Effects of ionic strength on physicochemical properties and toxicity of silver nanoparticles

Life cycle exposure to titanium dioxide nanoparticles (TiO2-NPs) induces filial toxicity and population decline in the nematode Caenorhabditis elegans

Titanium dioxide nanoparticle (TiO2-NP) exposure has raised significant concern due to their potential toxicity and adverse ecological impacts. Despite their ubiquitous presence in various environmental compartments, the long-term consequences of TiO2-NPs remain poorly understood. In this study, we combined data of in vivo toxicity and modeling to investigate the potential negative impacts of TiO2-NP exposure. We employed the nematode Caenorhabditis elegans, an environmental organism, to conduct a full life cycle TiO2-NP toxicity assays. Moreover, to assess the potential impact of TiO2-NP toxicity on population dynamics, we applied a stage-constructed matrix population model (MPM). Results showed that TiO2-NPs caused significant reductions in reproduction, survival, and growth of parental C. elegans (P0) at the examined concentrations. Moreover, these toxic effects were even more pronounced in the subsequent generation (F1) when exposed to TiO2-NPs. Furthermore, parental TiO2-NP exposure resulted in significant toxicity in non-exposed C. elegans progeny (TiO2-NPs free), adversely affecting their reproduction, survival, and growth. MPM analysis revealed decreased transition probabilities of surviving (Pi), growth (Gi), and fertility (Fi) in scenarios with TiO2-NP exposure. Additionally, the population growth rate (λmax) was found to be less than 1 in both P0 and F1, indicating a declining population trend after successive generations. Sensitivity analysis pinpointed L1 larvae as the most vulnerable stage, significantly contributing to the observed population decline in both P0 and F1 generations under TiO2-NP exposure. Our findings provide insight into the potential risk of an environmental organism like nematode by life cycle exposure to TiO2-NPs.

Evaluating the adverse effects and mechanisms of nanomaterial exposure on longevity of C. elegans: A literature meta-analysis and bioinformatics analysis of multi-transcriptome data

Exposure to large-size particulate air pollution (PM2.5 or PM10) has been reported to increase risks of aging-related diseases and human death, indicating the potential pro-aging effects of airborne nanomaterials with ultra-fine particle size (which have been widely applied in various fields). However, this hypothesis remains inconclusive. Here, a meta-analysis of 99 published literatures collected from electronic databases (PubMed, EMBASE and Cochrane Library; from inception to June 2023) was performed to confirm the effects of nanomaterial exposure on aging-related indicators and molecular mechanisms in model animal C. elegans. The pooled analysis by Stata software showed that compared with the control, nanomaterial exposure significantly shortened the mean lifespan [standardized mean difference (SMD) = -2.30], reduced the survival rate (SMD = -4.57) and increased the death risk (hazard ratio = 1.36) accompanied by upregulation of ced-3, ced-4 and cep-1, while downregulation of ctl-2, ape-1, aak-2 and pmk-1. Furthermore, multi-transcriptome data associated with nanomaterial exposure were retrieved from Gene Expression Omnibus (GSE32521, GSE41486, GSE24847, GSE59470, GSE70509, GSE14932, GSE93187, GSE114881, and GSE122728) and bioinformatics analyses showed that pseudogene prg-2, mRNAs of abu, car-1, gipc-1, gsp-3, kat-1, pod-2, acdh-8, hsp-60 and egrh-2 were downregulated, while R04A9.7 was upregulated after exposure to at least two types of nanomaterials. Resveratrol (abu, hsp-60, pod-2, egrh-2, acdh-8, gsp-3, car-1, kat-1, gipc-1), naringenin (kat-1, egrh-2), coumestrol (egrh-2) or swainsonine/niacin/ferulic acid (R04A9.7) exerted therapeutic effects by reversing the expression levels of target genes. In conclusion, our study demonstrates the necessity to use phytomedicines that target hub genes to delay aging for populations with nanomaterial exposure.

Environmental behaviors and toxic mechanisms of engineered nanomaterials in soil

Engineered nanomaterials (ENMs) are inevitably released into the environment with the exponential application of nanotechnology. Parts of ENMs eventually accumulate in the soil environment leading to potential adverse effects on soil ecology, crop production, and human health. Therefore, the safety application of ENMs on soil has been widely discussed in recent years. More detailed safety information and potential soil environmental risks are urgently needed. However, most of the studies on the environmental effects of metal-based ENMs have been limited to single-species experiments, ecosystem processes, or abiotic processes. The present review formulated the source and the behaviors of the ENMs in soil, and the potential effects of single and co-exposure ENMs on soil microorganisms, soil fauna, and plants were introduced. The toxicity mechanism of ENMs to soil organisms was also reviewed including oxidative stress, the release of toxic metal ions, and physical contact. Soil properties affect the transport, transformation, and toxicity of ENMs. Toxic mechanisms of ENMs include oxidative stress, ion release, and physical contact. Joint toxic effects occur through adsorption, photodegradation, and loading. Besides, future research should focus on the toxic effects of ENMs at the food chain levels, the effects of ENMs on plant whole-lifecycle, and the co-exposure and long-term toxicity effects. A fast and accurate toxicity evaluation system and model method are urgently needed to solve the current difficulties. It is of great significance for the sustainable development of ENMs to provide the theoretical basis for the ecological risk assessment and environmental management of ENMs.

Environmentally relevant exposure to tetrabromobisphenol A induces reproductive toxicity via regulating glucose-6-phosphate 1-dehydrogenase and sperm activation in Caenorhabditis elegans

Tetrabromobisphenol A (TBBPA), a ubiquitous brominated flame-retardant environmental pollutant, has been reported to cause reproductive toxicity by chronic exposure. However, the acute reproductive risk and mechanisms of TBBPA toxicity to individuals, especially at environmentally relevant levels, remains a topic of debate. In this study, Caenorhabditis elegans was used to investigate the reproductive toxicity of acute exposure to TBBPA at environmentally relevant doses. The reproductive end points (embryonic lethality ratio and brood size), oxidative stress, sperm activation, and molecular docking were evaluated. Results showed that, after 24 h of TBBPA treatment, even at the lowest concentration (1 μg/L), the embryonic lethality ratio of C. elegans increased significantly, from 1.63 % to 3.03 %. Furthermore, TBBPA induced oxidative stress with significantly increased expression of sod-3 in C. elegans, which further raised the level of reproductive toxicity through inhibiting the activation of sperm in nematodes. In addition, molecular docking suggested TBBPA might compete for the glucose-6-phosphate-binding site of glucose-6-phosphate 1-dehydrogenase, resulting in oxidative stress generation. Accordingly, our findings indicate that even acute exposure to environmental concentrations of TBBPA may induce reproductive toxicity through reducing sperm activation in nematodes.

Antioxidant response to ZnO nanoparticles in juvenile Takifugu obscurus: protective effects of salinity

The extensive utilization of Zinc Oxide nanoparticles (ZnO NPs) has garnered significant attention due to their detrimental impacts on ecosystem. Unfortunately, ecotoxicity of ZnO NPs in coastal waters with fluctuating salinity has been disregarded. This study mainly discussed the toxic effects of ZnO NPs on species inhabiting the transition zones between freshwater and brackish water, who are of great ecological and economic importance among fish. To serve as the model organism, Takifugu obscurus, a juvenile euryhaline fish, was exposed to different ZnO NPs concentrations (0-200 mg/L) and salinity levels (0 and 15 ppt). The results showed that a moderate increase in salinity (15 ppt) could alleviate the toxic effect of ZnO NPs, as evidenced by improved survival rates. The integrated biomarker response index on oxidative stress also revealed that the toxicity of ZnO NPs was higher in freshwater compared to brackish water. These outcomes can be attributed to higher salinity (15 ppt) reducing the bioavailability of ZnO NPs by facilitating their aggregation and inhibiting the release of metal ions. It is noteworthy that elevated salinity was found to alleviate ZnO NPs toxicity by means of osmotic adjustment via the activation of Na+/K+-ATPase activity. This study demonstrates the salinity-dependent effect of ZnO NPs on T. obscurus, suggesting the possibility for euryhaline fish like T. obscurus to adapt their habitat towards more saline environments, under constant exposure to ZnO NPs.

Characterization and Behaviour of Silica Engineered Nanocontainers in Low and High Ionic Strength Media

Mesoporous silica engineered nanomaterials are of interest to the industry due to their drug-carrier ability. Advances in coating technology include using mesoporous silica nanocontainers (SiNC) loaded with organic molecules as additives in protective coatings. The SiNC loaded with the biocide 4,5-dichloro-2-octyl-4-isothiazolin-3-one (DCOIT), i.e., SiNC-DCOIT, is proposed as an additive for antifouling marine paints. As the instability of nanomaterials in ionic-rich media has been reported and related to shifting key properties and its environmental fate, this study aims at understanding the behaviour of SiNC and SiNC-DCOIT in aqueous media with distinct ionic strengths. Both nanomaterials were dispersed in (i) low- (ultrapure water-UP) and (ii) high- ionic strength media-artificial seawater (ASW) and f/2 medium enriched in ASW (f/2 medium). The morphology, size and zeta potential (ζP) of both engineering nanomaterials were evaluated at different timepoints and concentrations. Results showed that both nanomaterials were unstable in aqueous suspensions, with the initial ζP values in UP below -30 mV and the particle size varying from 148 to 235 nm and 153 to 173 nm for SiNC and SiNC-DCOIT, respectively. In UP, aggregation occurs over time, regardless of the concentration. Additionally, the formation of larger complexes was associated with modifications in the ζP values towards the threshold of stable nanoparticles. In ASW, SiNC and SiNC-DCOIT formed aggregates (<300 nm) independently of the time or concentration, while larger and heterogeneous nanostructures (>300 nm) were detected in the f/2 medium. The pattern of aggregation detected may increase engineering nanomaterial sedimentation rates and enhance the risks towards dwelling organisms.

A critical review of advances in reproductive toxicity of common nanomaterials to Caenorhabditis elegans and influencing factors

In recent decades, nanotechnology has rapidly developed. Therefore, there is growing concern about the potential environmental risks of nanoparticles (NPs). Caenorhabditis elegans (C. elegans) has been used as a powerful tool for studying the potential ecotoxicological impacts of nanomaterials from the whole animal level to single cell level, especially in the area of reproduction. In this review, we discuss the reproductive toxicity of common nanomaterials in C. elegans, such as metal-based nanomaterial (silver nanoparticles (NPs), gold NPs, zinc oxide NPs, copper oxide NPs), carbon-based nanomaterial (graphene oxide, multi-walled carbon nanotubes, fullerene nanoparticles), polymeric NPs, silica NPs, quantum dots, and the potential mechanisms involved. This insights into the toxic effects of existing nanomaterials on the human reproductive system. In addition, we summarize how the physicochemical properties (e.g., size, charge, surface modification, shape) of nanomaterials influence their reproductive toxicity. Overall, using C. elegans as a platform to develop rapid detection techniques and prediction methods for nanomaterial reproductive toxicity is expected to reduce the gap between biosafety evaluation of nanomaterials and their application.

Recent advances in responses of arbuscular mycorrhizal fungi - Plant symbiosis to engineered nanoparticles

The application of engineered nanomaterials (ENMs) is increasing in all walks of life, inevitably resulting in a high risk of ENMs entering the natural environment. Recent studies have demonstrated that phytoaccumulation of ENMs in the environment may be detrimental to plants to varying degrees. However, plants primarily assimilate ENMs through the roots, which are inevitably affected by rhizomicroorganisms. In this review, we focus on a group of common rhizomicroorganisms-arbuscular mycorrhizal fungi (AMF). These fungi contribute to ENMs immobilization and inhibition of phytoaccumulation, improvement of host plant growth and activation of systematic protection in response to excess ENMs stress. In present review, we summarize the biological responses of plants to ENMs and the modulatory mechanisms of AMF on the immobilization of ENMs in substrate-plant interfaces, and indirectly regulatory mechanisms of AMF on the deleterious effects of ENMs on host plants. In addition, the information of feedback of ENMs on mycorrhizal symbiosis and the prospects of future research on the fate and mechanism of phyto-toxicity of ENMs mediated by AMF in the environment are also addressed. In view of above, synergistic reaction of plants and AMF may prove to be a cost-effective and eco-friendly technology to bio-control potential ENMs contamination on a sustainable basis.

In vitro and in vitro toxicity study of diesel exhaust particles using BEAS-2B cell line and the nematode Caenorhabditis elegans as biological models

It is well accepted that diesel exhaust particles (DEPs) are highly associated with improper function of organ systems. In this study, DEP toxicity was performed by using in vitro human BEAS-2B cell line and in vivo animal model, namely, Caenorhabditis elegans (C. elegans). The potential toxicity of DEP was assessed by the apical endpoints of BEAS-2B cell line and reflections of C. elegans under exposure scenarios of 0~50 μg mL^-1 DEP. With the increase of DEP exposure concentration, microscopic accumulations in the cytoplasm of cell line and intestine of C. elegans were observed. Such invasion of DEP impaired the behaviors of C. elegans as well as its un-exposed offspring and caused significant impeded locomotion. Moreover, the disorders of dopaminergic function were observed simultaneously under DEP exposure, specifically manifested by the decreased transcriptional expression of dat-1. The stress responses instructed by the expression of hsp-16.2 were also increased sharply in TJ375 strain of C. elegans at DEP concentrations of 1 and 10 μg mL^-1. In the case of cellular reactions to DEP exposure, the injuries of membrane integrity and the decreased viability of cell line were simultaneously identified, and reactive oxygen species (ROS), damaged DNA fragment, and upregulated apoptosis were monotonically elevated in cell lines with the increase of DEP concentrations. This study provided a systematic insight into toxicity of DEP both in vivo and vitro, demonstrating that DEP exposure could disturb the stability of cell system and further threat the stability of organism.

Research Advances on the Adverse Effects of Nanomaterials in a Model Organism, Caenorhabditis elegans

Along with the rapid development of nanotechnology, the biosafety assessment of nanotechnology products, including nanomaterials (NMs), has become more and more important. The nematode Caenorhabditis elegans is a valuable model organism that has been widely used in the field of biology because of its excellent advantages, including low cost, small size, short life span, and highly conservative genomes with vertebral animals. In recent years, the number of nanotoxicological researchers using C. elegans has been growing. According to these available studies, the present review classified the adverse effects of NMs in C. elegans into systematic, cellular, and molecular toxicity, and focused on summarizing and analyzing the underlying mechanisms of metal, metal oxide, and nonmetallic NMs causing toxic effects in C. elegans. Our findings provide insights into what further studies are needed to assess the biosafety of NMs in the ecosystem using C. elegans. Environ Toxicol Chem 2021;40:2406-2424. © 2021 SETAC.

The impacts of metal-based engineered nanomaterial mixtures on microbial systems: A review

The last decade has witnessed tremendous growth in the commercial use of metal-based engineered nanomaterials (ENMs) for a wide range of products and processes. Consequently, direct and indirect release into environmental systems may no longer be considered negligible or insignificant. Yet, there is an active debate as to whether there are real risks to human or ecological health with environmental exposure to ENMs. Previous research has focused primarily on the acute effects of individual ENMs using pure cultures under controlled laboratory environments, which may not accurately reveal the ecological impacts of ENMs under real environmental conditions. The goal of this review is to assess our current understanding of ENM effects as we move from exposure of single to multiple ENMs or microbial species. For instance, are ENMs' impacts on microbial communities predicted by their intrinsic physical or chemical characteristics or their effects on single microbial populations; how do chronic ENM interactions compare to acute toxicity; does behavior under simplified laboratory conditions reflect that in environmental media; finally, is biological stress modified by interactions in ENM mixtures relative to that of individual ENM? This review summarizes key findings and our evolving understanding of the ecological effects of ENMs under complex environmental conditions on microbial systems, identifies the gaps in our current knowledge, and indicates the direction of future research.

Detection of Silver Nanoparticles in Seawater Using Surface-Enhanced Raman Scattering

Nanomaterials significantly contribute to the development of new solutions to improve consumer products properties. Silver nanoparticles (AgNPs) are one of the most used, and as human exposure to such NPs increases, there is a growing need for analytical methods to identify and quantify nanoparticles present in the environment. Here we designed a detection strategy for AgNPs in seawater using surface-enhanced Raman Scattering (SERS). Three commercial AgNPs coated with polyvinylpyrrolidone (PVP) were used to determine the relative impact of size (PVP-15nmAgNPs and PVP-100nmAgNPs) and aggregation degree (predefined Ag aggregates, PVP-50-80nmAgNPs) on the SERS-based detection method. The study of colloidal stability and dissolution of selected AgNPs into seawater was carried out by dynamic light scattering and UV-vis spectroscopy. We showed that PVP-15nmAgNPs and PVP-100nmAgNPs remained colloidally stable, while PVP-50-80nmAgNPs formed bigger aggregates. We demonstrated that the SERS-based method developed here have the capacity to detect and quantify single and aggregates of AgNPs in seawater. The size had almost no effect on the detection limit (2.15 ± 1.22 mg/L for PVP-15nmAgNPs vs. 1.51 ± 0.71 mg/L for PVP-100nmAgNPs), while aggregation caused an increase of 2.9-fold (6.08 ± 1.21 mg/L). Our results demonstrate the importance of understanding NPs transformation in seawater since this can influence the detection method performance.

Epigenetic effects of silver nanoparticles and ionic silver in Tetrahymena thermophila

The widespread use of silver nanoparticles (Ag NPs) has raised substantial health risks, but little is known about the epigenetic toxicity induced by Ag⁺ and Ag NPs. This study characterized physiological and lncRNA profiles to explore the toxic effects and epigenetic mechanisms in Tetrahymena thermophila on exposure to Ag⁺ (in the form of AgNO₃) and different Ag NPs for 24 h. The Ag NPs studied varied in size (10 nm and 80 nm) and surface coating (citrate and polyvinylpyrrolidone). We found that both Ag⁺ and Ag NPs elicited strong growth-inhibiting effects on T. thermophila. The toxicity was mainly caused by high reactive oxygen species (ROS) levels, leading to lipid peroxidation and mitochondrial dysfunction. To combat the oxidative stress, the protist activated an antioxidative response, increasing the activity of glutathione peroxidase and other antioxidants. Notably, 1250 lncRNAs were differentially expressed under Ag⁺ or Ag NPs exposure relative to the non-exposure control, which were clustered into 15 expression modules in weighted gene co-expression network analysis. These gene modules exhibited toxicant-specific expression patterns, potentially playing regulatory roles, via their co-expressed mRNAs, to inhibit cell growth, activate cell membrane cation channel, and promote oxidoreductase activity. This research illuminates how post-transcriptional mechanisms of a ciliated protozoan regulate responses to Ag⁺ and Ag NPs toxicities.

Ceramide mediates radiation-induced germ cell apoptosis via regulating mitochondria function and MAPK factors in Caenorhabditis elegans

Studies about radiation damage in vivo are very significant for healthy risk assessment as well as cancer radiotherapy. Ceramide as a second messenger has been found to be related to radiation-induced apoptosis. However, the detailed mechanisms in living systems are still not fully understood. In the present study, the effects of ceramide in gamma radiation-induced response were investigated using Caenorhabditis elegans. Our results indicated that ceramide was required for gamma radiation-induced whole-body germ cell apoptosis by the production of radical oxygen species and decrease of mitochondrial transmembrane potential. Using genetic ceramide synthase-related mutated strains and exogenous C₁₆-ceramide, we illustrated that ceramide could regulate DNA damage response (DDR) pathway to mediate radiation-induced germ cell apoptosis. Moreover, ceramide was found to function epistatic to pmk-1 and mpk-1 in MAPK pathway to promote radiation-induced apoptosis in Caenorhabditis elegans. These results demonstrated ceramide could potentially mediated gamma radiation-induced apoptosis through regulating mitochondrial function, DDR pathway and MAPK pathway.

Silver Citrate Nanoparticles Inhibit PMA-Induced TNFα Expression via Deactivation of NF-κB Activity in Human Cancer Cell-Lines, MCF-7

Background

The nuclear factor kappa-B (NF-κB) is a major transcription factor responsible for the production of numerous inflammatory mediators, including the tumor necrosis factor (TNFα), which has a lethal association with cancer’s onset. The silver nanoparticles (AgNPs) are widely used in cancer treatment and several other biomedical applications.

Objective

The study aimed to determine the effects of silver citrate nanoparticles (AgNPs-CIT) on NF-κB activation together with TNFα mRNA/protein expressions in the phorbol myristate acetate (PMA)-stimulated MCF-7 human breast cancer cell-lines.

Methods

The AgNPs-CIT were synthesized by the reduction method, and the prepared AgNPs-CIT were characterized for their shape, absorption in UV-VIS electromagnetic radiations, size distribution, ζ-potential, and antioxidant activity. The MCF-7 cell-lines were pretreated with AgNPs-CIT and stimulated with PMA. The TNFα mRNA expressions were determined by real-time PCR, whereas the protein production was determined by the ELISA. The NF-κB activity was distinctly observed by highly-specific DNA-based ELISA, and by NF-κB-specific inhibitor, Bay 11–7082.

Results

The prepared AgNPs-CIT were spherical and have an absorption wavelength range of 381–452 nm wherein the particles size ranged between 19.2±0.1 to 220.77±0.12 nm with the charge range −9.99±0.8 to −34.63±0.1 mV. The prepared AgNPs-CIT showed comparative antioxidant activity at >40% inhibitions level of the DPPH radicals. The AgNPs-CIT were found to be non-toxic to MCF-7 cell-lines and inhibited PMA-induced activation of the NF-κBp65, and also the mRNA/protein expression of TNFα.

Conclusion

This is the first report that showed AgNPs-CIT inhibited TNFα expression via deactivation of the NF-κB signaling event in stimulated breast cancer cells. The results have important implications for the development of novel therapeutic strategies for the prevention/treatment of cancers and/or inflammatory disorders.

Molecular Effects of Silver Nanoparticles on Monogenean Parasites: Lessons from Caenorhabditis elegans

The mechanisms of action of silver nanoparticles (AgNPs) in monogenean parasites of the genus Cichlidogyrus were investigated through a microarray hybridization approach using genomic information from the nematode Caenorhabditis elegans. The effects of two concentrations of AgNPs were explored, low (6 µg/L Ag) and high (36 µg/L Ag). Microarray analysis revealed that both concentrations of AgNPs activated similar biological processes, although by different mechanisms. Expression profiles included genes involved in detoxification, neurotoxicity, modulation of cell signaling, reproduction, embryonic development, and tegument organization as the main biological processes dysregulated by AgNPs. Two important processes (DNA damage and cell death) were mostly activated in parasites exposed to the lower concentration of AgNPs. To our knowledge, this is the first study providing information on the sub-cellular and molecular effects of exposure to AgNPs in metazoan parasites of fish.

Silver nanoparticles: Toxicity in model organisms as an overview of its hazard for human health and the environment

Silver nanoparticles (AgNPs) have attracted remarkable attention due to their powerful antimicrobial action as well as their particular physicochemical properties. This has led to their application in a wide variety of products with promising results. However, their interaction with the environment and toxicity in live terrestrial or aquatic organisms is still a matter of intense debate. More detailed knowledge is still required about the toxicity of AgNPs, their possible uptake mechanisms and their adverse effects in live organisms. Several studies have reported the interactions and potential negative effects of AgNPs in different organisms. In this review, we report and discuss the current state of the art and perspectives for the impact of AgNPs on different organisms present in the environment. Recent progress in interpreting uptake, translocation and accumulation mechanisms in different organisms and/or living animals are discussed, as well as the toxicity of AgNPs and possible tolerance mechanisms in live organisms to cope with their deleterious effects. Finally, we discuss the challenges of accurate physicochemical characterization of AgNPs and their ecotoxicity in environmentally realistic conditions such as soil and water media.

Potential toxicity of nanopolystyrene on lifespan and aging process of nematode Caenorhabditis elegans

In the environment, nanoplastic particles, such as nanopolystyrene, potentially cause toxicity on organisms at various aspects. We here employed endpoints of lifespan and aging-related phenotypes to further investigate the possible long-term effects of nanopolystyrene (100 nm) in Caenorhabditis elegans. After exposure from L1-larvae to adult day-3, nanopolystyrene at high concentrations (100 and 1000 μg/L) reduced the lifespan. Although nanopolystyrene (1 or 10 μg/L) did not affect the lifespan, nanopolystyrene (1 or 10 μg/L) could induce the more severe intestinal reactive oxygen species (ROS) production and decrease in locomotion behavior during the aging process compared with control. Moreover, nanopolystyrene exposure could cause the severe decrease in expressions of some immune response genes, hsp-6 gene, and genes encoding manganese-superoxide dismutases (Mn-SODs) during aging process, suggesting the severe suppression in innate immune response, inhibition in antioxidation defense system, and suppression in mitochondrial unfolded protein response (mt UPR) by nanopolystyrene. Our results highlight the potential of long-term nanopolystyrene exposure in reducing longevity and in affecting health state during the aging process in environmental organisms.

Adverse effects of nanosilver on human health and the environment

Silver and silver nanoparticles (AgNPs) exhibit antimicrobial properties against some bacteria, fungi and viruses, however, the ever-increasing application of nanosilver in consumer products, water disinfection and healthcare settings, have raised concerns over the public health/environmental safety of this nanomaterial. The current ubiquity of nanosilver may result in repeated exposure through various routes (skin, inhalation, or ingestion) which may lead to health complications. While there are a number of review articles and case studies published to date on the subject, an updated coherent review that clearly delineates thresholds and safe doses is lacking. Thus, it is plausible to have an overview of the most recent findings on the threshold limits, safe doses of silver and its related nanoscale forms, and the needed actions to ensure the safety and health of human, terrestrial and aquatic lives. This review provides an account of the effects of nanosilver in our daily lives. STATEMENT OF SIGNIFICANCE: This manuscripts is a review of the toxicity of nanosized silver. With respect to the existing literature, it goes beyond stating that there is a knowledge gap, drawing the attention of a wider readership to the ever-growing evidence of nanosilver toxicity to human and nature, and outlining the dose thresholds based on comprehensive data mining and visualisation. There are nearly 500 consumer products that claim to contain nanosilver. Thus, we trust a review of recent conclusive findings is timely. This manuscript is in line with the scope of the Journal, enabling a better understanding of the biological response to a widely-used bionanomaterial. Moreover, it provides a bigger picture of the link between surface properties and biocompatibility of nanosilver in different forms.

Effect of ionic strength on bioaccumulation and toxicity of silver nanoparticles in Caenorhabditis elegans

The behavior of silver nanoparticles (AgNPs) is influenced by environmental factors which altered their bioaccumulation and toxicity. In this study, we comprehensively investigated the influence of ionic strength on the ecotoxicity of AgNPs to Caenorhabditis elegans (C. elegans) through the transfer from Escherichia coli (E. coli). Three different exposure media (deionized water, EPA water and KM) were used to pretreat AgNPs. E. coli was then exposed to these transformed AgNPs and fed to C. elegans. Our results indicated that ionic strength significantly enhanced the reproductive toxicity (germ cell corpses, brood size and lifespan) and neurotoxicity (head trash and body bend) of AgNPs in C. elegans. Moreover, ICP-MS analysis showed that higher ionic strength increased bioaccumulation of AgNPs in E. coli and the resulting Ag body burden of E. coli affected the transfer of AgNPs to C. elegans, which might be responsible for the increased toxicity to nematodes. Furthermore, we also found that the reactive oxygen species (ROS) level in C. elegans was significantly increased after exposed to E. coli contaminated with ionic strength-treated AgNPs, which might play another important role for the enhanced toxicity of AgNPs. Overall, this study showed that the bioavailability and potential ecotoxicity of AgNPs are associated with the environmental factors.

Chitosan-Stabilized Ag Nanoparticles with Superior Biocompatibility and Their Synergistic Antibacterial Effect in Mixtures with Essential Oils

Silver nanoparticles (AgNPs) are considered a promising alternative to the use of antibiotics in fighting multidrug-resistant pathogens. However, their use in medical application is hindered by the public concern regarding the toxicity of metallic nanoparticles. In this study, rationally designed AgNP were produced, in order to balance the antibacterial activity and toxicity. A facile, environmentally friendly synthesis was used for the electrochemical fabrication of AgNPs. Chitosan was employed as the capping agent, both for the stabilization and to improve the biocompatibility. Size, morphology, composition, capping layer, and stability of the synthesized nanoparticles were characterized. The in vitro biocompatibility and antimicrobial activities of AgNPs against common Gram-negative and Gram-positive bacteria were evaluated. The results revealed that chitosan-stabilized AgNPs were nontoxic to normal fibroblasts, even at high concentrations, compared to bare nanoparticles, while significant antibacterial activity was recorded. The silver colloidal dispersion was further mixed with essential oils (EO) to increase the biological activity. Synergistic effects at some AgNP–EO ratios were observed, as demonstrated by the fractionary inhibitory concentration values. Our results reveal that the synergistic action of both polymer-stabilized AgNPs and essential oils could provide a significant efficiency against a large variety of microorganisms, with minimal side effects.