Synergistic Effects of Organic Ligands and Visible Light on the Reductive Dissolution of CeO2 Nanoparticles: Mechanisms and Implications for the Transformation in Plant Surroundings

Cerium oxide (CeO2) nanoparticles are one of the most important engineered nanomaterials with demonstrated applications in industry. Although numerous studies have reported the plant uptake of CeO2, its fate and transformation pathways and mechanisms in plant-related conditions are still not well understood. This study investigated the stability of CeO2 in the presence of organic ligands (maleic and citric acid) and light irradiation. For the first time, we found that organic ligands and visible light had a synergistic effect on the reductive dissolution of CeO2 with up to 30% Ce releases after 3 days, which is the highest release reported so far under environmental conditions. Moreover, the photoinduced dissolution of CeO2 in the presence of citrate was much higher than that in maleate, which are adsorbed on the surface of CeO2 through inner-sphere and outer-sphere complexation, respectively. A novel ligand-dependent photodissolution mechanism was proposed and highlighted: upon electron-hole separation under light irradiation, the inner-sphere complexed citrate is more capable of consuming the hole, prolonging the life of electrons for the reduction of Ce(IV) to Ce(III). Finally, reoxidation of Ce(III) by oxygen was observed and discussed. This comprehensive work advances our knowledge of the fate and transformation of CeO2 in plant surroundings.

Detection, distribution and environmental risk of metal-based nanoparticles in a coastal bay

Metal-based nanoparticles (NPs) attract increasing concerns because of their adverse effects on aquatic ecosystems. However, their environmental concentrations and size distributions are largely unknown, especially in marine environments. In this work, environmental concentrations and risks of metal-based NPs were examined in Laizhou Bay (China) using single-particle inductively coupled plasma-mass spectrometry (sp-ICP-MS). First, separation and detection approaches of metal-based NPs were optimized for seawater and sediment samples with high recoveries of 96.7% and 76.3%, respectively. Spatial distribution results showed that Ti-based NPs had the highest average concentrations for all the 24 stations (seawater, 1.78 × 108 particles/L; sediments, 7.75 × 1012 particles/kg), followed by Zn-, Ag-, Cu-, and Au-based NPs. For all the NPs in seawater, the highest abundance occurred around the Yellow River Estuary, resulting from a huge input from Yellow River. In addition, the sizes of metal-based NPs were generally smaller in sediments than those in seawater (22, 20, 17, and 16 of 22 stations for Ag-, Cu-, Ti-, and Zn-based NPs, respectively). Based on the toxicological data of engineered NPs, predicted no-effect concentrations (PNECs) to marine species were calculated as Ag at 72.8 ng/L < ZnO at 2.66 µg/L < CuO at 7.83 µg/L < TiO2 at 72.0 µg/L, and the actual PNECs of the detected metal-based NPs may be higher due to the possible presence of natural NPs. Station 2 (around the Yellow River Estuary) was assessed as "high risk" for Ag- and Ti-based NPs with risk characterization ratio (RCR) values of 1.73 and 1.66, respectively. In addition, RCRtotal values for all the four metal-based NPs were calculated to fully assess the co-exposure environmental risk, with 1, 20, and 1 of 22 stations as "high risk", "medium risk", and "low risk", respectively. This study helps to better understand the risks of metal-based NPs in marine environments.

Nickel Nanoparticles Induced Hepatotoxicity in Mice via Lipid-Metabolism-Dysfunction-Regulated Inflammatory Injury

Nickel nanoparticles (NiNPs) have wide applications in industry and biomedicine due to their unique characteristics. The liver is the major organ responsible for nutrient metabolism, exogenous substance detoxification and biotransformation of medicines containing nanoparticles. Hence, it is urgent to further understand the principles and potential mechanisms of hepatic effects on NiNPs administration. In this study, we explored the liver impacts in male C57/BL6 mice through intraperitoneal injection with NiNPs at doses of 10, 20 and 40 mg/kg/day for 7 and 28 days. The results showed that NiNPs treatment increased serum levels of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) and induced pathological changes in liver tissues. Moreover, hepatic triglyceride (TG) content and lipid droplet deposition identified via de novo lipogenesis (DNL) progression were enhanced after NiNPs injection. Additionally, sustained NiNPs exposure induced a remarkable hepatic inflammatory response, significantly promoted endoplasmic reticulum stress (ER stress) sensors Ire1α, Perk and Atf6, and activated the occurrence of liver cell apoptosis. Overall, the research indicated that NiNPs exposure induced liver injury and disturbance of lipid metabolism. These findings revealed the public hazard from extreme exposure to NiNPs and provided new information on biological toxicity and biosafety evaluation.

Characterization and Polydispersity of Volcanic Ash Nanoparticles in Synthetic Lung Fluid

The inhalation of natural nanoparticles (NPs) emitted from volcanic activity may be a risk to human health. However, the literature rarely reports the fate and response of NPs once in contact with lung fluids. In this work, we studied the particle size distribution of ashfall from Popocatépetl volcano, Mexico. The collected ashes (n = 5) were analyzed with scanning electron microscopy (SEM) to obtain the elemental composition and morphology, and to determine the size of the ash particles using ParticleMetric software (PMS). The PMS reported most of the ash to have submicrometric size (<1 μm) and an average equivalent circle of 2.72 μm. Moreover, to our knowledge, this study investigated for the first time the behavior of ash NPs at different times (0 to 24 h) while in contact with in vitro lung fluid, Gamble Solution (GS) and Artificial Lysosomal Fluid (ALF) using dynamic light scattering (DLS). We found a large variability in the hydrodynamic diameter, with values less than 1 nm and greater than 5 μm. Furthermore, aggregation and disaggregation processes were recognized in GS and ALF, respectively. The results of this study increase the knowledge of the interaction between NPs and lung fluids, particularly within the alveolar macrophage region.

Electron Transfer, Atom Exchange, and Transformation of Iron Minerals in Soils: The Influence of Soil Organic Matter

Despite substantial experimental evidence of electron transfer, atom exchange, and mineralogical transformation during the reaction of Fe(II)_aq with synthetic Fe(III) minerals, these processes are rarely investigated in natural soils. Here, we used an enriched Fe isotope approach and Mössbauer spectroscopy to evaluate how soil organic matter (OM) influences Fe(II)/Fe(III) electron transfer and atom exchange in surface soils collected from Luquillo and Calhoun Experimental Forests and how this reaction might affect Fe mineral composition. Following the reaction of ⁵⁷Fe-enriched Fe(II)_aq with soils for 33 days, Mössbauer spectra demonstrated marked electron transfer between sorbed Fe(II) and the underlying Fe(III) oxides in soils. Comparing the untreated and OM-removed soils indicates that soil OM largely attenuated Fe(II)/Fe(III) electron transfer in goethite, whereas electron transfer to ferrihydrite was unaffected. Soil OM also reduced the extent of Fe atom exchange. Following reaction with Fe(II)_aq for 33 days, no measurable mineralogical changes were found for the Calhoun soils enriched with high-crystallinity goethite, while Fe(II) did drive an increase in Fe oxide crystallinity in OM-removed LCZO soils having low-crystallinity ferrihydrite and goethite. However, the presence of soil OM largely inhibited Fe(II)-catalyzed increases in Fe mineral crystallinity in the LCZO soil. Fe atom exchange appears to be commonplace in soils exposed to anoxic conditions, but its resulting Fe(II)-induced recrystallization and mineral transformation depend strongly on soil OM content and the existing soil Fe phases.

Silicon dioxide nanoparticles adsorption alters the secondary and tertiary structures of catalase and undermines its activity

The expanding production and use of nanomaterials in various fields caused big concern for human health. Oxidative stress is the most frequently described mechanism of nanomaterial toxicity. A state of oxidative stress can be defined as the imbalance of reactive oxygen species (ROS) production and antioxidant enzyme activities. Although nanomaterials-triggered ROS generation has been extensively investigated, little is known regarding the regulation of antioxidant enzyme activities by nanomaterials. This study used two typical nanomaterials, SiO₂ nanoparticles (NPs) and TiO₂ NPs, to predict their binding affinities and interactions with antioxidant enzymes catalase (CAT) and superoxide dismutase (SOD). The molecular docking results showed that CAT and SOD had different binding sites, binding affinity, and interaction modes with SiO₂ NPs and TiO₂ NPs. The binding affinities of the two NPs to CAT were more potent than those to SOD. Consistently, the experimental work indicated NPs adsorption caused the perturbation of the second and tertiary structures of both enzymes and thus resulted in the loss of enzyme activities.

Spatio-temporal variation of soil microplastics as emerging pollutant after long-term application of plastic mulching and organic compost in apple orchards

Microplastics (MPs) pollution in agroecosystems have aroused great alarm and widespread concern. However, the spatial distribution and temporal variation characteristics of MPs in apple orchards with long-term plastic mulching and organic compost input are still poorly understood. This study investigated MPs accumulation characteristics and vertical distribution after applying plastic mulch and organic compost in apple orchards for 3 (AO-3), 9 (AO-9), 17 (AO-17), and 26 (AO-26) years on the Loess Plateau. The clear tillage (no plastic mulching and organic composts) area was used as a control (CK). At a soil depth of 0-40 cm, AO-3, AO-9, AO-17, and AO-26 treatments increased the abundances of MPs, and the black fibers and fragments of rayon and polypropylene were dominant. In the 0-20 cm soil layer, the abundances of MPs increased with the treatment time; the abundance was 4333 pieces kg^-1 after 26 years of treatment, gradually decreasing with soil depth. In different treatments and soil layers, the percentages of MPs <1000 μm were dominant (>50%). The AO-17 and AO-26 treatments significantly increased the MPs with the size of 0-500 μm at 0-40 cm and the abundances of pellets in 0-60 cm soil. In conclusion, the long-term (≥17 years) application of plastic mulching and organic composts increased the abundances of small particles at 0-40 cm, and plastic mulching contributed the most to MPs, while organic composts increased the complexity and diversity of MPs.

Nanoplastics alter ecosystem multifunctionality and may increase global warming potential

Although the presence of nanoplastics in aquatic and terrestrial ecosystems has received increasing attention, little is known about its potential effect on ecosystem processes and functions. Here, we evaluated if differentially charged polystyrene (PS) nanoplastics (PS-NH2 and PS-SO3 H) exhibit distinct influences on microbial community structure, nitrogen removal processes (denitrification and anammox), emissions of greenhouse gases (CO2 , CH4 , and N2 O), and ecosystem multifunctionality in soils with and without earthworms through a 42-day microcosm experiment. Our results indicated that nanoplastics significantly altered soil microbial community structure and potential functions, with more pronounced effects for positively charged PS-NH2 than for negatively charged PS-SO3 H. Ecologically relevant concentration (3 g kg-1 ) of nanoplastics inhibited both soil denitrification and anammox rates, while environmentally realistic concentration (0.3 g kg-1 ) of nanoplastics decreased the denitrification rate and enhanced the anammox rate. The soil N2 O flux was always inhibited 6%-51% by both types of nanoplastics, whereas emissions of CO2 and CH4 were enhanced by nanoplastics in most cases. Significantly, although N2 O emissions were decreased by nanoplastics, the global warming potential of total greenhouse gases was increased 21%-75% by nanoplastics in soils without earthworms. Moreover, ecosystem multifunctionality was increased 4%-12% by 0.3 g kg-1 of nanoplastics but decreased 4%-11% by 3 g kg-1 of nanoplastics. Our findings provide the only evidence to date that the rapid increase in nanoplastics is altering not only ecosystem structure and processes but also ecosystem multifunctionality, and it may increase the emission of CO2 and CH4 and their global warming potential to some extent.

Toxicity of Nanoscale Zero-Valent Iron to Soil Microorganisms and Related Defense Mechanisms: A Review

Soil pollution is a global environmental problem. Nanoscale zero-valent iron (nZVI) as a kind of emerging remedial material is used for contaminated soil, which can quickly and effectively degrade and remove pollutants such as organic halides, nitrates and heavy metals in soil, respectively. However, nZVI and its composites can enter the soil environment in the application process, affect the physical and chemical properties of the soil, be absorbed by microorganisms and affect the growth and metabolism of microorganisms, thus affecting the ecological environment of the entire soil. Because of the potential risks of nZVI to the environment and ecosystems, this paper summarizes the current application of nZVI in the remediation of contaminated soil environments, summarizes the various factors affecting the toxic effects of nZVI particles and comprehensively analyzes the toxic effects of nZVI on microorganisms, toxic mechanisms and cell defense behaviors to provide a theoretical reference for subsequent biosafety research on nZVI.

Transfer of CeO2 nanoparticles between freshwater omnivorous organisms: Effect of feces and necrophagy

Transfer of CeO₂ engineered nanoparticles (NPs) through feces was investigated between two omnivorous organisms, red crucian carp (Carassius auratus red var.) and crayfish (Procambarus clarkii). Upon water exposure (5 mg/L, 7 days), the highest bioaccumulation was observed in carp gills (5.95 μg Ce/g D.W.) and crayfish hepatopancreas (648 μg Ce/g D.W.), with the bioconcentration factors (BCFs) at 0.45 and 3.61, respectively. In addition, 97.4% and 73.0% of ingested Ce were excreted by carp and crayfish, respectively. The feces of carp and crayfish were collected and fed to crayfish and carp, respectively. After feces exposure, bioconcentration was observed in both carp (BCF, 3.00) and crayfish (BCF, 4.56). After feeding crayfish with carp bodies (1.85 μg Ce/g D.W.), CeO₂ NPs were not biomagnified (biomagnification factor, 0.28). Upon water exposure, CeO₂ NPs were transformed into Ce(III) in the feces of both carp (24.6%) and crayfish (13.6%), and the transformation was stronger after subsequent feces exposure (100% and 73.7%, respectively). Feces exposure lowered histopathological damage, oxidative stress, and nutritional quality (e.g., crude proteins, microelements, amino acids) to carp and crayfish in comparison with water exposure. This research highlights the importance of feces exposure on the transfer and fate of NPs in aquatic ecosystems.

Nanoparticulate pollutants in the environment: Analytical methods, formation, and transformation

The wide application of nanomaterials and plastic products generates a substantial number of nanoparticulate pollutants in the environment. Nanoparticulate pollutants are quite different from their bulk counterparts because of their unique physicochemical properties, which may pose a threat to environmental organisms and human beings. To accurately predict the environmental risks of nanoparticulate pollutants, great efforts have been devoted to developing reliable methods to define their occurrence and track their fate and transformation in the environment. Herein, we summarized representative studies on the preconcentration, separation, formation, and transformation of nanoparticulate pollutants in environmental samples. Finally, some perspectives on future research directions are proposed.

The design of strut/TPMS-based pore geometries in bioceramic scaffolds guiding osteogenesis and angiogenesis in bone regeneration

The pore morphology design of bioceramic scaffolds plays a substantial role in the induction of bone regeneration. Specifically, the effects of different scaffold pore geometry designs on angiogenesis and new bone regeneration remain unclear. Therefore, we fabricated Mg/Sr co-doped wollastonite bioceramic (MS-CSi) scaffolds with three different pore geometries (gyroid, cylindrical, and cubic) and compared their effects on osteogenesis and angiogenesis in vitro and in vivo. The MS-CSi scaffolds were fabricated by digital light processing (DLP) printing technology. The pore structure, mechanical properties, and degradation rate of the scaffolds were investigated. Cell proliferation on the scaffolds was evaluated using CCK-8 assays while angiogenesis was assessed using Transwell migration assays, tube formation assays, and immunofluorescence staining. The underlying mechanism was explored by western blotting. Osteogenic ability of scaffolds was evaluated by alkaline phosphatase (ALP) staining, western blotting, and qRT-PCR. Subsequently, a rabbit femoral defect model was prepared to compare differences in the scaffolds in osteogenesis and angiogenesis in vivo. Cell culture experiments showed that the gyroid pore scaffold downregulated YAP/TAZ phosphorylation and enhanced YAP/TAZ nuclear translocation, thereby promoting proliferation, migration, tube formation, and high expression of CD31 in human umbilical vein endothelial cells (HUVECs) while strut-based (cubic and cylindrical pore) scaffolds promoted osteogenic differentiation in bone marrow mesenchymal stem cells and upregulation of osteogenesis-related genes. The gyroid pore scaffolds were observed to facilitate early angiogenesis in the femoral-defect model rabbits while the strut-based scaffolds promoted the formation of new bone tissue. Our study indicated that the pore geometries and pore curvature characteristics of bioceramic scaffolds can be precisely tuned for enhancing both osteogenesis and angiogenesis. These results may provide new ideas for the design of bioceramic scaffolds for bone regeneration.

Smectite phase separation is driven by hydration-mediated interfacial charge

Smectite clay minerals have an outsize impact on the response of clay-rich media to common stimuli, such as hydration and ion exchange, motivating extensive effort to understand behaviors resulting from these processes such as swelling and exfoliation. Smectites are common and historic systems for investigating colloidal and interfacial phenomena, with two swelling regimes commonly identified across myriad clays: osmotic swelling at high water activity and crystalline swelling at low water activity. However, no current swelling model seamlessly spans the full ranges of water, salt and clay content encountered in natural or engineered settings. Here, we show that structures previously rationalized as either osmotic or crystalline coexist as a rich array of distinct colloidal phases that differ by water content, layer stacking thickness, and curvature. We present an analytical model for intermolecular potentials among water, salt and clay in both mono- and divalent electrolytes that predicts swelling pressures across high and low water activities. Our results indicate that all clay swelling is osmotic swelling, but that the osmotic pressure of charged mineral interfaces becomes attractive and dominates that of the electrolyte at high clay activities. Global energy minima are often not reached on experimental timescales due to many local energy minima that promote long-lived intermediate states with vast differences in clay, ion, and water mobilities, leading to hyperdiffusive layer dynamics driven by variable hydration-mediated interfacial charge. Teaser Distinct colloidal phases of swelling clays emerge via ion (de)hydration at mineral interfaces that drives hyperdiffusive layer dynamics as metastable smectites approach equilibrium.

Oxide- and Silicate-Water Interfaces and Their Roles in Technology and the Environment

Interfacial reactions drive all elemental cycling on Earth and play pivotal roles in human activities such as agriculture, water purification, energy production and storage, environmental contaminant remediation, and nuclear waste repository management. The onset of the 21st century marked the beginning of a more detailed understanding of mineral aqueous interfaces enabled by advances in techniques that use tunable high-flux focused ultrafast laser and X-ray sources to provide near-atomic measurement resolution, as well as by nanofabrication approaches that enable transmission electron microscopy in a liquid cell. This leap into atomic- and nanometer-scale measurements has uncovered scale-dependent phenomena whose reaction thermodynamics, kinetics, and pathways deviate from previous observations made on larger systems. A second key advance is new experimental evidence for what scientists hypothesized but could not test previously, namely, interfacial chemical reactions are frequently driven by "anomalies" or "non-idealities" such as defects, nanoconfinement, and other nontypical chemical structures. Third, progress in computational chemistry has yielded new insights that allow a move beyond simple schematics, leading to a molecular model of these complex interfaces. In combination with surface-sensitive measurements, we have gained knowledge of the interfacial structure and dynamics, including the underlying solid surface and the immediately adjacent water and aqueous ions, enabling a better definition of what constitutes the oxide- and silicate-water interfaces. This critical review discusses how science progresses from understanding ideal solid-water interfaces to more realistic systems, focusing on accomplishments in the last 20 years and identifying challenges and future opportunities for the community to address. We anticipate that the next 20 years will focus on understanding and predicting dynamic transient and reactive structures over greater spatial and temporal ranges as well as systems of greater structural and chemical complexity. Closer collaborations of theoretical and experimental experts across disciplines will continue to be critical to achieving this great aspiration.

Crystallization-based upcycling of iron oxyhydroxide for efficient arsenic capture in contaminated soils

Arsenic (As)-contaminated soil inevitably exists in nature and has become a global challenge for a sustainable future. Current processes for As capture using natural and structurally engineered nanomaterials are neither scientifically nor economically viable. Here, we established a feasible strategy to enhance As-capture efficiency and ecosystem health by structurally reorganizing iron oxyhydroxide, a natural As stabilizer. We propose crystallization to reorganize FeOOH-acetate nanoplatelets (r-FAN), which is universal for either scalable chemical synthesis or reproduction from natural iron oxyhydroxide phases. The r-FAN with wide interlayer spacing immobilizes As species through a synergistic mechanism of electrostatic intercalation and surface chemisorption. The r-FAN rehabilitates the ecological fitness of As-contaminated artificial and mine soils, as manifested by the integrated bioassay results of collembolan and plants. Our findings will serve as a cornerstone for crystallization-based material engineering for sustainable environmental applications and for understanding the interactions between soil, nanoparticles, and contaminants.

Direct Measurement of Microplastics by Carbon Detection via Single Particle ICP-TOFMS in Complex Aqueous Suspensions

Multiple analytical techniques to measure microplastics (MPs) in complex environmental matrices are currently under development, and which is most suited often depends on the aim(s) of the research question and the experimental design. Here, we further broaden the suite of possible techniques which can directly detect MPs in suspension while differentiating the carbon contained in MPs from other natural particles and dissolved organic carbon (DOC). Single particle inductively coupled plasma mass spectrometry (sp-ICP-MS) is well suited to measuring particles at trace concentrations, and the use of ICP time-of-flight-MS (ICP-TOFMS) allows one to simultaneously monitor the entire elemental spectrum to assess the full elemental composition of individual particles through developing elemental fingerprints. Because carbon is not detected in a standard operation mode with icp TOF, a dedicated optimization was necessary. Subsequently, to assess the feasibility of monitoring ¹²C particle pulses for the detection of MPs in more complex natural waters, two proof-of-principle studies were performed to measure MPs in waters with environmentally relevant DOC backgrounds (≤20 mg/L) and in the presence of other carbon containing particles, here, algae. Elevated DOC concentrations did not impact the enumeration of particles in suspension, and individual MPs, single algae, and aggregates of MPs and algae were clearly distinguished. The simultaneous identification of different analytes of interest allows for multiplexed sp-ICP-TOFMS experiments utilizing elemental fingerprinting of particles and is a step forward in quantifying MPs in aqueous environmental samples.

Aging of Copper Nanoparticles in the Marine Environment Regulates Toxicity for a Coastal Phytoplankton Species

Environmental conditions in aquatic ecosystems transform toxic chemicals over time, influencing their bioavailability and toxicity. Using an environmentally relevant methodology, we tested how exposure to seawater for 1-15 weeks influenced the accumulation and toxicity of copper nanoparticles (nano-Cu) in a marine phytoplankton species. Nano-Cu rapidly agglomerated in seawater and then decreased in size due to Cu dissolution. Dissolution rates declined during weeks 1-4 and remained low until 15 weeks, when the large agglomerates that had formed began to rapidly dissolve again. Marine phytoplankton species were exposed for 5-day periods to nano-Cu aged from 1 to 15 weeks at concentrations from 0.01 to 20 ppm. Toxicity to phytoplankton, measured as change in population growth rate, decreased significantly with particle aging from 0 to 4 weeks but increased substantially in the 15-week treatment due apparently to elevated Cu dissolution of reagglomerated particles. Results indicate that the transformation, fate, and toxicity of nano-Cu in marine ecosystems are influenced by a highly dynamic physicochemical aging process.

Polystyrene microplastics facilitate the biotoxicity and biomagnification of ZnO nanoparticles in the food chain from algae to daphnia

Ubiquitous microplastics (MPs) may affect the trophic transfer of nanoparticles (NPs), in turn threatening aquatic organisms and even human health. Thus, this study explored the influence of polystyrene microplastics (PS MPs) on the biotoxicity and biomagnification of ZnO nanoparticles (ZnO NPs) in the aquatic food chain from Chlorella vulgaris (C. vulgaris) to Daphnia magna (D. magna). The results showed that PS MPs facilitated the biotoxicity of ZnO NPs towards D. magna after dietary exposure. Compared to the control (single ZnO NPs), the heart rate and the level of reactive oxygen species were remarkably increased by 21.25% and 16.32% in the combined system (PS MPs + ZnO NPs), respectively. Notably, PS MPs suppressed the ZnO NPs accumulation in C. vulgaris, while remarkably facilitating the trophic transfer of ZnO NPs to D. magna. The biomagnification of ZnO NPs was evident with a maximal biomagnification factor (BMF) of 1.49 under acute dietary exposure of PS MPs (72 h), but was absent in the single ZnO NPs system (BMF <0.90). Moreover, PS MPs resulted in a larger biomagnification of ZnO NPs with a maximal BMF of 2.11 under chronic dietary exposure (21 days). Furthermore, the Zn element (including ZnO NPs and released Zn²⁺) was observed to accumulate in the intestine, thus causing ultrastructural damage and lipid droplet (LD) aggregate. Overall, these findings highlight the importance of considering the impact of MPs on co-existed pollutants and contribute to a better understanding of the ecological risks of MPs in aquatic ecosystems.

Eco-friendly PVA-LYS fibers for gold nanoparticle recovery from water and their catalytic performance

In this work, we grafted lysine on PVA electrospun fibers, using a green preparation technique. The resulting fiber mats were proposed for gold nanoparticles (AuNPs) removal from water. The efficiency of three fibers with different lysine amounts (10, 20, and 30%) was investigated. The incorporation of amino groups in PVA fibers was firstly proved by FTIR, SEM, and elemental analysis, confirming the presence of lysine. Among the three different fibers, PVA-LYS 30% has shown the best removal efficiency, reaching 65%, at pH equal to 5. Adsorption isotherms were studied and showed that the Langmuir model is the best model fitting our experimental results, with a maximum adsorption capacity of 20.1 mg g^-1. Metal-ligand interactions and electrostatic attraction between protonated amino groups of lysine on the fibers and negatively charged, citrate capped, AuNPs are the main proposed mechanisms for AuNP adsorption on the fibers. Sustainability of AuNPs adsorbed on these fibers has been checked through their reuse as catalyst for the reduction of 4-nitrophenol to 4-aminophenol. The process was completed within 60 min, and their reusability showed more than 99% efficiency after 5 reduction cycles. Our results prove that green PVA-LYS fibers can extract nanoparticles from water, as low cost-effective and eco-friendly adsorbent, and contribute to the promotion of a circular economy approach, through their reuse as catalyst in the reduction of pollutants.

Human dendritic cell maturation induced by amorphous silica nanoparticles is Syk-dependent and triggered by lipid raft aggregation

BACKGROUND

Synthetic amorphous silica nanoparticles (SAS-NPs) are widely employed in pharmaceutics, cosmetics, food and concretes. Workers and the general population are exposed daily via diverse routes of exposure. SAS-NPs are generally recognized as safe (GRAS) by the Food and Drug Administration, but because of their nanoscale size and extensive uses, a better assessment of their immunotoxicity is required. In the presence of immune "danger signals", dendritic cells (DCs) undergo a maturation process resulting in their migration to regional lymph nodes where they activate naive T-cells. We have previously shown that fumed silica pyrogenic SAS-NPs promote the two first steps of the adaptative immune response by triggering DC maturation and T-lymphocyte response, suggesting that SAS-NPs could behave as immune "danger signals". The present work aims to identify the mechanism and the signalling pathways involved in DC phenotype modifications provoked by pyrogenic SAS-NPs. As a pivotal intracellular signalling molecule whose phosphorylation is associated with DC maturation, we hypothesized that Spleen tyrosine kinase (Syk) may play a central role in SAS-NPs-induced DC response.

RESULTS

In human monocyte-derived dendritic cells (moDCs) exposed to SAS-NPs, Syk inhibition prevented the induction of CD83 and CD86 marker expression. A significant decrease in T-cell proliferation and IFN-γ, IL-17F and IL-9 production was found in an allogeneic moDC:T-cell co-culture model. These results suggested that the activation of Syk was necessary for optimal co-stimulation of T-cells. Moreover, Syk phosphorylation, observed 30 min after SAS-NP exposure, occurred upstream of the c-Jun N-terminal kinase (JNK) Mitogen-activated protein kinases (MAPK) and was elicited by the Src family of protein tyrosine kinases. Our results also showed for the first time that SAS-NPs provoked aggregation of lipid rafts in moDCs and that MβCD-mediated raft destabilisation altered Syk activation.

CONCLUSIONS

We showed that SAS-NPs could act as an immune danger signal in DCs through a Syk-dependent pathway. Our findings revealed an original mechanism whereby the interaction of SAS-NPs with DC membranes promoted aggregation of lipid rafts, leading to a Src kinase-initiated activation loop triggering Syk activation and functional DC maturation.

Priming effects of nZVI on carbon sequestration and iron uptake are positively mediated by AM fungus in semiarid agricultural soils

We investigated the priming effect of nanoscale zero-valent iron (nZVI) on carbon sink and iron uptake, and the possible mediation by AMF (arbuscular mycorrhizal fungi, Funneliformis mosseae) in semiarid agricultural soils. Maize seed dressings comprised of three nZVI concentrations of 0, 1, 2 g·kg^-1 and was tested with and without AMF inoculation under high and low soil moistures, respectively. The ICP-OES observations indicated that both low dose of nZVI (1 g·kg^-1) and high dose of nZVI (2 g·kg^-1) significantly increased the iron concentrations in roots (L: 54.5-109.8 %; H: 119.1-245.4 %) and shoots (L: 40.8-78.9 %; H: 81.1-99.4 %). Importantly, the absorption and translocation rate of iron were substantially improved by AMF inoculation under the low-dose nZVI. Yet, the excess nanoparticles as a stress were efficiently relieved by rhizosphere hyphae, and the iron concentration in leaves and stems can maintain as high as about 300 mg·kg^-1 while the iron translocation efficiency was reduced. Moreover, next-generation sequencing confirmed that appropriate amount of nZVI clearly improved the rhizosphere colonization of Funneliformis mosseae (p < 0.001) and the development of soil fungal community. Soil observations further showed that the hyphae development and GRSP (glomalin-related soil protein) secretion were significantly promoted (p < 0.05), with the increased R_0.25 (< 0.25 mm) by 35.97-41.16 %. As a return, AMF and host plant turned to input more organic matter into soils for microbial growth and Fe uptake, and such interactions became more pronounced under drought stress. In contrast, high dose of nZVI (2 g·kg^-1) tended to agglomerate on the surface of hyphae and spores, causing severe deformation and inactivation of AMF symbionts. Therefore, the priming effects of nZVI on carbon sequestration and Fe uptake in agricultural soils were positively mediated by AMF via the feedback loop of the plant-soil-microbe system for enhanced adaptation to global climate change.

Antagonism toxicity of CuO nanoparticles and mild ocean acidification to marine algae

The toxicity of CuO nanoparticles (NPs) to marine microalgae (Emiliania huxleyi) under ocean acidification (OA) conditions (pHs 8.10, 7.90, 7.50) was investigated. CuO NPs (5.0 mg/L) caused significant toxicity (e.g., 48-h growth inhibition, 20%) under normal pH (8.10), and severe OA (pH 7.50) increased the toxicity of CuO NPs (e.g., 48-h growth inhibition, 68%). However, toxicity antagonism was observed with a growth inhibition (48 h) decreased to 37% after co-exposure to CuO NPs and mild OA (pH 7.90), which was attributed to the released Cu²⁺ ions from CuO NPs. Based on biological responses as obtained from RNA-sequencing, the dissolved Cu²⁺ ions (0.078 mg/L) under mild OA were found to increase algae division (by 17%) and photosynthesis (by 28%) through accelerating photosynthetic electron transport and promoting ATP synthesis. In addition, mild OA enhanced EPS secretion by 41% and further increased bioavailable Cu²⁺ ions, thus mitigating OA-induced toxicity. In addition, excess Cu²⁺ ions could be transformed into less toxic Cu₂S and Cu₂O based on X-ray absorption near-edge spectroscopy (XANES) and high-resolution transmission electron microscopy (HR-TEM), which could additionally regulate the antagonism effect of CuO NPs and mild OA. The information advances our knowledge in nanotoxicity to marine organisms under global climate change.

Vertical distribution of inorganic nanoparticles in a Norwegian fjord

Due to the analytical challenges of detecting and quantifying nanoparticles in seawater, the data on distributions of NPs in the marine environment is limited to qualitative studies or by ensemble measurements subject to various analytical artifacts. Single particle inductively coupled plasma mass spectrometry (SP-ICP-MS) allows determination of individual inorganic NPs at environmentally relevant concentrations, yet only few studies have been conducted on selected elements in surface sea water. Here, a sequential multi-element screening method was developed and implemented to provide a first survey of the horizontal and vertical distributions of inorganic nanoparticles and trace elements in a pristine Norwegian fjord prospect for submarine tailings deposition. Statistical control of false-positive detections while minimizing the size detection limit was ensured using a novel raw signal processing. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) gave confirmative and qualitative information regarding particle morphology and composition. Following SP-ICP-MS screening for particles of 16 elements, particulate Al, Fe, Mn, Pb, Si and Ti were found and determined to mass concentrations in ng/L of 1-399, 1-412, below limit of detection (<LOD) - 269, <LOD - 1, <LOD - 1981 and <LOD - 127 ng/L with particle number concentrations up to 10⁸ particles per liter. Total metals concentrations were at least an order of magnitude higher, at concentrations in μg/L of 1-12 for Al, 2-13 for Fe, 0.3-11 Mn, 0.02-0.5 for Pb, 46 to 318 Si and 0.04-0.4 for Ti. A strong depth dependence was observed for both trace elements and particles with concentrations increasing with depth. Our results provide a baseline for the fjord and new data on environmental levels of both total metals and metal containing nanoparticles including the vertical and horizontal distribution of natural nanoparticles.

Fascinating strategies of marine benthic organisms to cope with emerging pollutant: Titanium dioxide nanoparticles

Titanium dioxide nanoparticles (NPs) have numerous applications, and their demands have increased as an alternative for banned sunscreen filters. However, the underlying mechanisms of their toxicity, remain largely unknown. Here, we investigate the mechanism of TiO₂ NP cytotoxicity and detoxification through time-course experiments (1, 6, and 24 h) based on cellular observations and single-cell transcriptome analyses in a marine benthic foraminifer strain, derived from a common unicellular eukaryotic organism worldwide. After exposure for 1 h, cells enhanced the production of reactive oxygen species (ROS) in acidic endosomes containing TiO₂ NPs as well as in mitochondria. In acidic endosomes, ROS were produced through the Fenton reaction on the surface of charged TiO₂ NPs. In mitochondria, ROS were associated with porphyrin synthesis that chelated metal ions. Glutathione peroxide and neutral lipids acted as a sink for free radicals, whereas lipid peroxides were excreted to prevent further radical chain reactions. By 24 h, aggregated TiO₂ NPs were encapsulated in organic compounds, possibly ceramide, and excreted as mucus, thereby preventing their further uptake. Thus, we reveal that foraminifers can tolerate the toxicity of TiO₂ NPs and even prevent their further phagocytosis and uptake by trapping TiO₂ NPs inside mucus. This previously unknown strategy could be applied in bioremediation to sequester NPs from the marine environment and can guide management of TiO₂ pollution.

Predicting accidental release of engineered nanomaterials to the environment

Challenges in distinguishing between natural and engineered nanomaterials (ENMs) and the lack of historical records on ENM accidents have hampered attempts to estimate the accidental release and associated environmental impacts of ENMs. Building on knowledge from the nuclear power industry, we provide an assessment of the likelihood of accidental release rates of ENMs within the next 10 and 30 years. We evaluate risk predictive methodology and compare the results with empirical evidence, which enables us to propose modelling approaches to estimate accidental release risk probabilities. Results from two independent modelling approaches based on either assigning 0.5% of reported accidents to ENM-releasing accidents (M1) or based on an evaluation of expert opinions (M2) correlate well and predict severe accidental release of 7% (M1) in the next 10 years and of 10% and 20% for M2 and M1, respectively, in the next 30 years. We discuss the relevance of these results in a regulatory context.

Uptake of TiO2 Nanoparticles was Linked to Variation in net Cation flux in Wheat Seedlings

Titanium dioxide nanoparticles (TiO₂ NPs) are ubiquitous in the environment and enter the terrestrial food chain via plant uptake. However, plant uptake behaviors of TiO₂ NPs remain elusive. Here, the uptake kinetics of TiO₂ NPs by wheat (Triticum aestivum L.) seedlings and the effects on cation flux in roots were examined in a hydroponic system. Uptake rate of TiO₂ NPs ranged from 119.0 to 604.2 mg kg^- 1 h^- 1 within 8 h exposure. NP uptake decreased by 83% and 47%, respectively, in the presence of sodium azide (NaN₃) and carbonyl cyanide m-chlorophenylhydrazone (CCCP), indicating an energy-dependent uptake of TiO₂ NPs. Moreover, accompanied with TiO₂ NP uptake, net influx of Cd²⁺ decreased by 81%, while Na⁺ flux shifted from inflow to outflow at the meristematic zone of root. These findings provide valuable information for understanding plant uptake of TiO₂ NPs.

Analytical methods for assessing antimicrobial activity of nanomaterials in complex media: advances, challenges, and perspectives

Assessing the antimicrobial activity of engineered nanomaterials (ENMs), especially in realistic scenarios, is of great significance for both basic research and applications. Multiple analytical methods are available for analysis via off-line or on-line measurements. Real-world samples are often complex with inorganic and organic components, which complicates the measurements of microbial viability and/or metabolic activity. This article highlights the recent advances achieved in analytical methods including typical applications and specifics regarding their accuracy, cost, efficiency, and user-friendliness. Methodological drawbacks, technique gaps, and future perspectives are also discussed. This review aims to help researchers select suitable methods for gaining insight into antimicrobial activities of targeted ENMs in artificial and natural complex matrices.

Impact of iron/aluminum (hydr)oxide and clay minerals on heteroaggregation and transport of nanoplastics in aquatic environment

Nanoplastics (NPs) are emerging contaminants in the environment, where the transport and fate of NPs would be greatly affected by interactions between NPs and minerals. In the present study, the interactions of two types of polystyrene nanoplastics (PSNPs), i.e., bare-PSNPs and carboxylated PSNPs-COOH, with iron (hydr)oxides (hematite, goethite, magnetite, and ferrihydrite), aluminum (hydr)oxides (boehmite and gibbsite), and clay minerals (kaolinite, montmorillonite, and illite) were investigated. The positively charged iron/aluminum (hydr)oxide minerals could form heteroaggregates with negatively charged PSNPs. Electrostatic and hydrophobic interaction dominate for the heteroaggregation of bare-PSNPs with iron/aluminum (hydr)oxide minerals, while ligand exchange and electrostatic interaction are involved in the heteroaggregation of PSNPs-COOH with iron/aluminum (hydr)oxides minerals. However, heteroaggregation between PSNPs and negatively charged clay minerals was negligible. Humic acid markedly suppressed such heteroaggregation between PSNPs and minerals due to enhanced electrostatic repulsion, steric hindrance, and competition of surface attachment sites. The heteroaggregation rates of both bare-PSNPs and PSNPs-COOH with hematite decreased with increasing solution pH. Increased ionic strength enhanced the heteroaggregation of PSNPs-COOH but inhibited that of bare-PSNPs. The results of the present study suggested that the heteroaggregation of PSNPs in environments could be strongly affected by minerals, solution pH, humic acid, and ionic strength.

Environmental safety of nanotechnologies: The eco-design of manufactured nanomaterials for environmental remediation

Nanosafety is paramount considering the risks associated with manufactured nanomaterials (MNMs) whose implications could outweigh their advantages for environmental applications. Although nanotechnology-based solutions to implement pollution control, remediation and prevention are incremental with clear benefits for public health and Earth' natural ecosystems, nanoremediation is having a setback due to the risks associated with the safety of MNMs for humans and the environment. MNMs are diverse, work differently and bionano-interactions occurring upon environmental exposure will guide their fate and hazardous outcomes. Here we propose a new ecologically-based design strategy (eco-design) having its roots in green nanoscience and LCA that will ground on an Ecological Risk Assessment approach, which introduces the evaluation of MNMs' ecotoxicity along with their performances and efficacies at the design stage. As such, the proposed eco-design strategy will allow recognition and design-out since the very beginning of material synthesis, those hazardous peculiar features that can be hazardous to living beings and the natural environment. A more ecologically sound eco-design strategy in which nanosafety is conceptually included in MNMs design will sustain safer nanotechnologies including those for the environment as remediation by leveraging any risks for humans and natural ecosystems.

Combustion conditions and feed coals regulating the Fe- and Ti-containing nanoparticles in various coal fly ash

Quantitative characteristics and sizes of nanoparticles (NPs) in coal fly ash (CFA) produced in coal-fired power plants as a function of coal type and plant design will help reveal the NP emission likelihood and their environmental implications. However, little is known about how combustion conditions and types of coal regulate the NP abundance in CFAs. In this study, based on single particle (SP)-ICP-MS technology, particle number concentrations (PNCs) and sizes of Fe- and Ti-containing NPs in CFAs were determined for samples collected from power plants of different designs and burning different types of coal. The PNCs of Fe- and Ti-containing NPs in all CFAs measured were in the range of 1.3 × 10⁷ - 3.4 × 10⁸ and 6.8 × 10⁶ - 2.2 × 10⁸ particles/mg, with the average particle sizes of 111 nm and 87 nm, respectively. The highest Fe-NP PNCs likely relate to the highest contents of Fe and pyrite in the feed coal. In addition, high TOC in CFAs are associated with metal-containing NPs, resulting in elevated abundances of these NPs with relatively large sizes. Moreover, elevated PNCs of NPs were found in CFAs produced by coal-fired power plants burning low-rank coals and with small installed capacity (especially those under 100-MW units). Compared to cyclone filters, ESPs and FFs with higher removal efficiency typically retain more Fe-/Ti- containing NPs with smaller sizes. Based on a structural equation (SE) model, raw coal properties (coal rank and Fe/Ti content), boiler types, and efficiency of particulate emission control devices likely indirectly affect PNCs of Fe- and Ti-containing NPs by influencing TOC contents and their corresponding metal concentrations of CFAs. This study provides the first analytic and comprehensive information concerning the direct and indirect regulating factors on NPs in various CFAs.

The co-occurrent microplastics and nano-CuO showed antagonistic inhibitory effects on bacterial denitrification: Interaction of pollutants and regulations on functional genes

The wide occurrence of microplastics (MPs) and nanoparticles resulted in their inevitable coexistence in environment. However, the joint effects of these two types of particulate emerging contaminants on denitrification have seldomly been investigated. Herein, non-biodegradable polyvinyl chloride, polypropylene, polyethylene and biodegradable polyhydroxyalkanoate (PHA) MPs were chosen to perform the co-occurrent effects with nano copper oxide (nano-CuO). Both the nano-CuO and MPs inhibited the denitrification process, and biodegradable PHA-MPs showed severer inhibition than non-biodegradable MPs. However, the presence of MPs significantly alleviated the inhibition of nano-CuO, suggesting an antagonistic effect. Other than MPs decreasing copper ion release from nano-CuO, MPs and nano-CuO formed agglomerations and induced lower levels of oxidative stress compared to individual exposure. Transcriptome analysis indicated that the co-occurrent MPs and nano-CuO induced different regulation on denitrifying genes (e. g. nar and nor) compared to individual ones. Also, the expressions of genes involved in denitrification-associated metabolic pathways, including glycolysis and NADH electron transfer, were down-regulated by nano-CuO or MPs, but exhibiting recovery under the co-occurrent conditions. This study firstly discloses the antagonistic effect of nano-CuO and MPs on environmental process, and these findings will benefit the systematic evaluation of MPs environmental behavior and co-occurrent risk with other pollutants.

Effects of physicochemical properties and co-existing zinc agrochemicals on the uptake and phytotoxicity of PFOA and GenX in lettuce

Even though the potential toxicity and treatment methods for per- and polyfluoroalkyl substances (PFAS) have attracted extensive attention, the plant uptake and accumulation of PFAS in edible plant tissues as a potential pathway for human exposure received little attention. Our study in a hydroponic system demonstrated that perfluorooctanoic acid (PFOA) and its replacing compound, 2,3,3,3-tetrafluoro-2-(heptafluoropropoxy) propanoic acid (GenX) displayed markedly different patterns of plant uptake and accumulation. For example, the root concentration factor (RCF) of PFOA in lettuce is almost five times of that of GenX while the translocation factor (TF) of GenX is about 66.7% higher than that for PFOA. The co-presence of zinc amendments affected the phyto-effect of these two compounds and their accumulation in plant tissues, and the net effect on their plant accumulation depended on both the properties of Zn amendments and PFAS. Zinc oxide nanoparticles (ZnONPs) at 100 mg/L did not affect the uptake of PFOA in either lettuce roots or shoots; however, Zn2+ at the same concentration significantly increased PFOA accumulation in both tissues. In contrast, both Zn amendments significantly lowered the accumulation of GenX in lettuce roots, but only ZnONPs significantly hindered the GenX accumulation in lettuce shoots. The co-exposure to ZnONPs and PFOA/GenX resulted in lower oxidative stress than the plants exposed to PFOA or GenX alone. However, both zinc agrochemicals with or without PFAS led to lower root dry biomass. The results shed light on the property-dependent plant uptake of PFAS and the potential impact of co-existing nanoagrochemicals and their dissolved ions on plant uptake of PFOA and GenX.

Effects of Different Nanoparticles on Microbes

Nanoparticles widely exist in nature and may be formed through inorganic or organic pathways, exhibiting unique physical and chemical properties different from those of bulk materials. However, little is known about the potential consequences of nanomaterials on microbes in natural environments. Herein, we investigated the interactions between microbes and nanoparticles by performing experiments on the inhibition effects of gold, ludox and laponite nanoparticles on Escherichia coli in liquid Luria–Bertani (LB) medium at different nanoparticle concentrations. These nanoparticles were shown to be effective bactericides. Scanning electron microscopy (SEM) images revealed the distinct aggregation of cells and nanoparticles. Transmission electron microscopy (TEM) images showed considerable cell membrane disruption due to nanoparticle accumulation on the cell surfaces, resulting in cell death. We hypothesized that this nanoparticle accumulation on the cell surfaces not only disrupted the cell membranes but also physically blocked the microbes from accessing nutrients. An iron-reducing bacterium, Shewanella putrefaciens, was tested for its ability to reduce the Fe (III) in solid ferrihydrite (HFO) or aqueous ferric citrate in the presence of laponite nanoparticles. It was found that the laponite nanoparticles inhibited the reduction of the Fe (III) in solid ferrihydrite. Moreover, direct contact between the cells and solid Fe (III) coated with the laponite nanoparticles was physically blocked, as confirmed by SEM images and particle size measurements. However, the laponite particles had an insignificant effect on the extent of aqueous Fe (III) bioreduction but slightly enhanced the rate of bioreduction of the Fe (III) in aqueous ferric citrate. The slightly increased rate of bioreduction by laponite nanoparticles may be due to the removal of inhibitory Fe (II) from the cell surface by its sorption onto the laponite nanoparticle surface. This result indicates that the scavenging of toxic heavy metals, such as Fe (II), by nanoparticles may be beneficial for microbes in the environment. On the other hand, microbial cells are also capable of detoxifying nanoparticles by coagulating nanoparticles with extracellular polymeric substances or by changing nanoparticle morphologies. Hence, the interactions between microbes and nanoparticles in natural environments should receive more attention.

Effects of natural nanoparticles on the acute toxicity, chronic effect, and oxidative stress response of phenicol antibiotics in Daphnia magna

Natural nanoparticles (NNP) are ubiquitous in natural water and can interact with other contaminants, causing ecotoxic effects on aquatic nontarget organisms. However, the impact of NNPs on the ecotoxicity of antibiotics remains largely unknown. This work investigated the acute toxicity, chronic effect, and oxidative response and damage in Daphnia magna co-exposed to phenicol antibiotics (chloramphenicol, thiamphenicol) and different concentrations of NNPs (10 mg/L: environmentally relevant concentration; 100 mg/L: a high concentration that caused no apparent immobilization in D. magna). The results showed that the acute toxicity of chloramphenicol was increased by 10 mg/L NNPs but decreased by 100 mg/L NNPs; both concentrations of NNPs increased and decreased acute toxicities of thiamphenicol and chloramphenicol + thiamphenicol treatments, respectively. After long-term exposure, phenicol antibiotics (1 μg/L) and NNP (10 mg/L) mixtures in environmentally relevant concentrations significantly affected the reproduction of D. magna but did not influence their growth. The catalase activity, reduced glutathione level, and malonaldehyde content in D. magna also varied with the NNPs concentrations. Notably, the lowest concentration of thiamphenicol and chloramphenicol + thiamphenicol combined with NNPs significantly increased the malondialdehyde content in D. magna compared with the control, indicating membrane lipid peroxidation occurred in daphnids. This study suggests that the toxic effects of contaminants and NNPs on aquatic organisms should be considered thoroughly to avoid underestimating the hazard of these pollutants in the actual aquatic environment.

Redispersion Behavior of 2D MoS2 Nanosheets: Unique Dependence on the Intervention Timing of Natural Organic Matter

The aggregation-redispersion behavior of nanomaterials determines their transport, transformation, and toxicity, which could be largely influenced by the ubiquitous natural organic matter (NOM). Nonetheless, the interaction mechanisms of two-dimensional (2D) MoS₂ and NOM and the subsequent influences on the redispersion behavior are not well understood. Herein, we investigated the redispersion of single-layer MoS₂ (SL-MoS₂) nanosheets as influenced by Suwannee River NOM (SRNOM). It was found that SRNOM played a decisive role on the redispersion of MoS₂ 2D nanosheets that varied distinctly from the 3D nanoparticles. Compared to the poor redispersion of MoS₂ aggregates in the absence or post-addition of SRNOM to the aggregates, co-occurrence of SRNOM in the dispersion could largely enhance the redispersion and mobility of MoS₂ by intercalating into the nanosheets. Upon adsorption to SL-MoS₂, SRNOM enhanced the hydration force and weakened the van der Waals forces between nanosheets, leading to the redispersion of the aggregates. The SRNOM fractions with higher molecular mass imparted better dispersity due to the preferable sorption of the large molecules onto SL-MoS₂ surfaces. This comprehensive study advances current understanding on the transport and fate of nanomaterials in the water system and provides fresh insights into the interaction mechanisms between NOM and 2D nanomaterials.

Bio- and eco-corona related to plants: Understanding the formation and biological effects of plant protein coatings on nanoparticles

The thriving nano-enabled agriculture facilitates the interaction of nanomaterials with plants. Recently, these interactions and their biological effects are receiving increasing attention. Upon entering plants via leaves, roots, stems, and other organs, nanoparticles adsorb numerous biomolecules inside plants and form bio-corona. In addition, nanoparticles that enter plants through roots may have formed eco-corona with root exudates in the rhizosphere environment before contacting with plant exogenous proteins. The most significant biological effects of plant protein corona include changes in protein structure and function, as well as changes in nanoparticle toxicity and targeting ability. However, the mechanisms, particularly how protein corona affects plant protein function, plant development and growth, and rhizosphere environment properties, require further investigation. Our review summarizes the current understanding of the formation and biological effects of nanoparticle-plant protein corona and provides an outlook on future research.

The use and detection of quantum dots as nanotracers in environmental fate studies of engineered nanoparticles

Investigations of the behavior and effects of engineered nanoparticles (ENPs) on human health and the environment need detailed knowledge of their fate and transport in environmental compartments. Such studies are highly challenging due to low environmental concentrations, varying size distribution of the particles and the interference with the natural background. A strategy to overcome these limits is to use mimics of ENPs with unique detectable properties that match the properties of the ENPs as nanotracers. A special class of ENPs that can be tracked are quantum dots (QDs). QDs are composed of different metals, metalloids, or more recently also carbon (e.g., graphene), that result in unique optical properties. This allows the tracking of such particles by fluorescence microscopic and photometric techniques. Many types of QDs consist of heavy elements, allowing to track and visualize these particles also by electron microscopy and to quantitate the particles indirectly based on these elements. QDs can also be surface modified in various ways which enable them to be used as a label or as traceable mimics for ENPs. This review reflects a broad range of methods to synthesize and modify QDs based on metals, metalloids, and graphene for studying the environmental fate of nanoparticles and discusses and compares analytical methods that can be used for tracking and quantifying QDs. In addition, we review applications of QDs as ENP mimics in environmental studies of surface waters, soils, microorganisms, and plants with respect to the applied analytical techniques.

The environmental fate of nanoplastics: What we know and what we need to know about aggregation

The presence of nanoplastics in the environment has been proven. There is now an urgent need to determine how nanoplastics behave in the environment and to assess the risks they may pose. Here, we examine nanoplastic homo- and heteroaggregation, with a focus on environmentally relevant nanoplastic particle models. We made a systematic analysis of experimental studies, and ranked the environmental relevance of 377 different solution chemistries, and 163 different nanoplastic particle models. Since polymer latex spheres are not environmentally relevant (due to their monodisperse size, spherical shape, and smooth surface), their aggregation behavior in natural conditions is not transferable to nanoplastics. A few recent studies suggest that nanoplastic particle models that more closely mimic incidentally produced nanoplastics follow different homoaggregation pathways than latex sphere particle models. However, heteroaggregation of environmentally relevant nanoplastic particle models has seldom been studied. Despite this knowledge gap, the current evidence suggests that nanoplastics may be more sensitive to heteroaggregation than previously expected. We therefore provide an updated hypothesis about the likely environmental fate of nanoplastics. Our review demonstrates that it is essential to use environmentally relevant nanoplastic particle models, such as those produced with top-down methods, to avoid biased interpretations of the fate and impact of nanoplastics. Finally, it will be necessary to determine how the heteroaggregation kinetics of nanoplastics impact their settling rate to truly understand nanoplastics' fate and effect in the environment.

Assessment of multiple biomarkers in Lithobates catesbeianus (Anura: Ranidae) tadpoles exposed to zinc oxide nanoparticles and zinc chloride: integrating morphological and behavioral approaches to ecotoxicology

The ecotoxicological risk to vertebrates posed by zinc oxide nanoparticles (ZnO NPs) is still poorly understood, especially in animals with a biphasic life cycle, which have aquatic and terrestrial phases, such as amphibians. In the present study, we investigated whether acute exposure (7 days) to ZnO NPs and zinc chloride (ZnCl₂) at three environmentally relevant concentrations (0.1, 1.0, and 10 mg L^-1) induces changes in the morphology, chondrocranium, and behavior of the tadpoles of Lithobates catesbeianus (Anura: Ranidae). Tadpoles exposed to both forms of Zn did not undergo any morphological or behavioral changes at the lowest concentrations (0.1 and 1.0 mg L^-1). However, the animals exposed to the highest concentration (10 mg L^-1) lacked oral disc structures, were smaller in size, had a longer tail, and presented changes in the position and coiling of the intestine and malformations of the chondrocranium in comparison with the control group. This indicates that ZnO NPs and ZnCl₂ altered the development of the tadpoles, causing delays in their metamorphosis and even reducing individual fitness. The tadpoles exposed to both forms of Zn at 10 mg L^-1 also had reduced mobility, especially in the presence of conspecifics. Based on these findings, we emphasize the importance of studying morphological, skeletal, and behavioral biomarkers to evaluate the toxic effects of metal-based nanoparticles in amphibians.

The aggregation of natural inorganic colloids in aqueous environment: A review

Natural inorganic colloids (NICs) are the most common and dominant existence in the ecosystem, with high concentration and wide variety. In spite of the low toxicity, they can alter activity and mobility of hazardous engineered nanoparticles (ENPs) through different interactions, which warrants the necessity to understand and predict the fate and transport of NICs in aquatic ecosystems. Here, this review summarized NICs properties and behaviors, interaction mechanisms and environmental factors at the first time. Various representative NICs and their physicochemical properties were introduced across the board. Then, the aggregation and sedimentation behaviors were discussed systematically, mainly concerning the heteroaggregation between NICs and ENPs. To speculate their fate and elucidate the corresponding mechanisms, the classical Derjaguin-Landau-Verwey-Overbeek (DLVO) and extended DLVO (X-DLVO) theories were focused. Furthermore, a range of intrinsic and extrinsic factors was presented in different perspective. Last but not the least, this paper pointed out theoretical and analytical gaps in current researches, and put forward suggestions for further research, aiming to provide a more comprehensive and original perspective in the fields of natural occurring colloids.

Insight into the formation and biological effects of natural organic matter corona on silver nanoparticles in water environment using biased cyclical electrical field-flow fractionation

Natural organic matter (NOM) readily interacts with nanoparticles, leading to the formation of NOM corona structures on their surface. NOM corona formation is closely related to the surface coatings and bioavailability of nanoparticles. However, the mechanism underlying NOM corona formation on silver nanoparticles (AgNPs) remains largely unknown due to the lack of effective analytical methods for identifying the changes in the AgNP surface. Herein, the separation ability of biased cyclical electrical field-flow fractionation (BCyElFFF) for same-sized polyvinyl pyrrolidone-coated and poly(ethylene glycol)-coated silver nanoparticles (AgNPs) with different electrophoretic mobilities was evaluated under various electrical conditions. Then, the mechanism behind the NOM corona formation on these AgNP surfaces was elucidated based on the changes in the elution time and off-line characterization of the collected fractions during their elution time in a BCyElFFF run. Finally, the survival rates of E. coli exposed to polyvinyl pyrrolidone-coated and poly(ethylene glycol)-coated AgNPs with or without NOM collected during repeated BCyElFFF runs were observed to increase with increasing NOM concentration, clearly demonstrating the negative effect of NOM corona structures on the bioavailability of AgNPs. These findings highlight the powerful separation and isolation ability of BCyElFFF in studying the transformation and fate of nanoparticles in aqueous environments.

Rhizosphere effect of nanoscale zero-valent iron on mycorrhiza-dependent maize assimilation

Rhizosphere effect of nanoscale zero-valent iron (nZVI) is crucial but little reported. Maize seeds were dressed with four nZVI concentrations (0, 1.0, 1.5, 2 g kg^-1 ) and inoculated with arbuscular mycorrhizal fungus (AMF) (Funneliformis mosseae). The SEM images illuminated that excessive nZVI particles (2 g kg^-1 ) were agglomerated on the surface of hyphae and spore, causing severe deformation and inactivation of AMF symbionts and thereafter inhibiting water uptake in maize seedlings. This restrained the scavenging effects of enzymatic (superoxide dismutase, peroxidase) and non-enzymatic compounds (proline & malondialdehyde) on ROS, and leaf photoreduction activity and gas exchange ability (p < 0.05). Interestingly, the inoculation with AMF effectively alleviated above negative effects. In contrast, appropriate dose of nZVI, that is, ≤1.5 g kg^-1 , can be evenly distributed on the hyphae surface and form the ordered symbionts with AMF. This help massively to enhance hyphae growth and water and nutrient uptake. The enhanced mycorrhizal infection turned to promote rhizosphere symbiont activity and leaf Rubisco and Rubisco activase activity. Light compensation point was massively lowered, which increased photosynthetic carbon supply for AMF symbionts. Particularly, such priming effects were evidently enhanced by drought stress. Our findings provided a novel insight into functional role of nZVI in agriculture and AMF-led green production.

Development of New Health Risk Assessment of Nanoparticles: EPA Health Risk Assessment Revised

The concentration of nanoparticles in the ambient air can lead to induced toxicities; however, it appears that nanoparticles’ unique properties are completely omitted when assessing health risks. This paper aims to enhance the EPA health risk assessment by incorporating two new variables that consider the size of nanoparticles: the toxicity multiplier and the size multiplier. The former considers the qualitative aspect of the size of particles within a concentration, whilst the latter takes into account the effects associated with the number of particles of the specific i-th size distribution interval. To observe the impact of the new variables, a case study was performed. The studied element was cadmium, which was measured using ICP-MS to discover concentrations of size fractions, ranging from <15.1 to <9830 nm. Next, the cadmium concentration is assessed using both the current state-of-the-art method and the proposed method with adjustments. Based on the new approach, the final risk was 1.1 × 10−5, which was almost 24 times higher compared with the current method. The contribution of nanoparticles to the risk value grew from barely 6% to an alarming 88%. Therefore, the enhanced method can lead to more realistic results when assessing the health risks of nanoparticles.

Environmental Risk of Arsenic Mobilization from Disposed Sand Filter Materials

Arsenic (As)-bearing water treatment residuals (WTRs) from household sand filters are usually disposed on top of floodplain soils and may act as a secondary As contamination source. We hypothesized that open disposal of these filter-sands to soils will facilitate As release under reducing conditions. To quantify the mobilization risk of As, we incubated the filter-sand, the soil, and a mixture of the filter-sand and soil in anoxic artificial rainwater and followed the dynamics of reactive Fe and As in aqueous, solid, and colloidal phases. Microbially mediated Fe(III)/As(V) reduction led to the mobilization of 0.1-4% of the total As into solution with the highest As released from the mixture microcosms equaling 210 μg/L. Due to the filter-sand and soil interaction, Mössbauer and X-ray absorption spectroscopies indicated that up to 10% Fe(III) and 32% As(V) were reduced in the mixture microcosm. Additionally, the mass concentrations of colloidal Fe and As analyzed by single-particle ICP-MS decreased by 77-100% compared to the onset of reducing conditions with the highest decrease observed in the mixture setups (>95%). Overall, our study suggests that (i) soil provides bioavailable components (e.g., organic matter) that promote As mobilization via microbial reduction of As-bearing Fe(III) (oxyhydr)oxides and (ii) As mobilization as colloids is important especially right after the onset of reducing conditions but its importance decreases over time.

Nano-scale analysis of uranium release behavior from river sediment in the Ili basin

Due to the limitations of the conventional water sample pretreatment methods, some of the colloidal uranium (U) has long been misidentified as "dissolved" phase. In this work, the U species in river water in the Ili Basin was classified into submicron-colloidal (0.1-1 μm), nano-colloidal (0.1 μm-3 kDa) and dissolved phases (< 3 kDa) by using high-speed centrifugation and ultrafiltration. The U concentration in the river water was 5.39-8.75 μg/L, which was dominated by nano-colloidal phase (55-70%). The nano-colloidal particles were mainly composed of particulate organic matter (POM) and had a very high adsorption capacity for U (accounting for 70 ± 23% of colloidal U). Sediment disturbance, low temperature, and high inorganic carbon greatly improved the release of nano-colloidal U, but high levels of Ca²⁺ inhibited it. The simulated river experiments indicated that the flow regime determined the release of nano-colloidal U, and large amounts of nano-colloidal U might be released during spring floods in the Ili basin. Moreover, global warming increases river flow and inorganic carbon content, which may greatly promote the release and migration of nano-colloidal U.

Potential use of engineered nanoparticles in ocean fertilization for large-scale atmospheric carbon dioxide removal

Artificial ocean fertilization (AOF) aims to safely stimulate phytoplankton growth in the ocean and enhance carbon sequestration. AOF carbon sequestration efficiency appears lower than natural ocean fertilization processes due mainly to the low bioavailability of added nutrients, along with low export rates of AOF-produced biomass to the deep ocean. Here we explore the potential application of engineered nanoparticles (ENPs) to overcome these issues. Data from 123 studies show that some ENPs may enhance phytoplankton growth at concentrations below those likely to be toxic in marine ecosystems. ENPs may also increase bloom lifetime, boost phytoplankton aggregation and carbon export, and address secondary limiting factors in AOF. Life-cycle assessment and cost analyses suggest that net CO₂ capture is possible for iron, SiO₂ and Al₂O₃ ENPs with costs of 2-5 times that of conventional AOF, whereas boosting AOF efficiency by ENPs should substantially enhance net CO₂ capture and reduce these costs. Therefore, ENP-based AOF can be an important component of the mitigation strategy to limit global warming.