Biotransformation of arsenate to the tetramethylarsonium ion in the marine polychaetes Nereis diversicolor and Nereis virens

Arsenic compounds in aqueous extracts of the marine polychaetes Nereis diversicolor and Nereis virens were determined by HPLC-ICP-MS. Both polychaetes contained most of their water-soluble arsenic as arsenobetaine (approximately 60%), and the tetramethylarsonium ion was also a significant arsenic constituent (approximately 20% in N. diversicolor and approximately 30% in N. virens). Trimethylarsoniopropionate and arsenosugars were present in the Nereis species as minor constituents, and traces of arsenocholine, trimethylarsine oxide, and arsenate were also detected. When N. diversicolor and N. virens were exposed in laboratory experiments to different concentrations of arsenate in seawater (10, 50, 100, 500, and 1000 microg of As L(-1)), both species accumulated arsenic in a dose-dependent manner. Atthe highest exposure level, they achieved mean arsenic concentrations (dry mass) of approximately 70 mg of As kg(-1) (N. virens) and 90 mg of As kg(-1) (N. diversicolor), which represented about a 5-fold increase when compared with the control animals. The arsenic taken up by the polychaetes was readily methylated, and the major metabolite was the tetramethylarsonium ion (up to approximately 85% of the accumulated arsenic). Two other products of arsenic methylation, methylarsonate and trimethylarsine oxide, were also produced to a small extent; however, dimethylarsinate, another likely intermediate in the formation of the tetramethylarsonium ion, could not be detected in these experiments. The remaining accumulated arsenic was present as unchanged arsenate. This is the first report of significant biomethylation of arsenic to the tetramethyl stage and provides a ready explanation for the widespread occurrence of tetramethylarsonium ion in marine animals.     

沙蚕多肽提取及功能研究

目的通过研究沙蚕酶解及其多肽产物的功能,提高沙蚕的利用率。方法采用碱性蛋白酶、胃蛋白酶、中性蛋白酶对沙蚕进行酶解,以水解度为评价指标,比较3种酶解产物的抗氧化活性、总还原力能力和降血糖功能。结果 3种酶中中性蛋白酶在6 h达到最高水解度37.8%。碱性蛋白酶酶解7 h的产物其亚铁离子螯合力最高,可达32.7%;DPPH自由基清除能力最高可达85.8%,为中性蛋白酶酶解6 h的产物;胃蛋白酶酶解6 h产物的总还原力最高;胃蛋白酶酶解3 h的酶解产物其DPP-4抑制率最高,可达52.9%。结论胃蛋白酶更适于沙蚕的酶解。酶解产物具有较理想的抗氧化及降血糖功能,为沙蚕多肽产品的开发奠定基础。     

Mucus and microbiota as emerging players in gut nanotoxicology: The example of dietary silver and titanium dioxide nanoparticles

Given the growing use of nanotechnology in many common consumer products, including foods, evaluation of the consequences of chronic exposure to nanoparticles in humans has become a major public health issue. The oral route of exposure has been poorly explored, despite the presence of a fraction of nanosized particles in certain food additives/supplements and the incorporation of such particles into packaging in contact with foods. After their ingestion, these nanoparticles pass through the digestive tract, where they may undergo physicochemical transformations, with consequences for the luminal environment, before crossing the epithelial barrier to reach the systemic compartment. In this review, we consider two examples, nanosilver and nanotitanium dioxide. Despite the specific features of these particles and the differences between them, both display a close relationship between physicochemical reactivity and bioavailability/biopersistence in the gastrointestinal tract. Few studies have focused on the interactions of nanoparticles of silver or titanium dioxide with the microbiota and mucus. However, the microbiota and mucus play key roles in intestinal homeostasis and host health and are undoubtedly involved in controlling the distribution of nanoparticles in the systemic compartment.     

Surface charge-dependent toxicity of silver nanoparticles

As a result of the extensive number of applications of silver nanoparticles (AgNPs), their potential impacts, once released into the environment, are of concern. The toxicity of AgNPs was reported to be dependent on various factors such as particle size, shape and capping agent. Although these factors may play a role in AgNPs toxicity, the results presented herein suggest that surface charge is one of the most important factors that govern the toxicity of AgNPs. In the current study, the toxicity of four AgNPs representing various surface charging scenarios ranging from highly negative to highly positive was investigated. These AgNPs were (1) uncoated H(2)-AgNPs, (2) citrate coated AgNPs (Citrate-AgNPs), (3) polyvinylpyrrolidone coated AgNPs (PVP-AgNPs), and (4) branched polyethyleneimine coated AgNPs (BPEI-AgNPs). Our results clearly demonstrate that the AgNPs exhibited surface charge-dependent toxicity on the bacillus species investigated. Furthermore, ultrafiltration membranes were utilized to purify the AgNPs suspensions from residual impurities prior to the introduction to the microbes. This step was crucial in determining the true AgNPs toxicity and is either missing or not explicitly mentioned in most of the reported toxicity studies.     

Size-controlled dissolution of organic-coated silver nanoparticles

The solubility of Ag NPs can affect their toxicity and persistence in the environment. We measured the solubility of organic-coated silver nanoparticles (Ag NPs) having particle diameters ranging from 5 to 80 nm that were synthesized using various methods, and with different organic polymer coatings including poly(vinylpyrrolidone) and gum arabic. The size and morphology of Ag NPs were characterized by transmission electron microscopy (TEM). X-ray absorption fine structure (XAFS) spectroscopy and synchrotron-based total X-ray scattering and pair distribution function (PDF) analysis were used to determine the local structure around Ag and evaluate changes in crystal lattice parameters and structure as a function of NP size. Ag NP solubility dispersed in 1 mM NaHCO(3) at pH 8 was found to be well correlated with particle size based on the distribution of measured TEM sizes as predicted by the modified Kelvin equation. Solubility of Ag NPs was not affected by the synthesis method and coating as much as by their size. Based on the modified Kelvin equation, the surface tension of Ag NPs was found to be ～1 J/m(2), which is expected for bulk fcc (face centered cubic) silver. Analysis of XAFS, X-ray scattering, and PDFs confirm that the lattice parameter, a, of the fcc crystal structure of Ag NPs did not change with particle size for Ag NPs as small as 6 nm, indicating the absence of lattice strain. These results are consistent with the finding that Ag NP solubility can be estimated based on TEM-derived particle size using the modified Kelvin equation for particles in the size range of 5-40 nm in diameter.     

Intracellular silver accumulation in Chlamydomonas reinhardtii upon exposure to carbonate coated silver nanoparticles and silver nitrate

The intracellular silver accumulation ({Ag}(in)) upon exposure to carbonate coated silver nanoparticles (AgNP, 0.5-10 μM, average diameter 29 nm) and silver nitrate (20-500 nM) was examined in the wild type and in the cell wall free mutant of the green alga Chlamydomonas reinhardtii at pH 7.5. The {Ag}(in) was measured over time up to 1 h after a wash procedure to remove silver ions (Ag(+)) and AgNP from the algal cell surface. The {Ag}(in) increased with increasing exposure time and with increasing AgNP and AgNO(3) concentrations in the exposure media, reaching steady-state concentrations between 10(-5) and 10(-3) mol L(cell)(-1). According to estimated kinetic parameters, high Ag(+) bioconcentration factors were calculated (>10(3) L L(cell)(-1)). Higher accumulation rate constants were assessed in the cell wall free mutant, indicating a protective role of the cell wall in limiting Ag(+) uptake. The bioavailability of AgNP was calculated to be low in both strains relative to Ag(+), suggesting that AgNP internalization across the cell membrane was limited.     

Antimicrobial efficacy of silver nanoparticles in transparent wood coatings

Results on the antimicrobial efficacy of silver nanoparticles in transparent wood coatings for outdoor application are presented. The performance of different hydrophobic, transparent coating systems with and without silver was studied during 2 years of natural weathering. In addition, laboratory efficacy tests were carried out on non-weathered and weathered specimens to assess the resistance of the coatings against mold, blue stain and algae. The protective effect of the tested silver containing coatings against common microorganisms was insufficient, even under initial, non-weathered conditions. Reasons for the failure are the inadequate initial silver concentrations below 50 ppm in the coatings and the associated insufficient availability of free silver ions on the coating surface.     

Toxicogenomic responses of nanotoxicity in Daphnia magna exposed to silver nitrate and coated silver nanoparticles

Applications for silver nanomaterials in consumer products are rapidly expanding, creating an urgent need for toxicological examination of the exposure potential and ecological effects of silver nanoparticles (AgNPs). The integration of genomic techniques into environmental toxicology has presented new avenues to develop exposure biomarkers and investigate the mode of toxicity of novel chemicals. In the present study we used a 15k oligonucleotide microarray for Daphnia magna, a freshwater crustacean and common indicator species for toxicity, to differentiate between particle specific and ionic silver toxicity and to develop exposure biomarkers for citrate-coated and PVP-coated AgNPs. Gene expression profiles revealed that AgNO(3) and AgNPs have distinct expression profiles suggesting different modes of toxicity. Major biological processes disrupted by the AgNPs include protein metabolism and signal transduction. In contrast, AgNO(3) caused a downregulation of developmental processes, particularly in sensory development. Metal responsive and DNA damage repair genes were induced by the PVP AgNPs, but not the other treatments. In addition, two specific biomarkers were developed for the environmental detection of PVP AgNPs; although further verification under different environmental conditions is needed.     

采用天草柑果皮提取液制备纳米银

目的用天草柑果皮制备纳米银,并优化其合成工艺条件。方法以纳米银得率为指标,采用单因素和正交试验对反应时间、温度和AgNO_3浓度进行优化。进一步考察上述反应条件对提取液还原率、所得纳米银的平均粒径、粒径分布和zeta电位值的影响。结果各因素对纳米银得率的影响主次顺序为反应温度AgNO_3浓度反应时间。反应最佳条件为反应时间2 h、反应温度90℃、AgNO_3浓度10 mmol/L。在优化条件下,提取液对Ag~+的还原率为91.1%,所得纳米银的平均粒径为29.8 nm,且zeta电位为(-30.8±0.10)mV。结论所得纳米银具有较为均匀的粒径,且在水溶液中可稳定分散,可用做抗菌填料加入食品包装中。     

Aggregation and dissolution of silver nanoparticles in natural surface water

This study investigated aggregation and silver release of silver nanoparticles suspended in natural water in the absence and presence of artificial sun light. The influence of the capping layer was investigated using uncoated particles and particles coated with citrate or Tween 80. The experiments were conducted over 15 days in batch mode using a river water matrix. Silver release was monitored over this time while the aggregation state and morphological changes of the silver nanoparticles were tracked using dynamic light scattering and transmission electron microscopy. Results indicate sterically dispersed particles coated with Tween released silver quicker than did bare- and citrate-coated particles, which rapidly aggregated. A dissolved silver concentration of 40 μg/L was reached after just 6 h in the Tween-coated particle systems, accounting for ca. 3% of the total silver. Similar levels of dissolved silver were reached in the uncoated and citrate-coated systems at the end of the 15 days. Silver release was not significantly impacted by the artificial sun light; however, the light (and citrate) imparted significant morphological changes to the particles. Their impact was masked by aggregation, which seemed to be the controlling process in this study.     

Some new findings on the potential use of biocompatible silver nanoparticles in winemaking

There is currently an increasing commercial demand for silver nanoparticles (Ag NPs) due to their wide applicability in various markets. Because of their powerful antimicrobial properties, these nanoparticles are frequently used for food-associated consumer products. In this paper, the effect of two Ag NPs coated with biocompatible materials – PEG-Ag NPs 20 (polyethylene glycol) and GSH-Ag NPs (reduced glutathione) – to control microbial growth in wines was assessed. Both Ag NPs were subjected to an in vitro three-step digestion, and changes in their morphology and an assessment of their cytotoxicity against Caco-2 cells were determined. Both Ag NPs were effective against the different microbial population present in tested wines. Regarding their in vitro digestion, the size and shape of the nanoparticles were almost unaltered in the case of GSH-Ag NPs, while in PEG-Ag NPs 20 some particle agglomeration was observed. Overall, these results suggest that Ag NPs may reach the intestine in a nano-scaled form. Finally, Caco-2 cell experiments seemed to exclude toxicity of Ag NPs at the intestinal epithelium.Industrial relevanceTraditionally, sulphur dioxide (SO₂) has been used by oenologists to control the microbial population in wine. As a result of increasing evidence of possible health risks associated with this additive in wine, there has been growing interest in finding new alternatives to replace it. Silver nanoparticles display a broad spectrum of antimicrobial activity, so they could constitute a very promising approach to reducing SO₂ in winemaking.     

Antibacterial properties of silk fabric treated with silver nanoparticles

Silk is hygroscopic and is affected by microorganisms easily. Hence, treatment with antimicrobial agents can facilitate to make silk resistant to microbes. Silver nanoparticles have been attempted by researchers and applied as antimicrobial chemical finish on textiles. Silk has also been applied with silver nanoparticles through exhaust method to obtain antimicrobial properties. However, use of cross-linking agents such as 1,2,3,4 butane tetra carboxylic acid (BTCA) for entrapping silver nanoparticles in the interstitials of the silk molecular chain has not been attempted. The present study is focused on the application of BTCA on silk in the presence of sodium hypophosphite (SHP) simultaneously using silver nanoparticles has been done by pad-dry-cure (2dip/2nip) method. Application of 6% BTCA with 3% SHP and 250 ppm of silver nanoparticles gave satisfactory antimicrobial properties. Infrared spectroscopic (FTIR) studies showed good cross-linking of BTCA. X-ray diffraction studies depict that the crystal structure and crystallinity % of treated silk did not change due to the treatment. SEM studies showed the impregnation of silver nanoparticles on to the fibre matrix. Different physical properties of silk fabric did not change due to the treatment. Based on the studies, it is inferred that BTCA cross-links with silk fibroin at the carboxyl and amine groups, create a lattice void and trap silver nanoparticles giving durable antimicrobial finish.     

Sulfidation of silver nanoparticles decreases Escherichia coli growth inhibition

Sulfidation of metallic nanoparticles such as silver nanoparticles (AgNPs) released to the environment may be an important detoxification mechanism. Two types of AgNPs-an engineered polydisperse and aggregated AgNP powder, and a laboratory-synthesized, relatively monodisperse AgNP aqueous dispersion-were studied. The particles were sulfidized to varying degrees and characterized to determine the effect of initial AgNP polydispersity and aggregation state on AgNP sulfidation, and then exposed to Escherichia coli to determine if the degree of sulfidation of pristine AgNPs affects growth inhibition of bacteria. The extent of sulfidation was found to depend on the HS(-)/Ag ratio. However, for the same reaction times, the more monodisperse particles were fully transformed to Ag(2)S, and the polydisperse, aggregated particles were not fully sulfidized, thus preserving the toxic potential of Ag(0) in the aggregates. A higher Ag(2)S:Ag(0) ratio in the sulfidized nanoparticles resulted in less growth inhibition of E. coli over 6 h of exposure. These results suggest that the initial properties of AgNPs can affect sulfidation products, which in turn affect microbial growth inhibition, and that these properties should be considered in assessing the environmental impact of AgNPs.     

Antibacterial properties of cotton fabric treated with silver nanoparticles

In recent years nano‐sized particles have been focused on bacteriostasis. We investigated antimicrobial activities by applying two types of silver nanoparticles on cotton fabric. These are MesoSilver particles and silver chloride compounds (Silpure). Silver chloride, used in aqueous dispersion, is mixed with a monomer prior to the application on the fabric. MesoSilver is pure silver sub‐nanometer sized particles suspended in deionized water. Silpure solutions were padded and cured on cotton fabric. MesoSilver was padded onto the fabric followed by air drying. SEM images of Silpure‐ and MesoSilver‐treated fabric samples showed good particle dispersion on the fabric. EDX analysis was conducted to confirm the presence of silver particles on the fabric surface. Biological studies exhibited that no growth took place with zones of inhibition on both the treated samples; while the untreated samples did show bacterial growth. The Silpure sample exhibited excellent wash durability; however, the MesoSilver specimen did not.     

Mobility of capped silver nanoparticles under environmentally relevant conditions

The mobility and deposition of capped silver (Ag) nanoparticles (NPs) on silica surfaces were characterized over a wide range of pH and ionic strength (IS) conditions, including seawater and freshwater. Two common organic capping agents (citrate and PVP) were evaluated. Both the capped Ag NPs and the silica surfaces were negatively charged under these environmentally relevant conditions, resulting in net repulsive electrostatics under most conditions. The steric repulsion introduced by the capping agents significantly reduced aggregation and deposition. In addition, the presence of natural organic matter in solution further decreased the deposition of either Ag NP on silica. Ag NPs were found to be highly mobile under these environmentally relevant conditions, with little or no deposition.     

Colloidal stability of carbonate-coated silver nanoparticles in synthetic and natural freshwater

To gain important information on fate, mobility, and bioavailability of silver nanoparticles (AgNP) in aquatic systems, the influence of pH, ionic strength, and humic substances on the stability of carbonate-coated AgNP (average diameter 29 nm) was systematically investigated in 10 mM carbonate and 10 mM MOPS buffer, and in filtered natural freshwater. Changes in the physicochemical properties of AgNP were measured using nanoparticle tracking analysis, dynamic light scattering, and ultraviolet-visible spectroscopy. According to the pH-dependent carbonate speciation, below pH 4 the negatively charged surface of AgNP became positive and increased agglomeration was observed. Electrolyte concentrations above 2 mM Ca(2+) and 100 mM Na(+) enhanced AgNP agglomeration in the synthetic media. In the considered concentration range of humic substances, no relevant changes in the AgNP agglomeration state were measured. Agglomeration of AgNP exposed in filtered natural freshwater was observed to be primarily controlled by the electrolyte type and concentration. Moreover, agglomerated AgNP were still detected after 7 days of exposure. Consequently, slow sedimentation and high mobility of agglomerated AgNP could be expected under the considered natural conditions. A critical evaluation of the different methods used is presented as well.     

Behavior of metallic silver nanoparticles in a pilot wastewater treatment plant

We investigated the behavior of metallic silver nanoparticles (Ag-NP) in a pilot wastewater treatment plant (WWTP) fed with municipal wastewater. The treatment plant consisted of a nonaerated and an aerated tank and a secondary clarifier. The average hydraulic retention time including the secondary clarifier was 1 day and the sludge age was 14 days. Ag-NP were spiked into the nonaerated tank and samples were collected from the aerated tank and from the effluent. Ag concentrations determined by inductively coupled plasma-mass spectrometry (ICP-MS) were in good agreement with predictions based on mass balance considerations. Transmission electron microscopy (TEM) analyses confirmed that nanoscale Ag particles were sorbed to wastewater biosolids, both in the sludge and in the effluent. Freely dispersed nanoscale Ag particles were only observed in the effluent during the initial pulse spike. X-ray absorption spectroscopy (XAS) measurements indicated that most Ag in the sludge and in the effluent was present as Ag(2)S. Results from batch experiments suggested that Ag-NP transformation to Ag(2)S occured in the nonaerated tank within less than 2 h. Physical and chemical transformations of Ag-NP in WWTPs control the fate, the transport and also the toxicity and the bioavailability of Ag-NP and therefore must be considered in future risk assessments.     

Effects of small-diameter silver nanoparticles on microbial load in cow milk

Controlling bacterial growth in fluid milk is of economic interest, and supplemental methods to stop or reduce bacterial growth before and during the cooling chain may be valuable. Silver is effective in controlling growth of single-celled organisms, but has no effect on tissue cells. Smaller diameter (6-8 nm) silver nanoparticles were produced, with purity over 99.99% (no chemical reaction used in the process), by using a terminated gas condensation principle. The first trial investigated effects of time, temperature, and accelerating voltages on total aerobic bacteria count in control milk and milk treated with silver nanoparticles. Metal braids were coated with silver nanoparticles using 3 accelerating voltages, 0, 100, and 200V, the results of which indicated that the braids coated using 100V (AgNP100) were optimal. The AgNP100 particles were effective at all treatment temperatures and durations except for 10h, which indicated that the treated milk could be used after 10h for other dairy products such as yogurt, which require microbial activity. The second experiment investigated the effects of silver nanoparticles on counts of yeasts and molds, coliform bacteria, Escherichia coli, and Staphylococcus aureus in cow milk by treating milk with AgNP100 braids at 22 °C for 1h. Inductively coupled plasma mass spectrometry analyses indicated that the maximum amount of silver found in the AgNP100-treated milk was 6.1μg/L, which is below the safety limits. Counts in milk samples containing the nanoparticle-coated braids were lower for all yeasts and molds and bacteria investigated compared with the control milk samples, which were kept under the same conditions but without the braids. The differences were significant for coliforms, Escherichia coli, and Staphylococcus aureus but not for yeasts and molds, although ranking of the counts (AgNP100 < initial load < control) were the same for all microorganisms. Small-diameter, silver nanoparticle-coated braids can stop or reduce bacterial growth in fluid milk. Silver nanoparticles inhibited microbial growth and may be useful in complementing the cooling chain and the thermal processes. These results warrant more research on the sensory properties and long-term safety of the use of silver nanoparticles in dairy products.     

Influence of silver nanoparticles on the fabrics functions prepared by in-situ technique

The development of multifunctional fabrics is an important purpose for their application in many fields. This study provided a simple approach for innovative textile design by applying the optical properties of Plasmonic noble metal nanoparticles. The utilization of feasible technique to functionalize both semi-synthetic and synthetic fabrics namely viscose and acrylic fabric has been accomplished. Where, fabrics functions have been developed by in situ synthesis of silver nanoparticles (Ag NPs) into their surface using trisodium citrate as multifunctional agent (reductant, stabilizer, and linker). The silver NPs incorporated into fabrics has been characterized by UV–visible spectroscopy, scanning electron microscopy, energy dispersive X-ray, and X-ray photoelectron spectroscopy. The mechanism of assembling Ag NPs in situ incorporated fabric matrix has been discussed. The influence of silver nanoparticles on the coloration, UV-protection, and antibacterial properties of the fabrics has also been examined. The overall results indicated that, the in situ Ag NPs-incorporated into fabrics has been applied as a colorant for both viscose and acrylic fabrics effectively beside the improvement for UV-blocking and anti-bacterial properties.     

More than the ions: the effects of silver nanoparticles on Lolium multiflorum

Silver nanoparticles (AgNPs) are increasingly used as antimicrobial additives in consumer products and may have adverse impacts on organisms when they inadvertently enter ecosystems. This study investigated the uptake and toxicity of AgNPs to the common grass, Lolium multiflorum. We found that root and shoot Ag content increased with increasing AgNP exposures. AgNPs inhibited seedling growth. While exposed to 40 mg L(-1) GA-coated AgNPs, seedlings failed to develop root hairs, had highly vacuolated and collapsed cortical cells and broken epidermis and rootcap. In contrast, seedlings exposed to identical concentrations of AgNO(3) or supernatants of ultracentrifuged AgNP solutions showed no such abnormalities. AgNP toxicity was influenced by total NP surface area with smaller AgNPs (6 nm) more strongly affecting growth than did similar concentrations of larger (25 nm) NPs for a given mass. Cysteine (which binds Ag(+)) mitigated the effects of AgNO(3) but did not reduce the toxicity of AgNP treatments. X-ray spectro-microscopy documented silver speciation within exposed roots and suggested that silver is oxidized within plant tissues. Collectively, this study suggests that growth inhibition and cell damage can be directly attributed either to the nanoparticles themselves or to the ability of AgNPs to deliver dissolved Ag to critical biotic receptors.