Ryo Sekine

Silver speciation and release in commercial antimicrobial textiles as influenced by washing

The use of nanoscale Ag in textiles is one the most often mentioned uses of nano-Ag. It has previously been shown that significant amounts of the Ag in the textiles are released upon washing. However, the form of Ag present in the textiles remains largely unknown as product labelling is insufficient. The aim of this study was therefore to investigate the solid phase speciation of Ag in original and washed silver textiles using XANES. The original Ag speciation in the textiles was found to vary greatly between different materials with Ag(0), AgCl, Ag2S, Ag-phosphate, ionic Ag and other species identified. Furthermore, within the same textile a number of different species were found to coexist. This is likely due to a combination of factors such as the synthesis processes at industrial scale and the possible reaction of Ag with atmospheric gases. Washing with two different detergents resulted in marked changes in Ag-speciation. For some textiles the two detergents induced similar transformation, in other textiles they resulted in very different Ag species. This study demonstrates that in functional Ag textiles a variety of different Ag species coexist before and after washing. These results have important implications for the risk assessment of Ag textiles because they show that the metallic Ag is only one of the many silver species that need to be considered.

Fate of zinc and silver engineered nanoparticles in sewerage networks

Engineered zinc oxide (ZnO) and silver (Ag) nanoparticles (NPs) used in consumer products are largely released into the environment through the wastewater stream. Limited information is available regarding the transformations they undergo during their transit through sewerage systems before reaching wastewater treatment plants. To address this knowledge gap, laboratory-scale systems fed with raw wastewater were used to evaluate the transformation of ZnO- and Ag-NPs within sewerage transfer networks. Two experimental systems were established and spiked with either Ag- and ZnO-NPs or with their dissolved salts, and the wastewater influent and effluent samples from both systems were thoroughly characterised. X-ray absorption spectroscopy (XAS) was used to assess the extent of the chemical transformation of both forms of Zn and Ag during transport through the model systems. The results indicated that both ZnO- and Ag-NPs underwent significant transformation during their transport through the sewerage network. Reduced sulphur species represented the most important endpoint for these NPs in the sewer with slight differences in terms of speciation; ZnO converted largely to Zn sulfide, while Ag was also sorbed to cysteine and histidine. Importantly, both ionic Ag and Ag-NPs formed secondary Ag sulfide nanoparticles in the sewerage network as revealed by TEM analysis. Ag-cysteine was also shown to be a major species in biofilms. These results were verified in the field using recently developed nanoparticle in situ deployment devices (nIDDs) which were exposed directly to sewerage network conditions by immersing them into a municipal wastewater network trunk sewer and then retrieving them for XAS analysis.

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

Abstract 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.

Analytical characterisation of nanoscale zero-valent iron: A methodological review.

Zero-valent iron nanoparticles (nZVI) have been widely tested as they are showing significant promise for environmental remediation. However, many recent studies have demonstrated that their mobility and reactivity in subsurface environments are significantly affected by their tendency to aggregate. Both the mobility and reactivity of nZVI mainly depends on properties such as particle size, surface chemistry and bulk composition. In order to ensure efficient remediation, it is crucial to accurately assess and understand the implications of these properties before deploying these materials into contaminated environments. Many analytical techniques are now available to determine these parameters and this paper provides a critical review of their usefulness and limitations for nZVI characterisation. These analytical techniques include microscopy and light scattering techniques for the determination of particle size, size distribution and aggregation state, and X-ray techniques for the characterisation of surface chemistry and bulk composition. Example characterisation data derived from commercial nZVI materials is used to further illustrate method strengths and limitations. Finally, some important challenges with respect to the characterisation of nZVI in groundwater samples are discussed.

Surface Immobilization of Engineered Nanomaterials for in Situ Study of their Environmental Transformations and Fate

The transformation and environmental fate of engineered nanomaterials (ENMs) is the focus of intense research due to concerns about their potential impacts in the environment as a result of their uniquely engineered properties. Many approaches are being applied to investigate the complex interactions and transformation processes ENMs may undergo in aqueous and terrestrial environments. However, major challenges remain due to the difficulties in detecting, separating, and analyzing ENMs from environmental matrices. In this work, a novel technique capable of in situ study of ENMs is presented. By exploiting the functional interactions between surface modified silver nanoparticles (AgNPs) and plasma-deposited polymer films, AgNPs were immobilized on to solid supports that can be deployed in the field and retrieved for analysis. Either negatively charged citrate or polyethylene glycol, or positively charged polyethyleneimine were used to cap the AgNPs, which were deployed in two field sites (lake and marina), two standard ecotoxicity media, and in primary sewage sludge for a period of up to 48 h. The chemical and physical transformations of AgNPs after exposure to different environments were analyzed by a combination of XAS and SEM/EDX, taken directly from the substrates. Cystine- or glutathione-bound Ag were found to be the dominant forms of Ag in transformed ENMs, but different extents of transformation were observed across different exposure conditions and surface charges. These results successfully demonstrate the feasibility of using immobilized ENMs to examine their likely transformations in situ in real environments and provide further insight into the short-term fate of AgNPs in the environment. Both the advantages and the limitations of this approach are discussed.

Non-labile silver species in biosolids remain stable throughout 50 years of weathering and ageing

Increasing commercial use of nanosilver has focussed attention on the fate of silver (Ag) in the wastewater release pathway. This paper reports the speciation and lability of Ag in archived, stockpiled, and contemporary biosolids from the UK, USA and Australia, and indicates that biosolids Ag concentrations have decreased significantly over recent decades. XANES revealed the importance of reduced-sulfur binding environments for Ag speciation in materials ranging from freshly produced sludge to biosolids weathered under ambient environmental conditions for more than 50 years. Isotopic dilution with (110 m)Ag showed that Ag was predominantly non-labile in both fresh and aged biosolids (13.7% mean lability), with E-values ranging from 0.3 to 60 mg/kg and 5 mM CaNO3 extractable Ag from 1.2 to 609 μg/kg (0.002-3.4% of the total Ag). This study indicates that at the time of soil application, biosolids Ag will be predominantly Ag-sulfides and characterised by low isotopic lability.

Quantifying the adsorption of ionic silver and functionalized nanoparticles during ecotoxicity testing: Test container effects and recommendations.

Abstract Silver nanoparticles (Ag-NPs) are used in a wide variety of products, prompting concerns regarding their potential environmental impacts. To accurately determine the toxicity of Ag-NPs it is necessary to differentiate between the toxicity of the nanoparticles themselves and the toxicity of ionic silver (Ag) released from them. This is not a trivial task given the reactive nature of Ag in solution, and its propensity for both adsorption and photoreduction. In the experiments reported here, we quantified the loss of silver from test solutions during standard ecotoxicity testing conducted using a variety of different test container materials and geometries. This sensitive 110mAg isotope tracing method revealed a substantial underestimation of the toxicity of dissolved Ag to the green algae Pseudokirchneriella subcapitata when calculated only on the basis of the initial test concentrations. Furthermore, experiments with surface-functionalized Ag-NPs under standard algal growth inhibition test conditions also demonstrated extensive losses of Ag-NPs from the solution due to adsorption to the container walls, and the extent of loss was dependent on Ag-NP surface-functionality. These results hold important messages for researchers engaged in both environmental and human nanotoxicology testing, not only for Ag-NPs but also for other NPs with various tailored surface chemistries, where these phenomena are recognized but are also frequently disregarded in the experimental design and reporting.

Aging of dissolved copper and copper-based nanoparticles in five different soils: short-term kinetics vs long-term fate

With the growing availability and use of copper-based nanomaterials (Cu-NMs), there is increasing concern regarding their release and potential impact on the environment. In this study, the short-term (≤5 d) aging profile and the long-term (135 d) speciation of dissolved Cu, copper oxide, and copper sulfide nanoparticles (CuO-NPs and CuS-NPs) were investigated in five different soils using X-ray absorption spectroscopy. Soil pH was found to strongly influence the short-term chemistry of the Cu-NMs added at 100 mg kg above background. Low pH soils promoted rapid dissolution of CuO-NPs that effectively aligned their behavior to that of dissolved Cu within 3 d. In higher pH soils, CuO-NPs persisted longer due to slower dissolution in the soil and resulted in contrasting short-term speciation compared with dissolved Cu, which formed copper hydroxides and carbonates that were reflective of the soil chemistry. Organic matter appeared to slow the dissolution process, but in the long term, the speciation of Cu added as dissolved Cu, CuO-NPs, and CuS-NPs were found to be same for each soil. The results imply that, in the short term, Cu-NMs may exhibit unique behavior in alkaline soils compared with their conventional forms (e.g., in the event of an adverse leaching event), but in the long term (≥135 d), their fates are dictated by the soil properties, are independent of the initial Cu form, and are likely to present minimal risk of nanospecific Cu-NM impact in the soil environment for the concentration studied here.

Hard X-ray synchrotron biogeochemistry: piecing together the increasingly detailed puzzle

Synchrotron techniques have increasingly been used to explore complex biogeochemical processes over the last two decades. In this reasonably short period of time the advances in optics, detector systems and ultimately beamline performance and capabilities have been staggering. Although a very large number of synchrotron methods are available and are employed in biogeochemistry, this perspective article will mainly explore recent developments and trajectories for ‘hard’ X-ray techniques. State-of-the-art beamlines, such as the nano-imaging and nanoanalysis (NINA) end-stations at the European Synchrotron Radiation Facility, will increasingly provide users with unprecedented analytical capabilities. For instance, the NINA end-stations will provide nanoscale resolution (10–20 nm for imaging and 50–100 nm for X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD)) together with high photon fluxes, a wide energy range and sophisticated sample environments. It is pertinent to note that the scientific case for the development of this project specifically mentions environmental and earth science as one of the three main drivers. To take full advantage of this increase in lateral resolution two further areas also need to simultaneously develop: sample preparation or preservation and detector technologies. The need for fast detection is dictated by both the necessity to representatively explore the heterogeneity of environmental samples and to minimise the risk of beam damage. In the last few years, the advent of a new generation of fast fluorescence detectors has gone a long way towards meeting this need (e.g. Lombi et al.). Similarly, an increasing number of beamlines are developing cryo-compatible platforms to reduce radiation damage and allow hydrated samples to be investigated in a frozen state. With several upgrade programs at synchrotrons throughout the world and new facilities coming online (http://www. lightsources.org, accessed 15 November 2013), biogeochemists will be able to delve more and more deeply into the complexity of small scale processes that drive element cycling. However, we would argue that this will also translate into a substantial increase in responsibility for users. First of all, sample preparation and preservation, which is always a key step in any successful spectroscopic investigation, will become even more critical. Some approaches, such as 2-D and 3-D tomography approaches (e.g. de Jonge and Vogt, [5] De Samber et al.) will benefit from the development of cryo-stages. However, in many

Thermal Treatment of Chromium(III) Oxide with Carbonates Analyzed by Far-Infrared Spectroscopy

The chemical state of thermochemically treated chromium(III) oxide (Cr2O3) with various carbonates was analyzed by far-infrared (far-IR) spectroscopy (spectral region 700–25 cm−1). Non-toxic Cr2O3 was oxidized with potassium, sodium, and calcium carbonate, respectively, to toxic Cr(VI) and Cr(V) compounds during thermal treatment at 1000 °C. In reverse, thermochemical treatment of Cr2O3 with magnesium carbonate lead to the formation of the Cr(III) compound MgCr2O4. Higher temperatures (>1200 °C) or reducing atmospheric conditions prevent the formation of Cr(VI)/Cr(V) compounds, too. Additionally, it was found that polyethylene powder with a low particle size (<70 μm) is favorable for the collection of good far-IR spectra of inorganic powders.