High Levels Of Silver Research Articles

Brazing of Different Metal Alloys with Highly-Silver Flux Addition and Microstructure Investigation

In this study, it was investigated that two different metal alloys can be soldered with the help of industrial flux. Thus, the soldered state of two different metals used in areas such as defense, automotive, and battery was examined. A low-carbon steel alloy and a GBZ20 grade bronze material were used for brazing. An industrial flux was used as an intermediate material. Flux contains high levels of silver (Ag), as well as Cu, Zn, Pb, and Ni elements. A design is prepared between the two materials during soldering. With the flame heating method, the sample temperature was increased to approximately 800°C. After the experiment, rapid cooling was done in water. Inspection of the solder intermediate zone was examined with the help of a scanning electron microscope (SEM). Chemical analyzes of the materials were followed. Thus, two different metals are combined with a flux-assisted soldering process.

The Influence of Anions on the Release of Ag(I) Ions from Silver Nanoparticles (AgNPs)

Silver nanoparticles (AgNPs) are widely being incorporated into products such as socks [1, 2], sports wears and wound dressings [3, 4] to serve as antibacterials and to inhibit unwanted odours. As these products are washed, the silver nanoparticles leach out, dispersing in water where they may release silver ions. Although the only contraindication of high levels of silver in humans is argyria [5], it is said to be very toxic to aquatic organisms that make up the base of a series of food chains. In this study, silver nanoparticles were synthesised by the citrate reduction method following the procedure of Lee and Meisel [6]. The nanoparticles were prepared in the presence of various anions and in pure water in order to examine the effect of the medium on the release of Ag(I). AgNPs were characterised by UV-Vis spectrometry, dynamic light scattering (DLS) and atomic force microscopy (AFM). The decrease in surface plasmon resonance (SPR) peak of the nanoparticles after dialysis indicates that quite a number of conduction electrons have gone into reaction, hence lowering of resonant frequency. The diameters of the nanoparticles as measured by DLS ranged from 102 nm in the 10 mM chloride AgNPs before dialysis to 892 nm in the 50 mM sample after dialysis, indicating aggregation over the dialysis period. On the other hand, particle sizes in terms of both height and diameter as measured by AFM decreased after dialysis. This could be explained that in spite of aggregation in solution, the AgNPs deposit as islands about 1 particle in height on the AFM substrate (Si wafer). Release of Ag(I) from the NPs was monitored by anodic stripping voltammetry at glassy carbon electrodes. Two interesting observations were made: (i) there is substantial (90 mM) Ag(I) present in the initial NP preparation and (ii) the concentration of Ag(I) after 73 h of dialysis remained easily detectable at about 4 µM irrespective of the concentration of chloride present. References 1 T.M. Benn, P.Westerhoff. Environ. Sci. Technol. 2008, 42, 4133-4139. 2 D.E Meyer, M.A. Curran, M.A. Gonzalez. J Nanopart Res. 2011, 13, 147-156. 3 A. Hebeish, M.H. El-Rafie, M.A. El-Sheikh, A.A. Saleem, M.E. El-Naggar. Intnal. Journ. of Macromolecules. 2014, 65, 509-515. 4 T. Maneerung, S. Tokura, R. Rujiavanit. Carbohydrate Polymers. 2008, 72, 43-51. 5 WHO Guidelines for Drinking-water quality. 2003. World Health Organisation, Geneva. 6 P.C. Lee, D. Meisel. J. Phys. Chem. 1982, 86, 3391-3395. Figure 1

Silver nanoparticles inhibit fish gill cell proliferation in protein-free culture medium

While short-term exposures of vertebrate cells, such as from fish, can be performed in defined, serum-free media, long-term cultures generally require addition of growth factors and proteins, normally supplied with a serum supplement. However, proteins are known to alter nanoparticle properties by binding to nanoparticles. Therefore, in order to be able to study nanoparticle–cell interactions for extended periods, the rainbow trout (Oncorhynchus mykiss) gill cell line, RTgill-W1, was adapted to proliferate in a commercial, serum-free medium, InVitrus VP-6. The newly adapted cell strain was named RTgill-W1-pf (protein free). These cells proliferate at a speed similar to the RTgill-W1 cells cultured in a fully supplemented medium containing 5% fetal bovine serum. As well, they were successfully cryopreserved in liquid nitrogen and fully recovered after thawing. Yet, senescence set in after about 10 passages in InVitrus VP-6 medium, revealing that this medium cannot fully support long-term culture of the RTgill-W1 strain. The RTgill-W1-pf cell line was subsequently applied to investigate the effect of silver nanoparticles (AgNP) on cell proliferation over a period of 12 days. Indeed, cell proliferation was inhibited by 10 μM AgNP. This effect correlated with high levels of silver being associated with the cells. The new cell line, RTgill-W1-pf, can serve as a unique representation of the gill cell–environment interface, offering novel opportunities to study nanoparticle–cell interactions without serum protein interference.

Adsorption Cooling System Using Metal-Impregnated Zeolite-4A

The adsorption cooling systems have been developed to replace vapor compression due to their benefits of being environmentally friendly and energy saving. We prepared zeolite-4A and experimental cooling performance test of zeolite-water adsorption system. The adsorption cooling test-rig includes adsorber, evaporator, and condenser which perform in vacuum atmosphere. The maximum and minimum water adsorption capacity of different zeolites and COP were used to assess the performance of the adsorption cooling system. We found that loading zeolite-4A with higher levels of silver and copper increased COP. The Cu6%/zeolite-4A had the highest COP at 0.56 while COP of zeolite-4A alone was 0.38. Calculating the acceleration rate of zeolite-4A when adding 6% of copper would accelerate the COP at 46%.

Evaluation of nanosilver-induced toxicity in aquatic environment using the Chinese rare minnow

Nanosilver, a popular disinfectant with excellent antibacterial activity, is used in a variety of fields, including the food industry, medical appliance maintenance, and water treatment. Given its widespread use, there is increasing concern regarding the biosafety of nanosilver. We evaluated the toxicity of a nanosilver-based disinfectant at the suggested effective doses for water treatment (1-20 mg/L) using the Chinese rare minnow ( Gobiocyprisrarus ). The silver nanoparticles were coated with polyvinylpyrrolidone (PVP) and dispersed in the water. TEM characterization revealed the particle size was within 10 nm. The hydrodynamic size was ~3.76 nm based on measurement of dynamic light scattering. The zeta potential was -5.5 mV and the UV absorbance was weak. High levels of both silver ion and nanosilver exposure were lethal to the fish. The 24-h half lethal concentrations (24 h LC 50 ) were 12.79 mg/L and 22 μg/L for nanosilver and silver ions, respectively, suggesting the toxicity of nanosilver was much lower than that of the silver ion. We conducted a total silver analysis using ICP-MS to evaluate the accumulation and depuration of silver in the exposed fish. Both nanosilver and silver ions were able to enter into fish tissues, the bioaccumulation was not high though. The liver, gill, and intestine contained relatively high levels of silver and the bioaccumulation was in a dose-dependent manner for nanosilver exposure. Silver levels increased slowly with exposure time and decreased rapidly during the depuration period. Silver ions were characterized by a higher bioavailability to the the Chinese rare minnow than nanosilver. The histological observations using scanning electron microscopy (SEM) revealed that both silver ions and nanosilver had obvious deleterious effects on the target tissues, including gill and liver. The ultrastructural alterations of the gill tissues included a fall-off of the flat epithelial cell, disappearance of the surface microridges, and distorted taste buds. Similarly, nanosilver and silver ion exposure resulted in obvious damages to the liver surface such as irregular hepatocyte shape. Silver ion exposure caused in much more severe effects on these target tissues than nanosilver, likely because silver ions were more readily taken up. Our results are consistent with observations in other fish species (e.g., rainbow trout and zebrafish), suggesting that the Chinese rare minnow is a good model for evaluating the aquatic toxicity of nanosilver. Ultrastructural observations using SEM also provided a sensitive approach for toxicological studies. Given that these subchronic deleterious effects were induced by nanosilver at the doses suggested for water disinfection, there is an urgent need for risk assessment on the potential aquatic toxicological effects of nanosilver.

Rapid determination of silver in cultivated Japanese and South Korean oysters and Japanese rock oysters using the 24.6-s neutron activation product 110Ag and estimation of its average daily intake

Soft tissues of cultivated Japanese (Miyagi Prefecture) and South Korean (Koje-do and Kosong) oysters and Japanese rock oysters (Honshu Island) were analyzed to measure silver levels. The soft tissues, namely hepatopancreas, gill, muscle, and mantle were separated, freeze-dried, pulverized, and analyzed by an instrumental neutron activation analysis method in conjunction with compton suppression spectrometry (INAA-CSS). The method consisted of the irradiation of samples in a neutron flux of 5 × 1011 cm−2 s−1 using the rapid transfer system in an inner pneumatic irradiation site of the Dalhousie University SLOWPOKE-2 reactor (DUSR) facility for 12–15 s, decay for 20 s, and counting for 60 s. The 657.8-keV gamma-ray of the 24.6-s nuclide 110Ag was used for assaying silver. The method was validated using NIST, NRC and NIES certified reference materials. An absolute detection limit of 0.05 μg silver using NIST SRM 1566b Oyster Tissue was achieved. About 10–50 times higher levels of silver were found in cultivated Japanese oysters compared to the South Korean ones. The silver concentrations in cultivated oysters in Miyagi Prefecture showed the following trend: gill > mantle > hepatopancreas > muscle as well as on the age. Rock oysters generally had higher silver content compared to cultivated oysters. A very preliminary value of about 0.466 μg silver average intake per person per day was estimated from the consumption of oysters by the people living in the Sendai city of Miyagi Prefecture.

The Pembrey copper cathode

The world’s first copper electrorefinery started production in 1869 at Pembrey in South Wales and was closed in March 1912. Refining principles pioneered there form the foundation of modern electrorefining practice. A cathode recovered at closure and now in the collection of the Swansea Museum, Wales, is the earliest authenticated British example of electrorefined copper as cathode. This unique artefact was sampled and assayed to establish its composition and market quality and to help elucidate refining capability at that time. The sampling method was based upon drilling into the edge of the cathode plate in order to protect its display integrity; assaying was by inductively coupled plasma mass spectrometry, the present received method for refined copper. Comparison with contemporaneous cathode and wire bar assays indicates that the Pembrey cathode would have been competitive in the copper market of its day, but with questions about its relatively high levels of silver and, to a lesser extent, arsenic.

The benefits of silver in hygiene, personal care and healthcare

Silver has been used for centuries as an antimicrobial agent to reduce bioburden and prevent infection. Its usage diminished when antibiotics were introduced but remained one of the most popular agents for wound infections, especially in burned patients. Incorporation of silver into a range of hygiene and healthcare applications has increased, and this has raised concerns over the development of silver resistance, toxicity, methods of testing products and evidence of efficacy. The published evidence for resistance and toxicity is limited and associated with frequent and high levels of silver used. Increasing evidence of improved antimicrobial activity of nanoparticles of silver and possible dual immunomodulatory effects are exciting. This may lead to further product development as potential alternative preservatives as some currently available preservatives have an increasing incidence of allergic reactions. Acknowledging the role of the carrier is important, and as silver is active when in solution, opens a window of opportunity in personal hygiene area. This is important in an age when multiple antibiotic-resistant bacteria are becoming prevalent.

The mechanism of metal nanoparticle formation in plants: limits on accumulation

Metal nanoparticles have many potential technological applications. Biological routes to the synthesis of these particles have been proposed including production by vascular plants, known as phytoextraction. While many studies have looked at metal uptake by plants, particularly with regard to phytoremediation and hyperaccumulation, few have distinguished between metal deposition and metal salt accumulation. This work describes the uptake of AgNO3, Na3Ag(S2O3)2, and Ag(NH3)2NO3 solutions by hydroponically grown Brassica juncea and the quantitative measurement of the conversion of these salts to silver metal nanoparticles. Using X-ray absorption near edge spectroscopy (XANES) to determine the metal speciation within the plants, combined with atomic absorption spectroscopy (AAS) for total Ag, the quantity of reduction of AgI to Ag0 is reported. Transmission electron microscopy (TEM) showed Ag particles of 2–35 nm. The factors controlling the amount of silver accumulated are revealed. It is found that there is a limit on the amount of metal nanoparticles that may be deposited, of about 0.35 wt.% Ag on a dry plant basis, and that higher levels of silver are obtained only by the concentration of metal salts within the plant, not by deposition of metal. The limit on metal nanoparticle accumulation, across a range of metals, is proposed to be controlled by the total reducing capacity of the plant for the reduction potential of the metal species and limited to reactions occurring at an electrochemical potential greater than 0 V (verses the standard hydrogen electrode).

Analysis of silver in the water column of the Pra and the Eture estuaries in Ghana

Silver is a rare but naturally occurring metal, often found deposited as mineral ore in association with other elements like gold, manganese and aluminium. Emission from smelting and gold mining operations as well as indiscriminate disposal of waste from photographic laboratories and other chemical laboratories are some of the anthropogenic sources of silver in the environment. This work analysed the concentration of total recoverable silver in the water column of the Eture and the Pra estuaries in Ghana. The result indicated high concentrations in the two estuaries, higher than the values that should be tolerated in the estuarine environment. The high levels in the Pra estuary could be attributed to the numerous mining activities upstream and this was the same for the Eture estuary which also runs through Cape Coast and the University of Cape Coast. The higher levels of silver reported in this study area suggest that much work has to be done to monitor and improve the quality of these ecosystems in the Ghanaian environment.

Does pre-treatment with lamivudine prime for adefovir resistance of hepatitis B virus infection?

My recent leading article on silver-based products as antimicrobial agents was intended primarily to address microbiological issues such as bacterial susceptibility and the potential for the development of resistance to these products. Consequently, I did not consider the toxicological issues raised by Bayston et al. in their comment upon my article. Obviously, a heavy-metal cation such as silver has the potential to inhibit processes in mammalian cells and as noted by Bayston et al., various forms of silver-associated toxicity have been reported, although fortunately they are rare in clinical practice. Experience with antibiotics tells us that dosing with sub-MIC levels creates conditions favourable for the selection of resistant organisms. Applying these principles to the silver situation led me to conclude that products releasing high levels of silver were unlikely to generate conditions for the selection of silver-resistant microorganisms. However, I agree with Bayston et al. that the use of such products could pose a greater risk of toxicity than low silver release formulations and that the therapeutic index for silver-based products may be rather low. Concerning the issue of zones of inhibition raised by Bayston et al., it may well be true that free silver ions capable of diffusion are not released from nanoparticle systems. Unfortunately, the abstract, cited by Bayston et al., does not appear to support this claim. No zones of microbial inhibition were observed with the silver-impregnated catheters used by the authors, implying no diffusion of free silver ions from the catheter material. However, there appeared to be insufficient silver in this product even to affect the viability of bacteria (Staphylococcus epidermidis) bound to the catheter surface. Consequently, it is difficult for Bayston et al. to argue from these data that organisms attached to the surface of the catheter can be killed by silver in the absence of diffusion of the cation from the device.

Alloy development for the enhanced stability of Ω precipitates in Al-Cu-Mg-Ag alloys

The coarsening resistance and thermal stability of several Ω plate-dominated microstructures were controlled through altering the chemistry and thermomechanical processing of various Al-Cu-Mg-Ag alloys. Quantitative comparisons of Ω nucleation density, particle size, and thermal stability were used to illustrate the effects of alloy composition and processing conditions. The long-term stability of Ω plates was found to coincide with relatively high levels of silver and moderate magnesium additions, with the latter limiting the competition for solute with S-phase precipitation. This analysis revealed that certain microstructures initially dominated by Ω precipitation were found to remain stable through long-term isothermal and double-aging heat treatments, which represents significant improvement over the previous generation of Al-Cu-Mg-Ag alloys, in which Ω plates dissolved sacrificially after long aging times. The quantitative precipitate data, in conjunction with a thermodynamic database for the aluminum-rich corner of the Al-Cu-Mg-Ag quaternary system, were used to estimate the chemistry of the α/Ω-interphase boundary. These calculations suggest that silver is the limiting species at the α/Ω interfacial layer and that Ω plates form with varying interfacial chemistries during the early stages of artificial aging, which is directly related to the overall stability of certain plates.

Elevated silver, barium and strontium in antlers, vegetation and soils sourced from CWD cluster areas: Do Ag/Ba/Sr piezoelectric crystals represent the transmissible pathogenic agent in TSEs?

High levels of Silver (Ag), Barium (Ba) and Strontium (Sr) and low levels of copper (Cu) have been measured in the antlers, soils and pastures of the deer that are thriving in the chronic wasting disease (CWD) cluster zones in North America in relation to the areas where CWD and other transmissible spongiform encephalopathies (TSEs) have not been reported. The elevations of Ag, Ba and Sr were thought to originate from both natural geochemical and artificial pollutant sources – stemming from the common practise of aerial spraying with `cloud seeding' Ag or Ba crystal nuclei for rain making in these drought prone areas of North America, the atmospheric spraying with Ba based aerosols for enhancing/refracting radar and radio signal communications as well as the spreading of waste Ba drilling mud from the local oil/gas well industry across pastureland. These metals have subsequently bioconcentrated up the foodchain and into the mammals who are dependent upon the local Cu deficient ecosystems. A dual eco-prerequisite theory is proposed on the aetiology of TSEs which is based upon an Ag, Ba, Sr or Mn replacement binding at the vacant Cu/Zn domains on the cellular prion protein (PrP)/sulphated proteoglycan molecules which impairs the capacities of the brain to protect itself against incoming shockbursts of sound and light energy. Ag/Ba/Sr chelation of free sulphur within the biosystem inhibits the viable synthesis of the sulphur dependent proteoglycans, which results in the overall collapse of the Cu mediated conduction of electric signals along the PrP-proteoglycan signalling pathways; ultimately disrupting GABA type inhibitory currents at the synapses/end plates of the auditory/circadian regulated circuitry, as well as disrupting proteoglycan co-regulation of the growth factor signalling systems which maintain the structural integrity of the nervous system. The resulting Ag, Ba, Sr or Mn based compounds seed piezoelectric crystals which incorporate PrP and ferritin into their structure. These ferrimagnetically ordered crystals multireplicate and choke up the PrP-proteoglycan conduits of electrical conduction throughout the CNS. The second stage of pathogenesis comes into play when the pressure energy from incoming shock bursts of low frequency acoustic waves from low fly jets, explosions, earthquakes, etc. (a key eco-characteristic of TSE cluster environments) are absorbed by the rogue `piezoelectric' crystals, which duly convert the mechanical pressure energy into an electrical energy which accumulates in the crystal-PrP-ferritin aggregates (the fibrils) until a point of `saturation polarization' is reached. Magnetic fields are generated on the crystal surface, which initiate chain reactions of deleterious free radical mediated spongiform neurodegeneration in surrounding tissues. Since Ag, Ba, Sr or Mn based piezoelectric crystals are heat resistant and carry a magnetic field inducing pathogenic capacity, it is proposed that these ferroelectric crystal pollutants represent the transmissible, pathogenic agents that initiate TSE.

Fate and effect of silver on the anaerobic digestion process

Laboratory assays were conducted to assess the anaerobic biodegradability of a silver-bearing, waste activated sludge as well as the effect of silver compounds on the anaerobic digestion process. All assays were performed at 35°C in the dark. The ultimate biodegradability of a silver-bearing waste activated sludge (5.0 g silver/kg sludge dry solids) was 61% as compared to 59% for the control (i.e., silver-free) sludge. The rate and extent of methane production was similar for both sludge samples. Addition of either silver nitrate or silver sulfide to methanogenic, mixed cultures up to an equivalent concentration of 100 mg Ag/l did not affect the rate and extent of methane production. Silver thiosulfate when tested at an equivalent concentration of 100 mg Ag/l (and 1000 mg S/l), resulted in accumulation of ca. 28 mM of fatty acids (mainly acetate), 90% inhibition of methanogenesis and 39% inhibition of acidogenesis. However, when using silver-free, thiosulfate-amended controls, it was concluded that the observed inhibition in the silver thiosulfate-amended cultures was not attributed to the silver but rather to the excess thiosulfate (used as an alternative electron acceptor resulting in the production of soluble sulfide at inhibitory levels). Computer simulations under typical anaerobic digestion conditions using the geochemical equilibrium speciation program MINTEQA2 resulted in extremely low concentrations (<10 −14 M) of free silver ions (Ag +). The two predominant insoluble silver species were Ag 2S and Ag°. Therefore, due to the high complexing capacity of the anaerobic digester mixed liquor as well as the reduction to elemental silver, relatively high levels of silver (at least up to 100 mg Ag/l) can be tolerated by anaerobic digestion systems. The results of this study have important implications on the biological treatment and management of photoprocessing wastewaters.

Variations inter-spécifiques de la bioaccumulation et de la toxicité de l'argent á l'égard de trois mollusques bivalves marins

Previous data about silver in marine molluscs have shown a high variability of both accumulation and toxicity of this metal. A potential relationship between these factors has been examined. In a preliminary experiment, three species of bivalves ( Crassostrea gigas, Mytilus galloprovincialis, Chlamys varia) were exposed to silver concentrations varying from 1 to 1000 μg Agl −1 in order to determine parameters of lethal toxicity. Then, specimens of the same species were exposed to sub-lethal levels of silver through food (groups 2), water (groups 3) or both food and water (groups 4). In this main experiment, the level of silver was identical (20 μg Ag1 −1 in the culture medium of algae used as food and in the rearing medium of bivalves. Since the nominal levels of silver in water decreased during the experiment (Tables 1 and 2), seawater and contaminant were renewed every day. The species-related variations of mean lethal time (Table 3) revealed that the most resistant species was the oyster and the lesser one was the scallop. The resistance of oysters was mentioned previously by Martoja et al. (1988) who did not observe any cytological lesion in individuals exposed to silver in experimental conditions similar to those applied in the present study. The susceptibility of scallops has been confirmed since a moderate level of silver of 20 μg Ag l −1 was sufficient to disturb their attachment to the substratum (Table 4) as a consequence of a heavy accumulation of silver sulphide in glandular cells which secrete byssus threads (Martoja et al., 1990). The patterns of bioaccumulation in soft tissues were different in oysters—in which the maximal concentration was reached within 2 weeks (Fig. 1)—and in mussels—which this maximum was not reached after 4 weeks (Fig. 2). Exposure to silver via food induced a significant uptake of this metal in soft tissues of bivalves but it was low compared to uptake from seawater and to the contamination due to the double way of exposure (Table 5). However, the biomass of molluses per unit volume of culture medium varied from species to species. In order to compare strictly the specific ability to concentrate silver, we have determined the quantity of metal available (from food and/or water) per unit weight of filter-feeding organism over a definite period. Then we calculated the percentage of available silver retained by each species (Table 6). These results, as well as the literature data (Brooks and Rumsby, 1965; Folsom and Young, 1965; Preston et al., 1968; Bryan, 1973; Pouvreau and Amiard, 1974), show that Pectinidae and Ostreidae are able to retain very high levels of silver compared to Mytilidae. The species-related behaviour of silver may be interpreted from the point of view of ecotoxicological consequences: • -Species such as the oyster, with a low susceptibility and high ability to concentrate silver, could have an important role as the vector of contamination in food webs. • -Species such as the scallop, able to concentrate high levels of silver and very susceptible, could be eliminated from polluted ecosystens but, in these conditions, their role in trophic transfer will be limited. • -Species such as the mussel, which accumulate only low quantities of silver, will not have any role in food chain contamination and their intermediate susceptibility could have consequences only in highly polluted environments.

Comparison of silver results for canadian reference ores and concentrates and zinc-processing products by acid decomposition, tribenzylamine/chloroform extraction and fire-assay combined with atomic-absorption spectrophotometry

The results obtained for silver in Canadian reference ores and concentrates and in zinc-processing products by three atomic-absorption spectrophotometric methods are compared. “Wet chemical” methods based on the decomposition of the sample with mixed acids yield more accurate results than those based on fire-assay collection techniques. A direct acid-decomposition method involving the determination of silver in a 20% v/v hydrochloric acid-1% v/v diethylenetriamine medium is recommended for the determination of ≈10 μg g or higher levels of silver. A method based on chloroform extraction of the tribenzylamine-silver bromide ion-association complex from 0.08 M potassium bromide-2 M sulphuric acid is recommended for samples containing < 10 μg of silver per g.