Effects of Ag nanoparticles on survival and oxygen consumption of zebra fish embryos, Danio rerio

Developmental impacts and toxicological hallmarks of silver nanoparticles across diverse biological models

Silver nanoparticles (AgNPs), revered for their antimicrobial prowess, have become ubiquitous in a range of products, from biomedical equipment to food packaging. However, amidst their rising popularity, concerns loom over their possible detrimental effects on fetal development and subsequent adult life. This review delves into the developmental toxicity of AgNPs across diverse models, from aquatic species like zebrafish and catfish to mammalian rodents and in vitro embryonic stem cells. Our focus encompasses the fate of AgNPs in different contexts, elucidating associated hazardous results such as embryotoxicity and adverse pregnancy outcomes. Furthermore, we scrutinize the enduring adverse impacts on offspring, spanning impaired neurobehavior function, reproductive disorders, cardiopulmonary lesions, and hepatotoxicity. Key hallmarks of developmental harm are identified, encompassing redox imbalances, inflammatory cascades, DNA damage, and mitochondrial stress. Notably, we explore potential explanations, linking immunoregulatory dysfunction and disrupted epigenetic modifications to AgNPs-induced developmental failures. Despite substantial progress, our understanding of the developmental risks posed by AgNPs remains incomplete, underscoring the urgency of further research in this critical area.

Assessing the effects of silver nanoparticles on the ecophysiology of Gammarus roeseli

Being part of the macrobenthic fauna, gammarids are efficient indicators of contamination of aquatic ecosystems by nanoparticles that are likely to sediment on the bottom. The present study investigates the effects of silver nanoparticles (nAg) on ecophysiological functions in Gammarus roeseli by using a realistic scenario of contamination. Indeed, an experiment was conducted during 72 h, assessing the effects of 5 silver nAg from 10 to 100 nm diluted at concentrations of maximum 5 µg L^-1 in a natural water retrieved from a stream and supplemented with food. The measured endpoints in gammarids were survival, silver concentrations in tissues, consumption of oxygen and ventilation of gills. Additionally, a set of biomarkers of the energetic metabolism was measured. After a 72-h exposure, results showed a concentration-dependent increase of silver levels in G. roeseli that was significant for the smallest nAg size (10 nm). Ecophysiological responses in G. roeseli were affected and the most striking effect was a concentration-dependent increase in oxygen consumption especially for the smallest nAg (10 to 40 nm), whereas ventilation of gills by gammarids was not changed. The potential mechanisms underlying these findings are discussed. Thus, we demonstrated the very low exposure concentration of 0.5 µg L^-1 for the small nAg size led to significant ecophysiological effects reinforcing the need to further investigate subtle effects on nanoparticles on aquatic organisms.

Investigation of the Oxidative Stress Response of a Green Synthesis Nanoparticle (RP-Ag/ACNPs) in Zebrafish

Silver nanoparticles (AgNPs) are prominent nanomaterials that are efficiently used in different industries including medical products, water treatment, and cosmetics. However, AgNPs are known to cause adverse effects on the ecosystem and human health. In this study, aqueous extract of Rumex patientia (RP) was used as a reducing and stabilizing agent in AgNP biosynthesis. The obtained activated carbon (AC) from Chenopodium album (CA) plant was combined with RP-AgNPs to synthesize RP-Ag/AC NPs. Next, the effects of these green synthesis RP-Ag/AC NPs on zebrafish (Danio rerio) embryos and larvae were investigated. First, we characterized the RP-Ag/AC NPs by using X-ray diffraction (XRD) and transmission electron microscopy (TEM) and determined LC₅₀ value as 217.23 mg/L at 96 h. Next, the alterations in survival rate, hatching rate, and morphology of the larvae at 96 h were monitored. The survival rates decreased in a dose-dependent manner. Morphological defects such as yolk sac edema, pericardial edema, spinal curvature, and tail malformation in the NP-treated larvae were observed. RP-Ag/AC NPs stimulated the production of neuronal NOS (nNOS) and 8-OHdG in zebrafish brain tissues in a dose-dependent manner and enhanced neutrophil degeneration and necrosis at concentrations of 50 and 100 mg/L. Thus, the obtained data suggest that the green synthesis process is not sufficient to reduce the effect of oxidative stress caused by AgNPs on oxidative signaling.

The specification of zebrafish (Danio rerio) heart electrocardiogram index characteristic responses to different types of pollutants

Water quality was highly affected by common pollutants. Metals, pesticides and small molecules are ubiquitous pollutants. Advancement in engineering technology (computer-based monitoring systems) increased the efficiency of quantifying toxicity of different chemicals in an organism. The cardiovascular system reflects internal and external stress of an organism, and electrocardiogram (ECG) data reliably measure external stress. As ECG data can accurately reflect the physiological conditions of organisms, and zebrafish (Danio rerio) are considered to be good models for cardiovascular research, it is hypothesized that ECG parameters of zebrafish could indicate the toxicity of water-borne chemicals. To achieve this, we treated zebrafish with different concentrations of target chemicals (CuSO₄, C₁₀H₁₉O₆PS₂ and NH₄Cl) for 48 h and ECG data were measured. P-wave, R-wave, T-wave, PR-interval, QRS-complex and QT-interval data were the focus of this study. The results of self-organizing maps and Pearson correlation analysis indicate that the QRS-complex can be used as an indicator for CuSO₄ stress. The QT-interval could be used to assess the C₁₀H₁₉O₆PS₂ stress. The QT-interval and P-wave can be used to evaluate the NH₄Cl stress. Responses of zebrafish ECG parameters were identical with other vertebrate model, and were specific to toxicant types. It is proved that zebrafish heart ECG index could be used as a potential indicator in early detection of environmental stress.

Nanosized-Ag-doped porous β-tricalcium phosphate for biological applications

The treatment of infectious or potentially infective bone defects remains a major problem in clinical practice. Silver has the ability to potentiate antibiotics against resistant bacterial strains. In order to reduce the risk of long-term infections, it is necessary for the biomaterial scaffold to release Ag⁺ in a controlled manner during the entire healing process. In this study, given the antimicrobial characteristics of nanosized Ag (NSAg), we synthesized β-tricalcium phosphate (β-TCP) doped with 5 and 10 wt% NSAg (5 wt% NSAgTCP and 10 wt% NSAgTCP, respectively). The NSAgTCP composites exhibited similar macroporous structures to pure β-TCP. The NSAgTCP samples were examined by scanning electron microscopy at 10,000-times magnification, which revealed that silver was still present at the nanometer scale. X-ray diffraction revealed that silver does not change the crystalline properties of β-TCP. In addition, we observed that the mechanical strength of NSAgTCP increased with increasing amounts of added Ag. The antibacterial, physical, and chemical properties of NSAgTCP were investigated in vitro. We found that NSAgTCP is effective at inhibiting the growth of Staphylococcus aureus and Escherichia coli and is not cytotoxic to human bone marrow mesenchymal stem cells. Moreover, it does not hinder liver or kidney function when tested in vivo. As the bioceramic degrades, Ag ions are slowly released and new bone is formed. No significant cytotoxic effects were observed even when 10 wt% NSAgTCP was used. NSAgTCP has the ability to simultaneously repair bone defects and act as an anti-infective agent; hence, we expect that this material, with its good bone-repairing and anti-infective properties, will find wide spread use as a novel bone substitute.

Effects of iron oxide nanoparticles (Fe3O4) on life history and metabolism of the Neotropical cladoceran Ceriodaphnia silvestrii

Nanoparticles (NPs) production is increasing worldwide. These products are likely to end up in aquatic environments. However, few studies evaluated the chronic toxicity of iron-based NPs (Fe-NPs) to cladocerans and their potential ecotoxicological hazards. In this study we aimed to investigate the effects of iron oxide nanoparticles (Fe₃O₄-NPs) to Ceriodaphnia silvestrii Daday, 1902, assessing acute (48 h) and chronic toxicity (up to 14 d). Besides traditional endpoints (immobility and lethality), we also evaluated physiological responses (respiration rates) in a 48 h-exposure. No immobility was observed (EC₅₀ > 100 mg L^-1) after 48 h, whereas respiration rates at the highest concentration were 400% of that in control, indicating that this endpoint was more sensitive during acute toxicity. In chronic assays, Fe₃O₄-NPs affected body length (8.24% growth inhibition in 7 d-exposure) and number of eggs (7-d IC₁₀: 3.53, IC₂₀: 6.69 mg Fe L^-1) and neonates (7-d IC₁₀: 1.25, IC₂₀: 3.75 mg Fe L^-1). Based on species sensitivity distribution (SSD), C. silvestrii was a sensitive organism, suggesting Fe-NPs as a possible threat for this species. Our results also indicate that the NPs caused a physical barrier, impairing food absorption, since we observed NPs agglomerations into cladocerans' gut. We demonstrate that Fe₃O₄-NPs affects C. silvestrii metabolism and reproduction and our results support the use of sublethal endpoints to assess environmental safety. The release of these NPs into freshwater environments should be carefully evaluated, since disturbances on cladoceran population dynamics could cause strong impacts on the entire food web structure and ultimately on ecosystem functioning.

The in vivo effects of silver nanoparticles on terrestrial isopods, Porcellio scaber, depend on a dynamic interplay between shape, size and nanoparticle dissolution properties

The present work aims to study the effects that acute exposure to low concentrations of silver nanoparticles (AgNPs) cause in digestive glands of terrestrial isopods (Porcellio scaber). The experiments were designed to integrate different analytical techniques, such as transmission electron microscopy, atomic absorption spectroscopy, proton induced X-ray emission, and Fourier transform IR imaging (FTIRI), in order to gain a comprehensive insight into the process from the AgNPs' synthesis to their interaction with biological tissues in vivo. To this aim, terrestrial isopods were fed with AgNPs having different shapes, sizes, and concentrations. For all the tested conditions, no toxicity at the whole organism level was observed after 14 days of exposure. However, FTIRI showed that AgNPs caused detectable local changes in proteins, lipids, nucleic acids and carbohydrates at the tissue level, to an extent dependent on the interplay of the AgNPs' properties: shape, size, concentration and dissolution of ions from them.

Moina macrocopa as a non-target aquatic organism for assessment of ecotoxicity of silver nanoparticles: Effect of size

The release of nanomaterials in water reservoirs is hazardous. Very few reports are available on the interaction of different sized nanoparticles with aquatic organisms and aquatic environment. In the present study, silver nanoparticles (AgNPs) having an average particle size of 20.80 ± 2.31 and 40.04 ± 4.72 nm were synthesized using polyvinylpyrrolidone and l-tyrosine. Ecotoxicological effects of AgNPs were evaluated on less explored crustacean species, Moina macrocopa. The 48 h lethal values (48 h LC₅₀) of 20 and 40 nm AgNPs were 0.11 ± 0.02 and 0.12 ± 0.03 mg/L, respectively. Further, a size dependent inhibition of AgNPs on acetyl cholinesterase and digestive enzymes (trypsin, amylase, β-galactosidase) was observed, while that of the antioxidant enzymes (catalase, superoxide dismutase, glutathione-S-transferase) and alkaline phosphatase were enhanced as compared to control group. These results strengthen the potential of enzymes as biomarker in environmental risk assessment of AgNPs. AgNPs accumulated in the gut of M. macrocopa which could not be completely eliminated, thereby resulting in an increased metal body burden. The accumulation of AgNPs of 20 nm was lower than that of 40 nm indicating the influence of size of nanoparticles on uptake and toxicity. AgNPs agglomerated in moderately hard water medium (MHWM) and this agglomeration influenced the exposure the organism thereto. The size of AgNPs influenced the toxicity to M. macrocopa through interplay between uptake, accumulation, aggregation, and excretion in the organism and environment.

Oocyte exposure to ZnO nanoparticles inhibits early embryonic development through the γ-H2AX and NF-κB signaling pathways

The impacts of zinc oxide nanoparticles on embryonic development following oocyte stage exposure are unknown and the underlying mechanisms are sparsely understood. In the current investigation, intact nanoparticles were detected in ovarian tissue in vivo and cultured cells in vitro under zinc oxide nanoparticles treatment. Zinc oxide nanoparticles exposure during the oocyte stage inhibited embryonic development. Notably, in vitro culture data closely matched in vivo embryonic data, in that the impairments caused by Zinc oxide nanoparticles treatment passed through cell generations; and both gamma-H2AX and NF-kappaB pathways were involved in zinc oxide nanoparticles caused embryo-toxicity. Copper oxide and silicon dioxide nanoparticles have been used to confirm that particles are important for the toxicity of zinc oxide nanoparticles. The toxic effects of zinc oxide nanoparticles emanate from both intact nanoparticles and Zn²⁺. Our investigation along with others suggests that zinc oxide nanoparticles are toxic to the female reproductive system [ovaries (oocytes)] and subsequently embryo-toxic and that precaution should be taken regarding human exposure to their everyday use.

Green synthesis of silver nanoparticles using Piper nigrum: tissue-specific bioaccumulation, histopathology, and oxidative stress responses in Indian major carp Labeo rohita

The aim of the present investigation is to assess the sublethal toxicity of biologically synthesized silver nanoparticles (Ag NPs) in Indian major carp Labeo rohita. Ag NPs used in the study were synthesized by using AgNO₃ with aqueous leaf extract of Piper nigrum. Median lethal concentration (LC₅₀) of synthesized Ag NPs was determined for 96 h (25 μg/L); 2.5 μg/L (1/10th LC₅₀) and 5 μg/L (1/5th LC₅₀) were taken as sublethal concentrations to evaluate the toxicity for 35 days. The results of the TEM, SEM, and EDX analyses revealed that Ag NPs were considerably accumulated in the gill, liver, and kidney of fish at both concentrations (2.5 and 5 μg/L). Consequently, the activity of the antioxidant enzymes, SOD and CAT, was significantly (P < 0.05) decreased in the gill, liver, and kidney when compared to the control group during the study period. However, lipid peroxidase (LPO) activity in the gill, liver, and kidney was significantly (P < 0.05) increased, and the result concluded a possible sign of free radical-induced oxidative stress in Ag NP-exposed fish than the sham-exposed individuals. The histopathological study also confirmed the alterations such as degeneration of lamella, lifting of lamellar epithelium, hepatic necrosis, pyknotic nuclei, increased intracellular space, and shrinkage of glomerulus elicited by Ag NPs in the gill, liver, and kidney of Labeo rohita with two different concentrations. The findings of the present study revealed that green synthesis of Ag NPs from Piper nigrum at sublethal concentrations leads to accumulation of Ag, oxidative stress, and histopathological alterations in the target organs of the fish, Labeo rohita.

The physiological characteristics of zebra fish (Danio rerio) based on metabolism and behavior: A new method for the online assessment of cadmium stress

In order to illustrate heavy metal ecotoxicology associated with interactions between chemicals and biological systems, we investigated physiological changes (metabolism and behavior response) of zebra fish (Danio rerio) under 48 h Cadmium chloride (CdCl₂) exposure using online monitoring technique. The concentrations of CdCl₂ were designed as 4.26, 42.6 and 85.2 mg/L, which were 0.1, 1.0, and 2.0 based on toxic unit (TU), respectively. The metabolism was assessed using the oxygen consumption (OC), and the behavior response was analyzed in behavior strength (BS). Significant inhibition of both OC and BS could be observed: OC was 617.39 ± 30.48 mg/kg/h in the control, and it decreased rapidly to 229.07 ± 28.66 mg/kg/h in 2.0 TU treatment. BS changed from 0.76 ± 0.07 (control) to 0.39 ± 0.04 (2.0 TU) with the increase of exposure concentrations. Further results suggested that both factors were related to diurnal variation during 48 h exposure, which could be regarded as circadian rhythms: the average values of OC and BS during photo-phase were significantly higher than both during scoto-phase in CdCl₂ treatments (p < 0.05). After integrated analysis, the original values of both OC and BS with wide fluctuation showed a negative linear relationship with CdCl₂ concentration. The levels of both OC and BS were positively correlated with CdCl₂ (r = 0.93 and p < 0.01). It is suggested that both OC and BS provide an objective ground for CdCl₂ stress assessment, and that also could be applied to test the changes of organisms quantitatively in toxic physiology.

Effect of nanosilver on metabolism in rainbow trout (Oncorhynchus mykiss): An investigation using different respirometric approaches

Nanosilver (nAg) has been incorporated into many consumer products, including clothing and washing machines, because of its antimicrobial properties. Consequently, the potential for its release into aquatic environments is of significant concern. Documented toxic effects on fish include altered gene expression, gill damage, and impaired gas exchange, as well as mortality at high nAg concentrations. The present study reports the effects of nAg on the metabolism of rainbow trout (Oncorhynchus mykiss). Fish were exposed to environmentally relevant concentrations (0.28 ± 0.02 μg/L) and higher (47.60 ± 5.13 μg/L) for 28 d, after which their standard metabolic rate (SMR), forced maximum metabolic rate (MMR_f ), and spontaneous maximum metabolic rate (MMR_s ) were measured. There was no effect observed in SMR, MMR_f , or MMR_s , suggesting that nAg is unlikely to directly affect fish metabolism. On average, MMR_s tended to be greater than MMR_f , and most MMR_s occurred when room lighting increased. The timing of MMR_f chase protocols was found to affect both MMR_f and SMR estimates, in that chasing fish before respirometric experiments caused higher MMR_f estimates and lower SMR estimates. Although compounded effects involving nAg and other environmental stressors remain unknown, the present study indicates that the tested range of nAg is unlikely to constrain fish metabolism. Environ Toxicol Chem 2017;36:2722-2729. © 2017 SETAC.

Developmental and reproductive toxicity of PVP/PEI-coated silver nanoparticles to zebrafish

Cellular and molecular mechanisms of toxicity of silver nanoparticles (NPs) and their toxicity to fish embryos after waterborne exposure have been widely investigated, but much less information is available regarding the effect of Ag NPs on physiological functions such as growth or reproduction. In this work, the effects of waterborne exposure of adult zebrafish (Danio rerio) to PVP/PEI coated Ag NPs (~5nm) on reproduction (fecundity) were investigated. Moreover, the development of the embryos after parental exposure was compared with the development of embryos after direct waterborne exposure to the NPs. For this, two experiments were run: 1) embryos from unexposed parents were treated for 5days with Ag NPs (10μgAgL^-1-10mgAgL^-1) and development was monitored, and 2) selected breeding zebrafish were exposed for 3weeks to 100ngAgL^-1 (environmentally relevant concentration) or to 10μgAgL^-1 of Ag NPs, fecundity was scored and development of resulting embryos was monitored up to 5days. Waterborne exposure of embryos to Ag NPs resulted in being highly toxic (LC50 at 120h=50μgAgL^-1), causing 100% mortality during the first 24h of exposure at 0.1mgAgL^-1. Exposure of adults, even at the environmentally relevant silver concentration, caused a significant reduction of fecundity by the second week of treatment and resulting embryos showed a higher prevalence of malformations than control embryos. Exposed adult females presented higher prevalence of vacuolization in the liver. These results show that Ag NPs at an environmentally relevant concentration are able to affect population level parameters in zebrafish.

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.

Adapting OECD Aquatic Toxicity Tests for Use with Manufactured Nanomaterials: Key Issues and Consensus Recommendations

The unique or enhanced properties of manufactured nanomaterials (MNs) suggest that their use in nanoenabled products will continue to increase. This will result in increased potential for human and environmental exposure to MNs during manufacturing, use, and disposal of nanoenabled products. Scientifically based risk assessment for MNs necessitates the development of reproducible, standardized hazard testing methods such as those provided by the Organisation of Economic Cooperation and Development (OECD). Currently, there is no comprehensive guidance on how best to address testing issues specific to MN particulate, fibrous, or colloidal properties. This paper summarizes the findings from an expert workshop convened to develop a guidance document that addresses the difficulties encountered when testing MNs using OECD aquatic and sediment test guidelines. Critical components were identified by workshop participants that require specific guidance for MN testing: preparation of dispersions, dose metrics, the importance and challenges associated with maintaining and monitoring exposure levels, and the need for reliable methods to quantify MNs in complex media. To facilitate a scientific advance in the consistency of nanoecotoxicology test results, we identify and discuss critical considerations where expert consensus recommendations were and were not achieved and provide specific research recommendations to resolve issues for which consensus was not reached. This process will enable the development of prescriptive testing guidance for MNs. Critically, we highlight the need to quantify and properly interpret and express exposure during the bioassays used to determine hazard values.

Comparative toxicity of silver nanoparticles on oxidative stress and DNA damage in the nematode, Caenorhabditis elegans

This study examined the effects of polyvinylpyrrolidone (PVP) surface coating and size on the organismal and molecular toxicity of silver nanoparticles (AgNPs) on the nematode, Caenorhabditis elegans. The toxicity of bare AgNPs and 8 and 38 nm PVP-coated AgNPs (PVP8-AgNPs, PVP38-AgNPs) were compared. The toxicity of AgNO3 was also tested because ion dissolution and particle-specific effects are often important characteristics determining Ag nanotoxicity. Comparative toxicity across AgNO3 and the three different types of AgNPs was first evaluated using a C. elegans mortality test by a direct comparison of the LC50 values. Subsequently, mutant screening followed by oxidative stress, mitochondrial toxicity and DNA damage assays were carried out at equitoxic (LC10 and LC50) concentrations to further assess the toxicity mechanism of AgNO3 and AgNPs. AgNO3 and bare AgNPs had similar toxicities, whereas PVP coating reduced the toxicity of the AgNPs significantly. Of the PVP-AgNPs, the smaller NPs were more toxic. Different groups of mutants responded differently to AgNO3 and AgNPs, which indicates that their toxicity mechanism might be different. AgNO3 and bare AgNPs induced mitochondrial membrane damage. None of the silver materials tested caused detectable polymerase-inhibiting DNA lesions in either the nucleus or mitochondria as measured by a quantitative PCR assay, but AgNO3, bare AgNPs and PVP8-AgNPs induced oxidative DNA damage. These results show that coatings on the AgNPs surface and the particle size make a clear contribution to the toxicity of the AgNPs, and oxidative stress-related mitochondrial and DNA damage appear to be potential mechanisms of toxicity.

DNA methylation and temperature stress in an Antarctic polychaete, Spiophanes tcherniai

Epigenetic modifications of DNA and histones are a primary mechanism by which gene expression activities may be modified in response to environmental stimuli. Here we characterize patterns of methyl-cytosine composition in the marine polychaete Spiophanes tcherniai from McMurdo Sound, Antarctica. We cultured adult worms at two temperatures, -1.5°C (ambient control) and +4°C (warm treatment), for 4 weeks. We observed a rapid capacity for S. tcherniai organismal respiration rates and underlying catalytic rates of citrate synthase at +4°C to return to control levels in less than 4 weeks. We profiled changes in the methylation states of CpG sites in these treatments using an NGS strategy to computationally reconstruct and quantify methylation status across the genome. In our analysis we recovered 120,000 CpG sites in assembled contigs from both treatments. Of those, we were able to align 28,000 CpG sites in common between the two sample groups. In comparing these aligned sites between treatments, only 3000 (11%) evidenced a change in methylation state, but over 85% of changes involved a gain of a 5-methyl group on a CpG site (net increase in methyation). The ability to score CpG sites as partially methylated among gDNA copies in a sample opens up a new avenue for assessing DNA methylation responses to changing environments. By quantitatively distinguishing a "mixed" population of copies of one CpG site, we can begin to identify dynamic, non-binary, continuous-response reactions in DNA methylation intensity or density that previously may have been overlooked as noise.

Nanoparticle toxicity by the gastrointestinal route: evidence and knowledge gaps

The increasing interest in nanoparticles for advanced technologies, consumer products, and biomedical applications has led to great excitement about potential benefits but also concern over the potential for adverse human health effects. The gastrointestinal tract represents a likely route of entry for many nanomaterials, both directly through intentional ingestion or indirectly via nanoparticle dissolution from food containers or by secondary ingestion of inhaled particles. Additionally, increased utilisation of nanoparticles may lead to increased environmental contamination and unintentional ingestion via water, food animals, or fish. The gastrointestinal tract is a site of complex, symbiotic interactions between host cells and the resident microbiome. Accordingly, evaluation of nanoparticles must take into consideration not only absorption and extraintestinal organ accumulation but also the potential for altered gut microbes and the effects of this perturbation on the host. The existing literature was evaluated for evidence of toxicity based on these considerations. Focus was placed on three categories of nanomaterials: nanometals and metal oxides, carbon-based nanoparticles, and polymer/dendrimers with emphasis on those particles of greatest relevance to gastrointestinal exposures.

Impact of organic carbon on the stability and toxicity of fresh and stored silver nanoparticles

Studies investigating the impact of particle size and capping agents on nanosilver toxicity in pristine laboratory conditions are becoming available. However, the relative importance of known environmental mitigating factors for dissolved silver remains poorly characterized for nanosilver in context with existing predictive toxicity models. This study investigated the implications of freshly prepared versus stored 20 and 100 nm nanosilver stocks to freshwater zooplankton (Ceriodaphnia dubia) in presence and absence of dissolved organic carbon (DOC). Results indicated that while the acute toxicity of nanosilver decreased significantly with larger size and higher DOC, storage resulted in significant increases in toxicity and ion release. The most dramatic decrease in toxicity due to DOC was observed for the 20 nm particle (2.5-6.7 fold decrease), with more modest toxicity reductions observed for the 100 nm particle (2.0-2.4 fold) and dissolved silver (2.7-3.1 fold). While a surface area dosimetry presented an improvement over mass when DOC was absent, the presence of DOC confounded its efficacy. The fraction of dissolved silver in the nanosilver suspensions was most predictive of acute toxicity regardless of system complexity. Biotic Ligand Model (BLM) predictions based on the dissolved fraction in nanosilver suspensions were comparable to observed toxicity.

Magnetic nanobeads decorated with silver nanoparticles as cytotoxic agents and photothermal probes

A versatile method for decorating magnetic nanobeads (being composite materials from polymers and superparamagnetic nanoparticles) with silver nanoparticles of 3-6 nm size is presented. Control over the silver nanoparticle coverage at the nanobead surface is achieved by changing the reaction parameters. Moreover, the silver-decorated magnetic nanobeads (Ag-MNBs) are studied with respect to their in vitro cytotoxicity on two distinct tumour cell lineages under different parameters, i.e., dose, incubation time, magnetic field applied during the culturing, silver ion leakage, and colloidal stability. It is found that enhanced magnetically mediated cellular uptake and silver ion leakage from the Ag-MNBs surface are the main factors which affect the toxicity of the Ag-MNBs and allow the half-maximal inhibitory dose of silver to be reduced to only 32 μg mL(-1) . Furthermore, a synergic cytotoxicity induced by photo-activation of silver nanoparticles was also found.

Nanosilver Application in Dental Cements

Streptococcus mutans is the microorganism mostly responsible for initiation of tooth decay and also for the progression of an established lesion. Silver has been used for its antibacterial properties for many years, in different forms: ionised and elementary forms, as silver zeolites or as nanoparticles. The purpose of this study was to evaluate the antibacterial activity of three dental cements modified by nanosilver. Three cements were used: Sealapex, RelyX ARC, and Vitrebond. The cements were incorporated with 0.05 mL of silver nanoparticles solution. Control groups were prepared without silver. Six Petri plates with BHI were inoculated with S. mutans using sterile swabs. Three cavities were made in each agar plate (total = 18) and filled with the manipulated cements. They were incubated at 37°C for 48 h, and the inhibition halos were measured. The paired t-Test was used for statistical analysis (P<0.05). No inhibition halos were obtained for Sealapex and Rely X, but Vitrebond showed bactericidal activity without silver and enhanced effect with silver incorporation.

The progress of silver nanoparticles in the antibacterial mechanism, clinical application and cytotoxicity

Nanotechnology is a highly promising field, with nanoparticles produced and utilized in a wide range of commercial products. Silver nanoparticles (AgNPs) has been widely used in clothing, electronics, bio-sensing, the food industry, paints, sunscreens, cosmetics and medical devices, all of which increase human exposure and thus the potential risk related to their short- and long-term toxicity. Many studies indicate that AgNPs are toxic to human health. Interestingly, the majority of these studies focus on the interaction of the nano-silver particle with single cells, indicating that AgNPs have the potential to induce the genes associated with cell cycle progression, DNA damage and mitochondrial associated apoptosis. AgNPs administered through any method were subsequently detected in blood and were found to cause deposition in several organs. There are very few studies in rats and mice involving the in vivo bio-distribution and toxicity, organ accumulation and degradation, and the possible adverse effects and toxicity in vivo are only slowly being recognized. In the present review, we summarize the current data associated with the increased medical usage of nano-silver and its related nano-materials, compare the mechanism of antibiosis and discuss the proper application of nano-silver particles.

Histopathological studies and oxidative stress of synthesized silver nanoparticles in Mozambique tilapia (Oreochromis mossambicus)

To evaluate the potential environmental effects of engineered nano metals, it is important to determine the adverse effects of various nanomaterials on aquatic species. Adult tilapia (Oreochromis mossambicus) were maintained in 10 L glass aquaria, and exposed to a graded series of synthesized silver nanoparticles (AgNPs) at 25, 50 and 75 mg/L for eight days. The LC50 value was 12.6 mg/L. Reduced activities of antioxidant enzymes and the contents of antioxidants were lowered in the gills and liver of fishes treated with AgNPs, which resulted in heavy accumulation of free radicals. Histopathological results imply that the balance between the oxidative and antioxidant system in the fish was broken down during Ag-NPs exposure. The principal concern related with the release of nanomaterials and their smaller particle may change the materials transport and potential toxicity to aquatic organisms compared to larger particles.