Pristine AgNPs Research Articles

Multivalent Weak Protections Ultimately Enable Customizable DNA Grafting on Pristine Ag Colloids for Nanoplasmonics

Silver nanoparticles (AgNPs) have superior plasmonic properties surpassing other metals. However, a long‐standing difficulty in valence/density‐tunable DNA grafting of AgNPs disfavors their use in DNA‐directed nanoplasmonics. Herein a close‐to‐ideal surface protection of pristine AgNPs against various notorious stability issues of Ag is achieved based on multidentate weak nucleobase bindings of non‐programming FSDNA (fish sperm DNA). This further allows grafting of thiolated DNA with tunable valence/density on AgNPs. The end‐on format of the thiolated DNA grafts and the very thin FSDNA layer benefit DNA hybridization and plasmon coupling, respectively. Significantly promoted optical coupling and Raman enhancing are achieved. The compatibility of FSDNA‐capped AgNPs with Au enables DNA‐bonded symmetry‐broken Au‐Ag heterodimers with strong near‐field coupling and an easily seen Fano‐induced feature. Our work provides a treasured freedom of using AgNPs in DNA‐programmed, better‐behaving plasmonic devices.

Toxicokinetics of silver and silver sulfide nanoparticles in Chironomus riparius under different exposure routes

Engineered nanoparticles released into surface water may accumulate in sediments, potentially threatening benthic organisms. This study determined the toxicokinetics in Chironomus riparius of Ag from pristine silver nanoparticles (Ag NPs), a simulating aged Ag NP form (Ag2S NPs), and AgNO3 as an ionic control. Chironomid larvae were exposed to these Ag forms through water, sediment, or food. The potential transfer of Ag from larvae to adult midges was also evaluated. Results revealed higher Ag uptake by C. riparius upon exposure to Ag2S NPs, while larvae exposed to pristine Ag NPs and AgNO3 generally presented similar uptake kinetics. Uptake patterns of the different Ag forms were generally similar in the tests with water or sediment exposures, suggesting that uptake from water was the most important route of Ag uptake in both experiments. For the sediment bioaccumulation test, uptake was likely a combination of water uptake and sediment particles ingestion. Ag uptake via food exposure was only significant for Ag2S NPs. Ag transfer to the terrestrial compartment was low. In our environmentally relevant exposure scenario, chironomid larvae accumulated relatively high Ag concentrations and elimination was extremely low in some cases. These results suggest that bioaccumulation of Ag in its nanoparticulate and/or ionic form may occur in the environment, raising concerns regarding chronic exposure and trophic transfer. This is the first study determining the toxicokinetics of NPs in Chironomus, providing important information for understanding chironomid exposure to NPs and their potential interactions in the environment.

The effect of sulfidation and soil type on the uptake of silver nanoparticles in annelid Enchytraeus crypticus

Hazard assessment of silver nanoparticles is crucial as their presence in agricultural land is increasing through sewage sludge application. This study compared the uptake and elimination kinetics in the annelid Enchytraeus crypticus of AgNPs with different core sizes and coatings in Lufa 2.2 soil, and of Ag2S NPs (simulating aged AgNPs) in three different soils. For both experiments, AgNO3 was used as ionic control. E. crypticus was exposed to soil spiked at 10 μg Ag g−1 dry soil for 14 days and then transferred to clean soil for a 14-day elimination phase. The uptake rate constants were similar for 3–8 nm and 60 nm AgNPs and AgNO3, but significantly different between 3 and 8 nm and 50 nm AgNPs. The uptake kinetics of Ag from Ag2S NPs did not significantly differ compared to pristine AgNPs. Therefore, Ag bioavailability was influenced by AgNP form and characteristics. Uptake and elimination rate constants of both Ag forms (AgNO3 and Ag2S NPs) significantly differed between different test soils (Lufa 2.2, Dorset, and Woburn). For AgNO3, significantly higher uptake and elimination rate constants were found in the Dorset soil compared to the other soils, while for Ag2S NPs this soil showed the lowest uptake and elimination rate constants. Therefore, not only the form and characteristics but also soil properties affect the bioavailability and uptake of Ag nanoparticles.

Garlic capped silver nanoparticles for rapid detection of cholesterol

A fluorescent biosensor based on garlic (Allium sativum L.) capped Ag nanoparticles (G-Ag NPs) has been synthesized for cholesterol detection. Pristine Ag NPs and G-Ag NPs were synthesized through the chemical reduction process. The effect of different capping agents such as 3-aminopropyltriethoxysilane (APTS), glutathione, 8-hydroxyquinoline, garlic/APTS, garlic/glutathione, and garlic/8-hydroxyquinoline on Ag NPs was evaluated. These NPs were characterized using Fourier transform infrared (FTIR), energy-dispersive X-ray (EDX), X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HRTEM), X-Ray diffraction (XRD), UV–visible spectra, and Zeta potential. The HRTEM micrographs illustrated that Ag NPs with particles size ranging from 2.98 to 14.34 nm were aggregated. G-Ag NPs images showed uniformly distributed spherical particles with particles size from 4.52 to 12.8 nm. The reduction in the plasmonic bands of Ag NPs and G-Ag NPs occurred by 96.4% and 11.7%, respectively after 12 months. The developed sensor for cholesterol based on the fluorescence enhancement had a linear response in a concentration range of 0.4–5.17 mM with a sensitivity of 4.36 Mm−1 and a limit of detection of 0.186 mM. The high selectivity toward cholesterol in presence of different interferes such as glucose, cysteine, glycine, urea, sucrose, nickel, and copper, and their mixture was evaluated. The applicability of this developed sensor for real serum samples was detected with a recovery percentage from 99.1 to 101.3%. Repeatability and reproducibility experiments displayed relative standard deviations (RSD) of 0.88% and 0.62%, respectively.

Controlling silver release from antibacterial surface coatings on stainless steel for biofouling control

This study focuses on the in-situ nucleation of silver nanoparticles (AgNPs) on stainless steel (SS) to provide a localized antibacterial action for biofouling control during space missions. Since AgNPs rapidly dissolve in water, partial passivation of AgNPs was provided to slow down silver release and extend the lifetime of the antibacterial coating. Two different passivation approaches, based on the formation of low solubility silver sulfide (Ag2S) or silver bromide (AgBr) shells, were compared to identify the optimal passivation for biofouling control. Highest bacterial inactivation (up to 75%) occurred with sulfidized AgNPs as opposed to bromidized (up to 50%) NPs. The optimal passivation treatment for biofouling control was found at 10−5 M Na2S (for Ag2S) and 10−3 M NaBr (for AgBr) concentrations. Scanning Electron Microscopy (SEM) analyses confirmed the presence of AgNPs on AgBr and Ag2S-coated samples. Further investigation revealed that compared to pristine AgNPs, Ag release from both sulfidized and bromidized NPs was significantly lower (16% vs 6% or less). Overall, both sulfidized and bromidized AgNPs were effective at controlling biofilm formation; however, sulfidized NPs exhibited the maximum antibacterial activity, making it the preferable passivation strategy for AgNPs on SS surfaces.

Potential application of Au core labeling for tracking Ag nanoparticles in the aquatic and biological system

The entering of silver nanoparticles (Ag NPs) in natural environments constantly increases due to their widespread production and application. While the environmental behavior, impacts, and fate of Ag NPs were critically assessed, the main challenge represents continuous tracking and quantification of Ag NPs in environmental and biological matrices. A group of labeled Ag NPs with gold cores (Au@Ag NPs) was developed for distinguishing between pristine Ag NPs and their other forms, and we comprehensively compared their physicochemical properties, environmental behavior, and biological effects with unlabeled Ag NPs. The electron transfer process from the Au core to the Ag shell gradually decreased with the increase of Ag shell thickness, then the inhibition of Ag+ release induced by the Au core was gradually alleviated, but the generation of superoxide radicals was intensified sharply. Then, the effect of the Au core on the dissolution capacity and free radicals' generation significantly altered the biological toxicity of Ag NPs, and the influence degree was related to the test organism's species. Nevertheless, the Au core retained the surface properties of Ag NPs, leading to the uptake of Au@Ag NPs, entirely consistent with the behavior of unlabeled Ag NPs. These findings confirmed that Au core labeling provides new opportunities for tracking Ag NPs in environmental and biological systems, and the exposure conditions and test organisms should be carefully assessed before employing the Au core labeling technology.

Polystyrene microplastics sunlight-induce oxidative dissolution, chemical transformation and toxicity enhancement of silver nanoparticles

The coexistence of microplastics (MPs) and nanomaterials has been increasingly studied, but the influence of MPs on the chemical transformation of nanomaterials remains unclear. Herein, it was demonstrated that polystyrene (PS) MPs induce the oxidative dissolution, transformation and toxicity of silver nanoparticles (Ag NPs) under simulated sunlight irradiation. The PS MPs induced the oxidation dissolution of pristine Ag NPs by 1O2, OH and/or acid release and simultaneously reduced the released Ag+ to secondary Ag NPs by O2−. The sizes, functional groups and ageing status of the PS MPs and pH characterized secondary Ag NPs formation. Secondary formation of Ag NPs induced by PS MPs also occurred in realistic water and was governed by dissolved organic matter (DOM) and Cl−, rather than SO42− or CO32−. Moreover, PS MPs remarkably promoted Ag+ release, altered the Ag+:Ag0 ratio, and presented vehicle effects on Ag+ toxicity to Daphnia magna. The concentration addition model demonstrated that the ion-related toxicity of Ag NPs was significantly increased by PS MPs. Therefore, PS MPs induced the oxidative dissolution, transformation and toxicity enhancement of Ag NPs under sunlight irradiation, and accordingly, the coexistence of PS MPs and Ag NPs in freshwater environments should be seriously considered.

Silver Nanoprism for Selective and Sensitive Detection of Hg+2 Ions.

In this article, we propose high-performance colorimetric detection of Hg+2 using silver nanoprisms. The spherical and triangular AgNPs were synthesized using varied concentration of NaBH4. Pristine AgNPs without any further modification were used for the detection of various metal ions including Hg2+, Pb2+, Cl-, Cd2+, Co2+, Cu2+, Ba2+, Pb2+, Cr3+, Cr₂O2-7 , Fe2+, Fe3+ etc. AgNPs were not only selective in detecting the ions of Cl- and Hg+2 ions but also highly sensitive. Minimum detection limit was observed to be as low as 10-7 ppm for both Hg+2 and Cl-. Water samples collected from various locations detected for the presence of various heavy metals. Silver nanoprisms owing to their surface plasmon resonance exhibit highly selective tendency towards detection against Hg+2.

Insights into the lower trophic transfer of silver ions than silver containing nanoparticles along an aquatic food chain

Silver nanoparticles (AgNPs) released into the environment are subject to environmental transformation processes before accumulating in aquatic organisms and transferring along the food chain. Lack of understanding on how environmental transformation affects trophic transfer of AgNPs hinders accurate prediction of the environmental risks of these widely present nanomaterials. Here we discover that pristine AgNPs as well as their sulfidation products (Ag2S-NPs) and dissolution products (Ag+) tend to be accumulated in Daphnia magna and subsequently transferred to zebrafish. In D. magna, Ag+ exhibits the highest bioaccumulation potential whereas Ag2S-NPs show the lowest bioaccumulation. Surprisingly, the biomagnification factor of Ag+ along the D. magna-zebrafish food chain appears to be significantly lower relative to AgNPs and Ag2S-NPs, likely due to the limited release of Ag from D. magna to zebrafish during digestion. Moreover, AgNPs and their transformation products mainly accumulate in the internal organs, particularly intestine, of zebrafish. Adsorption of AgNPs on the surface of the intestinal cell membrane mitigates depuration of AgNPs and, at least in part, leads to the larger biomagnification factor of AgNPs, relative to their transformation products. This research highlights the necessity of considering environmental transformation processes of nanomaterials in assessing their bioavailability and risk.

Toxicokinetics of silver nanoparticles in the mealworm Tenebrio molitor exposed via soil or food.

Silver nanoparticles (AgNPs) may reach the soil compartment via sewage sludge or nanoagrochemical applications. Understanding how NPs interact with biological systems is crucial for an accurate hazard assessment. Therefore, this study aimed at determining the Ag toxicokinetics in the mealworm Tenebrio molitor, exposed via Lufa 2.2 soil or via food to different Ag forms (uncoated 50nm AgNPs, paraffin coated 3-8nm and PVP-stabilised 60nm, Ag2S NPs 20nm, and ionic Ag). Mealworms were exposed for 21days followed by a 21-day elimination phase (clean soil/food). A one-compartment kinetics model with inert fraction (simulating a storage compartment, where detoxified forms are located) was used to describe Ag accumulation. Fully understanding the uptake route in mealworms is difficult. For that reason several approaches were used, showing that food, soil and pore water all are valid uptake routes, but with different importance. Silver taken up from soil pore water or from soil showed to be related to Ag dissolution in soil pore water. In general, the uptake and elimination rate constants were similar for 3-8nm and 60nm AgNPs and for AgNO3, but significantly different for the uncoated 50nm AgNPs. Upon food exposure, uptake rate constants were similar for 50nm AgNPs and AgNO3, while those for 60nm and 3-8nm AgNPs and for Ag2S NPs also grouped together. NP exposure in soil appeared more difficult to characterize, with different patterns obtained for the different NPs. But it was evident that upon soil or food exposure, particle characteristics highly affected Ag bioavailability and bioaccumulation. Although Ag2S NPs were taken up, their elimination was faster than for other Ag forms, showing the lowest inert fraction. The significantly different elimination rate constants suggest that the mechanism of elimination may not be the same for different AgNPs either.

Transport of environmental natural organic matter coated silver nanoparticle across cell membrane based on membrane etching treatment and inhibitors

Environmental natural organic matters (NOMs) have great effects on the physicochemical properties of engineering nanoparticles, which may impact the transport of nanoparticles across plasma membrane and the cytotoxicity. Therefore, the kinetics, uptake pathway and mass of transporting into A549 cell membrane of silver nanoparticles (AgNPs) coated with citric acid (CA), tartaric acid (TA) and fulvic acid (FA) were investigated, respectively. CA, FA and TA enhanced the colloidal stability of AgNPs in culture medium and have greatly changed the surface plasmon resonance spectrum of AgNPs due to the absorption of CA, FA and TA on surface of AgNPs. Internalizing model showed that velocity of CA-, TA- and FA-nAg transporting into A549 cell were 5.82-, 1.69- and 0.29-fold higher than those of the control group, respectively. Intracellular mass of Ag was dependent on mass of AgNPs delivered to cell from suspension, which obeyed Logistic model and was affected by NOMs that CA- and TA-nAg showed a large promotion on intracellular mass of Ag. The lipid raft/caveolae-mediated endocytosis (LME) of A549 cell uptake of AgNPs were susceptible to CA, TA and FA that uptake of CA-, TA- and FA-nAg showed lower degree of dependent on LME than that of the control (uncoated AgNPs). Actin-involved uptake pathway and macropinocytosis would have less contribution to uptake of FA-nAg. Overall, transmembrane transport of NOMs-coated AgNPs differs greatly from that of the pristine AgNPs.

Epigenetic effects induced by silver nanoparticles in Caenorhabditis elegans after multigenerational exposure

Multigenerational effects of silver nanoparticles (Ag-NPs) on reproduction of the soil nematode Caenorhabditis elegans have been observed previously. However, mechanisms of this reproductive sensitivity are unknown. Here we examine whether epigenetic changes occur as a result of multigenerational exposure to Ag-NPs and whether such modifications can be inherited by unexposed generations. Changes at histone methylation markers, histone 3 lysine 4 dimethylation (H3K4me2) and histone 3 lysine 9 trimethylation (H3K9me3), known to affect reproduction, as well as changes in the expression of the genes encoding demethylases and methyltransferases associated with the selected markers, were investigated. We exposed C. elegans at EC30 to AgNO3, pristine Ag-NPs, and its environmentally transformed product, sulfidized Ag-NPs (sAg-NPs). Histone methylation levels at H3K4me2 increase in response to pristine Ag-NP exposure and did not recover after rescue from the exposure, suggesting transgenerational inheritance. Compared to pristine Ag-NPs, exposure to transformed sAg-NPs significantly decreased H3K4me2 and H3K9me3 levels. These changes in the histone methylation were also supported by expression of spr-5 and jmjd-2 (H3K4me2 and H3K9me3 demethylases, respectively) and set-30 (H3K4me2 methyltransferase). Our study demonstrates that multigenerational exposure to Ag-NPs induces epigenetic changes that are inherited by unexposed offspring. However, environmental transformations of Ag-NPs may also reduce toxicity via epigenetic mechanisms, such as changes at histone methylation.

The Food Matrix and the Gastrointestinal Fluids Alter the Features of Silver Nanoparticles.

Silver nanoparticles (AgNPs) are used in the agri-food sector, which can lead to their ingestion. Their interaction with food and their passage through the gastrointestinal tract can alter their properties and influence their fate upon ingestion. Therefore, this study aims at developing an in vitro method to follow the fate of AgNPs in the gastrointestinal tract. After incorporation of AgNPs into a standardized food matrix, a precolonic digestion is simulated and AgNPs are characterized by different techniques. The presence of food influences the AgNPs properties by forming a corona around nanoparticles. Even if the salivary step does not impact significantly the AgNPs, the pH decrease and the digestive enzymes induce the agglomeration of AgNPs during the gastric phase, while the addition of intestinal fluids disintegrates these clusters. AgNPs can thus reach the intestinal cells under nanometric form, although the presence of food and gastrointestinal fluids modifies their properties compared to pristine AgNPs. They can form a corona around the nanoparticles and act as colloidal stabilizer, which can impact the interaction of AgNPs with intestinal epithelium. This study demonstrates the importance of taking the fate of AgNPs in the gastrointestinal tract into account to perform an accurate risk assessment of nanomaterials.

Comparative biokinetics of pristine and sulfidized Ag nanoparticles in two arthropod species exposed to different field soils

Ag bioaccumulation upon exposure to pristine Ag NPs is of bigger concern in acidic sandy soils, but not in case of the environmentally relevant sulfidized Ag NPs, which do not bioaccumulate in P. scaber or F. candida.

Impact of in vitro digestion on gastrointestinal fate and uptake of silver nanoparticles with different surface modifications

Nanomaterials, especially silver nanoparticles (AgNPs), are used in a broad range of products owing to their antimicrobial potential. Oral ingestion is considered as a main exposure route to AgNPs. This study aimed to investigate the impact of the biochemical conditions within the human digestive tract on the intestinal fate of AgNPs across an intestinal in vitro model of differentiated Caco-2/HT29-MTX cells. The co-culture model was exposed to different concentrations (250–2500 µg/L) of pristine and in vitro digested (IVD) AgNPs and silver nitrate for 24 h. ICP-MS and spICP-MS measurements were performed for quantification of total Ag and AgNPs. The AgNPs size distribution, dissolution, and particle concentration (mass- and number-based) were characterized in the cell fraction and in the apical and basolateral compartments of the monolayer cultures. A significant fraction of the AgNPs dissolved (86–92% and 48–70%) during the digestion. Cellular exposure to increasing concentrations of pristine or IVD AgNPs resulted in a concentration dependent increase of total Ag and AgNPs content in the cellular fractions. The cellular concentrations were significantly lower following exposure to IVD AgNPs compared to the pristine AgNPs. Transport of silver as either total Ag or AgNPs was limited (<0.1%) following exposure to pristine and IVD AgNPs. We conclude that the surface chemistry of AgNPs and their digestion influence their dissolution properties, uptake/association with the Caco-2/HT29-MTX monolayer. This highlights the need to take in vitro digestion into account when studying nanoparticle toxicokinetics and toxicodynamics in cellular in vitro model systems.

Exposure to a nanosilver-enabled consumer product results in similar accumulation and toxicity of silver nanoparticles in the marine mussel Mytilus galloprovincialis

The incorporation of silver nanoparticles (AgNPs) in commercial products is increasing rapidly. The consequent release of AgNPs into domestic and industrial wastewater raises environmental concerns due to their anti-microbial properties and toxicity to non-target aquatic organisms. The aim of the present study was to investigate the effects of nanArgen™ (Nanotek S.A.), a AgNP-enabled consumer product, in the marine bivalve Mytilus galloprovincialis. Two environmentally relevant concentrations of nanArgen™ (1 and 10 μg/L) were tested in vivo for 96 h, and Ag was quantified in mussel soft tissue and natural seawater (NSW). nanArgen™ suspensions were characterized via TEM, SEM, EDS, DLS, and UV–vis optical analysis. Several molecular and biochemical responses were investigated in exposed mussels: lysosomal membrane stability by Neutral Red Retention Time (NRRT) assay; micronucleus (MN) frequency in hemocytes; metallothionein (MT) protein content and gene expression (mt10 and mt20); catalase (CAT) and glutathione-S-transferase (GST) activities; malondialdehyde (MDA) accumulation in digestive glands; and efflux activity of ATP-binding cassette transport proteins (ABC) in gill biopsies. SEM, TEM and DLS analyses confirmed the presence of well-defined AgNPs in nanArgen™ which were roughly spherical with an average particle size of approx. 30 ± 10 nm. DLS analysis revealed the formation of AgNP aggregates in nanArgen™ suspension in NSW (Z-average of 547.80 ± 90.23 nm; PDI of 0.044). A significant concentration-dependent accumulation of Ag was found in mussels’ whole soft tissue in agreement with a concentration-dependent decrease in NRRT and an increase of MN frequency in hemocytes and GST activities in digestive glands. A significant increase in MDA levels and MT via both molecular and biochemical tests, were also observed but only at the highest nanArgen™ concentration (10 μg/L). No changes were observed in CAT activities. ABC efflux activities in gill biopsies showed a significant decrease (p < 0.05) only at the lowest concentration (1 μg/L). On such basis, nanArgen™ is shown to be able to induce toxicity and Ag accumulation in marine mussels similarly to AgNPs and in short-term exposure conditions at environmentally relevant concentrations. AgNP-enabled products, instead of pristine AgNPs, should be the focus of future ecotoxicity studies in order to address any risks associated to their widespread use, disposal and uncontrolled release into the aquatic environment for non target species.

Green-synthesis of Ag nanoparticles and its composite with PVA nanofiber as a promising Cd2+ adsorbent and antimicrobial agent

Simple and eco-friendly biosynthesis of Silver Nanoparticle (Ag-NPs) and Silver Nanoparticle supported by Polyvinyl Alcohol and then crosslinked by Glutaraldehyde to form Ag-NPs/PVA-NF using Pomegranate peel extract as the reducing agent. The shape morphologies of the fabricated nanoparticles were characterized by field emission scanning electron microscopy (FE-SEM), crystal structure was investigated by X-ray diffraction (XRD) and nitrogen adsorption/desorption isotherm using for detecting the surface area of the prepared samples. The functionalized groups of prepared samples have been confirmed using Fourier-transform infrared spectroscopy (FTIR). The TEM analysis demonstrate ultrafine nanoparticles with the average particles size ranges about 7–13 nm. To achieve high adsorption capacity of Cd+2 using neat Ag-NPs and Ag-NPs/PVA-NF, the adsorption process was optimized and investigated under various conditions. It was found that the optimum pH for Cd2+ adsorption was 8 and the equilibrium was reached in 240 min. The Ag-NPs/PVA-NF standalone achieved excellent removal performance with a maximum adsorption efficiency of (40.65 mg/g) compared to pristine Ag-NPs (28.4 mg/g). The adsorption isotherm fitted well to both Langmuir and Freundlich isotherms. The adsorption mechanism was investigated. The positive values of ΔHo indicated that the Cd2+ adsorption on the Ag-NPs and Ag-NPs/PVA-NF were endothermic in nature. Moreover, the antibacterial activity of Ag-NPs and Ag-NPs/PVA-NF were examined against different species of Gram-Positive and Gram-Negative bacteria revealing significant response for both types. Interestingly, the solution of Ag-NPs/PVA-NF- Cd+2 after adsorption show durable antimicrobial activities. Overall, this proposed route opens new avenue to synthesize different kind of Ag-NPs via facile, green and economic strategy for multifunctional environmental applications.

Comparative multi-generation study on long-term effects of pristine and wastewater-borne silver and titanium dioxide nanoparticles on key lifecycle parameters in Daphnia magna

The rising production volume of engineered nanoparticles (NPs) leads to an increasing risk of environmental pollution. After passing sewage treatment plants (STPs), a significant concentration of NPs may end up in the aquatic environment where NPs can accumulate in the aquatic food chain and may cause harmful effects on aquatic organisms. However, when passing STPs some NPs such as silver nanoparticles (AgNPs) are transformed and enter the aquatic environment mostly as sulphide species with lower bioavailability and reduced toxicity compared to pristine NPs. For the environmental risk assessment of NPs, it is thus crucial to consider the transformation processes of nanomaterials during STP processes. For other NPs, such as titanium dioxide nanoparticles (TiO2NPs), knowledge about the acute and chronic toxicity of NPs from STP effluents on aquatic organisms is still missing. Chronic studies, such as the Daphnia reproduction test following OECD TG 211, cover a period of only 21 days and hence allow only to evaluate the reproduction performance of a single generation. Multi-generation studies provide a more realistic exposure scenario and offer the opportunity to identify transgenerational effects which may possess a significant impact on the population dynamic. Hence, the aim of this study was to assess the impact of wastewater-borne AgNPs and TiO2NPs on the aquatic invertebrate Daphnia magna in a multi-generation approach covering six generations. The effects of long-term exposure to pristine AgNPs (NM-300K; 14.9 ± 2.4 nm) and TiO2 NPs (NM-105; 21 ± 9 nm) on the reproductive success (number of offspring), mortality, time to first brood and body size of adult Daphnia were measured and compared to those caused by wastewater-borne AgNP and TiO2NPs. In all six generations, the exposure to environmentally relevant concentrations (determined by inductively coupled plasma mass spectrometry, ICP-MS) of pristine AgNPs caused a significant reduction in the mean number of offspring compared to the control. However, wastewater-borne AgNPs had no effects on reproduction in any generation. STEM analysis shows, that the AgNPs particles were transformed to Ag2S while passing the STP. No effects could be detected following exposure to environmentally relevant concentrations (determined by inductively coupled plasma optical emission spectrometry, ICP-OES) of pristine TiO2NPs and wastewater-borne TiO2NPs. The present study is the first multi-generation study on long-term effects of pristine and wastewater-borne nanoparticles on Daphnia. No transgenerational effects of wastewater-borne AgNPs nor TiO2NPs were observed. The results confirm that realistic exposure conditions are required in order to allow for a reliable environmental risk assessment of NPs.

Stability of silver nanoparticle sulfidation products

The adoption of silver nanoparticles in consumer goods has raised concerns about the potential environmental harm of their widespread use. We studied chemical transformations that Ag NPs may undergo as they pass through sulfide-rich conditions common in waste water treatment plants (WWTPs), which may limit the release of Ag+ from Ag NPs due to the formation of low-solubility silver sulfide (Ag2S). However, it is uncertain whether sulfidation is complete and if sulfidized Ag NPs continue to release Ag+. To address these uncertainties, we monitored the reaction of Ag NPs with various levels of sulfide with an ion selective electrode and UV/visible spectrophotometry over the course of two months. We characterized the products of the sulfidation reactions with a purge-and-trap acid volatile sulfide (AVS) analysis, which served as a measure of the stability of the sulfidized products because sulfide would be readily lost to oxidation unless it is stabilized as Ag2S. The Ag NP surface plasmon resonance (SPR) absorbance peak was initially diminished and then returned over the course of several days after reaction with limited amounts of sulfide, suggesting a dynamic system that may retain some characteristics of the pristine Ag NPs. However, ICP-MS analysis of sulfidized Ag NP suspensions over a two-month period demonstrates that sulfidation limits the release of Ag+ ions from nanosilver that pass through a WWTP, even when sulfide concentrations are limited relative to silver.

Effects of ionic strength on physicochemical properties and toxicity of silver nanoparticles

In the environment, silver nanoparticles (AgNPs) undergo a number of potential transformations, such as aggregation, dissolution, and redox reactions. However, the transformation in ionic strength condition, as well as their related toxicity was not quite clear, especially in the in vivo system. In the present study, we comprehensively evaluated three different characteristics (ddH2O, EPA water and K+ medium (KM)) mediated changes in the physical morphology of AgNPs and the alteration of the toxicity to Caenorhabditis elegans (C. elegans). Our results showed besides the changes of AgNPs behavior such as the transformation of morphological, with the transmission electron microscopy we found for the first time that smaller nanoparticles (<5 nm) appeared around the pristine AgNPs after incubation in EPA or KM for 5 days. Together with these changes, the toxicity of AgNPs to C. elegans changed significantly, showing that a higher ionic strength medium resulted in greater toxicity to C. elegans, as measured by germ cell apoptosis, brood size and lifespan. More importantly, our results indicated that the higher toxicity of AgNPs to C. elegans reproduction was probably related to the appearance of the smaller-size AgNPs in higher ionic strength media. These findings highlight that toxicity assessments for the release of nanomaterial to the environment need to be improved to assess environmental safety more accurately.