Ag Speciation Research Articles

Effect of chloride concentration on the cytotoxicity, bioavailability, and bioreactivity of copper and silver in the rainbow trout gut cell line, RTgutGC.

Chloride (Cl-) influences the bioavailability and toxicity of metals in fish, but the mechanisms by which it influences these processes is poorly understood. Here, we investigated the effect of chloride on the cytotoxicity, bioavailability (i.e., accumulation) and bioreactivity (i.e., induction of mRNA levels of metal responsive genes) of copper (Cu) and silver (Ag) in the rainbow trout gut cell line (RTgutGC). Cells were exposed to metals in media with varying Cl- concentrations (0, 1, 5 and 146 mM). Metal speciation in exposure medium was analyzed using Visual MINTEQ software. Cytotoxicity of AgNO3 and CuSO4 was measured based on two endpoints: metabolic activity and membrane integrity. Cells were exposed to 500 nM of AgNO3 and CuSO4 for 24 h in respective media to determine metal bioavailability and bioreactivity. Ag speciation changes from free ionic (Ag+) to neutral (AgCl), to negatively charged chloride complexes (AgCl2-, AgCl3-) with increasing Cl- concentration in exposure media whereas Cu speciation remains in two forms (Cu2+ and CuHPO4) across all media. Chloride does not affect Ag bioavailability but decreases metal toxicity and bioreactivity. Cells exposed to Ag expressed significantly higher metallothionein mRNA levels in low Cl- media (0, 1, and 5 mM) than in high Cl- medium (146 mM). This suggests that chloride complexation reduces silver bioreactivity and toxicity. Conversely, Cu bioavailability and toxicity were higher in the high chloride medium (146 mM) than in the low Cl- (0, 1, and 5 mM) media, supporting the hypothesis that Cu uptake may occur via a chloride dependent mechanism. CLINICAL TRIALS REGISTRATION: This study did not require clinical trial registration.

A Deeper Insight in Metal Binding to the hCtr1 N-terminus Fragment: Affinity, Speciation and Binding Mode of Binuclear Cu2+ and Mononuclear Ag+ Complex Species.

Ctr1 regulates copper uptake and its intracellular distribution. The first 14 amino acid sequence of the Ctr1 ectodomain Ctr1(1-14) encompasses the characteristic Amino Terminal Cu2+ and Ni2+ binding motif (ATCUN) as well as the bis-His binding motif (His5 and His6). We report a combined thermodynamic and spectroscopic (UV-vis, CD, EPR) study dealing with the formation of Cu2+ homobinuclear complexes with Ctr1(1-14), the percentage of which is not negligible even in the presence of a small Cu2+ excess and clearly prevails at a M/L ratio of 1.9. Ascorbate fails to reduce Cu2+ when bound to the ATCUN motif, while it reduces Cu2+ when bound to the His5-His6 motif involved in the formation of binuclear species. The histidine diade characterizes the second binding site and is thought to be responsible for ascorbate oxidation. Binding constants and speciation of Ag+ complexes with Ctr1(1-14), which are assumed to mimic Cu+ interaction with N-terminus of Ctr1(1-14), were also determined. A preliminary immunoblot assay evidences that the anti-Ctr1 extracellular antibody recognizes Ctr1(1-14) in a different way from the longer Ctr1(1-25) that encompasses a second His and Met rich domain.

Role of polystyrene microplastics in sunlight-mediated transformation of silver in aquatic environments: Mechanisms, kinetics and toxicity

Sunlight-oxidative ageing is a common and critical process for microplastics (MPs) in aquatic environments. O2•−, 1O2, and •OH generation has been widely proven in this process, which can alter metal speciation based on its reduction and oxidation potential. Herein, chemical speciation of Ag mediated by polystyrene (PS) MPs was determined under simulated sunlight irradiation. The O2•− generation on the PS MPs surfaces is the vital factor for Ag+ reduction, regardless of acid or base conditions. The 1O2 and •OH are dominant factors, and 1O2 played a more important role than •OH for its higher formation amount, causing oxidative dissolution of newly formed Ag0 nanoparticles (NPs). The Ag NPs can hetero-aggregate with PS MPs through electrostatic interactions with O–containing groups (C–O, C–OH and CO), and co-precipitate from the water phase. This hetero-aggregation can stabilize Ag NPs by inhibiting Ag NPs surface photooxidation and suppressing Ag+ release. Transformation of Ag species (from Ag+ to Ag0 NPs) mediated by sunlight with PS MPs significantly suppressed acute toxicity of Ag+ to Escherichia coli, Selenastrum capricornutum, Daphnia magna and zebrafish. This study emphasized that PS MPs play an important role in the speciation, migration and toxicity of Ag+ in freshwater environments.

Reduction of Ionic Silver by Sulfur Dioxide as a Source of Silver Nanoparticles in the Environment.

The natural formation of silver nanoparticles (AgNPs) via biotic and abiotic pathways in water and soil media contributes to the biogeochemical cycle of silver metal in the environment. However, the formation of AgNPs in the atmosphere has not been reported. Here, we describe a previously unreported source of AgNPs via the reduction of Ag(I) by SO2 in the atmosphere, especially in moist environments, using multipronged advanced analytical and surface techniques. The rapid reduction of Ag(I) in the atmospheric aqueous phase was mainly caused by the sulfite ions formed from the dissolution of SO2 in water, which contributed to the formation of AgNPs and was consistent with the Finke-Watzky model with a major contribution of the reduction-nucleation process. Sunlight irradiation excited SO2 to form triplet SO2, which reacted with water to form H2SO3 and greatly enhanced Ag(I) reduction and AgNP formation. Different pH values affected the speciation of Ag(I) and S(IV), which were jointly involved in the reduction of Ag(I). The formation of AgNPs was also observed in the atmospheric gas phase via direct reduction of Ag(I) by SO2(gas), which occurred even in 50 ppbv SO2(gas). The natural occurrence of AgNPs in the atmosphere may also be involved in silver corrosion, AgNP transformation and regeneration, detoxification of gaseous pollutants, and the sulfur cycle in the environment.

Long-term accumulation, depth distribution, and speciation of silver nanoparticles in biosolids-amended soils.

Biosolids can be a source of metals and metal nanoparticles. The objective of this study was to quantify and characterize the accumulation and transport of silver (Ag) in a natural soil that has received agronomically recommended rates of biosolids as fertilizer from 1994 to 2017. Total Ag concentrations were measured in biosolids and soil samples collected from 0 to 10cm between 1996 and 2017. The depth distribution of Ag in soil to 60-cm depth was measured in 2017. Electron microscopy, in combination with X-ray spectroscopy, and X-ray absorption spectroscopy were used to characterize the Ag. The Ag concentrations in the biosolids-amended soil increased steadily from 1996 until 2007, after which the concentrations leveled off at about 1.25mg Ag kg-1 soil. This corresponded with a decrease of Ag concentrations in biosolids over time. The majority of the Ag (82%) was confined to the top 10cm of the soil, small amounts (14%) were detected at 10-to-20-cm depth, and trace amounts (4%) were detected at 30-to-40-cm depth. The Ag in the biosolids was identified as S-containing nanoparticles (Ag2 S) with a diameter of 10-12nm; however, in soil, the Ag concentrations were too low to allow identification of Ag speciation. This study shows that in a real-world field scenario, biosolids applied at agronomic rates represent a long-term, economically viable source of crop nutrients without increasing the concentration of total Ag in soil above a maximum of 1.5mg Ag kg-1 . This concentration is below estimated ecotoxicity limits for Ag2 S in soil.

Medium-term effects of Ag supplied directly or via sewage sludge to an agricultural soil on Eisenia fetida earthworm and soil microbial communities

The widespread use of silver nanoparticles (AgNPs) in consumer products that release Ag throughout their life cycle has raised potential environmental concerns. AgNPs primarily accumulate in soil through the spreading of sewage sludge (SS). In this study, the effects of direct exposure to AgNPs or indirect exposure via SS contaminated with AgNPs on the earthworm Eisenia fetida and soil microbial communities were compared, through 3 scenarios offering increasing exposure concentrations. The effects of Ag speciation were analyzed by spiking SS with AgNPs or AgNO3 before application to soil. SS treatment strongly impacted Ag speciation due to the formation of Ag2S species that remained sulfided after mixing in the soil. The life traits and expression of lysenin, superoxide dismutase, cd-metallothionein genes in earthworms were not impacted by Ag after 5 weeks of exposure, but direct exposure to Ag without SS led to bioaccumulation of Ag, suggesting transfer in the food chain. Ag exposure led to a decrease in potential carbon respiration only when directly added to the soil. The addition of SS had a greater effect on soil microbial diversity than the form of Ag, and the formation of Ag sulfides in SS reduced the impact of AgNPs on E. fetida and soil microorganisms compared with direct addition.

Antibacterial mechanism for inactivation of E. Coli by AgNPs@polydoamine/titania nanotubes via speciation analysis of silver ions and silver nanoparticles by cation exchange reaction

In this method, silver nanoparticles (AgNPs) were anchored on titania nanotubes (TNT) surface by chelation of polydopamine (PD) to generate an AgNPs@polydopamine/titania nanotubes (TPAS). To reveal the antibacterial mechanism of TPAS, a speciation analysis of silver ion (Ag+) and AgNPs was developed based on cation exchange reaction (CER). Owing to only the Ag+ can exchange the Cd2+ in the CdTe quantum dots (QDs), the speciation of Ag+ and AgNPs was realized via detecting the Cd2+ for the indirect but ultrasensitive detection of Ag+ by hydride generation (HG)-atomic fluorescence spectrometer (AFS). The limit of detections (LODs) of Ag+ and AgNPs were 0.0001 ng mL−1. Relative standard deviations (n = 7) are better than 2.2% at a concentration of 0.02 ng mL−1 Ag+. Due to this strategy, the trace AgNPs and Ag+ in antibacterial assay were accurately detected. The results show AgNPs anchored on TPAS predominantly contributed to bactericidal action by contact-killing. Ag+, released from TPAS, synergistically increased the antibacterial activity by release-killing. The proposed method has been successfully utilized for inactivation of E. Coli to explore the antibacterial mechanisms of AgNPs.

Redesigning Water Disinfection Using Recyclable Nanomaterials and Metal Ions: Evaluation with Escherichia coli

We present a novel disinfection method that redesigns the conventional approach, by recycling the disinfectant. This can lead to lower energy requirements and minimize environmental impacts. In this study, metal ions were mixed with target microorganisms in water for disinfection, followed by the sorption of metal ions with magnetic nanoparticles for reuse. As a proof of concept, the disinfection effectiveness values of various metal ions (e.g., Ag+, Cu2+, and Zn2+) on a target microorganism, Escherichia coli K12, were compared. Only Ag+ exhibited a bactericidal effect on E. coli K12, while Cu2+ and Zn2+ just reduced the growth rate. The disinfection efficiency of Ag+ remained stable within a range of environmental conditions (pH, temperature, water hardness, nutrient content, and initial cell concentration), indicating that Ag+ speciation and effectiveness are not modified. The initial ratio of Ag+ per cell is a major factor that will determine disinfection effectiveness. Sorption of Ag+ by one type of magnetic nanomaterial (Mag-Ligand) was studied to explore the removal of Ag+ after disinfection. Mag-Ligand can effectively decrease the concentration of Ag+ from 100 mg/L to ∼100 μg/L in one cycle, and below 10 μg/L in three recovery cycles. Changes in environmental conditions (pH, concentration of Cl–, water hardness, and addition of E. coli K12) were studied to determine how these changes will affect the sorption process. The results showed that sorption capacity will be influenced when the concentration of free Ag+ is decreased (e.g., when the Cl– concentration is increased) or when there are competitive metal ions in the aqueous environment (i.e., water hardness). Sorption efficiency remained stable when the speciation of Ag+ was not influenced (e.g., pH and addition of E. coli K12). The regeneration of Ag+ was studied to evaluate the reuse of the disinfectant. We demonstrate that Ag+ can be recovered after sorption in an acidic environment, and the recovery remains >80% after five continuous cycles, indicating that this disinfection method may be sustainable for practical use.

Accumulation, speciation and localization of silver nanoparticles in the earthworm Eisenia fetida.

The use of silver nanoparticles (AgNPs) in agriculture and many consumer products has led to a significant release of Ag in the environment. Although Ag toxicity in terrestrial organisms has been studied extensively, very little is known about the accumulation capacity and coping mechanisms of organisms in Ag-contaminated soil. In this context, we exposed Eisenia fetida earthworms to artificial OECD soil spiked with a range of concentrations of Ag (AgNPs or AgNO3). The main aims were to (1) identify the location and form of accumulation of Ag in the exposed earthworms and (2) better understand the physiological mechanisms involved in Ag detoxification. The results showed that similar doses of AgNPs or AgNO3 did not have the same effect on E. fetida survival. The two forms of Ag added to soil exhibited substantial differences in speciation at the end of exposure, but the Ag speciation and content of Ag in earthworms were similar, suggesting that biotransformation of Ag occurred. Finally, 3D images of intact earthworms obtained by X-ray micro-computed tomography revealed that Ag accumulated preferentially in the chloragogen tissue, coelomocytes, and nephridial epithelium. Thus, E. fetida bioaccumulates Ag, but a regulation mechanism limits its impact in a very efficient manner. The location of Ag in the organism, the competition between Ag and Cu, and the speciation of internal Ag suggest a link between Ag and the thiol-rich proteins that are widely present in these tissues, most probably metallothioneins, which are key proteins in the sequestration and detoxification of metals.

Multi-method assessment of PVP-coated silver nanoparticles and artificial sweat mixtures

Research presented here utilizes silver nanoparticles (AgNPs) as a case study for how the immediate local environment alters the physical and chemical properties of nanomaterials. Dermal exposure is a primary route for exposure to many of the consumer products containing AgNPs. Interactions between AgNPs and human sweat/perspiration are critical for understanding how changes in Ag speciation will impact exposure. Previous studies have examined silver release from AgNP-containing products after exposure to artificial sweat (AS), however there is no basic assessment of how mixtures of AgNPs and AS alter the physical and chemical properties of AgNPs. The current research evaluated changes in size, aggregation, chemical composition, and silver speciation of four different sizes of AgNPs exposed to four different formulations of AS. The AS formulations were from standardized methods with different chemical compositions, ionic strengths, and pH. Samples were collected at four-time intervals for analysis using dynamic light scattering , UV–Vis spectroscopy, and single-particle inductively coupled plasma-mass spectrometry . Each mixture was also prepared for speciation analysis using X-ray absorption spectroscopy and scanning electron microscopy coupled to energy-dispersive X-ray analysis. The equivalent diameter measurements from the three techniques followed the order of DLS > UV–Vis > spICP-MS. Speciation analyses indicate significant changes for the smaller NPs, while the largest (100 nm) NPs had less measurable differences. This study shows the need to fully understand what specific information an analytical technique might provide and to use those techniques properly in tandem to give the fullest answer to a given research question.

An XAS study of silver species evolution in silver-catalysed chalcopyrite bioleaching

The catalysing effect of Ag+ or Ag nanoparticle (AgNp) on chalcopyrite (bio)leaching at 30 °C was studied in this paper, and the change of Ag speciation was investigated by Ag K-edge X-ray Absorption Near-edge Spectroscopy (XANES). The solution studies indicate that the addition of 0.2% Ag (fraction of Ag to chalcopyrite) can effectively improve the dissolution of chalcopyrite in both bioleaching and chemical leaching. Further increasing the silver concentration to 1% only marginally increase the rate of chalcopyrite dissolution compared with the rate with 0.2% Ag added. No obvious difference has been found between the catalytic effect of Ag+ and AgNp (Silver Nanoparticle). XRD studies indicate the formation of jarosite, elemental sulfur in both bioleaching and chemical leaching. However, the speciation of Ag in the residual cannot be confirmed by XRD analysis. Ag k-edge XANES spectra show that Ag+ or AgNp have completely changed to Ag2S within 7 days in both bioleaching and chemical leaching process. In-situ XANES analysis shows that the Ag+ or AgNp changed to Ag2S very rapidly in the absence of Fe3+. In contrast, AgCl was firstly detected with the presence of 3 g/L Fe3+, which only partially changed to Ag2S in about 36 h, which is likely because the stability of Ag2S was decreased by Fe3+.

Growth inhibition in Raphidocelis subcapita – Evidence of nanospecific toxicity of silver nanoparticles

Silver, known for its antibacterial properties and for its toxicity to aquatic organisms, is one of the most frequently used nanomaterials and silver nanoparticles can be found in a range of consumer products as well as medical applications. The present study investigated the toxicity of three different silver nanomaterials (Mesosilver (M-Ag), NM300K and NM302) and AgNO3, in the algae Raphidocelis subcapitata. Exposures in the low μg L−1 range were combined with characterization of exposure media to determine whether differences in toxicity could be linked to changes in Ag speciation and/or any nanospecific mechanisms. All tested Ag compounds, except the NM302, reduced growth in the following order AgNO3 ≥ M-Ag > NM300K > NM302 with 50% effect concentrations of 7.09 (3.83–10.52), 9.7 (range not calculated) and 24.18 (15.66–98.16) μg L−1, for AgNO3, Mesosilver and NM300K, respectively. Characterization of exposure media showed that both concentration and time influenced the speciation and stability of Ag in algal test media, regardless of Ag source, and also affected the toxicity to R. subcapitata. In both AgNO3 and Mesosilver exposure the toxicity was correlated with the presence of dissolved Ag species (<10 kDa), however levels of dissolved Ag were too low to account for the observed Mesosilver effects, indicating a nanospecific contribution. Nanospecific toxicity was also observed for NM300K after 24 h of exposure, however the algal population recovered over time, probably due to changes in exposure caused by aggregation of the nanoparticles.

Selective ionic liquid solvent bar micro-extraction for estimation of ultra-trace silver fractions in marine waters

Ag can be found in the ocean at the ultra-trace level, mainly as AgCln(n−1)− and complexed by dissolved organic matter (Ag-DOM). However, methods for studying Ag speciation in marine waters are limited by the lack of extractants capable to separate organic and inorganic silver species in natural conditions of seawater samples.In this work, a two-phase solvent bar micro-extraction method using the ionic liquid trihexyltetradecylphosphonium chloride (Cyphos® 101) was applied for selective micro-extraction of AgCln(n−1)− from organic silver in marine waters, working at seawater pH,. The application to real samples was performed under the following conditions: 2.5% Cyphos® 101 in kerosene solution with 10% dodecan-1-ol inside the fiber, and 30 min of sample extraction at a stirring rate of 800 rpm. The proposed SBME was successfully used for estimation of Ag fractions in waters from the Bay of Cádiz (South-west Spain) showing its applicability for a simple, fast and environmentally friendly speciation of silver in marine water samples. The method presented a linear response up to 500 ng L−1 and a detection limit of 0.4 ng L−1, using GF-AAS for instrumental determination.

The solubility of silver in magmatic fluids: Implications for silver transfer to the magmatic-hydrothermal ore-forming environment

Silver is a common and economically important constituent of many magmatic-hydrothermal ore deposits, yet little is known about its mobility during magma degassing. We performed experiments to determine the effect of various chemical components (NaCl, KCl, LiCl, HCl, CaCl2, H2S) on the solubility and speciation of Ag in high-temperature, low-density fluids (≈0.38–0.54 g/cm3). The experiments were conducted at T = 900 °C, P = 2000 bar and oxygen fugacity (fO2) of 0.5 log units below Ni-NiO buffer (NNO-0.5) in rapid-quench Molybdenum-Hafnium Carbide externally-heated pressure vessel assemblies. The fluid phase was sampled at run conditions by the entrapment of synthetic fluid inclusions (SFI) in in situ fractured quartz chips. As capsule material, Au97Ag2Cu1 alloy was used, which imposed an Ag activity of 0.005. The apparent Ag solubility, defined as the equilibrium concentration of Ag in the fluid phase at an Ag activity of 0.005, exponentially increases as a function of total chloride concentration in the NaCl-H2O and NaCl-HCl-H2O systems. In the mixed NaCl-HCl system, at a fixed total Cl concentration of 1 mol/kg (1 m) H2O and varying NaCl/HCl ratios, the apparent solubility of Ag reaches a maximum (432 ± 123 μg/g) at equal NaCl and HCl concentration (0.5 m each) and then decreases towards both end-members (1 m for NaCl or HCl) following a parabolic function. Apparent silver solubilities predicted using the HKF model and thermodynamic properties for traditional Ag-chloride and bisulfide complexes greatly underestimate the measured values. Model calculations suggest that instead of charged AgCl2−, a neutral NaAgCl2 species is the dominant dissolved Ag species in S-free, chloride-bearing fluids with the additional presence of NaAgHSCl in S-bearing fluids. Comparison of the solubility data in high-temperature fluids to measured Ag solubilities in silicate melts suggests that efficient Ag partitioning into magmatic fluids will only take place when the composition of the silicate melt is felsic enough (rhyodacitic to rhyolitic), similarly to the behavior of Cu but in contrast to that of Au.

Analysis of metallic nanoparticles and their ionic counterparts in complex matrix by reversed-phase liquid chromatography coupled to ICP-MS

Developing quantification and characterization methodology for metallic nanoparticles (MNPs) and their ionic component in complex matrix are crucial for the evaluation of their environmental behavior and health risks to humans. In this study, reversed phase high performance liquid chromatography combined ICP-MS was established for the characterization of MNPs in complex matrix. The ionic component could be separated from NPs with the optimized parameters of aqueous mobile phase. Good linear relationship between average diameter and retention time of NPs was obtained using HPLC-ICP-MS and the size smaller than 40 nm could be determined with this method, the detected results were in accordance with TEM results. The low detection limit of AuNPs and Au(Ⅲ) (both in sub-μg/L level) showed that this method was promising for the characterization of AuNPs and Au(Ⅲ) in environmental water. The mass concentration of ionic Au(Ⅲ) in environmental water could be detected using the proposed HPLC-ICP-MS and the concentration of AuNPs was obtained by subtracting the Au(Ⅲ) concentration from the total Au (The concentration of total Au was detected by ICP-MS after microwave digestion). Furthermore this proposed HPLC-ICP-MS method and single particle-ICPMS (SP-ICP-MS) was used for the analysis of the Ag speciation in commercial antibacterial products.

Cytotoxicity and Physiological Effects of Silver Nanoparticles on Marine Invertebrates.

Silver nanoparticles (AgNPs) incorporation in commercial products is increasing due to their remarkable physical and chemical properties and their low cost on the market. Silver has been known for a long time to be highly toxic to bacterial communities, aquatic organisms, and particularly to marine biota. Strong chloro-complexes dominate Ag speciation in seawater and facilitate its persistence in dissolved form. It has a great impact on marine organisms because low concentration of silver can lead to strong bioaccumulation, partly because the neutral silver chloro complex (AgCl0) is highly bioavailable. Owing to the fact that estuaries and coastal areas are considered as the ultimate fate for AgNPs, the study of their toxic effects on marine invertebrates can reveal some environmental risks related to nanosilver exposure. In an attempt to reach this goal, many invertebrate taxa including mollusks, crustaceans, echinoderms and polychaetes have been used as biological models. The main findings related to AgNP toxicity and marine invertebrates are summarized hereafter. Some cellular mechanisms involving nano-internalization (cellular uptake, distribution and elimination), DNA damaging, antioxidant cellular defenses and protein expression are discussed. Physiological effects on early stage development, silver metabolic speciation, immune response, tissue damaging, anti-oxidant effects and nano-depuration are also described. Finally, we paid attention to some recent interesting findings using sea urchin developmental stages and their cells as models for nanotoxicity investigation. Cellular and physiological processes characterizing sea urchin development revealed new and multiple toxicity mechanisms of both soluble and nano forms of silver.

Impact of a Model Soil Microorganism and of Its Secretome on the Fate of Silver Nanoparticles.

Sulfidation is a key process for silver nanoparticles released from consumer products in the environment. This study focuses on the impact of a model soil microorganism, Bacillus subtilis, on the fate of pristine and already sulfidized Ag-NPs. The nanoparticles were incubated with the initial growth medium, isolated secretome, and living bacteria, and characterized for their size and morphology, agglomeration state, structure, and Ag speciation. No Ag internalization or sorption on the cell wall was detected. A partial sulfidation, leading to an Ag-Ag2S core-shell structure, was observed in the presence of the secretome, and the rate limiting step of the reaction was the oxidation of Ag0, and it was favored near the crystal dislocations. The sulfidation was complete in the presence of the living bacteria and followed an indirect pathway. Both crystalline Ag2S and amorphous Ag2S and/or Ag-thiol were identified. At the opposite, the bacteria had no impact on Ag2S. These results suggest that microorganisms participate in the sulfidation of Ag-NPs in aerobic systems such as unsaturated soils, and thus affect the bioavailability of Ag. It is important to take these transformations into account during exposure experiments, since they drastically change the exposure conditions. Finally, the secretome of B. subtilis might be used for the green synthesis of Ag-Ag2S core-shell nanoparticles.

Silver Recovery from Laundry Washwater: The Role of Detergent Chemistry

The use of silver nanoparticles as an antimicrobial agent on textiles is rising. Ag leaching during laundry and its subsequent discharge in the environment pose ecotoxicological risks. Removing Ag from laundry washwater is therefore an environmental necessity, but its recovery also leads to environmental sustainability. Low Ag concentration, competition from other cations (such as Ca2+, Mg2+, and Na+), and complexity of the detergent matrix make the recovery process challenging. The present study utilizes a thiol-group functionalized ion-exchange resin in a fixed-bed column to remove Ag from laundry washwater and recover it as Ag2S nanoparticles or high-purity powder. The role of each detergent component in affecting Ag speciation and the resin performance has been analyzed. Builders and bleaching agents are reported to negatively impact the resin performance. pH and cocationic species (Ca2+) concentration are reported to be critical parameters for the successful recovery scheme. The work demonstrates a c...

Silver Nanoparticles and Wheat Roots: A Complex Interplay

Agricultural soils are major sinks of silver nanoparticles in the environment, and crops are directly exposed to these emerging contaminants. A clear picture of their chemical transformations, uptake and transport mechanisms, and phytotoxic impacts is still lacking. In this work, wheat plants were exposed to pristine metallic (Ag-NPs) and sulfidized (Ag2S-NPs) silver nanoparticles and ionic Ag. Data on Ag distribution and speciation, phytotoxicity markers, and gene expression were studied. A multi-technique and multi-scale approach was applied, combining innovating tools at both the laboratory and synchrotron. Various chemical transformations were observed on the epidermis and inside roots, even for Ag2S-NPs, leading to an exposure to multiple Ag forms, which likely evolve over time. Genes involved in various functions including oxidative stress, defense against pathogens, and metal homeostasis were impacted in different ways depending upon the Ag source. This study illustrates the complexity of the toxicity pattern for plants exposed to Ag-NPs, the necessity of monitoring several markers to accurately evaluate the toxicity, and the interest of interpreting the toxicity pattern in light of the distribution and speciation of Ag.

Uptake and Distribution of Silver in the Aquatic Plant Landoltia punctata (Duckweed) Exposed to Silver and Silver Sulfide Nanoparticles.

Aquatic ecosystems are expected to receive Ag0 and Ag2S nanoparticles (NPs) through anthropogenic waste streams. The speciation of silver in Ag-NPs affects their fate in ecosystems, but its influence on interactions with aquatic plants is still unclear. Here, the Ag speciation and distribution was measured in an aquatic plant, duckweed (Landoltia punctata), exposed to Ag0 or Ag2S NPs, or to AgNO3. The silver distribution in duckweed roots was visualized using synchrotron-based micro X-ray fluorescence (XRF) mapping and Ag speciation was determined using extended X-ray absorption fine structure (EXAFS) spectroscopy. Duckweed exposed to Ag2S-NPs or Ag0-NPs accumulated similar Ag concentrations despite an order of magnitude smaller dissolved Ag fraction measured in the exposure medium for Ag2S-NPs compared to Ag0-NPs. By 24 h after exposure, all three forms of silver had accumulated on and partially in the roots regardless of the form of Ag exposed to the plants. Once associated with duckweed tissue, Ag0-NPs had transformed primarily into silver sulfide and silver thiol species. This suggests that plant defenses were active within or at the root surface. The Ag2S-NPs remained as Ag2S, while AgNO3 exposure led to Ag0 and sulfur-associated Ag species in plant tissue. Thus, regardless of initial speciation, Ag was readily available to duckweed.