Fractionating nanosilver: importance for determining toxicity to aquatic test organisms

This investigation applied novel techniques for characterizing and fractionating nanosilver particles and aggregates and relating these measurements to toxicological endpoints. The acute toxicity of eight nanosilver suspensions of varying primary particle sizes (10-80 nm) and coatings (citrate, polyvinylpyrrolidone, EDTA, proprietary) was assessed using three aquatic test organisms (Daphnia magna, Pimephales promelas, Pseudokirchneriella subcapitata). When 48-h lethal median concentrations (LC50) were expressed as total silver, both D. magna and P. promelas were significantly more sensitive to ionic silver (Ag(+)) as AgNO(3) (mean LC50 = 1.2 and 6.3 μg/L, respectively) relative to a wide range in LC50 values determined for the nanosilver suspensions (2 -126 μg/L). However, when LC50 values for nanosilver suspensions were expressed as fractionated nanosilver (Ag(+) and/or <4 nm particles), determined by ultracentrifugation of particles and confirmed field-flow-fractograms, the LC50 values (0.3-5.6 μg/L) were comparable to the values obtained for ionic Ag(+) as AgNO(3). These results suggest that dissolved Ag(+) plays a critical role in acute toxicity and underscores the importance of characterizing dissolved fractions in nanometal suspensions.     

Nanoparticle silver released into water from commercially available sock fabrics

Manufacturers of clothing articles employ nanosilver (n-Ag) as an antimicrobial agent, but the environmental impacts of n-Ag release from commercial products are unknown. The quantity and form of the nanomaterials released from consumer products should be determined to assess the environmental risks of nanotechnology. This paper investigates silver released from commercial clothing (socks) into water, and its fate in wastewater treatment plants (WWTPs). Six types of socks contained up to a maximum of 1360 microg-Ag/g-sock and leached as much as 650 microg of silver in 500 mL of distilled water. Microscopy conducted on sock material and wash water revealed the presence of silver particles from 10 to 500 nm in diameter. Physical separation and ion selective electrode (ISE) analyses suggest that both colloidal and ionic silver leach from the socks. Variable leaching rates among sock types suggests that the sock manufacturing process may control the release of silver. The adsorption of the leached silver to WWTP biomass was used to develop a model which predicts that a typical wastewater treatment facility could treat a high concentration of influent silver. However, the high silver concentration may limitthe disposal of the biosolids as agricultural fertilizer.     

Prospective environmental life cycle assessment of nanosilver T-shirts

A cradle-to-grave life cycle assessment (LCA) is performed to compare nanosilver T-shirts with conventional T-shirts with and without biocidal treatment. For nanosilver production and textile incorporation, we investigate two processes: flame spray pyrolysis (FSP) and plasma polymerization with silver co-sputtering (PlaSpu). Prospective environmental impacts due to increased nanosilver T-shirt commercialization are estimated with six scenarios. Results show significant differences in environmental burdens between nanoparticle production technologies: The "cradle-to-gate" climate footprint of the production of a nanosilver T-shirt is 2.70 kg of CO(2)-equiv (FSP) and 7.67-166 kg of CO(2)-equiv (PlaSpu, varying maturity stages). Production of conventional T-shirts with and without the biocide triclosan has emissions of 2.55 kg of CO(2)-equiv (contribution from triclosan insignificant). Consumer behavior considerably affects the environmental impacts during the use phase. Lower washing frequencies can compensate for the increased climate footprint of FSP nanosilver T-shirt production. The toxic releases from washing and disposal in the life cycle of T-shirts appear to be of minor relevance. By contrast, the production phase may be rather significant due to toxic silver emissions at the mining site if high silver quantities are required.     

Silver nanoparticles and total aerosols emitted by nanotechnology-related consumer spray products

Products containing silver nanoparticles are entering the market rapidly, but little is known about the potential for inhalation exposure to nanosilver. The objectives of this work were to characterize the emissions of airborne particles from consumer products that claim to contain silver nanoparticles or ions, determine the relationship between emissions and the products' liquid characteristics, and assess the potential for inhalation exposure to silver during product use. Three products were investigated: an antiodor spray for hunters, a surface disinfectant, and a throat spray. Products emitted 0.24-56 ng of silver in aerosols per spray action. The plurality of silver was found in aerosols 1-2.5 μm in diameter for two products. Both the products' liquid characteristics and the bottles' spray mechanisms played roles in determining the size distribution of total aerosols, and the size of silver-containing aerosols emitted by the products was largely independent of the silver size distributions in the liquid phase. Silver was associated with chlorine in most samples. Results demonstrate that the normal use of silver-containing spray products carries the potential for inhalation of silver-containing aerosols. Exposure modeling suggests that up to 70 ng of silver may deposit in the respiratory tract during product use.     

基于柠檬提取液的银纳米颗粒绿色制备工艺优化

为实现绿色制备银纳米颗粒,研究以硝酸银为原料,采用柠檬提取液为还原剂和稳定剂,在水溶剂环境中采用生物法绿色合成银纳米颗粒。研究探讨了柠檬提取液(柠檬汁、柠檬皮醇提液、柠檬皮水提液)用量,硝酸银浓度,pH调节剂,反应时间,反应温度等因素对银纳米颗粒粒径、形貌、稳定性的影响,并借助紫外-可见分光光度法(UV-Vis)、SEM对银纳米颗粒进行表征。通过工艺优化,分别确定了以柠檬汁、柠檬皮醇提液、柠檬皮水提液为原料的银纳米颗粒最佳制备工艺,所得银纳米颗粒都具有分散性能良好,颗粒均匀,粒径范围为70 nm左右,其中以柠檬皮醇提液工艺制备银纳米颗粒的形貌及稳定性最佳,即硝酸银1.0 mmol/L、柠檬皮醇提液9 mL、反应时间12 min、pH调节剂为1 mol·L^-1的NaOH。该工艺采用生物法合成银纳米颗粒,绿色安全、环境友好,具有较好的实际应用价值。     

真丝织物的氯菊酯纳米银抗菌整理

以商用氯菊酯除螨剂为保护剂,硼氢化钠为还原剂,常温下还原硝酸银制备得到纳米银溶液。最优的纳米银制备工艺为:纳米银溶液质量浓度800 mg/L,保护剂质量浓度36 g/L,反应温度30℃。所制备的纳米银为球形,平均粒径约为27 nm。将制得的纳米银溶液利用浸轧烘工艺对真丝织物进行抗菌处理。整理后的真丝织物负载量为1 356 mg/kg时,对大肠埃希菌和金黄葡萄球菌的抑菌圈分别达到10.6 mm和10.4 mm,抑菌率均达到99.99%,显示出优异的抑菌性能。扫描电镜观察发现纳米银均匀分布在蚕丝纤维表面,无团聚现象。     

Determination of silver release from antibacterial finished cotton and polyester fabrics into water

Silver compounds have extensive use among the antimicrobial agents in textiles. Silver particles are released into the water during washing processes in particular and they are released from the textile in time due to use. In this work, silver ion release from cotton and polyester antimicrobial fabrics which are the most widely used textiles have been studied. Two well-known silver-based commercial agents and silver-doped calcium phosphate powder-based antibacterial finishing agent which was developed in our previous work were applied to the fabric samples. The release of silver from the fabric samples during washing and incubation was determined by ICP-OES. The effects of fabric composition, time and laundering process on the silver release were studied. It was found that significant amount of silver was released from textile fabrics during washing due to the mechanical forces exerted on the fabrics. The total released silver varied from 73.43 to 92.27% for cotton fabrics and 76.49 to 89.70% for PES fabrics after 20 washing cycles. Results also showed that calcium phosphate can reduce the amount of silver release significantly. It was also found that even a smaller quantity of nanosilver particles was sufficient for strong antibacterial activity.     

Characterization of silver nanoparticles migration from package materials destined for contact with foods

There was studied migration of artificial silver nanoparticles from polyethylene films destined for package of such foods as bread and poultry into model media reproducing physico-chemical properties and composition of said products. Modification of films was performed by 5- or 10-fold spraying of silver nanoparticles on the surface of package material. Model media were composed from water, alcohol and plant oil according to US FDA and Russian Federal Service for Surveillance of Consumer Rights Protection and Human Well-Being official recommendation. Nanoparticles were detected in model media by means of transmission electron and atomic force microscopy. Quantification of silver in nanoparticles migrating from films was performed by mass-spectrometry with inductively coupled plasma. The results obtained showed that silver migrated from films into test media in form of nanoparticles with mean diameter close to 10-20 nm. Migrated particles were partially aggregated to complexes with dimension about 50 nm with degree of aggregation depending on media composition. Quantification showed that amounts of silver nanoparticles migrating in foods did not exceed save level of this nanomaterial consumption even in aggravated conditions when almost all volume of product was consumed in form packaged in films modified with nanosilver.     

纳米银整理棉织物的制备及其抗菌性能

利用柠檬酸三钠和硝酸银溶液制备纳米Ag整理棉织物,通过X射线衍射仪、扫描电镜和X射线光电子能谱仪对纳米Ag整理棉织物进行表征。考察了柠檬酸三钠与硝酸银物质的量比、温度及浸泡时间对棉织物中Ag质量分数及棉织物抗菌性能的影响。结果表明,棉织物中Ag质量分数和棉织物抗菌性能随着柠檬酸三钠与硝酸银物质的量比的增大先增大后减小,随温度的升高及浸泡时间的延长而增大。当柠檬酸三钠与硝酸银物质的量比为5、温度为80℃、浸泡时间为60 min时,抗菌棉织物对革兰氏阴性菌和革兰氏阳性菌的抑菌圈直径分别达到2.7、2.3 mm。洗涤5次后,纳米Ag整理棉织物仍具有较好的抗菌活性。     

The rheology of colloidal and noncolloidal food dispersions

ABSTRACT:  Rheological data on a food together with data on its composition and structure or microstructure should lead to understanding the interrelationships between them. A number of foods are dispersions of solids in liquids, liquids in liquids, or gas in liquids. The dispersed particles may be colloidal in nature with dimensions < 10 μm, or larger noncolloidal particles (> 10 μm). For both colloidal and noncolloidal dispersions (either in dilute or concentrated regimes), several theoretical equations exist that provide insights into the role of key rheological parameters, such as particle volume fraction and size, interparticle forces, and fractal dimension on their viscosity, yield stress, and modulus. When theoretical models cannot be easily applied to foods with complex structures, structural analysis and structure-based models provide insight into the role of solids loading and interparticle bonding on rheological behavior. In this review, recent studies on colloidal and noncolloidal food dispersions in which theoretical models as well as structural analysis were employed are discussed.     

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.     

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.     

固着剂与助留剂协同控制DCS时的胶体聚集研究

将固着剂聚胺(PA)、助留剂阳离子聚丙烯酰胺(CPAM)单独以及协同处理旧报纸脱墨浆,采用聚焦光束反射测定仪(FBRM)考察浆料中残余胶体粒子的数量、尺寸及其分布,探讨固着剂与助留剂单独及协同控制溶解与胶体物质(DCS)时的胶体聚集现象。结果表明,实验所用的PA单独处理纸浆时,会产生部分不能固着于纤维或被纤维网络截留的胶体聚集体;CPAM单独处理纸浆时,其电荷容易被DCS中和,导致其降低纸浆胶体粒子数量的效果明显下降,但并不产生胶体聚集体;PA-CPAM协同处理纸浆时,CPAM能将PA预处理纸浆时产生的部分胶体聚集体进一步固着到纤维上,达到更好的降低胶体粒子数量的效果,且不产生更大的胶体聚集体。     

Size dependent and reactive oxygen species related nanosilver toxicity to nitrifying bacteria

The intrinsic slow growth of nitrifying bacteria and their high sensitivity to environmental perturbations often result in cell growth inhibition by toxicants. Nanoparticles are of great concern to the environment because of their small size and high catalytic properties. This work sought to determine size-dependent inhibition by Ag nanoparticles and evaluate the relationship between the inhibition and reactive oxygen species (ROS). Nanoparticles with an average size range of 9-21 nm were synthesized by varying the molar ratios of BH4-/Ag+ in the solution. The resulting ROS generation was quantified in the presence and absence of the bacteria while the degree of inhibition was inferred from specific oxygen uptake rate measurements, determined by extant respirometry. By examining the correlation between nanoparticle size distribution, photocatalytic ROS generation, intracellular ROS accumulation, and nitrification inhibition, we observed that inhibition to nitrifying organisms correlated with the fraction of Ag nanoparticles less than 5 nm in the suspension. It appeared that these size nanoparticles could be more toxic to bacteria than any other fractions of nanoparticles or their counterpart bulk species. Furthermore, inhibition by Ag nanoparticles as well as other forms of silver (AgCl colloid and Ag+ ion) correlated well with the intracellular ROS concentrations, but not with the photocatalytic ROS fractions. The ROS correlations were different for the different forms of silver, indicating that factors other than ROS are also important in determining nanosilver toxicity.     

The role of polysaccharides on the stability of colloidal particles of beer

This study aimed at understanding the influence of beer colloidal composition and size on physical stability of the colloidal suspensions in beer before filtration. The percentages of retention during filtration indicate that colloidal particles consist principally of polysaccharides (97.04%) and smaller amounts of proteins (2.87%) and polyphenols (0.22). The viscosity of a colloidal dispersion can be modelled as the sum of a hard‐sphere contribution and a colloidal force contribution. The colloidal force contribution is determined from the volume fraction of particles, the viscosity colloidal dispersion and the beer viscosity without particles. The volume fraction of particles could be estimated from the particle density and the total solid present in the beer. The fitting parameters of the correlation between the particles volume fraction and the colloidal force viscosity could explain the low stability of the colloidal particles of beer. This last determination is more specific than the simple viscosity of beer and could help to improve the prediction of the filtration flow.     

Characterzation of colloidal and humic-bound Ni and U in the "dissolved" fraction of contaminated sediment extracts

The dissolved phase of environmental aqueous samples is generally defined by filtration at 0.2 microm or even 0.45 microm. However, it is also acknowledged that colloids <0.2 microm suspended in the aqueous phase can be important for determining contaminant availability and mobility. We have used flow field-flow fractionation (FI FFF) and size exclusion chromatography (SEC) coupled to UV-absorbance (UVA) and inductively coupled plasma mass spectrometry (ICP-MS) to study the dissolved organic matter (DOM) and colloidal binding of U and Ni in water extracts of sediments collected from a contaminated area of the Savannah River Site, a U.S. Department of Energy former nuclear materials production and processing facility, near Aiken, SC. High-performance SEC-UVA-ICP-MS was well-suited to the separation of DOM overthe molecular weight (MW) range of approximately 200-7000 Da. The ICP-MS element specific data indicated that a significant fraction of U was associated with DOM. Uranium exhibited a bimodal distribution and the other fraction was greater than the exclusion limit for the column and coeluted with Al. Flow FFF was used to size this fraction as colloidal with an approximate effective spherical diameter of 0.09-0.12 microm. Element specific ICP-MS data confirmed that U and Al were associated with the colloidal phase. High-field FI FFF was also applicable to sizing DOM but resolution was poorer than SEC. The results of this study suggest that "dissolved" U at this site is predominantly either complexed by DOM or bound to a colloidal fraction while Ni is predominately present as labile complexes or the free cation and, therefore, potentially bioavailable.     

Colloidal approach to prepare colour blends from colourants with different solubility profiles

Food colouring plays a vital and a determining role in the processing and the manufacturing of food products because the appearance of products is critical for attracting consumers and influencing their food choices. However, factors such as legislative restrictions, limited number of approved colourants and the processing, formulation and stability issues of the natural colourants severely limits the application of food colouring in actual product formats. Hence, finding alternatives to the currently utilised formulation practises, represents an important area of research. Here, we report a simple colloidal approach to prepare colour blends by co-incorporating colourants with contrasting aqueous solubility profiles in composite colloidal particles. Curcumin and indigocarmine were selected as water insoluble and water soluble food-grade colourants respectively and incorporated in the colloidal particles prepared from food protein-zein. Composite particles obtained by loading of curcumin and indigocarmine (at different ratios) had mean particle size ranging from 76 to 300 nm. The spherical shape of the colloidal particles was confirmed using transmission electron microscopy and the colloidal dispersions were further characterised using UV–Vis and fluorescence spectroscopy. The incorporation of colourants in colloidal particles led to the generation of different shade of colour in yellow–green–blue range. The encapsulation also led to the stabilization of individual pigments against photodegradation. Such composite colloidal particles could potentially serve as an approach for developing tuneable colouring system for food and nutraceutical applications.     

Modeling of simultaneous exchange of colloids and sorbing contaminants between streams and streambeds

Contaminant transport in streams can be significantly modified by both stream-subsurface exchange and the presence of colloidal particles, but the interaction of these effects is notwell understood. Exchange with the hyporheic zone exposes contaminants to surface-chemical reactions with streambed sediments, while colloidal particles have a large reactive surface area that allows them to carry pollutants that would otherwise be transported primarily as dissolved species. A new theoretical model is developed to predict the role of colloids in mediating advective contaminant exchange between streams and streambeds. Bedform-induced pumping theory is applied to model physical transport, and colloid filtration and reversible contaminant sorption are used to calculate the local distributions of colloids and contaminants within the streambed. Residence time functions of both colloids and contaminants in the bed are then used to link contaminant concentrations in the pore water and streamwater. Model simulations indicate that, under conditions of low colloid filtration and strong contaminant sorption to colloids, contaminants are mobilized by colloids and there is less retention of contaminants in the streambed. This is the case of "colloid-facilitated contaminant transport" commonly considered in groundwater transport. On the other hand, when colloid filtration is high and contaminants still sorb strongly to colloids, contaminant mobility decreases and there is greater contaminant retention in the streambed. We term this case "colloid-impeded contaminant transport". Thus, we find that a variety of contaminanttransport behavior can occur depending on the concentration and mobility of suspended particles in the system and the relative affinity of contaminants for colloids and other solid phases.     

六堡茶茶汤中胶体颗粒及沉淀性状研究

黑茶主要由微生物发酵形成,六堡茶是典型的黑茶之一,发酵对茶汤胶体性质与茶乳酪的成分组成是否有影响,尚未明确。本文通过动态光散射、扫描电子显微镜和高效液相色谱等方法比较了六堡茶毛茶以及发酵后的成品茶茶汤的胶体颗粒性质。结果表明,六堡茶毛茶和成品茶的茶汤均存在丁达尔现象,即存在胶体体系。两种茶汤在冷却过程的浊度变化率逐渐减少,接近常温时,成品茶茶汤浊度增加率小于毛茶;两种茶汤中均存在球形或椭球形的胶体颗粒,且胶粒粒径与Zeta电位具有温度响应。室温下成品茶茶汤的胶体颗粒平均粒径(2131 nm)显著低于毛茶(3045.8 nm),成品茶Zeta电位绝对值(-24.8 mV)高于毛茶(-19.2 mV)。两种茶汤成分差异导致二者沉淀差异,成品茶固形物相对沉淀率(2.22%)少于毛茶(2.79%),成品茶沉淀主要成分为茶红素、茶褐素和多糖,占沉淀94.11%,毛茶则为多酚、蛋白质和多糖,占沉淀75.76%,两种茶汤沉淀中酯型儿茶素总量均高于非酯型儿茶素总量,其酯型儿茶素、蛋白质、多糖和黄酮较易参与沉淀形成。因此,发酵使成品六堡茶的茶汤的胶体颗粒的稳定性增加,使其形成的茶乳酪与发酵前存在明显的差异。本研究为黑茶饮料等食品的开发提供了理论基础。     

纳米银-聚乙烯复合包装中助剂对银向食品模拟物迁移的影响

为探究纳米银-聚乙烯复合包装中添加剂对纳米银颗粒向食品模拟物迁移的影响,在20、40 ℃和70 ℃条件下分别将空白纳米银聚乙烯复合包装和含有助剂（抗氧化剂1076、抗氧化剂168、光稳定剂622和光稳定剂944）的纳米银聚乙烯复合包装在3 g/100 mL乙酸溶液和体积分数50%乙醇溶液两种食品模拟物中浸泡1～30 h,然后蒸干定容并用电感耦合等离子体质谱测定银的含量。结果表明：食品模拟物中银的加标回收率在84.19%～115.69%之间,相对标准偏差在3.21%～8.75%之间;在8 h内塑料中的添加剂会促进银向两种食品模拟物的迁移;同时银的迁移率会随着迁移温度的升高和迁移时间的增加而增大直至平衡;平衡时,塑料中的添加剂反而阻碍银向这两种食品模拟物的迁移;银在酸性模拟物中的迁移率大于在酒精类模拟物中的迁移率。