Application of ZnO Nanoparticles Encapsulated in Mesoporous Silica on the Abaxial Side of a Solanum lycopersicum Leaf Enhances Zn Uptake and Translocation via the Phloem.

Foliar application of nutrient nanoparticles (NPs) is a promising strategy for improving fertilization efficiency in agriculture. Phloem translocation of NPs from leaves is required for efficient fertilization but is currently considered to be feasible only for NPs smaller than a cell wall pore size exclusion limit of <20 nm. Using mass spectrometry imaging, we provide here the first direct evidence for phloem localization and translocation of a larger (∼70 nm) fertilizer NP comprised of ZnO encapsulated in mesoporous SiO2 (ZnO@MSN) following foliar deposition. The Si content in the phloem tissue of the petiole connected to the dosed leaf was ∼10 times higher than in the xylem tissue, and ∼100 times higher than the phloem tissue of an untreated tomato plant petiole. Direct evidence of NPs in individual phloem cells has only previously been shown for smaller NPs introduced invasively in the plant. Furthermore, we show that uptake and translocation of the NPs can be enhanced by their application on the abaxial (lower) side of the leaf. Applying ZnO@MSN to the abaxial side of a single leaf resulted in a 56% higher uptake of Zn as well as higher translocation to the younger (upper) leaves and to the roots, than dosing the adaxial (top) side of a leaf. The higher abaxial uptake of NPs is in alignment with the higher stomatal density and lower density of mesophyll tissues on that side and has not been demonstrated before.

Mechanistic study of the increased phototoxicity of titanium dioxide nanoparticles to Chlorella vulgaris in the presence of NOM eco-corona.

Widespread applications and release of photoactive nanoparticles (NPs) such as titanium dioxide (TiO2) into environmental matrices warrant mechanistic investigations addressing toxicity of NPs under environmentally relevant conditions. Accordingly, we investigated the effects of surface adsorbed natural organic matters (NOMs) such as humic acid, tannic acid and lignin on the band gap energy, abiotic reactive oxygen species (ROS) generation, surface chemistry and phototoxicity of TiO2 NPs. Initially, a liquid assisted grinding method was optimized to produce TiO2 NPs with a NOM layer of defined thickness for further analysis. Generally, adsorption of NOM reduced the band-gap energy of TiO2 NPs from 3.08 eV to 0.56 eV with humic acid, 1.92 eV with tannic acid and 2.48 eV with lignin. Light activated ROS generation by TiO2 NPs such as hydroxyl radicals, however, was reduced by 4, 2, 9 times in those coated with humic acid, tannic acid and lignin, respectively. This reduction in ROS despite decrease in band gap energy corroborated with the decreased surface oxygen vacancy (as revealed by X-ray Photoelectron Spectroscopy (XPS)) and quenching of ROS by surface adsorbed NOM. Despite the reduced ROS generation, the NOM-modified TiO2 NPs exhibited an increased phototoxicity to Chlorella vulgaris in comparison to pristine TiO2 NPs. Further analysis suggested that photoactivation of NOM modified TiO2 NPs releases toxic degradation products. Findings from our studies thus provide mechanistic insight into the ecotoxic potential of NOM-modified TiO2 NPs when exposed to light in the environment.

Effect of nanopesticides (azoxystrobin and bifenthrin) on the phenolic content and metabolic profiles of strawberries (Fragaria × ananassa).

BACKGROUND: Nanoencapsulation has opened promising fields of innovation for pesticides. Conventional pesticides can cause side effects on plant metabolism. To date, the effect of nanoencapsulated pesticides on plant phenolic contents has not been reported. RESULTS: In this study, a comparative evaluation of the phenolic contents and metabolic profiles of strawberries was performed for plants grown under controlled field conditions and treated with two separate active ingredients, azoxystrobin and bifenthrin, loaded into two different types of nanocarriers (Allosperse® polymeric nanoparticles and SiO2 nanoparticles). There were small but significant decreases of the total phenolic content (9%) and pelargonidin 3-glucoside content (6%) in strawberries treated with the nanopesticides. An increase of 31% to 125% was observed in the levels of gallic acid, quercetin, and kaempferol in the strawberries treated with the nanoencapsulated pesticides compared with the conventional treatments. The effects of the nanocarriers on the metabolite and phenolic profiles was identified by principal component analysis. CONCLUSION: Overall, even though the effects of nanopesticides on the phenological parameters of strawberry plants were not obvious, there were significant changes to the plants at a molecular level. In particular, nanocarriers had some subtle effects on plant health and fruit quality through variations in total and individual phenolics in the fruits. Further research will be needed to assess the impact of diverse nanopesticides on other groups of plant metabolites. © 2023 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Hazard Profiling of Commercially Relevant Quantum Dot Components Revealed Synergistic Interactions between Heavy Metals and Polymers.

Commercially used quantum dots (QDs) exemplify complex nanomaterials with multiple components, though little is known about the type of interactions between these components in determining the overall toxicity of this material. We synthesized and characterized a functional QD (CdSe/ZnS_P&E) that was identical in structure and composition to a patented and commercially applied QD and the combinations of its components (CdSe, CdSe/ZnS, ZnS, CdSe_P&E, ZnS_P&E, and P&E). Cells exposed to incremental concentrations of these materials were investigated for cell viability and cellular perturbations, contributing to a final common pathway of cell death using high-content screening assays in model human intestinal epithelial cells (HIEC-6). The concentrations that resulted in a loss of 20% cell viability (EC20 values) for each tested component were used for estimating the combination index (CI) to evaluate synergistic or antagonistic effects between the components. Complete QD (core/shell-polymer) showed the highest toxic potential due to synergistic interactions between core and surface functional groups. The cationic polymer coating enhanced cellular uptake of the QD, ensuing lysosome acidification and release of heavy metal ions to the intracellular milieu, and caused oxidative stress and cytotoxicity. Overall, this study advances our understanding of the collective contribution of individual components of a functional QD toward its toxic potential and emphasizes the need to study multilayered nanomaterials in their entirety for hazard characterization.

Uptake and Translocation of a Silica Nanocarrier and an Encapsulated Organic Pesticide Following Foliar Application in Tomato Plants.

Pesticide nanoencapsulation and its foliar application are promising approaches for improving the efficiency of current pesticide application practices, whose losses can reach 99%. Here, we investigated the uptake and translocation of azoxystrobin, a systemic pesticide, encapsulated within porous hollow silica nanoparticles (PHSNs) of a mean diameter of 253 ± 73 nm, following foliar application on tomato plants. The PHSNs had 67% loading efficiency for azoxystrobin and enabled its controlled release over several days. Thus, the nanoencapsulated pesticide was taken up and distributed more slowly than the nonencapsulated pesticide. A total of 8.7 ± 1.3 µg of the azoxystrobin was quantified in different plant parts, 4 days after 20 µg of nanoencapsulated pesticide application on a single leaf of each plant. In parallel, the uptake and translocation of the PHSNs (as total Si and particulate SiO2) in the plant were characterized. The total Si translocated after 4 days was 15.5 ± 1.6 µg, and the uptake rate and translocation patterns for PHSNs were different from their pesticide load. Notably, PHSNs were translocated throughout the plant, although they were much larger than known size-exclusion limits (reportedly below 50 nm) in plant tissues, which points to knowledge gaps in the translocation mechanisms of nanoparticles in plants. The translocation patterns of azoxystrobin vary significantly following foliar uptake of the nanosilica-encapsulated and nonencapsulated pesticide formulations.

Chemotactic Bacteria Facilitate the Dispersion of Nonmotile Bacteria through Micrometer-Sized Pores in Engineered Porous Media.

Recent research has demonstrated that chemotactic bacteria can disperse inside microsized pores while traveling toward favorable conditions. Microbe-microbe cotransport might enable nonmotile bacteria to be carried with motile partners to enhance their dispersion and reduce their deposition in porous systems. The aim of this study was to demonstrate the enhancement in the dispersion of nonmotile bacteria (Mycobacterium gilvum VM552, a polycyclic aromatic hydrocarbon-degrader, and Sphingobium sp. D4, a hexachlorocyclohexane-degrader, through micrometer-sized pores near the exclusion-cell-size limit, in the presence of motile Pseudomonas putida G7 cells. For this purpose, we used bioreactors equipped with two chambers that were separated with membrane filters with 3, 5, and 12 µm pore sizes and capillary polydimethylsiloxane (PDMS) microarrays (20 µm × 35 µm × 2.2 mm). The cotransport of nonmotile bacteria occurred exclusively in the presence of a chemoattractant concentration gradient, and therefore, a directed flow of motile cells. This cotransport was more intense in the presence of larger pores (12 µm) and strong chemoeffectors (γ-aminobutyric acid). The mechanism that governed cotransport at the cell scale involved mechanical pushing and hydrodynamic interactions. Chemotaxis-mediated cotransport of bacterial degraders and its implications in pore accessibility opens new avenues for the enhancement of bacterial dispersion in porous media and the biodegradation of heterogeneously contaminated scenarios.

Density Functional Theory Calculations Decipher Complex Reaction Pathways of 6:2 Fluorotelomer Sulfonate to Perfluoroalkyl Carboxylates Initiated by Hydroxyl Radical.

6:2 Fluorotelomer sulfonate (6:2 FTSA) is a ubiquitous environmental contaminant belonging to the family of per- and polyfluoroalkyl substances. Previous studies showed that hydroxyl radical (•OH) efficiently transforms 6:2 FTSA into perfluoroalkyl carboxylates (PFCAs) of different chain lengths (C2-C7), yet the reaction mechanisms were not elucidated. This study used density functional theory (DFT) calculations to map the entire reaction path of 6:2 FTSA initiated by •OH and experimentally verified the theoretical results. Optimal reaction pathways were obtained by comparing the rate constants calculated from the transition-state theory. We found that 6:2 FTSA was first transformed to C7 PFCA and C6F13•; C6F13• was then further reacted to C2-C6 PFCAs. The parallel addition of •OH and O2 to CnF2n+1• was essential to producing C2-C6 PFCAs. The critical step is the generation of alkoxyl radicals, which withdraw electrons from the adjacent C-C groups to result in chain cleavage. The validity of the calculated optimal reaction pathways was further confirmed by the consistency with our experimental data in the aspects of O2 involvement, identified intermediates, and the final PFCA profile. This study provides valuable insight into the transformation of polyfluoroalkyl substances containing aliphatic carbons in •OH-based oxidation processes.

Uptake and Translocation of Mesoporous SiO2-Coated ZnO Nanoparticles to Solanum lycopersicum Following Foliar Application.

Nanoparticles composed of ZnO encapsulated in a mesoporous SiO2 shell (nZnO@SiO2) with a primary particle diameter of ∼70 nm were synthesized for delivery of Zn, a micronutrient, by foliar uptake. Compared to the rapid dissolution of bare nZnO (90% Zn dissolution after 4 h) in a model plant media (pH = 5), nZnO@SiO2 released Zn more slowly (40% Zn dissolution after 3 weeks), thus enabling sustained Zn delivery over a longer period. nZnO@SiO2, nZnO, and ZnCl2 were exposed to Solanum lycopersicum by dosing 40 µg of Zn micronutrient (in a 20 µL suspension) on a single leaf. No Zn uptake was observed for the nZnO treatment after 2 days. Comparable amounts of Zn uptake were observed 2 days after ZnCl2 (15.5 ± 2.4 µg Zn) and nZnO@SiO2 (11.4 ± 2.2 µg Zn) dosing. Single particle inductively coupled plasma mass spectrometry revealed that for foliar applied nZnO@SiO2, almost all of the Zn translocated to upper leaves and the stem were in nanoparticulate form. Our results suggest that the SiO2 shell enhances the uptake of ZnO nanoparticles in Solanum lycopersicum. Sustained and controlled micronutrient delivery in plants through foliar application will reduce fertilizer, energy, and water use.

Recent Advances in Sulfidated Zerovalent Iron for Contaminant Transformation.

2021 marks 10 years since controlled abiotic synthesis of sulfidated nanoscale zerovalent iron (S-nZVI) for use in site remediation and water treatment emerged as an area of active research. It was then expanded to sulfidated microscale ZVI (S-mZVI) and together with S-nZVI, they are collectively referred to as S-(n)ZVI. Heightened interest in S-(n)ZVI stemmed from its significantly higher reactivity to chlorinated solvents and heavy metals. The extremely promising research outcomes during the initial period (2011-2017) led to renewed interest in (n)ZVI-based technologies for water treatment, with an explosion in new research in the last four years (2018-2021) that is building an understanding of the novel and complex role of iron sulfides in enhancing reactivity of (n)ZVI. Numerous studies have focused on exploring different S-(n)ZVI synthesis approaches, and its colloidal, surface, and reactivity (electrochemistry, contaminant selectivity, and corrosion) properties. This review provides a critical overview of the recent milestones in S-(n)ZVI technology development: (i) clear insights into the role of iron sulfides in contaminant transformation and long-term aging, (ii) impact of sulfidation methods and particle characteristics on reactivity, (iii) broader range of treatable contaminants, (iv) synthesis for complete decontamination, (v) ecotoxicity, and (vi) field implementation. In addition, this review discusses major knowledge gaps and future avenues for research opportunities.

Self-Assembled Surfactant-Templated Synthesis of Porous Hollow Silica Nanoparticles: Mechanism of Formation and Feasibility of Post-Synthesis Nanoencapsulation.

SiO2 is bioinert and highly functionalizable, thus making it a very attractive material for nanotechnology applications such as drug delivery and nanoencapsulation of pesticides. Herein, we synthesized porous hollow SiO2 nanoparticles (PHSNs) by using cetyltrimethylammonium bromide (CTAB) and Pluronic P123 as the structure-directing agents. The porosity and hollowness of the SiO2 structure allow for the protective and high-density loading of molecules of interest inside the nanoshell. We demonstrate here that loading can be achieved post-synthesis through the pores of the PHSNs. The PHSNs are monodisperse with a mean diameter of 258 nm and a specific surface area of 287 m2 g-1. The mechanism of formation of the PHSNs was investigated using 1-D and 2-D solid-state nuclear magnetic resonance (SS-NMR) and Fourier-transform infrared spectroscopy (FTIR). The data suggest that CTAB and Pluronic P123 interact, forming a hydrophobic spherical hollow cage that serves as a template for the porous hollow structure. After synthesis, the surfactants were removed by calcination at 550 °C and the PHSNs were added to an Fe3+ solution followed by addition of the reductant NaBH4 to the suspension, which led to the formation of Fe(0) NPs both on the PHSNs and inside the hollow shell, as confirmed by transmission electron microscopy imaging. The imaging of the formation of Fe(0) NPs inside the hollow shell provides direct evidence of transport of solute molecules across the shell and their reactions within the PHSNs, making it a versatile nanocarrier and nanoreactor.

Transformation of 6:2 Fluorotelomer Sulfonate by Cobalt(II)-Activated Peroxymonosulfate.

Peroxymonosulfate (PMS)-based advanced oxidation processes generate highly reactive SO4•- and are promising for water treatment. In this study, we investigated the reaction mechanism of 6:2 fluorotelomer sulfonate (6:2 FTS) with Co2+-activated PMS. 6:2 FTS was simultaneously transformed to perfluoroalkyl carboxylic acids (C2-C7 PFCAs) of different chain lengths, with perfluorohexanoic acid (C6) as the predominant one. The mass balance of the intermediates and products versus the initially added 6:2 FTS was close to 100% over the reaction period. Using chemical scavenging methods, we identified that •OH, instead of SO4•-, was the oxidant initiating the reaction of 6:2 FTS. •OH was mainly produced from SO4•- reacting with H2O. Thus, the reactivity of 6:2 FTS was controlled by the factors affecting the production and scavenging of both SO4•- and •OH. Density functional theory calculations showed that •OH oxidizes 6:2 FTS by H-abstraction from ethyl carbons. This is the first study that demonstrates that •OH in Co2+-activated PMS can play a significant role in contaminant transformations. The results indicate that great caution should be taken when PMS or other agents that generate •OH are used for the treatment of water containing 6:2 FTS or its structural analogs.

New Insights into the Degradation Mechanism of Perfluorooctanoic Acid by Persulfate from Density Functional Theory and Experimental Data.

Thermally activated persulfate is a promising oxidant for in situ remediation of perfluorooctanoic acid (PFOA), yet a comprehensive understanding of the degradation mechanism is still lacking. In this study, we used density functional theory (DFT) calculations and experimental data to map entire reaction pathways for the degradation of PFOA by persulfate, with specific considerations on the influence of pH. The DFT results showed that the rate-limiting step was the first electron abstraction from PFOA, yet the generation of SO4•- from the decomposition of persulfate contributed a large part of the free energy of activation (ΔG‡) for the overall reaction. The subsequent steps did not contribute to the ΔG‡. For the electron abstraction from PFOA, we investigated reactions using protonated and deprotonated species of PFOA and SO4•- and showed that the reaction of anionic PFOA with HSO4• was most favorable with a ΔG‡ of 7.2 kJ/mol. This explains why low pH (<3.5) is a sine qua non condition for the degradation of PFOA by persulfate. The overall ΔG‡ derived theoretically based on the pathway involved HSO4• was consistent with the ΔG‡ determined experimentally. This study provides valuable insight into remediation strategies that include persulfate as an oxidizing agent for perfluoroalkyl carboxylic acids.

Impacts of Continuous Inflow of Low Concentrations of Silver Nanoparticles on Biological Performance and Microbial Communities of Aerobic Heterotrophic Wastewater Biofilm.

Attached-growth wastewater processes are currently used in water resource recovery facilities (WRRFs) for required upgrades due to an increase in influent loading or to reach more stringent discharge criteria. Yet, the distribution and long-term inhibitory effects of silver nanoparticles (AgNPs) in attached-growth biological wastewater processes and their impact on involved microbial communities are poorly understood at relevant, low concentrations. Retention, distribution, and long-term inhibitory effect of polyvinylpyrrolidone (PVP)-coated AgNPs were evaluated in bench-scale moving bed biofilm reactors (MBBRs), achieving soluble organic matter removal, over a 64 day exposure to nominal concentrations of 10 and 100 µg/L. Distributions of continuously added AgNPs were characterized in the influent, bioreactor, and effluent of MBBRs using single particle inductively coupled plasma mass spectroscopy (spICP-MS). Aerobic heterotrophic biofilms in MBBRs demonstrated limited retention capacity for AgNPs over long-term exposure, with release of AgNPs, and Ag-rich biofilm sloughed from the carriers. Continuous exposure to both influent AgNP concentrations significantly decreased soluble chemical oxygen demand (SCOD) removal efficiency (11% to 31%) and reduced biofilm viability (8% to 30%). Specific activities of both intracellular dehydrogenase (DHA) and extracellular α-glucosidase (α-Glu) and protease (PRO) enzymes were significantly inhibited (8% to 39%) with an observed NP dose-dependent intracellular reactive oxygen species (ROS) production and shift in biofilm microbial community composition by day 64. Our results indicated that long-term exposure to AgNPs in biofilm processes at environmentally relevant concentrations can impact the treatment process stability and the quality of the discharged effluent.

Optimal Design of Sulfidated Nanoscale Zerovalent Iron for Enhanced Trichloroethene Degradation.

Sulfidated nanoscale zerovalent iron (S-nZVI) has the potential to be a cost-effective remediation agent for a wide range of environmental pollutants, including chlorinated solvents. Various synthesis approaches have yielded S-nZVI consisting of a Fe0 (or Fe0/S0) core and FeS shell, which are significantly more reactive to trichloroethene (TCE) than nZVI. However, their reactivity is not as high as palladium-doped nZVI (Pd-nZVI). We synthesized S-nZVI by the co-precipitation of FeS and Fe0 by using Na2S during the borohydride reduction of FeSO4 (S-nZVIco). This resulted in FeS structures bridging the nZVI core and the surface, as confirmed by electron microscopy and X-ray analyses. The TCE degradation capacity of up to 0.46 mol TCE/mol Fe0 was obtained for S-nZVIco at a high S loading and was comparable to Pd-nZVI but 60% higher than the currently most reactive S-nZVI, in which FeS only coats the nZVI (S-nZVIpost). The high TCE degradation was due to complete utilization of Fe0 (2 e-/mol Fe0) toward the formation of acetylene. Although Pd-nZVI yielded 3 e-/mol Fe0, TCE degradation was comparable because it reduced acetylene further to ethene and ethane. Under Fe0-limited conditions, the S-nZVIco TCE degradation rate was 16 times higher than that of Pd-nZVI (0.5 wt % Pd) and 90 times higher than that of S-nZVIpost.

Sorption of Perfluoroalkyl Acids to Fresh and Aged Nanoscale Zerovalent Iron Particles.

The sorption of perfluoroalkyl acids (PFAAs), particularly perfluorooctanesulfonic acid (PFOS), to freshly synthesized nanoscale zerovalent iron (nZVI) and aged (oxidized) and sulfidated nZVI, was investigated under anaerobic conditions. The sorption of PFAAs to nZVI was 2-4 orders of magnitude higher than what has been reported for sediments, soils, and iron oxides. The hydrophobicity of the perfluorocarbon chain dominated the sorption, although FTIR spectra indicated specific interactions between sulfonate and carboxylate head groups and nZVI. The contributions from electrostatic interactions depended on the surface charge and pH. Humic acids influenced sorption only at concentrations above 50 mg/L. nZVI aged in deoxygenated water up to 95 days showed similar sorption isotherms for PFOS to fresh nZVI, because Fe(OH)2 was the predominant phase on the nZVI surface independent of aging time. Sulfidation of nZVI reduced sorption of PFOS by 1 log unit owing to the FeS deposited, but the sorption affinity was restored after aging because of formation of Fe(OH)2. Oxidation of nZVI by water and dissolved oxygen also resulted in similar sorption of PFOS as fresh nZVI at environmentally relevant concentrations. The results suggest that injection of nZVI could reduce PFAA concentrations in groundwater despite changes to its surface chemistry with aging.

Amendment of Agricultural Soil with Metal Nanoparticles: Effects on Soil Enzyme Activity and Microbial Community Composition.

Several types of engineered nanoparticles (ENPs) are being considered for direct application to soils to reduce the application and degradation of pesticides, provide micronutrients, control pathogens, and increase crop yields. This study examined the effects of different metal ENPs and their dissolved ions on the microbial community composition and enzyme activity of agricultural soil amended with biosolids. The activity of five extracellular nutrient-cycling enzymes was measured in biosolid-amended soils treated with different concentrations (1, 10, or 100 mg ENP/kg soil) of silver (nAg), zinc oxide (nZnO), copper oxide (nCuO), or titanium dioxide (nTiO2) nanoparticles and their ions over a 30-day period. At 30 days, nZnO and nCuO either had no significant effect on soil enzyme activity or enhanced enzyme activity. In contrast, Ag inhibited selected enzymes when dosed in particulate or dissolved form (at 100 mg/kg). nTiO2 either had no significant effect or slightly decreased enzyme activity. Illumina MiSeq sequencing of microbial communities indicated a shift in soil microbial community composition upon exposure to high doses of metal ions or nAg and negligible shift in the presence of nTiO2. Some taxa responded differently to nAg and Ag+. This work shows how metal ENPs can impact soil enzyme activity and microbial community composition upon introduction into soils amended with biosolids, depending on their type, concentration, and dissolution behavior, hence providing much needed information for the sustainable application of nanotechnology in agriculture.

Phase Transfer of Palladized Nanoscale Zerovalent Iron for Environmental Remediation of Trichloroethene.

Palladium-doped nanoscale zerovalent iron (Pd-NZVI) has been shown to degrade environmental contaminants such as trichloroethene (TCE) to benign end-products through aqueous phase reactions. In this study we show that rhamnolipid (biosurfactant)-coated Pd-NZVI (RL-Pd-NZVI) when reacted with TCE in a 1-butanol organic phase with limited amounts of water results in 50% more TCE mass degradation per unit mass of Pd-NZVI, with a 4-fold faster degradation rate (kobs of 0.413 day(-1) in butanol organic phase versus 0.099 day(-1) in aqueous phase). RL-Pd-NZVI is preferentially suspended in water in biphasic organic liquid-water systems because of its hydrophilic nature. We demonstrate herein for the first time that their rapid phase transfer to a butanol/TCE organic phase can be achieved by adding NaCl and creating water-in-oil emulsions in the organic phase. The significant enhancement in reactivity is caused by a higher electron release (3e(-) per mole of Fe(0)) from Pd-NZVI in the butanol organic phase compared to the same reaction with TCE in the aqueous phase (2e(-) per mole of Fe(0)). XPS characterization studies of Pd-NZVI show Fe(0) oxidation to Fe(III) oxides for Pd-NZVI reacted with TCE in the butanol organic phase compared to Fe(II) oxides in the aqueous phase, which accounted for differences in the TCE reactivity extents and rates observed in the two phases.

Dissolution Behavior of Silver Nanoparticles and Formation of Secondary Silver Nanoparticles in Municipal Wastewater by Single-Particle ICP-MS.

Ag nanoparticles (nAg) are used in various consumer products and a significant fraction is eventually discharged with municipal wastewater (WW). In this study we assessed the release of Ag from polyvinylpyrrolidone (PVP)- and citrate-coated 80 nm nAg in aerobic WW effluent and mixed liquor and the related changes in nAg size, using single particle ICP-MS (spICP-MS). The concentration of dissolved (nonparticulate) Ag in WW effluent was 0.89 ± 0.05 ppb at 168 h and was 71% lower than in deionized (DI) water, in batch reactors spiked with 5 × 106 PVP-nAg particles/mL (10 µg/L), an environmentally relevant concentration. Dissolved Ag in WW was partly reformed into ∼22 nm nAgxSy by inorganic sulfides and organosulfur dissolved organic carbon (DOC) after 120 h, whereas the parent nAg mean diameter decreased to 65.89 ± 0.9 nm. Reformation of nAgxSy from Ag+ also occurred in cysteine solutions but not in DI water, or humic and fulvic acid solutions. Dissolution experiments with nAg in WW mixed liquor showed qualitatively similar dissolution trends. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) and X-ray photoelectron spectroscopy (XPS) analyses indicated binding of thiol- and amine-containing DOC as well as inorganic sulfides with nAg. Those WW components, as well as limited dissolved oxygen, decreased dissolution in WW.

Effects of Rhamnolipid and Carboxymethylcellulose Coatings on Reactivity of Palladium-Doped Nanoscale Zerovalent Iron Particles.

Nanoscale zerovalent iron (NZVI) particles are often coated with polymeric surface modifiers for improved colloidal stability and transport during remediation of contaminated aquifers. Doping the NZVI surface with palladium (Pd-NZVI) increases its reactivity to pollutants such as trichloroethylene (TCE). In this study, we investigate the effects of coating Pd-NZVI with two surface modifiers of very different molecular size: rhamnolipid (RL, anionic biosurfactant, M.W. 600 g mol(-1)) and carboxymethylcellulose (CMC, anionic polyelectrolyte, M.W. 700 000 g mol(-1)) on TCE degradation. RL loadings of 13-133 mg TOC/g NZVI inhibited deposition of Pd in a concentration-dependent manner, thus limiting the number of available Pd sites and decreasing the TCE degradation reaction rate constant from 0.191 h(-1) to 0.027 h(-1). Furthermore, the presence of RL in solution had an additional inhibitory effect on the reactivity of Pd-NZVI by interacting with the exposed Pd deposits after they were formed. In contrast, CMC had no effect on reactivity at loadings up to 167 mg TOC/g NZVI. There was a lack of correlation between Pd-NZVI aggregate sizes and TCE reaction rates, and is explained by cryo-transmission electron microscopy images that show open, porous aggregate structures where TCE would be able to easily access Pd sites.