Effects of silver nanoparticles on zebrafish (Danio rerio) and Escherichia coli (ATCC 25922): a comparison of toxicity based on total surface area versus mass concentration of particles in a model eukaryotic and prokaryotic system

Mechanisms of PVP-functionalized silver nanoparticle toxicity in fish: Intravascular exposure disrupts cardiac pacemaker function and inhibits Na+/K+-ATPase activity in heart, but not gill

Polyvinylpyrrolidone-functionalized silver nanoparticles (nAgPVP) are popular in consumer products for their colloidal stability and antimicrobial activity. Whole lake additions of nAgPVP cause long term, ecosystem-scale changes in fish populations but the mechanisms underlying this effect are unclear. We have previously shown that in fish, nAgPVP impairs cardiac contractility and Na+/K+-ATPase (NKA) activity in vitro, raising the possibility that heart dysfunction could underlie population-level exposure effects. The goal of this study was to determine if nAgPVP influences the control of heart rate (fh), blood pressure, or cardiac NKA activity in vivo. First, a dose-response curve for the effects of 5 nm nAgPVP on contractility was completed on isometrically contracting ventricular muscle preparations from Arctic char (Salvelinus alpinus) and showed that force production was lowest at 500 μg L-1 and maximum pacing frequency increased with nAgPVP concentration. Stroke volume, cardiac output, and power output were maintained in isolated working heart preparations from brook char (Salvelinus fontinalis) exposed to 700 μg L-1 nAgPVP. Both fh and blood pressure were elevated after 24 h in brook char injected with 700 μg kg body mass-1 nAgPVP and fh was insensitive to modulation with blockers of β-adrenergic and muscarinic cholinergic receptors. Na+/K+-ATPase activity was significantly lower in heart, but not gill of nAgPVP injected fish. The results indicate that nAgPVP influences cardiac function in vivo by disrupting regulation of the pacemaker and cardiomyocyte ionoregulation. Impaired fh regulation may prevent fish from appropriately responding to environmental or social stressors and affect their ability to survive.

Modified toxic potential of multi-walled carbon nanotubes to zebrafish (Danio rerio) following a two-year incubation in water

Multi-walled carbon nanotubes (MWCNTs), widely used in several industrial fields, are not readily degradable thus, persist in environmental matrices, serving as a source of environmental toxicity to organisms. However, the effects of environmental weathering on nanomaterial toxicity remain unclear. Herein, we prepared aged-MWCNTs (a-CNTs) by incubating commercial pristine-MWCNTs (p-CNTs) for two years and compared their changes in physicochemical properties and toxic effects on zebrafish. The characterization of a-CNTs by transmission electron microscopy, X-ray photoelectron spectra, Raman spectroscopy, and Fourier-transform infrared spectroscopy showed an increased surface area, pore size, structural defects, and surface oxidation than those of p-CNTs. Zebrafish were exposed to 100 mg/L p-CNT and a-CNT for four days. Subsequently, the mRNA expression of antioxidant enzymes, including cat, gst, and sod, in a-CNT group increased by 1.5- to 1.7-fold, consistent with increased expression of genes associated with inflammation (interleukin-8) and apoptosis (p53) compared to control. The higher toxicity of a-CNTs to zebrafish than p-CNT might be due to the increased oxidative potential by altered physicochemical properties. These findings provide new insights into the risk assessment and environmental management of MWCNTs in the aquatic environment. However, further testing at environmentally relevant doses, different exposure durations, and diverse weathering parameters is warranted.

Synthesis and characterization of activated carbon supported bimetallic Pd based nanoparticles and their sensor and antibacterial investigation

Activated carbon (AC) supported palladium cobalt bimetallic nanoparticles (PdCo@AC NPs) were obtained by green synthesis method using Cinnamomum verum (C. Verum) extract. The obtained NPs were characterized by Fourier Transform Infrared Spectroscopy (FTIR), X-Ray Crystallography (XRD), Transmission Electron Microscope (TEM) and Ultraviolet Visible (UV-VIS) spectroscopy, and the functional groups and morphology of the nanoparticle were elucidated. The resulting particle size was found to be 2.467 nm. NPs were evaluated using Cyclic Voltammetry (CV), Scan Rate (SR), and Differential Pulse Voltammetry (DPV) techniques for potential dopamine sensors application. According to the obtained DPV results, Limit of Detection (LOD) and Limit of Quantitation (LOQ) values are found to be 5.68 pM and 17.21 pM, respectively. It was also observed that AC supported PdCo nanoparticles obtained from C. verum extract sensed dopamine quite well. Besides, to examine the antibacterial properties of NPs, antibacterial analyzes were performed with Escherichia coli (E. Coli) and Staphylococcus aureus (S. Aureus). It was observed that it showed good antibacterial properties against gram positive (S. aureus) and gram negative (E. coli) bacteria. The study gave important results in terms of the synthesis of bimetallic NPs using the green synthesis method and their usability in different areas. With this study, it was observed that a good antibacterial dopamine sensor were obtained with the successful biogenic synthesis of AC supported PdCo bimetallic NPs.

Unveiling the nanotoxicological aspects of Se nanomaterials differing in size and morphology

Although the general concept of nanotechnology relies on exploitation of size-dependent properties of nanoscaled materials, the relation between the size/morphology of nanoparticles with their biological activity remains not well understood. Therefore, we aimed at investigating the biological activity of Se nanoparticles, one of the most promising candidates of nanomaterials for biomedicine, possessing the same crystal structure, but differing in morphology (nanorods vs. spherical particles) and aspect ratios (AR, 11.5 vs. 22.3 vs. 1.0) in human cells and BALB/c mice. Herein, we report that in case of nanorod-shaped Se nanomaterials, AR is a critical factor describing their cytotoxicity and biocompatibility. However, spherical nanoparticles (AR 1.0) do not fit this statement and exhibit markedly higher cytotoxicity than lower-AR Se nanorods. Beside of cytotoxicity, we also show that morphology and size substantially affect the uptake and intracellular fate of Se nanomaterials. In line with in vitro data, in vivo i.v. administration of Se nanomaterials revealed the highest toxicity for higher-AR nanorods followed by spherical nanoparticles and lower-AR nanorods. Moreover, we revealed that Se nanomaterials are able to alter intracellular redox homeostasis, and affect the acidic intracellular vesicles and cytoskeletal architecture in a size- and morphology-dependent manner. Although the tested nanoparticles were produced from the similar sources, their behavior differs markedly, since each type is promising for several various application scenarios, and the presented testing protocol could serve as a concept standardizing the biological relevance of the size and morphology of the various types of nanomaterials and nanoparticles.

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Three types of Se nanomaterials are synthesized with the same crystallinity.

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Se nanomaterials differ in size and morphology.

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Size and morphology markedly affects uptake and intracellular fate in vitro.

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Aspect ratio is a critical factor predetermining cytotoxicity of Se nanorods.

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High aspect ratio of nanorods is linked with serious kidney tissue damage.

Proteomic evaluation of nanotoxicity in aquatic organisms: A review

The alteration of organisms protein functions by engineered nanoparticles (ENPs) is dependent on the complex interplay between their inherent physicochemical properties (e.g., size, surface coating, shape) and environmental conditions (e.g., pH, organic matter). To date, there is increasing interest on the use of 'omics' approaches, such as proteomics, genomics, and others, to study ENPs-biomolecules interactions in aquatic organisms. However, although proteomics has recently been applied to investigate effects of ENPs and associated mechanisms in aquatic organisms, its use remain limited. Herein, proteomics techniques widely applied to investigate ENPs-protein interactions in aquatic organisms are reviewed. Data demonstrates that 2DE and mass spectrometry and/or their combination, thereof, are the most suitable techniques to elucidate ENPs-protein interactions. Furthermore, current status on ENPs and protein interactions, and possible mechanisms of nanotoxicity with emphasis on those that exert influence at protein expression levels, and key influencing factors on ENPs-proteins interactions are outlined. Most reported studies were done using synthetic media and essay protocols and had wide variability (not standardized); this may consequently limit data application in actual environmental systems. Therefore, there is a need for studies using realistic environmental concentrations of ENPs, and actual environmental matrixes (e.g., surface water) to aid better model development of ENPs-proteins interactions in aquatic systems.

The Design of Anionic Surfactant-Based Amino-Functionalized Mesoporous Silica Nanoparticles and their Application in Transdermal Drug Delivery

Melanoma remains the most lethal form of skin cancer and most challenging to treat despite advances in the oncology field. Our work describes the utilization of nanotechnology to target melanoma locally in an attempt to provide an advanced and efficient quality of therapy. Amino-functionalized mesoporous silica nanoparticles (MSN-NH₂) were developed in situ through the utilization of anionic surfactant and different volumes of 3-aminopropyltriethoxysilane (APTES) as a co-structure directing agent (CSDA). Prepared particles were characterized for their morphology, particles size, 5-flurouracol (5-FU) and dexamethasone (DEX) loading capacity and release, skin penetration, and cytotoxicity in vitro in HT-144 melanoma cells. Results of transmission electron microscopy (TEM) and nitrogen adsorption-desorption isotherm showed that using different volumes of APTES during the functionalization process had an impact on the internal and external morphology of the particles, as well as particle size. However, changing the volume of APTES did not affect the diameter of formed mesochannels, which was about 4 nm. MSN-NH₂ showed a relatively high loading capacity of 5-FU (12.6 ± 5.5) and DEX (44.72 ± 4.21) when using drug: MSN-NH₂ ratios of 5:1 for both drugs. The release profile showed that around 83% of 5-FU and 21% of DEX were released over 48 h in pH 7.4. The skin permeability study revealed that enhancement ratio of 5-Fu and DEX using MSN-NH₂ were 4.67 and 5.68, respectively, relative to their free drugs counterparts. In addition, the accumulation of drugs in skin layers where melanoma cells usually reside were enhanced approximately 10 times with 5-FU and 5 times with DEX when delivering drugs using MSN-NH₂ compared to control. MSN-NH₂ alone was nontoxic to melanoma cells when incubated for 48 h in the range of 0 to 468 µg/mL. The combination of 5-FU MSN-NH₂ and DEX MSN-NH₂ showed significant increase in toxicity compared to their free dug counterparts and exhibited a synergetic effect as well as the ability to circumvent DEX induced 5-FU resistance in melanoma cells.

Defective defence in Daphnia daughters: silver nanoparticles inhibit anti-predator defence in offspring but not in maternal Daphnia magna

One major environmental problem of our time are emerging contaminants in the aquatic environment. While nanoparticles exhibit attractive features such as antimicrobial properties in the case of silver nanoparticles (AgNPs), earlier studies suggest that NPs are not completely filtered out at wastewater treatment plants and may therefore be continuously introduced into the aquatic environment. Although adverse effects of AgNPs on aquatic organisms have been extensively studied, there is still a lack of knowledge on how this chemical stressor interacts with natural cues on the maternal and subsequent generation of aquatic organisms. We tested whether AgNPs (NM-300K, 14.9 ± 2.4 nm, concentration range: 2.5 µg/L - 20 µg/L) affect the kairomone-induced adaptive anti-predator defence mechanism in maternal Daphnia and their offspring. While maternal Daphnia developed typical anti-predator defence mechanisms when exposed to kairomones and AgNPs, their offspring could not develop such adaptive defensive traits. The lack of this defence mechanism in offspring could have dramatic negative consequences (e.g. reduced Daphnia population) for the entire complex food web in the aquatic ecosystem. For a realistic risk assessment, it is extremely important to test combinations of chemical stressors because aquatic organisms are exposed to several natural and artificial chemical stressors at the same time.

Protective effect of dietary vitamin E on immunological and biochemical induction through silver nanoparticles (AgNPs) inclusion in diet and silver salt (AgNO3) exposure on Zebrafish (Danio rerio)

The present study evaluated silver nanoparticle (AgNPs) toxicity using biomarkers of oxidative and metabolic stress, immunological impairment and cellular damage in zebrafish (Danio rerio), as well as the optimal dose of vitamin E neutralizing undesirable effects. Fish were fed for ten days and eight study groups were investigated: controls, AgNPs exposure alone (1.5 mg L^-1) and combined with three different vitamin E doses (1.5 mg L^-1 of AgNPs + vitamin E 100, 200 or 400 mg kg^-1 of food), also one positive control group exposed to AgNO₃ alone or combined with the same vitamin E doses. D. rerio exposed to AgNPs alone or combined with the lower vitamin E dose showed overall worse results in comparison with the control groups and the groups combining nanoparticles and 200 or 400 mg kg^-1 of food of vitamin E-supplemented diet. AgNPs caused cell impairment by increasing LDH activity and cortisol levels, generated oxidative stress by inhibiting SOD and CAT activity and immunosuppression by inhibiting ACH50 and lysozyme activity. The groups exposed to Ag salt showed the same response-pattern found for the NPs groups, reinforcing that Ag toxicity of AgNPs is mediated by Ag⁺. In conclusion, although AgNPs are toxic to Danio rerio, vitamin E supplementation at 200 or 400 mg kg^-1 can act protectively against its toxic effects.

Differential lethal and sublethal effects in embryonic zebrafish exposed to different sizes of silver nanoparticles

Various parameters can influence the toxic response to silver nanoparticles (Ag NPs), including the size and surface properties, as well as the exposure environment and the biological site of action. Herein, we assess the intestinal toxicity of three different sizes (10, 40, and 100 nm) of Ag NPs in embryonic zebrafish, and describe the relationship between the properties and behavior of Ag NPs in the exposure medium, and induction of lethal and sublethal effects. We find that the composition of the medium and the size contribute to differential NPs agglomeration, release of Ag ions, and subsequent effects during exposure. The exposure medium causes dramatic reduction in silver dissolution due to the presence of salts and divalent cations, which limits the lethal potential of silver ions. Lethality is observed primarily for embryos exposed to medium sized Ag NPs (40 nm), but not to the supernatant originated from particles, which suggests that the exposure to particulate silver is the main cause of mortality. On the other hand, the exposure to 10 nm and 100 nm NPs, as well as Ag ions, only causes sublethal developmental defects in skeletal muscles and intestine, and induces a nitric oxide imbalance.

Aquatic animals promote antibiotic resistance gene dissemination in water via conjugation: Role of different regions within the zebra fish intestinal tract, and impact on fish intestinal microbiota

The aqueous environment is one of many reservoirs of antibiotic resistance genes (ARGs). Fish, as important aquatic animals which possess ideal intestinal niches for bacteria to grow and multiply, may ingest antibiotic resistance bacteria from aqueous environment. The fish gut would be a suitable environment for conjugal gene transfer including those encoding antibiotic resistance. However, little is known in relation to the impact of ingested ARGs or antibiotic resistance bacteria (ARB) on gut microbiota. Here, we applied the cultivation method, qPCR, nuclear molecular genetic marker and 16S rDNA amplicon sequencing technologies to develop a plasmid-mediated ARG transfer model of zebrafish. Furthermore, we aimed to investigate the dissemination of ARGs in microbial communities of zebrafish guts after donors carrying self-transferring plasmids that encode ARGs were introduced in aquaria. On average, 15% of faecal bacteria obtained ARGs through RP4-mediated conjugal transfer. The hindgut was the most important intestinal region supporting ARG dissemination, with concentrations of donor and transconjugant cells almost 25 times higher than those of other intestinal segments. Furthermore, in the hindgut where conjugal transfer occurred most actively, there was remarkable upregulation of the mRNA expression of the RP4 plasmid regulatory genes, trbBp and trfAp. Exogenous bacteria seem to alter bacterial communities by increasing Escherichia and Bacteroides species, while decreasing Aeromonas compared with control groups. We identified the composition of transconjugants and abundance of both cultivable and uncultivable bacteria (the latter accounted for 90.4%-97.2% of total transconjugants). Our study suggests that aquatic animal guts contribute to the spread of ARGs in water environments.

Functional Silver-Silicone-Nanofilament-Composite Material for Water Disinfection

The roughness of superhydrophobic silicone nanofilaments (SNFs) is exploited to enlarge the contact area of conventional filter material. As an efficient wetting of the filter material is crucial for water treatment, the wettability of SNFs is readily modified from superhydrophobic to hydrophilic during the functionalization process. SNFs are coated on glass beads and subsequently modified with biocidal silver nanoparticles (AgNPs). The enlarged surface area of SNFs allows a 30 times higher loading of AgNPs in comparison to glass beads without SNF coating. Thus, in column experiments, the AgNP-SNF-nanocomposite-modified glass beads exert superior antibacterial activity towards suspensions of E. coli K12 compared to AgNP functionalized glass beads without SNFs. Additionally, reusing the AgNP-SNF-nanocomposite-coated glass beads with fresh bacteria contaminated medium increases their efficacy and reduces the colony forming units by ≈6 log units. Thereby, the silver loss during percolation is below 0.1 μg mL^-1 . These results highlight, first, the potential of AgNP-SNF-nanocomposite-modified glass beads as an effective filter substrate for water disinfection, and second, the efficiency of SNF coating in increasing the contact area of conventional filter material.

Governing factors affecting the impacts of silver nanoparticles on wastewater treatment

Silver nanoparticles (nanosilver or AgNPs) enter municipal wastewater from various sources, raising concerns about their potential adverse effects on wastewater treatment processes. We argue that the biological effects of silver nanoparticles at environmentally realistic concentrations (μgL^-1 or lower) on the performance of a full-scale municipal water resource recovery facility (WRRF) are minimal. Reactor configuration is a critical factor that reduces or even mutes the toxicity of silver nanoparticles towards wastewater microbes in a full-scale WRRF. Municipal sewage collection networks transform silver nanoparticles into silver(I)-complexes/precipitates with low ecotoxicity, and preliminary/primary treatment processes in front of biological treatment utilities partially remove silver nanoparticles to sludge. Microbial functional redundancy and microbial adaptability to silver nanoparticles also greatly alleviate the adverse effects of silver nanoparticles on the performance of a full-scale WRRF. Silver nanoparticles in a lab-scale bioreactor without a sewage collection system and/or a preliminary/primary treatment process, in contrast to being in a full scale system, may deteriorate the reactor performance at relatively high concentrations (e.g., mgL^-1 levels or higher). However, in many cases, silver nanoparticles have minimal impacts on lab-scale bioreactors, such as sequencing batch bioreactors (SBRs), especially when at relatively low concentrations (e.g., less than 1mgL^-1). The susceptibility of wastewater microbes to silver nanoparticles is species-specific. In general, silver nanoparticles have higher toxicity towards nitrifying bacteria than heterotrophic bacteria.

Cytotoxicity of Nanoparticles Contained in Food on Intestinal Cells and the Gut Microbiota

Toxicity of nanoparticles (NPs) upon oral exposure has been studied in animals using physiological changes, behavior, histology, and blood analysis for evaluation. The effects recorded include the combination of the action on cells of the exposed animal and the reaction of the microorganisms that populate the external and internal surfaces of the body. The importance of these microorganisms, collectively termed as microbiota, for the health of the host has been widely recognized. They may also influence toxicity of NPs but these effects are difficult to differentiate from toxicity on cells of the gastrointestinal tract. To estimate the likelihood of preferential damage of the microbiota by NPs the relative sensitivity of enterocytes and bacteria was compared. For this comparison NPs with antimicrobial action present in consumer products were chosen. The comparison of cytotoxicity with Escherichia coli as representative for intestinal bacteria and on gastrointestinal cells revealed that silver NPs damaged bacteria at lower concentrations than enterocytes, while the opposite was true for zinc oxide NPs. These results indicate that silver NPs may cause adverse effects by selectively affecting the gut microbiota. Fecal transplantation from NP-exposed animals to unexposed ones offers the possibility to verify this hypothesis.

The effect of electromagnetic fields, from two commercially available water treatment devices, on bacterial culturability

Commercially available pulsed-electromagnetic field (PEMF) devices are currently being marketed and employed to ostensibly manage biofouling. The reliable application and industry acceptance of such technologies require thorough scientific validation - and this is currently lacking. We have initiated proof-of-principle research in an effort to investigate whether such commercially available PEMF devices can influence the viability (culturability) of planktonic bacteria in an aqueous environment. Thus two different commercial PEMF devices were investigated via a static (i.e. non-flowing) treatment system. 'Healthy' Escherichia coli cells, as well as cultures that were physiologically compromised by silver nano-particles, were exposed to the PEMFs from both devices under controlled conditions. Although relatively minor, the observed effects were nevertheless statistically significant and consistent with the hypothesis that PEMF exposure under controlled conditions may result in a decrease in cellular viability and culturability. It has also been observed that under certain conditions bacterial growth is actually stimulated.

Manufactured nanoparticles in the aquatic environment-biochemical responses on freshwater organisms: A critical overview

The enormous investments in nanotechnology have led to an exponential increase of new manufactured nano-enabled materials whose impact in the aquatic systems is still largely unknown. Ecotoxicity and nanosafety studies mostly resulted in contradictory results and generally failed to clearly identify biological patterns that could be related specifically to nanotoxicity. Generation of reactive oxygen species (ROS) is one of the most discussed nanotoxicity mechanism in literature. ROS can induce oxidative stress (OS), resulting in cyto- and genotoxicity. The ROS overproduction can trigger the induction of anti-oxidant enzymes such as catalase (CAT), superoxide dismutase (SOD) and glutathione peroxidases (GPx), which are used as biomarkers of response. A critical overview of the biochemical responses induced by the presence of NPs on freshwater organisms is performed with a strong interest on indicators of ROS and general stress. A special focus will be given to the NPs transformations, including aggregation, and dissolution, in the exposure media and the produced biochemical endpoints.

Amine modification of nonporous silica nanoparticles reduces inflammatory response following intratracheal instillation in murine lungs

Amorphous silica nanoparticles (NPs) possess unique material properties that make them ideal for many different applications. However, the impact of these materials on human and environmental health needs to be established. We investigated nonporous silica NPs both bare and modified with amine functional groups (3-aminopropyltriethoxysilane (APTES)) in order to evaluate the effect of surface chemistry on biocompatibility. In vitro data showed there to be little to no cytotoxicity in a human lung cancer epithelial cell line (A549) for bare silica NPs and amine-functionalized NPs using doses based on both mass concentration (below 200μg/mL) and exposed total surface area (below 14m(2)/L). To assess lung inflammation, C57BL/6 mice were administered bare or amine-functionalized silica NPs via intra-tracheal instillation. Two doses (0.1 and 0.5mg NPs/mouse) were tested using the in vivo model. At the higher dose used, bare silica NPs elicited a significantly higher inflammatory response, as evidence by increased neutrophils and total protein in bronchoalveolar lavage (BAL) fluid compared to amine-functionalized NPs. From this study, we conclude that functionalization of nonporous silica NPs with APTES molecules reduces murine lung inflammation and improves the overall biocompatibility of the nanomaterial.

Gaining a Critical Mass: A Dose Metric Conversion Case Study Using Silver Nanoparticles

Mass concentration is the standard convention to express exposure in ecotoxicology for dissolved substances. However, nanotoxicology has challenged the suitability of the mass concentration dose metric. Alternative metrics often discussed in the literature include particle number, surface area, and ion release (kinetics, equilibrium). It is unlikely that any single metric is universally applicable to all types of nanoparticles. However, determining the optimal metric for a specific type of nanoparticle requires novel studies to generate supportive data and employ methods to compensate for current analytical capability gaps. This investigation generated acute toxicity data for two standard species (Ceriodaphnia dubia, Pimephales promelas) exposed to five sizes (10, 20, 30, 60, 100 nm) of monodispersed citrate- and polyvinylpyrrolidone-coated silver nanoparticles. Particles were sized by various techniques to populate available models for expressing the particle number, surface area, and dissolved fraction. Results indicate that the acute toxicity of the tested silver nanoparticles is best expressed by ion release, and is relatable to total exposed surface area. Particle number was not relatable to the observed acute silver nanoparticle effects.

Silver nanoparticles affect the neural development of zebrafish embryos

Silver nanoparticles (AgNPs) have been widely used in commercial products. This study aims to understand the impact of AgNPs on the early developmental stages in zebrafish (Danio rerio) embryos. Embryos were exposed to two sizes of AgNPs at three dose levels, as well to free Ag(+) ions, for a range of 4-96 h post-fertilization (hpf). The acute exposure study showed that exposure to AgNPs affected the neurological development, and the exposed embryos exhibited anomalies such as small head with hypoplastic hindbrain, small eye and cardiac defects. At the molecular level, AgNPs altered the expression profiles of neural development-related genes (gfap, huC and ngn1), metal-sensitive metallothioneins and ABCC genes in exposed embryos. The expression of AhR2 and Cyp1A, which are usually considered to mediate polycyclic aromatic hydrocarbon toxicity, were also significantly changed. A size-dependent uptake of AgNPs was observed, whereby 4 nm AgNPs were more efficiently taken up compared with the 10 nm-sized particles. Importantly, the head area accumulated AgNPs more efficiently than the trunk area of exposed zebrafish embryos. No free Ag(+) ions, which can be potentially released from the AgNP solutions, were detected. This study suggests that AgNPs could affect the neural development of zebrafish embryos, and the toxicity of AgNPs may be partially attributed to the comparatively higher uptake in the head area. These results indicate the potential neurotoxicity of AgNPs and could be extended to other aquatic organisms.

Size-dependent impacts of silver nanoparticles on the lifespan, fertility, growth, and locomotion of Caenorhabditis elegans

The increased bioavailability of nanoparticles engineered for good dispersion in water may have biological and environmental impacts. To examine this issue, the authors assessed the biological effects in nematodes as they relate to exposure to silver nanoparticles (AgNPs) of different sizes at low (1 mg/L Ag), medium (10 mg/L Ag), and high concentrations (100 mg/L Ag). Over multiple generations, the authors found that the smallest particle, at 2 nm, had a notable impact on nematode fertility. In contrast, the largest particle, at 10 nm, significantly reduced the lifespan of parent nematodes (P0 ) by 28.8% and over the span of 3 generations (F1 -F3). In addition, a computer vision system automatically measured the adverse effects in body length and motility, which were not size-dependent.

Combined effects of silver nanoparticles and 17α-ethinylestradiol on the freshwater mudsnail Potamopyrgus antipodarum

Ecotoxicological studies have shown that nanosilver is among the most toxic nanomaterials to aquatic organisms. However, research has so far focused on the determination of acute effects. Combined effects of nanosilver with other substances have not yet been studied in aquatic organisms. The present study aimed to investigate the chronic toxicity of nanosilver as well as the potential of nanosilver to influence the effects of co-occurring substances on the freshwater mudsnail Potamopyrgus antipodarum. In 28-day chronic toxicity experiments, the effects of nanosilver on the reproduction of P. antipodarum were assessed. In order to evaluate the influence of nanosilver on other substances, 17α-ethinylestradiol (EE2) was chosen as model compound due to the well-characterized effects on P. antipodarum. In addition to effects on reproduction, exposure to nanosilver and EE2 was monitored by determining the expression of estrogen-responsive transcripts (estrogen receptor and vitellogenin encoding genes). Exposure to nanosilver decreased the reproduction of P. antipodarum (EC10: 5.57 μg l(-1); EC50: 15.0 μg l(-1)). Exposure to EE2 significantly stimulated the embryo production at 25 ng l(-1). The presence of nanosilver led to increased EE2 effects at EE2 concentrations that had no influence on reproduction when applied in absence of nanosilver. In contrast, combined exposure to nanosilver decreased EE2 effects at concentrations that stimulated reproduction and the expression of estrogen responsive genes when applied in the absence of nanosilver. This is the first study demonstrating an influence of nanosilver on the effects of co-contaminants on aquatic organisms. The study further highlights the need for chronic experiments to properly assess environmental risks of nanosilver and their effects on co-occurring contaminants.

Size-dependent toxicity of silver nanoparticles to bacteria, yeast, algae, crustaceans and mammalian cells in vitro

The concept of nanotechnologies is based on size-dependent properties of particles in the 1–100 nm range. However, the relation between the particle size and biological effects is still unclear. The aim of the current paper was to generate and analyse a homogenous set of experimental toxicity data on Ag nanoparticles (Ag NPs) of similar coating (citrate) but of 5 different primary sizes (10, 20, 40, 60 and 80 nm) to different types of organisms/cells commonly used in toxicity assays: bacterial, yeast and algal cells, crustaceans and mammalian cells in vitro. When possible, the assays were conducted in ultrapure water to minimise the effect of medium components on silver speciation. The toxic effects of NPs to different organisms varied about two orders of magnitude, being the lowest (∼0.1 mg Ag/L) for crustaceans and algae and the highest (∼26 mg Ag/L) for mammalian cells. To quantify the role of Ag ions in the toxicity of Ag NPs, we normalized the EC₅₀ values to Ag ions that dissolved from the NPs. The analysis showed that the toxicity of 20–80 nm Ag NPs could fully be explained by released Ag ions whereas 10 nm Ag NPs proved more toxic than predicted. Using E. coli Ag-biosensor, we demonstrated that 10 nm Ag NPs were more bioavailable to E. coli than silver salt (AgNO₃). Thus, one may infer that 10 nm Ag NPs had more efficient cell-particle contact resulting in higher intracellular bioavailability of silver than in case of bigger NPs. Although the latter conclusion is initially based on one test organism, it may lead to an explanation for “size-dependent“ biological effects of silver NPs. This study, for the first time, investigated the size-dependent toxic effects of a well-characterized library of Ag NPs to several microbial species, protozoans, algae, crustaceans and mammalian cells in vitro.

Hormetic dose-responses in nanotechnology studies

While exposure to nanoparticles is a growing concern, research into their toxicological impact and possible hazard for human health is limited. There remains a lack of information concerning the nature of the dose-response relationship especially at low level exposures. The present paper assesses the occurrence of hormetic-like biphasic dose responses within the nanotoxicology literature. The findings indicate that nanoparticles may induce hormetic-like biphasic dose responses in a wide range of biological cell types, and that these responses can be highly dependent upon the physical and chemical properties of the agent. While the mechanistic foundations of hormetic dose responses induced by chemicals and pharmaceuticals have markedly advanced over the past decade, this remains an important data need for nanotoxicology.

A general strategy to achieve ultra-high gene transfection efficiency using lipid-nanoparticle composites

Gene therapy provides a new hope for previously "incurable" diseases. Low gene transfection efficiency, however, is the bottle-neck to the success of gene therapy. It is very challenging to develop non-viral nanocarriers to achieve ultra-high gene transfection efficiencies. Herein, we report a novel design of "tight binding-but-detachable" lipid-nanoparticle composite to achieve ultrahigh gene transfection efficiencies of 60∼82%, approaching the best value (∼90%) obtained using viral vectors. We show that Fe@CNPs nanoparticles coated with LP-2000 lipid molecules can be used as gene carriers to achieve ultra-high (60-80%) gene transfection efficiencies in HeLa, U-87MG, and TRAMP-C1 cells. In contrast, Fe@CNPs having surface-covalently bound N,N,N-trimethyl-N-2-methacryloxyethyl ammonium chloride (TMAEA) oligomers can only achieve low (23-28%) gene transfection efficiencies. Similarly ultrahigh gene transfection/expression was also observed in zebrafish model using lipid-coated Fe@CNPs as gene carriers. Evidences for tight binding and detachability of DNA from lipid-nanoparticle nanocarriers will be presented.

Integrative nanomedicine: treating cancer with nanoscale natural products

Finding safer and more effective treatments for specific cancers remains a significant challenge for integrative clinicians and researchers worldwide. One emerging strategy is the use of nanostructured forms of drugs, vaccines, traditional animal venoms, herbs, and nutraceutical agents in cancer treatment. The recent discovery of nanoparticles in traditional homeopathic medicines adds another point of convergence between modern nanomedicine and alternative interventional strategies. A way in which homeopathic remedies could initiate anticancer effects includes cell-to-cell signaling actions of both exogenous and endogenous (exosome) nanoparticles. The result can be a cascade of modulatory biological events with antiproliferative and pro-apoptotic effects. The Banerji Protocols reflect a multigenerational clinical system developed by homeopathic physicians in India who have treated thousands of patients with cancer. A number of homeopathic remedy sources from the Banerji Protocols (eg, Calcarea phosphorica; Carcinosin-tumor-derived breast cancer tissue prepared homeopathically) overlap those already under study in nonhomeopathic nanoparticle and nanovesicle tumor exosome cancer vaccine research. Past research on antineoplastic effects of nano forms of botanical extracts such as Phytolacca, Gelsemium, Hydrastis, Thuja, and Ruta as well as on homeopathic remedy potencies made from the same types of source materials suggests other important overlaps. The replicated finding of silica, silicon, and nano-silica release from agitation of liquids in glassware adds a proven nonspecific activator and amplifier of immunological effects. Taken together, the nanoparticulate research data and the Banerji Protocols for homeopathic remedies in cancer suggest a way forward for generating advances in cancer treatment with natural product-derived nanomedicines.

The coating makes the difference: acute effects of iron oxide nanoparticles on Daphnia magna

The surface of nanoparticles (NP) is often functionalized with a capping agent to increase their colloidal stability. Having a strong effect on the characteristics of NP, the coating might already determine the risk from NP to organisms and the environment. In this study identical iron oxide nanoparticles (IONP; Ø 5-6nm) were functionalized with four different coatings: ascorbate (ASC-IONP), citrate (CIT-IONP), dextran (DEX-IONP), and polyvinylpyrrolidone (PVP-IONP). Ascorbate and citrate stabilize NP via electrostatic repulsion whereas dextran and polyvinylpyrrolidone are steric stabilizers. All IONP were colloidally stable over several weeks. Their acute effects on neonates of the waterflea Daphnia magna were investigated over 96h. The highest immobilizing effect was found for ASC- and DEX-IONP. In the presence of neonates, both agglomerated or flocculated and adsorbed to the carapace and filtering apparatuses, inducing high immobilization. Lower immobilization was found for CIT-IONP. Their effect was hypothesized to partly originate from an increased release of dissolved iron and the ability to form reactive oxygen species (ROS). Furthermore, incomplete ecdysis occurred at high concentrations of ASC-, DEX-, and CIT-IONP. PVP-IONP did not induce any negative effect, although high quantities were visibly ingested by the daphnids. PVP-IONP had the highest colloidal stability without any occurring agglomeration, adsorption, or dissolution. Only strong swelling of the PVP coating was observed in medium, highly increasing the hydrodynamic diameter. Each coating caused individual effects. Toxicity cannot be correlated to hydrodynamic diameter or the kind of stabilizing forces. Effects are rather linked to decreasing colloidal stability, the release of ions from the core material or the ability to form ROS, respectively.

Adaptation of the Daphnia sp. acute toxicity test: miniaturization and prolongation for the testing of nanomaterials

Manufacturing of nanomaterials (NMs) is often complex and expensive, and their environmental risks are poorly understood or even unknown. An economization of testing NMs is therefore desirable, which can be achieved by miniaturizing test systems. However, the downsizing of test vessels and volumes can enlarge the surface/volume ratio (SVR) which in turn can affect the bioavailable concentration of adsorbing substances like NMs. The present study focused on the miniaturization of the acute toxicity test with Daphnia magna. The adaptations were verified with three reference substances, the non-adsorbing potassium dichromate (K2Cr2O7) and as potentially highly-adsorbing substances silver nanoparticles (AgNPs) and silver nitrate (AgNO3). The miniaturized test was conducted in 24-well microtiter plates (MT) and simultaneously compared to the OECD standard test (ST). Furthermore, the test duration was prolonged from 48 to 96 h since NMs tend to show effects only after extended exposure. The toxicity of K2Cr2O7 and AgNPs continued to increase within the prolonged test span. The test comparisons with K2Cr2O7 did not reveal any significant differences between ST and MT. AgNO3 toxicity was significantly decreased in MT compared to ST due to the enlarged SVR. The toxicity of AgNPs in MT after 24 h was equal to ST. Contrary to our expectations an exposure longer than 24 h resulted in an increase of AgNP toxicity in MT, possibly due to enhanced dissolution of silver. Microtiter plates are appropriate alternative test vessels for the Daphnia sp. acute toxicity test; thus, its miniaturization is feasible. The enlarged SVR has to be taken into account since it can affect the toxicity of potentially adsorbing substances. Furthermore, the standard test duration of 48 h might underestimate the toxicity of many substances, especially of NMs.

A molecular method for assessing the effects of potential contaminants on the rate of zebrafish (Danio rerio) development

Monitoring expression of the developmentally regulated genes shh, sox2, and tnnt1 by reverse transcriptase polymerase chain reaction (RT-PCR) allows determination of the rate of embryogenesis in zebrafish (Danio rerio) embryos without direct visual observation. The utility of combining this approach and morphological methods during toxicity studies was demonstrated with embryos developing at either 28.5 °C or 24.5 °C and with embryos exposed to sublethal doses of silver nanoparticles.

Effects of material morphology on the phototoxicity of nano-TiO2 to bacteria

Nanostructured titania (nano-TiO2) is produced in diverse shapes, but it remains largely unknown how tuning the morphology of nano-TiO2 may alter its toxicity. Herein, we show that material morphology plays a critical role in regulating the phototoxicity of nano-TiO2 to bacteria. Low-dimensional nano-TiO2, including nanotubes, nanorods, and nanosheets, were synthesized hydrothermally, and their effects on the bacterial viability of Escherichia coli and Aeromonas hydrophila were compared to spherical nanostructures (anatase nanospheres and P25). Results reveal that TiO2 nanotubes and nanosheets are less phototoxic than their rod- and sphere-shape counterparts under simulated solar irradiation. None of the tested nano-TiO2 shows toxicity in the dark. In contrast to their diminished phototoxicity, however, TiO2 nanotubes and nanosheets exhibit comparable or even higher photoactivity than other nanostructures. Observations by scanning transmission electron microscopy suggest that material morphology influences nano-TiO2 phototoxicity by governing how nano-TiO2 particles align at the bacterial cell surface. Overall, when comparing materials with different morphologies and dimensionality, nano-TiO2 phototoxicity is not a simple function of photocatalytic reactivity or ROS production. Instead, we propose that the evaluation of nano-TiO2 phototoxicity encompasses a three-pronged approach, involving the intrinsic photoactivity, aggregation of nano-TiO2, and the nano-TiO2/bacteria surface interactions.

Evaluating nanoparticle breakthrough during drinking water treatment

BACKGROUND

Use of engineered nanoparticles (NPs) in consumer products is resulting in NPs in drinking water sources. Subsequent NP breakthrough into treated drinking water is a potential exposure route and human health threat.

OBJECTIVES

In this study we investigated the breakthrough of common NPs--silver (Ag), titanium dioxide (TiO2), and zinc oxide (ZnO)--into finished drinking water following conventional and advanced treatment.

METHODS

NPs were spiked into five experimental waters: groundwater, surface water, synthetic freshwater, synthetic freshwater containing natural organic matter, and tertiary wastewater effluent. Bench-scale coagulation/flocculation/sedimentation simulated conventional treatment, and microfiltration (MF) and ultrafiltration (UF) simulated advanced treatment. We monitored breakthrough of NPs into treated water by turbidity removal and inductively coupled plasma-mass spectrometry (ICP-MS).

RESULTS

Conventional treatment resulted in 2-20%, 3-8%, and 48-99% of Ag, TiO2, and ZnO NPs, respectively, or their dissolved ions remaining in finished water. Breakthrough following MF was 1-45% for Ag, 0-44% for TiO2, and 36-83% for ZnO. With UF, NP breakthrough was 0-2%, 0-4%, and 2-96% for Ag, TiO2, and ZnO, respectively. Variability was dependent on NP stability, with less breakthrough of aggregated NPs compared with stable NPs and dissolved NP ions.

CONCLUSIONS

Although a majority of aggregated or stable NPs were removed by simulated conventional and advanced treatment, NP metals were detectable in finished water. As environmental NP concentrations increase, we need to consider NPs as emerging drinking water contaminants and determine appropriate drinking water treatment processes to fully remove NPs in order to reduce their potential harmful health outcomes.

Cytotoxicity of commercial nano-TiO2 to Escherichia coli assessed by high-throughput screening: effects of environmental factors

The extensive use of nano-TiO2 in industry has led to growing concerns about its potential environmental impacts. However, negligible toxicity is commonly reported under insufficient illumination and artificial solution conditions in the literature, which rarely includes discussion of the regulating role of environmental factors. Herein, we report the results of a high-throughput screening assay to evaluate the acute cytotoxicity of six commercial nano-TiO2 materials to Escherichia coli (E. coli) using Lake Michigan water as a model for aquatic surface environments. In particular, we investigate the specific effects of illumination wavelength and natural organic matter (NOM) content. Under simulated solar irradiation, four anatase-based nano-TiO2 materials including Pigment White 6 exhibit significant bacterial toxicity (2 h-IC50 value of 2.7-9.1 mg/L), with toxicity thresholds much lower than previously reported. Negligible toxicity is caused either by pure-phase rutile or under dark condition. Formation of nano-TiO2 aggregates well beyond nano-scale does not eliminate their toxic effect, but photoactivity dominates over the primary size and extent of aggregation in determining the acute cytotoxicity of nano-TiO2. Under visible light irradiation (UVA&B blocked) the antibacterial activity of nano-TiO2 is essentially erased, whereas removing only UVB wavelengths slightly mitigates the toxicity. Suwannee River fulvic acid, acting as a natural dispersant, reverses the extent of nano-TiO2 aggregation, but also reduces its bacterial cytotoxicity. These results demonstrate that despite particle aggregation, the short-term cytotoxicity of nano-TiO2 is predominantly attributed to its phototoxicity, emphasizing the importance of illumination conditions in toxicological screening of photoactive nanomaterials. In the natural aquatic environment, however, this acute toxicity may be mitigated by the attenuation of UV irradiation and increased NOM concentration in the water column.