Free silver ion as the main cause of acute and chronic toxicity of silver nanoparticles to cladocerans

Ecotoxicological assessment of magnetite and magnetite/Ag nanoparticles on terrestrial and aquatic biota from different trophic levels

The aim of the study is an ecotoxicological assessment of magnetite iron oxide-based nanoparticles (NPs), which have risen in popularity in the last decade, on selected terrestrial and aquatic organisms from various levels of the food chain. In the presented study various organisms, from both the terrestrial and aquatic environment, were used as targets for the assessment of NPs ecotoxicity. Plants (radish, oat), marine bacteria (A. fischeri) and crustacean (H. incongruens) were used to represent producers, decomposers, and consumers, respectively. It was found that examined NPs were harmful (to a different degree) to biota from three different trophic levels. Physicochemical characterization (size/morphology, crystallinity, composition, and magnetic properties) of the tested nanoparticles was performed by: transmission electron microscopy, X-ray diffraction, energy dispersive spectroscopy, and Mossbauer spectroscopy, respectively. Phytotoxicity was evaluated according to the OECD 208 Guideline, while acute and chronic toxicity of NPs was conducted using bioassays employing bacteria and crustacea, respectively. The phytotoxicity of all investigated iron oxide-based NPs was dependent on concentration and type of NPs formulation and was measured via biomass, seed germination, root length, shoot height, and content of plant pigments. Increasing the concentration of NPs increased phytotoxicity and mortality of aquatic organisms. Ecotoxicity of iron oxide/silver was dependent on the size and content of silver. Iron oxide NPs coated with nanosilver in a percentage ratio of 69/31 were found to be the most toxic on tested terrestrial and aquatic biota.

Extrapolating Contaminant Effects from Individuals to Populations: A Case Study on Nanoparticle Toxicity to Daphnia Fed Environmentally Relevant Food Levels

Ecological risk assessment (ERA) is charged with assessing the likelihood a chemical will have adverse environmental or ecological effects. When assessing the risk of a potential contaminant to biological organisms, ecologists are most concerned with the sustainability of populations of organisms, rather than protecting every individual. However, ERA most commonly relies on data on the effect of a potential contaminant on individuals because these experiments are more feasible than costly population-level exposures. In this work, we address the challenge of extrapolating these individual-level results to predict population-level effects. Previous per-capita population growth rate estimates calculated from individual-level exposures of Daphnia pulicaria to silver nanoparticles (AgNPs) at different food rations predict a critical daily food requirement for daphnid populations exposed to 200 μg/L AgNPs to avoid extinction. To test this, we exposed daphnid populations to the same AgNP concentration at three different food inputs, with the lowest ration close to the extinction threshold predicted from data on individuals. The two populations with the higher food inputs persisted, and the population with the lowest food input went extinct after 50 days but did persist through two generations. We demonstrate that we can extrapolate between these levels of biological organization by parameterizing an individual-level biomass model with data on individuals' response to AgNPs and using these parameters to predict the outcome for control and AgNP-exposed populations. Key to successful extrapolation is careful modeling of temporal changes in resource density, driven by both the experimental protocols and feedback from the consumer. The implication for ecotoxicology is that estimates of extinction thresholds based on studies of individuals may be reliable predictors of population outcomes, but only with careful treatment of resource dynamics.

Low Concentrations of Silver Nanoparticles Inhibit Spore Germination and Disturb Gender Differentiation of Ceratopteris thalictroides (L.) Brongn

Because of their excellent antibacterial properties, silver nanoparticles (AgNPs) are widely used in all walks of life, which has caused them to be discharged into aquatic environments with possible negative effects on aquatic plants. In the present study, we used an aquatic fern, Ceratopteris thalictroides, as a model to investigate the effects of AgNPs on its spore germination, gametophytes, sex differentiation, and growth. The results demonstrated that AgNPs significantly inhibited spore germination of C. thalictroides at a AgNP concentration higher than 0.02 mg/L. Additionally, we found sex-dependent effects of AgNPs on the development and growth of the gametophyte of C. thalictroides. The proportion of hermaphrodites in the gametophytes and the area of gametophytes significantly decreased under AgNP treatment, while no significant effect was observed in the male gametophytes. Using the AgNP filtrate (without nanoparticles) and AgNPs plus cysteine (Ag⁺ chelator), we found that the release of Ag⁺ from nanoparticles was not the cause of the toxicity of AgNPs on C. thalictroides. The EC₅₀ of AgNPs on spore germination was 0.0492 mg/L, thus indicating an ecological risk of AgNPs on this species even at concentrations lower than the Ag element concentration of the WHO guidelines for drinking-water quality.

Building the Bridge From Aquatic Nanotoxicology to Safety by Design Silver Nanoparticles

Nanotechnologies have rapidly grown, and they are considered the new industrial revolution. However, the augmented production and wide applications of engineered nanomaterials (ENMs) and nanoparticles (NPs) inevitably lead to environmental exposure with consequences on human and environmental health. Engineered nanomaterial and nanoparticle (ENM/P) effects on humans and the environment are complex and largely depend on the interplay between their peculiar properties such as size, shape, coating, surface charge, and degree of agglomeration or aggregation and those of the receiving media/body. These rebounds on ENM/P safety and newly developed concepts such as the safety by design are gaining importance in the field of sustainable nanotechnologies. This article aims to review the critical characteristics of the ENM/Ps that need to be addressed in the safe by design process to develop ENM/Ps with the ablility to reduce/minimize any potential toxicological risks for living beings associated with their exposure. Specifically, we focused on silver nanoparticles (AgNPs) due to an increasing number of nanoproducts containing AgNPs, as well as an increasing knowledge about these nanomaterials (NMs) and their effects. We review the ecotoxicological effects documented on freshwater and marine species that demonstrate the importance of the relationship between the ENM/P design and their biological outcomes in terms of environmental safety.

Metallic, metal oxide, and metalloid nanoparticles toxic effects on freshwater microcrustaceans: An update and basis for the use of new test species

In this article, we performed a literature review on the metallic, metal oxide, and metalloid nanoparticles (NP) effects on freshwater microcrustaceans, specifically focusing on (i) the main factors influencing the NP toxicity and (ii) their main ecotoxicological effects. Also, given that most studies are currently developed on the standard test species Daphnia magna Straus, we analyzed (iii) the potential differences in the biological responses between D. magna and other freshwater microcrustacean, and (iv) the ecological implications of considering only D. magna as surrogate of other microcrustaceans. We found that NP effects on microcrustaceans depended on their intrinsic properties as well as the exposure conditions. Among the general responses to different NP, we identified body burial, feeding inhibition, biochemical effects, metabolic changes, and reproductive and behavioral alterations. The differences in the biological responses between D. magna and other freshwater microcrustacean rely on the morphology (size and shape), ecological traits (feeding mechanisms, life cycles), and intrinsic sensitivities. Thus, we strongly recommend the use of microcrustaceans species with different morphological, physiological, and ecological characteristics in future ecotoxicity tests with NP to provide relevant information with regulation purposes regarding the discharge of NP into aquatic environments. PRACTITIONER POINTS: Nanoparticles effects depend on intrinsic and external factors. Nanoparticles affect the morphology, physiology, and behavior. Effects on Daphnia differ from other microcrustaceans. The use of more diverse test species is suggested.

Exposure of silver nanocolloids causes glycosylation disorders and embryonic deformities in medaka

Silver nanomaterials such as silver nanocolloids (SNC) contribute to environmental pollution and have adverse ecological effects on aquatic organisms. In particular, chemical exposure of fish during embryogenesis leads to deformities and puts the population at risk. Although glycans and glycosylation are known to be important for proper morphology in embryogenesis, little glycobiology-based research has examined morphological disorders caused by environmental pollutants. This study addressed the glycobiological effects of SNC exposure on medaka embryogenesis. After exposure of medaka embryos to SNC, deformities such as small heads and deformed eyes were observed. The expression of five glycan-related genes (alg2, gnsb, b4galt2, b3gat1a, and b3gat2) was significantly altered, with changes depending on the embryonic stage at exposure, with more severe deformities with exposure at earlier stages. In situ hybridization analyses indicated that the five genes were expressed mainly in the head region; exposure of SNC suppressed alg2 and gnsb and enhanced b4galt2 and b3gat1a expression relative to controls on day 7. Loss (siRNA)- and gain (RNA overexpression)-of-function experiments confirmed that alg2, gnsb, and b4galt2 are essential for embryogenesis. The effects of SNC exposure on glycan synthesis were estimated by glycan structure analysis. In the medaka embryo, high mannose-type glycans were dominant, and SNC exposure altered glycan synthesis. The alteration was more significant when exposure occurred at an early stage of medaka embryogenesis. Thus, SNC exposure causes embryonic deformities in medaka embryos through disordered glycosylation.

Comparison of uptake and elimination kinetics of metallic oxide nanomaterials on the freshwater microcrustacean Daphnia magna

The widespread use and release of nanomaterials (NMs) in aquatic ecosystems is a concerning issue as well as the fate and behavior of the NMs in relation to the aquatic organisms. In this work, the freshwater microcrustacean Daphnia magna was exposed to 12 different and well-known NMs under the same conditions for 24 h and then placed in clean media for 120 h, in order to determine their different uptake and elimination behaviors. The results showed that most of the tested NMs displayed a fast uptake during the first hours arriving to a plateau by the end of the uptake phase. The elimination behavior was determined by a fast loss of NMs during the first hours in the clean media, mainly stimulated by the presence of food. Remaining NMs concentrations can still be found at the end of the elimination phase. Two NMs had a different profile (i) ZnO-NM110 exhibited increase and loss during the uptake phase, and (ii) SiO₂-NM204 did not show any uptake. A toxicokinetic model was applied and the uptake and elimination rates were found along with the dynamic bioconcentration factors. These values allowed to compare the NMs, to cluster them by their similar rates, and to determine that the TiO₂-NM102 is the one that has the fastest uptake and elimination behavior, SiO₂-NM204 has the slowest uptake and CeO₂ <10 nm has the slowest elimination. The present work represents a first attempt to compare different NMs based on their uptake and elimination behaviors from a perspective of the nano-bio interactions influence.

Silver nanocolloid affects hindbrain vascular formation during medaka embryogenesis

Angiogenesis is essential for the normal development of an embryo. Silver nanocolloid (SNC) is known to induce vascular malformation in the medaka embryo. We focused on the development of the central arteries (CtAs) in the hindbrain of Japanese medaka. The CtAs and the basilar artery from which they branch are essential for transporting the blood and nutrients necessary to support the hindbrain parenchyma and the development of the pons and cerebellum from the hindbrain. We exposed medaka embryos at developmental stage 21 (6 somite stage), to 0, 0.5, 5, or 10 mg/L SNC and evaluated hatching rate, number of thrombi per embryo, head size (length and width), body length, and angiogenesis. Although all SNC-exposed embryos hatched, their head size and body length were small in comparison to controls; in addition, the number of thrombi in the head increased and head size and body length decreased as the SNC concentration increased. To evaluate vasculogenic abnormalities, we performed whole-mount in situ hybridization using a vascular marker (eg, fl7) and visualized the CtAs in medaka embryos. In control embryos, CtAs started to sprout at stage 32 (somite completion stage) and their extension was complete by stage 35 (pectoral fin blood circulation stage). In contrast, CtAs failed to sprout in SNC-exposed embryos, and thrombi were present. Furthermore, qRT-PCR analysis showed that SNC significantly suppressed the egfl7 expression level at stage 35. Together, our findings suggest that SNC induced decreased developments of head and body in medaka embryos due to insufficient angiogenesis and hindbrain vascular formation.

Roles of ROS and cell cycle arrest in the genotoxicity induced by gold nanorod core/silver shell nanostructure

To understand the genotoxicity induced in the liver by silver nanoparticles (AgNPs) and silver ions, an engineered gold nanorod core/silver shell nanostructure (Au@Ag NR) and humanized hepatocyte HepaRG cells were used in this study. The involvement of oxidative stress and cell cycle arrest in the DNA and chromosome damage induced by 0.4-20 µg mL^-1 Au@Ag NR were investigated by comet assay, γ-H2AX assay and micronucleus test. Further, the distribution of Au@Ag NR was analyzed. Our results demonstrated that both Ag⁺ and Au@Ag NR led to DNA cleavage and chromosome damage (clastogenicity) in HepaRG cells and that the Au@Ag NR retained in the nucleus may further release Ag⁺, aggravating the damages, which are mainly caused by cell cycle arrest and ROS formation. The results reveal the correlation between the intracellular accumulation, Ag⁺ ion release and the potential genotoxicity of AgNPs.

Nanotechnology-based Drug Delivery, Metabolism and Toxicity

BACKGROUND

Nanoparticles (NPs) are being used extensively owing to their increased surface area, targeted delivery and enhanced retention. NPs have the potential to be used in many disease conditions. Despite widespread use, their toxicity and clinical safety still remain a major concern.

OBJECTIVE

The purpose of this study was to explore the metabolism and toxicological effects of nanotherapeutics.

METHODS

Comprehensive, time-bound literature search was done covering the period from 2010 till date. The primary focus was on the metabolism of NP including their adsorption, degradation, clearance, and bio-persistence. This review also focuses on updated investigations on NPs with respect to their toxic effects on various in vitro and in vivo experimental models.

RESULTS

Nanotechnology is a thriving field of biomedical research and an efficient drug delivery system. Further their applications are under investigation for diagnosis of disease and as medical devices.

CONCLUSION

The toxicity of NPs is a major concern in the application of NPs as therapeutics. Studies addressing metabolism, side-effects and safety of NPs are desirable to gain maximum benefits of nanotherapeutics.

Behavior of Ag species in presence of aquatic sediment minerals - In context of aquatic environmental safety

In recent years, there has been a growth in the number of products containing Ag nanoparticles (AgNPs) in many areas and their use suggests that the water-soil environment may be exposed to the contaminant with different Ag species. Therefore, the sorption of two Ag forms (i.e. Ag(I) ions and nanoparticles - AgNPs) on clay minerals (montmorillonite and kaolinite) and iron (oxyhydr)oxides (ferrihydrite) as a function of solution:mineral ratio (100:1, 250:1, 500:1), solution pH (3.0, 5.5 and 7.0) and initial Ag concentration (0.1-100 mg/dm³) was studied using batch method. In addition the binding strength/mobility of the bonded Ag species was researched. The results show a great sorption potential of clay minerals for both Ag forms and lower sorption capacity of ferrihydrite, in particular for Ag(I) ions. The maximum sorption capacities of montmorillonite, kaolinite and ferrihydrite estimated from three-parameter isotherm model of Sips were 94.39 mg/g, 117.8 mg/g and 26.48 mg/g for AgNPs and 17.92 mg/g, 21.14 mg/g and 3.072 mg/g for Ag(I) ions, respectively. Aggregation process plays an important role in sorption and mobility of AgNPs. The sequential extraction study indicated different binding mechanisms of the Ag forms onto the clay minerals and ferrihydrite, which depended on the active sites of minerals as well as the Ag species nature in the solution. Ag(I) was weakly bound by clay minerals but presence of iron (oxyhydr)oxides decreased the Ag(I) mobility and bioavailability. On the other hand, AgNPs bound with the active centers of minerals in a very strong way and were not able to release into water. The study of the binding of Ag forms by clay minerals and (oxyhydr)oxides allows to determine the influence of their physicochemical and structural properties, including e.g. pore size on Ag sorption. These results allow these properties to be taken into account in the study of environmental samples, including waters and soils. Moreover, the results showed that in the study of behavior of Ag forms in contact with the minerals, in addition to the sorption capacity, the susceptibility to their release is very important. Studies on sorption/desorption of AgNPs and Ag(I) ions as a form of oxidation of AgNPs is important for understanding the transport and fate of the Ag species in soil, sediments and surface water because of different their behavior in contact with the minerals.

The Toxicity of Nanoparticles to Organisms in Freshwater

Nanotechnology is a rapidly growing industry yielding many benefits to society. However, aquatic environments are at risk as increasing amounts of nanoparticles (NPs) are contaminating waterbodies causing adverse effects on aquatic organisms. In this review, the impacts of environmental exposure to NPs, the influence of the physicochemical characteristics of NPs and the surrounding environment on toxicity and mechanisms of toxicity together with NP bioaccumulation and trophic transfer are assessed with a focus on their impacts on bacteria, algae and daphnids. We identify several gaps which need urgent attention in order to make sound decisions to protect the environment. These include uncertainty in both estimated and measured environmental concentrations of NPs for reliable risk assessment and for regulating the NP industry. In addition toxicity tests and risk assessment methodologies specific to NPs are still at the research and development stage. Also conflicting and inconsistent results on physicochemical characteristics and the fate and transport of NPs in the environment suggest the need for further research. Finally, improved understanding of the mechanisms of NP toxicity is crucial in risk assessment of NPs, since conventional toxicity tests may not reflect the risks associated with NPs. Behavioural effects may be more sensitive and would be efficient in certain situations compared with conventional toxicity tests due to low NP concentrations in field conditions. However, the development of such tests is still lacking, and further research is recommended.

Toxicopathological and immunological studies on different concentrations of chitosan-coated silver nanoparticles in rats

Background

Much consideration has been paid to the toxicological assessment of nanoparticles prior to clinical and biological applications. While in vitro studies have been expanding continually, in vivo investigations of nanoparticles have not developed a cohesive structure. This study aimed to assess the acute toxicity of different concentrations of chitosan-coated silver nanoparticles (Ch-AgNPs) in main organs, including liver, kidneys, and spleen.

Materials and methods

Twenty-eight male albino rats were used and divided into 4 groups (n=7). Group 1 was kept as a negative control group. Groups 2, 3, and 4 were treated intraperitoneally with Ch-AgNPs each day for 14 days at doses of 50, 25, and 10 mg/kg body weight (bwt) respectively. Histopathological, morphometric and immunohistochemical studies were performed as well as oxidative stress evaluations, and specific functional examinations for each organ were elucidated.

Results

It was revealed that Ch-AgNPs induced dose-dependent toxicity, and the repeated dosing of rats with 50 mg/kg Ch-AgNPs induced severe toxicities. Histopathological examination showed congestion, hemorrhage, cellular degeneration, apoptosis and necrosis in hepatic and renal tissue as well as lymphocytic depletion with increasing tangible macrophages in the spleen. The highest levels of malondialdehyde, alanine aminotransferase, aspartate aminotransferase (MDA, ALT, AST) and the lowest levels of reduced glutathione, immunoglobulin G, M and total protein (GSH, IgG, IgM, TP) were observed in this group. On the other hand, repeated dosing with 25 mg/kg induced mild to moderate disturbance in the previous parameters, while there was no significant difference in results of pathological examination and biochemical tests between the control group and those treated with 10 mg/kg bwt Ch-AgNPs.

Conclusion

Chitosan-coated silver nanoparticles induce dose-dependent adverse effects on rats.

The combined effects of acute irradiation and food supply on survival and fertility in Daphnia magna

The results of recent studies have provided strong evidence for the combined effects of diet restriction and exposure to chemical on the survival and reproduction of aquatic organisms. However, the combined effects of diet restriction and exposure to ionizing radiation remain poorly understood. To establish whether parental irradiation and diet restriction can affect the survival and fertility of directly exposed crustaceans and their progeny, Daphnia magna were given 10, 100 and 1000 mGy of acute γ-rays either during chronic diet restriction or normal food supply. Acute exposure to 1000 mGy significantly compromised the viability of irradiated Daphnia and their first-generation progeny, but did not affect the second-generation progeny. Similarly acute exposure to 100 and 1000 mGy also significantly compromised the fertility of F₀ and F₁Daphnia and did not affect the F₂ generation. Low level of food supply compromised the viability of non-exposed and irradiated Daphnia, whereas their fertility was substantially affected by all diets. The dose-response for the effects of irradiation on viability and fertility of Daphnia received different food supply were practically similar, thus implying that the level of nutrition and acute exposure to ionizing radiation independently affect the life history traits in crustacean.

Uptake and Transformation of Silver Nanoparticles and Ions by Rice Plants Revealed by Dual Stable Isotope Tracing

Knowledge on the uptake and transformation of silver nanoparticles (AgNPs) and Ag⁺ ions by organisms is critical for understanding their toxicity. Herein, the differential uptake, transformation, and translocation of AgNPs and Ag⁺ ions in hydroponic rice ( Oryza sativa L.) is assessed in modified Hewitt (with Cl^- ions, HS(Cl)) and Hogland solutions (without Cl^- ions, HS) using dual stable isotope tracing (¹⁰⁷AgNO₃ and ¹⁰⁹AgNPs). After coexposure to ¹⁰⁷Ag⁺ ions and ¹⁰⁹AgNPs at 50 μg L^-1 (as Ag for both) for 14 days, a stimulatory effect was observed on root elongation (increased by 68.8 and 71.9% for HS(Cl) and HS, respectively). Most of the Ag⁺ ions (from ¹⁰⁷Ag⁺ ions and ¹⁰⁹AgNPs) were retained on the root surface, while the occurrence of AgNPs (from ¹⁰⁹AgNPs and ¹⁰⁷Ag⁺ ions) was observed in the root, suggesting the direct uptake of AgNPs and/or reduction of Ag⁺ ions. Higher fractions of Ag⁺ ions in the shoot suggest an in vivo oxidation of AgNPs. These results demonstrated the intertransformation between Ag⁺ ions and AgNPs and the role of AgNPs as carriers and sources of Ag⁺ ions in organisms, which is helpful for understanding the fate and toxicology of Ag.

The toxicity of coated silver nanoparticles to Daphnia carinata and trophic transfer from alga Raphidocelis subcapitata

Nanoparticles (NPs) are causing threats to the environment. Silver NPs (AgNPs) are increasingly used in commercial products and may end up in freshwater ecosystems. The freshwater organisms are vulnerable due to water-borne and dietary exposure to AgNPs. Surface properties play an important role in the fate and behavior of AgNPs in the aquatic environment and their effects on organisms. However, effects of surface properties of AgNPs on organisms are poorly understood. In this study, we explored the effects of AgNPs coated with three different ligands; Tyrosine (T-AgNP), Epigallocatechin gallate (E-AgNP) and Curcumin (C-AgNP) in relation to the toxicity to a key aquatic organism; Daphnia carinata. The study focused on how coatings determine fate of NPs in the medium, mortality, feeding behaviour, bioaccumulation and trophic transfer from the freshwater alga, Raphidocelis subcapitata to daphnids. NP stability tests indicated that T-AgNPs were least stable in the ASTM daphnia medium while C-AgNPs were most stable. 48 h EC50 values of AgNPs to D. carinata were in the order of E-AgNP (19.37 μg L-1) > C-AgNP (21.37 μg L-1) > T-AgNP (49.74 μg L-1) while the 48 h EC50 value of Ag+ ions was 1.21 μg L-1. AgNP contaminated algae significantly decreased the feeding rates of daphnids. However, no significant differences were observed in feeding rates between algae contaminated with differently coated AgNPs. Trophic transfer studies showed that AgNPs were transferred from algae to daphnids. The bioacumulation of AgNPs in algae and the diet-borne bioaccumulation of AgNPs in daphnids varied for differently coated AgNPs. Bioaccumulation of C-AgNPs in algae was 1.5 time higher than T-AgNPs. However, the accumulation of T-AgNPs in daphnids via trophic transfer was 2.6 times higher than T-AgNPs. The knowledge generated from this study enhances the understanding of surface property dependent toxicity, bioaccumulation and trophic transfer of AgNPs in aquatic environments.

Transformation-dissolution reactions partially explain adverse effects of metallic silver nanoparticles to soil nitrification in different soils

Risk assessment of metallic nanoparticles (NPs) is critically affected by the concern that toxicity goes beyond that of the metallic ion. The present study addressed this concern for soils with silver nanoparticles (AgNPs) using the Ag-sensitive nitrification assay. Three agricultural soils (A, B, and C) were spiked with equivalent doses of either AgNP (diameter = 13 nm) or AgNO₃ . Soil solution was isolated and monitored over 97 d with due attention to accurate Ag fractionation at low (∼10 μg L^-1 ) Ag concentrations. Truly dissolved (<1 kDa) Ag in the AgNO₃ -amended soils decreased with reaction half-lives of 4 to 22 d depending on the soil, denoting important Ag-aging reactions. In contrast, truly dissolved Ag in AgNP-amended soils first increased by dissolution and subsequently decreased by aging, the concentration never exceeding that in the AgNO₃ -amended soils. The half-lives of AgNP transformation-dissolution were approximately 4 d (soils A and B) and 36 d (soil C). The Ag toxic thresholds (10% effect concentrations, milligrams of Ag per kilogram of soil) of nitrification, evaluated at 21 or 35 d after spiking, were similar between the 2 Ag forms (soils A and B) but were factors of 3 to 8 lower for AgNO₃ than for AgNP (soil C), largely corroborating dissolution differences. This fate and bioassay showed that AgNPs are not more toxic than AgNO₃ at equivalent total soil Ag concentrations and that differences in Ag dissolution at least partially explain toxicity differences between the forms and among soils. Environ Toxicol Chem 2018;37:2123-2131. © 2018 SETAC.

Comparative toxicities of silver nitrate, silver nanocolloids, and silver chloro-complexes to Japanese medaka embryos, and later effects on population growth rate

Fish embryo toxicology is important because embryos are more susceptible than adults to toxicants. In addition, the aquatic toxicity of chemicals depends on water quality. We examined the toxicities to medaka embryos of three types of silver-AgNO₃, silver nanocolloids (SNCs), and silver ions from silver nanoparticle plates (SNPPs)-under three pH conditions (4.0, 7.0, and 9.0) in embryo-rearing medium (ERM) or ultrapure water. Furthermore, we tested the later-life-stage effects of SNCs on medaka and their population growth. "Later-life-stage effects" were defined here as delayed toxic effects that occurred during the adult stage of organisms that had been exposed to toxicant during their early life stage only. AgNO₃, SNCs, and silver ions were less toxic in ERM than in ultrapure water. Release of silver ions from the SNPPs was pH dependent: in ERM, silver toxicity was decreased owing to the formation of silver chloro-complexes. SNC toxicity was higher at pH 4.0 than at 7.0 or 9.0. AgNO₃ was more toxic than SNCs. To observe later-life effects of SNCs, larvae hatched from embryos exposed to 0.01 mg/L SNCs in ultrapure water were incubated to maturity under clean conditions. The mature medaka were then allowed to reproduce for 21 days. Calculations using survival ratios and reproduction data indicated that the intrinsic population growth rate decreased after exposure of embryos to SNC. SNC exposure reduced the extinction time as a function of the medaka population-carrying capacity.

Standardized toxicity testing may underestimate ecotoxicity: Environmentally relevant food rations increase the toxicity of silver nanoparticles to Daphnia

Daphnia in the natural environment experience fluctuations in algal food supply, with periods when algal populations bloom and seasons when Daphnia have very little algal food. Standardized chronic toxicity tests, used for ecological risk assessment, dictate that Daphnia must be fed up to 400 times more food than they would experience in the natural environment (outside of algal blooms) for a toxicity test to be valid. This disconnect can lead to underestimating the toxicity of a contaminant. We followed the growth, reproduction, and survival of Daphnia exposed to 75 and 200 µg/L silver nanoparticles (AgNPs) at 4 food rations for up to 99 d and found that AgNP exposure at low, environmentally relevant food rations increased the toxicity of AgNPs. Exposure to AgNP at low food rations decreased the survival and/or reproduction of individuals, with potential consequences for Daphnia populations (based on calculated specific population growth rates). We also found tentative evidence that a sublethal concentration of AgNPs (75 µg/L) caused Daphnia to alter energy allocation away from reproduction and toward survival and growth. The present findings emphasize the need to consider resource availability, and not just exposure, in the environment when estimating the effect of a toxicant. Environ Toxicol Chem 2017;36:3008-3018. © 2017 SETAC.

Dimension-dependent toxicity of silver nanomaterials on the cladocerans Daphnia magna and Daphnia galeata

Silver nanomaterials (AgNMs) are widely used in many fields because of their antimicrobial properties. Depending on the shapes and dimensions of the AgNMs, their potential uses and needs vary. Consequently, vast quantities of multi-dimensional AgNMs are being manufactured and released into aquatic ecosystems, where they have toxic effects on aquatic organisms. Therefore, an assessment of the toxicities of each multi-dimensional AgNM on aquatic ecosystems is necessary. In this study, important aquatic model species, Daphnia magna and Daphnia galeata, were used to assess and compare the toxic effects of silver ions (Ag⁺ ions) and multi-dimensional AgNMs, including silver nanoparticles (AgNPs), silver nanowires (AgNWs), and silver nanoplates (AgPLs). The results indicated that Ag⁺ ions were more toxic than AgNMs of different dimensions and sizes, and that AgPLs were the most toxic of the AgNMs. In the case of AgNWs, the longer (20 μm) nanowire was more toxic than the shorter (10 μm) one. In addition, D. galeata was more sensitive than D. magna to both Ag⁺ ions and AgNMs. This study elucidates the dimension-dependent toxicity of and silver ions and nanomaterials in the cladocerans D. magna and D. galeata. Further studies will be necessary to further elucidate the actual risk of multi-dimensional nanomaterials in ecosystems.

Acute toxicity and genotoxicity of silver nanoparticle in rats

Objective

The potential risk of a nanoparticle as a medical application has raised wide concerns, and this study aims to investigate silver nanoparticle (AgNP)-induced acute toxicities, genotoxicities, target organs and the underlying mechanisms.

Methods

Sprague-Dawley rats were randomly divided into 4 groups (n = 4 each group), and AgNP (containing Ag nanoparticles and released Ag⁺, 5 mg/kg), Ag⁺ (released from the same dose of AgNP, 0.0003 mg/kg), 5% sucrose solution (vechicle control) and cyclophophamide (positive control, 40 mg/kg) were administrated intravenously for 24 h respectively. Clinical signs and body weight of rats were recorded, and the tissues were subsequently collected for biochemical examination, Ag⁺ distribution detection, histopathological examination and genotoxicity assays.

Results

The rank of Ag detected in organs from highest to lowest is lung>spleen>liver>kidney>thymus>heart. Administration of AgNP induced a marked increase of ALT, BUN, TBil and Cre. Histopathological examination results showed that AgNP induced more extensive organ damages in liver, kidneys, thymus, and spleen. Bone marrow micronucleus assay found no statistical significance among groups (p > 0.05), but the number of aberration cells and multiple aberration cells were predominately increased from rats dosed with Ag⁺ and AgNP (p < 0.01), and more polyploidy cells were generated in the AgNP group (4.3%) compared with control.

Conclusion

Our results indicated that the AgNP accumulated in the immune system organs, and mild irritation was observed in the thymus and spleen of animals treated with AgNP, but not with Ag⁺. The liver and kidneys could be the most affected organs by an acute i.v. dose of AgNP, and significantly increased chromosome breakage and polyploidy cell rates also implied the potential genotoxicity of AgNP. However, particle-specific toxicities and potential carcinogenic effect remain to be further confirmed in a chronic toxicity study.

Effects of silver adsorbed on fumed silica, silver phosphate glass, bentonite organomodified with silver and titanium dioxide in aquatic indicator organisms

In order to reduce the level of transmission of diseases caused by bacteria and fungi, the development of antimicrobial additives for use in personal care, hygiene products, clothing and others has increased. Many of these additives are based on metals such as silver and titanium. The disposal of these products in the environment has raised concerns pertaining to their potential harmfulness for beneficial organisms. The objective of this study was to evaluate the influence of the shape, surface chemistry, size and carrier of three additives containing silver and one with titanium dioxide (TiO₂) on microcrustacean survival. Daphnia magna was used as a bioindicator for acute exposure test in suspensions from 0.0001 to 10,000ppm. Ceriodaphnia dubia was used for chronic test in TiO₂ suspensions from 0.001 to 100ppm. D. magna populations presented high susceptibility to all silver based additives, with 100% mortality after 24hr of exposure. A different result was found in the acute experiments containing TiO₂ suspensions, with mortality rates only after 48hr of incubation. Even on acute and chronic tests, TiO₂ did not reach a linear concentration-response versus mortality, with 1ppm being more toxic than 10,000ppm on acute test and 0.001 more toxic than 0.01ppm on chronic assay. Silver based material toxicity was attributed to silver itself, and had no relation to either form (nano or ion) or carrier (silica, phosphate glass or bentonite). TiO₂ demonstrated to have a low acute toxicity against D. magna.

Natural water as the test medium for Ag and CuO nanoparticle hazard evaluation: An interlaboratory case study

Engineered nanoparticles (NPs) have realistic potential of reaching natural waterbodies and of exerting toxicity to freshwater organisms. The toxicity may be influenced by the composition of natural waters as crucial NP properties are influenced by water constituents. To tackle this issue, a case study was set up in the framework of EU FP7 NanoValid project, performing an interlaboratory hazard evaluation of NPs in natural freshwater. Ag and CuO NPs were selected as model NPs because of their potentially high toxicity in the freshwater. Daphnia magna (OECD202) and Danio rerio embryo (OECD236) assays were used to evaluate NP toxicity in natural water, sampled from Lake Greifen and Lake Lucerne (Switzerland). Dissolution of the NPs was evaluated by ultrafiltration, ultracentrifugation and metal specific sensor bacteria. Ag NP size was stable in natural water while CuO NPs agglomerated and settled rapidly. Ag NP suspensions contained a large fraction of Ag(+) ions and CuO NP suspensions had low concentration of Cu(2+) ions. Ag NPs were very toxic (48 h EC50 1-5.5 μg Ag/L) to D. magna as well as to D. rerio embryos (96 h EC50 8.8-61 μg Ag/L) in both standard media and natural waters with results in good agreement between laboratories. CuO NP toxicity to D. magna differed significantly between the laboratories with 48 h EC50 0.9-11 mg Cu/L in standard media, 5.7-75 mg Cu/L in Lake Greifen and 5.5-26 mg Cu/L in Lake Lucerne. No toxicity of CuO NP to zebrafish embryos was detected up to 100 mg/L independent of the medium used. The results show that Ag and CuO NP toxicity may be higher in natural water than in the standard media due to differences in composition. NP environmental hazard evaluation can and should be carried out in natural water to obtain more realistic estimates on the toxicity.

Impact of silver nanoparticles on marine diatom Skeletonema costatum

When silver nanoparticles (AgNPs) are used commercially at a large scale, they infiltrate the environment at a rapid pace. However, the impact of large quantities of AgNPs on aquatic ecosystems is still largely unknown. In aquatic ecosystems, the phytoplanktons have a vital ecological function and, therefore, the potential impact of AgNPs on the microalgae community has elicited substantial concern. Therefore, in this study, the impacts of AgNPs on a marine diatom, the Skeletonema costatum, are investigated, with a focus on their photosynthesis and associated mechanisms. Exposure to AgNPs at a concentration of 0.5 mg l(-1) significantly induces excess intracellular reactive oxygen species (ROS, 122%) and reduces 28% of their cell viability. More importantly, exposure to AgNPs reduces the algal chlorophyll-a content. Scanning electron microscopy (SEM) was conducted, which revealed that AgNPs obstruct the light absorption of algae because they adhere to their surface. The maximum photochemical efficiency of photosystem II (Fv/Fm) demonstrates that exposure to AgNPs significantly inhibits the conversion of light energy into photosynthetic electron transport. Moreover, the genes of the photosystem II reaction center protein (D1) are significantly down-regulated (P < 0.05) upon exposure to 5 mg l(-1) AgNPs. These results suggest that the physical adhesion and effects of shading of AgNPs on algae might affect their light energy delivery system and damage the crucial protein function of PSII. The photosynthesis inhibition effect of AgNPs is largely different from Ag(+) . This study shows that AgNPs at higher concentrations might have serious consequences for the succession of the phytoplankton communities and aquatic ecosystem equilibrium. Copyright © 2016 John Wiley & Sons, Ltd.

Genetic correlations and little genetic variance for reaction norms may limit potential for adaptation to pollution by ionic and nanoparticulate silver in a whitefish (Salmonidae)

For natural populations to adapt to anthropogenic threats, heritable variation must persist in tolerance traits. Silver nanoparticles, the most widely used engineered nanoparticles, are expected to increase in concentrations in freshwaters. Little is known about how these particles affect wild populations, and whether genetic variation persists in tolerance to permit rapid evolutionary responses. We sampled wild adult whitefish and crossed them in vitro full factorially. In total, 2896 singly raised embryos of 48 families were exposed to two concentrations (0.5 μg/L; 100 μg/L) of differently sized silver nanoparticles or ions (silver nitrate). These doses were not lethal; yet higher concentrations prompted embryos to hatch earlier and at a smaller size. The induced hatching did not vary with nanoparticle size and was stronger in the silver nitrate group. Additive genetic variation for hatching time was significant across all treatments, with no apparent environmental dependencies. No genetic variation was found for hatching plasticity. We found some treatment‐dependent heritable variation for larval length and yolk volume, and one instance of additive genetic variation for the reaction norm on length at hatching. Our assessment suggests that the effects of silver exposure on additive genetic variation vary according to trait and silver source. While the long‐term fitness consequences of low‐level silver exposure on whitefish embryos must be further investigated to determine whether it is, in fact, detrimental, our results suggest that the evolutionary potential for adaptation to these types of pollutants may be low.

Brain-targeted distribution and high retention of silver by chronic intranasal instillation of silver nanoparticles and ions in Sprague-Dawley rats

The wide applications of silver nanoparticles (AgNPs) have been concerned regarding their unintentional toxicities. Different exposure modes may cause distinct accumulation, retention and elimination profiles, which are closely related with their toxicities. Unlike silver accumulation profiles through other regular administration modes, the biodistribution, accumulation and elimination of AgNPs by intranasal instillation are not fully understood. This study conducted intranasal instillation of polyvinylpyrrolidone-coated AgNPs in neonatal Sprague-Dawley rats at doses of 1 and 0.1 mg kg(-1) day(-1) for 4 and 12 weeks, respectively. The 4-week recovery was also designed after the 12-week exposure. Silver concentrations in the main tissues or organs were periodically monitored. Parallel exposures using silver ion were performed for the comparative studies. No physiological alterations were observed in AgNP exposures. In comparison, 1 mg kg(-1) day(-1) silver ions decreased body weight gain and caused mortality of 18.2%, showing ionic silver had a relatively higher toxicity than AgNPs. A relatively higher silver accumulation was observed in silver ion groups than AgNP groups. The silver ion release could not fully explain silver accumulation in AgNP exposures, showing silver distribution caused by particulate silver occurred in vivo. The highest silver concentration was in the liver at week 4, while it shifted to the brain after a 12-week exposure. Dose-related silver accumulation occurred for both AgNP and silver ion groups. The time course revealed a uniquely high concentration and retention of brain silver, implying chronic intranasal instillation caused brain-targeted silver accumulation. These findings provided substantial evidence on the potential neuronal threat from the intranasal administration of AgNPs or silver colloid-based products.

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.