Aggregation kinetics of UV irradiated nanoplastics in aquatic environments

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.

Impact of organic carbon-Mn oxide interactions on colloid stability and contaminant metals in aquatic environments

Interactions between organic carbon and Mn oxides can lead to the formation of C-Mn colloids, which play a crucial role in regulating Mn mobility in the environment. Despite the significance of these interactions, the impact of C-Mn oxide interactions on the mobility of these colloids, particularly in the presence of contaminant metals, remains poorly understood. This study investigated the aggregation kinetics of C-Mn colloids formed through the reaction between humic acid and Mn oxides at three C:Mn molar ratios in the presence of divalent cations (Ca2+ and Mg2+). The introduction of organic carbon increased the stability (i.e., ability to resist aggregation) of C-Mn colloids compared to pure Mn(IV) colloids, as reflected in the higher critical coagulation concentration (CCC). As C:Mn molar ratios rose from 0.5 to 3 during colloid formation, the CCCs for the resulting C-Mn colloids increased from 3.6 mM to 7.2 mM Ca2+. However, at the highest C:Mn ratio (C:Mn=15), the CCCs decreased slightly to 7.0 mM Ca2+, with a similar trend observed for Mg2+. The stability of C-Mn colloids was affected by characteristics including electrostatic repulsion, surface functional groups, and Mn(II) content, resulting from reaction with dissolved organic carbon. Based on CCCs, C-Mn colloids were most stable in the presence of Mn2+ (6.9 mM), followed by Co2+ (5.9 mM), Zn2+ (2.7 mM), and Cd2+ (1.9 mM). The capacity of contaminant metals to destabilize C-Mn colloids followed the reverse order, with Cd2+ having the greatest destabilizing effect. Variations among the metals were influenced by factors such as atomic radius, hydration shell, electronegativity, and electrostatic repulsion. These results provide new insight into the aggregation behavior of C-Mn colloids and the mechanisms controlling the fate and mobility of associated contaminant metals. This knowledge has important implications for understanding contaminant transport in natural waters and optimizing water treatment processes.

Escherichia coli and phosphate mediated the distinct retention of small-sized nano-plastic particles in seawater-saturated porous sands

Small nano-plastics (NPs, < 30 nm) with a high accumulation in biological organisms in coastal areas might react with widely presented bacteria and phosphate, which remains unclear. Therefore, the mechanisms governing the transport of two-sized NPs with Escherichia coli (E. coli) and phosphate were investigated in hyper-saline water-saturated sand porous media. The results showed that 20 nm NPs exhibited more hetero-aggregation with E. coli than 80 nm NPs, associated with lower k1d/k1 values (0.268 vs. 0.412) and more substantially suppressed depth of φmax (17.83 KBT vs. 23.44 KBT), based on two-site kinetic attachment retention model fitting and extended-Derjaguin-Landau-Verwey-Overbeek theory. Accordingly, even though the mass recovery percentage of both sized NPs alone was similar, the irreversible deposition of 20 nm NPs doubled by E. coli, increasing the coastal environmental risks. In contrast, 80 nm NPs reversibly attached to the sands with less effect by E. coli, causing secondary pollution. The copresence of phosphate pronouncedly enhanced the transportability of two-sized NPs with E. coli, especially increasing 20 nm NP mobility from 17.7 % to 39.2 % in 200 mM NaCl by preferentially adsorbing onto E. coli to avoid agglomeration with NPs. This study highlights the potential risk of small NPs in complicated coastal ecosystems.

Robust polyaniline coating magnetic biochar nanoparticles for fast and wide pH and temperature range removal of nanoplastics and achieving label free detection

Nanoplastics as an emerging pollutant are ubiquitous in water and still not easy to measure and remove. In this regard, polyaniline coating magnetic biochar nanoparticles constructed by pyrolysis of ferrate pretreated bagasse and ball milling and coating surface with polyaniline (PA@MBCBM) were tested for their capability to attach and remove polystyrene nanoplastics in water. Porousness and rich functional groups and positive charging property of PA@MBCBM was responsible for fast, high capacity and robust attaching of nanoplastics. 94.9 % - 99.0 % of nanoplastics were removed at wide range of pH conditions (1 - 10) and PA@MBCBM was reusable for seven times with less changing of performance, and maximum adsorption capacities reached 276.24 - 334.45 mg/g at both cold and warm temperatures (5 - 35 °C). Moreover, taking advantages of efficient nanoplastics adhesion, high conductivity and electrochemical activity, the PA@MBCBM, was tested to fabricate a label free screen-printed electrode for nanoplastics detection, and achieved reasonable sensitivity with the lowest detection limit being 1.26 μg/L. In addition, exceptional performances of adsorption and detection in real water samples were also successfully realized. The proposed PA@MBCBM having dual function of robust and efficient adsorption removal, and label free and sensitive determination of nanoplastics, would be greatly constructive for reliable, cost effective and effective control and monitoring of the nanoplastics contamination.

Interfacial interactions of submicron plastics with carbon dots: Insights into the interface properties of microplastic weathering

The interfacial properties and environmental behavior of microplastics (MPs) will change with weathering. A new idea to study the interfacial properties of MPs is provided based on fluorescence response and light scattering changes. Submicron microspheres (PS-AA) obtained by soap-free emulsion polymerization have a well-defined composition and clean surface with carboxyl groups. The interfacial properties of PS-AA changed after Fenton and UV aging, and the sharp edges became blurred. Information on the interfacial interactions of leaf-derived carbon dots (R-CDs) and citrate carbon dots (B-CDs) with aged PS-AA was obtained by recording fluorescence and scattering changes. R-CDs can fluorescently respond to carrying contaminants on aged PS-AA, and their correlation increases with the degree of aging (R2=0.8388). The scattering peak of PS-AA decreased after aging, and the change in scattering/fluorescence ratios with concentration had a good linear relationship under the coexistence of B-CDs (R2=0.9983). Aging of PS-AA increases the contamination-carrying capacity and decreases the optical properties, which may be attributed to the increased oxygen-containing functional groups, ring opening of substituted benzene, and shell decomposition. The response mechanism of carbon dots (CDs), the aging process of PS-AA, and the interfacial behavior were further explained based on the density functional theory (DFT). This study reveals the changes in interfacial properties of submicron plastics with the aging process based on fluorescence response and scattering changes.

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.

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.

Aggregation behavior of photoaging nanoplastics in artificial sweat solutions

The aging process and aggregation behavior of nanoplastics govern their fate and ecological risk in aquatic environments. Unfortunately, the aggregation behavior of nanoplastics in sweat and the effect of aging on this process remains unknown. This study investigated the aggregation kinetics of polystyrene nanoplastics (PS-NPs) in three types of artificial sweat before and after photoaging. The aggregation rates (k) of PS-NPs before and after photoaging followed the order ofAmerican-Association-of-Textile-Chemists-and-Colorists-pH-4.3 (kaged =0.6381 nm/s, koriginal =0.4337 nm/s) > British-Standard-pH-6.5 (kaged =0.3589 nm/s, koriginal =0.1297 nm/s) >International-Standard-Organization-pH-8.0 (kaged =0 nm/s, koriginal =0 nm/s). Photoaging decreased the C-O content on the surface of PS-NPs from 4.47 % to 1.97 %, thus to promote the aggregation of PS-NPs. Moreover, decrease of the pH value of three types of artificial sweat (from 8.0 to 4.3) all increased the aggregation rate of the PS-NPs. Inorganic constituents (NaCl and Na2HPO4) promoted the aggregation of PS-NPs by increasing the positive charges on the surface of PS-NPs, while organic constituents (L-histidine, lactic acid, and urea) stabilized PS-NPs by adsorbing on the surface of PS-NPs. These findings demonstrated that the solution conditions of sweat and photoaging process together determined the transport and distribution of nanoplastics in sweat, offering new insights for assessing and predicting the skin exposure risk of nanoplastics.

Towards quality-assured measurements of microplastics in soil using fluorescence microscopy

Fluorescence microscopy is increasingly seen as a fast, user-friendly, and high-throughput method for detecting microplastics (MPs) in soil; however, its effectiveness across diverse MP types and soil properties remains underexplored. This study tested a fluorescence microscopy-Nile red (NR) staining approach on eight MP types, covering both biodegradable and non-biodegradable plastics, in three size ranges (≤ 150 µm, 100-250 µm, 500-1000 µm) across loamy, clayey, and sandy soils. Each sample, processed in triplicate, underwent a relatively quick and straightforward extraction procedure involving density separation, organic digestion, and NR staining, followed by fluorescence and bright-field microscopy. A new digital image analysis pipeline using Image J was developed to expedite and (semi)automate MP quantification. Recoveries ranged from 80% to 90% for MPs with a Feret diameter of 500-1000 µm, regardless of soil type. In contrast, the recovery of smaller MPs (Feret dia. ≤ 250 µm) varied depending on the soils and plastic types: recoveries for low-density polyethylene (LDPE) reached 85% in sandy soil and 90% in loamy soil, whereas those for biodegradable polybutylene adipate terephthalate/polylactic acid (PBAT/PLA) were only 60% and 10%, respectively. The lowest recovery rate was observed in clayey soil and for biodegradable plastics. The method was tested on non-agricultural soil samples, yielding a MP mean number concentration of 20.7 ± 9.0 MPs/g for MPs sized from dia. ≥ 25 µm, comparable to Fourier transform infrared (FPA-µ-FTIR) results of 13.1 ± 7.3 MPs/g (p > 0.05). We conclude that fluorescence microscopy with NR staining and automated particle quantification offers a time-efficient, reproducible, and accurate method for MP detection in light-textured soils, whereas limitations remain for reliable MP analysis in clay-dominated soils.

Crystallinity- dependent heteroaggregation and co-sedimentation between polystyrene nanoplastics and iron (hydro)oxides

Iron (hydro)oxides (IOs) with different crystallinities are widespread in the aquatic environment. They coexist with nanoplastics (NPs) and tend to interact with each other. The properties of minerals can greatly influence the heteroaggregation of minerals and NPs, being manifested not only in the heteroaggregation capacity but also in the interaction mode. This study investigated the heteroaggregation and co-sedimentation between polystyrene nanoplastics (PSNPs) and IOs with different crystallinity. We found that the zeta potential of IOs increased with rising IOs crystallinity. DLVO calculations indicated stronger electrostatic attraction between negatively-charged NPs and highly-crystalline IOs, resulting in greater heteroaggregation capacity. In addition, the heteroaggregation capacity of PSNPs with IOs declined as the pH value and ion strength increased. The Fourier transform infrared spectra (FTIR) and two-dimensional correlation spectroscopy (2D-COS) analyses indicated that there was strong hydrogen bonding between IOs with high crystallinity and PSNPs, contributing to a greater heteroaggregation capacity of PSNPs on highly-crystalline IOs than low-crystalline IOs. Zeta potential measurements revealed that negatively charged PSNPs heteroaggregated on the surface of positively charged IOs, capable of neutralizing or even reversing the surface charge. This, in turn, affected the sedimentation of IOs-PSNPs agglomerates and their fate. These findings elucidated the key role of crystallinity on the heteroaggregation between IOs and PSNPs, and offered insight into their environmental fate.

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.

Subchronic Exposure to Polystyrene Nanoplastics Disrupts Placental Development and Calcium Homeostasis: Insights from In Vivo and In Vitro Models

Nanoplastics have recently emerged as persistent pollutants of global concern that pose substantial risks to human health. However, the long-term adverse effects of nanoplastics on the female reproductive system remain unclear. Polystyrene nanoplastics (PS-NPs; 50 nm diameter) were selected as representative nanosized plastic particles to investigate the potential effects of subchronic prenatal and gestational exposure via drinking water on placental development in ICR (CD-1) mice. Maternal exposure to 10 mg/L PS-NPs induced an increase in fetal resorption rate and significantly increased fetal weight. Further observation of the placental morphology showed that PS-NPs exposure led to an aberrant placental structure and damaged the trophoblast cells. At the cellular level, PS-NPs exposure promoted the proliferation, migration, and invasion of HTR-8/SVneo cells. Mechanistically, transcriptomic and proteomic analyses revealed that PS-NPs triggered placental calcium disturbances and upregulated the Stam2 expression in mice. STAM2 induced by PS-NPs mediates the disruption of trophoblastic calcium homeostasis and regulates cell functions by disturbing the lysosomal degradation of the calcium channel protein IP3R3 and promoting intracellular calcium inflow by increasing the level of TRPV6 in HTR-8/SVneo cells. Therefore, our results indicated that trophoblastic calcium dyshomeostasis is the main mechanism by which subchronic PS-NPs exposure induces abnormal placental development. These findings reveal a link between subchronic PS-NPs exposure and placental damage and elucidate the underlying molecular mechanism, providing evidence for environmental triggers of adverse pregnancy and highlighting the risk of plastic products to pregnant women.

Understanding the structure, distribution, and retention of nanoplastics in montmorillonite nanopore by multi-scale computational simulations

The interfacial adsorption, aggregation and deposition processes of nanoplastics (NPs) on clay mineral surfaces critically regulate their environmental mobility, transformation pathways, and ecotoxicological risks in aquatic ecosystems. A quantitative understanding of the nanoscale interfacial processes is essential. This study employs molecular dynamics (MD) simulations and density functional theory (DFT) calculations to elucidate the aggregation and deposition mechanisms of three types of NPs in their pristine and aged states in the nanopore solution of montmorillonite (Mt). In the wet environment, NPs tend to form aggregates in the nanopore and migrate in solution, increasing environmental risk, while in the dry environment, NPs are more likely to deposit on the basal surface to form larger aggregates, consequently reducing their mobility. Results show hydrophobic interactions play as the primary driving force for the aggregation of pristine NPs, and both hydrophilic and hydrophobic interactions contribute to the aggregation of aged NPs. Aged NPs exhibit stronger binding affinity to Mt through mechanism such as Ca²⁺ bridging and hydrogen bonding, compared to their pristine counterparts. DFT calculations further reveal the formation of hydrogen bonds between the hydroxyl groups of aged NPs and the tetrahedral oxygen atoms in Mt. Through atomic-level characterization of interfacial processes, this work establishes a predictive framework for NP environmental behavior by resolving migration dynamics and retention processes in nanopore water.

Review of Techniques for the Detection, Removal, and Transformation of Environmental Microplastics and Nanoplastics

Plastic residues have emerged as a significant challenge in the environmental sector. Microplastics, which are plastic fragments smaller than 5 mm, have the ability to disperse through the atmosphere, oceans, and land, posing a serious threat to human health by accumulating in the food chain. However, their minuscule size makes it difficult to effectively remove them from the environment using the current technologies. This work provides a comprehensive overview of recent advancements in microplastic detection and removal technologies. For detection methods, we discuss commonly used techniques such as microscopic analysis, thermal analysis, mass spectrometry, spectroscopic analysis, and energy spectrometry. We also emphasize the importance of integrating various analytical and data-processing techniques to achieve efficient and nondestructive detection of microplastics. In terms of removal strategies, we explored innovative methods and technologies for extracting microplastics from the environment. These include physical techniques like filtration, adsorption, and magnetic separation; chemical techniques such as coagulation-flocculation-sedimentation and photocatalytic conversion; and bioseparation methods such as activated sludge and biodegradation. We also highlight the promising potential for converting microplastic contaminants into high-value chemicals. Additionally, we identify current technical challenges and suggest future research directions for the detection and removal of microplastics. We advocate for the development of unified and standardized analytical methods to guide further research on the removal and transformation of microplastics.

Deciphering the inhibition mechanisms of microplastics on the full-stage sludge anaerobic digestion via enrichment to anaerobic microbes and toxicity of released compounds

Increasingly accumulated microplastics (MPs) in sludge could affect the sludge treatment process, while the contributions and mechanisms of MP particles and the released organic matters (MP-DOM) are not fully understood. To fill this gap, this study systematically investigates the effects and mechanisms of MPs on sludge anaerobic digestion. In the presence of MPs, the hydrolysis and acidogenesis of organic matters and methanogenesis all decreased due to the inhibition on the activity of anaerobic microorganisms and key enzymes. Mechanism analysis showed that MPs mainly acted as substrates to enrich anaerobic microorganisms and reduced the abundance and function of free microorganisms in sludge that metabolized organic matters. Moreover, a large amount of organic compounds including various plasticizers (dibutyl phthalate) and chain-scission products (benzoic acid) from physical abrasions of MPs with sludge particles, which made a 50.9-51.6 % contribution to the MP-inhibited sludge anaerobic digestion by the chemical toxicity and generated reactive oxygen species. Owing to the decreased digestion performance, the risk associated with ARGs and pathogenic bacteria increased distinctly. The findings highlight the concerns about MP-derived organic compounds compared to the substrate themselves and suggest the necessity for removing MPs in the sludge of wastewater treatment plants (WWTP).

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.

Colloidal stability of UV-aged and protein-coated nanoplastics in natural waters under warming

Nanoplastics, particles smaller than 1000 nm that are produced by degradation of plastic debris, pose an environmental threat and may endanger natural ecosystems and human health. In aquatic environments, the large surface area and high surface energy of NPs facilitate their interactions with the surroundings; thus, understanding their behavior, transport, and fate is essential. In this study, we investigated the individual and combined effects of UV aging and protein coating on the stability of NPs in aquatic environments under elevated temperatures. UV-aged NPs were created via indoor UV lamp exposure, and protein coating was achieved by introducing bovine serum albumin (BSA). Sequential processes produced UV + BSA and BSA + UV-coated NPs for comprehensive analysis. Aggregation kinetics and stability were examined in electrolyte solutions (NaCl and CaCl2) and natural waters. Results indicated that BSA coating improved the colloidal stability of NPs in electrolyte solutions by promoting steric repulsion, a trend observed in rivers, lakes, and seawater but not in groundwater. Sequential UV aging after BSA coating caused protein denaturation, reducing the stability of NPs. Additionally, increased temperatures led to a greater level of NP aggregation due to lower energy barriers. These findings highlight UV aging, protein coating, and temperature as critical factors influencing the behavior and fate of NPs in natural environments.

Uncovering layer by layer the risk of nanoplastics to the environment and human health

Nanoplastics (NPs), defined as plastic particles with dimensions less than 100 nm, have emerged as a persistent environmental contaminant with potential risk to both environment and human health. Nanoplastics might translocate across biological barriers and accumulate in vital organs, leading to inflammatory responses, oxidative stress, and genotoxicity, already reported in several organisms. Disruptions to cellular functions, hormonal balance, and immune responses were also linked to NPs exposure in in vitro assays. Further, NPs have been found to adsorb other pollutants, such as persistent organic pollutants (POPs), and leach additives potentially amplifying their advere impacts, increasing the threat to organisms greater than NPs alone. However, NPs toxic effects remain largely unexplored, requiring further research to elucidate potential risks to human health, especially their accumulation, degradation, migration, interactions with the biological systems and long-term consequences of chronic exposure to these compounds. This review provides an overview of the current state-of-art regarding NPs interactions with environmental pollutants and with biological mechanisms and toxicity within cells.

Polystyrene nanoplastics are unlikely to aggregate in freshwater bodies

The fate and toxicity of nanoplastics (NPs) in the environment is largely determined by their stability. We explored how water composition, nanoplastic size, and surface carboxyl group density influenced the aggregation of polystyrene (PS) NPs in fresh water. Unfunctionalized 200, 300, 500, and 1000 nm PS NPs and 310 nm carboxylated PS NPs with carboxyl group densities of 0.35 and 0.6 mmol g-1 were used to simulate pristine and aged NPs. Natural water matrices tested in this study include synthetic surface water (SSW), water from the Schie canal (Netherlands) and tap water. Suwannee River Natural Organic Matter (SRNOM) was included to mimic organic matter concentrations. In CaCl2, we found PS NPs are more stable as their size increases with the increase of the critical coagulation concentration (CCC) from 44 mM to 59 mM and 77 mM for NP sizes of 200 nm, 300 nm and 500 nm. Conversely, 1000 nm PS NPs remained stable even at 100 mM CaCl2. Increasing the carboxyl group density decreased the stability of NPs as a result of the interaction between Ca2+ and the carboxyl group. These results were consistent with the mass of Ca2+ adsorbed per mass of NPs. The presence of SRNOM decreased the stability of PS NPs via particle bridging facilitated by SRNOM. However, in SSW, Schie water and tap water with low divalent cation concentrations, the hydrodynamic size of PS NPs did not change, even at prolonged durations up to one week. We concluded that PS NPs are unlikely to aggregate in water with low divalent cation concentrations, like natural freshwater bodies. Ecotoxicologists and water treatment engineers will have to consider treating PS NPs as colloidally stable particles as the lack of aggregation in fresh surface water bodies will affect their ecotoxicity and may pose challenges to their removal in water treatment.

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.

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.

A comparative study on the stability and coagulation removal of aged vs. nonaged nanoplastics in surface water

Nanoplastics (NPs) are released into surface water due to the widespread use of plastics, undergoing aging from environmental and human factors that alter their physical and chemical characteristics. However, detecting NPs remains challenging, resulting in limited research on their behavior in surface water and their removal efficiency by drinking water treatment. This study utilizes palladium-doped polystyrene nanoplastics (PSNPs) as tracers to enable precise detection and quantification through ICP-MS, thereby overcoming the limitations of conventional detection methods. PSNPs are aged using solar irradiation and ozone to simulate both natural and artificial aging processes, affecting the physical and chemical properties of NPs, which in turn influence their behavior in water treatment systems. Moreover, the study investigates the impact of various coagulation conditions, including different coagulants (AlCl3 and PACl), pH levels (4-9), and humic acid (HA) concentrations (0-10 mg/L), on the of both aged and nonaged NPs. The results demonstrate solar aging triggers significant morphological changes in PSNPs, while ozone aging induces more oxygen functional groups on PSNPs (CIozone=20.99; CIsolar=0.70), increasing sensitivity to HA concentrations and resulting in reduced removal efficiencies for ozone aged PSNPs by AlCl3 (68.68 %) and PACl (74.74 %). In addition, PACl achieves higher PSNPs removal efficiencies (REmin=88.59 %) than that of AlCl3 (REmin=85.57 %) under varied pH levels. This research fills a gap in understanding aged NPs behavior in surface water and offers practical solutions for optimizing coagulation for NPs removal, enhancing our ability to predict NPs environmental fate and manage NPs pollution to ensure drinking water safety.

A perspective on the algae-derived dissolved organic matter and its dynamic influence on the aggregation of nanoplastics in eutrophic waters

The aggregation behavior of nanoplastics (NPs) is crucial in determining their fate in aquatic environments. Dissolved organic matter (DOM), characterized by its complex molecular structure and diverse functional groups, can spontaneously absorb on the surface of NPs, thus altering their colloidal stability. In eutrophic waters, DOM primarily originates from metabolic byproducts released by phytoplankton, and its molecular composition and hydrophilic properties change dynamically as the progression of algal blooms. This perspective aims to summarize the heterogeneity of DOM during the initiation, outbreak and recession of algal blooms. And we investigate the influence of molecular-level variations in DOM composition on the aggregation behavior of NPs. Additionally, this study provides insights into the underlying mechanisms relating to the interactions between DOM and NPs. Ultimately, it tackles the challenges and future directions, highlighting the necessity for comprehensive studies to understand the fate of NPs in eutrophic waters.

Assessing the size transformation of nanoplastics in natural water matrices

Understanding the stability of NPs in different aqueous environments, related with their size is crucial for assessing their potential risks. This is influenced by several factors, including pH, ionic strength, and the presence of biomolecules, or dissolved organic matter (DOM). In this study, dispersions of NPs derived from common plastic waste materials, including polystyrene (PS), polyethylene terephthalate (PET), polyvinyl chloride (PVC), polymethyl methacrylate (PMMA), and polycarbonate (PC), were synthesized by a nanoprecipitation method with sizes: 189 ± 7, 58 ± 3, 123 ± 4, 151 ± 7 and 182 ± 6 nm, respectively. Stability for a period of 14 days of these NPs was assessed in various natural water matrices. Different analytical techniques were used, including Asymmetric Flow Field-Flow Fractionation (AF4) coupled with UV-Vis and Dynamic Light Scattering (DLS) in series, batch DLS, Fourier-Transform Infrared Spectroscopy-Attenuated Total Reflection (FTIR-ATR), and Transmission Electron Microscopy (TEM). None of the studied NPs was stable in seawater and NPs were transformed in microplastics (MPs) by aggregation. PET was more prone to aggregation in all waters and PS was the most stable followed for PC, PVC and PMMA. However, bottle and tap waters maintained better the original size of NPs. For the most stable dispersion PS, the influence of heteroaggregation in tap and lagoon waters and aging from exposure to UV light in sea water were tested. In both cases, the stability over time was worse for PS. The results can contribute to a more comprehensive understanding of the fate and behaviour of NPs in natural aquatic environments, emphasizing the importance of studying a wide range of polymers.

Deciphering the Roles of Molecular Weight and Carboxyl Richness of Organic Matter on Their Adsorption onto Ferrihydrite Nanoparticles and the Resulting Aggregation

The aggregation behavior of ferrihydrite nanoparticles (FNPs) can control the fate of associated aqueous contaminants, trace elements, and organic compounds. However, FNP aggregation is difficult to predict in the presence of organic matter (OM), given the heterogeneity in the OM properties. Five model OMs based on (poly)acrylic acid (PAA or AA) and polyethylene glycol with or without terminal carboxyl groups (PEG or PEGbis, respectively) were chosen to probe the influence of key OM properties─specifically, carboxyl richness and molecular weight (MW)─and the dominant mechanisms by which they influence OM adsorption onto FNPs and the resulting aggregation. For OMs with similar MWs, those with a higher carboxyl richness adsorbed more extensively onto FNPs: PAA2k > PEGbis > PEG. Meanwhile, for OMs with the same carboxyl richness, higher MW OMs adsorbed more: PAA25k > PAA2k > AA. Furthermore, the subsequent aggregation of FNPs was largely controlled by the adsorbed mass. OMs with negligible adsorption (i.e., PEG and AA) did not change the aggregation behavior of FNPs. For OMs with low carboxyl richness (PEGbis), accelerated aggregation occurred through a bridging effect with low adsorbed mass. For OMs with high carboxyl richness (PAA2k and PAA25k), aggregation was accelerated at moderate adsorbed OM masses by patch-charge attraction and was inhibited with high adsorbed OM mass due to steric repulsion. This study provided new insights into understanding and predicting the transport and fate of FNPs and natural organic matter (NOM) in natural environments with various NOM compositions.

Heteroaggregation, disaggregation, and migration of nanoplastics with nanosized activated carbon in aquatic environments: Effects of particle property, water chemistry, and hydrodynamic condition

Nanosized activated carbon (NAC) as emerging engineered nanomaterials may interact with nanoplastics prevalent in aquatic environments to affect their fate and transport. This study investigated the effects of particle property (charge and concentration), water chemistry [electrolytes, pH, humic acid (HA), and sodium alginate (SA)], and hydrodynamic condition [wave (i.e., sonication) and turbulence (i.e., stirring)] on the heteroaggregation, disaggregation, and migration of NAC with positively charged amino-modified polystyrene (APS) or negatively charged bare polystyrene (BPS) nanoplastics. The homoaggregation rate of APS was slower than its heteroaggregation rate with NAC, with critical coagulation concentrations (CCC) decreasing at higher NAC concentrations. However, the homoaggregation rate of BPS was intermediate between its heteroaggregation rates under low (10 mg/L) and high (40 mg/L) NAC concentrations. The heteroaggregation rate of APS+NAC enhanced as pH increasing from 3 to 10, whereas the opposite trend was observed for BPS+NAC. In NaCl solution or at CaCl2 concentration below 2.5 mM, HA stabilized APS+NAC and BPS+NAC via steric hindrance more effectively than SA. Above 2.5 mM CaCl2, SA destabilized APS+NAC and BPS+NAC by calcium bridging more strongly than HA. The migration process of heteroaggregates was simulated in nearshore environments. The simulation suggests that without hydrodynamic disturbance, APS+NAC (971 m) may travel farther than BPS+NAC (901 m). Mild wave (30-s sonication) and intense turbulence (1500-rpm stirring) could induce disaggregation of heteroaggregates, thus potentially extending the migration distances of APS+NAC and BPS+NAC to 1611 and 2160 m, respectively. Conversely, intense wave (20-min sonication) and mild turbulence (150-rpm stirring) may further promote aggregation of heteroaggregates, shortening the migration distances of APS+NAC and BPS+NAC to 262 and 552 m, respectively. Particle interactions mainly involved van der Waals attraction, electrostatic repulsion, steric hindrance, calcium bridging, π-π interactions, hydrogen bonding, and hydrophobic interactions. These findings highlight the important influence of NAC on the fate, transport, and risks of nanoplastics in aquatic environments.

Can Mammalian Reproductive Health Withstand Massive Exposure to Polystyrene Micro- and Nanoplastic Derivatives? A Systematic Review

The widespread use of plastics has increased environmental pollution by micro- and nanoplastics (MNPs), especially polystyrene micro- and nanoplastics (PS-MNPs). These particles are persistent, bioaccumulative, and linked to endocrine-disrupting toxicity, posing risks to reproductive health. This review examines the effects of PS-MNPs on mammalian reproductive systems, focusing on oxidative stress, inflammation, and hormonal imbalances. A comprehensive search in the Web of Science Core Collection, following PRISMA 2020 guidelines, identified studies on the impact of PS-MNPs on mammalian fertility, including oogenesis, spermatogenesis, and folliculogenesis. An analysis of 194 publications revealed significant reproductive harm, such as reduced ovarian size, depleted follicular reserves, increased apoptosis in somatic cells, and disrupted estrous cycles in females, along with impaired sperm quality and hormonal imbalances in males. These effects were linked to endocrine disruption, oxidative stress, and inflammation, leading to cellular and molecular damage. Further research is urgently needed to understand PS-MNPs toxicity mechanisms, develop interventions, and assess long-term reproductive health impacts across generations, highlighting the need to address these challenges given the growing environmental exposure.

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.

In situ surface-enhanced Raman spectroscopy for the detection of nanoplastics: A novel approach inspired by the aging of nanoplastics

Nanoplastics (NPs) present a hidden risk to organisms and the environment via migration and enrichment. Detecting NPs remains challenging because of their small size, low ambient concentrations, and environmental variability. There is an urgency to exploit detection approaches that are more compatible with real-world environments. Herein, this study provides a surface-enhanced Raman spectroscopy (SERS) technique for the in situ reductive generation of silver nanoparticles (Ag NPs), which is based on photoaging-induced modifications in NPs. The feasibility of generating Ag NPs on the surface of NPs was derived by exploring the photoaging mechanism, which was then utilized to SERS detection. The approach was applied successfully for the detection of polystyrene (PS), polyvinyl chloride (PVC), and polyethylene terephthalate (PET) NPs with excellent sensitivity (e.g., as low as 1 × 10-6 mg/mL for PVC NPs, and an enhancement factor (EF) of up to 2.42 × 105 for small size PS NPs) and quantitative analytical capability (R2 > 0.95579). The method was successful in detecting NPs (PS NPs) in lake water. In addition, satisfactory recoveries (93.54-105.70 %, RSD < 12.5 %) were obtained by spiking tap water as well as lake water, indicating the applicability of the method to the actual environment. Therefore, the proposed approach offers more perspectives for testing real environmental NPs.

Topic modeling discovers trending topics in global research on the ecosystem impacts of microplastics

The ecological threats of microplastics (MPs) have sparked research worldwide. However, changes in the topics of MP research over time and space have not been evaluated quantitatively, making it difficult to identify the next frontiers. Here, we apply topic modeling to assess global spatiotemporal dynamics of MP research. We identified nine leading topics in current MP research. Over time, MP research topics have switched from aquatic to terrestrial ecosystems, from distribution to fate, from ingestion to toxicology, and from physiological toxicity to cytotoxicity and genotoxicity. In most of the nine leading topics, a disproportionate amount of independent and collaborative research activity was conducted in and between a few developed countries which is detrimental to understanding the environmental fates of MPs in a global context. This review recognizes the urgent need for more attention to emerging topics in MP research, particularly in regions that are heavily impacted but currently overlooked.

Influence of macromolecules and electrolytes on heteroaggregation kinetics of polystyrene nanoplastics and goethite nanoparticles in aquatic environments

Fate and transport of nanoplastics in aquatic environments are affected by their heteroaggregation with minerals in the presence of macromolecules. This study investigated the heteroaggregation of polystyrene nanoplastics (PSNPs) with goethite nanoparticles (GNPs) under the influence of macromolecules [humic acid (HA), bovine serum albumin (BSA), and DNA] and electrolytes. Under 1 mg C/L macromolecule, raising electrolyte concentration promoted heteroaggregation via charge screening, except that calcium bridging with HA also enhanced heteroaggregation at CaCl2 concentration above 5 mM. At all NaCl concentrations and CaCl2 concentration below 5 mM, 1 mg C/L macromolecules strongly retarded heteroaggregation, ranking BSA > DNA > HA. Raising macromolecule concentration strengthened such stabilization effect of all macromolecules in NaCl solution and that of DNA and BSA in CaCl2 solution by enhancing steric hindrance. However, 0.1 mg C/L BSA slightly promoted heteroaggregation in CaCl2 solution due to stronger electrostatic attraction than steric hindrance. In CaCl2 solution, raising HA concentration strengthened its destabilization effect via calcium bridging. Macromolecules having more compact globular structure and higher molecular weight may exert greater steric hindrance to inhibit heteroaggregation more effectively. This study provides new insights on the effects of macromolecules and electrolytes on heteroaggregation between nanoplastics and iron minerals in aquatic environments.

Combined toxicity of pristine or artificially aged tire wear particles and bisphenols to Tigriopus japonicus

Tire wear particles (TWPs) are considered an important component of microplastic pollution in the marine environment and occur together with a variety of aquatic pollutants, including frequently detected bisphenols. The adverse effects of TWPs or bisphenols on aquatic organisms have been widely reported. However, the combined toxicity of TWPs and bisphenols is still unknown. In this study, the combined toxicity of both pristine (p-) and aged TWPs (a-TWPs) and four bisphenols ((bisphenol A (BPA), bisphenol F (BPF), bisphenol S (BPS), and bisphenol AF (BPAF)) to Tigriopus japonicus was evaluated. TWPs increased the toxicity of BPA and BPF but decreased the toxicity of BPAF. For BPS, there was synergistic toxic effect in the presence of p-TWPs, but slightly antagonistic effect was observed in the presence of a-TWPs. This adsorption of BPAF by TWPs resulted in a reduction of its toxicity to the copepod. A-TWPs could release more Zn than p-TWPs, and the released Zn contributed to the synergistic effect of TWPs and BPA or BPF. The aggregation formed by TWPs in certain sizes (e.g., 90-110 μm) could cause intestinal damage and lipid peroxidation in T. japonicus. The synergistic effect of p-TWPs and BPS might be due to the aggregation size of the binary mixture. The results of the current study will be important to understand the combined toxic effect of TWPs and bisphenols and the potential toxic mechanisms of the binary mixture.

Heteroaggregation kinetics of oppositely charged nanoplastics in aquatic environments: Effects of particle ratio, solution chemistry, and interaction sequence

Interactions between positively charged amino-modified (APS) and negatively charged bare (BPS) polystyrene nanoplastics may cause heteroaggregation in aquatic environments. This study investigated the effects of particle concentration ratio, solution chemistry [electrolytes, pH, and natural organic matter (NOM)], and interaction sequence on their heteroaggregation kinetics. In the absence of electrolytes and NOM, the APS/BPS ratio for attaining maximum heteroaggregation rate (khetero) increased from APS/BPS= 3/7 to APS/BPS= 1/1 as pH increased from 4 to 10, indicating that electrostatic interactions dominated heteroaggregation. In the absence of NOM, khetero ranked APS/BPS= 2/3 > APS/BPS= 1/1 > APS/BPS= 3/2. Colloidal stability decreased linearly as pH increased from 4 to 8 at APS/BPS= 1/1, while diffusion-limited heteroaggregation persisted at pH 10. In NaCl solution, humic acid (HA) retarded heteroaggregation more effectively than sodium alginate (SA) via steric hindrance and weakening electrostatic interactions, following the modified Derjaguin-Landau-Verwey-Overbeek (MDLVO) theory. Compared with simultaneous interactions among APS, BPS, NaCl, and NOM, the NOM retardation effects on heteroaggregation weakened if delaying its interaction with others. In CaCl2 solution, the effects of NOM on heteroaggregation depended on counterbalance among charge screening, steric hindrance, and calcium bridging. These findings highlight the important role of heteroaggregation between oppositely charged nanoplastics on their fate and transport in aquatic environments.

Co-photoaging inhibited the heteroaggregation between polystyrene nanoplastics and different titanium dioxide nanoparticles

Heteroaggregation between nanoplastics (NPs) and titanium dioxide nanoparticles (TiO2NPs) determines their environmental fates and ecological risks in aquatic environments. However, the co-photoaging scenario of NPs and TiO2NPs, interaction mechanisms of TiO2NPs with (aged) NPs, as well as the dependence of their heteroaggregation on TiO2NPs facets remain elusive. We found the critical coagulation concentration (CCC) of polystyrene nanoplastics (PSNPs) with coexisting RTiO2NPs was 1.9 - 2.2 times larger than that with coexisting ATiO2NPs, suggesting a better suspension stability of PSNPs+RTiO2NPs. In addition, CCC of TiO2NPs with coexisting photoaged PSNPs (APSNPs) was larger 1.7 - 2.2 times than that with PSNPs coexisting, indicating photoaging inhibited their heteroaggregation due to increasing electrostatic repulsion derived from increased negative charges on APSNPs and the polymer-derived dissolved organic carbon. Coexisted TiO2NPs promoted oxidation of PSNPs with the action of HO· and O2·- under UV light, leading to inhibited heteroaggregation. Moreover, Van der Waals and Lewis-acid interaction dominated the formation of primary heteroaggregates of PSNPs-TiO2NPs (ESE = ‒2.20 ∼ ‒2.78 eV) and APSNPs-TiO2NPs (ESE = ‒3.29 ∼ ‒3.67 eV), respectively. The findings provide a mechanistic insight into the environmental process of NPs and TiO2NPs, and are significant for better understanding their environmental risks in aquatic environments.

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.

Heteroaggregation kinetics of nanoplastics and soot nanoparticles in aquatic environments

Heteroaggregation between polystyrene nanoplastics (PSNPs) and soot nanoparticles (STNPs) in aquatic environments may affect their fate and transport. This study investigated the effects of particle concentration ratio, electrolytes, pH, and humic acid on their heteroaggregation kinetics. The critical coagulation concentration (CCC) ranked CCCPSNPs > CCCPSNPs-STNPs > CCCSTNPs, indicating that heteroaggregation rates fell between homoaggregation rates. In NaCl solution, as the PSNPs/STNPs ratio decreased from 9/1 to 3/7, heteroaggregation rate decreased and CCCPSNPs-STNPs increased from 200 to 220 mM due to enhanced electrostatic repulsion. Outlier was observed at PSNPs/STNPs= 1/9, where CCCPSNPs-STNPs= 170 mM and homoaggregation of STNPs dominated. However, in CaCl2 solution where calcium bridged with STNPs, heteroaggregation rate increased and CCCPSNPs-STNPs decreased from 26 to 5 mM as the PSNPs/STNPs ratio decreasing from 9/1 to 1/9. In composite water samples, heteroaggregation occurred only at estuarine and marine salinities. Acidic condition promoted heteroaggregation via charge screening. Humic acid retarded or promoted heteroaggregation in NaCl or CaCl2 solutions by steric hindrance or calcium bridging, respectively. Other than van der Waals attraction and electrostatic repulsion, heteroaggregation was affected by steric hindrance, hydrophobic interactions, π - π interactions, and calcium bridging. The results highlight the role of black carbon on colloidal stability of PSNPs in aquatic environments.

The suspension stability of nanoplastics in aquatic environments revealed using meta-analysis and machine learning

Nanoplastics (NPs) aggregation determines their bioavailability and risks in natural aquatic environments, which is driven by multiple environmental and polymer factors. The back propagation artificial neural network (BP-ANN) model in machine learning (R2 = 0.814) can fit the complex NPs aggregation, and the feature importance was in the order of surface charge of NPs > dissolved organic matter (DOM) > functional group of NPs > ionic strength and pH > concentration of NPs. Meta-analysis results specified low surface charge (0 ≤ |ζ| < 10 mV) of NPs, low concentration (< 1 mg/L) and low molecular weight (< 10 kg/mol) of DOM, NPs with amino groups, high ionic strength (IS > 700 mM) and acidic solution, and high concentration (≥ 20 mg/L) of NPs with smaller size (< 100 nm) contribute to NPs aggregation, which is consistent with the prediction in machine learning. Feature interaction synergistically (e.g., DOM and pH) or antagonistically (e.g., DOM and cation potential) changed NPs aggregation. Therefore, NPs were predicted to aggregate in the dry period and estuary of Poyang Lake. Research on aggregation of NPs with different particle size,shapes, and functional groups, heteroaggregation of NPs with coexisting particles and aging effects should be strengthened in the future. This study supports better assessments of the NPs fate and risks in environments.

UV-aged polystyrene nanoplastics aggravate intestinal barrier damage by overproduction of ROS

UV irradiation significantly alters nanoplastics (NPs) physicochemical properties, thus affecting their biological toxicity. This study is the first to assess the influence of virgin and UV-aged polystyrene NPs (v-PS NPs, a-PS NPs) on the intestinal barrier of ICR mice. We found that a-PS NPs can cause more severe intestinal barrier damage compared with v-PS NPs. The reason may be attributed to that a-PS NPs produced more ROS in intestinal tissue. Moreover, the strong oxidizing property of hydroxyl radicals (·OH) generated from the a-PS NPs can damage cell membranes through lipid peroxidation, thereby leading to a low clearance rate of ·OH due to the impaired intestinal tissue function, in turn, causing more ROS to accumulate and inducing severe oxidative damage. This research underscores the crucial role of ·OH in mediating oxidative damage from UV-aged nanoparticles, emphasizing the need to consider environmental factors in assessing NPs toxicity.

New Insights into Aggregation Behaviors of the UV-Irradiated Dissolved Biochars (DBioCs) in Aqueous Environments: Effects of Water Chemistries and Variation in the Hamaker Constant

The aggregation behavior of ubiquitous dissolved black carbon (DBC) largely affects the fate and transport of its own contaminants and the attached contaminants. However, the photoaging processes and resulting effects on its colloidal stability remain yet unknown. Herein, dissolved biochars (DBioCs) were extracted from common wheat straw biochar as a proxy for an anthropogenic DBC. The influences of UV radiation on their aggregation kinetics were systematically investigated under various water chemistries (pH, electrolytes, and protein). The environmental stability of the DBioCs before and after radiation was further verified in two natural water samples. Hamaker constants of pristine and photoaged DBioCs were derived according to Derjaguin-Landau-Verwey-Overbeek (DLVO) prediction, and its attenuation (3.19 ± 0.15 × 10-21 J to 1.55 ± 0.07 × 10-21 J after 7 days of radiation) was described with decay kinetic models. Pearson correlation analysis revealed that the surface properties and aggregation behaviors of DBioCs were significantly correlated with radiation time (p < 0.05), indicating its profound effects. Based on characterization and experimental results, we proposed a three-stage mechanism (contended by photodecarboxylation, photo-oxidation, and mineral exposure) that DBioCs might experience under UV radiation. These findings would provide an important reference for potential phototransformation processes and relevant behavioral changes that DBC may encounter.

Spotlight on the vertical migration of aged microplastics in coastal waters

Coastal waters are complex and dynamic areas with unique environmental attributes that complicate the vertical migration of microplastics (MPs). The MPs that enter coastal waters from diverse sources, including terrestrial, riverine, oceanic, and shoreline inputs undergo various aging pathways. In this study, the variations in the physiochemical characteristics of MPs undergoing various aging pathways and their vertical migration under dynamic conditions subjected to the effects of different MP characteristics and coastal environmental features were comprehensively explored. Opposite effects of aging on the vertical migration of hydrophobic and hydrophilic MPs were observed, with aging appearing to promote the dispersion of hydrophobic MPs but enhance the vertical migration of hydrophilic ones. The positive role of salinity and the negative role of humic acid (HA) concentrations on MP vertical migration were identified, and the mechanisms driving these effects were analyzed. Notably, intense turbulence not only promoted the floating of positively buoyant MPs but also reversed the migration direction of negatively buoyant MPs from downward to upward. Aging-induced changes in MP characteristics had a limited effect on MP vertical migration. The inherent characteristics of MPs and the surrounding environmental features, however, played major roles in their vertical migration dynamics. ENVIRONMENTAL IMPLICATION: Microplastics (MPs) have emerged as a significant global environmental concern and the coastal zones are the hotspots for MP pollution due to their high population density. This study comprehensively investigated the variations in the physiochemical characteristics of MPs undergoing various aging pathways. Their vertical migration patterns under dynamic conditions subjected to the effects of different MP characteristics and coastal environmental features were revealed. The roles of turbulence and MP density in their migration were identified. The findings of this study have important implications for understanding the transport and determining the ecological risks of MPs in coastal waters.

Understanding microplastic aging driven by photosensitization of algal extracellular polymeric substances

The aging of microplastics (MPs) is extremely influenced by photochemically-produced reactive intermediates (PPRIs), which are mediated by natural photosensitive substances. Algal extracellular polymeric substances (EPS) can produce PPRIs when exposed to sunlight. Nonetheless, the specific role of EPS in the aging process of MPs remains unclear. This work systematically explored the aging process of polystyrene (PS) MPs in the EPS secreted by Chlorella vulgaris under simulated sunlight irradiation. The results revealed that the existence of EPS accelerated the degradation of PS MPs into particles with sizes less than 1 µm, while also facilitating the formation of hydroxy groups on the surface. The release rate of dissolved organic matter (DOM) from PS MPs was elevated from 0.120 mg·L-1·day-1 to 0.577 mg·L-1·day-1. The primary factor contributing to the elevated levels of DOM was humic acid-like compounds generated through the breakdown of PS. EPS accelerated the aging process of PS MPs by primarily mediating the formation of triplet excited states (3EPS*), singlet oxygen (1O2), and superoxide radicals (O2∙-), resulting in indirect degradation. 3EPS* was found to have the most substantial impact. This study makes a significant contribution to advance understanding of the environmental fate of MPs in aquatic environments impacted by algal blooms.

Co-impacts of cation type and humic acid on migration of polystyrene microplastics in saturated porous media

The aging process of microplastics (MPs) could significantly change their physical and chemical characteristics and impact their migration behavior in soil. However, the complex effects of different cations and humic acids (HA) on the migration of aged MPs through saturated media are not clear. In this research, the migration and retention of pristine/aged PSMPs (polystyrene microplastics) under combined effects of cations (Na+, Ca2+) (ionic strength = 10 mM) and HA (0, 5, 15 mg/L) were investigated and analyzed in conjunction with the two-site kinetic retention model and DLVO theory. The findings showed that the aging process accelerated PSMPs migration under all tested conditions. Aged PSMPs were less susceptible to Ca2+ than pristine PSMPs. Under Ca2+ conditions, pristine/aged PSMPs showed higher retention than under Na+ conditions in the absence of HA. Furthermore, under Na+ conditions, the migration of aged PSMPs significantly increased at higher concentrations of HA. However, under Ca2+ conditions, the migration of aged PSMPs decreased significantly at higher concentrations of HA. In higher HA conditions, HA, Ca2+, and PSMPs interact to cause larger aggregations, resulting in the sedimentation of aged PSMPs. The DLVO calculations and two-site kinetic retention models' results showed the detention of PSMPs was irreversible under higher HA conditions (15 mg/L) with Ca2+, and aged PSMPs were more susceptible to clogging. These findings may help to understand the potential risk of migration behavior of PSMPs in the soil-groundwater environment.

Preferential deposition of buoyant small microplastics in surface sediments of the Three Gorges Reservoir, China: Insights from biomineralization

Sediments act as sinks of microplastics (MPs) derived from terrestrial ecosystems. However, the fate and transport of MPs at the zone of sediment-overlying water in reservoir environment are poorly understood. Here, the MPs distribution patterns in surface sediments of the Three Gorges Reservoir (TGR) and dominant mechanisms responsible for the sinking of MPs at the zone of sediment-overlying water were comprehensively investigated. The predominant occurrence of small microplastics (<300 µm, SMPs) in surface sediments of the TGR was found, with buoyant polyethene (PE) was dominant polymer types. Interestingly, the high abundance of SMPs in sediments correlated well with the Ca2+/Mg2+ in overlying water, suggesting that divalent cations in overlying water may enhance the preferential deposition of SMPs. Simulation sinking experiments under the presence of Microcystis aeruginosa and two divalent cations using different-sized PE MPs demonstrated that the greater deposition of SMPs was mainly the result of the formation of biogenic calcite on the surface of MPs rather than magnesium minerals, which provides stronger ballasting effects for SMPs than for large MPs. This study first highlights that the impact of biomineralization on preferential sinking of SMPs and enhances the understanding of the transport behaviour of MPs in aquatic environment.

Tracking the micro- and nanoplastics in the terrestrial-freshwater food webs. Bivalves as sentinel species

Micro- (MPs) and nanoplastics (NPs) are currently ubiquitous in the ecosystems, and freshwater biota is still insufficiently studied to understand the global fate, transport paths, and consequences of their presence. Thus, in this study, we investigated the role of bivalves and a trophic transfer of MPs and NPs in an experimental food chain. The food chain consisted of terrestrial non-selective detritivore Dendrobaena (Eisenia) sp., freshwater benthic filter feeder Unio tumidus, and freshwater benthic detritivore-collectors Asellus aquaticus or Gammarus sp. Animals were exposed to different fluorescently labeled micro- and nanoplastics (PMMA 20 μm, nanoPS 15-18 nm, and 100 nm, PS 1 μm and 20 μm, PE from cosmetics) as well as to the faeces of animals exposed to plastics to assess their influence on the environmental transportation, availability to biota, and bioaccumulation of supplied particles. Damaged and intact fluorescent particles were observed in the faeces of terrestrial detritivores and in the droppings of aquatic filter feeders, respectively. They were also present in the guts of bivalves and of crustaceans which were fed with bivalve droppings. Bivalves (Unio tumidus, and additionally Unio pictorum, and Sphaerium corneum) produced droppings containing micro- and nanoparticles filtered from suspension and deposited them onto the tank bottom, making them available for broader feeding guilds of animals (e.g. collectors, like crustaceans). Finally, the natural ageing of PS and its morphological changes, leakage of the fluorescent labelling, and agglomeration of particles were demonstrated. That supports our hypothesis of the crucial role of the characterization of physical and chemical materials in adequately understanding the mechanisms of their interaction with biota. Microscopical methods (confocal, fluorescent, scanning electron) and Raman and FT-IR spectroscopy were used to track the particles' passage in a food web and monitor structural changes of the MPs' and NPs' surface.

Interactions between inhalable aged microplastics and lung surfactant: Potential pulmonary health risks

The relationship between microplastics (MPs) and human respiratory health has garnered significant attention since inhalation constitutes the primary pathway for atmospheric MP exposure. While recent studies have revealed respiratory risks associated with MPs, virgin MPs used as plastic surrogates in these experiments did not represent the MPs that occur naturally and that undergo aging effects. Thus, the effects of aged MPs on respiratory health remain unknown. We herein analyzed the interaction between inhalable aged MPs with lung surfactant (LS) extracted from porcine lungs vis-à-vis interfacial chemistry employing in-vitro experiments, and explored oxidative damage induced by aged MPs in simulated lung fluid (SLF) and the underlying mechanisms of action. Our results showed that aged MPs significantly increased the surface tension of the LS, accompanied by a diminution in its foaming ability. The stronger adsorptive capacity of the aged MPs toward the phospholipids of LS appeared to produce increased surface tension, while the change in foaming ability might have resulted from a variation in the protein secondary structure and the adsorption of proteins onto MPs. The adsorption of phospholipid and protein components then led to the aggregation of MPs in SLF, where the aged MPs exhibited smaller hydrodynamic diameters in comparison with the unaged MPs, likely interacting with biomolecules in bodily fluids to exacerbate health hazards. Persistent free radicals were also formed on aged MPs, inducing the formation of reactive oxygen species such as superoxide radicals (O2•-), hydrogen peroxide (HOOH), and hydroxyl radicals (•OH); this would lead to LS lipid peroxidation and protein damage and increase the risk of respiratory disease. Our investigation was the first-ever to reveal a potential toxic effect of aged MPs and their actions on the human respiratory system, of great significance in understanding the risk of inhaled MPs on lung health.

Quantitative analysis of nanoplastics in environmental and potable waters by pyrolysis-gas chromatography-mass spectrometry

Nanoplastics are emerging environmental contaminants, but their presence in environmental and potable water remains largely understudied due to the absence of quantitative analytical methods. In this study, we developed and validated a pretreatment method that combines hydrogen peroxide digestion and Amicon® Stirred Cell ultrafiltration (at 100 kDa, approximately 10 nm) with subsequent detection by pyrolysis gas chromatography-mass spectrometry (Pyr-GC/MS). This method allows for the simultaneous identification and quantification of nine selected nanoplastic types, including poly(ethylene terephthalate) (PET), polyethylene (PE), polycarbonate (PC), polypropylene (PP), poly(methyl methacrylate) (PMMA), polystyrene (PS), polyvinylchloride (PVC), nylon 6, and nylon 66, in environmental and potable water samples based on polymer-specific mass concentration. Limits of quantification ranged from 0.01 to 0.44 µg/L, demonstrating the method's ability to quantitatively detect nanoplastics in environmental and potable water samples. Most of the selected nanoplastics were detected at concentrations of between 0.04 and 1.17 µg/L, except for PC, which was consistently below the limit of detection (<0.44 µg/L). The prevalent polymer components in the samples were PE (0.10 - 1.17 µg/L), PET (0.06 - 0.91 µg/L), PP (0.04 - 0.79 µg/L), and PS (0.06 - 0.53 µg/L) nanoplastics. The presented analytical method offers an accurate means to identify, quantify, and monitor nanoplastics in complex environmental and potable water samples. It fills gaps in our understanding of nanoplastic pollution levels, providing a valuable methodology and crucial reference data for future studies.

Photodegradation of biodegradable plastics in aquatic environments: Current understanding and challenges

Direct and indirect photolysis are important abiotic processes in aquatic environments through which plastics can be transformed physically and chemically. Transport of biodegradable plastics in water is influenced by vertical mixing and turbulent flow, which make biodegradable plastics remain susceptible to sunlight and photolysis despite their high density. In general, biodegradable plastics are composed of ester containing polymers (e.g., poly(butylene succinate), polyhydroxyalkanoate, and polylactic acid), whereas non-biodegradable plastics are composed of long chains of saturated aliphatic hydrocarbons in their backbones (e.g., polyethylene, polypropylene, and polystyrene). Based on the reviewed knowledge and discussion, we may hypothesize that 1) direct photolysis is more pronounced for non-biodegradation than for biodegradable plastics, 2) smaller plastics such as micro/nano-plastics are more prone to photodegradation and photo-transformation by direct and indirect photolysis, 3) the production rate of reactive oxygen species (ROS) on the surface of biodegradable plastics is higher than that of non-biodegradable plastics, 4) the photodegradation of biodegradable plastics may be promoted by ROS produced from biodegradable plastics themselves, and 5) the subsequent reactions of ROS are more active on biodegradable plastics than non-biodegradable plastics. Moreover, micro/nanoplastics derived from biodegradable plastics serve as more effective carriers of organic pollutants than those from non-biodegradable plastics and thus biodegradable plastics may not necessarily be more ecofriendly than non-biodegradable plastics. However, biodegradable plastics have been largely unexplored from the viewpoint of direct or indirect photolysis. Roles of reactive oxygen species originating from biodegradable plastics should be further explored for comprehensively understanding the photodegradation of biodegradable plastics.

Nanoplastics Affect the Bioaccumulation and Gut Toxicity of Emerging Perfluoroalkyl Acid Alternatives to Aquatic Insects (Chironomus kiinensis): Importance of Plastic Surface Charge

Persistent organic pollutants (POPs) have been widely suggested as contributors to the aquatic insect biomass decline, and their bioavailability is affected by engineered particles. However, the toxicity effects of emerging ionizable POPs mediated by differentially charged engineered nanoparticles on aquatic insects are unknown. In this study, 6:2 chlorinated polyfluoroalkyl ether sulfonate (F-53B, an emerging perfluoroalkyl acid alternative) was selected as a model emerging ionizable POP; the effect of differentially charged nanoplastics (NPs, 50 nm, 0.5 g/kg) on F-53B bioaccumulation and gut toxicity to Chironomus kiinensis were investigated through histopathology, biochemical index, and gut microbiota analysis. The results showed that when the dissolved concentration of F-53B remained constant, the presence of NPs enhanced the adverse effects on larval growth, emergence, gut oxidative stress and inflammation induced by F-53B, and the enhancement caused by positively charged NP-associated F-53B was stronger than that caused by the negatively charged one. This was mainly because positively charged NPs, due to their greater adsorption capacity and higher bioavailable fraction of associated F-53B, increased the bioaccumulation of F-53B in larvae more significantly than negatively charged NPs. In addition, positively charged NPs interact more easily with gut biomembranes and microbes with a negative charge, further increasing the probability of F-53B interacting with gut biomembranes and microbiota and thereby aggravating gut damage and key microbial dysbacteriosis related to gut health. These findings demonstrate that the surface charge of NPs can regulate the bioaccumulation and toxicity of ionizable POPs to aquatic insects.

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

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

Bioenergetic effects of pristine and ultraviolet-weathered polydisperse polyethylene terephthalate and polystyrene nanoplastics on human intestinal Caco-2 cells

The ubiquitous human exposure to nanoplastics (NPs) increasingly raises concerns regarding impact on our health. However, little is known on the biological effects of complex mixtures of weathered NPs with heterogenous size and irregular shape present in the environment. In this study, the bioenergetic effects of four such NPs mixtures on human intestinal Caco-2 cells were investigated. To this aim, Caco-2 cells were exposed to polydisperse nanoPET (<800 nm) and nanoPS (mixture of 100 and 750 nm) samples with and without ultraviolet (UV) weathering at low concentration range (102-107 particles/mL) for 48 h. Mitochondrial respiration, glycolytic functions and ATP production rates of exposed cells were measured by Seahorse XFe96 Analyzer. Among four NPs samples, polydisperse nanoPET with irregular shapes induced significant stimulation of mitochondrial respiration, glycolysis and ATP production rates in Caco-2 cells. Spherical nanoPS caused significant stimulation on glycolytic functions of Caco-2 cells at the highest concentration used (106 particles/mL). ATR-FTIR spectra and carbonyl index indicated formation of carbonyl groups in nanoPET and nanoPS after UV weathering. UV weathering could alleviate bioenergetic stress caused by NPs in Caco-2 cells and even shifted the energy pathways from mitochondrial respiration to glycolysis due to electrostatic repulsion between negatively charged UV-aged NPs and cell membranes. This research is the first to study in-vitro bioenergetic responses of NPs samples with multidimensional features (polymer type, irregular shape, heterogenous size, UV-weathering) on human health. It highlights that effects between pristine and weathered NPs are different at a bioenergetic level, which has important implications for the risk assessment of NPs on human health.