Effects of particle size on toxicity, bioaccumulation, and translocation of zinc oxide nanoparticles to bok choy (Brassica chinensis L.) in garden soil.

The indiscriminate use of zinc oxide nanoparticles (ZnO NPs) in daily life can lead to their release into soil environment. These ZnO NPs can be taken up by crops and translocated to their edible part, potentially causing risks to the ecosystem and human health. In this study, we conducted pot experiments to determine phytotoxicity, bioaccumulation and translocation depending on the size (10 - 30 nm, 80 - 200 nm and 300 nm diameter) and concentration (0, 100, 500 and 1000 mg Zn/kg) of ZnO NPs and Zn ion (Zn2+) in bok choy, a leafy green vegetable crop. After 14 days of exposure, our results showed that large-sized ZnO NPs (i.e., 300 nm) at the highest concentration exhibited greater phytotoxicity, including obstruction of leaf and root weight (42.5 % and 33.8 %, respectively) and reduction of chlorophyll a and b content (50.2 % and 85.2 %, respectively), as well as changes in the activities of oxidative stress responses compared to those of small-sized ZnO NPs, although their translocation ability was relatively lower than that of smaller ones. The translocation factor (TF) values decreased as the size of ZnO NPs increased, with TF values of 0.68 for 10 - 30 nm, 0.55 for 80 - 200 nm, and 0.27 for 300 nm ZnO NPs, all at the highest exposure concentration. Both the results of micro X-ray fluorescence (µ-XRF) spectrometer and bio-transmission electron microscopy (bio-TEM) showed that the Zn elements were mainly localized at the edges of leaves exposed to small-sized ZnO NPs. However, the Zn elements upon exposure to large-sized ZnO NP were primarily observed in the primary veins of leaves in the µ-XRF data, indicating a limitation in their ability to translocate from roots to leaves. This study not only advances our comprehension of the environmental impact of nanotechnology but also holds considerable implications for the future of sustainable agriculture and food safety.

Transport of citrate-coated silver nanoparticles in saturated porous media.

In this study, the influences of physical and chemical factors [e.g., ionic strength (IS), pH, and flow rate] on the fate and transport of citrate-coated silver nanoparticles (AgNPs) were investigated through experiments using saturated columns. For the transport behavior of AgNPs under various conditions, retardation was confirmed with an increase in ionic strength (IS) while early elution developed with an increase in pH and flow rate. These transport experiment outcomes were simulated through Hydrus-1D, and the observed breakthrough curves were confirmed to have a significant correlation with the fitted results. Interestingly, the AgNPs and quartz sand used in this study showed a negative charge in the investigated experimental conditions. Although the reaction between AgNPs and quartz sand was expected to be unfavorable, AgNPs were observed to have been deposited onto the sand surface during the column test. To clarify the mechanism of the deposition of AgNPs even in unfavorable conditions, the interaction energy profiles were calculated based on the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. From the results, unfavorable interactions were expected in the NP-NP and NP-sand interactions in every condition. It was concluded that the deposition of AgNPs onto the sand surface under the unfavorable conditions in this study was mainly because of the physical roughness of the sand surface. Moreover, this hypothesis was supported by the zone of influence calculation in accordance with IS, the interpretation results of the fractional sand surface coverage in accordance with concentration changes of AgNPs, and series column tests.

Impact of surface modification on the toxicity of zerovalent iron nanoparticles in aquatic and terrestrial organisms.

Nanoscale zerovalent iron (nZVI)-based materials are increasingly being applied in environmental remediation, thereby lead to their exposure to aquatic and terrestrial biota. However, little is known regarding the toxic effects of surface-modified nZVI on multiple species in the ecosystem. In this study, we systematically compared the toxicities of different forms of nZVIs, such as bare nZVI, carboxymethyl cellulose (CMC)-stabilized nZVI, tetrapolyphosphate (TPP)-coated nZVI and bismuth (Bi)-doped nZVI, on a range of aquatic and terrestrial organisms, including bacteria (Escherichia coli and Bacillus subtilis), plant (Arabidopsis thaliana), water flea (Daphnia magna) and earthworm (Eisenia fetida). The Bi- and CMC-nZVI induced adverse biological responses across all the test systems, except E. fetida, varying from cell death in E. coli and B. subtilis to inhibition of the physiological states in D. magna and A. thaliana. The particle characterization under exposure conditions indicated that the surface modification of nZVI played a significant role in their toxicities by changing their physicochemical properties. The underlying mechanisms by which nZVI induces toxicity might be a combination of oxidative stress and another mechanism such as cell membrane disruption, chlorosis and hypoxia. Overall, our findings could provide important implications for the development of environment-friendly nanomaterials and direct further ecotoxicological researches regarding interspecies exploration.

Activation of Persulfates by Graphitized Nanodiamonds for Removal of Organic Compounds.

This study introduces graphited nanodiamond (G-ND) as an environmentally friendly, easy-to-regenerate, and cost-effective alternative catalyst to activate persulfate (i.e., peroxymonosulfate (PMS) and peroxydisulfate (PDS)) and oxidize organic compounds in water. The G-ND was found to be superior for persulfate activation to other benchmark carbon materials such as graphite, graphene, fullerene, and carbon nanotubes. The G-ND/persulfate showed selective reactivity toward phenolic compounds and some pharmaceuticals, and the degradation kinetics were not inhibited by the presence of oxidant scavengers and natural organic matter. These results indicate that radical intermediates such as sulfate radical anion and hydroxyl radical are not majorly responsible for this persulfate-driven oxidation of organic compounds. The findings from linear sweep voltammetry, thermogravimetric analysis, Fourier transform infrared spectroscopy, and electron paramagnetic resonance spectroscopy analyses suggest that the both persulfate and phenol effectively bind to G-ND surface and are likely to form charge transfer complex, in which G-ND plays a critical role in mediating facile electron transfer from phenol to persulfate.

Elucidating adsorption mechanisms of benzalkonium chlorides (BACs) on polypropylene and polyethylene terephthalate microplastics (MPs): Effects of BACs alkyl chain length and MPs characteristics.

Since the onset of the COVID-19 pandemic, there has been an increase in the use of disposable plastics and disinfectants. This study systematically investigated the adsorption behavior and mechanisms of benzalkonium chlorides (BACs), commonly used disinfectants, on polypropylene (PP) and polyethylene terephthalate (PET) microplastics (MPs), considering various factors, such as characteristics of MPs, alkyl chain length of BACs, and environmental conditions. Our results demonstrated a higher adsorption capacity for PP-MPs with relatively hydrophobic properties compared to PET-MPs, where longer alkyl chains in BACs (i.e., higher octanol-water partition coefficients, Kow) significantly enhanced adsorption through hydrophobic interactions. The inverse relationship between particle size of MPs and adsorption was evident. While changes in pH minimally affected adsorption on PP-MPs, adsorption on PET-MPs increased with rising pH, highlighting the influence of pH on electrostatic interactions. Moreover, MP aging with UV/H2O2 amplified BAC adsorption on PP-MPs due to surface oxidation and fragmentation, whereas the properties of PET-MPs remained unaltered, resulting in unchanged adsorption capacities. Spectroscopy studies and density functional theory (DFT) calculations confirmed hydrophobic and electrostatic interactions as the primary adsorption mechanisms. These findings improve our understanding of MPs and BACs behavior in the environment, providing insights for environmental risk assessments related to combined pollution.

Comparative bioaccumulation, translocation, and phytotoxicity of metal oxide nanoparticles and metal ions in soil-crop system.

Exposure of the soil environment to metal nanoparticles (MNPs) has been extensive because of their indiscriminate use and the disposal of MNP products in various applications. In MNP-amended soil, various crops can absorb the nanoparticles, and accumulation of the MNPs in farm products has potential risks for bioconcentration in humans and livestock. Here, we evaluated the comparative bioaccumulation, translocation, and phytotoxicity of MNPs (ZnO and CuO NPs) and metal ions (Zn(NO3)2 and Cu(NO3)2) in four different crops, namely lettuce, radish, bok choy, and tomato. We carried out pot experiments to evaluate the phytotoxicity in the crops from the presence of MNPs and metal ions. Phytotoxicity from different treatments differed depending on the plant species, and metal types. In addition, exposure to Zn and Cu showed positive dose-dependent effects on their bioaccumulation in each crop. However, there were no significant differences in metal bioaccumulation depending on whether the crops were exposed to MNPs or metal ions. By calculating the bioconcentration factor (BCF) and translocation factor (TF), we were able to estimate the biological uptake and translocation abilities of MNPs and metal ions for each crop. It was found that lettuce and radish had greater BCFs than bok choy and tomato, while bok choy and tomato had higher TFs. Also, the uptake and translocation of Zn were better than those of Cu. However, the values for BCF and TF for each crop showed no significant differences between MNP and metal ion exposure. A micro X-ray fluorescence (µ-XRF) spectrometer analysis demonstrated that only Zn elements appeared in the primary veins and edges of all leaves and the storage root of radish. Our study aims to estimate bioaccumulation, translocation, and the implied potential risks from MNPs accumulated in different plant species.

Adsorption of benzalkonium chlorides onto polyethylene microplastics: Mechanism and toxicity evaluation.

Usage of disposable plastic products and disinfectants has been skyrocketing due to the COVID-19 pandemic. The random disposal of plastic products may result in greater microplastic pollution. Benzalkonium chloride is known as one of the most common ingredients of disinfectants. In this study, the adsorption behavior of benzalkonium chlorides (BAC12, BAC14, BAC16) on polyethylene microplastics (PE-MPs) and the combined toxic effects were investigated using batch adsorption experiment and Daphnia magna. The results showed that PE-MPs had strong adsorption capacity for BACs and the adsorption capacity increased (11.03-22.77 mg g-1) with their octanol-water distribution coefficients. The effect of pH was negligible while dissolved organic matter inhibited the adsorption. A slightly inverse relationship between particle size of PE-MPs and adsorption was observed. Additionally, the MP aging with UV/H2O2 increased the adsorption of BAC12 but decreased that of relatively hydrophobic BAC14 and BAC16. The survival rate of Daphnia magna increased up to 100% in the presence of PE-MPs depending upon their adsorption capacities, suggesting that PE-MPs do not act as a carrier but rather as a scavenger for BACs. This study provides important information necessary for environmental risk assessment with regard to the combined pollution of MPs and toxic chemicals.

Metabolome and transcriptome analyses of plants grown in naturally attenuated soil after hydrogen fluoride exposure.

Accidental chemical leaks and illegal chemical discharges are a global environmental issue. In 2012, a hydrogen fluoride leak in Gumi, South Korea, killed several people and contaminated the environment. This leak also led to a significant decline in crop yield, even after the soil concentration of hydrogen fluoride decreased to below the standard level following natural attenuation. To determine the cause of this decreased plant productivity, we designed direct and indirect exposure tests by evaluating the metabolome, transcriptome, and phenome of the plants. In an indirect exposure test, soil metabolomics revealed downregulation of metabolites in vitamin B6, lipopolysaccharide, osmolyte, and exopolysaccharide metabolism. Next-generation sequencing of the plants showed that ABR1 and DREB1A were overexpressed in response to stress. Plant metabolomics demonstrated upregulation of folate biosynthesis and nicotinate and nicotinamide metabolism associated with detoxification of reactive oxygen species. These results demonstrate impaired metabolism of soil microbes and plants even after natural attenuation of hydrogen fluoride in soil. The novel chemical exposure testing used in this study can be applied to identify hidden damage to organisms after natural attenuation of chemicals in soil, as well as biomarkers for explaining the decline in yield of plants grown in soil near pollutant-emitting industrial facilities.

UV irradiation and humic acid mediate aggregation of aqueous fullerene (nC60) nanoparticles.

The transport and fate of engineered nanomaterials is affected by multiple environmental factors, including sunlight and natural organic matter. In this study, the initial aggregation kinetics of aqueous fullerene (nC(60)) nanoparticles before and after UVA irradiation was investigated in solutions varying in ionic strength, ionic composition, and humic acid concentration. In NaCl solutions, surface oxidation induced by UV irradiation remarkably increased nC(60) stability due to the increased negative surface charge and reduced particle hydrophobicity; although humic acid greatly enhanced the stability of pristine nC(60) via the steric hindrance effect, it had little influence on the stability of UV-irradiated nC(60) in NaCl due to reduced adsorption on oxidized nC(60) surface. In contrast, UV irradiation reduced nC(60) stability in CaCl(2) due to specific interactions of Ca(2+) with the negatively charged functional groups on UV-irradiated nC(60) surface and the consequent charge neutralization. By neutralizing surface charges of both UV-irradiated nC(60) and humic acid as well as forming intermolecular bridges, Ca(2+) facilitated humic acid adsorption on UV-irradiated nC(60), resulting in enhanced stability in the presence of humic acid. These results demonstrate the critical role of nC(60) surface chemistry in its environmental transport and fate.

Effect of sediment particle size on polycyclic aromatic hydrocarbon bioaccessibility and degradation by ultrasound.

The effect of particle size on sonochemical desorption, degradation and change in bioaccessibility of polycyclic aromatic hydrocarbons (PAHs) on contaminated sediments was investigated. Batch experiments were performed with the whole sediment (WS < 850 µm), a large size range fraction (150 µm < LSR < 850 µm), and a small size range fraction (SSR < 150 µm) of the whole sediment. PAH degradation followed pseudo first-order kinetics; PAHs on LSR sediments underwent more rapid degradation than on SSR and WS sediments (νPAH,LSR > νPAH,WS > νPAH,SSR). In addition, a higher sediment slurry concentration resulted in slower degradation of PAHs. Results are consistent with the more rapid particle size reduction of the LSR. More rapid particle size reduction and faster PAH degradation for the LSR fraction combined with analysis of particle velocities in both size ranges indicates that microjets as opposed to particle-particle collisions due to shockwaves are effective in rapid particle size reduction and PAH degradation. Moreover, the bioaccessible fraction (FPAH,fast,t) of sorbed PAHs in both particle size fractions was found to increase with sonication time but was more rapid with the LSR. Likewise, the more tightly bound PAHs, those in the slow desorbing fraction (FPAH,slow,t) of PAHs, decreased faster with sonication of LSR particles compared to SSR particles, consistent with the trend of particle size reduction. Results of this study suggest that ultrasonic treatment is more effective for larger size particle sediments, although sonication is also viable for small sediment sizes.

A multidisciplinary assessment of the impact of spilled acids on geoecosystems: an overview.

We developed and applied a multidisciplinary approach to the impact of an accidentally spilled acid on the underlying geomedia and subsurface environment, based on the concept of geoecosystem. We used mineralogical, geochemical, microbiological, and ecotoxicological techniques to identify and assess the multiple aspects involved. First, we constructed a conceptual model for the acid interactions with the underlying subsurface environment by introducing the concept of a geoecosystem-a multicomponent system composed of inorganic, organic, and biological components to describe the subsurface environment. Second, we designed and manufactured a two dimensional cell to visualize acid transport through geomedia. Third, we hypothesized that the acids are neutralized through dissolution of minerals and protonation of functional groups on the surfaces of minerals and organic matter. We tested this hypothesis by conducting batch-type geomedia-acid reaction and surface titration experiments. Fourth, we observed changes in soil microbial communities before and after the acid exposure and neutralization treatment. Fifth, we performed flow-through experiments using columns packed with soil samples pre-contaminated with arsenic to investigate potential longer term, secondary effects of remnant acids on geoecosystems. Finally, we conducted ecotoxicological investigations using various geomedia and observed that suitability of the geoecosystem as a habitat deteriorated to different degrees depending on the respective systems' acid neutralizing power. We conclude that a holistic understanding of the interactions among the multiple components of geoecosystems and subsequent estimation of the influenced area requires a multidisciplinary approach such as those used in this study. Based on the findings of this study, we propose geoecosystems' vulnerability defined as the reciprocal of their acid-neutralizing capacity against the moving acid fronts and present this concept as central to a quantitative assessment of the impact of acid spills on geoecosystems. We also inventoried the essential components, factors, and parameters necessary in developing geoecosystems' acid vulnerability assessment system.

Effects of nanoTiO2 on tomato plants under different irradiances.

In this study, we investigated the physiological and photochemical influences of nanoTiO2 exposure on tomato plants (Lycopersicum esculentum Mill.). Tomato plants were exposed to 100 mg L-1 of nanoTiO2 for 90 days in a hydroponic system. Light irradiances of 135 and 550 µmolphoton m-2 s-1 were applied as environmental stressors that could affect uptake of nanoTiO2. To quantify nanoTiO2 accumulation in plant bodies and roots, we used transmission electron microscopy, energy-dispersive X-ray spectroscopy, inductively coupled plasma mass spectrometry, and X-ray powder diffraction. Phenotypic and physiological influences such as color change, growth rate, fruit productivity, pigment concentration, and enzyme activity (SOD, CAT, APX) were monitored. We observed numerous effects caused by high irradiance and nanoTiO2 exposure, such as rapid chlorophyll decrease, increased anthocyanin and carotenoid concentrations, high enzymatic activity, and an approximately eight-fold increase in fruit production. Moreover, light absorption in the nanoTiO2-treated tomato plants, as measured by a ultraviolet-visible light spectrometer, increased by a factor of approximately 19, likely due to natural pigments that worked as sensitizers, and this resulted in an ∼120% increase in photochemical activities on A, ФPSII, ФCO2, gsw, and E.

Development of a model (SWNano) to assess the fate and transport of TiO2 engineered nanoparticles in sewer networks.

A new model, SWNano (Sewer-Water Nano), has been developed in the present study that quantitatively simulates the spatio-temporal changes in the concentrations of TiO2 ENPs of dispersed and aggregated forms in the sewage water and sediment of a sewer network. As a brief example of SWNano applications, a small section of the entire sewer network of Seoul, Korea, was chosen to study where the sewage water was experimentally characterized. The predictions of SWNano present important findings that i) heteroaggregation is the most significant process following the advective transport among the fate and transport processes in the sewer pipes, ii) the heteroaggregation of TiO2 ENPs with SPMs in the sewage water can substantially (a few % to more than 50%) reduce the freely dispersed TiO2 ENPs depending on the magnitude of attachment efficiency, and iii) accurate determination of attachment efficiency is of critical importance in predicting the quantity of individual forms of ENPs exiting the sewer system. The predictions strongly suggest that the fate and transport of TiO2 ENPs in the sewer networks be taken into account to improve the assessment of exposure to TiO2 ENPs in the aquatic ecosystems, which warrants further development and use of models like SWNano.

The dependence of hematite site-occupancy standard state triple-layer model parameters on inner-layer capacitance.

Potentiometric acid-base titration data for three hematite samples that differed on the basis of specific surface area (17.4, 33, 83 m2/g for hematite A, B, and C, respectively) was analyzed using the triple-layer model (TLM). The sensitivity of the TLM fits of the data to the choice of site density (N(s)) was evaluated from 1.5 to 22 sites/nm2. In general, little dependence in the quality of fit was determined, irrespective of the value of Ns. Values of the electrolyte adsorption equilibrium constants (log K cation 0 and log K anion 0) steadily increased with decreasing Ns. These constants are consistent with the commonly used 1.0 M standard state and when converted into comparable constants consistent with the site-occupancy standard state (log K cation theta and log K anion theta) a single value for each respective constant was determined. Values of the inner-layer capacitance (C1) were varied during these optimizations and increased with decreasing Ns, particularly below 5 sites/nm2. The optimized C1 values exhibited an apparent inverse relationship with specific surface area (i.e., C1 for hematite A>C1 for hematite B>C1 for hematite C). The magnitude of change in C1 with respect to Ns depended upon the magnitude of C1 for each hematite as the higher the C1 value, the greater was the change with respect to Ns. These results suggest when the site-occupancy standard state parameters are used to predict constants at different site density values without re-regression of titration data that variations in C1 should be accounted for, particularly for low specific surface area samples that have a high C1.

Effects of functionalized multi-walled carbon nanotubes on toxicity and bioaccumulation of lead in Daphnia magna.

Increased production of carbon nanotubes (CNTs) and their widespread application in industrial and consumer products have led to a rise in the release of CNTs into the aquatic environment. CNTs have a very strong adsorption affinity for various environmental contaminants; therefore, they may also influence the toxic effects of other pollutants, such as toxic metals. In this study, the effect of two different functionalized carbon nanotubes, carboxylate and polyethyleneimine modified multi-walled carbon nanotubes (C-MWCNTs and N-MWCNT, respectively) on lead toxicity and bioaccumulation was investigated with a freshwater zooplankton Daphnia magna. The acute toxicity results indicate that the different surface properties of the two types of MWCNTs have different effects on lead toxicity to D. magna. The negatively charged C-MWCNT showed a notable decrease in lead toxicity (LC50 value increased from 0.15 mg L-1 to 1.08 mg L-1 in the presence of 10 mg L-1 C-MWCNT), whereas the positively charged N-MWCNT had only a slight effect on lead toxicity (LC50 value increased from 0.15 mg L-1 to 0.16 mg L-1 in the presence of 10 mg L-1 N-MWCNT). The decrease of lead toxicity was related with the reduced bioavailability of free metal form (Pb2+) caused by greater adsorption of lead onto the MWCNTs. The present study suggests that there is a need to consider carefully the complex interaction of CNTs with toxic metals in future ecotoxicological studies.

Surface complexes of phthalic acid at the hematite/water interface.

The adsorption of o-phthalic acid at the hematite/water interface was investigated experimentally using batch adsorption experiments and attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy over a wide range of solution pH, surface loading, and ionic strength conditions. Molecular orbital calculations for several possible surface complexes were also performed to assign atomistic structures to the features observed in the ATR-FTIR spectra. The results of the batch adsorption experiments exhibit typical anionic characteristics with high adsorption at low pH and low adsorption at high pH. The adsorption of phthalic acid also exhibits a strong dependence on ionic strength, which suggests the presence of outer-sphere complexes. ATR-FTIR spectra provide evidence of three fully deprotonated phthalate surface complexes (an outer-sphere complex and two inner-sphere complexes) under variable chemical conditions. A fully deprotonated outer-sphere complex appears to dominate adsorption in the circumneutral pH region, while two fully deprotonated inner-sphere complexes that shift in relative importance with surface coverage increase in importance at low pH. Comparison of experimental and theoretical calculations suggests the two inner-sphere complexes are best described as a mononuclear bidentate (chelating) complex and a binuclear bidentate (bridging) complex. The mononuclear bidentate inner-sphere complex was favored at relatively low surface coverage. With increasing surface coverage, the relative contribution of the binuclear bidentate inner-sphere complex increased in importance.

Citrate coated silver nanoparticles change heavy metal toxicities and bioaccumulation of Daphnia magna.

Citrate-coated AgNPs (c-AgNPs) have negatively charged surfaces and their surface interactions with heavy metals can affect metal toxicity in aquatic environments. This study used Daphnia magna to compare the acute toxicities and bioaccumulation of As(V), Cd, and Cu when they interact with c-AgNPs. The 24-h acute toxicities of As(V) and Cu were not affected by the addition of c-AgNPs, while bioaccumulation significantly decreased in the presence of c-AgNPs. In contrast, both the 24-h acute toxicity and bioaccumulation of Cd increased in the presence of c-AgNPs. These toxicity and bioaccumulation trends can be attributed to the interactions between the AgNP surface and the heavy metals. As(V) and c-AgNPs compete by negative charge, decreasing As(V) toxicity. Copper adheres readily to c-AgNP citrate, decreasing Cu bioavailability, and thus reducing Cu toxicity and bioaccumulation. Citrate complexes with divalent cations such as Ca and Mg reduce the competition between divalent cations and Cd on biotic ligand, increasing toxicity and bioaccumulation of Cd. This study shows that surface properties determine the effect of c-AgNPs on heavy metal toxicities and bioaccumulations; hence, further studies on the effect of nanoparticle by it surface properties are warranted.

A novel method of utilizing permeable reactive kiddle (PRK) for the remediation of acid mine drainage.

Numerous technologies have been developed and applied to remediate AMD, but each has specific drawbacks. To overcome the limitations of existing methods and improve their effectiveness, we propose a novel method utilizing permeable reactive kiddle (PRK). This manuscript explores the performance of the PRK method. In line with the concept of green technology, the PRK method recycles industrial waste, such as steel slag and waste cast iron. Our results demonstrate that the PRK method can be applied to remediate AMD under optimal operational conditions. Especially, this method allows for simple installation and cheap expenditure, compared with established technologies.

Characterization of Silver Nanoparticles under Environmentally Relevant Conditions Using Asymmetrical Flow Field-Flow Fractionation (AF4).

The development of methods to monitor manufactured nanomaterials in the environment is one of the crucial areas for the assessment of their risk. More specifically, particle size analysis is a key element, because many properties of nanomaterial are size dependent. The sizing of nanomaterials in real environments is challenging due to their heterogeneity and reactivity with other environmental components. In this study, the fractionation and characterization of a mixture of polyvinylpyrrolidone-coated silver nanoparticles (PVP-AgNPs) of three different sizes were investigated using asymmetrical flow field-flow fractionation (AF4) coupled with UV-Vis spectrophotometry. In particular, the effects of electrolyte composition and natural organic matter (NOM) on the particle size and stability were evaluated. The fractogram peaks (i.e., stability) of three different AgNPs decreased in the presence of both 10 mM NaCl and 10 mM CaCl2, while increased with increasing concentration of humic acid (HA). In addition, the hydrodynamic diameters of AgNPs in both electrolytes slightly increased with an increase of HA concentration, suggesting the adsorption (coating) of HA onto the particle surface. It is also interesting to note that an increase in the particle size depended on the types of electrolyte, which could be explained by the conformational characteristics of the adsorbed HA layers. Consistent these results, AgNPs suspended in lake water containing relatively high concentration of organic carbon (TOC) showed higher particle stability and larger particle size (i.e., by approximately 4 nm) than those in river water. In conclusion, the application of AF4 coupled with highly sensitive detectors could be a powerful method to characterize nanoparticles in natural waters.