Effects of silver nanoparticle properties, media pH and dissolved organic matter on toxicity to Daphnia magna

Toxic Effects of Different Coating-Related Functionalized Nanoparticles on Aquatic Organisms

The peculiar physico-chemical characteristics of nanomaterials (NMs) and the use of different coatings to improve their expected properties result in a huge amount of nanoforms, which vary in chemical composition, size, shape and surface characteristics. This makes it almost impossible to test all the nanoforms available, and efforts have been made to establish grouping or read-across strategies. The aim of this work was to find a behavior pattern of effect among nanoforms of different metallic core nanoparticles (NPs) (TiO2, CeO2 and Ag NP) with the same coatings (sodium citrate, poly (ethylene glycol), dodecylphosphonic acid or oleylamine). Daphnia magna, rainbow trout and two fish cell lines (PLHC-1 and RTH-149) were exposed to a range of concentrations (up to 100 mg/L) of the uncoated or coated NPs. Ag NPs were the most toxic, followed by CeO2 NPs and finally by TiO2 NPs. The results show that a clear pattern of toxicity in the studied species could not be established related to the coatings. However, it was possible to confirm different inter-species sensitivities. RTH-149 was the most sensitive cell line, and Daphnia magna was more sensitive than fish. Moreover, some differences in coating-core interactions were found between the metal oxide and the metal NPs in Daphnia magna.

Recent advancement of nanotherapeutics in accelerating chronic wound healing process for surgical wounds and diabetic ulcers

One of the greatest challenges faced during surgical procedures is closing and healing of wounds, which are essential in the field of orthopaedics, trauma, intensive care and general surgery. One of the main causes of death has been linked to chronic wounds, especially in immunosuppressant or diabetic patients. Due to increasing chronic wound fatality along with different pathologies associated with them, the current therapeutic methods are insufficient which has established an eminent need for innovative techniques. Traditionally, wound healing was carried out using formulations and ointments containing silver combined with different biomaterial, but was found to be toxic. Hence, the advent of alternative nanomaterial-based therapeutics for effective wound healing have come into existence. In this review, we have discussed an overview of wound infections such as different wound types, the wound healing process, dressing of wounds and conventional therapies. Furthermore, we have explored various nanotechnological advances made in wound healing therapy which include the use of promising candidates such as organic, inorganic, hybrid nanoparticles/nanocomposites and synthetic/natural polymer-based nanofibers. This review further highlights nanomaterial-based applications for regeneration of tissue in wound healing and can provide a base for researchers worldwide to contribute to this advancing medical area of wound therapy.

Proteomic evaluation of nanotoxicity in aquatic organisms: A review

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

Plant-Mediated Green Synthesis of Ag NPs and Their Possible Applications: A Critical Review

The potential applications of Ag NPs are exciting and beneficial in a variety of fields; however, there is less awareness of the new risks posed by inappropriate disposal of Ag NPs. The Ag NPs have medicinal, plasmonic, and catalytic properties. The Ag NPs can be prepared via physical, chemical, or biological routes, and the selection of any specific route depends largely on the end-use. The downside of a physical and chemical approach is that it requires a wide space, high temperature, high temperature for a longer time to preserve the thermal stability of synthesized Ag NPs, and the use of toxic chemicals. Although these methods produce nanoparticles with high purity and well-defined morphology, it is critical to develop cost-effective, energy-efficient, and facile route, such as green synthesis; it suggests the desirable use of renewable resources by avoiding the use of additional solvents and toxic reagents in order to achieve the ultimate goal. However, each method has its pros and cons. The synthesized Ag NPs obtained using the green approach have larger biocompatibility and are less toxic towards the biotic systems. However, identifying the phytoconstituents that are responsible for nanoparticle synthesis is difficult and has been reported as a suitable candidate for biological application. The concentration of the effective bioreducing phytoconstituents plays a crucial role in deciding the morphology of the nanoparticle. Besides these reaction times, temperature, pH, and concentration of silver salt are some of the key factors that determine the morphology. Hence, careful optimization in the methodology is required as different morphologies have different properties and usage. It is due to which the development of methods to prepare nanoparticles effectively using various plant extracts is gaining rapid momentum in recent days. To make sense of what involves in the bioreduction of silver salt and to isolate the secondary metabolites from plants are yet challenging. This review focuses on the contribution of plant-mediated Ag NPs in different applications and their toxicity in the aquatic system.

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.

Acute Adverse Effects of Metallic Nanomaterials on Cardiac and Behavioral Changes in Daphnia magna

Nanomaterials are widely believed to induce toxic effects on organisms by evoking oxidative stress. We evaluated the toxic effects of nanomaterials on the cardiac and behavioral changes in Daphnia magna under varying exposure conditions. Titanium dioxide nanoparticles (TiO2 NPs), silver nanoparticles (AgNPs), and silver nitrate (AgNO3) were selected for the acute toxicity tests. The adverse effects of the substances on the neonates including heart rate, swimming speed, and oxidative stress were measured. The heart rate level decreased as the concentration of both NPs and silver ions (Ag+) increased. The average swimming speed was measured to be approximately 15 mm/min for the control group. The swimming speed generally increased with a longer exposure to both NPs although it reached a plateau at the lowest concentration of AgNPs. A similar but less clear trend was observed for Ag+. For all substances, the overall swimming speed exhibited no correlation or weak negative correlations with the exposure concentration. The oxidative stress levels increased after exposure compared with the control group. We conclude that aquatic nanotoxicity tests should consider multilevel physicochemical, physiological, and behavioral parameters for the official guidelines to quantify more robust adverse outcomes.

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.

Effects of Co-Exposure of Nanoparticles and Metals on Different Organisms: A Review

Wide nanotechnology applications and the commercialization of consumer products containing engineered nanomaterials (ENMs) have increased the release of nanoparticles (NPs) to the environment. Titanium dioxide, aluminum oxide, zinc oxide, and silica NPs are widely implicated NPs in industrial, medicinal, and food products. Different types of pollutants usually co-exist in the environment. Heavy metals (HMs) are widely distributed pollutants that could potentially co-occur with NPs in the environment. Similar to what occurs with NPs, HMs accumulation in the environment results from anthropogenic activities, in addition to some natural sources. These pollutants remain in the environment for long periods and have an impact on several organisms through different routes of exposure in soil, water, and air. The impact on complex systems results from the interactions between NPs and HMs and the organisms. This review describes the outcomes of simultaneous exposure to the most commonly found ENMs and HMs, particularly on soil and aquatic organisms.

Nanomaterials in Wound Healing and Infection Control

Wounds continue to be a serious medical concern due to their increasing incidence from injuries, surgery, burns and chronic diseases such as diabetes. Delays in the healing process are influenced by infectious microbes, especially when they are in the biofilm form, which leads to a persistent infection. Biofilms are well known for their increased antibiotic resistance. Therefore, the development of novel wound dressing drug formulations and materials with combined antibacterial, antibiofilm and wound healing properties are required. Nanomaterials (NM) have unique properties due to their size and very large surface area that leads to a wide range of applications. Several NMs have antimicrobial activity combined with wound regeneration features thus give them promising applicability to a variety of wound types. The idea of NM-based antibiotics has been around for a decade at least and there are many recent reviews of the use of nanomaterials as antimicrobials. However, far less attention has been given to exploring if these NMs actually improve wound healing outcomes. In this review, we present an overview of different types of nanomaterials explored specifically for wound healing properties combined with infection control.

Transition metal oxide and chalcogenide-based nanomaterials for antibacterial activities: an overview

A new battle line is drawn where antibiotic misuse and mismanagement have made treatment of bacterial infection a thorny issue. It is highly desirable to develop active antibacterial materials for bacterial control and destruction without drug resistance. A large amount of effort has been devoted to transition metal oxide and chalcogenide (TMO&C) nanomaterials as possible candidates owing to their unconventional physiochemical, electronic and optical properties and feasibility of functional architecture assembly. This review expounds multiple TMO&C-based strategies to combat pathogens, opening up new possibilities for the design of simple, yet highly effective systems that are crucial for antimicrobial treatment. A special emphasis is placed on the multiple mechanisms of these nanoagents, including mechanical rupture, photocatalytic/photothermal activity, Fenton-type reaction, nanozyme-assisted effect, released metal ions and the synergistic action of TMO&C in combination with other antibacterial agents. The applications of TMO&C nanomaterials mostly in air/water purification and wound healing along with their bactericidal activities and mechanisms are also described. Finally, the contemporary challenges and trends in the development of TMO&C-based antibacterial strategies are proposed.

Multigenerational Toxic Effects on Daphnia magna Induced by Silver Nanoparticles and Glyphosate Mixture

Multigenerational toxicological effects of a binary mixture of silver nanoparticles (AgNPs) with glyphosate were identified in Daphnia magna using acute and chronic toxicity tests. Acute toxicity interactions were analyzed with the Abbott method. In the chronic tests, the survival, growth, reproduction, and age at first brood were evaluated for the parents and the exposed (F1E) and non-exposed (F1NE) descendants. The scales tested for binary mixture, at the acute level, presented antagonistic and additive interactions, possibly associated with the complexation of the AgNPs by glyphosate. Multigenerational chronic effects related to the parameters, reproduction, and age at first brood were observed in the descendants tested with the individual compounds, with no recovery for F1E and F1NE. In organisms exposed to binary mixture, there was a delay in the age at first brood and also a significant change in the reproduction parameter, with a strong reduction for the parents, F1E, and F1NE, indicating a higher toxicity than the compounds tested individually. Although the results for acute interactions between AgNP and glyphosate did not provide clear evidence, multigenerational chronic binary mixture trials have resulted in unexpected toxicity compared with individual treatments, increasing the concerns associated with this co-exposure in other scenarios. Therefore, the interaction of binary mixture with the organisms merits further investigation and the results reported in the present study will be useful in this regard. Environ Toxicol Chem 2021;40:1123-1131. © 2020 SETAC.

Eco-corona formation on the nanomaterials in the aquatic systems lessens their toxic impact: A comprehensive review

Recent studies have shown that nanosized materials including plastics as a major cause of concern in the aquatic ecosystem. Fortunately, in the aquatic environment, the surface of the materials is often colonized by exudates of aquatic microorganisms (biofilm), where these materials are attached and surrounded by a secreted matrix with a sticky layer. The significance of these biofilms on the existence and beneficial implications of these pollutants has been studied in recent decades. Here we develop the concept of these pollutants as a complex matrix of polymers to which Extracellular Polymeric Substances (EPS) binds to form eco-corona modifying its density and surface charge of these particles. This review critically integrates the outstanding properties and functions of algal EPS in the aquatic environment and their dynamic interactions of early colonization on the surface of these pollutants, the impact of biofilm formation on stability, reactivity and, toxicity from the current literature. Due to the modifications of the environmental processes, EPS can have an impact on the toxicity thus special attention is focused on their behavior to decrease the toxicity of the pollutants in the aquatic environment. Although there has been an increasing number of researches in this area, further progress is needed to explore the extent to which ecological processes could be impacted, including the modifications in the behavior of aquatic pollutants. Thus, this review provides a recent perspective into the mechanisms of how eco-corona formation mitigates the toxicity of nanomaterials prevalent in aquatic ecosystems.

Inhibition of the filamentation of Candida albicans by Borojoa patinoi silver nanoparticles

Candida albicans is fungus capable of changing from yeast to filamentous form when it’s transformed from a normal commensal to an opportunistic pathogen. The development of alternatives that interfere with this transition could be an effective way to reduce candidiasis. In this regard, evaluate the inhibitory effect of two Borojoa patinoi silver nanoparticles (AgNPs) produced by green synthesis at 5 °C and 25 °C on the process of filamentation of Candida albicans. The percentage of inhibition of filamentous forms of C. albicans ATCC10231 and C. albicans SC5314 with AgNPs was determined. Results showed that temperature of synthesis affected both the shape and size of silver nanoparticles synthesized using Borojoa patinoi extracts. The inhibition percentage of filamentous forms of Candida albicans ATCC10231 when treated with silver nanoparticles synthesized at 5 °C was 85.9% and at 25 °C it was 40%. C. albicans SC5314 when treated with AgNP synthesized at 5 °C was 97.2% and at 25 °C it was 64%. Cell toxicity assay showed that at 100ng/ml, AgNPs synthesized at 25 °C were safe in MES-OV CRL-3272 cell line. Our results showed that the silver nanoparticles obtained from Borojoa patinoi are inhibitors of the filamentous process of C. albicans.

Rationale and decision rules behind the ECETOC NanoApp to support registration of sets of similar nanoforms within REACH

New registration requirements for nanomaterials under REACH consider the possibility to form 'sets of similar nanoforms' for a joined human health and environmental hazard, exposure and risk assessment. We developed a tool to create and justify sets of similar nanoforms and to ensure that each of the nanoforms is sufficiently similar to all other nanoforms. The decision logic is following the ECHA guidance in a transparent and evidence-based manner. For each two nanoforms the properties under consideration are compared and corresponding thresholds for maximal differences are proposed. In tier1, similarity is assessed based on intrinsic properties that mostly correspond to those required for nanoform identification under REACH: composition, impurities/additives, size, crystallinity, shape and surface treatment. Moreover, potential differences in the agglomeration/aggregation state resulting from different production processes are considered. If nanoforms were not sufficiently similar based on tier1 criteria, additional data from functional assays are required in tier2. In rare cases, additional short-term in vivo rodent data could be required in a third tier. Data required by tier 2 are triggered by the intrinsic properties in the first tier that did not match the similarity criteria. Most often this will be data on dissolution and surface reactivity followed by in vitro toxicity, dispersion stability, dustiness. Out of several nanoforms given by the user, the tool concludes which nanoforms could be justified to be in the same set and which nanoforms are outside. It defines the boundaries of sets of similar nanoforms and generates a justification for the REACH registration.

Beyond the Nanomaterials Approach: Influence of Culture Conditions on the Stability and Antimicrobial Activity of Silver Nanoparticles

Silver nanoparticles (AgNPs) as antimicrobial agents have been extensively studied. It is generally assumed that their inhibitory activity heavily depends on their physicochemical features. Yet, other parameters may affect the AgNP traits and activity, such as culture medium composition, pH, and temperature, among others. In this work, we evaluated the effect of the culture medium physicochemical traits on both the stability and antibacterial activity of AgNPs. We found that culture media impact the physicochemical traits of AgNPs, such as hydrodynamic size, surface charge, aggregation, and the availability of ionic silver release rate. As a consequence, culture media play a major role in AgNP stability and antimicrobial potency. The AgNP minimal inhibitory concentration (MIC) values changed up to 2 orders of magnitude by the influence of culture media alone when single-stock AgNPs were tested on the same strain of Escherichia coli. Furthermore, a meta-analysis of the AgNP MIC values confirms that the "chemical complexity" of culture media influences the AgNP activity. Studies that address only the antimicrobial activities of nanoparticles on common bacterial models should be performed by standardized susceptibility assays, thus generating replicable, comparable reports regarding the antimicrobial potency of nanomaterials.

The nature of dissolved organic matter determines the biosorption capacity of Cu by algae

The role of dissolved organic matter (DOM) on the biochemical behavior and toxicity of heavy metals in water is very important but complex and unclear. The present work extracted DOM from a natural water and separated it into three fractions, namely humic acid (HA), fulvic acid (FA) and transphilic acid (TPA). Optical detection showed that HA had most aromatic ring skeletons, FA had more aromatic ring hydrophilic groups, and TPA had the largest number of hydroxyl or carboxyl groups. Their effects on the toxicity of Cu by Chlorella pyrenoidosa depended on types and concentration of DOM. In the case of algal exposure to 0.003 mM initial Cu concentration, the final algal optical density increased from 0.317 of the control group to 0.345, 0.645 and 0.435 in the presence of 20, 10 mg L^-1 HA, and 10 mg L^-1 TPA, respectively, but were suppressed to 0.246, 0.117 and 0.234 in the presence of 10, 20 mg L^-1 FA and 20 mg L^-1 TPA. Most adsorption isotherms lost the linearity in the presence of HA, FA and TPA. The adsorbed Cu increased from 0.242 to 0.477 mmol g^-1, following the order of increased concentration of HA, FA, and TPA. The formation of ternary complex and the multi-layer adsorption were proposed to explain the significant enhancement adsorption of Cu in the presence of FA and TPA. This study showed that the type and the density of effective functional groups in DOM determined its effects on Cu toxicity and bioavailability to algae.

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

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

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.

Revealing the Importance of Aging, Environment, Size and Stabilization Mechanisms on the Stability of Metal Nanoparticles: A Case Study for Silver Nanoparticles in a Minimally Defined and Complex Undefined Bacterial Growth Medium

Although the production and stabilization of metal nanoparticles (MNPs) is well understood, the behavior of these MNPs (possible aggregation or disaggregation) when they are intentionally or unintentionally exposed to different environments is a factor that continues to be underrated or overlooked. A case study is performed to analyze the stability of silver nanoparticles (AgNPs)-one of the most frequently used MNPs with excellent antibacterial properties-within two bacterial growth media: a minimally defined medium (IDL) and an undefined complex medium (LB). Moreover, the effect of aging, size and stabilization mechanisms is considered. Results clearly indicate a strong aggregation when AgNPs are dispersed in IDL. Regarding LB, the 100 nm electrosterically stabilized AgNPs remain stable while all others aggregate. Moreover, a serious aging effect is observed for the 10 nm electrostatically stabilized AgNPs when added to LB: after aggregation a restabilization effect occurs over time. Generally, this study demonstrates that the aging, medium composition (environment), size and stabilization mechanism-rarely acknowledged as important factors in nanotoxicity studies-have a profound impact on the AgNPs stabilization and should gain more attention in scientific research.

The Toxicity of Nonaged and Aged Coated Silver Nanoparticles to Freshwater Alga Raphidocelis subcapitata

The transformation of coated silver nanoparticles (AgNPs) and their impacts on aquatic organisms require further study. The present study investigated the role of aging on the transformation of differently coated AgNPs and their sublethal effects on the freshwater alga Raphidocelis subcapitata. The stability of AgNPs was evaluated over 32 d, and the results indicated that transformation of AgNPs occurred during the incubation; however, coating-specific effects were observed. Fresh AgNPs increased reactive oxygen species (ROS) formation, whereas aged AgNPs induced excessive ROS generation compared with their fresh counterparts. Increased ROS levels caused increased lipid peroxidation (LPO) in treatment groups exposed to both fresh and aged NPs, although LPO was comparatively higher in algae exposed to aged AgNPs. The observed increase in catalase (CAT) activity of algal cells was attributed to early stress responses induced by excessive intracellular ROS generation, and CAT levels were higher in the aged NP treatment groups. In conclusion, AgNPs increased ROS levels and LPO in algae and caused the activation of antioxidant enzymes such as CAT. Overall, the results suggest that aging and coating of AgNPs have major impacts on AgNP transformation in media and their effects on algae. Environ Toxicol Chem 2019;38:2371-2382. © 2019 SETAC.

Exposure pathway dependent effects of titanium dioxide and silver nanoparticles on the benthic amphipod Gammarus fossarum

The increasing production of engineered inorganic nanoparticles (EINPs) elevates their release into aquatic ecosystems raising concerns about associated environmental risks. Numerous investigations indicate sediments as the final sink, facilitating the exposure of benthic species to EINPs. Although reports of sub-lethal EINP effects on benthic species are increasing, the importance of exposure pathways (either waterborne or dietary) is poorly understood. This study investigates the influence of two EINPs, namely titanium dioxide (nTiO₂) and silver (nAg), on the benthic model organism Gammarus fossarum specifically addressing the relative relevance of these pathways. For each type of EINP an individual 30-day long bioassay was conducted, applying a two-factorial test design. The factors include the presence or absence of the EINPs (nTiO₂: ∼80 nm, 4 mg/L or nAg: ∼30 nm, 0.125 mg/L; n = 30) in the water phase (waterborne), combined with a preceding 6-day long aging of their diet (black alder leaves) also in presence or absence of the EINPs (dietary). Response variables were mortality, food consumption, feces production and energy assimilation. Additionally, the physiological fitness was examined using lipid content and dry weight of the organisms as measures. Results revealed a significantly reduced energy assimilation (up to ∼30%) in G. fossarum induced by waterborne exposure towards nTiO₂. In contrast, the dietary exposure towards nAg significantly increased the organisms' energy assimilation (up to ∼50%). Hence, exposure pathway dependent effects of EINPs cannot be generalized and remain particle specific resting upon their intrinsic properties affecting their potential to interact with the surrounding environment. As a result of the different properties of the EINPs used in this study, we clearly demonstrated variations in type and direction of observed effects in G. fossarum. The results of the present study are thus supporting current approaches for nano-specific grouping that might enable an enhanced accuracy in predicting EINP effects facilitating their environmental risk assessment.

Impact of light and Suwanee River Fulvic Acid on O2 and H2O2 Mediated Oxidation of Silver Nanoparticles in Simulated Natural Waters

In this work, we investigate the impact of natural organic matter (NOM) and light on silver nanoparticle (AgNP) dissolution kinetics with particular emphasis on determining the (i) mechanism via which NOM affects the oxidative dissolution of AgNPs, (ii) the role of photogenerated organic radicals and reactive oxygen species (ROS) in oxidative dissolution of AgNPs, and (iii) the mechanism of formation of AgNPs in NOM solution under dark and irradiated conditions. We measured the oxidation of citrate stabilized AgNPs by O₂ and hydrogen peroxide (H₂O₂) in the dark and in irradiated Suwannee River fulvic acid (SRFA) solutions at pH 8.0. Results show that the reactivity of AgNPs toward O₂ and H₂O₂ in the dark decreased in the presence of SRFA as a result of blocking of AgNP surface sites through either steric or electrostatic effects. Irradiation promoted dissolution of AgNPs by O₂ and H₂O₂ in the presence of low concentrations (≤20 mg·L^-1) of SRFA as a result of contribution from photogenerated H₂O₂ formed on irradiation of SRFA as well as photofragmentation of AgNPs. Furthermore, our results show that photogenerated superoxide can induce formation of AgNPs by reducing Ag(I) ions. Based on our experimental results, we have developed a kinetic model to explain AgNP transformation by O₂ and H₂O₂ in the dark and in irradiated SRFA solutions with this model of use in predicting the transformation and fate of AgNPs in natural waters.

A blessing in disguise? Natural organic matter reduces the UV light-induced toxicity of nanoparticulate titanium dioxide

Besides their economic value, engineered inorganic nanoparticles (EINPs) may pose a risk for the integrity of ecosystems. Among EINPs, titanium dioxide (nTiO₂) is frequently used and released into surface waters in the μg range. There, nTiO₂ interacts with environmental factors, influencing its potential to cause adverse effects on aquatic life. Although factors like ultra violet (UV) light and natural organic matter (NOM) are considered as ubiquitous, their joint impact on nTiO₂-induced toxicity is poorly understood. This study addressed the acute toxicity of nTiO₂ (P25; 0.00-64.00 mg/L; ~60 nm) at ambient UV light (0.00-5.20 W UVA/m²) and NOM levels (seaweed extract; 0.00-4.00 mg TOC/L), using the immobility of Daphnia magna as response variable. Confirming previous studies, effects caused by nTiO₂ were elevated with increasing UV radiation (up to ~280 fold) and mitigated by higher NOM levels (up to ~12 fold), possibly due to reduced reactive oxygen species (ROS; measured as ^•OH radicals) formation at lower UV intensities. However, contradicting to former studies, nTiO₂-mediated ROS formation was not proportional to increasing NOM levels: lower concentrations (0.04-0.40 mg TOC/L) slightly diminished, whereas a higher concentration (4.00 mg TOC/L) promoted the ROS quantity, irrespective of UV intensity. Measured ROS levels do not fully explain the observed nTiO₂-induced toxicity, whereas increasing acetylcholinesterase and glutathione-S-transferase activities in daphnids (in presence of 8.00 mg/L nTiO₂ and elevated UV intensity) point towards neurotoxic and oxidative stress as a driver for the observed effects. Hence, despite higher ^•OH levels in the treatments where 4.00 mg TOC/L were present, NOM was still capable of reducing nTiO₂-induced stress and ultimately adverse effects in aquatic life.

Silver nanoparticles: An integrated view of green synthesis methods, transformation in the environment, and toxicity

Nowadays, silver nanoparticles (AgNPs) are the most widely used nanoparticles (NPs) in the industry due to their peculiar biocidal features. However, the use of these NPs still runs into limitations mainly because of the low efficiency of environmental friendly synthesis methods and lack of size standardization. When NPs are release in the environment, they can be transformed by oxidation, adsorption or aggregation. These modification shows a dual role in toxic response of AgNPs. The adsorption of natural organic matter from environment on AgNPs, for example, can decrease their toxicity. Otherwise oxidation occurred in the environment is also able to increase the release of toxic Ag⁺ from NPs. Thus, the current review proposes an integrated approach of AgNP synthetic methods using bacteria, fungi, and plants, AgNP cytotoxic and genotoxic effects as well as their potential therapeutic applications are also presented.

Fate and toxicity of silver nanoparticles in freshwater from laboratory to realistic environments: a review

The fate and risk assessment of silver nanoparticles (Ag NPs) is an important environmental health issue. The toxic effects, mechanisms, and modes of action of Ag NPs on aquatic organisms have been extensively determined in the laboratory. However, knowledge gaps and discrepancies exist between laboratory studies and realistic environmental research; such inconsistencies hinder the development of health and safety regulations. To bridge these gaps, this review summarizes how environmental conditions and the physicochemical properties of Ag NPs affect the inconsistent findings between laboratory studies and realistic environmental research. Moreover, this paper systematically reviews different toxic effects of Ag NPs in a realistic environment and compares these effects with those in the laboratory, which is helpful for assessing the environmental fate and risk of Ag NPs. The hazardous effects of Ag NPs on the whole aquatic ecosystem with low concentrations (μg L^-1) and long-term periods (months to years) are detailed. Furthermore, two perspectives of future toxicity studies of Ag NPs in realistic freshwater environments are emphasized.

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.

What kind of effects do Fe2O3 and Al2O3 nanoparticles have on anaerobic digestion, inhibition or enhancement?

Fe₂O₃ and Al₂O₃ nanoparticles are widely used in products and find their way to wastewater treatment plants through the contact of water with these products. In this study, impacts of Fe₂O₃ and Al₂O₃ nanoparticles on methane potential of waste activated sludge (WAS) were investigated by comparing long and short term toxicity test results, modelling and FISH analysis. Methane production from the samples treated with the maximum concentration of Fe₂O₃ nanoparticles decreased 28.9% at the end of the long term BMP test. EC₅₀ value for BMP test of the Fe₂O₃ nanoparticles was calculated as 901.94 mg/gTS with high coefficient of determination. Methane production from the samples treated with Al₂O₃ nanoparticles increased up to 14.8% (p > 0.05) at the end of the BMP test. However, short term toxicity tests for Fe₂O₃ and Al₂O₃ nanoparticles showed no impact on anaerobic digestion of WAS. Kinetic parameters obtained from models and captured FISH images were consistent with these results. Different impacts of nanoparticles on methane production suggested that anaerobic microorganisms can be affected from nanoparticles in various mechanisms. Hydrolysis (k_H) and overall reaction rates (k_R) values were determined as 0.0277 and 0.1441 d^-1, respectively for each concentration of Al₂O₃ nanoparticles and raw WAS. Similarly, methane production from WAS containing 5, 50, 150 and 250 mgFe₂O₃/gTS were modeled with same kinetic values. However, k_H constant was calculated as 0.0149 d^-1 for 500 mgFe₂O₃/gTS. This means that Fe₂O₃ nanoparticles starting from this concentration inhibited the methanogenic consortium and caused decreased biogas production and spesific methane production rate.

Green synthesis of silver nanoparticles toward bio and medical applications: review study

Development of biologically inspired green synthesis of silver nanoparticles has attracted considerable worldwide attention in matter of medical science and disease treatment. Herein, the green synthesis of silver nanomaterials using organic green sources has been evaluated and discussed. These kinds of materials are widely used for treatment of antibiotic-resistant bacteria, cancer and etc due to their elegant properties compared with other chemical ways and drugs. Moreover, the outcome of green-based approaches were compared with chemical procedures and obtained data were examined via various analyses including UV-visible spectroscopy, scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDX), transmission electron microscope (TEM), atomic force microscopy (AFM) and Fourier transforms infrared spectroscopy (FT-IR). In this study, variety of green methods were investigated to present a summary of recent achievements toward highlighting biocompatible nanoparticles, all of which can reduce the toxicity of nanoparticles, make them eco-friendly, reduce their side effects and decrease the production cost. The nature of these biological organisms also affect the structure, shape, size and morphology of synthesized nanoparticles.

Toxicity of silver nanoparticles to Lumbriculus variegatus is a function of dissolved silver and promoted by low sediment pH

Toxicity of silver nanoparticles (AgNPs) to benthic organisms is a major concern. The use of AgNPs in industry and consumer products leads to increasing release of AgNPs into the aquatic environment-sediments being the major sink. Effects of sediment pH on the toxicity of AgNPs to benthic oligochaeta Lumbriculus variegatus were studied in a 23-d toxicity test. Artificially prepared sediments (pH 5 and 7) were spiked with varying concentrations of uncoated AgNP, polyvinylpyrrolidone (PVP)-coated AgNP, and silver nitrate (AgNO₃ ) as dissolved Ag reference. Number of individuals and biomass change were used as endpoints for the toxicity. The toxic effects were related to the bioaccessible concentration of dissolved Ag in the sediments, assessed with a 2-step extraction procedure. The toxicity of 2 AgNPs was similar and greatly enhanced in the acidic sediment. Because the toxic effects were well related to the bioaccessible concentration of dissolved Ag in the sediments, the toxicity of sediment-associated AgNPs to L. variegatus is suggested to be a function of dissolved Ag rather than a result from NP-specific modes of toxicity. Environ Toxicol Chem 2018;37:1889-1897. © 2018 SETAC.

Distinct toxicity of silver nanoparticles and silver nitrate to Daphnia magna in M4 medium and surface water

Toxicity of silver nanoparticles (AgNPs) has been studied in various culture media. However, these media notably differ from the natural aquatic system, thus the conclusions may be inapplicable for real environment condition. The toxicity and its underlying mechanism of AgNPs in surface waters warrant more investigations. This study investigated the acute toxicity, chronic toxicity, bioaccumulation, and alga-daphnia food chain transfer of citrate-coated AgNPs (C-AgNPs) and Ag⁺ (from AgNO₃) to D. magna in a culture medium (M4) and a surface water sample. Results show that the acute toxicity in the surface water was significantly lower than that in the M4 medium and the toxicity of Ag⁺ was greatly higher than that of C-AgNPs. The 48h median effect concentration (EC₅₀) of C-AgNPs to D. magna in the M4 medium and the surface water was 110±9.3μg/L and 270±26μg/L, respectively, while that of Ag⁺ was 1.8±0.7μg/L and 8.0±0.6μg/L, respectively. The released Ag⁺ contributed to but not dominated the acute toxicity of C-AgNPs. At the EC₅₀ of C-AgNPs, the contribution of released Ag⁺ was 35.7% and 28.0% to the apparent nanotoxicity in the M4 medium and the surface water sample, respectively. The chronic toxicity of C-AgNPs and Ag⁺ was also lower in the surface water sample than in the M4 medium as indicated by the significantly higher survival of daphnia in the surface water during the 21d exposure. The daphnia took up less but depurated more Ag in the surface water than in the M4 medium, which could account for the lower toxicity in the surface water. Biological magnification of Ag through the alga-daphnia food chain was not observed. These findings will be helpful for assessing the environmental risk of AgNPs and understanding the mechanism of nanotoxcity.

Nanoparticles in the environment: where do we come from, where do we go to?

Nanoparticles serve various industrial and domestic purposes which is reflected in their steadily increasing production volume. This economic success comes along with their presence in the environment and the risk of potentially adverse effects in natural systems. Over the last decade, substantial progress regarding the understanding of sources, fate, and effects of nanoparticles has been made. Predictions of environmental concentrations based on modelling approaches could recently be confirmed by measured concentrations in the field. Nonetheless, analytical techniques are, as covered elsewhere, still under development to more efficiently and reliably characterize and quantify nanoparticles, as well as to detect them in complex environmental matrixes. Simultaneously, the effects of nanoparticles on aquatic and terrestrial systems have received increasing attention. While the debate on the relevance of nanoparticle-released metal ions for their toxicity is still ongoing, it is a re-occurring phenomenon that inert nanoparticles are able to interact with biota through physical pathways such as biological surface coating. This among others interferes with the growth and behaviour of exposed organisms. Moreover, co-occurring contaminants interact with nanoparticles. There is multiple evidence suggesting nanoparticles as a sink for organic and inorganic co-contaminants. On the other hand, in the presence of nanoparticles, repeatedly an elevated effect on the test species induced by the co-contaminants has been reported. In this paper, we highlight recent achievements in the field of nano-ecotoxicology in both aquatic and terrestrial systems but also refer to substantial gaps that require further attention in the future.

Implications of Pony Lake Fulvic Acid for the Aggregation and Dissolution of Oppositely Charged Surface-Coated Silver Nanoparticles and Their Ecotoxicological Effects on Daphnia magna

Citrate (Cit) and polyethylenimine (BPEI)-coated silver nanoparticles (AgNPs) were used to understand how the type of capping agents and surface charge affect their colloidal stability, dissolution, and ecotoxicity in the absence/presence of Pony Lake Fulvic Acid (PLFA). In the presence of PLFA, Cit-AgNPs were stabilized, while BPEI-AgNPs were aggregated. The aggregation of BPEI-AgNPs decreased with the time, and their stabilizing effect increased at high PLFA concentration. The dissolution also differed between both AgNPs and was influenced by the PLFA concentration. Generally, BPEI-AgNPs showed a lower amount of dissolved Ag than Cit-AgNPs. The dissolved Ag concentration decreased for both AgNPs at low PLFA concentration (5 mg/L). In contrast, the extent of nanoparticle dissolution increased at high PLFA concentration (30 mg/L) but only for BPEI-AgNPs. In the absence of PLFA, the ecotoxicity of Cit-AgNPs to Daphnia magna was higher than that of BPEI-AgNPs. However, the ecotoxicity of AgNPs in the presence of PLFA was up to 70% lower than in their absence. We demonstrated that the differences in colloidal stability, dissolution, and ecotoxicity may be attributed to the different capping agents, surface charge, and concentration of natural organic matter (NOM) as well as to the formation of dissolved Ag complexes with NOM.

Toxic Effects and Molecular Mechanism of Different Types of Silver Nanoparticles to the Aquatic Crustacean Daphnia magna

Silver nanoparticles (AgNPs) have been assessed to have a high exposure risk for humans and aquatic organisms. Toxicity varies considerably between different types of AgNPs. This study aimed to investigate the toxic effects of AgNPs with different particle sizes (40 and 110 nm) and different surface coatings (sodium citrate and polyvinylpyrrolidone, PVP) on Daphnia magna and their mechanisms of action. The results revealed that the citrate-coated AgNPs were more toxic than PVP-coated AgNPs and that the 40 nm AgNPs were more toxic than the 110 nm AgNPs. Transcriptome analysis further revealed that the toxic effects of AgNPs on D. magna were related to the mechanisms of ion binding and several metabolic pathways, such as the "RNA polymerase" pathway and the "protein digestion and absorption" pathway. Moreover, the principal component analysis (PAC) results found that surface coating was the major factor that determines the toxicities compared to particle size. These results could help us better understand the possible mechanism of AgNP toxicity in aquatic invertebrates at the transcriptome level and establish an important foundation for revealing the broad impacts of nanoparticles on aquatic environments.

Variable silver nanoparticle toxicity to Daphnia in boreal lakes

Variable sensitivity of organisms to silver nanoparticles (AgNPs) caused by changes in physico-chemical variables in aquatic ecosystems is receiving increasing attention. Variables such as dissolved organic carbon, pH, light, the presence of algae and bacteria, dissolved oxygen and different ions have all been studied individually, but it is still unclear how these variables in combination alter AgNP toxicity in natural ecosystems. Here we examined AgNP toxicity on survival of wild-caught Daphnia using AgNP suspensions placed in water from several different lakes at the IISD-Experimental Lakes Area, which span a gradient of water quality parameters. The partitioning of AgNPs between particulate and dissolved organic matter fractions was also assessed due to the potential for algal sequestration and detoxification of AgNPs. We found that toxicity varied between lakes with LC₅₀ values ranging between 34 and 292μg AgL^-1. Time of year in terms of days since ice-off and carbon to nitrogen ratios of particulate matter were the major predictors of toxicity between ecosystems. Total dissolved phosphorus, dissolved organic carbon, and particulate carbon to phosphorus ratios also played minor roles in influencing survival of Daphnia between water types. We found variable partitioning of silver into the particulate fraction within lakes and no significant differences between lakes. Silver associated with particulate organic matter increased with increasing concentrations of AgNPs in the ecosystem. Overall, we found strong evidence that AgNP toxicity is highly context dependent in natural lake ecosystems.

Partitioning of nanoparticle-originated dissolved silver in natural and artificial sediments

Sediments are believed to be a major sink for silver nanoparticles (AgNPs) in the aquatic environment, but there is a lack of knowledge about the environmental effects and behavior of AgNPs in sediments. The release of highly toxic Ag⁺ through dissolution of AgNPs is one mechanism leading to toxic effects in sediments. We applied an ultrasound-assisted sequential extraction method to evaluate the dissolution of AgNPs and to study the partitioning of dissolved Ag in sediments. Silver was spiked into artificial and 2 natural sediments (Lake Höytiäinen sediment and Lake Kuorinka sediment) as silver nitrate (AgNO₃ ), uncoated AgNPs, or polyvinylpyrrolidone-coated AgNPs (PVP-AgNPs). In addition, the total body burdens of Ag in the sediment-dwelling oligochaete Lumbriculus variegatus were assessed over a 28-d exposure period. The dissolution rate was found to be similar between the uncoated AgNP and PVP-AgNP groups. In all sediments, dissolved Ag was mainly bound to the residual fraction of the sediment, followed by iron and manganese oxides or natural organic matter. In Lake Kuorinka sediment, dissolved Ag that originated from PVP-AgNPs was relatively more bioaccessible, also resulting in higher total body burden in L. variegatus than that from uncoated AgNPs or AgNO₃ . In artificial sediment and Lake Höytiäinen sediment, AgNO₃ was significantly more bioaccessible than AgNPs. Our results highlight the importance of sediment properties and AgNP surface chemistry when evaluating the environmental exposure of AgNPs. Environ Toxicol Chem 2017;36:2593-2601. © 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.

Effects of water chemistry and surface contact on the toxicity of silver nanoparticles to Bacillus subtilis

The growing use of silver nanoparticles (AgNPs) has created concerns about its potential impacts on natural microbial communities. In this study, the physicochemical properties of AgNPs and its toxicity on natural bacteria Bacillus subtilis (B. subtilis) were investigated in aqueous conditions. The characterization data showed that AgNPs highly aggregated in aqueous conditions, and the hydrodynamic diameter of AgNPs in aqueous conditions was larger than its primary size. The studied AgNPs was less toxic to B. subtilis in estuarine water as compared to that in Milli-Q water and artificial seawater, which might be due to the observed enhanced aggregation of AgNPs in estuarine water. The toxicity of AgNPs to B. subtilis was greatly reduced when their surface contact was blocked by a dialysis membrane. Scanning electron microscope images showed that exposure contact to AgNPs resulted in damage of the microbial cell wall and enhanced formation of fibrillar structures. These results suggest that particle-cell contact is largely responsible for the observed toxicity of AgNPs in B. subtilis. This study can help to understand the potential impacts of AgNPs to natural microbes, especially in the complex aquatic environments.

Silver nanoparticles alter learning and memory formation in an aquatic organism, Lymnaea stagnalis

We tested the effect of silver nanoparticles (AgNPs) on the ability of the pond snail, Lymnaea stagnalis, to learn and form long-term memory (LTM) following operant conditioning of aerial respiration. We hypothesized that the AgNPs would act as a stressor and prevent learning and LTM formation. We tested snails exposed for either 72 h or only during training and testing for memory (i.e. 0.5 h) and found no difference between those treatments. We found that at a low concentration of AgNPs (5 μg/L) neither learning and nor memory formation were altered. When we increased the concentration of AgNPs (10 μg/L) we found that memory formation was enhanced. Finally, at a higher concentration (50 μg/L) memory formation was blocked. To determine if the disassociation of Ag⁺ from the AgNPs caused the effects on memory we performed similar experiments with AgNO₃ and found similar concentration-dependent results. Finally, we found that snails perceive the AgNPs differently from Ag+ as there was context specific memory. That is, snails trained in AgNPs did not show memory when tested in Ag⁺ and vice-versa. We believe that changes in memory formation may be a more sensitive determination of AgNPs on aquatic organisms than the determination of a LC₅₀.

Toxicity of silver nanoparticles in biological systems: Does the complexity of biological systems matter?

Currently, nanomaterials are more frequently in our daily life, specifically in biomedicine, electronics, food, textiles and catalysis just to name a few. Although nanomaterials provide many benefits, recently their toxicity profiles have begun to be explored. In this work, the toxic effects of silver nanoparticles (35nm-average diameter and Polyvinyl-Pyrrolidone-coated) on biological systems of different levels of complexity was assessed in a comprehensive and comparatively way, through a variety of viability and toxicological assays. The studied organisms included viruses, bacteria, microalgae, fungi, animal and human cells (including cancer cell lines). It was found that biological systems of different taxonomical groups are inhibited at concentrations of silver nanoparticles within the same order of magnitude. Thus, the toxicity of nanomaterials on biological/living systems, constrained by their complexity, e.g. taxonomic groups, resulted contrary to the expected. The fact that cells and virus are inhibited with a concentration of silver nanoparticles within the same order of magnitude could be explained considering that silver nanoparticles affects very primitive cellular mechanisms by interacting with fundamental structures for cells and virus alike.

How test vessel properties affect the fate of silver nitrate and sterically stabilized silver nanoparticles in two different test designs used for acute tests with Daphnia magna

The relation between test conditions such as medium composition or pH on silver nanoparticle (AgNP) behavior and its link to toxicity is one of the major topics in nanoecotoxicological research in the last years. In addition, the adaptation of the ecotoxicological standard tests for nanomaterials is intensely discussed to increase comparability and reliability of results. Due to the limitation of test material production volumes and the need for high-throughput screening, miniaturization has been proposed for several test designs. In the present study, the effect of a miniaturization of the acute Daphnia immobilization test on AgNP behavior was investigated. For this purpose, available, adsorbed, and dissolved silver fractions were measured using AgNP and silver nitrate in the following two test designs: a standard test (ST) design and a miniaturized test (MT) design with reduced test volume and less animals. Despite the increase in surface area in relation to the test volume in MT, more AgNP attached to the ST vessel surface, so that in this case, exposure concentrations were significantly lower compared to the MT assessment. Ionic silver concentrations resulting from AgNP dissolution were similar in both test designs. The same was observed for ionic silver concentrations in silver nitrate (AgNO₃) treatments, but adsorbed silver was also higher in ST treatments. Assessing the structure-activity relationships revealed that surface properties such as hydrophobicity, potential binding sites, or surface roughness were of higher importance than surface:volume ratios for both test substances.

Transport of soil-aged silver nanoparticles in unsaturated sand

Engineered nanoparticles released into soils may be coated with humic substances, potentially modifying their surface properties. Due to their amphiphilic nature, humic coating is expected to affect interaction of nanoparticle at the air-water interface. In this study, we explored the roles of the air-water interface and solid-water interface as potential sites for nanoparticle attachment and the importance of hydrophobic interactions for nanoparticle attachment at the air-water interface. By exposing Ag nanoparticles to soil solution extracted from the upper soil horizon of a floodplain soil, the mobility of the resulting "soil-aged" Ag nanoparticles was investigated and compared with the mobility of citrate-coated Ag nanoparticles as investigated in an earlier study. The mobility was determined as a function of hydrologic conditions and solution chemistry using column breakthrough curves and numerical modeling. Specifically, we compared the mobility of both types of nanoparticles for different unsaturated flow conditions and for pH=5 and pH=9. The soil-aged Ag NP were less mobile at pH=5 than at pH=9 due to lower electrostatic repulsion at pH=5 for both types of interfaces. Moreover, the physical flow field at different water contents modified the impact of chemical forces at the solid-water interface. An extended Derjaguin-Landau-Verwey-Overbeek (eDLVO) model did not provide satisfactory explanation of the observed transport phenomena unlike for the citrate-coated case. For instance, the eDLVO model assuming sphere-plate geometry predicts a high energy barrier (>90 kT) for the solid-water interface, indicating that nanoparticle attachment is less likely. Furthermore, retardation through reversible sorption at the air-water interface was probably less relevant for soil-aged nanoparticles than for citrate-coated nanoparticles. An additional cation bridging mechanism and straining within the flow field may have enhanced nanoparticle retention at the solid-water interface. The results indicate that the mobility of engineered Ag nanoparticles is sensitive to solution chemistry, especially pH and the concentration of multivalent cations, and to the unsaturated flow conditions influencing particle interaction at biogeochemical interfaces.

Governing factors affecting the impacts of silver nanoparticles on wastewater treatment

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

Sprayable peptide-modified silver nanoparticles as a barrier against bacterial colonization

Sprayable formulations of AgNPs were prepared by exchanging citrate capping agents with LL37-SH peptides. The AgNP@LL37 material was then combined with type I collagen to form a stable film once sprayed. The AgNP@LL37 spray prevented Pseudomonas aeruginosa (P. aeruginosa) proliferation and eradicated a P. aeruginosa biofilm, while being non-toxic for human skin fibroblasts embedded within 3D artificial skin constructs. Finally, no silver infiltration was observed after spraying on a full-thickness skin wound in a mouse model.

Acute and chronic effects from pulse exposure of D. magna to silver and copper oxide nanoparticles

Aquatic toxicity testing of nanoparticles (NPs) is challenged by their dynamic behavior in test suspensions. The resulting difficulties in controlling and characterizing exposure concentrations are detrimental to the generation of concentration-response data needed for hazard identification of NPs. This study explores the applicability of short-term (1, 2 and 3h) pulse exposures as means to keep the exposure stable and at the same time disclose acute and chronic effects of AgNPs and CuONPs in D. magna. Dissolution, agglomeration and sedimentation were found to have less influence on exposure concentrations during 1-3h pulses than for 24-48h continuous exposures. For AgNPs, preparation of test suspensions in medium 24h before toxicity testing (aging) increased stability during the short-term pulses. In pulse tests, organisms were exposed to the test materials, AgNPs and CuONPs for 1, 2 and 3h, and afterwards transferred to clean medium and observed for 48h (post-exposure period) for acute effects and for 21 d for chronic effects. AgNO₃ and CuCl₂ were used as reference materials for dissolved silver and copper, respectively. For all test materials, a 3h pulse caused comparable immobility in D. magna (observed after 48h post-exposure) as 24h continuous exposure, as evidenced by overlapping 95% confidence intervals of EC₅₀-values. In the 21 d post-exposure period, no trends in mortality or body length were identified. AgNP and AgNO₃ pulses had no effect on the number of moltings, days to first live offspring or cumulated number of offspring, but the number of offspring increased for AgNPs (3h pulse only). In contrast, CuONP and CuCl₂ pulses decreased the number of moltings and offspring, and for CuONPs the time to first live offspring was prolonged. After CuONP exposures, the offspring production decreased more with increasing concentrations than for CuCl₂ exposures when taking the measured dissolved copper into account. This indicates a nanoparticle-specific effect for CuONPs, possibly related to the CuONPs accumulated in the gut of D. magna during the pulse exposure. Pulse exposure is an environmentally relevant exposure scenario for NPs, which for AgNPs and CuONPs enables more stable exposures and cause acute immobility of D. magna comparable to continuous 24h exposures. Pulse exposure is likely relevant and applicable for other toxic and dissolving metal NPs, but this requires further research.

Monitoring the Fate and Transformation of Silver Nanoparticles in Natural Waters

There is potential for silver nanoparticles (AgNPs) to be released into surface waters and thus affect aquatic organisms. However, agglomeration, dissolution, surface modifications and chemical speciation are important transformation processes that control the toxicity of AgNPs. Analytical methods are needed to determine the size distribution, mass and form of AgNPs and other silver species in natural waters. Cloud point extraction, single particle inductively coupled plasma mass spectrometry (spICP-MS) and asymmetric flow field flow fractionation with on-line ICP-MS (AF4-ICP-MS) are analytical techniques that show potential for quantitative analysis of AgNPs in aquatic matrices at environmentally relevant concentrations. In this review, we discuss the fate processes for AgNPs in natural waters and the analytical methods that can be used to determine the distribution of AgNPs and their transformation products.

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.

Palladium Nanoparticles: Is There a Risk for Aquatic Ecosystems?

Nano-sized palladium (nano-Pd) is used in catalytic converters of automobiles, where it can be released into the environment by abrasion. Although these particles may subsequently be transported into surface water bodies, no data estimating their fate and toxicity in aquatic systems exists. This study characterized the particle size development of nano-Pd (advertised size ~12 nm; hydrodynamic size ~70 nm) in media with variable ionic strength (IS). Additionally, the particles' acute toxicity for daphnids and chironomids was assessed. While nano-Pd agglomerated more quickly with increasing IS, it caused only marginal effects in both test species after 96 h of exposure. After 144 h of exposure, however, an EC50 value of 1.23 mg nano-Pd/L for daphnids was determined indicating effects over the long run. When considering the relatively low environmental concentration of elemental Pd in surface waters (usually ng/L), though, this study suggests only a low aquatic risk in response to nano-Pd.