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The global pollution of micro- and nano-plastics (MNPs) calls for monitoring methods. As diverse mixtures of various sizes, morphologies, and chemical compositions in the environment, MNPs are currently quantified based on mass or number concentrations. Here, we show total organic carbon (TOC) as an index for quantifying the pollution of total MNPs in environmental waters. Two parallel water samples are respectively filtered with a carbon-free glass fiber membrane. Then, one membrane with the collected particulate substances is treated by potassium peroxodisulfate oxidation and Fenton digestion in sequence for quantifying the sum of MNPs and particulate black carbon (PBC) as TOC

A new borophosphate, NH4(B6PO10(OH)4)·H2O, has been obtained, which exhibits the largest birefringence of all reported borophosphates to date.

Nanoplastics (NPs) have been successively detected in different environmental matrixes and have aroused great concern worldwide. However, the fate of NPs in real environments such as seawater remains unclear, impeding their environmental risk assessment. Herein, multiple techniques were employed to monitor the particle number concentration, size, and morphology evolution of polystyrene NPs in seawater under simulated sunlight over a time course of 29 days. Aggregation was found to be a continuous process that occurred constantly and was markedly promoted by light irradiation. Moreover, the occurrence of NP swelling, fragmentation, and polymer leaching was evidenced by both transmission electron microscopy and scanning electron microscopy techniques. The statistical results of different transformation types suggested that swelling induces fragmentation and polymer leakage and that light irradiation plays a positive but not decisive role in this transformation. The observation of fragmentation and polymer leakage of poly(methyl methacrylate) and poly(vinyl chloride) NPs suggests that these transformation processes are general for NPs of different polymer types. Facilitated by the increase of surface functional groups, the ions in seawater could penetrate into NPs and then stretch the polymer structure, leading to the swelling phenomenon and other transformations.

The distribution and chemical speciation of arsenic (As) in different sized atmospheric particulate matters (PMs), including total suspended particles (TSP), PM10, and PM2.5, collected from Baoding, China were analyzed. The average total mass concentrations of As in TSP, PM10, and PM2.5 were 31.5, 35.3, and 54.1 µg/g, respectively, with an order of PM2.5 >PM 10 > TSP, revealing that As is prone to accumulate on fine particles. Due to the divergent toxicities of different As species, speciation analysis of As in PMs is further conducted. Most of previous studies mainly focused on inorganic arsenite (iAsIII), inorganic arsenate (iAsV), monomethylarsonate (MMA), and dimethylarsinate (DMA) in PMs, while the identification and sensitive quantification of trimethylarsine oxide (TMAO) were rarely reported. In this study, a high-performance liquid chromatography coupled to inductively coupled plasma mass spectrometry system was optimized for As speciation including TMAO in PMs. An anion exchange column was used to separate MMA, DMA and iAsV, while a cation exchange column to separate TMAO and iAsIII. Results showed that iAsV was the dominate component in all the samples, corresponding to a portion of 79.2% ± 9.3% of the total extractable species, while iAsIII, TMAO and DMA made up the remaining 21%. Our study demonstrated that iAsIII accounted for about 14.4% ± 11.4% of the total extracted species, with an average concentration of 1.7 ± 1.6 ng/m3. It is worth noting that TMAO was widely present in the samples (84 out of 97 samples), which supported the assumption that TMAO was ubiquitous in atmospheric particles.

Application of selenium nanoparticle (SeNP)-based fertilizers results in the release of SeNPs to aquatic systems, where SeNPs may transform into inorganic selenite (Se(IV)) and selenate (Se(VI)) with higher toxicity. However, methods for the speciation analysis of different Se species are lacking, hindering the accurate assessment of the risks of SeNPs. Herein, for the first time, a Triton X-45 (TX-45)-based dual-cloud point extraction (CPE) method was established for the selective determination of SeNPs, Se(IV), and Se(VI) in water. TX-45 can adsorb on the surface of SeNPs and facilitate the extraction of SeNPs into the lower TX-45-rich phase in the first CPE, while Se(VI) and Se(IV) retain in the upper aqueous phase. In the second CPE, Se(IV) can selectively associate with diethyldithiocarbamate and be concentrated in the TX-45-rich phase, whereas Se(VI) remains in the upper phase. Different Se species can be isolated and then quantified by ICP-MS. The presence of coexisting ions and dissolved organic matter (0-30 mg C/L) did not interfere with extraction and separation. The feasibility of the presented method was confirmed by the analysis of natural water samples, with a detection limit of 0.03 μg/L and recoveries in the ranges of 61.1-104, 65.5-113, and 80.3-131% for SeNPs, Se(IV), and Se(VI), respectively. This study aims to provide an effective method to track the fate and transformation of SeNPs in aquatic systems and further contribute to estimating the potential risks of SeNPs to environmental organisms and human bodies.

Determination of particulate black carbon (PBC) in the environment is of great importance but faces a new challenge due to the increasing occurrence of coexisting microplastics (MPs), which are an emerging contaminant with properties very similar to those of PBC and cannot be discriminated in the chemical digestion procedure of the reported PBC analysis method. Herein, a comprehensive method has been developed for accurately determining PBC by digestive elimination of the coexisting MPs and other non-black carbon organic matter. Water samples were filtered with a glass fiber membrane (0.3 μm pore size), and the collected substances with the membrane were subjected to sulfonation with chlorosulfonic acid and Fenton digestion in sequence and then to the total organic carbon analyzer for quantification of PBC. Under the optimized conditions, MPs of various sizes and polymer types were efficiently eliminated (>91.0%), whereas various PBC samples were undigested with recoveries over 91.7% except for the relatively low recovery of 65.6% for the PBC prepared at a low pyrolysis temperature of 400 °C. The feasibility of the proposed method was verified by analysis of real water samples with a spike recovery of 88.6-100.2%. We anticipate that this work will pave an avenue for reliable determination of PBC in the presence of MPs.

Although nanoplastics (NPs) are recognized as emerging anthropogenic particulate pollutants, the occurrence of NPs in the environment is rarely reported, partly due to the lack of sensitive methods for the concentration and detection of NPs. Herein, we present an efficient method for enriching NPs of different compositions and various sizes. Alkylated ferroferric oxide (Fe

The globally raising concern for nanoplastics (NPs) pollution calls for analytical methods for investigating their occurrence, fates, and effects. Counting NPs with sizes down to 50 nm in real environmental waters remains a great challenge. Herein, we developed a full method from sample pretreatment to quantitative detection for NPs in environmental waters. Various NPs of common plastic types and sizes (50-1200 nm) were successfully labeled by in situ growth of gold nanoparticles and counted by single particle inductively coupled plasma mass spectrometry. Sucrose density gradient centrifugation enables the isolation of gold-labeled NPs from homogeneously nucleated Au nanoparticles, enhancing the particle number detection limit to 4.6 × 108 NPs/L for 269 nm spherical polystyrene NPs. For real environmental water samples, the pretreatment of acid digestion with a mixture of 5 mM HNO3 and 40 mM HF eliminates the coexisting inorganic nanoparticles, while the following dual cloud-point extraction efficiently isolates NPs from various matrices and thus improves the Au-labeling efficiency. The high spiked recoveries (72.9%-92.8%) of NPs in different waters demonstrated the applicability of this method in different scenarios.

Respective detection of microplastics (MPs) and nanoplastics (NPs) is of great importance for their different environmental behaviors and toxicities. Using spherical polystyrene (PS) and poly(methyl methacrylate) (PMMA) plastics as models, the efficiency for sequential isolation of MPs and NPs by membrane filtration and cloud-point extraction was evaluated. After filtering through a glass membrane (1 μm pore size), over 90.7% of MPs were trapped on the membrane, whereas above 93.0% of NPs remained in the filtrate. The collected MPs together with the glass membrane were frozen in liquid nitrogen, ground, and suspended in water (1 mL) and subjected to pyrolysis-gas chromatography-mass spectrometry (Py-GC/MS) determination. The NPs in the filtrate were concentrated by cloud-point extraction, heated at 190 °C to degrade the extractant, and then determined by Py-GC/MS. For MPs and NPs spiked in pure water, the method detection limits are in the range of 0.05-1.9 μg/L. The proposed method is applied to analyze four real water samples, with the detection of 1.6-7.6 μg/L PS MPs and 0.6 μg/L PMMA MPs in three samples, and spiked recoveries of 75.0-102% for MPs and 67.8-87.2% for NPs. Our method offers a novel sample pretreatment approach for the respective determination of MPs and NPs.

Hazardous waste of chemical oxygen demand (COD) test (HW

Borophosphates are an ideal material class for the design of deep-UV optical functional crystals, yet their practical applications are limited by their small birefringence. Herein, a new mixed-coordinated borophosphate, NH

Water pollution by toxic heavy metals poses a threat to the environment and human bodies. Herein, a novel hydrated ferric oxide nanoparticle (HFO) based hybrid adsorbent was fabricated for the removal of toxic Cu(II), Cd(II) and Pb(II) from water. HFOs were immobilized into a porous resin D-201, and then this nanocomposite HFO-D201 was coated with humic acid (HA) to enhance the binding sites of target metals. Both HFOs and HA contribute to the sequestration of heavy metals. The as-synthesized hybrid adsorbent HA-HFO-D201 exhibited excellent performance on the removal of Cu(II), Cd(II), and Pb(II) in a pH range of 3-9, while no Fe leaching was observed. The presence of natural organic matter (20 mg C/L) has limited influences on the adsorption, and more than 85% of the target metals can be removed after treatment. HA-HFO-D201 showed preferable adsorption toward Cu(II) and Pb(II) (1 mg/L) from the background Ca

Quantification of Cd

Pyrolysis-gas chromatography-mass spectrometry (Py-GC/MS) has been widely used for the detection of micro- and nanoplastics (MNPs) in the environment. However, there is a lack of thorough investigation on the effects of pyrolysis temperature and time, as well as the particle source, size and mass of MNPs on the pyrolysis efficiency and pyrolysis product distribution of MNPs. Herein, taking the common plastics polystyrene (PS) as a model, we systematically evaluated the influences of the above factors on the pyrolysis of PS MNPs. Results showed that pyrolysis temperature and time significantly affect the pyrolysis efficiency. By measuring the relative response values of the indicator compound styrene trimers to styrene monomer, the optimum condition was determined as the temperature of 510 ℃ and pyrolysis time longer than 18 s. Meanwhile, the mass of MNPs also affected the distribution of PS pyrolysis products. The proportions of styrene dimers and trimers increased slightly with PS MNP mass, while the source, particle size of MNPs have little effect on the pyrolysis product distribution. This work proposed a suitable pyrolysis temperature and time for the determination of PS by Py-GC/MS, which would contribute to the accurate analysis of PS MNPs in the environment.

A new method was developed to determine the nanoparticulate and ionic silver (Ag) species in bacteria (Escherichia coli, E. coli). By removal of the cell wall with lysozyme, the cell surface-adsorbed Ag species were separated from the intracellular Ag species, which were extracted by tetramethylammonium hydroxide and determined by size-exclusion chromatography coupled with inductively coupled plasma mass spectrometry (SEC-ICP-MS). The detection limit is 3 ng/107 CFU/mL (where CFU is colony-forming unit) for both silver nanoparticles (AgNPs) and ionic Ag(I) species. The cell wall-adsorbed Ag was calculated by subtracting the contents of the intra- and extracellular Ag from the total exposure dose of Ag, and therefore the biodistribution of Ag species was profiled. We then applied this strategy to quantitatively analyze extra- and intracellular Ag species in E. coli after respective exposure to Ag+ and 10 and 30 nm AgNPs at different effective concentrations (EC10, EC50, and EC90). Results showed that the intracellular and cell wall-bound Ag account for 5.98-15.21% and 25.13-64.43% of the exposed dose, respectively, and AgNPs could transform into complexed or free Ag+. Our method opens new avenues for the quantitative analysis of the uptake and biodistribution of nanoparticles and their transformation species in bacteria.

Two barium-containing borates BaMBO4 (M = Al, Ga) were synthesized via the solid-state method under atmospheric pressure. The 3D configurations of BaGaBO4 and BaAlBO4 are comprised of ∞2[Ba4O16]24–...

A new borosilicate, NaCa5BO3(SiO4)2, has been synthesized by a high-temperature solution method, which crystallizes in the centrosymmetric monoclinic space group P21/c (No. 14), having a tangled three-dimensional (3D) network including isolated [BO3] triangles, isolated [SiO4] tetrahedra, and [CaOn] (n = 7–9) and [NaO7] polyhedra. According to our surveys, it is the first compound containing both isolated [BO3] triangles and isolated [SiO4] tetrahedra in alkali- and alkaline-earth-metal borosilicates, which enriches the structure chemistry of borosilicates. The UV–vis–NIR diffuse reflectance spectrum shows that NaCa5BO3(SiO4)2 exhibits a wide transparent region which covers the near-IR, visible, and UV windows and displays a short UV cutoff edge at about 240 nm. Additionally, the thermal behavior (TG and DSC) and IR spectrum were also analyzed. For a deeper understanding of the relationships between the structure and properties, an analysis of theoretical calculations by density functional theory was also...

A new complex alkaline-earth metal borosilicate chloride Ba3Ca4(BO3)3(SiO4)Cl has been successfully synthesized by the high-temperature solution method. It crystallizes in the space group P63mc (no. 186) of the hexagonal system. Its structure features a 3∞[Ca4(BO3)3(SiO4)] framework formed by interconnected 1∞[Ca4(BO3)3(SiO4)O9] chains with large octagonal star-like channels, in which the 1∞[Ba3Cl] chains are located. The second harmonic generation (SHG) measurement shows that Ba3Ca4(BO3)3(SiO4)Cl has an SHG of about 0.6 times that of KH2PO4 and it is phase matchable. In addition, it melts congruently and exhibits a wide transparent range with the UV cut-off edge below 190 nm. All the above indicates that Ba3Ca4(BO3)3(SiO4)Cl could be regarded as a potential ultraviolet nonlinear optical material.

The globally raising concern for nanoplastics (NPs) pollution calls for analytical methods for investigating their occurrence, fates, and effects. Counting NPs with sizes down to 50 nm in real environmental waters remains a great challenge. Herein, we developed a full method from sample pretreatment to quantitative detection for NPs in environmental waters. Various NPs of common plastic types and sizes (50-1200 nm) were successfully labeled by

The degradation of plastic debris may result in the generation of nanoplastics (NPs). Their high specific surface area for the sorption of organic pollutions and toxic heavy metals and possible transfer between organisms at different nutrient levels make the study of NPs an urgent priority. However, there is very limited understanding on the occurrence, distribution, abundant, and fate of NPs in the environment, partially due to the lack of suitable techniques for the separation and identification of NPs from complex environmental matrices. In this review, we first overviewed the state-of-the-art methods for the extraction, separation, identification and quantification of NPs in the environment. Some of them have been successfully applied for the field determination of NPs, while some are borrowed from the detection of microplastics or engineered nanomaterials. Then the possible fate and transport of NPs in the environment are thoroughly described. Although great efforts have been made during the recent years, large knowledge gaps still exist, such as the relatively high detection limit of existing method failing to detect ultralow masses of NPs in the environment, and spherical polystyrene NP models failing to represent the various compositions of NPs with different irregular shapes, which needs further investigation.

This study investigated heteroaggregation of three surface-functionalized polystyrene nanoparticles (PSNPs), i.e. negatively charged unfunctionalized nanoparticles (Bare-PS) and carboxylated nanoparticles (COOH-PS), and positively charged amino-functionalized nanoparticles (NH2-PS), with two model natural colloids, positively charged hematite and negatively charged kaolin, respectively. Heteroaggregation was conducted at a constant natural colloid concentration and variable NP/colloid concentration ratios. Electrostatic interaction was the main mechanism driving the formation of heteroaggregates. In binary systems containing hematite and Bare-PS/COOH-PS, a charge neutralization - charge inverse mechanism was observed with the increase of PSNP concentration. At NP/hemetite concentration ratios much smaller or larger than the full charge neutralization point, the primary heteroaggregates were stable, while full charge neutralization induced the formation of large secondary heteroaggregates. Large aggregates were not observed in suspensions containing kaolin and NH2-PS, as highly positively charged NH2-PS reversed surface charges of kaolin at extremely low concentrations. Heteroaggregation between PSNPs and natural colloids with the same charge is unfavorable due to strong electrostatic repulsion. In the presence of electrolytes, homoaggregation and heteroaggregation both occurred, and homoaggregation of hematite played a key role when the concentration of PSNPs was low. The presence of Suwannee River natural organic matter (SRNOM) could modify surface charges of nanoparticles, and thus affect heteroaggregation behaviors of the binary suspension. When SRNOM and electrolytes were both present, whether SRNOM inducing or hindering the stability of the binary system was a combined effect of NP/colloid concentration ratios, SRNOM concentrations, electrolyte types and ionic strength. Mechanisms extensively reported in homoaggregation such as steric hindrance and cation bridging effects between SRNOM and Ca2+ also stand for heteroaggregation. These results highlight the critical role of surface modification on the environmental behaviors of NPs, and will underpin our understanding of the fate and transport of NPs in the aquatic environment.

Silver nanoparticles (AgNPs) are well known for their excellent antibacterial ability and superior physiochemical properties, and are widely used in a growing number of applications, including home disinfectants, medical devices and water purificants. During the production, use and disposal of AgNP-containing products, AgNPs may be released into the environment. AgNPs are highly dynamic in aqueous systems. They could undergo different chemical and morphology transformation, which greatly affects their final fate, transport, distribution and potential bioeffects. The study on the fate and transformation of AgNPs in natural systems is the basis and prerequisite for the accurate assessment of environmental and biological safety of AgNPs. Herein, we reviewed the recent progress of the natural formation and transformation of AgNPs in the aquatic environment, including the chemical and biosynthesis of AgNPs, the aggregation, enrichment in water surface microlayer, oxidation and dissolution, sulfidation and chlorination of AgNPs in the aquatic environment. The prospects and possible directions in the field are also discussed.

Photo-reduction of Ag+ to silver nanoparticle (AgNPs) by dissolved organic matter (DOM) is a possible source of naturally occurring AgNPs. However, how this photo-reduction process is influenced by ubiquitous metal ions is still not well understood. In addition, in previous studies, the formation of AgNPs in DOM solution was usually monitored by UV-Vis spectroscopy, and there is still lack of quantitative analysis for the formed AgNPs. In the present study, the role of Fe2+/Fe3+ at environmental concentration level on this photochemical process was investigated, and the enhanced formation of AgNPs by Fe2+/Fe3+ was probed and quantified by using UV-Vis spectroscopy, transmission electron microscopy, and liquid chromatography-inductively coupled plasma mass spectrometry. It was demonstrated that while Fe3+ can oxidize AgNPs to release Ag+, Fe2+ can reduce Ag+ into AgNPs. However, the DOM-induced reduction of Fe3+ makes iron an effective electron shuttle between DOM and Ag+, and both Fe2+ and Fe3+ enhanced AgNP formation. The impacts of environmentally relevant factors, including DOM concentration and solution pH, on this process were studied comprehensively, which showed that the catalytic role of iron was more significant at higher DOM concentration and lower pH. This iron-enhanced formation of AgNPs in photo-irradiated Ag+-DOM solution have great environmental implications on the formation of natural AgNPs and the transformation of engineered AgNPs in acidic surface water with high iron content.

The rapidly growing applicability of metal-containing engineered nanoparticles (MENPs) has made their environmental fate, biouptake, and transformation important research topics. However, considering the relatively low concentration of MENPs and the high concentration of background metals in the environment and in organisms, tracking the fate of MENPs in environment-related scenarios remains a challenge. Intrinsic labeling of MENPs with radioactive or stable isotopes is a useful tool for the highly sensitive and selective detection of MENPs in the environment and organisms, thus enabling tracing of their transformation, uptake, distribution, and clearance. In this review, we focus on radioactive/stable isotope labeling of MENPs for their environmental and biological tracing. We summarize the advantages of intrinsic radioactive/stable isotopes for MENP labeling and discuss the considerations in labeling isotope selection and preparation of labeled MENPs, as well as exposure routes and detection of labeled MENPs. In addition, current practice in the use of radioactive/stable isotope labeling of MENPs to study their environmental fate and bioaccumulation is reviewed. Future perspectives and potential applications are also discussed, including imaging techniques for radioactive- and stable-isotope-labeled MENPs, hyphenated multistable isotope tracers with speciation analysis, and isotope fractionation as a MENP tracer. It is expected that this critical review could provide the necessary background information to further advance the applications of isotope tracers to study the environmental fate and bioaccumulation of MENPs.

AgCl and Ag2S prevalently exist in the environment as minerals and/or the chlorination and sulfidation products of ionic silver and elemental silver nanoparticles (AgNPs). In this work, we investigated the chemical transformation of AgCl and Ag2S under simulated sunlight (in water) and incineration (in sludge and simulated municipal solid waste, SMSW). In the presence of natural organic matter, AgCl in river water was observed to be transformed into AgNPs under simulated sunlight, while photo-reduction of Ag2S could not take place under the same experimental conditions. During the course of incineration, pure Ag2S was transformed into elemental silver while AgCl remained stable; however, both Ag2S in sludge and AgCl in SMSW can be transformed to elemental silver under incineration, evident by the results of X-ray absorption spectroscopy and scanning electron microscopy measurements. Incineration temperature played an important role in the transformation of Ag2S and AgCl into elemental silver. These results suggest that chemical transformations of Ag2S and AgCl into elemental silver could be a possible source of naturally occurring or unintentionally produced AgNPs, affecting the fate, transport, bioavailability and toxicity of silver. Therefore, it is necessary to include the contributions of this transformation process when assessing the risk of ionic silver/AgNPs and the utilization and management of incineration residues.

To track transformations of silver nanoparticles (AgNPs) in vivo, HepG2 and A549 cells were cocultured with two enriched stable Ag isotopes (107AgNPs and 109AgNO3) at nontoxic doses. After enzymati...

Two barium-containing borates BaMBO

The intentional production and degradation of plastic debris may result in the formation of nanoplastics. Currently, the scarce information on the environmental behaviors of nanoplastics hinders accurate assessment of their potential risks. Herein, the aggregation kinetics of different surface-modified polystyrene nanoparticles in monovalent and divalent electrolytes was investigated to shed some light on the fate of nanoplastics in the aquatic environment. Three monodisperse nanoparticles including unmodified nanoparticles (PS-Bare), carboxylated nanoparticles (PS–COOH) and amino modified nanoparticles (PS–NH2), as well as one polydisperse nanoparticles that formed by laser ablation of polystyrene films (PS-Laser) were used as models to understand the effects of surface groups and morphology. Results showed that aggregation kinetics of negatively charged PS-Bare and PS-COOH obeyed the DLVO theory in NaCl and CaCl2 solutions. The presence of Suwannee river natural organic matters (SRNOM) suppressed the aggregation of PS-Bare and PS-COOH in monovalent electrolytes by steric hindrance. However, in divalent electrolytes, their stability was enhanced at low concentrations of SRNOM (below 5 mg C L−1), while became worse at high concentrations of SRNOM (above 5 mg C L−1) due to the interparticle bridging effect caused by Ca2+ and carboxyl groups of SRNOM. The cation bridging effect was also observed for PS-laser in the presence of high concentrations of divalent electrolytes and SRNOM. The adsorption of SRNOM could neutralize or even reverse surface charges of positively charged PS-NH2 at high concentrations, thus enhanced or inhibited the aggregation of PS-NH2. No synergistic effect of Ca2+ and SRNOM was observed on the aggregation of PS-NH2, probably due to the steric repulsion imparted by the surface modification. Our results highlight that surface charge and surface modification significantly influence aggregation behaviors of nanoplastics in aquatic systems.

A new borosilicate, NaCa

Silver nanoparticles (AgNPs) are rather mutable in water columns, and the oxidation of AgNPs to release Ag+ and reduction of Ag+ to regenerate AgNPs exist simultaneously in certain environments, making it rather difficult to monitor the reaction kinetics. In this study, we synthesized isotopically labeled AgNPs (99.5% 107Ag, 107AgNPs) and AgNO3 (99.81% 109Ag, 109AgNO3). For the first time, two stable Ag isotopes were used in the same experiment to track the transformation kinetics of AgNPs and Ag+ independently in aquatic environments. It was found that the oxidation of AgNPs dominated the reaction in simple water solutions containing both 107AgNPs and 109Ag+. Sunlight significantly accelerated the dissolution of the 107AgNPs, but longer solar irradiation (8 h) triggered aggregation of the 107AgNPs and therefore reduced the reaction rate. With the addition of 5 mg C L−1 dissolved organic matter, the reduction of 109Ag+ played the leading role. The corrected concentration of dissolved 107Ag+ began to decrease after some time, indicating other reduction mechanisms were happening. An elevated pH (pH 8.5) could even completely inhibit the oxidation of 107AgNPs. All the reactions seemed stalled at low temperature (6 °C) except the dissolution of 107AgNPs under solar irradiation, suggesting a non-negligible effect of sunlight. The presence of divalent cations induced agglomeration of 107AgNPs, but the reduction of 109Ag+ was not significantly affected. These findings implied that the transformation between AgNPs and Ag+ was rather complex and greatly depended on the external conditions. Given the fact that Ag+ has been shown to be much more toxic than AgNPs, the speciation change may dramatically impact the final toxicity and bioavailability of AgNPs, so there is a high demand for assessing the environmental risks of AgNPs under more realistic conditions.

Hollow fiber supported liquid membrane (HFSLM) extraction was coupled with ICP-MS for speciation analysis of labile Ag(I) and total Ag(I) in dispersions of silver nanoparticles (AgNPs) and environmental waters. Ag(I) in aqueous samples was extracted into the HFSLM of 5%(m/v) tri-n-octylphosphine oxide in n-undecane, and stripped in the acceptor of 10 mM Na2S2O3 and 1 mM Cu(NO3)2 prepared in 5 mM NaH2PO4-Na2HPO4 buffer (pH 7.5). Negligible depletion and exhaustive extraction were conducted under static and 250 rpm shaking to extract the labile Ag(I) and total Ag(I), respectively. The extraction equilibration was reached in 8 h for both extraction modes. The extraction efficiency and detection limit were (2.97 ± 0.25)% and 0.1 μg/L for labile Ag(I), and (82.3 ± 2.0)% and 0.5 μg/L for total Ag(I) detection, respectively. The proposed method was applied to determine labile Ag(I) and total Ag(I) in different sized AgNP dispersions and real environmental waters, with spiked recoveries of total Ag(I) in the range of 74.0-98.1%. With the capability of distinguishing labile and total Ag(I), our method offers a new approach for evaluating the bioavailability and understanding the fate and toxicity of AgNPs in aquatic systems.

Ubiquitous natural organic matter (NOM) plays an important role in the aggregation state of engineered silver nanoparticles (AgNPs) in aquatic environment, which determines the transport, transformation, and toxicity of AgNPs. As various capping agents are used as coatings for nanoparticles and NOM are natural polymer mixture with wide molecular weight (MW) distribution, probing the particle coating-dependent interaction of MW fractionated natural organic matter (Mf-NOM) with various coatings is helpful for understanding the differential aggregation and transport behavior of engineered AgNPs as well as other metal nanoparticles. In this study, we investigated the role of pristine and Mf-NOM on the aggregation of AgNPs with Bare, citrate, and PVP coating (Bare-, Cit-, and PVP-AgNP) in mono- and divalent electrolyte solutions. We observed that the enhanced aggregation or dispersion of AgNPs in NOM solution highly depends on the coating of AgNPs. Pristine NOM inhibited the aggregation of Bare-AgNPs but enhanced the aggregation of PVP-AgNPs. In addition, Mf-NOM fractions have distinguishing roles on the aggregation and dispersion of AgNPs, which also highly depend on the AgNPs coating as well as the MW of Mf-NOM. Higher MW Mf-NOM (100 kDa and 30-100 kDa) enhanced the aggregation of PVP-AgNPs in mono- and divalent electrolyte solutions, whereas lower MW Mf-NOM (10-30 kDa, 3-10 kDa and3 kDa) inhibited the aggregation of PVP-AgNPs. However, all the Mf-NOM fractions inhibited the aggregation of Bare-AgNPs. For PVP- and Bare-AgNPs, the stability of AgNPs in electrolyte solution was significantly correlated to the MW of Mf-NOM. But for Cit-AgNPs, pristine NOM and Mf-NOM has minor influence on the stability of AgNPs. These findings about significantly different roles of Mf-NOM on aggregation of engineered AgNPs with various coating are important for better understanding of the transport and subsequent transformation of AgNPs in aquatic environment.

Dissolved organic matter (DOM) is ubiquitous in the environment and has high reactivity. Once engineered nanoparticles (ENPs) are released into natural systems, interactions of DOM with ENPs may significantly affect the fate and transport of ENPs, as well as the bioavailability and toxicity of ENPs to organisms. However, because of the complexity of DOM and the shortage of useful characterization methods, large knowledge gaps exist in our understanding of the interactions between DOM and ENPs. In this article, we systematically reviewed the interactions between DOM and ENPs, discussed the effects of DOM on the environmental behavior of ENPs, and described the changes in bioavailability and toxicity of ENPs caused by DOM. Critical evaluations of published references suggest further need for assessing and predicting the influences of DOM on the transport, transformation, bioavailability, and toxicity of ENPs in the environment.

Photoinduced reduction of silver ion (Ag(+)) to silver nanoparticles (AgNPs) by dissolved organic matter (DOM) plays a crucial role in the transformation and transport of engineered AgNPs and Ag(+) in aquatic environments. DOM is a mixture of natural polymers with wide molecular weight (MW) distribution, and the roles of specific components of DOM in the photoreduction of Ag(+) to AgNPs are still not understood. In this study, MW fractionated natural organic matter (Mf-NOM) were investigated for their roles on the photoreduction process and stabilization of the formed AgNPs. This photoinduced reduction process depends highly on pH, concentration of Ag(+) and NOM, light quality, and the MW of Mf-NOM. Monochromatic radiation and light attenuation correction suggested that the difference of Mf-NOM on reduction was mainly ascribed to the differential light attenuation of Mf-NOM rather than the "real" reductive ability. More importantly, compared with low MW fractions, the high MW Mf-NOMs exhibit drastically higher capability in stabilizing the photosynthesized AgNPs against Ca(2+)-induced aggregation. This finding is important for a better understanding of the differential roles of Mf-NOM in the transformation and transport of Ag(+) and engineered AgNPs in DOM-rich surface water.

Due to its antimicrobial activity, nanosilver (nAg) has become the most widely used nanomaterial. Thus far, the mechanisms responsible for nAg-induced antimicrobial properties and nAg-mediated toxicity to organisms have not been clearly recognized. Silver (Ag) ions certainly play a crucial role, and the form of nanoparticles can change the dissolution rate, bioavailability, biodistribution, and cellular uptake of Ag. However, whether nAg exerts direct "particle-specific" effects has been under debate. Here we demonstrated that nAg exhibited a robust inhibition on RNA polymerase activity and overall RNA transcription through direct Ag binding to RNA polymerase, which is separated from the cytotoxicity pathway induced by Ag ions. nAg treatment in vitro resulted in reduced hemoglobin concentration in erythroid cells; in vivo administration of nAg in mice caused profound reduction of hemoglobin content in embryonic erythrocytes, associated with anemia in the embryos. Embryonic anemia and general proliferation deficit due to the significant inhibition on RNA synthesis, at least partially, accounted for embryonic developmental retardation upon nAg administration. To date, there is no conclusive answer to the sources of nAg-mediated toxicity: Ag ions or "particle-specific" effects, or both. We here demonstrated that both Ag ions and nAg particles simultaneously existed inside cells, demonstrating the "Trojan horse" effects of nAg particles in posing biological impacts on erythroid cells. Moreover, our results suggested that "particle-specific" effects could be the predominant mediator in eliciting biological influences on erythroid cells under relatively low concentrations of nAg exposure. The combined data highlighted the inhibitory effect of nAg on RNA polymerase activity through a direct reciprocal interaction.

The toxic mechanism of silver nanoparticles (AgNPs) is still debating, partially because of the common co-occurrence and the lack of methods for separation of AgNPs and Ag(+) in biological matrices. For the first time, Triton-X 114-based cloud point extraction (CPE) was proposed to separate AgNPs and Ag(+) in the cell lysates of exposed HepG2 cells. Cell lysates were subjected to CPE after adding Na2S2O3, which facilitated the transfer of AgNPs into the nether Triton X-114-rich phase by salt effect and the preserve of Ag(+) in the upper aqueous phase through the formation of hydrophilic complex. Then the AgNP and Ag(+) contents in the exposed cells were determined by ICP-MS after microwave digestion of the two phases, respectively. Under the optimized conditions, over 67% of AgNPs in cell lysates were extracted into the Triton X-114-rich phase while 94% of Ag(+) remained in the aqueous phase, and the limits of detection for AgNPs and Ag(+) were 2.94 μg/L and 2.40 μg/L, respectively. This developed analytical method was applied to quantify the uptake of AgNPs to the HepG2 cells. After exposure to 10 mg/L AgNPs for 24 h, about 67.8 ng Ag were assimilated per 10(4) cells, in which about 10.3% silver existed as Ag(+). Compared to the pristine AgNPs (with 5.2% Ag(+)) for exposure, the higher ratio of Ag(+) to AgNPs in the exposed cells (10.3% Ag(+)) suggests the transformation of AgNPs into Ag(+) in the cells and/or the higher uptake rate of Ag(+) than that of AgNPs. Given that the toxicity of Ag(+) is much higher than that of AgNPs, the substantial content of Ag(+) in the exposed cells suggests that the contribution of Ag(+) should be taken into account in evaluating the toxicity of AgNPs to organisms, and previous results obtained by regarding the total Ag content in organisms as AgNPs should be reconsidered.

Photo-reduction of Ag

AgCl and Ag

There is a growing production and application of silver nanoparticles (AgNPs) (e.g., in cosmetics products, food technology, textiles and fabrics, and medical products and devices). The rapid growth in the commercial use of AgNPs will inevitably increase exposure to silver in the environment and among the general population. Compared to the vast application of silver, information on the fate, the transformation and the toxicity of AgNPs is very limited. Lack of proper techniques to trace AgNPs in complex matrixes hinders investigation. Thus, development of methods for analysis of AgNPs is very important to achieve detailed insights into the fate, the transport and exposure of AgNPs in environment. This review presents state-of-the-art methods for separation, identification, characterization and quantification of AgNPs. We also discuss perspectives on future developments. (C) 2012 Elsevier Ltd. All rights reserved.

The inevitable release of engineered silver nanoparticles (AgNPs) into aquatic environments has drawn great concerns about its environmental toxicity and safety. Although aggregation and transformation play crucial roles in the transport and toxicity of AgNPs, how the water chemistry of environmental waters influences the aggregation and transformation of engineered AgNPs is still not well understood. In this study, the aggregation of polyvinylpyrrolidone (PVP) coated AgNPs was investigated in eight typical environmental water samples (with different ionic strengths, hardness, and dissolved organic matter (DOM) concentrations) by using UV-visible spectroscopy and dynamic light scattering. Raman spectroscopy was applied to probe the interaction of DOM with the surface of AgNPs. Further, the photo-transformation and morphology changes of AgNPs in environmental waters were studied by UV-visible spectroscopy, inductively coupled plasma mass spectrometry, and transmission electron microscopy. The results suggested that both electrolytes (especially Ca(2+) and Mg(2+)) and DOM in the surface waters are key parameters for AgNP aggregation, and sunlight could accelerate the morphology change, aggregation, and further sedimentation of AgNPs. This water chemistry controlled aggregation and photo-transformation should have significant environmental impacts on the transport and toxicity of AgNPs in the aquatic environments.

The production and use of silver nanoparticles (AgNPs) in industrial and commercial products increased significantly in recent years. During the production, manufacturing, use and disposal of AgNP containing products, AgNPs would be released into the environment inevitably. Moreover, AgNPs could also be naturally occurred in the environment through biological and chemical reduction processes. In recent years, various chemical and biological pathways, including reduction of Ag+ by natural organic matters, plants and microorganisms, and generation of AgNPs from macroscale elemental silver objects through dissolution and reduction, were demonstrated for the occurrence of naturally occurred AgNPs. In this chapter, we introduce the occurrences of natural AgNPs in the environments and their possible formation pathways and mechanisms, and discuss the anthropogenic pathways for intentionally and unintentionally produced AgNPs and their release into the environment.