate that during the aging process, the carbon-oxygen double bonds in the ester group of PMMANPs were the first to be degraded under simulated sunlight exposure. In single transport experiments, the 14dPMMANPs exhibited higher mass recovery percentage, which can be attributed to their smaller hydrodynamic diameter and higher oxygen-containing functional groups. Interestingly, the oxygenated functional groups exposed on the 14dPMMANPs may provide more cation binding sites, resulting in stronger migration inhibition under Ca2+ conditions compared to Na+ conditions. In contrast, the 30dPMMANPs displayed more negative zeta potential and a lower rate of particle size increase, weakening the inhibitory effect of divalent cations. Under co-transport conditions, FF promoted the migration of 30dPMMANPs in low IS, neutral solutions. Overall, FF reached a new equilibrium between transport inhibition (reduced electrostatic repulsion, increased hydrodynamic diameter of PMMANPs, and additional deposition sites on quartz sand (QS)) and transport promotion (PMMANPs as a carrier and competition for deposition sites on the QS surface). Changes in pH disrupted this equilibrium. Furthermore, the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory, considering surface roughness (SR), provides a good explanation for the breakthrough curves (BTC) of aged PMMANPs during single and co-transport. The surface collapse, inter-particle aggregation, higher SR, and surface inhomogeneity observed in 30dPMMANPs suggest significant chemical heterogeneity, resulting in a lower energy barrier for migration. This study reveals the dynamic relationship between the physicochemical properties and the migration capacity of PMMANPs at different aging stages, demonstrates the dynamic equilibrium of the competition-carrier effect in the co-transport system (FF and PMMANPs), and uncovers the synergistic effect between cation valence and the coordination ability of surface functional groups on nanoplastics, overcoming the limitation of traditional studies that focus only on ionic strength.

Microplastics in groundwater: Environmental fate and possible interactions with coexisting contaminants

Microplastics (MPs) are emerging environmental pollutants which represent a serious threat to ecosystems and human health and have received significant attention from the global community. Currently, a growing number of studies have found the presence of MPs in groundwater. This study exhaustively reviewed varying degrees of recent publications in Web of Science database and investigated the characteristics of MPs (concentration, types, sizes and shapes) in groundwater ecosystems, their migration characteristics, and interactions with co-occurring contaminants. Results suggested that current global research on MPs in groundwater has primarily focused on countries such as India, South Korea, China, Italy and United States. Pollution levels of MPs in groundwater show significant variability, ranging from 0 to 6832 n/L. The predominant plastic polymer types include PP, PE, PS, PA, PET and PVC. The sources of MPs in groundwater are primarily classified as associated with natural processes and anthropogenic activities. The physical, chemical and biological properties can influence the migration of MPs into groundwater. Furthermore, MPs can act as carriers, interacting with co-occurring contaminants, thereby enhancing their migration and toxicity, potentially posing a threat to groundwater ecosystems and human health. Consequently, the major challenges and associated recommendations for forthcoming research on MPs in groundwater are proposed.

Effect of pH and salinity on the release of polystyrene microplastics derived dissolved organic matter as revealed by experimental studies and molecular dynamic simulations

Microplastics-derived dissolved organic matter (MPs-DOM) poses a significant risk to aquatic systems. This study characterized MPs-DOM from polystyrene microplastics (PSMPs) upon photoaging in freshwater and seawater. For pristine PSMPs, plastic additives are the predominant substances in MPs-DOM. As the degree of aging increases, intermediates emerge as the new predominant substances in MPs-DOM. Both higher pH and salinity accelerate the aging of PSMPs and MPs-DOM release. Molecular dynamics simulations align with experiments showing that increased pH and salinity levels enhance the release of MPs-DOM. Interaction energy calculations revealed a link between MPs-DOM release amount and the interaction intensity between PSMPs and MPs-DOM. Generally, MPs-DOM having lower interaction energy with PSMPs is more liable to release, and aging of PSMPs leads to a decrease in their interaction energy with MPs-DOM. For example, the interaction energies in the pH 10 seawater system were slightly lower than those in the pH 7 seawater system. In the pH 7 seawater system, the interaction energy between butyl acetate and PSMPs was -41.97 kJ/mol, while in the pH 10 seawater system, this value was -26.86 kJ/mol. These insights are crucial for assessing the environmental behavior of MPs and MPs-DOM in aqueous environments.

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.

UV-weathering affects heteroaggregation and subsequent sedimentation of polystyrene microplastic particles with ferrihydrite

Microplastic (MP) particles are ubiquitous in aquatic environments where they become exposed to UV-irradiation with subsequent alteration of surface properties. Such particles will interact with naturally occurring colloids being subject to processes like heteroaggregation that affect both MP surface properties and their removal rates from the water column. In this study, we investigated heteroaggregation and subsequent sedimentation of 1 μm polystyrene (PS, pristine and UV-weathered) with ferrihydrite (Fh), an iron (oxy)hydroxide commonly found in nature. Heteroaggregation of pristine PS with Fh was controlled by electrostatic attraction. At neutral pH values, strong heteroaggregation was observed which led to the sedimentation of almost all PS particles. UV-weathering of PS led to lower negative surface charge, decrease of particle size, and formation of degradation products. Changes in surface properties of PS resulted in a different aggregation behavior with Fh. With increasing weathering time, the isoelectric point (pHIEP) of suspensions with PS and Fh shifted to lower pH values. Furthermore, we observed aggregation and subsequent sedimentation of weathered PS and Fh for a wider pH range (pH 3-7) compared to pristine PS (pH 6.5-7.5). We attribute this observation to increased surface reactivity of PS due to the formation of functional groups on the surface through UV-weathering. In addition, degradation products (e.g. oligomers) formed during weathering might have also interacted with PS and Fh and therefore further affected the surface properties of the particles. Overall, UV-weathering but also interactions of MP particles with environmental particles cause changes of MP surface properties, which influence its environmental behavior in water and might lead to a removal from the water column and accumulation in sediments.

Impact of the hydrated functional zone on the adsorption of ciprofloxacin to microplastics under the influence of UV aging

The inevitable UV aging of microplastics (MPs) is one of the key factors affecting their interaction with antibiotics. In this study, polyethylene (PE) and polystyrene (PS) MPs were aged with UV irradiation. The adsorption isotherms and kinetics of ciprofloxacin (CIP) to virgin and aged MPs were investigated through various models, and the effects of pH on the adsorption amount were explored. Characterization revealed that the surfaces of aged MPs became rougher, and the hydrophilicity increased. These aged MPs were still in the early stage of aging on the basis of their carbonyl index (CI) (<0.2) and O/C (<0.04) values. The adsorption isotherms indicated that the adsorption mechanism of aged PE was different from that of virgin PE. Compared with virgin PE, the adsorption amount of aged PE increased by 87.80-95.45%, and the adsorption rate decreased by 65.52-80.74%. However, aging did not significantly affect the equilibrium adsorption amount or adsorption rate of aged PS. The external diffusion rate (Kext) (about 2.29-0.36 h-1) was almost 30 times greater than the internal diffusion rate (Kint) in the film-pore mass transfer (FPMT) model, indicating that CIP adsorption rate was dominated by external diffusion. A hydrated functional zone is thought to form around aged MPs, thus changing the adsorption mechanism and adsorption amount of aged PE. Therefore, more attention should be given to alterations in the hydrated functional zone in the early stage of MPs aging.

Adsorption of Macrolide Antibiotics by Aged Microplastics of Different Sizes: Mechanisms and Effects

Microplastics (MPs) and antibiotics are widely detected in water bodies. However, the adsorption behavior and mechanism of different particle size polystyrene (PS) MPs on macrolide antibiotics under natural aging remain to be elucidated. In this study, potassium persulfate (K2S2O8) was used to simulate the natural aging process of PS MPs. The adsorption behavior and mechanism of different size PS (80 and 400 μm) toward azithromycin (AZI), clarithromycin (CLA), and erythromycin (ERY) were investigated. Results of SEM showed that the surface roughness of aged PS MPs increased with the appearance of cracks, pits, and pores. XPS and FTIR analyses showed enhanced C=O functional groups in the aging process. The adsorption isotherm models revealed that the aging processes enhanced the AZI, CLA, and ERY adsorption tendency, as evidenced by the highest adsorption capacity for aged-80 μm (645, 665, 184 mg/kg) > original-80 μm (412, 420, 120 mg/kg), and aged-400 μm (280, 330, 110 mg/kg) > original-400 μm (197, 308, 100 mg/kg). Kinetic model fitting revealed that the adsorption process occurred in three stages: rapid, slow, and saturation. Adsorption kinetic curves for original and aged PS MPs conformed to the pseudo-second-order kinetic model. In contrast, the adsorption isotherm data fit the Langmuir model, indicating that the process primarily involved uniform monolayer chemical adsorption. Our findings provide insights into the substantial changes in the interactions between PS and macrolide antibiotics with aging processes.

The wheel of time: The environmental dance of aged micro- and nanoplastics and their biological resonance

The aging of micro- and nanoplastics (MNPs) significantly affects their environmental behavior and ecological impacts in both aquatic and terrestrial ecosystems. This review explored the known effects of aging on MNPs and identified several key perspectives. Firstly, aging can alter the environmental fate and transport of MNPs due to changes in their surface properties. This alteration accelerates their accumulation in specific habitats like oceans and soils, resulting in increased bioaccumulation by organisms. In addition, aged MNPs interact differently with living organisms than their pristine counterparts by influencing the attachment of biofilms and other microorganisms in aquatic ecosystems. Moreover, the aging processes of MNPs exhibit adverse effects on aquatic and terrestrial organisms via increasing the bioavailability and potential toxicity of MNPs as degradation products are released. Last but not least, the biodegradation potential of MNPs can be altered by the aging process, thus affecting their degradation rates and pathways in the environment. However, there are still knowledge gaps regarding the natural aging behaviors of MNPs, such as the aging mechanisms of different types of plastic, the influence of environmental factors, the release of pollutants, and even the effects of aging on their transformation in different ecosystems. Therefore, a great contribution can be made to sustainable plastic use and environmental preservation by studying the natural aging of common MNPs and their subsequent biological effects.

Distribution and Biological Response of Nanoplastics in Constructed Wetland Microcosms: Mechanistic Insights into the Role of Photoaging

Concern over nanoplastic contamination of wetland ecosystems has been increasing. However, little is known about the effect of photoaging on the distribution and biological response of the nanoplastics. Here, palladium-labeled polystyrene nanoplastics (PS-Pd NPs) at 0.05-50 mg/L were exposed to constructed wetland microcosms containing floating (Eichhornia crassipes) and submerged (Vallisneria natans) macrophytes. Results demonstrate that PS-Pd NPs' concentration in surface water after 2-4 weeks of exposure was decreased by over 98.4% as compared with that in the 1st week. Photoaging enhanced the surface charge and colloidal stability of PS-Pd NPs, with a subsequent increase of the content of PS-Pd NPs in surface and middle layer water by 264.6 and 207.4%, respectively. Additionally, photoaging significantly enhanced the accumulation of PS-Pd NPs in E. crassipes roots by 6.9-65.0% and significantly decreased it in V. natans shoots by 59.7-123.0%. PS-Pd NPs inhibited the growth of V. natans by 43.8% at 50 mg/L. Mechanistically, PS-Pd NPs induced oxidative stress in V. natans, leading to the disruption of the metabolic pathway. Interestingly, PS-Pd NP exposure inhibited nitrification in wetland ecosystems due to the alteration of the related bacterial community (Ellin6067 decreased by 13.19%). These findings deepen our understanding of the environmental fate and risk of plastic particles in wetland ecosystems.

Aging-mediated selective adsorption of antibiotics by tire wear particles: Hydrophobic and electrostatic interactions effects

Tire wear particles (TWPs), as a prevalent form of microplastic pollution in aquatic environments, have been shown to adsorb antibiotics, potentially exacerbating their toxic effects. This study provides a comprehensive analysis of the adsorption of ofloxacin (OFL), ciprofloxacin (CIP), sulfadiazine (SDZ), and tetracycline (TC) on TWPs that have undergone various aging processes, including cyclic freeze-thaw and ozone aging. We observed a significant increase in the specific surface area (SBET) of TWPs after aging, from an initial 2.81 ± 0.29 to 6.63 ± 0.16 m2/g for ozone-aged TWPs. This enhancement in surface area and pore volume led to a respective 1.36-fold and 28-fold increase in adsorption capacity for OFL and CIP, highlighting the substantial impact of aging on TWPs' adsorptive properties. Conversely, the adsorption of SDZ and TC was reduced post-aging, suggesting a complex interaction between antibiotic physicochemical properties and TWPs' surface characteristics. The pseudo-second-order model, indicating chemisorption interactions, effectively described the adsorption kinetics, with the Freundlich isotherm model capturing the adsorption behavior more accurately than the Langmuir model. Our findings underscore the critical role of hydrophobic and electrostatic interactions in the adsorption process, particularly for SDZ and TC. This study's results offer crucial insights into the environmental implications of TWPs, emphasizing the need for further research on their role in the transport and fate of antibiotics in aquatic ecosystems.

Cotransport of nanoplastics with nZnO in saturated porous media: From brackish water to seawater

The ocean serves as a repository for various types of artificial nanoparticles. Nanoplastics (NPs) and nano zinc oxide (nZnO), which are frequently employed in personal care products and food packaging materials, are likely simultaneously released and eventually into the ocean with surface runoff. Therefore, their mutual influence and shared destiny in marine environment cannot be ignored. This study examined how nanomaterials interacted and transported through sea sand in various salinity conditions. Results showed that NPs remained dispersed in brine, while nZnO formed homoaggregates. In seawater of 35 practical salinity units (PSU), nZnO formed heteroaggregates with NPs, inhibiting NPs mobility and decreasing the recovered mass percentage (Meff) from 24.52% to 12.65%. In 3.5 PSU brackish water, nZnO did not significantly aggregate with NPs, and thus barely affected their mobility. However, NPs greatly enhanced nZnO transport with Meff increasing from 14.20% to 25.08%, attributed to the carrier effect of higher mobility NPs. Cotransport from brackish water to seawater was simulated in salinity change experiments and revealed a critical salinity threshold of 10.4 PSU, below which the mobility of NPs was not affected by coexisting nZnO and above which nZnO strongly inhibited NP transport. This study highlights the importance of considering the mutual influence and shared destiny of artificial nanoparticles in the marine environment and how their interaction and cotransport are dependent on changes in seawater salinity.

Natural Organic Matter Stabilizes Pristine Nanoplastics but Destabilizes Photochemical Weathered Nanoplastics in Monovalent Electrolyte Solutions

Photochemical weathering and eco-corona formation through natural organic matter (NOM) adsorption play vital roles in the aggregation tendencies of nanoplastics (NPs) in aquatic environments. However, it remains unclear how photochemical weathering alters the adsorption patterns of NOM and the conformation of the eco-corona, subsequently affecting the aggregation tendencies of NPs. This study examined the effect of Suwannee River NOM adsorption on the aggregation kinetics of pristine and photoaged polystyrene (PS) NPs in monovalent electrolyte solutions. The results showed that photochemical weathering influenced the conformation of the eco-corona, which, in turn, determined NP stability in the presence of NOM. Hydrophobic components of NOM predominantly bound to pristine NPs through hydrophobic and π-π interactions, and extended hydrophilic segments in water hindered NP aggregation via steric repulsion. Conversely, hydrogen bonding facilitated the binding of these hydrophilic segments to multiple photoaged NPs, thereby destabilizing them through polymer bridging. Additionally, the stabilization and destabilization capacities of NOM increased with its concentration and molecular weight. These findings shed light on the destabilizing role of NOM in weathered NPs, offering new perspectives on environmental colloidal chemistry and the fate of NPs in complex aquatic environments.

Microplastics in soils: A comprehensive review

Microplastics (MPs) have become pervasive pollutants in terrestrial ecosystems, raising significant ecological risks and human health concerns. Despite growing attention, a comprehensive understanding of their quantification, sources, emissions, transport, degradation, and accumulation in soils remains incomplete. This review synthesizes the current knowledge on the anthropogenic activities contributing to soil MP contamination, both intentional and unintentional behaviors, spanning sectors including agriculture, domestic activities, transportation, construction, and industry. Furthermore, it examines the spatial distribution, accumulation, and abundance of MPs across various land use types, alongside a critical assessment of existing quantification methodologies. While the predominant metric for MP quantification is particle number concentration, integrating mass and area concentration enhances the ability to compare pollution levels, assess fluxes, and conduct risk analyses. Additionally, the review explores the transport behavior of MPs in soil, distinguishing between external mechanisms (abiotic factors: wind, leaching, and runoff, biotic factors: soil bioturbation and food chain interactions), and internal mechanisms that are impacted by the characteristics of MPs themselves (e.g., shape, color, size, density, surface properties), soil properties (e.g., porosity, pH, ionic strength, organic matter and mineral content), coexisting substances, and soil structural dynamics. The study of MP transport in soil remains in its early stages, with substantial gaps in knowledge. Future research should focus on integrating number, mass concentration, and area concentration for the more holistic quantification of MP abundance, and prioritize the development of more accurate and efficient methodologies. In addition, the investigation of MP transport and degradation processes under varying environmental conditions and soil management practices is critical for addressing this emerging environmental challenge.

UV-Aged Nanoplastics Increase Mercury Toxicity in a Marine Copepod under Multigenerational Exposure: A Carrier Role

Aged plastics possess diverse interactive properties with metals compared to pristine ones. However, the role of aging for nanoplastics (NPs) in being a carrier of mercury (Hg), a common marine environmental pollutant, and their combined effects remain unclear. This study investigated the carrier effect of ultraviolet-aged NPs on Hg and the ensuing toxicity in a marine copepod Tigriopus japonicus under a multigenerational scenario. Aged NPs revealed a better carrier role in Hg bioaccumulation than pristine ones, which was increased by 1.61, 1.52, and 1.54 times in F0, F1, and F2, respectively, probably attributed to increased levels of O-containing functional groups and better adsorption for Hg. Consequently, relative to Hg alone, Hg combined with aged NPs (rather than pristine ones) significantly compromised the copepod's fitness, e.g., the survival rate decreasing by 74.2 and 62.1% in F1 and F2, respectively. This is possibly linked to the most pronounced transcriptomic response under Hg combined with aged NPs, including disturbed cuticle formation, activated antioxidants, and down-regulation of reproductive genes. Overall, our findings emphasize the non-negligible risk of aged NPs as carriers of toxic metals and provide a better understanding about the long-term effects of coexisting NPs and metal pollution on organisms in real marine environments.

Identification and detection of label-free polystyrene microplastics in maize seedlings by Raman spectroscopy

Microplastics are a new type of pollutants that have attracted attention recently. However, there is limited research on the uptake of environmental microplastics by plants. In this study, scanning electron microscopy (SEM), micro-Raman spectroscopy, and Raman mapping were employed to identify and detect label-free micron-sized polystyrene (PS) microplastics accumulated in the roots and stems of maize (Zea mays L.) seedlings. The results demonstrated that the Raman spectra of PS microplastics were predominantly concentrated in the xylem and ducts of seedlings, confirming the transfer behavior of microplastics in the plants. The Raman spectra of PS microplastics in seedlings exhibited distinctive peaks at 621, 1002, 1030, and 1604 cm-1, and the matching scores of these spectra with the standard PS Raman spectrum ranged from 40.61 % to 86.93 %. Additionally, the Raman mapping facilitated the precise identification and visualization of microplastics within the roots and stems of seedlings. The smallest size of the detected PS microplastics was ∼2 μm. This study provides new insights into the use of Raman spectroscopy for the detection of microplastics in plants.

Aging process potentially aggravates microplastic toxicity in aquatic organisms: Evidence from a comprehensive synthesis

Microplastics (MPs; <5 mm) will inevitably encounter aging processes after being released into the environment. However, the effect of aging on MPs toxicity in aquatic environment is still unclear despite that aging plays a critical role in changing MPs characteristics and behavior. Here, we conducted a meta-analysis to assess the effects of aging on MPs biotoxicity in aquatic environment. We found that aging displayed an overall aggravating effect (Hedges' g = -0.595, P < 0.05) on MPs toxicity in aquatic organisms, while the effects varied across different taxa; namely, aging potentially alleviates MPs biotoxicity to hydrophytes (Hedges' g = 0.383, P > 0.05) while significantly exacerbates MPs toxicity to other organisms, such as algae (Hedges' g = -0.784, P < 0.05), zooplanktons (Hedges' g = -0.366, P < 0.05), and fish (Hedges' g = -0.560, P < 0.05). Moreover, the aggravating effects of aging on MPs biotoxicity were closely related to biological traits (e.g., Hedges' g = -0.378 for growth and development, Hedges' g = -0.957 for metabolism, and Hedges' g = 0.054 for immune system). We further found that aging methods, MPs characteristics, and environmental designs were also crucial regulators for the aging impacts on MPs toxicity. Taken together, our findings demonstrated that aging process appears to boost MPs biotoxicity, and there are complex factors determining aging impacts on MPs biotoxicity. Given the persistent release of MPs and the aggravating effects of aging in aquatic environments, the risk posed by MPs should be carefully considered in the future.

Adsorption and Desorption Behavior of Cr(VI) on Two Typical UV-Aged Microplastics in Aqueous Solution

Microplastics (MPs) are novel pollutants that can adsorb heavy metals in water environments and migrate together as carriers and are prone to aging due to the light in water. However, few reports have been published on the synergistic behavior and effects of these different types of aged MPs on the adsorption and desorption of Cr(VI). Here, two MP types─polyamide (PA) and polylactic acid (PLA)─were aged by UV irradiation, and the adsorption and desorption behaviors of MPs on Cr(VI) were studied. The results indicated that UV light can rapidly age MPs. After the MPs were exposed to UV light, their specific surface area, negative charge, and oxygenic groups increased, resulting in enhanced hydrophilicity. The aged MPs depicted a markedly enhanced adsorption capacity for Cr(VI) compared with the results of aged-PA > pristine-PA > aged-PLA > pristine-PLA. The process followed the Langmuir and pseudo-second-order models, confirming that chemical and monolayer adsorption are the primary processes involved in the adsorption of Cr(VI) by aged MPs. Cr(VI) was more easily desorbed in the simulated gastric fluid environment. The desorption rate of aged MPs was lower than that of pristine MPs because of their stronger binding forces to Cr(VI). The binding of Cr(VI) to MPs mainly depends on synergistic mechanisms such as electrostatic attraction, reduction reactions, and chelation of oxygenic groups. This study clarifies the reciprocity mechanism between aging MPs and Cr(VI) and provides further insights and guidance for controlling the joint pollution between MPs and heavy metal pollutants in the future.

A Critical Review of an Environmental Risk Substance Induced by Aging Microplastics: Insights into Environmentally Persistent Free Radicals

Microplastics (MPs), as an emerging contaminants category, can undergo complex aging in a variety of environmental matrices in which the chemical bonds of polymer molecules can be broken to form free radicals. While the existence of free radicals in aged plastics has been known for over half a century, only recently has significant research on a new type of environmentally risky substance, namely environmentally persistent free radicals (EPFRs), present in aged MPs and their environmental effects, been started, but it is still in its infancy. To address these issues, this work examines EPFR generation on MPs and their environmental effect by reviewing publications from 2012 to 2023. The aging processes and mechanisms of MPs in the environment are first summarized. Then, the occurrence and formation mechanisms of EPFRs on aged MPs are specifically discussed. Additionally, the reactivity of EPFRs on aging MPs and their influencing factors are comprehensively considered, such as their physicochemical properties, oxygen content, and coexisting substances. Due to their reactivity, EPFRs can interact directly with some substances (e.g., p-nitrophenol and proteins, etc.) or induce the generation of reactive oxygen species, leading to diverse environmental effects, including pollutant transformation, biotoxicity, and health risks. Finally, research challenges and perspectives for EPFRs formation on aging MPs and related environmental implications are presented. Given the environmental fate and risk of MPs-EPFRs, our urgent call for a better understanding of the potential hazards of aged MPs is to help develop a sustainable path for plastics management.

Factors Influencing the Vertical Migration of Microplastics up and down the Soil Profile

Soil ecosystems are under serious threat from microplastics (MPs), and this is causing worldwide concern. The relationship between soil and MPs has become a popular research topic, and the vertical migration of soil MPs is of increasing interest. This Review summarizes the current status of research into the factors affecting the vertical migration of soil MPs. Published research shows that the characteristics of MPs and the physicochemical properties of the soil affect the infiltration process. Soil organisms play a key role in the vertical migration by acting as vectors or as a result of adsorption. Dissolved organic matter and metal oxides transfer MPs by adsorption-desorption. In addition, rainfall and dry-wet cycles alter the mobility of soil MPs, leading to changes in migration processes. Agricultural activities such as tillage and irrigation may distribute MPs throughout the topsoil. Vertical migration of soil MPs is a process influenced by a combination of factors, and the role of these factors in MP deposition needs to be explored further.

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.

Mobility of biochar-derived dissolved organic matter and its effects on sulfamerazine transport through saturated soil porous media

Dissolved organic matter (DOM) released from biochar may impact antibiotic mobility and environmental fate in subsurface environments. Here, DOM samples derived from biochars (BDOM) generated by pyrolyzing corn straw at 300, 450, and 600 °C were employed to elucidate the mobility characteristics of these organic substances and their influences on the transport of sulfamerazine (SMZ, a typical sulfonamide antibiotic) in soil porous media. The results demonstrated that BDOM produced at a lower pyrolysis temperature exhibited greater mobility owing to the weaker hydrophobic and H-bonding interactions between BDOM and soil particles. Additionally and importantly, BDOM facilitated the promotion of SMZ mobility owing to the increased electrostatic repulsion between SMZ- forms and soil grains, the steric hindrance effect induced by the deposition of organic matter, and the competitive retention between SMZ molecules and BDOM. Meanwhile, the promotion effects of BDOM enhanced with improving pyrolysis temperature owing to the promoted deposition of organic matter on soil surfaces and the strengthened electrostatic repulsion. Moreover, the facilitated effects of BDOM on SMZ mobility declined as the solution pH values were raised from 5.0 to 9.0 or the flow rate increased from 0.18 to 0.51 cm min-1. This trend was due to decreased deposition competition and the steric effect caused by decreased retention of BDOM on soil particles. Furthermore, the cation-bridging effect emerged as an important mechanism contributing to the promotion effects of BDOM when the solution contained divalent cations (Cu2+ or Ca2+). Moreover, a two-site non-equilibrium model was used to interpret the controlling mechanisms for the effects of BDOM on the transport of SMZ. Findings from this work highlight that biochar-derived dissolved organic matter can remarkably affect the environmental behaviors of antibiotics in aquatic environments.

Micro/nano plastics inhibit the formation of barium sulfate scale on metal surface

Mineral scale (scale) is the crystalline inorganic precipitate from aqueous solution. Scale formation in pipelines has long been a challenge in various industrial systems. Micro/nano plastics (MNPs) have the potential to strongly influence scale formation process. However, comprehensive studies and mechanistic understanding of the interactions between MNPs and scales remain significantly underexplored. To fill this gap, we firstly adopted quartz crystal microbalance with dissipation (QCM-D) technology to monitor the in situ formation of barium sulfate (BaSO4) (0.001 M, saturation index 2.5) scale influenced by MNPs on metal surfaces. Microplastic (MP) (5 µm)-loaded surface exhibits hydrophobicity (contact angle > 123.1º), which reduces the rate of scale formation (90.86 ± 11.01 (ng cm-2 min-1)). Electrostatic repulsion impeded crystal growth while ion adsorption has a limited effect. Experiments on BaSO4 formation on metal pipes loaded with foam packaging debris were conducted over 30 days, and similar inhibition results were obtained. This study highlights the important role of MNPs in controlling heterogeneous nucleation and crystal growth of scale on metal surfaces, providing valuable insights for both MNPs and scale research.

A state-of-the-art review of environmental behavior and potential risks of biodegradable microplastics in soil ecosystems: Comparison with conventional microplastics

As the use of biodegradable plastics becomes increasingly widespread, their environmental behaviors and impacts warrant attention. Unlike conventional plastics, their degradability predisposes them to fragment into microplastics (MPs) more readily. These MPs subsequently enter the terrestrial environment. The abundant functional groups of biodegradable MPs significantly affect their transport and interactions with other contaminants (e.g., organic contaminants and heavy metals). The intermediates and additives released from depolymerization of biodegradable MPs, as well as coexisting contaminants, induce alterations in soil ecosystems. These processes indicate that the impacts of biodegradable MPs on soil ecosystems might significantly diverge from conventional MPs. However, an exhaustive and timely comparison of the environmental behaviors and effects of biodegradable and conventional MPs within soil ecosystems remains scarce. To address this gap, the Web of Science database and bibliometric software were utilized to identify publications with keywords containing biodegradable MPs and soil. Moreover, this review comprehensively summarizes the transport behavior of biodegradable MPs, their role as contaminant carriers, and the potential risks they pose to soil physicochemical properties, nutrient cycling, biota, and CO2 emissions as compared with conventional MPs. Biodegradable MPs, due to their great transport and adsorption capacity, facilitate the mobility of coexisting contaminants, potentially inducing widespread soil and groundwater contamination. Additionally, these MPs and their depolymerization products can disrupt soil ecosystems by altering physicochemical properties, increasing microbial biomass, decreasing microbial diversity, inhibiting the development of plants and animals, and increasing CO2 emissions. Finally, some perspectives are proposed to outline future research directions. Overall, this study emphasizes the pronounced effects of biodegradable MPs on soil ecosystems relative to their conventional counterparts and contributes to the understanding and management of biodegradable plastic contamination within the terrestrial ecosystem.

Transport of reduced PBAT microplastics in saturated porous media: Synergistic effects of enhanced surface energy and roughness

Microplastic (MP) pollution presents significant global environmental challenges, exacerbated by reduction aging processes in anoxic environments, thereby increasing environmental risks and potential threats to human health. However, the mechanisms underlying the transport of reduced MPs remain poorly understood. In this study, laboratory-scale column experiments were conducted to investigate the transport behavior of polybutylene adipate terephthalate (PBAT), a common biodegradable MPs, and its reduced products obtained through the aging process mediated by two typical reducing agents, NaBH4 and Na2S, under varying conditions (ionic strength (IS), divalent cations, and low molecular weight organic acids (LMWOAs)). The results indicated that reduction aging improved the hydrophilicity of PBAT by increasing the surface roughness (roughness factor increased from 1.300 to 1.642) and surface energy (from 51.80 to 107.03 mN m-1), thereby increasing the mobility of reduced PBAT (with recovery rate increased from 53.77 % to 63.18 %). Increased IS decreased the mobility of reduced PBAT by decreasing the surface negative charge density. Divalent cations inhibited the mobility of both pristine and reduced PBAT in porous media, with pristine PBAT, containing more oxygen functional groups, exhibiting stronger inhibition. Furthermore, LMWOAs promoted the retention of reduced PBAT in porous media, which was dependent on the type of LMWOAs. This study revealed the alterations in MPs properties caused by reduction aging and their effects on transport mechanisms, offering new insights into the transport behavior and environmental risks of reduced MPs.

Insights into the controlling factors of the transport of tire wear particles in saturated porous media: The facilitative role of aging and fulvic acid

The widespread distribution and potential adverse effects of tire wear particles (TWPs) on soil and groundwater quality pose a growing environmental concern. This study investigated the transport behavior of TWPs in saturated porous media and elucidated the underlying mechanisms influenced by environmental factors. Additionally, the effects of key environmental factors, such as aging, ionic strength, cation species, medium type, and natural organic matter (NOM), on the transport of TWPs were evaluated. The results showed that aging processes simulated through O3 and UV irradiation altered the physicochemical properties of TWPs, increased the mobility of TWPs at low ionic strengths. However, the high ionic strengths and the presence of Ca2+ significantly inhibited the mobility of TWPs due to enhanced aggregation. The transport mechanism of the original and aged TWPs shifted from blocking to ripening under favorable retention conditions (i.e., high ionic strengths, divalent cations, and fine sands). Interestingly, the presence of fulvic acid (FA) inhibited the ripening of the three TWPs, significantly promoting their transport through a spatial site resistance mechanism. The two-site kinetic attachment model (TSKAM), extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory, and colloid filtration theory (CFT) were applied to describe the transport behavior of the TWPs. The study provided a comprehensive understanding of the transport behavior of TWPs in groundwater environments, highlighting the environmental risks associated with their widespread distribution.

Rapid Generation of Microplastics and Plastic-Derived Dissolved Organic Matter from Food Packaging Films under Simulated Aging Conditions

In this study, we show that low-density polyethylene films, a prevalent choice for food packaging in everyday life, generated high numbers of microplastics (MPs) and hundreds to thousands of plastic-derived dissolved organic matter (DOM) substances under simulated food preparation and storage conditions. Specifically, the plastic film generated 66-2034 MPs/cm2 (size range 10-5000 μm) under simulated aging conditions involving microwave irradiation, heating, steaming, UV irradiation, refrigeration, freezing, and freeze-thaw cycling alongside contact with water, which were 15-453 times that of the control (plastic film immersed in water without aging). We also noticed a substantial release of plastic-derived DOM. Using ultrahigh-resolution mass spectrometry, we identified 321-1414 analytes with molecular weights ranging from 200 to 800 Da, representing plastic-derived DOM containing C, H, and O. The DOM substances included both degradation products of polyethylene (including oxidized forms of oligomers) and toxic plastic additives. Interestingly, although no apparent oxidation was observed for the plastic film under aging conditions, plastic-derived DOM was more oxidized (average O/C increased by 27-46%) following aging with a higher state of carbon saturation and higher polarity. These findings highlight the future need to assess risks associated with MP and DOM release from plastic wraps.

Effect of background ions and physicochemical factors on the cotransport of microplastics with Cu2+ in saturated porous media

Microplastics (MPs) in subsurface environments are migratory and can carry heavy metals, increasing the extent of MP and heavy metal pollution. This study used quartz sand-filled column experiments to investigate the adsorption and cotransport behaviours of PS-MPs, O3, UV-aged PS-MPs, and Cu2+ at different MP concentrations, ionic strengths, and ionic valences in a saturated porous medium. The results showed that when MPs migrate alone in the absence of an ionic background, higher concentrations have increased mobility. In contrast, an increase in the background ion concentration or ion valence inhibits the individual transport capacity of PS-MPs. An increase in the concentration of background ions or elevation in the valence state promotes Cu2+ transport because of the action of the double electric layer on the surface of the colloid and the electrostatic repulsive forces combined with the background ions. The adsorption capacity of aged PS-MPs was stronger than that of PS-MPs because of the binding of the aged PS-MPs to Cu2+ through complexation and electrostatic attraction. In the binary system of PS-MPs/Cu2+, PS-MPs promoted Cu2+ transport and the mobility of Cu2+ loaded by PS-MPs decreased with increasing background ion concentration. The cotransport results showed that MPs promote Cu2+ transport in the following order: O3-aged Ps > UV-aged Ps > Ps, as the increasing cation concentration in the MPs and Cu2+ occupies the PS surface adsorption sites. Overall, PS is an effective carrier for Cu2+. These findings offer fresh exploration concepts for the joint migration of MPs and heavy metals in underground settings.

Effect of shape on the transport and retention of nanoplastics in saturated quartz sand

Nanoplastics (NPs) pose great challenges to soil-groundwater systems. This study investigated the transport and retention of self-synthesized 0.5-μm polystyrene NPs with different shapes using column experiments. The regular NPs were with spherical shapes, while the irregular NPs were with toroid-like shapes. The toroid-like shapes were the irregular shapes (with low aspect ratio) which have not been studied yet. The explorations were carried out in both 5-25 mM NaNO3 and 1-10 mM Ca(NO3)2 solutions. Both breakthrough curves (BTCs) and retained profiles (RPs) were monitored. Our findings uncovered a clear disparity in the transport of irregular and regular NPs, with irregular particles exhibiting lower transport ability compared to the regular ones. For example, the average breakthrough plateaus of the regular and irregular NPs were ∼0.9 and ∼0.5, respectively, in 10 mM NaNO3. In-depth theoretical analysis indicated that the lower XDLVO interaction energy barrier between the irregular NPs and quartz sand was one factor, and the greater margination of irregular NPs on quartz sand, as verified by the numerical simulation, was another factor leading to the decreased transport and increased retention of the irregular NPs. The obtained results highlighted the significance of considering particle shape in future modelling and predicting the fate of NPs in real environmental circumstances.

A critical review of co-pollution of microplastics and heavy metals in agricultural soil environments

The soil environment is a primary destination for contaminants such as microplastics (MPs) and heavy metals (HMs), which are frequently detected simultaneously. The long-term coexistence of MPs and HMs in the soil necessitates unavoidable interactions, affecting their environmental chemical behavior and bioavailability. These co-contaminants pose potential threats to soil organism growth and reproduction, crop productivity, food security, and may jeopardize human health via the food chain. This paper summarizes the sources and trends of MPs in the soil environment, along with the mechanisms and current research status of MP adsorption or desorption of HMs. Additionally, this paper reviews factors affecting HM adsorption on MPs, including MP properties, HM chemical properties, and other environmental factors. Lastly, the effects of MPs and HMs on soil ecology and human health are summarized. The interaction mechanisms and potential biological effects of their co-contamination require further exploration. Future research should delve deeper into the ecotoxic effects of MP-HM co-contamination at cellular and molecular levels, to provide a comprehensive reference for understanding the environmental behavior of their co-contamination in soil.

Acute inhibitory effects of tire wear particles on the removal of biological phosphorus：The critical role of aging in improving environmentally persistent free radicals

A comparative study explored how photoaging, ozonation aging, and Fenton aging affect tire wear particles (TWPs) and their phosphorus (P) removal in activated sludge. Aging altered TWPs' properties, increasing surface roughness, porosity, and generating more small particles, especially environmental persistent free radicals (EPFRs) in ozonation and Fenton aging. Post-aging TWPs (50 mg/L) inhibited sludge P removal significantly (p < 0.05), with rates of 44.3% and 59.6% for ozonation and Fenton aging, respectively. In addition, the metabolites involved in P cycling (poly-β-hydroxyalkanoates: PHA and glycogen) and essential enzymes (Exopolyphosphatase: PPX and Polyphosphate kinase: PPK) were significantly inhibited (p < 0.05). Moreover, TWPs led to a decrease in microbial cells within the sludge and altered the community structure, a situation exacerbated by the aging of TWPs. P-removing bacteria decreased (e.g., Burkholderia, Candidatus), while extracellular polymeric substance-secreting bacteria increased (e.g., Pseudomonas, Novosphingobium). Pearson correlation analysis highlighted EPFRs' role in TWPs' acute toxicity to microbial cells, yet, emphasizing particle size's impact on the sludge system's purification and community structure.

Cotransport of 6PPD-Q and pristine/aged microplastics in porous media: An insight based on transport forms and mechanisms

The environmental fate and risks of microplastics (MPs) and their associated contaminants have attracted increasing concern in recent years. In this study, the cotransport of six kinds of pristine and aged MPs and the antiager ozonation product N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine-quinone (6PPD-Q) were investigated via a series of batch and transport experiments, and characteristic analysis (e.g., SEM, FTIR and XPS). Generally, pristine MPs exhibit higher adsorption ability than aged MPs due to the hydrophobic interaction. The 6PPD-Q usually exhibited both free moving and bond-MPs moving during transport process in presence of MPs, but none free 6PPD-Q was detected in presence of pristine PP MPs. The mobility of 6PPD-Q was generally facilitated in presence of MPs by bond-MPs moving due to the hydrogen bonding, halogen bonding, π-π interaction (the maximum total mass recovery of 84.11%), which efficiency was influenced with the combined effect of adsorption ability and mobility of MPs. The pristine PVC MPs showed highest facilitation on 6PPD-Q transport. The retained 6PPD-Q in porous media also was released by various MPs with different mass recovery ranged from 15.72% to 56.26% via surface moving of MPs around porous media. Both the dissolved and retained 6PPD-Q decreased the MPs mobility with the minimum mass recovery of 34.02%. Findings from this study contribute to the prediction and assessment of the combined risks of MPs and 6PPD-Q.

Hydrogen bonding-mediated interaction underlies the enhanced membrane toxicity of chemically transformed polystyrene microplastics by cadmium

The global attention on microplastic pollution and its implications for human health has grown in recent years. Additionally, the co-existence of heavy metals may significantly alter microplastics' physicochemical characteristics, potentially amplifying their overall toxicity-a facet that remains less understood. In this study, we focused the membrane toxicity of modified polystyrene microplastics (PS-MPs) following cadmium (Cd) pretreatment. Our findings revealed that Cd-pretreated PS-MPs exacerbated their toxic effects, including diminished membrane integrity and altered phase fluidity in simulated lipid membrane giant unilamellar vesicles (GUVs), as well as heightened membrane permeability, protein damage, and lipid peroxidation in red blood cells and macrophages. Mechanistically, these augmented membrane toxicities can be partially ascribed to modifications in the surface roughness and hydrophilicity of Cd-pretreated PS-MPs, as well as to interactions between PS-MPs and lipid bilayers. Notably, hydrogen bonds emerged as a crucial mechanism underlying the enhanced interaction of PS-MPs with lipid bilayers.

Agricultural film-derived microplastics elevate the potential risk of pesticides in soil ecosystem: The inhibited leaching by altering soil pore

The residue of mulch film is a crucial source of microplastics (MPs) in agricultural fields. The effects of mulch film-derived MPs on the environmental behavior of pesticides in agriculture remain unclear. In the present study, the effects of MPs of different sizes (5 mm, 1 mm, 30 µm, and 0.3 µm) at environmentally relevant concentrations on pesticide transport were evaluated, and the mechanism was explored with respect to adsorption and pore structure using fluorescence visualization, the extended Derjaguin-Landau-Verwey-Overbeek model, and microcomputed tomography. MPs were found to be retained in the soil due to size limitation, pore capture, and surface adhesion. The presence of mm-sized MPs (5 and 1 mm) at a concentration of 0.25 % inhibited the leaching behavior of atrazine, metolachlor, and tebuconazole. MPs did not significantly alter the pesticide adsorption ability of the soil. The reduced leaching originated from the impact of MPs on soil pore structure. Specifically, the porosity increased by 16.2-25.0 %, and the connectivity decreased by 34.5 %. These results demonstrate that mm-sized MPs inhibit pesticide leaching by obstructing the pores and altering the transport pathways, thereby potentially elevating environmental risks, particularly to the soil ecosystem.

Intrinsic Peroxidase-like Activity of Polystyrene Nanoplastics Mediates Oxidative Stress

Nanoplastics represent a global environmental concern due to their ubiquitous presence and potential adverse impacts on public and environmental health. There is a growing need to advance the mechanistic understanding of their reactivity as they interact with biological and environmental systems. Herein, for the first time, we report that polystyrene nanoplastics (PSNPs) have intrinsic peroxidase-like activity and are able to mediate oxidative stress. The peroxidase-like activity is dependent on temperature and pH, with a maximum at pH 4.5 and 40 °C. The catalytic activity exhibits saturation kinetics, as described by the Michaelis-Menten model. The peroxidase-like activity of PSNPs is attributed to their ability to mediate electron transfer from peroxidase substrates to H2O2. Ozone-induced PSNP aging can introduce oxygen-containing groups and disrupt aromatic structures on the nanoplastic surface. While ozonation initially enhances peroxidase-like activity by increasing oxygen-containing groups without degrading many aromatic structures, extended ozonation destroys aromatic structures, significantly reducing this activity. The peroxidase-like activity of PSNPs can mediate oxidative stress, which is generally positively correlated with their aromatic structures, as suggested by the ascorbic acid assay. These results help explain the reported oxidative stress exerted by nanoplastics and provide novel insights into their environmental and public health implications.

Fate and transport of fragmented and spherical microplastics in saturated gravel and quartz sand

Microplastics in urban runoff undergo rapid fragmentation and accumulate in the soil, potentially endangering shallow groundwater. To improve the understanding of microplastic transport in groundwater, column experiments were performed to compare the transport behavior of fragmented microplastics (FMPs ∼1-µm diameter) and spherical microplastics (SMPs ∼1-, 10-, and 20-µm diameter) in natural gravel (medium and fine) and quartz sand (coarse and medium). Polystyrene microspheres were physically abraded with glass beads to mimic the rapid fragmentation process. The experiments were conducted at a constant flow rate of 1.50 m day-1 by injecting two pore volumes of SMPs and FMPs. Key findings indicate that SMPs showed higher breakthrough, compared to FMPs in natural gravel, possibly due to size exclusion of the larger SMPs. Interestingly, FMPs exhibited higher breakthrough in quartz sand, likely due to tumbling and their tendency to align with flow paths, while both sizes (larger and smaller relative to FMPs) of SMPs exhibited higher removal in quartz sand. Therefore, an effect due to shape and size was observed.

Enhanced sinks of polystyrene nanoplastics (PSNPs) in marine sediment compared to freshwater sediment: Influencing factors and mechanisms

The difference in the transport behaviors of nanoplastics consistently assistant with their toxicities to benthic and other aquatic organisms is still unclear between freshwater and marine sediments. Here, the mobilities of polystyrene nanoplastics (PSNPs) and key environmental factors including salinity and humic acid (HA) were systematically studied. In the sand column experiments, both tested PSNPs in the freshwater system (100 nm NPs (100NPs): 90.15 %; 500 nm NPs (500NPs): 54.22 %) presented much higher penetration ratio than in the marine system (100NPs: 8.09 %; 500NPs: 19.04 %). The addition of marine sediment with a smaller median grain diameter caused a much more apparent decline in NPs mobility (100NPs: from 8.09 % to 1.85 %; 500NPs: from 19.04 % to 3.51 %) than that containing freshwater sediment (100NPs: from 90.15 % to 83.56 %; 500NPs: from 54.22 % to 41.63 %). Interestingly, adding HA obviously led to decreased and slightly increased mobilities for NPs in freshwater systems, but dramatically improved performance for NPs in marine systems. Electrostatic and steric repulsions, corresponding to alteration of zeta potential and hydrodynamic diameter of NPs and sands, as well as minerals owing to adsorption of dissolved organic matter (DOM) and aggregations from varied salinity, are responsible for the mobility difference.

Overview of the environmental risks of microplastics and their controlled degradation from the perspective of free radicals

Owing to the significant environmental threat posed by microplastics (MPs) of varying properties, MPs research has garnered considerable attention in current academic discourse. Addressing MPs in river-lake water systems, existing studies have seldom systematically revealed the role of free radicals in the aging/degradation process of MPs. Hence, this review aims to first analyze the pollution distribution and environmental risks of MPs in river-lake water systems and to elaborate the crucial role of free radicals in them. After that, the study delves into the advancements in free radical-mediated degradation techniques for MPs, emphasizing the significance of both the generation and elimination of free radicals. Furthermore, a novel approach is proposed to precisely govern the controlled generation of free radicals for MPs' degradation by interfacial modification of the material structure. Hopefully, it will shed valuable insights for the effective control and reduction of MPs in river-lake water systems.

Migration characteristics of microplastics in riparian soils and groundwater

Investigations have revealed the presence of microplastics in both soil and groundwater, but the migration characteristics from soil to groundwater remain incompletely understood. In this study, two sampling sections consisting of soil-groundwater-river water were established near Lianxi Bridge and Xilin Bridge along the Jiuxi River in Xiamen. A total of 22 soil samples, 36 groundwater samples, and 18 river water samples were collected. Microplastics were detected in all samples with an abundance range of 392-836 n/kg in soil (mean, 655 ± 177 n/kg), 0.58-2.48 n/L groundwater (mean, 1.23 ± 0.42 n/L), and 0.38-1.80 n/L in river water (mean, 0.86 ± 0.41 n/L). Flakes predominantly constituted the shape of microplastics found in soil, while fibers dominated those present in water. Black, yellow, and red were the dominant color types. Polyamide (PA) and polyethylene (PE) were the main components of microplastics within soils, whereas polyethylene terephthalate (PET), polypropylene (PP), and PA prevailed within water. Microplastic particle sizes ranged from 39 to 2498 μm in soils, mainly from 29 to 3394 μm in water. The upstream section displayed higher abundances of microplastic compared to the downstream, revealing the soil particles having an intercepting effect on microplastics. The distribution and migration of microplastics in soil and groundwater are affected by many factors, including natural and anthropogenic factors, such as soil depth, soil properties, pore structure, hydrodynamics, hydraulic connections between groundwater and surface water, the extensive utilization and disposal of plastics, irrational exploitation of groundwater, and morphology and types of microplastics. These research findings contribute to a better understanding of the pathways, migration capacity, and influencing factors associated with microplastic entry into groundwater, thereby providing valuable technical support for the development of strategies aimed at controlling microplastic pollution.

Molecular-level insight into the behavior of metal cations and organic matter during the aggregation of polystyrene nanoplastics

In this study, the behavior of metal cations and organic matter during polystyrene nanoplastics (PSNP) aggregation was explored combing experimental measurements and molecular dynamics simulation. The results indicated that coexisting organic matter, including organic pollutants and humic acid (HA), play a complex role in determining PSNP aggregation. The representative organic pollutant, bisphenol A, exhibited competitive behavior with HA during heteroaggregation, and the heteroaggregation between HA and PSNP was impaired by bisphenol A. The bridging effect of metal ions in aggregation is related to their interaction strength with functional groups, binding affinity with water molecules, and concentration. In particular, Mg2+ interacts more strongly with oxygen-containing functional groups on PSNP than Ca2+. However, Mg2+ is more favorable for binding with water and is therefore not as effective as Ca2+ for destabilizing PSNP. Compared with Ca2+ and Mg2+, Na+ showed a weaker association with PSNP; however, it still showed a significant effect in determining the aggregation behavior of PSNP owing to its high concentration in seawater. Overall, we provided a molecular-level understanding of PSNP aggregation and deepened our understanding of the fate of nanoplastics.

Mechanism Involved in Polyvinyl Chloride Nanoplastics Induced Anaerobic Granular Sludge Disintegration: Microbial Interaction Energy, EPS Molecular Structure, and Metabolism Functions

Nanoplastics (NPs) are emerging pollutants and have been reported to cause the disintegration of anaerobic granular sludge (AnGS). However, the mechanism involved in AnGS disintegration was not clear. In this study, polyvinyl chloride nanoplastics (PVC-NPs) were chosen as target NPs and their long-term impact on AnGS structure was investigated. Results showed that increasing PVC-NPs concentration resulted in the inhibition of acetoclastic methanogens, syntrophic propionate, and butyrate degradation, as well as AnGS disintegration. At the presence of 50 μg·L-1 PVC-NPs, the hydrophobic interaction was weakened with a higher energy barrier due to the relatively higher hydrophilic functional groups in extracellular polymeric substances (EPS). PVC-NPs-induced ROS inhibited quorum sensing, significantly downregulated hydrophobic amino acid synthesis, whereas it highly upregulated the genes related to the synthesis of four hydrophilic amino acids (Cys, Glu, Gly, and Lys), resulting in a higher hydrophily degree of protein secondary structure in EPS. The differential expression of genes involved in EPS biosynthesis and the resulting protein secondary structure contributed to the greater hydrophilic interaction, reducing microbial aggregation ability. The findings provided new insight into the long-term impact of PVC-NPs on AnGS when treating wastewater containing NPs and filled the knowledge gap on the mechanism involved in AnGS disintegration by PVC-NPs.