Μg Ag Research Articles

Comparison of toxicity of silver nanomaterials and silver nitrate on developing zebrafish embryos: Bioavailability, osmoregulatory and oxidative stress

The mechanisms of toxicity of engineered nanomaterials (ENMs) to the early life stages of freshwater fish, and the relative hazard compared to dissolved metals, is only partially understood. In the present study, zebrafish (Danio rerio) embryos were exposed to lethal concentrations of silver nitrate (AgNO3) or silver (Ag) ENMs (primary size 42.5 ± 10.2 nm). The 96 h-LC50 for AgNO3 was 32.8 ± 0.72 μg Ag L−1 (mean ± 95% CI) compared to 6.5 ± 0.4 mg L−1 of the whole material for Ag ENMs; with the ENMs being orders of magnitude less toxic than the metal salt. The EC50 for hatching success was 30.5 ± 1.4 μg Ag L−1 and 6.04 ± 0.4 mg L−1 for AgNO3 and Ag ENMs, respectively. Further sub-lethal exposures were performed with the estimated LC10 concentrations for both AgNO3 or Ag ENMs over 96 h, where about 3.7% of the total Ag as AgNO3 was internalised, as measured by Ag accumulation in the dechorionated embryos. However, for the ENM exposures, nearly all (99.8%) of the total Ag was associated with chorion; indicating the chorion as an effective barrier to protect the embryo in the short term. Calcium (Ca2+) and sodium (Na+) depletion was induced in embryos by both forms of Ag, but hyponatremia was more pronounced in the nano form. Total glutathione (tGSH) levels declined in embryos exposed to both Ag forms, but a superior depletion occurred with the nano form. Nevertheless, oxidative stress was mild as superoxide dismutase (SOD) activity stayed uniform and the sodium pump (Na+/K+-ATPase) activity had no appreciable inhibition compared to the control. In conclusion, AgNO3 was more toxic to the early life stage zebrafish than the Ag ENMs, still differences were found in the exposure and toxic mechanisms of both Ag forms.

Toxicokinetics and bioaccumulation of silver sulfide nanoparticles in benthic invertebrates in an indoor stream mesocosm

Mesocosms allow the simulation of environmentally relevant conditions and can be used to establish more realistic scenarios of organism exposure to nanoparticles. An indoor mesocosm experiment simulating an aquatic stream ecosystem was conducted to assess the toxicokinetics and bioaccumulation of silver sulfide nanoparticles (Ag2S NPs) and AgNO3 in the freshwater invertebrates Girardia tigrina, Physa acuta and Chironomus riparius, and determine if previous single-species tests can predict bioaccumulation in the mesocosm. Water was daily spiked at 10 μg Ag L−1. Ag concentrations in water and sediment reached values of 13.4 μg Ag L−1 and 0.30 μg Ag g−1 in the Ag2S NP exposure, and 12.8 μg Ag L−1 and 0.20 μg Ag g−1 in the AgNO3. Silver was bioaccumulated by the species from both treatments, but with approximately 1.5, 3 and 11 times higher body Ag concentrations in AgNO3 compared to Ag2S NP exposures in snails, chironomids and planarians, respectively. In the Ag2S NP exposures, the observed uptake was probably of the particulate form. This demonstrates that this more environmentally relevant Ag nanoform may be bioavailable for uptake by benthic organisms. Interspecies interactions likely occurred, namely predation (planarians fed on chironomids and snails), which somehow influenced Ag uptake/bioaccumulation, possibly by altering organisms´ foraging behaviour. Higher Ag uptake rate constants were determined for AgNO3 (0.64, 80.4 and 1.12 Lwater g−1organism day−1) than for Ag2S NPs (0.05, 2.65 and 0.32 Lwater g−1organism day−1) for planarians, snails and chironomids, respectively. Biomagnification under environmentally realistic exposure seemed to be low, although it was likely to occur in the food chain P. acuta to G. tigrina exposed to AgNO3. Single-species tests generally could not reliably predict Ag bioaccumulation in the more complex mesocosm scenario. This study provides methodologies/data to better understand exposure, toxicokinetics and bioaccumulation of Ag in complex systems, reinforcing the need to use mesocosm studies to improve the risk assessment of environmental contaminants, specifically NPs, in aquatic environments.

Toxicokinetics of Ag from Ag2S NP exposure in Tenebrio molitor and Porcellio scaber: Comparing single-species tests to indoor mesocosm experiments

Determining the potential for accumulation of Ag from Ag2S NPs as an environmentally relevant form of AgNPs in different terrestrial organisms is an essential component of a realistic risk assessment of AgNP emissions to soils. The objectives of this study were first to determine the uptake kinetics of Ag in mealworms (Tenebrio molitor) and woodlice (Porcellio scaber) exposed to Ag2S NPs in a mesocosm test, and second, to check if the obtained toxicokinetics could be predicted by single-species bioaccumulation tests. In the mesocosms, mealworms and woodlice were exposed together with plants and earthworms in soil columns spiked with 10 μg Ag g−1 dry soil as Ag2S NPs or AgNO3. The total Ag concentrations in the biota were measured after 7, 14, and 28 days of exposure. A one-compartment model was used to calculate the Ag uptake and elimination rate constants. Ag from Ag2S NPs appeared to be taken up by the mealworms with significantly different uptake rate constants in the mesocosm compared to single-species tests (K1 = 0.056 and 1.66 g dry soil g−1 dry body weight day−1, respectively), and a significant difference was found for the Ag bioaccumulation factor (BAFk = 0.79 and 0.15 g dry soil g−1 dry body weight, respectively). Woodlice did not accumulate Ag from Ag2S NPs in both tests, but uptake from AgNO3 was significantly slower in mesocosm than in single-species tests (K1 = 0.037 and 0.26 g dry soil g−1 dry body weight day−1, respectively). Our results are of high significance because they show that single-species tests may not be a good predictor for the Ag uptake in mealworms and woodlice in exposure systems having greater levels of biological complexity. Nevertheless, single-species tests could be used as a fast screening approach to assess the potential of a substance to accumulate in biota before more complex tests are conducted.

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.

Metal transfer to sediments, invertebrates and fish following waterborne exposure to silver nitrate or silver sulfide nanoparticles in an indoor stream mesocosm

The fate of engineered nanomaterials in ecosystems is unclear. An aquatic stream mesocosm explored the fate and bioaccumulation of silver sulfide nanoparticles (Ag2S NPs) compared to silver nitrate (AgNO3). The aims were to determine the total Ag in water, sediment and biota, and to evaluate the bioavailable fractions of silver in the sediment using a serial extraction method. The total Ag in the water column from a nominal daily dose of 10 μg L−1 of Ag for the AgNO3 or Ag2S NP treatments reached a plateau of around 13 and 12 μg L−1, respectively, by the end of the study. Similarly, the sediment of both Ag-treatments reached ~380 μg Ag kg−1, and with most of it being acid-extractable/labile. The biota accumulated 4–59 μg Ag g−1 dw, depending on the type of Ag-treatment and organism. The oligochaete worm, Lumbriculus variegatus, accumulated Ag from the Ag2S exposure over time, which was similar to the AgNO3 treatment by the end of the experiment. The planarian, Girardia tigrina, and the chironomid larva, Chironomus riparius, showed much higher Ag concentrations than the oligochaete worms; and with a clearer time-dependent statistically significant Ag accumulation relative to the untreated controls. For the pulmonate snail, Physa acuta, bioaccumulation of Ag from AgNO3 and Ag2S NP exposures was observed, but was lower from the nano treatment. The AgNO3 exposure caused appreciable Ag accumulation in the water flea, Daphnia magna, but accumulation was higher in the Ag2S NP treatment (reaching 59 μg g−1 dw). In the rainbow trout, Oncorhynchus mykiss, AgNO3, but not Ag2S NPs, caused total Ag concentrations to increase in the tissues. Overall, the study showed transfer of total Ag from the water column to the sediment, and Ag bioaccumulation in the biota, with Ag from Ag2S NP exposure generally being less bioavailable than that from AgNO3.

Pollution- induced community tolerance framework - disc diffusion method to assess the impact of silver nanoparticles in soils: Potential relevance for risk assessment

The toxicity of silver nanoparticles (AgNPs) in soil bacterial communities (SBC) has been widely reported. However, the bacterial related endpoints have not been effectively considered in the environmental risk assessment (ERA) for nanomaterials. Thus, we aimed to study the long-term effects of AgNPs, or AgNO3 (counterpart), [5 μg (Ag) kg−1] on SBC: (1) at structural level (using denaturing gradient gel electrophoresis-DGGE) and, (2) in terms of bacterial induced tolerance (which is the foundation of the pollution-induced community tolerance - PICT) using a disc diffusion assay (0.1 μg, 1 μg or 10 μg of each silver form). After day-56 of exposure, the structure of SBC was affected by AgNPs and AgNO3, though still sharing 71.9% similarity with the non-exposed SBC. Also, the SBC homogeneity significantly decreased after exposure to silver, suggesting a possible tolerance effect. Regarding tolerance assays, AgNO3 was more effective in inhibiting the SBC growth than AgNPs, and both in a dose-dependent manner (10 μg > 1 μg > 0.1 μg). A second exposure revealed a decrease in tolerance of SBC to AgNO3. Also, a lower amount of AgNO3 is needed to change SBC tolerance. PICT analysis revealed that previous exposure to AgNPs did not increase tolerance-effect in SBC. Overall, AgNPs changes the SBC structure and tolerance, but does not increase the tolerance on a second exposure. Thus, this study highlights the usefulness of combined bacterial endpoints (DGGE, and PICT-disc diffusion tests) for potential inclusion in the ERA of AgNPs in soil ecosystems.

Concentrations and size distribution of TiO2 and Ag engineered particles in five wastewater treatment plants in the United States

The growing use of engineered particles (e.g., nanosized and pigment sized particles, 1 to 100 nm and 100 to 300 nm, respectively) in a variety of consumer products increases the likelihood of their release into the environment. Wastewater treatment plants (WWTPs) are important pathways of introduction of engineered particles to the aquatic systems. This study reports the concentrations, removal efficiencies, and particle size distributions of Ag and TiO2 engineered particles in five WWTPs in three states in the United States. The concentration of Ag engineered particles was quantified as the total Ag concentration, whereas the concentration of TiO2 engineered particles was quantified using mass-balance calculations and shifts in the elemental ratio of Ti/Nb above their natural background elemental ratio. Ratios of Ti/Nb in all WWTP influents, activated sludges, and effluents were 2–12 times higher (e.g., 519 to 3243) than the natural background Ti/Nb ratio (e.g., 267 ± 9), indicating that 49–92% of Ti originates from anthropogenic sources. The concentration of TiO2 engineered particles (in μg TiO2 L−1) in the influent, activated sludge, and effluent varied within the ranges of 70–670, 3570–6700, and 7–30, respectively. The concentration of Ag engineered particles (in μg Ag L−1) in the influent, activated sludge, and effluent varied within the ranges of 0.11–0.33, 1.45–1.65, and 0.01–0.04, respectively. The overall removal efficiency (e.g., effluent/influent concentrations) of TiO2 engineered particles (e.g., 90 to 96%) was higher than that for Ag engineered particles (e.g., 82 to 95%). Particles entering WWTPs are in the nanosized range for Ag (e.g., >99%) and a mixture of nanosized (e.g., 15 to 90%) and pigment sized particles (e.g., 10 to 85%) for TiO2. Nearly all Ag (>99%) and 55 to 100% of TiO2 particles discharged to surface water with WWTP effluent are within the nanosize range. This study provides evidence that TiO2 and Ag engineered nanomaterials enter aquatic systems with WWTP effluents, and that their concentrations are expected to increase with the increased applications of TiO2 and Ag engineered nanomaterials in consumer products.

Silver nanoparticles-clays nanocomposites as feed additives: Characterization of silver species released during in vitro digestions. Effects on silver retention in pigs

Two different clay nanocomposites, as sepiolite-Ag and kaolinite-Ag, are studied as carriers for silver nanoparticles (AgNPs) oral administration as antimicrobial agent in additives for animal feed. A three-step digestibility assay, corresponding to stomach, small and large intestine simulations, has been followed. Ultrafiltration and asymmetrical flow field-flow fractionation (AF4) coupled to UV–Vis absorption and ICPMS detectors have been used for size characterisation of the silver species released during the in vitro digestibility assays. Less than 1% of the total silver is released in the stomach simulation step, probably due to the formation of silver chloride on the nanocomposite surface. In the case of the intestine simulation, silver released increases and tends to form complexes with the enzymes present in the media. A larger amount of silver was released from kaolinite-Ag compared to sepiolite-Ag (17 vs. 7%), probably due to a higher retention rate of silver shown by sepiolite, justified by its sorption capacity and fibrous structure. No evidences were found about a significant release of silver nanoparticles along the in vitro assay from any of the two nanocomposites studied. These results have been compared to the silver levels found in liver and faeces from weaned pigs fed with these supplements for 35 days and followed by basal diet free of silver for 4 weeks in an in vivo assay. Piglets fed with kaolinite-Ag retained more silver in liver than those receiving sepiolite-Ag, and the opposite was observed in faeces, although differences were not statistically significant. Silver levels found in muscles were below the limit of detection (0.009 μg Ag g−1) in all cases.

Transformation of AgCl Particles under Conditions Typical of Natural Waters: Implications for Oxidant Generation.

The engineered silver nanoparticles (AgNPs) used in consumer products are ultimately released to the environment either as Ag(0), silver sulfide (Ag2S(s)), silver chloride (AgCl(s)), and/or dissolved Ag(I) complexes. Of these, AgCl(s) and Ag2S(s) exhibit semiconducting properties and hence may have significant implications to oxidant generation and subsequent redox transformations in natural waters. In this work, we investigate the transformation and photoreactivity of AgCl(s) under simulated natural water conditions with the photoreactivity probed by measuring the oxidation of formate (HCOO-), a simple compound with a well-defined oxidation pathway. Our results show that AgCl(s) undergoes rapid dissolution in the presence of chloride concentrations representative of seawater (ca. 0.5 M NaCl) forming dissolved Ag(I) complexes but is stable in fresh waters and slightly brackish waters (≤200 mM NaCl). We further show that under these lower salinity conditions in which AgCl(s) is stable, pH has a significant impact on the reactivity of semiconducting AgCl(s). The photoreactivity (measured as initial HCOO- oxidation rate) of AgCl(s) is relatively constant at pH 4.0 for periods of 24 h or more; however, it decreases rapidly under alkaline conditions. The rapid transformation (or "aging") of AgCl(s) under alkaline conditions suggests that AgCl(s), potentially transported through wastewater effluent to fresh or brackish water environments, may not have a significant impact in such environments. In comparison, in situ formed AgCl(s), potentially formed as a result of the oxidation of high concentrations (≥60 μg Ag·L-1) of Ag(0) and/or Ag2S(s), may have significant implications to oxidant generation in natural waters. Our results further show that rapid cycling of Ag between the 0 and +I redox states in sunlit surface waters as a result of the presence of AgNP oxidants (such as H2O2 and organic radicals) will further enhance the rate and extent of oxidant generation by AgCl(s).

Nanosynthesis of Silver-Calcium Glycerophosphate: Promising Association against Oral Pathogens.

Nanobiomaterials combining remineralization and antimicrobial abilities would bring important benefits to control dental caries. This study aimed to produce nanocompounds containing calcium glycerophosphate (CaGP) and silver nanoparticles (AgNP) by varying the reducing agent of silver nitrate (sodium borohydride (B) or sodium citrate (C)), the concentration of silver (1% or 10%), and the CaGP forms (nano or commercial), and analyze its characterization and antimicrobial activity against ATCC Candida albicans (10231) and Streptococcus mutans (25175) by the microdilution method. Controls of AgNP were produced and silver ions (Ag+) were quantified in all of the samples. X-ray diffraction, UV-Vis, and scanning electron microscopy (SEM) analysis demonstrated AgNP associated with CaGP. Ag+ ions were considerably higher in AgCaGP/C. C. albicans was susceptible to nanocompounds produced with both reducing agents, regardless of Ag concentration and CaGP form, being Ag10%CaGP-N/C the most effective compound (19.5–39.0 µg Ag mL−1). While for S. mutans, the effectiveness was observed only for AgCaGP reduced by citrate, also presenting Ag10%CaGP-N the highest effectiveness (156.2–312.5 µg Ag mL−1). Notably, CaGP enhanced the silver antimicrobial potential in about two- and eight-fold against C. albicans and S. mutans when compared with the AgNP controls (from 7.8 to 3.9 and from 250 to 31.2 µg Ag mL−1, respectively). The synthesis that was used in this study promoted the formation of AgNP associated with CaGP, and although the use of sodium borohydride (B) resulted in a pronounced reduction of Ag+, the composite AgCaGP/B was less effective against the microorganisms that were tested.

Effects of Silver Nanoparticles on the Activities of Soil Enzymes Involved in Carbon and Nutrient Cycling

Soils are continuously exposed to large amounts of engineered nanoparticles, especially silver nanoparticles (AgNPs), which can affect the activity, stability, and specificity of microbial enzymes. Therefore, the measurement of specific enzyme activity can be used to identify major changes in soil environments. Accordingly, the aim of the present study was to investigate the effects of AgNPs on soil enzymes that play critical roles in mineralizing carbon and nutrients in soil. Soil samples (silt loam and sandy loam) were collected from the surface layer (0–15 cm) of a field at the George Washington Carver Farm, Lincoln University of Missouri, USA. The soils were then treated with AgNP solutions at 0, 1 600, or 3 200 μg Ag kg−1 dry soil, using either 10- or 50-nm AgNPs and a randomized complete block design, with three replicates per treatment. The AgNP-treated soil samples were homogenized and incubated for one month, and soil acid phosphatase, β-glucosaminidase, β-glucosidase, and arylsulfatase activities were measured after one hour, one week, and one month of incubation. The activities of all four enzymes were reduced by AgNP treatment after one hour and one week. However, AgNP size had no effect. After one month of incubation, the AgNP treatments had mixed effects, which suggests that soil enzymes are only affected on a short-term basis. Further studies are required to determine the mechanisms by which AgNPs reduce soil enzyme activity.

Comparative study of dissolved and nanoparticulate Ag effects on the life cycle of an estuarine meiobenthic copepod, Amphiascus tenuiremis

Many nanotoxicological studies have assessed the acute toxicity of nanoparticles (NPs) at high exposure concentrations. There is a gap in understanding NP chronic environmental effects at lower exposure concentrations. This study reports life-cycle chronic toxicity of sublethal exposures of polyvinylpyrrolidone-coated silver nanoparticles (PVP-AgNPs) relative to dissolved silver nitrate (AgNO3) for the estuarine meiobenthic copepod, Amphiascus tenuiremis, over a range of environmentally relevant concentrations, i.e., 20, 30, 45, and 75 µg-Ag L−1. A concentration-dependent increase in mortality of larval nauplii and juvenile copepodites was observed. In both treatment types, significantly higher mortality was observed at 45 and 75 µg-Ag L−1 than in controls. In AgNO3 exposures, fecundity declined sharply (1.8–7 fold) from 30 to 75 µg Ag L−1. In contrast, fecundity was not affected by PVP-AgNPs exposures. A Leslie matrix population-growth model predicted sharply 60–86% of decline in overall population sizes and individual life-stage numbers from 30–75 µg-Ag L−1 as dissolved AgNO3. In contrast, no population growth suppressions were predicted for any PVP-AgNPs exposures. Slower release of dissolved Ag from PVP-AgNPs and/or reduced Ag uptake in the nanoform may explain these sharp contrasts in copepod response.

Effect of silver concentration and chemical transformations on release and antibacterial efficacy in silver-containing textiles

Silver-enabled fabrics may be transformed during use in ways that may affect their release characteristics and antibacterial efficacy. Here, we assess how chemical transformations of silver in fabrics treated with Ag nanoparticles or AgCl particles, or containing interwoven Ag0 fibers affect silver leaching and their antibacterial efficacy under different use and end-of-life scenarios. Fabrics were exposed to artificial sweat (use phase) or artificial landfill leachate (sodium chloride, sodium sulfide, or acetic acid; end of life phase). Chemical transformations induced by exposure to sodium chloride, sodium sulfide and acetic acid result in variations in Ag release and corresponding changes in bactericidal properties of the Ag-treated textiles. Exposure to solutions containing chloride ions (sodium chloride and artificial sweat) generally increased leaching compared to deionized water. Conversely, exposure to sodium sulfide and acetic acid solutions decreased Ag release. Exposure to artificial sweat did not affect antibacterial efficacy for fabrics with greater than ~10 μg Ag (g fabric)−1. Sulfide solution exposure decreased antibacterial performance for all but the 500 μg Ag (g fabric)−1. The lower efficacy was consistent with chemical transformation of elemental Ag to AgCl/Ag0 or Ag2S, respectively for chloride and sulfide exposure. AgCl-coated fabrics were more resilient to chemical attack than Ag0-enabled fabrics. These results indicate that fabrics with as low as ~10 μg Ag (g fabric)−1 can maintain high antibacterial efficacy under normal use phase conditions, but below this concentration efficacy significantly decreases. Taken together, the data permit a comparison of the benefits (antimicrobial efficacy) in the context of the impacts (silver release) and inform selection and design of materials and loadings that give the best overall lifecycle benefit.

Incorporation of silver nanoparticles into magnetron-sputtered calcium phosphate layers on titanium as an antibacterial coating

A three-layer system of nanocrystalline hydroxyapatite (first layer; 1000nm thick), silver nanoparticles (second layer; 1.5μg Ag cm−2) and calcium phosphate (third layer, either 150 or 1000nm thick) on titanium was prepared by a combination of electrophoretic deposition of silver nanoparticles and the deposition of calcium phosphate by radio frequency magnetron sputtering. Scanning electron microscopy showed that the silver nanoparticles were evenly distributed over the surface. The adhesion of multilayered coating on the substrate was evaluated using the scratch test method. The resistance to cracking and delamination indicated that the multilayered coating has good resistance to contact damage. The release of silver ions from the hydroxyapatite/silver nanoparticle/calcium phosphate system into the phosphate-buffered saline (PBS) solution was measured by atomic absorption spectroscopy (AAS). Approximately one-third of the incorporated silver was released after 3days immersion into PBS, indicating a total release time of the order of weeks. There were no signs of cracks on the surface of the coating after immersion after various periods, indicating the excellent mechanical stability of the multilayered coating in the physiological environment. An antimicrobial effect against Escherichia coli was found for a 150nm thick outer layer of the calcium phosphate using a semi-quantitative turbidity test.

Natural ageing process accelerates the release of Ag from functional textile in various exposure scenarios.

Natural ageing process occurs throughout the life cycle of textile products, which may possess influences on the release behavior of additives such as silver nanoparticles (Ag NPs). In this study, we assessed the releasability of Ag NPs from a Ag NPs functionalized textile in five different exposure scenarios (i.e. tap water (TW), pond water (PW), rain water (RW), artificial sweat (AS), and detergent solution (DS) along with deionized water (DW) as reference), which were very likely to occur throughout the life cycle of the textile. For the pristine textile, although the most remarkable release was found in DW (6–15 μg Ag/g textile), the highest release rate was found in RW (around 7 μg Ag/(g textile·h)). After ageing treatment, the total released Ag could be increased by 75.7~386.0% in DW, AS and DS. Morphological analysis clearly showed that the Ag NPs were isolated from the surface of the textile fibre due to the ageing treatment. This study provides useful information for risk assessment of nano-enhanced textile products.

Disposition of intravenously or orally administered silver nanoparticles in pregnant rats and the effect on the biochemical profile in urine.

Few investigations have been conducted on the disposition and fate of silver nanoparticles (AgNP) in pregnancy. The distribution of a single dose of polyvinylpyrrolidone (PVP)-stabilized AgNP was investigated in pregnant rats. Two sizes of AgNP, 20 and 110 nm, and silver acetate (AgAc) were used to investigate the role of AgNP diameter and particle dissolution in tissue distribution, internal dose and persistence. Dams were administered AgNP or AgAc intravenously (i.v.) (1 mg kg-1 ) or by gavage (p.o.) (10 mg kg-1 ), or vehicle alone, on gestation day 18 and euthanized at 24 or 48 h post-exposure. The silver concentration in tissues was measured using inductively-coupled plasma mass spectrometry. The distribution of silver in dams was influenced by route of administration and AgNP size. The highest concentration of silver (μg Ag g-1 tissue) at 48 h was found in the spleen for i.v. administered AgNP, and in the lungs for AgAc. At 48 h after p.o. administration of AgNP, the highest concentration was measured in the cecum and large intestine, and for AgAc in the placenta. Silver was detected in placenta and fetuses for all groups. Markers of cardiovascular injury, oxidative stress marker, cytokines and chemokines were not significantly elevated in exposed dams compared to vehicle-dosed control. NMR metabolomics analysis of urine indicated that AgNP and AgAc exposure impact the carbohydrate, and amino acid metabolism. This study demonstrates that silver crosses the placenta and is transferred to the fetus regardless of the form of silver. Copyright © 2016 John Wiley & Sons, Ltd.

The role of PVP in the bioavailability of Ag from the PVP-stabilized Ag nanoparticle suspension

We assessed the bioavailability of Ag from Ag nanoparticles (NPs), stabilized with polyvinylpyrrolidone (PVP), to terrestrial isopods which were exposed to 10, 100 and 1000 μg Ag NPs/g of dry food. Different Ag species were determined in the NP suspension that was fed to isopods: (i) total Ag by atomic absorption spectroscopy, (ii) the sum of Ag-PVP complexes and free Ag+ by anodic stripping voltammetry at the bismuth-film electrode, and (iii) free Ag+ by ion-selective potentiometry. The amounts of Ag species in the consumed food were compared to the masses of Ag accumulated in the isopod digestive glands. Our results show that all three Ag species (Ag NPs, Ag-PVP complexes and free Ag+) could be the source of bioaccumulated Ag, but to various degrees depending on the exposure concentration and transformations in the digestive system. We provide a proof that (i) Ag NPs dissolve and Ag-PVP complexes dissociate in the isopod digestive tract; (ii) the concentration of free Ag+ in the suspension offered to the test organisms is not the only measure of bioavailable Ag. The type of NP stabilizer along with the NP transformations in the digestive system needs to be considered in the creation of new computational models of the nanomaterial fate.

Influence of polyethylene microplastic beads on the uptake and localization of silver in zebrafish (Danio rerio)

This study aimed to determine whether the uptake and localization of Ag in zebrafish was affected by the presence of polyethylene microplastic beads (PE MPBs). Zebrafish were exposed to 1 μg Ag L−1 (radiolabelled with 110mAg) for 4 and 24 h in the presence or absence of PE MPBs (10, 100 or 1000 MPBs mL−1), and one treatment in which MPBs (1000 MPBs mL−1) were incubated with Ag to promote adsorption. The presence of MPBs, at any of the tested doses, had no effect on the uptake or localization of Ag. However, exposure to the Ag-incubated MPBs (∽75% of the Ag bound to MPBs) significantly reduced Ag uptake at both time points and also significantly increased the proportion of intestinal Ag. This study demonstrates that microplastics can alter the bioavailability and uptake route of a metal contaminant in a model fish species.

Bioaccumulation and oxidative stress responses measured in the estuarine ragworm (Nereis diversicolor) exposed to dissolved, nano- and bulk-sized silver

The impact of Ag NPs on sediment-dwelling organisms has received relatively little attention, particularly in linking bioaccumulation to oxidative injury. The polychaete Nereis diversicolor was exposed to sediments spiked with dissolved Ag (added as AgNO3), Ag NPs (63 ± 27 nm) and larger bulk Ag particles (202 ± 56 μm), for up to 11 days at sublethal concentrations (nominally 2.5, 5, 10 μg Ag g−1 sediment (dw)). There were concentration- and time-dependent differences in the accumulation of the three Ag forms, but all three forms elicited an oxidative stress response. In the cases of Ag NPs and bulk Ag particles, changes in antioxidant markers (glutathione, SOD, CAT, GPx, SeGPx, GST and GR) occurred without significant Ag accumulation. Differences in biomarker profiles between the three Ag forms suggest that the mechanism of oxidative stress caused by particulate Ag is distinct from that of dissolved Ag.

Toxicity of silver nanoparticles and ionic silver: Comparison of adverse effects and potential toxicity mechanisms in the freshwater clam Sphaerium corneum

A range of studies has addressed possible environmental impacts of nanosilver, but most focused on acute effects in few species. Moreover, it remains unclear if toxic effects are particle-specific or mediated by released silver ions. We investigated chronic effects of nanosilver and soluble silver (AgNO3) on the freshwater bivalve Sphaerium corneum. Animals were exposed to nanosilver (0–500 μg Ag L−1) and AgNO3 (0–318 μg Ag L−1) over 28 days, and effects on reproduction and behavioral changes were assessed. To explore toxic mechanisms, we evaluated the effects on intracellular levels of reactive oxygen species (ROS) and the activity of antioxidant enzymes (superoxide dismutase, catalase, glutathione-S-transferase, glutathione peroxidase). We further explored the activity of the sodium–potassium adenosine triphosphatase (Na+/K+-ATPase). Chronic exposure to nanosilver and AgNO3 resulted in negative effects on reproduction at concentrations of 5 and 3.18 µg Ag L−1 (LOEC), respectively. ROS levels significantly increased after exposure to nanosilver at 10 µg Ag L−1 and AgNO3 at 63.5 µg Ag L−1. Both forms of silver altered the activities of antioxidant enzymes. Nanosilver (500 μg Ag L−1) and AgNO3 (318 μg Ag L−1) inhibited Na+/K+-ATPase activity by 82.6 and 78.9%, respectively. Nanoparticulate and soluble silver produced similar effects in S. corneum suggesting that toxicity of nanosilver is mainly mediated by dissolution of nanoparticles in the test media or after uptake by the test organisms.