Synchrotron speciation of silver and zinc oxide nanoparticles aged in a kaolin suspension

Molecular toxicity and defense mechanisms induced by silver nanoparticles in Drosophila melanogaster

The widely use of silver nanoparticles (AgNPs) as antimicrobial agents gives rise to potential environmental risks. AgNPs exposure have been reported to cause toxicity in animals. Nevertheless, the known mechanisms of AgNPs toxicity are still limited. In this study, we systematically investigated the toxicity of AgNPs exposure using Drosophila melanogaster. We show here that AgNPs significantly decreased Drosophila fecundity, the third-instar larvae weight and rates of pupation and eclosion in a dose-dependent manner. AgNPs reduced fat body cell viability in MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assays. AgNPs caused DNA damage in hemocytes and S2 cells. Interestingly, the mRNA levels of the entire metallothionein gene family were increased under AgNPs exposure as determined by RNA-seq analysis and validated by qRT-PCR, indicating that Drosophila responded to the metal toxicity of AgNPs by producing metallothioneins for detoxification. These findings provide a better understanding of the mechanisms of AgNPs toxicity and may provide clues to effect on other organisms, including humans.

Dissolution kinetics and solubility of copper oxide nanoparticles as affected by soil properties and aging time

Nano copper oxide (CuO NP) was added to eight soils to study the effect of aging time of copper on the concentration of diethylenetriaminepentaacetic acid (DTPA)-extracted copper (DTPA-Cu), with bulk copper oxide (CuO BP) and copper nitrate [Cu(NO₃)₂] used for comparison. Moreover, the effect of soil properties on the dissolution of CuO NP was studied. A dissolution model was used to quantitatively describe the dissolution kinetics of CuO NPs in different soils. The results showed that the concentration of DTPA-Cu decreased with increasing aging time in soils spiked with Cu(NO₃)₂, while the concentration increased to varying degrees in soils spiked with CuO NPs or CuO BPs. In acidic soils, the equilibrium concentrations of DTPA-Cu were 93.3-98.7 mg·kg^-1 for CuO NP treatments, 65.5-94.3 mg·kg^-1 for CuO BP treatments, and 81.4-90.0 mg·kg^-1 for Cu(NO₃)₂ treatments, which were greater than those in alkaline soils (43.4-56.9 mg·kg^-1, 6.26-8.61 mg·kg^-1, and 73.9-80.0 mg·kg^-1, respectively). In acidic soils, DTPA-Cu equilibrium concentration ranked the different forms of copper treatments as CuO NPs > Cu(NO₃)₂ > CuO BPs, while in alkaline soils, the order was Cu(NO₃)₂ > CuO NPs > CuO BPs. The dissolution rate constants and solubility of CuO NPs were 0.33-6.42 and 37.1-100.1 mg·kg^-1, respectively. Pearson correlation analysis indicated that the dissolution parameters of CuO NPs were negatively correlated with soil pH and positively correlated with the contents of organic matter, clay, iron oxides, and aluminum oxides. Further, the dissolution rate constant and solubility of CuO NPs could be well predicted by soil pH and the content of free or amorphous aluminum. Our study identified the main factors controlling the dissolution of CuO NPs in farmland soils and highlighted the higher availability of CuO NPs in acidic soils.

Impact of ZnO nanoparticles on soil lead bioavailability and microbial properties

In the present study, we investigated the responses of microbial respiration and community structure, enzyme activity and DTPA-extractable Pb within 60 days of incubation in soils treated with Pb and nano-ZnO. The results showed that when the concentration of nano-ZnO exceeded 10 mg/kg, the concentration of DTPA-extractable Pb significantly decreased by 10.6%-21.3% on the 60th day of the experiment. The addition of nano-ZnO decreased the Pb-contaminated soil pH from 6.18 to 6.08 at 7 days, which is part of the reason for the β-glucosidase activity change. Ten mg/kg nano-ZnO significantly reduced the qCO₂ value, which represented the microbial energy demand for the conversion of carbon sources into biomass. Nano-ZnO improved the microbial diversity and richness of some metal-tolerant bacteria at 60 days. The findings provide deeper insight into the responses of soil microbes and Pb bioavailability in the presence of nano-ZnO particles.

Plant response to silver nanoparticles: a critical review

Although several metal ions/metal nanoparticles (NPs) are toxic to both plants and animals, some of them are used as nutrients and growth promoters. Plants exposed to silver nanoparticles (Ag-NPs) have shown both beneficial and harmful effects. All concentrations of Ag-NPs are not effective for a given plant because any excess can block the passage of essential nutrients. Regulated treatment of plants by Ag-NPs may enhance their overall growth and development. It has been noticed that Ag-NPs decrease the mass of edible plants (Cucurbita pepo, Allium cepa, cabbage, and lettuce) and vegetables, but they also induce the germination of seeds in many cases. NPs interact with proteins, enzymes, and carbohydrates influencing the total biomass, root, and shoot growth of plants. Also, Ag-NPs act as an ethylene inhibitor and activate the antioxidants in onions. Their substantial quantity becomes deposited in onion leaves and bulbs. Size and concentration are the two major factors responsible for the increase/decrease of plant growth and biomass. Plants make adaptations to reduce the toxicity caused by Ag-NPs. In some cases, Ag-NPs induce root elongation and increase chlorophyll, carbohydrate, proteins, rate of photosynthesis and inhibit the biosynthesis of ethylene. This review article provides a comprehensive overview of both the beneficial and adverse effects of Ag-NPs on germination, growth, development, physiological, and biochemical characteristics of a wide range of edible and crop plants. We have also critically discussed: the chemistry, toxicity, uptake, translocation, and accumulation of Ag-NPs in plant systems.

Long-term dissolution and transformation of ZnO in soils: The roles of soil pH and ZnO particle size

The ongoing use of ZnO nanoparticles (NPs)-associated commercial products results in large release of ZnO NPs into soils and has prompted systematic investigation regarding their fractionation and fate in soils. To date, little information is available about the long-term dissolution and transformation of ZnO NPs in different soils. The distribution and speciation of Zn in two different soils (i.e., Red soil (RS) and Wushantu soil (WS)) treated with either ZnO NPs or bulk ZnO were elucidated by combining soil incubation study with synchrotron-based techniques. Results revealed that ZnO NPs and bulk ZnO were almost dissolved after 1 day, indicating their rapid dissolution upon entering RS (pH-acidic). Rapid dissolution of ZnO NPs was also observed even in WS (pH- circumneutral). The solubilized Zn²⁺ released from ZnO particles was completely transformed into stable forms (e.g., Zn-Al LDH, Zn-OM, and Zn(OH)₂) and Zn-Al LDH was the dominant species in WS after incubation for 360 days. A majority of solubilized Zn²⁺ released from ZnO particles was also transformed into Zn-Al LDH precipitate in RS. The findings of this study facilitate a better understanding of the fate of ZnO in soils, which could be leveraged for remediation of ZnO-polluted soils.

Ageing alters the physicochemical properties of silver nanoparticles and consequently compromises their acute toxicity in mammals

Despite numerous investigations into AgNP-induced toxicity, little has been taken into consideration the potential health impacts of aged AgNPs in comparison to fresh AgNPs. In the current study, we scrutinized the potential effects of aged AgNPs in animals. We first found that AgNPs underwent morphological transformations after natural ageing in aqueous solution upon exposure to air and sunlight for 9 days, as characterized by significant aggregation with increase of particle size approximately by 2 fold. Meanwhile, dissolved Ag ions from aged AgNPs increased by 33% compared to fresh AgNPs. Strikingly, the acute exposure results showed that aged AgNPs induced lower toxicity in mice relative to fresh AgNPs. Aged AgNPs caused milder local inflammation in the peritoneal cavity of mice, as evidenced by 63% reduction of tumor necrosis factor α (TNF-α) than that induced by fresh AgNPs. The deposition mass of aged AgNPs in the liver, spleen, lung and kidney was diminished by 69%, 39%, 83% and 40%, respectively, compared to the distribution profiles in response to fresh AgNPs. Whereby, milder splenic hyperemia was observed, and no significant hepatoxicity was found. Additionally, aged AgNPs provoked milder increase of periphery leukocytes and malondialdehyde (MDA) in mice in comparison to fresh AgNPs. Taken together, this study unraveled that the ageing process elicited remarkable alterations to physicochemical properties and toxic effects as well. This study would provide new insights into the potential health impacts of AgNPs under transformation-determined exposure scenarios.

Multi-method assessment of PVP-coated silver nanoparticles and artificial sweat mixtures

Research presented here utilizes silver nanoparticles (AgNPs) as a case study for how the immediate local environment alters the physical and chemical properties of nanomaterials. Dermal exposure is a primary route for exposure to many of the consumer products containing AgNPs. Interactions between AgNPs and human sweat/perspiration are critical for understanding how changes in Ag speciation will impact exposure. Previous studies have examined silver release from AgNP-containing products after exposure to artificial sweat (AS), however there is no basic assessment of how mixtures of AgNPs and AS alter the physical and chemical properties of AgNPs. The current research evaluated changes in size, aggregation, chemical composition, and silver speciation of four different sizes of AgNPs exposed to four different formulations of AS. The AS formulations were from standardized methods with different chemical compositions, ionic strengths, and pH. Samples were collected at four-time intervals for analysis using dynamic light scattering , UV-Vis spectroscopy, and single-particle inductively coupled plasma-mass spectrometry . Each mixture was also prepared for speciation analysis using X-ray absorption spectroscopy and scanning electron microscopy coupled to energy-dispersive X-ray analysis. The equivalent diameter measurements from the three techniques followed the order of DLS > UV-Vis > spICP-MS. Speciation analyses indicate significant changes for the smaller NPs, while the largest (100 nm) NPs had less measurable differences. This study shows the need to fully understand what specific information an analytical technique might provide and to use those techniques properly in tandem to give the fullest answer to a given research question.

The migration dynamics and the speciation of arsenic in the Hetao area, Inner Mongolia

Arsenic contamination of the groundwater in the Hetao area in Inner Mongolia, China, has been a serious problem since the 1980s. In this study, the behavioral mechanics of arsenic in soil in the Hetao area, in relation to arsenic concentrations in groundwater, were studied using elemental speciation analysis. It is for probing the possible mechanisms of correlation and interaction within water and soil of the area, which is little work on it not only in the Hetao area but also worldwide. Associated with our previous work on water in this area, soil samples were collected along transects through areas strongly affected by arsenic poisoning. Sequential extractions were used to determine the speciation in soil of arsenic and other elements (Cd, Cu, Mo, Pb, Sb, Sn, and Zn) which are with similar geochemical behaviors to arsenic in natural systems. The results show that the arsenic concentration in soil is correlated with arsenic concentration in groundwater. This implies that arsenic transformation as a main factor of the resident poisoning of the area could be related with groundwater and soil. These results suggest that arsenic poisoning in the Hetao area is related with water and soil. The tracers moving through water are retained in the shallow stratum including soil and persist in the water affected by the movement of arsenic through the shallow stratum and soil. Graphical abstract.

ZnO nanoparticles-induced oxidative stress in Chenopodium murale L, Zn uptake, and accumulation under hydroponic culture

To understand toxic effect of Zn oxide nanoparticles (ZnO NPs) on Chenopodium murale, 40-day-old plants were exposed to 10, 50, and 250 mg L^-1 of NPs using hydroponic system under controlled light and temperature conditions. Aboveground parts and roots were harvested 3 and 6 days after treatments and evaluated for some growth and biochemical indices. By increasing the concentration of ZnO NPs, the content of Zn increased in the roots more than the shoots. Our findings showed that all ZnO NPs treatments resulted in a decrease in growth, total chlorophyll content and soluble proteins, while the content of carotenoids, lipid peroxidation, leaf hydrogen peroxide (H₂O₂), and leaf electrolyte leakage increased significantly compared with the control. These changes, along with increased proline content and catalase (CAT), guaiacol peroxidase (GPX), and superoxide dismutase (SOD) activities in the treated plants, suggest that all concentrations of ZnO NPs used in this study strongly induced oxidative stress. A decline in growth-related indicators can be considered as an indicator of ZnO NPs phytoxicity in C. murale. Based on the concentration of Zn dissolved in the solution, the effects of Zn released into the nutrient solution may be greatly involved in induction of toxicity and retardation of growth at least under our experimental conditions. The results of this study suggest that an important mechanism of ZnO NPs phytotoxicity may be the exacerbation of oxidative stress and damage to biomembranes.

Subcellular targets of zinc oxide nanoparticles during the aging process: role of cross-talk between mitochondrial dysfunction and endoplasmic reticulum stress in the genotoxic response

Zinc oxide nanoparticles (ZnO NPs) are being produced abundantly and applied increasingly in various fields. The special physicochemical characteristics of ZnO NPs makes them incline to undergo physicochemical transformation over time (aging), which modify their bioavailability and toxicity. However, the subcellular targets and the underlying molecular mechanisms involved in the genotoxicity induced by ZnO NPs during aging process are still unknown. The present study found that the acute cytotoxic effects of fresh ZnO NPs was largely regulated by mitochondria-dependent apoptosis, which the level of cleaved Caspase-3 and mitochondria damage were significantly higher than that of 60 day-aged ZnO NPs. In contrast, aged ZnO NPs induced more reactive oxygen species (ROS) production and endoplasmic reticulum (ER) stress marker protein (BIP/GRP78) expression and their genotoxicity could be dramatically suppressed by either ROS scavengers (DMSO, CAT and NaN3) or ER stress inhibitor (4-PBA). Using mitochondrial-DNA deficient (ρ0) AL cells, we further found that ER stress induced by aged ZnO NPs was triggered by ROS generated from mitochondria, which eventually mediated the gentoxicity of aged NPs. Our data provided novel information on better understanding the contribution of subcellular targets to the genotoxic response of ZnO NPs during the aging process.

Biocompatibility and biodegradability of polyacrylate/ZnO nanocomposite during the activated sludge treatment process

Polymer nanocomposites have been widely used in the preparation of coating agents in the leather industry. Considering the complex bio-effect and ecological risk of nanomaterial, research on the biodegradability and biocompatibility of polyacrylate/metal nanocomposites in activated sludge system is of specific significance. We investigated the change of the bacterial community and diversity of activated sludge fed with polyacrylate/ZnO nanocomposites in both low (500 mg COD /L) and high (1000 mg COD/L) doses. COD removal, dehydrogenase activity, and total protein of activated sludge system were monitored in all treatments over 30 days. The results demonstrated that the exposure to both polyacrylate/ ZnO nanocomposite and polyacrylate decreased the dehydrogenase activity at early stage comparing to the control, but had no significant influence on COD removal. Overall, the bacterial communities in activated sludge were resistant to polyacrylate/ZnO nanocomposites, and had higher levels of metabolic activity, protein accumulation and bioavailability when exposed to these chemicals comparing to the control especially at later stages of incubation (15-30 days), which indicated that these polyacrylate/ZnO nanocomposites of certain amount were biocompatible to activated sludge system.

Effects of aged ZnO NPs and soil type on Zn availability, accumulation and toxicity to pea and beet in a greenhouse experiment

Most studies have assessed the toxicity of pristine NPs to plants without considering the likely changes that these NPs will undergo during their residence time in the soil. In this study, we assessed the effects of ZnO NPs (3, 20, and 225 mg Zn kg-1 soil) aged for a year in soil and after a previous crop on the Zn availability in soil, leaf accumulation and toxicity to green pea (Pisum sativum L.) and beet root (Beta vulgaris L). The effects were compared to bulk ZnO and ZnSO4 in two agricultural soils with different pH under greenhouse conditions. The Zn concentration in the plant leaf was 6-12-fold higher in acidic than in calcareous soil that could explain the different effects on plants caused by Zn applications depending on soil type. Thus, in acidic soil, ZnO NPs promoted ROS generation in both plant species with increases from 47% to 130%, increased the MDA content in pea up to 58 ± 8% in plant exposed to ZnSO4 at 225 mg Zn kg-1 soil and altered the ratio of photosynthetic pigments in beet between 12% and 41%, suggesting distressed chloroplast constituents. In calcareous soil, the changes seemed to be related to the supply of Zn in Zn deficient soils, whose principal effect was the 20-65% decrease of ROS levels in treated plants. The available and leaf Zn concentrations did not differ among Zn sources. Likewise, ZnO NPs showed comparable toxic or stimulatory effects to ZnO bulk and Zn salt, with some exceptions where Zn ion showed the highest phytotoxicity and effectiveness as a micronutrient. According to our results, we cannot affirm that NPs pose a higher potential environmental risk than their bulk counterparts after one-year of residence time in soil.

Engineered nano particles: Nature, behavior, and effect on the environment

Increased application of engineered nano particles (ENPs) in production of various appliances and consumer items is increasing their presence in the natural environment. Although a wide variety of nano particles (NPs) are ubiquitously dispersed in ecosystems, risk assessment guidelines to describe their ageing, direct exposure, and long-term accumulation characteristics are poorly developed. In this review, we describe what is known about the life cycle of ENPs and their impact on natural systems and examine if there is a cohesive relationship between their transformation processes and bio-accessibility in various food chains. Different environmental stressors influence the fate of these particles in the environment. Composition of solid media, pore size, solution chemistry, mineral composition, presence of natural organic matter, and fluid velocity are some environmental stressors that influence the transformation, transport, and mobility of nano particles. Transformed nano particles can reduce cell viability, growth and morphology, enhance oxidative stress, and damage DNA in living organisms.

Comparative cytotoxicity of nanoparticles and ions to Escherichia coli in binary mixtures

The objective of this study was to understand toxicity of mixture of nanoparticles (NPs) (ZnO and TiO₂) and their ions to Escherichia coli. Results indicated the decrease in percentage growth of E. coli with the increase in concentration of NPs both in single and mixture setups. Even a small concentration of 1mg/L was observed to be significantly toxic to E. coli in binary mixture setup (exposure concentration: 1mg/L ZnO and 1mg/L TiO₂; 21.15% decrease in plate count concentration with respect to control). Exposure of E. coli to mixture of NPs at 1000mg/L (i.e., 1000mg/L ZnO and 1000mg/L TiO₂) resulted in 99.63% decrease in plate count concentration with respect to control. Toxic effects of ions to E. coli were found to be lesser than their corresponding NPs. The percentage growth reduction was found to be 36% for binary mixture of zinc and titanium ions at the highest concentration (i.e., 803.0mg/L Zn and 593.3mg/L Ti where ion concentrations are equal to the Zn ions present in 1000mg/L ZnO NP solution and Ti⁺⁴ ions present in 1000mg/L TiO₂ NP solution). Nature of mixture toxicity of the two NPs to E. coli was found to be antagonistic. The alkaline phosphatase (Alp) assay indicated that the maximum damage was observed when E. coli was exposed to 1000mg/L of mixture of NPs. This study tries to fill the knowledge gap on information of toxicity of mixture of NPs to bacteria which has not been reported earlier.

Weathering in soil increases nanoparticle CuO bioaccumulation within a terrestrial food chain

This study evaluates the bioaccumulation of unweathered (U) and weathered (W) CuO in NP, bulk and ionic form (0-400 mg/kg) by lettuce exposed for 70 d in soil co-contaminated with field incurred chlordane. To evaluate CuO trophic transfer, leaves were fed to crickets (Acheta domestica) for 15 d, followed by insect feeding to lizards (Anolis carolinensis). Upon weathering, the root Cu content of the NP treatment increased 214% (327 ± 59.1 mg/kg) over unaged treatment. Cu root content decreased in bulk and ionic treatments from 70-130 mg/kg to 13-26 mg/kg upon aging in soil. Micro X-ray fluorescence (μ-XRF) analysis of W-NP-exposed roots showed a homogenous distribution of Cu (and Ca) in the tissues. Additionally, micro X-ray absorption near-edge (μ-XANES) analysis of W-NP-exposed roots showed near complete transformation of CuO to Cu (I)-sulfur and oxide complexes in the tissues, whereas in unweathered treatment, most root Cu remained as CuO. The expression level of nine genes involved in Cu transport shows that the mechanisms of CuO NPs (and bulk) response/accumulation are different than ionic Cu. The chlordane accumulation by lettuce upon co-exposure to CuO NPs significantly increased upon weathering. Conversely, bulk and ionic exposures decreased pesticide accumulation by plant upon weathering. The Cu cricket fecal content from U-NP-exposed insects was significantly greater than the bulk or ion treatments, suggesting a higher initial NP accumulation followed by significantly greater elimination during depuration. In the lizard, Cu content in the intestine, body and head did not differ as a function of weathering. This study demonstrates that CuO NPs may undergo transformation processes in soil upon weathering that subsequently impact NPs availability in terrestrial food chains.

Lessons learned: Are engineered nanomaterials toxic to terrestrial plants?

The expansion of nanotechnology and its ubiquitous applications has fostered unavoidable interaction between engineered nanomaterials (ENMs) and plants. Recent research has shown ambiguous results with regard to the impact of ENMs in plants. On one hand, there are reports that show hazardous effects, while on the other hand, some reports highlight positive effects. This uncertainty whether the ENMs are primarily hazardous or whether they have a potential for propitious impact on plants, has raised questions in the scientific community. In this review, we tried to demystify this ambiguity by citing various exposure studies of different ENMs (nano-Ag, nano-Au, nano-Si, nano-CeO2, nano-TiO2, nano-CuO, nano-ZnO, and CNTs, among others) and their effects on various groups of plant families. After scrutinizing the most recent literature, it seems that the divergence in the research results may be possibly attributed to multiple factors such as ENM properties, plant species, soil dynamics, and soil microbial community. The analysis of the literature also suggests that there is a knowledge gap on the effects of ENMs towards changes in color, texture, shape, and nutritional aspects on ENM exposed plants.

In situ detection of the Zn(2+) release process of ZnO NPs in tumour cells by confocal laser scanning fluorescence microscopy

The use of zinc oxide (ZnO) nanoparticles (NPs) for cancer is not yet clear for human clinical applications, which is primarily due to the lack of a better understanding of the action mechanisms and cellular consequences of the direct exposure of cells to these NPs. In this work, the authors have selected zinquin ethyl ester, a Zn(2+)-specific fluorescent molecular probe, to efficiently differentiate ZnO NPs and Zn(2+), and combined with confocal laser scanning microscopy (CLSM) to in situ study the Zn(2+) release process of ZnO NPs in cancer cell system through detecting the change of Zn(2+) level over time. During the experiments, the authors have designed the test group ZnO-2 in addition to assess the influence of a long-term storage on the characteristics of ZnO NPs in aqueous solution, and the Zn(2+) release process of ZnO NPs in cancer cell system. After three-month storage at room temperature, the release process became earlier and faster, which was consistent with previous results of transmission electron microscope, UV-Vis and PL spectra. It is a good detection method that combination of Zn(2+)-specific fluorescent molecular probe and CLSM, which will be helpful for ZnO NPs using in clinical research.

Mutagenicity of ZnO nanoparticles in mammalian cells: Role of physicochemical transformations under the aging process

Zinc oxide nanoparticles (ZnO NPs) potentially undergo physicochemical transformation in the environment, which may lead to unexpected environmental and health risks. The "aging" process is essential for better understanding the toxicity and fate of NPs in the environment. However, the mutagenic effects of aged ZnO NPs are still unexplored. The present study focused on investigating the physicochemical transformation during aging process and clarifying the mutagenicity of naturally aged ZnO NPs in human-hamster hybrid (AL) cells. It was found that ZnO NPs underwent sophisticated physicochemical transformations with aging regardless of original morphology or size, such as the microstructural changes, the formation of hydrozincite (Zn5(CO3)2(OH)6) and the release of free zinc ions. Interestingly, the aged ZnO NPs were investigated to be able to result in much lower cytotoxicity while relatively high degree mutation than fresh ZnO NPs. With characterization of the soluble and insoluble fractions of aged ZnO NPs suspension, together with the control measurements using metal chelator (TPEN) and endocytosis inhibitor (Nystatin), it was revealed that the release of zinc ions and nanoparticle uptake made significantly different contributions to the mutagenicity of fresh and aged ZnO NPs. This study clearly demonstrated that the physicochemical transformation of ZnO NPs with aging plays important and comprehensive roles in the ZnO NPs-induced mutagenicity in mammalian cells.

Fate of Zinc Oxide Nanoparticles Coated onto Macronutrient Fertilizers in an Alkaline Calcareous Soil

Zinc oxide (ZnO) nanoparticles may provide a more soluble and plant available source of Zn in Zn fertilizers due to their greater reactivity compared to equivalent micron- or millimetre-sized (bulk) particles. However, the effect of soil on solubility, spatial distribution and speciation of ZnO nanoparticles has not yet been investigated. In this study, we examined the diffusion and solid phase speciation of Zn in an alkaline calcareous soil following application of nanoparticulate and bulk ZnO coated fertilizer products (monoammonium phosphate (MAP) and urea) using laboratory-based x-ray techniques and synchrotron-based μ-x-ray fluorescence (μ–XRF) mapping and absorption fine structure spectroscopy (μ–XAFS). Mapping of the soil-fertilizer reaction zones revealed that most of the applied Zn for all treatments remained on the coated fertilizer granule or close to the point of application after five weeks of incubation in soil. Zinc precipitated mainly as scholzite (CaZn₂(PO₄)₂.2H₂O) and zinc ammonium phosphate (Zn(NH₄)PO₄) species at the surface of MAP granules. These reactions reduced dissolution and diffusion of Zn from the MAP granules. Although Zn remained as zincite (ZnO) at the surface of urea granules, limited diffusion of Zn from ZnO-coated urea granules was also observed for both bulk and nanoparticulate ZnO treatments. This might be due to either the high pH of urea granules, which reduced solubility of Zn, or aggregation (due to high ionic strength) of released ZnO nanoparticles around the granule/point of application. The relative proportion of Zn(OH)₂ and ZnCO₃ species increased for all Zn treatments with increasing distance from coated MAP and urea granules in the calcareous soil. When coated on macronutrient fertilizers, Zn from ZnO nanoparticles (without surface modifiers) was not more mobile or diffusible compared to bulk forms of ZnO. The results also suggest that risk associated with the presence of ZnO NPs in calcareous soils would be the same as bulk sources of ZnO.

Effects of silver nanoparticles to soil invertebrates: oxidative stress biomarkers in Eisenia fetida

Silver nanoparticles (Ag-NPs) are among the most produced NPs worldwide having several applications in consumer products. Ag-NPs are known to cause oxidative stress in several organisms and cell lines, however comparatively less information is available regarding their effects on soil living invertebrates. The purpose of this study was to investigate if Ag-NPs cause oxidative stress on soil invertebrates. The model soil species Eisenia fetida was used. Our results showed that total glutathione (TG) is the first mechanism triggered by Ag-NPs, followed by glutathione peroxidase (GPx) and glutathione reductase (GR), however oxidative damage was observed for higher doses and exposure time (increased lipid peroxidation, LPO). AgNO3 exposure caused impairment in GPx and glutathione-S-transferase (GST), probably as result of the higher bioavailability of Ag in the salt-form. The current results indicate that effects are partly caused by Ag ions released from Ag-NPs, but specific particle effects cannot be excluded.

Selective divalent cobalt ions detection using Ag2O3-ZnO nanocones by ICP-OES method for environmental remediation

Here, we have synthesized Ag₂O₃-ZnO nanocones (NCs) by a wet-chemical route using reducing agents at low temperature. The structural, optical and morphological properties of Ag₂O₃-ZnO NCs were investigated by several conventional techniques such as powder XRD, XPS, FESEM, XEDS, FTIR and UV/vis. spectroscopy. The analytical parameters of prepared NCs were also calculated for a selective detection of divalent cobalt [Co(II)] prior to its determination by inductively coupled plasma-optical emission spectrometry (ICP-OES). The selectivity of NCs toward various metal ions, including Cd(II), Co(II), Cr(III), Cu(II), Fe(III), Ni(II), and Zn(II) was studied. Results of the selectivity study demonstrated that Ag₂O₃-ZnO NC phase was the most selective towards Co(II) ion. The uptake capacity for Co(II) ion was experimentally calculated to be ∼76.69 mgg⁻¹. Moreover, adsorption isotherm data provided that the adsorption process was mainly monolayer on homogeneous adsorbent surfaces of Ag₂O₃-ZnO NCs. Kinetic study revealed that the adsorption of Co(II) on Ag₂O₃-ZnO NCs phase followed the pseudo-second-order kinetic model. In addition, thermodynamic results provided that the adsorption mechanism of Co(II) ions on Ag₂O₃-ZnO NCs was a spontaneous process and thermodynamically favorable. Finally, the proposed method was validated by applying it to real environmental water samples with reasonable results.

Effect of soil organic matter content and pH on the toxicity of ZnO nanoparticles to Folsomia candida

Organic matter (OM) and pH may influence nanoparticle fate and effects in soil. This study investigated the influence of soil organic matter content and pH on the toxicity of ZnO-NP and ZnCl2 to Folsomia candida in four natural soils, having between 2.37% and 14.7% OM and [Formula: see text] levels between 5.0 and 6.8. Porewater Zn concentrations were much lower in ZnO-NP than in ZnCl2 spiked soils, resulting in higher Freundlich sorption constants for ZnO-NP. For ZnCl2 the porewater Zn concentrations were significantly higher in less organic soils, while for ZnO-NP the highest soluble Zn level (23mgZn/l) was measured in the most organic soil, which had the lowest pH. Free Zn(2+) ion concentrations were higher for ZnCl2 than for ZnO-NP and were greatly dependent on pH (pHpw) and dissolved organic carbon content of the pore water. The 28-d EC50 values for the effect of ZnCl2 on the reproduction of F. candida increased with increasing OM content from 356 to 1592mgZn/kg d.w. For ZnO-NP no correlation between EC50 values and OM content was found and EC50 values ranged from 1695 in the most organic soil to 4446mgZn/kg d.w. in the higher pH soil. When based on porewater and free Zn(2+) concentrations, EC50 values were higher for ZnCl2 than for ZnO-NP, and consistently decreased with increasing pHpw. This study shows that ZnO-NP toxicity is dependent on soil properties, but is mainly driven by soil pH.

Fate and lability of silver in soils: effect of ageing

The fate and lability of added soluble Ag in soils over time was examined by measurement of labile metal (E-value) by isotopic dilution using the (110m)Ag radioactive isotope and the solid-phase speciation of Ag by X-ray absorption near edge structure (XANES) spectroscopy. After two weeks of ageing the E-values for Ag decreased by 20-90% with a further decrease of 10-40% after six months. The overall decrease in labile Ag for all soils after the 6 month ageing period was 50-100%. The ageing was more rapid and pronounced in the alkaline soils. XANES results for Ag in soils indicated that for the majority of soils the added Ag(+) was reduced to metallic Ag over time, and associations with Fe-oxohydroxides and reduced S groups in organic matter also decreased Ag lability. Strong positive correlations were found between metallic Ag and non-labile Ag and between organic carbon and Ag bonded with S species.

Multitechnique investigation of the pH dependence of phosphate induced transformations of ZnO nanoparticles

In order to properly evaluate the ecological and human health risks of ZnO manufactured nanomaterials (MNMs) released to the environment, it is critical to understand the likely transformation products in various environments, such as soils, surface and ground waters, and wastewater treatment processes. To address this knowledge gap, we examined the transformation of 30 nm ZnO MNMs in the presence of different concentrations of phosphate as a function of time and pH using a variety of orthogonal analytical techniques. The data reveal that ZnO MNMs react with phosphate at various concentrations and transform into two distinct morphological/structural phases: a micrometer scale crystalline zinc phosphate phase (hopeite-like) and a nanoscale phase that likely consists of a ZnO core with an amorphous Zn3(PO4)2 shell. The P species composition was also pH dependent, with 82% occurring as hopeite-like P at pH 6 while only 15% occurred as hopeite-like P at pH 8. These results highlight how reactions of ZnO MNMs with phosphate are influenced by environmental variables, including pH, and may ultimately result in structurally and morphologically heterogeneous end products.

Aged TiO2-based nanocomposite used in sunscreens produces singlet oxygen under long-wave UV and sensitizes Escherichia coli to cadmium

TiO2-based nanocomposite (NC) are widely used as invisible UV protectant in cosmetics. These nanomaterials (NMs) end in the environment as altered materials. We have investigated the properties of T-Lite SF, a TiO2-NC used as sunscreen, after weathering in water and under light. We have examined the formation of ROS and their consequences on cell physiology of Escherichia coli. Our results show that aged-T-Lite SF produced singlet oxygen under low intensity long wave UV and formed hydroxyl radicals at high intensity. Despite the production of these ROS, T-Lite SF had neither effect on the viability of E. coli nor on mutant impaired in oxidative stress, did not induce mutagenesis and did not impair the integrity of membrane lipids, thus seemed safe to bacteria. However, when pre-exposed to T-Lite SF under low intensity UV, cells turned out to be more sensitive to cadmium, a priority pollutant widely disseminated in soil and surface waters. This effect was not a Trojan horse: sensitization of cells was dependent on the formation of singlet oxygen. These results provide a basis for caution, especially on NMs that have no straight environmental toxicity. It is crucial to anticipate indirect and combined effects of environmental pollutants and NMs.

Residence time effects on phase transformation of nanosilver in reduced soils

Residence time effects on phase transformation of silver nanoparticles (AgNPs) (15-50 nm, with and without polyvinylpyrrolidone (PVP) coating) were investigated in reducing soils using experimental geochemistry and synchrotron-based x-ray techniques. After 30 days of anaerobic incubation, a substantial fraction of PVP-coated AgNPs (15 nm) were transformed into Ag₂S and or humic acid (HA) complexed Ag(I), whereas only the HA fraction was dominant in uncoated AgNPs (50 nm). Several investigations recently reported that sulfidation of AgNPs to Ag₂S was the predominant mechanism controlling the fate of AgNP in soil-water environments. However, this investigation showed each AgNP underwent particle-specific chemical transformations to different end compounds after 30 days. Considering the small contribution of Ag(I) dissolution from all AgNPs (less than 5%), we concluded that changes in solid-state chemical speciation of sorbed AgNPs was promoted by particle-specific interactions of NPs in soil chemical constituents, suggesting a critical role of soil absorbents in predicting the fate of AgNPs in terrestrial environments.

Speciation of metal(loid)s in environmental samples by X-ray absorption spectroscopy: a critical review

Element specificity is one of the key factors underlying the widespread use and acceptance of X-ray absorption spectroscopy (XAS) as a research tool in the environmental and geo-sciences. Independent of physical state (solid, liquid, gas), XAS analyses of metal(loid)s in complex environmental matrices over the past two decades have provided important information about speciation at environmentally relevant interfaces (e.g. solid-liquid) as well as in different media: plant tissues, rhizosphere, soils, sediments, ores, mineral process tailings, etc. Limited sample preparation requirements, the concomitant ability to preserve original physical and chemical states, and independence from crystallinity add to the advantages of using XAS in environmental investigations. Interpretations of XAS data are founded on sound physical and statistical models that can be applied to spectra of reference materials and mixed phases, respectively. For spectra collected directly from environmental matrices, abstract factor analysis and linear combination fitting provide the means to ascertain chemical, bonding, and crystalline states, and to extract quantitative information about their distribution within the data set. Through advances in optics, detectors, and data processing, X-ray fluorescence microprobes capable of focusing X-rays to micro- and nano-meter size have become competitive research venues for resolving the complexity of environmental samples at their inherent scale. The application of μ-XANES imaging, a new combinatorial approach of X-ray fluorescence spectrometry and XANES spectroscopy at the micron scale, is one of the latest technological advances allowing for lateral resolution of chemical states over wide areas due to vastly improved data processing and detector technology.

Fate of ZnO nanoparticles in soils and cowpea (Vigna unguiculata)

The increasing use of zinc oxide nanoparticles (ZnO-NPs) in various commercial products is prompting detailed investigation regarding the fate of these materials in the environment. There is, however, a lack of information comparing the transformation of ZnO-NPs with soluble Zn(2+) in both soils and plants. Synchrotron-based techniques were used to examine the uptake and transformation of Zn in various tissues of cowpea ( Vigna unguiculata (L.) Walp.) exposed to ZnO-NPs or ZnCl2 following growth in either solution or soil culture. In solution culture, soluble Zn (ZnCl2) was more toxic than the ZnO-NPs, although there was substantial accumulation of ZnO-NPs on the root surface. When grown in soil, however, there was no significant difference in plant growth and accumulation or speciation of Zn between soluble Zn and ZnO-NP treatments, indicating that the added ZnO-NPs underwent rapid dissolution following their entry into the soil. This was confirmed by an incubation experiment with two soils, in which ZnO-NPs could not be detected after incubation for 1 h. The speciation of Zn was similar in shoot tissues for both soluble Zn and ZnO-NPs treatments and no upward translocation of ZnO-NPs from roots to shoots was observed in either solution or soil culture. Under the current experimental conditions, the similarity in uptake and toxicity of Zn from ZnO-NPs and soluble Zn in soils indicates that the ZnO-NPs used in this study did not constitute nanospecific risks.

Environmental concentrations of engineered nanomaterials: review of modeling and analytical studies

Scientific consensus predicts that the worldwide use of engineered nanomaterials (ENM) leads to their release into the environment. We reviewed the available literature concerning environmental concentrations of six ENMs (TiO2, ZnO, Ag, fullerenes, CNT and CeO2) in surface waters, wastewater treatment plant effluents, biosolids, sediments, soils and air. Presently, a dozen modeling studies provide environmental concentrations for ENM and a handful of analytical works can be used as basis for a preliminary validation. There are still major knowledge gaps (e.g. on ENM production, application and release) that affect the modeled values, but over all an agreement on the order of magnitude of the environmental concentrations can be reached. True validation of the modeled values is difficult because trace analytical methods that are specific for ENM detection and quantification are not available. The modeled and measured results are not always comparable due to the different forms and sizes of particles that these two approaches target.

Sorption, dissolution and pH determine the long-term equilibration and toxicity of coated and uncoated ZnO nanoparticles in soil

To assess the effect of long-term dissolution on bioavailability and toxicity, triethoxyoctylsilane coated and uncoated zinc oxide nanoparticles (ZnO-NP), non-nano ZnO and ZnCl2 were equilibrated in natural soil for up to twelve months. Zn concentrations in pore water increased with time for all ZnO forms but peaked at intermediate concentrations of ZnO-NP and non-nano ZnO, while for coated ZnO-NP such a clear peak only was seen after 12 months. Dose-related increases in soil pH may explain decreased soluble Zn levels due to fixation of Zn released from ZnO at higher soil concentrations. At T = 0 uncoated ZnO-NP and non-nano ZnO were equally toxic to the springtail Folsomia candida, but not as toxic as coated ZnO-NP, and ZnCl2 being most toxic. After three months equilibration toxicity to F. candida was already reduced for all Zn forms, except for coated ZnO-NP which showed reduced toxicity only after 12 months equilibration.

Nano-silica fabricated with silver nanoparticles: antifouling adsorbent for efficient dye removal, effective water disinfection and biofouling control

A nano-silica-AgNPs composite material is proposed as a novel antifouling adsorbent for cost-effective and ecofriendly water purification. Fabrication of well-dispersed AgNPs on the nano-silica surface, designated as NSAgNP, has been achieved through protein mediated reduction of silver ions at ambient temperature for development of sustainable nanotechnology. The coated proteins on AgNPs led to the formation of stable NSAgNP and protected the AgNPs from oxidation and other ions commonly present in water. The NSAgNP exhibited excellent dye adsorption capacity both in single and multicomponent systems, and demonstrated satisfactory tolerance against variations in pH and dye concentration. The adsorption mainly occurred through electrostatic interaction, though π-π interaction and pore diffusion also contributed to the process. Moreover, the NSAgNP showed long-term antibacterial activity against both planktonic cells and biofilms of Gram-negative Escherichia coli and Pseudomonas aeruginosa. The antibacterial activity of AgNPs retarded the initial attachment of bacteria on NSAgNP and thus significantly improved the antifouling properties of the nanomaterial, which further inhibited biofilm formation. Scanning electron and fluorescence microscopic studies revealed that cell death occurred due to irreversible damage of the cell membrane upon electrostatic interaction of positively charged NSAgNP with the negatively charged bacterial cell membrane. The high adsorption capacity, reusability, good tolerance, removal of multicomponent dyes and E. coli from the simulated contaminated water and antifouling properties of NSAgNP will provide new opportunities to develop cost-effective and ecofriendly water purification processes.

ZnO nanoparticle fate in soil and zinc bioaccumulation in corn plants (Zea mays) influenced by alginate

Nanoparticles (NPs) can interact with naturally occurring inorganic and organic substances in soils, which may change their transport behavior in soil and plants. This study was performed in two steps. In the first step, corn (Zea mays) plants were cultivated for one month in soil amended with 10 nm commercial spheroid ZnO NPs at 0–800 mg kg−1 and sodium alginate at 10 mg kg−1. In the second step, the plants were grown with ZnO NPs at 400 mg kg−1 and alginate at 0, 10, 50, and 100 mg kg−1. The dynamics of Zn concentrations in soil solution and Zn accumulation in plant tissues were determined by ICP-OES. Biomass accumulation, chlorophyll concentration, and the activity of antioxidant enzymes in leaves were also quantified. Results indicate that ZnO NPs coexisting with Zn dissolved species were continuously released to the soil solution to replenish the Zn ions or ZnO NPs scavenged by roots. At 400 and 800 mg kg−1, without alginate, ZnO NPs significantly reduced the root and shoot biomass production; however, plants treated with these NP concentrations, plus alginate, had significantly more Zn in tissues with no reduction in biomass production. Alginate significantly reduced the activity of stress enzymes catalase and peroxidase, which could indicate damage in the defense system. The effects of ZnO NPs in a food crop grown in alginate enriched soil, showing an excess of Zn in the aerial parts, are yet to be reported.

Fate of zinc oxide nanoparticles during anaerobic digestion of wastewater and post-treatment processing of sewage sludge

The rapid development and commercialization of nanomaterials will inevitably result in the release of nanoparticles (NPs) to the environment. As NPs often exhibit physical and chemical properties significantly different from those of their molecular or macrosize analogs, concern has been growing regarding their fate and toxicity in environmental compartments. The wastewater-sewage sludge pathway has been identified as a key release pathway leading to environmental exposure to NPs. In this study, we investigated the chemical transformation of two ZnO-NPs and one hydrophobic ZnO-NP commercial formulation (used in personal care products), during anaerobic digestion of wastewater. Changes in Zn speciation as a result of postprocessing of the sewage sludge, mimicking composting/stockpiling, were also assessed. The results indicated that "native" Zn and Zn added either as a soluble salt or as NPs was rapidly converted to sulfides in all treatments. The hydrophobicity of the commercial formulation retarded the conversion of ZnO-NP. However, at the end of the anaerobic digestion process and after postprocessing of the sewage sludge (which caused a significant change in Zn speciation), the speciation of Zn was similar across all treatments. This indicates that, at least for the material tested, the risk assessment of ZnO-NP through this exposure pathway can rely on the significant knowledge already available in regard to other "conventional" forms of Zn present in sewage sludge.

Assessing the impact of copper and zinc oxide nanoparticles on soil: a field study

It is not known if the annual production of tonnes of industrial nanoparticles (NPs) has the potential to impact terrestrial microbial communities, which are so necessary for ecosystem functioning. Here, we have examined the consequences of adding zero valent copper and zinc oxide NPs to soil in pots that were then maintained under field conditions. The fate of these NPs, as well as changes in the microbial communities, was monitored over 162 days. Both NP types traveled through the soil matrix, albeit at differential rates, with Cu NPs retained in the soil matrix at a higher rate compared to ZnO NPs. Leaching of Cu and Zn ions from the parent NPs was also observed as a function of time. Analysis of microbial communities using culture-dependent and independent methods clearly indicated that Cu and ZnO NPs altered the microbial community structure. In particular, two orders of organisms found in rhizosphere, Flavobacteriales and Sphingomonadales, appeared to be particularly susceptible to the presence of NPs. Together, the migration of NPs through soil matrix and the ability of these potential pollutants to influence the composition of microbial community in this field study, cannot help but raise some environmental concerns.

Controlled evaluation of silver nanoparticle dissolution using atomic force microscopy

Incorporation of silver nanoparticles (AgNPs) into an increasing number of consumer products has led to concern over the potential ecological impacts of their unintended release to the environment. Dissolution is an important environmental transformation that affects the form and concentration of AgNPs in natural waters; however, studies on AgNP dissolution kinetics are complicated by nanoparticle aggregation. Herein, nanosphere lithography (NSL) was used to fabricate uniform arrays of AgNPs immobilized on glass substrates. Nanoparticle immobilization enabled controlled evaluation of AgNP dissolution in an air-saturated phosphate buffer (pH 7.0, 25 °C) under variable NaCl concentrations in the absence of aggregation. Atomic force microscopy (AFM) was used to monitor changes in particle morphology and dissolution. Over the first day of exposure to ≥10 mM NaCl, the in-plane AgNP shape changed from triangular to circular, the sidewalls steepened, the in-plane radius decreased by 5-11 nm, and the height increased by 6-12 nm. Subsequently, particle height and in-plane radius decreased at a constant rate over a 2-week period. Dissolution rates varied linearly from 0.4 to 2.2 nm/d over the 10-550 mM NaCl concentration range tested. NaCl-catalyzed dissolution of AgNPs may play an important role in AgNP fate in saline waters and biological media. This study demonstrates the utility of NSL and AFM for the direct investigation of unaggregated AgNP dissolution.

Dissolution and microstructural transformation of ZnO nanoparticles under the influence of phosphate

The toxicity and fate of nanoparticles (NPs) have been reported to be highly dependent on the chemistry of the medium, and the effects of phosphate have tended to be ignored despite the wide existence of phosphate contamination in aqueous environments. In the present study the influence of phosphate on the dissolution and microstructural transformation of ZnO NPs was investigated. Phosphate at a low concentration rapidly and substantially reduced the release of Zn(2+) into aqueous solution. Synchrotron X-ray absorption spectroscopy and X-ray diffraction analysis reveal that interaction between ZnO NPs and phosphate induced the transformation of ZnO into zinc phosphate. Transmission electronic microscopy observation shows that the morphology of the particles changed from structurally uniform nanosized spherical to anomalous and porous material containing mixed amorphous and crystalline phases of ZnO and zinc phosphate in the presence of phosphate. To our knowledge, this is the first study in which the detailed process of phosphate-induced speciation and microstructural transformation of ZnO NPs has been analyzed. In view of the wide existence of phosphate contamination in water and its strong metal-complexation capability, phosphate-induced transformations may play an important role in the behaviors, fate, and toxicity of many other metal-based nanomaterials in the environment.

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.

Pilot estuarine mesocosm study on the environmental fate of Silver nanomaterials leached from consumer products

Although nanosilver consumer products (CPs) enjoy widespread availability, the environmental fate, leaching, and bioaccumulation behaviors of silver nanoparticles (AgNPs) from these products are not well understood. In this work, three nanosilver CPs, two AgNP standards, and an ionic silver (Ag(+)) standard were studied in estuarine mesocosms. The CPs exhibited long-term release of significant amounts of silver over a 60d residence time in the mesocosms, and ultimately released 82 - 99% of their total silver loads. Measurements of total silver as a function of time, by inductively coupled plasma mass spectrometry (ICP-MS), indicated that the silver was transferred from the water column and accumulated in the estuarine biota, including hard clams, grass shrimp, mud snails, cordgrass stalks and leaves, biofilms, intertidal sediment, and sand. The ICP-MS results and calculations of bioconcentration and trophic transfer factors indicated that significant amounts of silver were taken up by the organisms through trophic transfer. Silver was also adsorbed from the seawater into the biofilms, sediment, and sand, and from the sand into the clams.

Alterations in physical state of silver nanoparticles exposed to synthetic human stomach fluid

The bioavailability of ingested silver nanoparticles (AgNPs) depends in large part on initial particle size, shape and surface coating, properties which will influence aggregation, solubility and chemical composition during transit of the gastrointestinal tract. Citrate-stabilized AgNPs were exposed to synthetic human stomach fluid (SSF) (pH 1.5) and changes in size, shape, zeta potential, hydrodynamic diameter and chemical composition were determined during a 1h exposure period using Surface Plasmon Resonance (SPR), High Resolution Transmission Electron Microscopy/Energy Dispersive X-ray Spectroscopy (TEM/EDS), Dynamic Light Scattering (DLS) and X-ray Powder Diffraction (XRD) combined with Rietveld analysis. Exposure of AgNPs to SSF produced a rapid decrease in the SPR peak at 414nm and the appearance of a broad absorbance peak in the near infrared (NIR) spectral region. During exposure to SSF, changes in zeta potential, aggregation and morphology of the particles were also observed as well as production of silver chloride which appeared physically associated with particle aggregates.

Aging and soil organic matter content affect the fate of silver nanoparticles in soil

Sewage sludge application on soils represents an important potential source of silver nanoparticles (Ag NPs) to terrestrial ecosystems, and it is thus important to understand the fate of Ag NPs once in contact with soil components. Our aim was to compare the behavior of three different forms of silver, namely silver nitrate, citrate stabilized Ag NPs (5nm) and uncoated Ag NPs (19nm), in two soils with contrasting organic matter content, and to follow changes in binding strength over time. Soil samples were spiked with silver and left to age for 2h, 2 days, 5 weeks or 10 weeks before they were submitted to sequential extraction. The ionic silver solution and the two Ag NP types were radiolabeled so that silver could be quantified by gamma spectrometry by measuring the (110m)Ag tracer in the different sequential extraction fractions. Different patterns of partitioning of silver were observed for the three forms of silver. All types of silver were more mobile in the mineral soil than in the soil rich in organic matter, although the fractionation patterns were very different for the three silver forms in both cases. Over 20% of citrate stabilized Ag NPs was extractible with water in both soils the first two days after spiking (compared to 1-3% for AgNO(3) and uncoated Ag NPs), but the fraction decreased to trace levels thereafter. Regarding the 19nm uncoated Ag NPs, 80% was not extractible at all, but contrary to AgNO(3) and citrate stabilized Ag NPs, the bioaccessible fraction increased over time, and by day 70 was between 8 and 9 times greater than that seen in the other two treatments. This new and unexpected finding demonstrates that some Ag NPs can act as a continuous source of bioaccessible Ag, while AgNO(3) is rapidly immobilized in soil.

Solubility of nano-zinc oxide in environmentally and biologically important matrices

Increasing manufacture and use of engineered nanoparticles is leading to a greater probability for release of engineered nanoparticles into the environment and exposure to organisms. In particular, zinc oxide (ZnO) is toxic, although it is unclear whether this toxicity is due to the zinc oxide nanoparticles, dissolution to Zn(2+) , or some combination thereof. The goal of this study was to determine the relative solubilities of both commercially available and in-house synthesized ZnO in matrices used for environmental fate and transport or biological toxicity studies. Dissolution of ZnO was observed in nanopure water (7.18-7.40 mg/L dissolved Zn, as measured by filtration) and Roswell Park Memorial Institute medium (RPMI-1640) (∼5 mg/L), but much more dissolution was observed in Dulbecco's modified Eagle's medium, in which the dissolved Zn concentration exceeded 34 mg/L. Moderately hard water exhibited low Zn solubility, likely because of precipitation of a Zn carbonate solid phase. Precipitation of a Zn-containing solid phase in RPMI also appeared to limit Zn solubility. Equilibrium conditions with respect to ZnO solubility were not apparent in these matrices, even after more than 1,000 h of dissolution. These results suggest that solution chemistry exerts a strong influence on ZnO dissolution and can result in limits on Zn solubility from precipitation of less soluble solid phases.

Cellular compatibility of biomineralized ZnO nanoparticles based on prokaryotic and eukaryotic systems

Zinc oxide nanoparticles (NPs) with the size of ∼100 nm were prepared via a facile biomineralization process in the template of silk fibroin (SF) peptide at room temperature. These ZnO NPs have shown the remarkable behavior of low toxicity to gram-positive bacteria (Staphylococcus aureus, Staphylococcus agalactiae), gram-negative bacteria (Escherichia coli), and eukaryotic cells (mouse L929 fibroblasts). Bacteriological testing indicated that ZnO NPs presented a 50% inhibitory effect on Streptococcus agalactiae at the concentrations of >100 mM, whereas at the same concentrations, the growth of Staphylococcus aureus and Escherichia coli were hardly inhibited. On the other hand, a remarkable proliferation of Staphylococcus aureus or Escherichia coli was observed at the concentrations of ZnO NPs <50 mM. Moreover, the cytotoxicity test demonstrated that ZnO NPs mineralized with SF peptide possessed a low toxicity to mouse L929 fibroblasts. The SF peptide coated on the surface of ZnO NPs permitted greater adhesion and consequently greater proliferation of mouse L929 fibroblasts. Besides, from TEM micrographs of the cell ultrastructure, endocytosis of NPs into the cytoplasm can be detected and the ultrastructure of the cell underwent few changes. The cell membrane retained integrity, euchromatin dispersed homogenously inside the cytoplasm, the mitochondrial architecture remained intact, and no intracellular vacuoles were observed. High-resolution transmission electron microscopy images and selected area electron diffraction patterns of ultrathin cell sections indicated that the crystal structure of NPs was not damaged by the organelle or cytoplasm. All these observations indicated that ZnO NPs mineralized with the SF peptide possess good cytocompatibility.

CuO and ZnO nanoparticles differently affect the secretion of fluorescent siderophores in the beneficial root colonizer, Pseudomonas chlororaphis O6

To understand the impact of environmental deposition of CuO and ZnO nanoparticles (NPs) on the production of bacterial metabolites, we examined the effects of their sub-lethal levels on the production of a pyoverdine (PVD) siderophore in a plant-beneficial bacterium, Pseudomonas chlororaphis O6 (PcO6). The NPs were characterized for size, shape, surface charge and ion release. Production of PVD by the cells was evaluated by fluorimetry and the expression of genes for PVD biosynthesis and export. The level of PVD in the presence of ZnO NPs was similar to that with Zn ions at 24 h, but the NPs maintained higher level than control at 48 h. In contrast, the reduction in PVD by CuO NPs was not duplicated by Cu ions. Expression of a gene encoding an inner membrane PVD transporter was inhibited by CuO NPs, supporting the observed low amounts of external PVD detected in those cells. These findings revealed NP-specific effect for CuO NPs on PcO6 metabolism, while for ZnO NPs, the release of ions was important. Because siderophores are part of the chemical communication between soil microbes and plants, the outcomes of plant-microbe interactions could be affected by responses to NPs.

Responses of a soil bacterium, Pseudomonas chlororaphis O6 to commercial metal oxide nanoparticles compared with responses to metal ions

The toxicity of commercially-available CuO and ZnO nanoparticles (NPs) to pathogenic bacteria was compared for a beneficial rhizosphere isolate, Pseudomonas chlororaphis O6. The NPs aggregated, released ions to different extents under the conditions used for bacterial exposure, and associated with bacterial cell surface. Bacterial surface charge was neutralized by NPs, dependent on pH. The CuO NPs were more toxic than the ZnO NPs. The negative surface charge on colloids of extracellular polymeric substances (EPS) was reduced by Cu ions but not by CuO NPs; the EPS protected cells from CuO NPs-toxicity. CuO NPs-toxicity was eliminated by a Cu ion chelator, suggesting that ion release was involved. Neither NPs released alkaline phosphatase from the cells' periplasm, indicating minimal outer membrane damage. Accumulation of intracellular reactive oxygen species was correlated with CuO NPs lethality. Environmental deposition of NPs could create niches for ion release, with impacts on susceptible soil microbes.

Cytogenetic and genotoxic effects of zinc oxide nanoparticles on root cells of Allium cepa

Increasing use of zinc oxide nanoparticles (ZnO NP) in consumer products may enhance its release into the environment. Phytotoxicity study is important to understand its possible environmental impact. Allium cepa (Onion bulb) is the best model organism to study genetic toxicology of nanoparticles. Here we have reported cytogenetic and genotoxic effects of ZnO NPs on the root cells of A. cepa. The effects of ZnO NPs on the mitotic index (MI), micronuclei index (MN index), chromosomal aberration index, and lipid peroxidation were determined through the hydroponic culturing of A. cepa. A. cepa roots were treated with the dispersions of ZnO NPs at four different concentrations (25, 50, 75, and 100 μg ml(-1)). With the increasing concentrations of ZnO NPs MI decreased with the increase of pycnotic cells, on the other hand MN and chromosomal aberration index increased. The frequency of micronucleated cells was higher in ZnO NPs treated cells as compared to control (deionized distilled water). The number of cells in each mitotic phase changed upon ZnO NPs treatment. The effect of ZnO NPs on lipid peroxidation as examined by measuring TBARS concentration was evident at all the concentrations compared to bulk ZnO. The TEM image showed internalization of ZnO NPs like particles. SEM image of treated A. cepa demonstrated that the internalized nanoparticles agglomerated depending on the physico-chemical environment inside the cell. Our results demonstrated that ZnO NPs can be a clastogenic/genotoxic and cytotoxic agent. In conclusion, the A. cepa cytogenetic test can be used for the genotoxicity monitoring of novel nanomaterials like ZnO NPs, which is used in many consumer products.