Comparative in vivo toxicokinetics of silver powder, nanosilver and soluble silver compounds after oral administration to rats.

Silver (Ag; massive, powder and nanoform) and Ag compounds are used in industrial, medical and consumer applications, with potential for human exposure. Uncertainties exist about their comparative mammalian toxicokinetic ('TK') profiles, including their relative oral route bioavailability, especially for Ag massive and powder forms. This knowledge gap impedes concluding on the grouping of Ag and Ag compounds for hazard assessment purposes. Therefore, an in vivo TK study was performed in a rat model. Sprague-Dawley rats were exposed via oral gavage for up to 28 days to silver acetate (AgAc; 5, 55, 175 mg/kg(bw)/d), silver nitrate (AgNO3; 5, 55, 125 mg/kg(bw)/d), nanosilver (AgNP; 15 nm diameter; 3.6, 36, 360 mg/kg(bw)/d) or silver powder (AgMP; 0.35 µm diameter; 36, 180, 1000 mg/kg(bw)/d). Total Ag concentrations were determined in blood and tissues to provide data on comparative systemic exposure to Ag and differentials in achieved tissue Ag levels. AgAc and AgNO3 were the most bioavailable forms with comparable and linear TK profiles (achieved systemic exposures and tissue concentrations). AgMP administration led to systemic exposures of about an order of magnitude less, with tissue Ag concentrations 2-3 orders of magnitude lower and demonstrating non-linear kinetics. The apparent oral bioavailability of AgNP was intermediate between AgAc/AgNO3 and AgMP. For all test items, highest tissue Ag concentrations were in the gastrointestinal tract and reticuloendothelial organs, whereas brain and testis were minor sites of distribution. It was concluded that the oral bioavailability of AgMP was very limited. These findings provide hazard assessment context for various Ag test items and support the prediction that Ag in massive and powder forms exhibit low toxicity potential.

Toxicokinetics of silver element following inhalation of silver nitrate in rats.

Silver (Ag) and its compounds are priority contaminants, for which toxicological effects are well documented, but their toxicokinetics are not fully documented for a proper risk assessment. While the toxicokinetics of insoluble Ag nanoparticles (Ag NPs) was recently documented, there is a lack of data on the kinetic behavior of the soluble form, such as one of the mostly used silver nitrate (AgNO3) form. This study aimed to better document the toxicokinetics of Ag element following inhalation of soluble AgNO3 for comparison with a previous study on the kinetics of inhaled Ag NPs using a similar experimental design. We exposed male Sprague-Dawley rats to AgNO3 during 6 continuous hours (typical of a daily worker exposure) to determine the kinetic time courses of Ag element in blood, tissues, and excreta over a 14-day period post-exposure. Only a small fraction of Ag was found in lungs following the onset of the 6-h inhalation of AgNO3 (on average (± SD) 0.3 ± 0.1% at the end of the 6-h inhalation). Blood profiles of Ag element showed peak levels right after the end of the 6-h inhalation period and levels decreased rapidly thereafter. Toxicokinetic parameter values calculated from the average blood-concentration profiles showed a mean residence time (MRT) of 135 h and mean half-life (t1/2) of 94 h, with AUC of 2.5 mg/L × h and AUMC of 338 mg/L × h2. In terms of percent of inhaled dose, highest levels of Ag in extrapulmonary organs were found in liver, which represented on average (± SD) 1.6 ± 0.6% of calculated inhaled dose followed by the kidney with 0.1 ± 0.08%. Peak levels in the GI tract (including contents) were found at the end of the 6-h inhalation and represented 20 ± 15.6% of the inhaled dose. The dominant excretion route of Ag was through feces. The time course of Ag element in the GI tract and feces following AgNO3 inhalation is also compatible with an intestinal reabsorption of Ag. When compared to results of Ag NPs of a prior study with the same design, this study showed differences in the kinetics of soluble AgNO3 compared to insoluble Ag NPs, with higher levels in blood, GI tract, and extrapulmonary tissues but lower levels in lungs following AgNO3 exposure.

Comparative toxicity of silver nanoparticle and ionic silver in juvenile common carp (Cyprinus carpio): Accumulation, physiology and histopathology.

Many studies have investigated the potential negative effects of silver on aquatic organisms, but most focused on short-term exposure in few species. Moreover, there are many uncertainties about differences in potential toxicity mechanisms and adverse effects of silver nanoparticles (AgNPs) and ionic form of silver (AgNO3). We investigated chronic effects of AgNPs and AgNO3 on the juvenile common carp (Cyprinus carpio). AgNPs and AgNO3 accumulated in the liver, gill and intestine, respectively and highest was related to AgNPs. Our results indicated, silver uptake was accompanied with histological alteration in the target organs such that different tissue lesions were observed in exposed groups. Superoxide dismutase (SOD), catalase (CAT) and lactate dehydrogenase (LDH) activity and also hsp70, ghrelin and IGF-1 genes expression were induced in both forms. After 7 days, highest hsp70 gene expression was observed in AgNO3 treatment and highest ghrelin and IGF-1 gene expression was observed in AgNPs treatment. The results revealed that adverse effects of AgNPs on different aspects of the health of juvenile common carp, may not be solely a result of particle dissolution. In addition, the main toxic mechanism of AgNPs was probably related to the accumulation of silver followed by the molecular and oxidative stress response.

Reproducibility of the effects of homeopathically potentised Argentum nitricum on the growth of Lemna gibba L. in a randomised and blinded bioassay.

BACKGROUND: A previous study reported a significant statistical interaction between experiment date and treatment effect of Argentum nitricum 14x-30x on the growth rate of duckweed (Lemna gibba L.). The aim of the present study was to investigate the stability of the test system and intra-laboratory reproducibility of the effects found. METHODS: Duckweed was treated with A. nitricum potencies (14x-30x) as well as succussed and unsuccussed water controls. The outcome parameter area-related growth rate for day 0-7 was determined by a computerised image analysis system in two series of independent randomised and blinded experiments. Systematic negative control (SNC) experiments were carried out to investigate test system stability. Statistical analysis was performed with full two-way analysis of variance (ANOVA) and protected Fisher's Least Significant Difference (LSD) test. RESULTS: In the first repetition series we found a significant treatment effect (p = 0.016), while in the second series no effect was observed. The negative control experiments showed that the experimental system was stable. An a posteriori subgroup analysis concerning gibbosity revealed the importance of this growth state of L. gibba for successful reproduction of the statistically significant interaction in the original study; flat: no interaction (p = 0.762); slight gibbosity: no interaction (p = 0.356); medium gibbosity: significant interaction (p = 0.031), high gibbosity: highly significant interaction (p = 0.005). CONCLUSIONS: With the original study design (disregarding gibbosity status of L. gibba) results of the original study could not be reproduced sensu stricto. We conclude that the growth state gibbosity is crucial for successful reproduction of the original study. Different physiological states of the test organisms used for bioassays for homeopathic basic research must carefully be considered.

Bioaccumulation of silver in Daphnia magna: Waterborne and dietary exposure to nanoparticles and dissolved silver.

Silver nanoparticles (Ag-NP) are incorporated into commercial products as antimicrobial agents, which potentiate their emission to the environment. The toxicity of Ag-NP has been associated with the release of Ag ions (Ag+), which are more toxic to aquatic organisms than Ag-NP. In this study, a toxicokinetics approach was applied to compare the potential of Daphnia magna to accumulate Ag from either Ag-NP or AgNO3 through different exposure routes: a) water, b) diet and c) water and diet. A one-compartment kinetics model was applied to describe the development of Ag body concentrations over time and derive uptake (k1w; k1d) and elimination (k2) rate constants. Under water-only exposure, AgNO3 induced higher Ag uptake rate constants and bioconcentration factors when compared to Ag-NP. For dietary exposure, no differences in Ag concentrations in D. magna, along with the kinetics parameters, were found for both Ag forms. Simultaneous water and dietary exposures to Ag-NP induced higher Ag concentrations in D. magna compared to AgNO3. In this combined exposure, uptake from water explains most for the increase in Ag body concentration in D. magna for Ag-NP exposure, whereas uptake from the diet was the major contributor for the increase in Ag concentration in D. magna under AgNO3 exposure. Biomagnification was not observed for any of the exposure routes applied in this study, neither for Ag-NP nor for AgNO3.

Nanoparticulate versus ionic silver: Behavior in the tank water, bioaccumulation, elimination and subcellular distribution in the freshwater mussel Dreissena polymorpha.

Zebra mussels (Dreissena polymorpha) were exposed to polyvinylpyrrolidone (PVP)-coated silver nanoparticles (AgNP; hydrodynamic diameter 80 nm; solid diameter 50 nm) to investigate the behavior of Ag in the tank water with respect to its uptake, bioaccumulation, elimination and subcellular distribution in the mussel soft tissue. Parallel experiments were performed with ionic Ag (AgNO3) to unravel possible differences between the metal forms. The recovery of the applied Ag concentration (500 µg/L) in the tank water was clearly affected by the metal source (AgNP < AgNO3) and water type (reconstituted water < tap water). Filtration (<0.45 µm) of water samples showed different effects on the quantified metal concentration depending on the water type and Ag form. Ag accumulation in the mussel soft tissue was neither influenced by the metal source nor by the water type. Ag concentrations in the mussel soft tissue did not decrease during 14 days of depuration. For both metal forms the Ag distribution within different subcellular fractions, i.e. metal-rich granules (MRG), cellular debris, organelles, heat-sensitive proteins (HSP) and metallothionein-like proteins (MTLP), revealed time-dependent changes which can be referred to intracellular Ag translocation processes. The results provide clear evidence for the uptake of Ag by the mussel soft tissue in nanoparticulate as well as in ionic form. Thus, zebra mussels could be used as effective accumulation indicators for environmental monitoring of both Ag forms.

Effects of developmental exposure to silver in ionic and nanoparticle form: A study in rats.

BACKGROUND: Evaluations of silver in both nanoparticle (Ag-NPs) and ionic forms indicate some adverse effects on living organisms, but little is known about their potential for developmental toxicity. In this study, developmental toxicity of Ag-NPs (from 0.2 to 20 mg/kg/day) and ionic Ag (AgNO3, 20 mg Ag/kg/day) were investigated in rats. METHODS: Animals were dosed by gavage from gestation day 7 - 20. The day after parturition, dams and pups were sacrificed and Ag level assessed in several maternal and pup organs. In addition, hepatotoxicity and oxidative stress parameters and histopathology were evaluated. RESULTS: No treatment related effects were found for gestational parameters including pregnancy length, maternal weight gain, implantations, birth weight and litter size at any dose level of Ag-NPs. Maternal weight gain was lower in dams receiving AgNO3 compared to the other groups, suggesting that the ionic form may exert a higher degree of toxicity compared to the NP form. Tissue contents of Ag were higher in all treated groups compared to control dams and pups, indicating transfer of Ag across the placenta. The findings furthermore suggest that Ag may induce oxidative stress in dams and their offspring, although significant induction was only observed after dosing with AgNO3. Histopathological examination of brain tissue revealed a high incidence of hippocampal sclerosis in dams treated with nanoparticle as well as ionic Ag. CONCLUSION: The difference in offspring deposition patterns between ionic and NP Ag and the observations in dam brain tissue, requires scrutiny, and, if corroborated, indicate that ionic and NP forms maybe need separate risk assessments and that the hazard ratings of silver in both ionic and nanoparticle forms should be increased, respectively. TRIAL REGISTRATION: Not applicable. Developmental Toxicity of Ag-NPs.

Distribution and accumulation of 10 nm silver nanoparticles in maternal tissues and visceral yolk sac of pregnant mice, and a potential effect on embryo growth.

We examined the distribution of silver in pregnant mice and embryos/fetuses following intravenous injections of 10 nm silver nanoparticles (AgNPs) or soluble silver nitrate (AgNO3) at dose levels of 0 (citrate buffer control) or 66 µg Ag/mouse to pregnant mice on gestation days (GDs) 7, 8 and 9. Selected maternal tissues and all embryos/fetuses from control, AgNP- and AgNO3-treated groups on GD10 and control and AgNP-treated groups on GD16 were processed for the measurement of silver concentrations, intracellular AgNP localization, histopathology and gross examination of tissue morphology. Inductively-coupled plasma mass spectrometry revealed silver in all examined tissues following either AgNP or AgNO3 treatment, with highest concentrations of silver in maternal liver, spleen and visceral yolk sac (VYS), and lowest concentrations in embryos/fetuses. For VYS, mean silver concentration following AgNO3 treatment (4.87 ng Ag/mg tissue) was approximately two-fold that following AgNP treatment (2.31 ng Ag/mg tissue); for all other tissues examined, mean silver concentrations following either AgNP or AgNO3 treatment were not significantly different from each other (e.g. 2.57 or 2.84 ng Ag/mg tissue in maternal liver and 1.61 or 2.50 ng Ag/mg tissue in maternal spleen following AgNP or AgNO3 treatment, respectively). Hyperspectral imaging revealed AgNP aggregates in maternal liver, kidney, spleen and VYS from AgNP-treated mice, but not AgNO3-treated mice. Additionally, one or more embryos collected on GD10 from eight of ten AgNP-treated mice appeared small for their age (i.e. Theiler stage 13 [GD8.5] or younger). In the control group (N = 11), this effect was seen in embryos from only one mouse. In conclusion, intravenous injection of 10 nm AgNPs to pregnant mice resulted in notable silver accumulation in maternal liver, spleen and VYS, and may have affected embryonic growth. Silver accumulation in embryos/fetuses was negligible.

Toxicokinetics and toxicodynamics of differently coated silver nanoparticles and silver nitrate in Enchytraeus crypticus upon aqueous exposure in an inert sand medium.

The aim of the present study was to evaluate the effect of silver nanoparticles (AgNPs) on Enchytraeus crypticus, applying a combined toxicokinetics and toxicodynamics approach to understand the relationship between survival and the development of internal Ag concentrations in the animals over time. Toxicity tests were conducted in medium composed of well-defined aqueous solutions added to inert quartz sand to avoid the complexity of soil conditions. Citrate-coated AgNPs (AgNP-Cit) and polyvinylpyrrolidone-coated AgNPs (AgNP-PVP) were tested and compared with silver nitrate (AgNO3), which was used as a positive control for Ag ion effects. The median lethal concentration (LC50) values based on Ag concentrations in the solution phase of the test medium decreased over time and reached steady state after 7 d, with AgNO3 and AgNP-PVP being more toxic than AgNP-Cit. Slow dissolution may explain the low uptake kinetics and lower toxicity of AgNP-Cit compared with the other 2 Ag forms. The LC50 values based on internal Ag concentrations in the animals were almost stable over time, highlighting the importance of integrating toxicokinetics and toxicodynamics and relating survival with internal Ag concentrations. Neither survival-based elimination rates nor internal LC50s in the organisms showed any significant evidence of nano-specific effects for both AgNPs, although they suggested some uptake of particulate Ag for AgNP-Cit. The authors conclude that the toxicity of both types of AgNP probably is mainly attributable to the release of Ag ions.

Effects of Differently Coated Silver Nanoparticles on the Photosynthesis of Chlamydomonas reinhardtii.

Various factors have been invoked to explain the toxicity of silver nanoparticles (AgNP) to microorganisms including particle size and the nature of stabilizing coatings as well as the amount of dissolved silver occurring in AgNP suspensions. In this study we have assessed the effects of nine differently coated AgNP (chitosan, lactate, polyvinylpyrrolidone, polyethelene glycol, gelatin, sodium dodecylbenzenesulfonate, citrate, dexpanthenol, and carbonate) and AgNO3 on the photosynthesis of the freshwater algae Chlamydomonas reinhardtii. We have thus examined how AgNP effects on algae relate to particle size, measured dissolved silver (Agd), and bioavailable silver (Agbioav). Agbioav was indirectly estimated in toxicity experiments by cysteine-silver complexation at the EC50. The EC50 calculated as a function of measured Agd concentrations showed for some coatings values similar to that of dissolved Ag, whereas other coated AgNP displayed lower EC50 values. In all cases, excess cysteine completely prevented effects on photosynthetic yield, confirming the role of Agd as a cause of the observed effect on the photosynthesis. Toxicity was related neither to particle size nor to the coatings. For all differently coated AgNP suspensions, the EC50 values calculated as a function of Agbioav were comparable to the value of AgNO3. Depending on the coatings Agbioav was comparable to or higher than measured Agd.

Influence of hardness on the bioavailability of silver to a freshwater snail after waterborne exposure to silver nitrate and silver nanoparticles.

The release of Ag nanoparticles (AgNPs) into the aquatic environment is likely, but the influence of water chemistry on their impacts and fate remains unclear. Here, we characterize the bioavailability of Ag from AgNO(3) and from AgNPs capped with polyvinylpyrrolidone (PVP AgNP) and thiolated polyethylene glycol (PEG AgNP) in the freshwater snail, Lymnaea stagnalis, after short waterborne exposures. Results showed that water hardness, AgNP capping agents, and metal speciation affected the uptake rate of Ag from AgNPs. Comparison of the results from organisms of similar weight showed that water hardness affected the uptake of Ag from AgNPs, but not that from AgNO(3). Transformation (dissolution and aggregation) of the AgNPs was also influenced by water hardness and the capping agent. Bioavailability of Ag from AgNPs was, in turn, correlated to these physical changes. Water hardness increased the aggregation of AgNPs, especially for PEG AgNPs, reducing the bioavailability of Ag from PEG AgNPs to a greater degree than from PVP AgNPs. Higher dissolved Ag concentrations were measured for the PVP AgNPs (15%) compared to PEG AgNPs (3%) in moderately hard water, enhancing Ag bioavailability of the former. Multiple drivers of bioavailability yielded differences in Ag influx between very hard and deionized water where the uptake rate constants (k(uw), l g(-1) d(-1) ± SE) varied from 3.1 ± 0.7 to 0.2 ± 0.01 for PEG AgNPs and from 2.3 ± 0.02 to 1.3 ± 0.01 for PVP AgNPs. Modeling bioavailability of Ag from NPs revealed that Ag influx into L. stagnalis comprised uptake from the NPs themselves and from newly dissolved Ag.

Silver sulfide nanoparticles (Ag2S-NPs) are taken up by plants and are phytotoxic.

Silver nanoparticles (NPs) are used in more consumer products than any other nanomaterial and their release into the environment is unavoidable. Of primary concern is the wastewater stream in which most silver NPs are transformed to silver sulfide NPs (Ag2S-NPs) before being applied to agricultural soils within biosolids. While Ag2S-NPs are assumed to be biologically inert, nothing is known of their effects on terrestrial plants. The phytotoxicity of Ag and its accumulation was examined in short-term (24 h) and longer-term (2-week) solution culture experiments with cowpea (Vigna unguiculata L. Walp.) and wheat (Triticum aestivum L.) exposed to Ag2S-NPs (0-20 mg Ag L(-1)), metallic Ag-NPs (0-1.6 mg Ag L(-1)), or ionic Ag (AgNO3; 0-0.086 mg Ag L(-1)). Although not inducing any effects during 24-h exposure, Ag2S-NPs reduced growth by up to 52% over a 2-week period. This toxicity did not result from their dissolution and release of toxic Ag(+) in the rooting medium, with soluble Ag concentrations remaining below 0.001 mg Ag L(-1). Rather, Ag accumulated as Ag2S in the root and shoot tissues when plants were exposed to Ag2S-NPs, consistent with their direct uptake. Importantly, this differed from the form of Ag present in tissues of plants exposed to AgNO3. For the first time, our findings have shown that Ag2S-NPs exert toxic effects through their direct accumulation in terrestrial plant tissues. These findings need to be considered to ensure high yield of food crops, and to avoid increasing Ag in the food chain.

Uptake and elimination kinetics of silver nanoparticles and silver nitrate by Raphidocelis subcapitata: The influence of silver behaviour in solution.

Raphidocelis subcapitata is a freshwater algae species that constitutes the basis of many aquatic trophic chains. In this study, R. subcapitata was used as a model species to investigate the kinetics of uptake and elimination of silver nanoparticles (AgNP) in comparison to silver nitrate (AgNO3) with particular focus on the Ag sized-fractions in solution. AgNP used in this study were provided in a suspension of 1 mg Ag/l, with an initial size of 3-8 nm and coated with an alkane material. Algae was exposed for 48 h to both AgNP and AgNO3 and sampled at different time points to determine their internal Ag concentration over time. Samples were collected and separated into different sized fractions: total (Agtot), water column Ag (Agwater), small particulate Ag (Agsmall.part.) and dissolved Ag (Agdis). At AgNO3 exposures algae reached higher bioconcentration factor (BCF) and lower elimination rate constants than at AgNP exposures, meaning that Ag is more readily taken up by algae in its dissolved form than in its small particulate form, however slowly eliminated. When modelling the kinetics based on the Agdis fraction, a higher BCF was found. This supports our hypothesis that Ag would be internalised by algae only in its dissolved form. In addition, algae images obtained by Coherent Anti-stokes Raman Scattering (CARS) microscopy demonstrated large aggregates of nanoparticles external to the algae cells with no evidence of its internalisation, thus providing a strong suggestion that these AgNP were not able to penetrate the cells and Ag accumulation happens through the uptake of Ag ions.

Bioconcentration and distribution of silver nanoparticles in Japanese medaka (Oryzias latipes).

The study of the bioconcentration of silver nanoparticles (AgNPs) is important to fully understand their hazard potential in the aquatic environment. We synthesized AgNPs radiolabeled with silver isotopes ((110m)Ag) to quantify the bioconcentration of AgNPs coated with citrate (AgNPs-CIT) and polyvinylpyrrolidone (AgNPs-PVP) in Japanese medaka, and to investigate the biodistribution of silver in organs, which were compared with (110m)AgNO3. BCF values were determined to be 39.8±7.4, 42.5±5.1 and 116.4±6.1Lkg(-1) for AgNPs-CIT, AgNPs-PVP and AgNO3, respectively. The release of more silver ions in AgNPs-PVP contributed to a different kinetic uptake pattern with AgNPs-CIT, which was similar to that of AgNO3. Bioconcentrated AgNPs in medaka were not observed to be eliminated, independent of surface coating differences, similarly to AgNO3. There was no difference in biodistribution in each organ before and after depuration in two types of AgNPs and AgNO3, all of which were mainly concentrated in the liver. This study quantified the bioconcentration and distribution of AgNPs and AgNO3 more precisely by utilizing a silver isotope, which is helpful in monitoring the toxicity of AgNPs to Japanese medaka.

Bioavailability and immunotoxicity of silver nanoparticles to the freshwater mussel Elliptio complanata.

The purpose of this study was to examine the effects of Ag nanoparticles (nAg) of two different sizes (20 and 80 nm) and Ag(+) on the immune system of the freshwater mussel Elliptio complanata. Mussels were exposed to increasing concentrations of nAg and dissolved Ag (AgNO3) for 48 h at 15°C and concentration of 0, 0.8, 4, or 20 µg/L. Immunocompetence was determined by hemocyte viability, phagocytosis, and cell cytotoxicity. Ag tissue loadings and levels of metallothioneins (MT), lipid peroxidation (LPO), and labile zinc (Zn) were also determined. Results revealed first that 20- and 80-nm nAg readily formed aggregates in freshwater. Ag was detected in soft tissues with each form of Ag with bioconcentration factors of 20, 9, and 7 for Ag(+), 20-nm nAg, and 80-nm nAg, respectively. Significant induction in phagocytosis and decreased cell cytotoxicity were observed. All forms of Ag were able to induce LPO in gills and digestive glands at concentrations below those from the initial fraction of dissolved Ag. The effects of nAg on MT levels in mussels were not discernible from those of dissolved Ag, but the 80-nm was 25-fold more potent than 20-nm nAg in inducing MT. Multivariate analysis revealed that the global responses of the 20- and 80-nm nAg were generally similar to those of dissolved Ag. Data also demonstrated that nAg are bioavailable for mussels where the immune system is a target during early exposure to nanoparticles.

Intracellular surface-enhanced Raman scattering (SERS) with thermally stable gold nanoflowers grown from Pt and Pd seeds.

SERS provides great sensitivity at low concentrations of analytes. SERS combined with near infrared (NIR)-resonant gold nanomaterials are important candidates for theranostic agents due to their combined extinction properties and sensing abilities stemming from the deep penetration of laser light in the NIR region. Here, highly branched gold nanoflowers (GNFs) grown from Pd and Pt seeds are prepared and their SERS properties are studied. The growth was performed at 80 °C without stirring, and this high temperature growth method is assumed to provide great shape stability of sharp tips in GNFs. We found that seed size must be large enough (>30 nm in diameter) to induce the growth of those SERS-active and thermally stable GNFs. We also found that the addition of silver nitrate (AgNO3) is important to induce sharp tip growth and shape stability. Incubation with Hela cells indicates that GNFs are taken up and reside in the cytoplasm. SERS was observed in those cells incubated with 1,10-phenanthroline (Phen)-loaded GNFs.

Toxic effects and bioaccumulation of nano-, micron- and ionic-Ag in the polychaete, Nereis diversicolor.

There is increasing concern about the toxicities and potential risks, both still poorly understood, of silver nanoparticles for the aquatic environment after their eventual release via wastewater discharges. In this study, the toxicities of sediment associated nano (<100 nm)-, micron (2-3.5 µm)- and ionic (AgNO(3))-Ag on the sediment-dwelling polychaete, Nereis diversicolor, were compared after 10 days of sediment exposure, using survival, DNA damage (comet assay) and bioaccumulation as endpoints. The nominal concentrations used in all exposure scenarios were 0, 1, 5, 10, 25, and 50 µg Ag/g dry weight (dw) sediment. Our results showed that Ag was able to cause DNA damage in Nereis coelomocytes, and that this effect was both concentration- and Ag form-related. There was significantly greater genotoxicity (higher tail moment and tail DNA intensities) at 25 and 50 µg/g dw in nano- and micron-Ag treatments and at 50 µg/g dw in the ionic-Ag treatment compared to the controls (0µg/g dw). The nano-Ag treatment had the greatest genotoxic effect of the three tested Ag forms, and the ionic-Ag treatment was the least genotoxic. N. diversicolor did accumulate sediment-associated Ag from all three forms. Ag body burdens at the highest exposure concentration were 8.56 ± 6.63, 6.92 ± 5.86 and 9.86 ± 4.94 µg/g dw for worms in nano-, micron- and ionic-Ag treatments, respectively, but there was no significant difference in Ag bioaccumulation among the three treatments.

Antimicrobial surface functionalization of plastic catheters by silver nanoparticles.

OBJECTIVES: To test the antimicrobial activity and evaluate the risk of systemic toxicity of novel catheters coated with silver nanoparticles. METHODS: Catheters were coated with silver using AgNO3, a surfactant and N,N,N ',N '-tetramethylethylenediamine as a reducing agent. Particle size was determined by electron microscopy. Silver release from the catheters was determined in vitro and in vivo using radioactive silver ((110m)Ag+). Activity on microbial growth and biofilm formation was evaluated against pathogens most commonly involved in catheter-related infections, and the risk for systemic toxicity was estimated by measuring silver biodistribution in mice implanted subcutaneously with (110 m)Ag+-coated catheters. RESULTS: The coating method yielded a thin ( approximately 100 nm) layer of nanoparticles of silver on the surface of the catheters. Variations in AgNO3 concentration translated into proportional changes in silver coating (from 0.1 to 30 microg/cm(2)). Sustained release of silver was demonstrated over a period of 10 days. Coated catheters showed significant in vitro antimicrobial activity and prevented biofilm formation using Escherichia coli, Enterococcus, Staphylococcus aureus, coagulase-negative staphylococci, Pseudomonas aeruginosa and Candida albicans. Approximately 15% of the coated silver eluted from the catheters in 10 days in vivo, with predominant excretion in faeces (8%), accumulation at the implantation site (3%) and no organ accumulation (< or = 0.1%). CONCLUSIONS: A method to coat plastic catheters with bioactive silver nanoparticles was developed. These catheters are non-toxic and are capable of targeted and sustained release of silver at the implantation site. Because of their demonstrated antimicrobial properties, they may be useful in reducing the risk of infectious complications in patients with indwelling catheters.

Penetration of silver nitrate into bleached enamel, dentin, and cementum.

OBJECTIVE: To observe the effect of 10% carbamide peroxide bleaching agent on the enamel, dentin, and cementum of human teeth. METHOD AND MATERIALS: Teeth were treated with one of two 10% carbamide peroxide bleaching agents (3M Zaris, 3M Espe; Nite White Excel, Discus Dental) for 2 hours/day for 7 or 14 days. Treated teeth and 10 additional nontreated teeth were immersed in 50% silver nitrate solution. The prepared surface was then viewed under a confocal laser scanning microscope, photomicrographs were taken, and the degree of penetration of silver nitrate into the structure of bleached teeth was determined. RESULTS: No penetration was seen in enamel of any group, and statistical analysis showed a significant difference in the degree of penetration only between treated and nontreated groups of dentin and cementum (P <.05). No significant difference was seen between 7 and 14 days. CONCLUSION: Although the effect was not significant, further investigation is needed to determine the effect of long-term treatment of carbamide peroxide on human tooth substance.

Influence of salinity and organic matter on silver accumulation in Gulf toadfish (Opsanus beta).

To help extend the freshwater based biotic ligand model for silver (Ag) into brackish and saltwater conditions, 50g Gulf toadfish (Opsanus beta) were acclimated to 2.5%, 5%, 10%, 20%, 40%, 80%, or 100% salt water and exposed for 6d to 1.0microM AgNO(3), with or without 10mg C/L organic matter. Suwannee River natural organic matter collected by reverse osmosis was used. Silver accumulation in toadfish gills and plasma decreased as salinity increased, indicating low bioavailability of AgCl complexes. Complexation of Ag by organic matter, normally important in freshwater conditions, was less important as salinity increased. Although relatively little intestinal Ag uptake was observed, both liver and bile accumulated Ag from water imbibed past the isosmotic salinity point ( approximately 1/3 salt water). Toadfish also produced intestinal carbonate pellets, minerals which did not influence Ag accumulation. Our results further stress the importance of Ag speciation, physiological mechanisms, and intestinal Ag uptake when modelling Ag uptake and toxicity beyond freshwater conditions.