Characterization of the effluent from a nanosilver producing washing machine

Preparation methods, applications, toxicity and mechanisms of silver nanoparticles as bactericidal agent and superiority of green synthesis method

Silver nanoparticles (SNPs) are a type of nanomaterial with wide applications in water treatment, medicine, food packaging, and industrial processes. Their unique optical, electrical, thermal conductivity, and biological properties distinguish them from other metal ions and liken them to noble metals like gold and copper. The present review explores the diverse applications, preparation techniques, mechanism of action of SNPs, and properties of SNPs focusing on their bactericidal activities and potential impacts on human health. Different preparation methods, encompassing chemical, physical, and biological techniques, were reviewed and analyzed to comprehend their effect on the properties and applications of SNPs. Studies revealed that the SNPs exhibit excellent antibactericidal properties. Mechanisms underlying their antimicrobial effects were explored, primarily focusing on pathogen-scavenging activities. Despite the promising benefits of SNPs, their potential toxicity to human health must be carefully managed. Regulatory standards, such as those set by WHO and USEPA; establish a maximum tolerable limit of 0.1 mg/L to mitigate health risks associated with SNP exposure. It is recommended to continue research into safer applications and alternative formulations of SNPs to minimize potential health risks while maximizing their beneficial applications across different industries.

Metallic nanoparticles and photosynthesis organisms: Comprehensive review from the ecological perspective

This review presents a comprehensive analysis of the ecological implications of metallic nanoparticles (MNPs) on photosynthetic organisms, particularly plants and algae. We delve into the toxicological impacts of various MNPs, including gold, silver, copper-based, zinc oxide, and titanium dioxide nanoparticles, elucidating their effects on the growth and health of these organisms. The article also summarizes the toxicity mechanisms of these nanoparticles in plants and algae from previous research, providing insight into the cellular and molecular interactions that underpin these effects. Furthermore, it discusses the reciprocal interactions between different types of MNPs, their combined effects with other metal contaminants, and compares the toxicity between MNPs with their counterpart. This review highlights the urgent need for a deeper understanding of the environmental impact, considering their escalating use and the potential risks they pose to ecological systems, especially in the context of photosynthetic organisms that are vital to ecosystem health and stability.

The adaptability of the ion-binding site by the Ag(I)/Cu(I) periplasmic chaperone SilF

The periplasmic chaperone SilF has been identified as part of an Ag(I) detoxification system in Gram-negative bacteria. Sil proteins also bind Cu(I) but with reported weaker affinity, therefore leading to the designation of a specific detoxification system for Ag(I). Using isothermal titration calorimetry, we show that binding of both ions is not only tighter than previously thought but of very similar affinities. We investigated the structural origins of ion binding using molecular dynamics and QM/MM simulations underpinned by structural and biophysical experiments. The results of this analysis showed that the binding site adapts to accommodate either ion, with key interactions with the solvent in the case of Cu(I). The implications of this are that Gram-negative bacteria do not appear to have evolved a specific Ag(I) efflux system but take advantage of the existing Cu(I) detoxification system. Therefore, there are consequences for how we define a particular metal resistance mechanism and understand its evolution in the environment.

Mass-Dependent Critical Value Expressions for Particle Finding in Single-Particle ICP-TOFMS

In time-of-flight mass spectrometry (TOFMS), ion detection is often achieved via electron multiplication followed by fast analog-to-digital conversion (ADC). This detection approach is chosen over time-to-digital conversion because it extends the dynamic range of TOFMS measurements, especially for transient analyses. However, fast ADC detection also introduces measurement noise fundamental to the electron multiplication process. In previous research, we demonstrated that TOFMS signals acquired with fast ADC follow a compound Poisson distribution in which the Poisson-distributed arrival of ions at the detector is compounded with the response profile of the electron multiplier. Here, we consider the influence of mass-to-charge (m/z)-dependent detector responses and their impact on particle-finding accuracy in single-particle inductively coupled plasma TOFMS (spICP-TOFMS). In spICP-TOFMS, highly time-resolved ion signals are recorded and particle signals are distinguished from background signals based on thresholding the data at m/z-specific critical values. Through Monte Carlo modeling with measured m/z-dependent detector responses, we generate compound Poisson model distributions and critical values that accurately account for the dispersion of measured signals. We test the accuracy of critical values through the analysis of dissolved element solutions and comparison of measured versus predicted event rates above critical value thresholds. The use of m/z-dependent compound Poisson critical values reduces false-positive particle identifications by one to two orders of magnitude compared to thresholding criteria based on normal or Poisson statistics. The improved accuracy and robustness of compound Poisson critical values enables automated multi-element particle finding in spICP-TOFMS.

Nanoparticles for Topical Application in the Treatment of Skin Dysfunctions-An Overview of Dermo-Cosmetic and Dermatological Products

Nanomaterials (NM) arouse interest in various fields of science and industry due to their composition-tunable properties and the ease of modification. They appear currently as components of many consumer products such as sunscreen, dressings, sports clothes, surface-cleaning agents, computer devices, paints, as well as pharmaceutical and cosmetics formulations. The use of NPs in products for topical applications improves the permeation/penetration of the bioactive compounds into deeper layers of the skin, providing a depot effect with sustained drug release and specific cellular and subcellular targeting. Nanocarriers provide advances in dermatology and systemic treatments. Examples are a non-invasive method of vaccination, advanced diagnostic techniques, and transdermal drug delivery. The mechanism of action of NPs, efficiency of skin penetration, and potential threat to human health are still open and not fully explained. This review gives a brief outline of the latest nanotechnology achievements in products used in topical applications to prevent and treat skin diseases. We highlighted aspects such as the penetration of NPs through the skin (influence of physical-chemical properties of NPs, the experimental models for skin penetration, methods applied to improve the penetration of NPs through the skin, and methods applied to investigate the skin penetration by NPs). The review summarizes various therapies using NPs to diagnose and treat skin diseases (melanoma, acne, alopecia, vitiligo, psoriasis) and anti-aging and UV-protectant nano-cosmetics.

Developmental neurotoxicity of silver nanoparticles: the current state of knowledge and future directions

The increasing production and use of silver nanoparticles (AgNPs) as an antimicrobial agent in an array of medical and commercial products, including those designed for infants and children, poses a substantial risk of exposure during the developmental period. This review summarizes current knowledge on developmental neurotoxicity of AgNPs in both pre- and post-natal stages with a focus on the biological specificity of immature organisms that predisposes them to neurotoxic insults as well as the molecular mechanisms underlying AgNP-induced neurotoxicity. The current review revealed that AgNPs increase the permeability of the blood-brain barrier (BBB) and selectively damage neurons in the brain of immature rats exposed pre and postnatally. Among the AgNP-induced molecular mechanisms underlying toxic insult is cellular stress, which can consequently lead to cell death. Glutamatergic neurons and NMDAR-mediated neurotransmission also appear to be a target for AgNPs during the postnatal period of exposure. Collected data indicate also that our current knowledge of the impact of AgNPs on the developing nervous system remains insufficient and further studies are required during different stages of development with investigation of environmentally-relevant doses of exposure.

Toxicokinetics of silver in the goldfish Carassius auratus under simultaneous waterborne and diet-borne exposures to silver nanoparticles

Silver nanoparticles (AgNPs) are applied in many products as antimicrobial agents and can be found in the environment. In this study, the uptake and elimination kinetics of silver nanoparticles in fish (Carassius auratus), via simultaneous water and dietary exposure, was investigated and compared with ionic silver (AgNO₃). Silver concentration in the tissues of C. auratus after the uptake phase was similar between nanoparticles and ionic treatments. Upon exposure to nanoparticles, Ag concentration in the different tissues of C. auratus was significantly different (Ag[liver] > Ag[intestine] > Ag[gill] > Ag[muscle]). The liver presented the highest amount of Ag among all organs, and no elimination was detected throughout the elimination period. Our results suggest that once uptake of Ag occurs in fish, the elimination takes very long which may pose ecological implications for bioaccumulation.

Recent developments in the removal of metal-based engineered nanoparticles from the aquatic environments by adsorption

Nowadays, metal-based engineered nanoparticles (m-ENPs) are ubiquitous in aquatic environments for their wide applications in all walks of life. m-ENPs have been demonstrated to exert ecotoxicity, cytotoxicity and genotoxicity towards organisms and even humans. Therefore, the removal of m-ENPs from water has recently become a hot global concerned issue. Adsorption is widely investigated for this purpose, owing to its advantages of low cost, easy operation, high removal efficiency and potential recycling use of both the adsorbents and adsorbates. As the adsorption and related technologies were hardly comprehensively overviewed for the removal of m-ENPs, herein, the present review particularly focuses on this topic. The fundamentals to the technology, including adsorption isotherm, adsorption dynamics, the adsorption process with the special emphasis on the relationship between surface area and porosity of the adsorbent and the adsorption capacity, etc., are fully discussed. As the kernel of the adsorption method, adsorbents with diversified chemical and physical properties in different types are comprehensively elaborated. The primary factors affecting the adsorption, and adsorption mechanisms are well summarized. Particularly, the regeneration of the adsorbents and the reuse of adsorbed m-ENPs are highlighted for the sustainability. Finally, challenges and prospects in this field are outlined. Overall, this review aims to provide valuable references for the development of new adsorbents with more efficient and practical applications to remove m-ENPs and direct the future study.

Effect of silver nanoparticles and chlorine reaction time on the regulated and emerging disinfection by-products formation

Silver nanoparticles (AgNPs) are used in many industries for multiple applications that inevitably release AgNPs into surface water sources. The formation kinetics of disinfection by-products (DBPs) in the presence of AgNPs was investigated during chlorination. Experiments were carried out with raw water from a canal in Songkhla, Thailand, which analyzed the formation potential (FP) of trihalomethanes FP (THMFP), iodo-trihalomethanes FP (I-THMFP), haloacetonitriles FP (HANFP), and trichloronitromethane FP. Increased AgNP concentrations by 10-20 mg/L led to a higher specific formation rate of chloroform which is described by zero- and first-order kinetics. The increase in the specific formation of chloroform as increasing chlorine contact time could enhance both the THMFP rates and the maximum THMFP concentrations in all tested AgNPs. The AgNP content did not have a significant influence on I-THMFP and HANFP concentrations or speciation. The I-THMFP and HANFP increased in a short-chlorination time as mostly complete formation <12 h, and then the rate decreased as the reaction proceeded. The levels of THMs and many emerging DBPs are related to the presence of AgNPs in chlorinated water and chlorine reaction time. THMFP had a higher impact on integrated toxic risk value (ITRV) than I-THMFP and HANFP because of the chlorination of water with AgNPs. The chlorine reaction time was more effective for increasing the ITRV of THMFP than the level of AgNPs. Water treatment plants should control the DBPs that cause possible health risks from water consumption by optimizing water distribution time.

Uptake, translocation, and transformation of silver nanoparticles in plants

This article reviews the plant uptake of silver nanoparticles (AgNPs) that occurred in soil systems and the in planta fate of Ag.

Particle Characterization of Washing Process Effluents by Laser Diffraction Technique

The dominant type of polymer particles in water, sediment, and various organisms partly derives from natural and synthetic fibres released in the washing process. Pollution of aquatic recipients with these particles poses an interdisciplinary problem throughout the world. Wastewater from washing represents a dispersion system with different particle sizes that is also loaded with the source of the particles. Due to this complex system, the qualification and quantification of this type of pollution is difficult. In this paper, the laser diffraction technique was applied to characterize particles in effluents from washing and rinsing materials made of a mixture of cotton and polyester. The results obtained through the analysis prove that the laser diffraction technique is acceptable for the characterization of a composite effluent sample. The advanced statistical technique of multivariate analysis confirmed the interrelationship of the parameters of this complex dispersion system.

Toxicological effects of silver nanoparticles and cadmium chloride in macrophage cell line (RAW 264.7): An in vitro approach

BACKGROUND

Silver nanoparticles (AgNP) are largely used in nanotechnological products, but the real risks for human and environment are still poorly understood if we consider the effects of mixtures of AgNP and environmental contaminants, such as non-essential metals.

METHODS

The aim of the present study was to investigate the cytotoxicity and toxicological interaction of AgNP (1-4 nm, 0.36 and 3.6 μg mL^-1) and cadmium (Cd, 1 and 10 μM) mixtures. The murine macrophage cell line RAW 264.7 was used as a model.

RESULTS

Effects were observed after a few hours (4 h) on reactive oxygen species (ROS) and became more pronounced after 24 h-exposure. Cell death occurred by apoptosis, and loss of cell viability (24 h-exposure) was preceded by increases of ROS levels and DNA repair foci, but not of NO levels. Co-exposure potentiated some effects (decrease of cell viability and increase of ROS and NO levels), indicating toxicological interaction.

CONCLUSION

These effects are important findings that must be better investigated, since the interaction of Cd with AgNP from nanoproducts may impair the function of macrophages and represent a health risk for humans.

Aquatic Toxicity Effects and Risk Assessment of 'Form Specific' Product-Released Engineered Nanomaterials

The study investigated the toxicity effects of 'form specific' engineered nanomaterials (ENMs) and ions released from nano-enabled products (NEPs), namely sunscreens, sanitisers, body creams and socks on Pseudokirchneriella subcapitata, Spirodela polyrhiza, and Daphnia magna. Additionally, risk estimation emanating from the exposures was undertaken. The ENMs and the ions released from the products both contributed to the effects to varying extents, with neither being a uniform principal toxicity agent across the exposures; however, the effects were either synergistic or antagonistic. D. magna and S. polyrhiza were the most sensitive and least sensitive test organisms, respectively. The most toxic effects were from ENMs and ions released from sanitisers and sunscreens, whereas body creams and sock counterparts caused negligible effects. The internalisation of the ENMs from the sunscreens could not be established; only adsorption on the biota was evident. It was established that ENMs and ions released from products pose no imminent risk to ecosystems; instead, small to significant adverse effects are expected in the worst-case exposure scenario. The study demonstrates that while ENMs from products may not be considered to pose an imminent risk, increasing nanotechnology commercialization may increase their environmental exposure and risk potential; therefore, priority exposure cases need to be examined.

Aquatic Environment Exposure and Toxicity of Engineered Nanomaterials Released from Nano-Enabled Products: Current Status and Data Needs

Rapid commercialisation of nano-enabled products (NEPs) elevates the potential environmental release of engineered nanomaterials (ENMs) along the product life cycle. The current review examined the state of the art literature on aquatic environment exposure and ecotoxicity of product released (PR) engineered nanomaterials (PR-ENMs). Additionally, the data obtained were applied to estimate the risk posed by PR-ENMs to various trophic levels of aquatic biota as a means of identifying priority NEPs cases that may require attention with regards to examining environmental implications. Overall, the PR-ENMs are predominantly associated with the matrix of the respective NEPs, a factor that often hinders proper isolation of nano-driven toxicity effects. Nevertheless, some studies have attributed the toxicity basis of observed adverse effects to a combination of the released ions, ENMs and other components of NEPs. Notwithstanding the limitation of current ecotoxicology data limitations, the risk estimated herein points to an elevated risk towards fish arising from fabrics' PR-nAg, and the considerable potential effects from sunscreens' PR-nZnO and PR-nTiO2 to algae, echinoderms, and crustaceans (PR-nZnO), whereas PR-nTiO2 poses no significant risk to echinoderms. Considering that the current data limitations will not be overcome immediately, we recommend the careful application of similar risk estimation to isolate/prioritise cases of NEPs for detailed characterisation of ENMs' release and effects in aquatic environments.

Ovarian toxicity of nanoparticles

The ovary is a highly important organ for female reproduction. The main functions include sex steroid hormone synthesis, follicular development, and achievement of oocyte meiotic and development competence for proper fertilization. Nanoparticle (NP) exposure is becoming unavoidable because of its wide use in different products, including cosmetics, food, health, and personal care products. Studies examining different nonreproductive tissues or systems have shown that characteristics such as the size, shape, core material, agglomeration, and dissolution influence the effects of NPs. However, most studies evaluating NP-mediated reproductive toxicity have paid little or no attention to the influence of the physicochemical characteristics of NP on the observed effects. As accumulating evidence indicates that NP may reach the ovary to impair proper functions, this review summarizes the available data on NP accumulation in ovarian tissue, as well as data describing toxicity to ovarian functions, including sex steroid hormone production, follicular development, oocyte quality, and fertility. Due to their toxicological relevance, this review also describes the main physicochemical characteristics involved in NP toxicity and the importance of considering NP physicochemical characteristics as factors influencing the ovarian toxicity of NPs. Finally, this review summarizes the main mechanisms of toxicity described in ovarian cells.

Impacts of Nanosilver-Based Textile Products Using a Life Cycle Assessment

Due to their properties, silver nanoparticles (AgNPs) are widely used in consumer products. The widespread use of these products leads to the release of such nanoparticles into the environment, during manufacturing, use, and disposal stages. Currently there is a high margin of uncertainty about the impacts of nano products on the environment and human health. Therefore, different approaches including life cycle assessment (LCA) are being used to evaluate the environmental and health impacts of these products. In this paper, a comparison between four different AgNP synthesis methods was conducted. In addition, four textile products that contain AgNPs were subjected to comparison using LCA analysis to assess their environmental and public health impacts using SimaPro modeling platform. Study results indicate that using alternative methods (green) to AgNPs synthesis will not necessarily reduce the environmental impacts of the synthesizing process. To the best of our knowledge, this is the first study that has compared and assessed the environmental burdens associated with different nanosilver-based textile products at different disposal scenarios. The synthesis of 1 kg of AgNPs using modified Tollens’ method resulted in 580 kg CO2 eq, while 531 kg CO2 eq resulted from the chemical approach. Furthermore, the manufacturing stage had the highest overall impacts as compared to other processes during the life cycle of the product, while the product utilization and disposal stages had the highest impacts on ecotoxicity. Sensitivity analysis revealed that under the two disposal scenarios of incineration and landfilling, the impacts were sensitive to the amount of AgNPs.

A critical review on silver nanoparticles: From synthesis and applications to its mitigation through low-cost adsorption by biochar

Silver nanoparticles are one of the most beneficial forms of heavy metals in nanotechnology applications. Due to its exceptional antimicrobial properties, low electrical and thermal resistance, and surface plasmon resonance, silver nanoparticles are used in a wide variety of products, including consumer goods, healthcare, catalysts, electronics, and analytical equipment. As the production and applications of silver nanoparticles containing products increase daily, the environmental pollution due to silver nanoparticles release is increasing and affecting especially the aqueous ecosystem. Silver nanoparticles can kill useful bacteria in soil and water, and bioaccumulate in living organisms even at low concentrations from 10^-2 to 10 μg/mL silver can show antibacterial effect. On the other hand, the maximum silver discharge limit into freshwater is 0.1 μg/L and 3.2 μg/L for Australia and the USA, respectively. To reduce its toxic consequences and meet the regulatory guidelines, it is crucial to remove silver nanoparticles from wastewater before it is discharged into other water streams. Several technologies are available to remove silver nanoparticles, but the adsorption process using low-cost adsorbents is a promising alternative to mitigate silver nanoparticle pollution in the bulk stage. As one of the low-cost adsorbents, biochar produced from the biomass waste could be a suitable adsorbent. This review focuses on collating the latest evidence on silver nanoparticle production, applications, environmental consequences, and cost-effective technological approaches for silver removal from wastewater.

Proteomic Profiles of Thyroid Gland and Gene Expression of the Hypothalamic-Pituitary-Thyroid Axis Are Modulated by Exposure to AgNPs during Prepubertal Rat Stages

Silver nanoparticles (AgNPs) have potent antimicrobial activity and, for this reason, are incorporated into a variety of products, raising concern about their potential risks and impacts on human health and the environment. The developmental period is highly dependent on thyroid hormones (THs), and puberty is a sensitive period, where changes in the hormonal environment may have permanent effects. We evaluated the hypothalamic-pituitary (HP)-thyroid axis after exposure to low doses of AgNPs using a validated protocol to assess pubertal development and thyroid function in immature male rats. For stimulatory events of the HP-thyroid axis, we observed an increase in the expression of Trh mRNA and serum triiodothyronine. Negative feedback reduced the hypothalamic expression of Dio2 mRNA and increased the expression of Thra1, Thra2, and Thrb2 mRNAs. In the pituitary, there was a reduced expression of Mct-8 mRNA and Dio2 mRNA. For peripheral T3-target tissues, a reduced expression of Mct-8 mRNA was observed in the heart and liver. An increased expression of Dio3 mRNA was observed in the heart and liver, and an increased expression of Thrb2 mRNA was observed in the liver. The quantitative proteomic profile of the thyroid gland indicated a reduction in cytoskeletal proteins (Cap1, Cav1, Lasp1, Marcks, and Tpm4; 1.875 μg AgNP/kg) and a reduction in the profile of chaperones (Hsp90aa1, Hsp90ab1, Hspa8, Hspa9, P4hb) and proteins that participate in the N-glycosylation process (Ddost, Rpn1 and Rpn2) (15 μg AgNP/kg). Exposure to low doses of AgNPs during the window of puberty development affects the regulation of the HP-thyroid axis with further consequences in thyroid gland physiology.

Combined effects of exposure to engineered silver nanoparticles and the water-soluble fraction of crude oil in the marine copepod Calanus finmarchicus

While it is likely that ENPs may occur together with other contaminants in nature, the combined effects of exposure to both ENPs and environmental contaminants are not studied sufficiently. In this study, we investigated the acute and sublethal toxicity of PVP coated silver nanoparticles (AgNP) and ionic silver (Ag⁺; administered as AgNO₃) to the marine copepod Calanus finmarchicus. We further studied effects of single exposures to AgNPs (nominal concentrations: low 15 μg L^-1 NPL, high 150 μg L^-1 NPH) or Ag⁺ (60 μg L^-1), and effects of co-exposure to AgNPs, Ag⁺ and the water-soluble fraction (WSF; 100 μg L^-1) of a crude oil (AgNP + WSF; Ag⁺+WSF). The gene expression and the activity of antioxidant defense enzymes SOD, CAT and GST, as well as the gene expression of HSP90 and CYP330A1 were determined as sublethal endpoints. Results show that Ag⁺ was more acutely toxic compared to AgNPs, with 96 h LC₅₀ concentrations of 403 μg L^-1 for AgNPs, and 147 μg L^-1 for Ag⁺. Organismal uptake of Ag following exposure was similar for AgNP and Ag⁺, and was not significantly different when co-exposed to WSF. Exposure to AgNPs alone caused increases in gene expressions of GST and SOD, whereas WSF exposure caused an induction in SOD. Responses in enzyme activities were generally low, with significant effects observed only on SOD activity in NPL and WSF exposures and on GST activity in NPL and NPH exposures. Combined AgNP and WSF exposures caused slightly altered responses in expression of SOD, GST and CYP330A1 genes compared to the single exposures of either AgNPs or WSF. However, there was no clear pattern of cumulative effects caused by co-exposures of AgNPs and WSF. The present study indicates that the exposure to AgNPs, Ag⁺, and to a lesser degree WSF cause an oxidative stress response in C. finmarchicus, which was slightly, but mostly not significantly altered in combined exposures. This indicated that the combined effects between Ag and WSF are relatively limited, at least with regard to oxidative stress.

Monitoring and modelling of influent patterns, phase distribution and removal of 20 elements in two primary wastewater treatment plants in Norway

Many small- or medium-sized communities in Northern Europe employ only primary wastewater treatment plants (WWTPs) and effluent discharges can be a relevant source of pollution. The current study combines monitoring and modelling approaches to investigate concentrations, influent patterns, size distribution and removal of 20 elements for the two primary WWTPs (Ladehammeren, LARA; Høvringen, HØRA) serving Trondheim, the third largest city in Norway. Element concentrations were determined in raw influent wastewater, effluents and biosolids, and diurnal inflow patterns were assessed. The elemental distribution in particulate, colloidal and dissolved fractions of untreated wastewater was characterized using filtration separation and electron microscopy. An influent generator model and multivariate statistical analyses were used to determine release patterns and to predict the (co-)occurrence of selected elements. Raw influent wastewater concentrations for most elements were similar in the two WWTPs, with only Ca, Mn, Fe, Co and Ba being significantly higher (p < 0.05) in HØRA (which receives more household and hospital discharges). Removal efficiencies varied between elements, but in most cases reflected their association with particulates. Nanosized particles of several elements were detected, with Cu/Zn being most common. Measured concentrations of most elements followed typical diurnal wastewater discharge patterns and enrichment factors calculated for biosolids confirmed the importance of anthropogenic sources for P, Cu, Zn, Cd, As, Cr, Ni, Pb, V, Co and Fe. Elemental concentrations generally correlated well with total suspended solid (TSS) concentrations at HØRA, while this was less pronounced in LARA (possibly due to higher industrial contributions). In one of its first applications for WWTP influent pattern examination, principal component analysis was found to be instrumental for source identification of target elements, showing significant differences between LARA and HØRA influents. The combined experimental, statistical and modelling approaches used herein allowed for improved understanding of element sources, patterns of discharge and fate in primary WWTPs.

Engineered silver nanoparticle (Ag-NP) behaviour in domestic on-site wastewater treatment plants and in sewage sludge amended-soils

Untreated sludge from small-scale on-site domestic wastewater treatment systems (septic tanks) was spiked with 20, 60 and 100 nm silver nanoparticles (Ag-NPs) to investigate Ag-NP behaviour in these systems that are widely distributed in rural areas. In addition, the release of Ag-NPs from a previously spiked clay-rich loam reference soil (LUFA 2.4) was evaluated, in the presence and absence of untreated sludge, to simulate the common practice of sludge disposal by spreading on agricultural land. Single particle ICP-MS was used to determine Ag-NP size distribution and the results were compared with total Ag (Ag-NP and ionic) measured in acid digested samples. As documented previously for large municipal scale wastewater treatment plants, Ag-NPs are found to be overwhelmingly (~98%) retained in the sludge in these small-scale systems. The Ag-NP retention efficiency on the LUFA reference soil amended with sludge is approximately 10 times greater than that of LUFA soil alone (in the absence of sludge). For soil spiked with 60 nm Ag-NPs, the calculated average diameter of Ag-NPs in the supernatant, after 24 h was 45 ± 3 nm (dissolution rate 7.2E-06 mol/m²·h for 60 nm Ag-NP), smaller than that of supernatant from the combined sludge/soil system (52 ± 2 nm), indicating lower Ag-NP dissolution rates in the sludge-amended soil. This study provides new information about the leachability of Ag-NPs from septic tank sludge and suggests that the effluent and sludge from septic tanks are potential sources of both nano- and dissolved ionic-Ag to environmental waters.

Flow and fate of silver nanoparticles in small French catchments under different land-uses: The first one-year study

This study focused on surface waters from three small creeks, within the Seine River watershed, which are characterized by different land-uses, namely forested, agricultural and urban. Silver nanoparticles (Ag-NPs) in these waters were detected and quantified by single-particle ICPMS during one-year of monthly sampling. Their temporal and spatial variations were investigated. Ag-NPs, in the three types of surface water, were found to range from 1.5 × 10⁷ to 2.3 × 10⁹ particles L^-1 and from 0.4 to 28.3 ng L^-1 at number and mass concentrations, respectively. These values are in consistent with the very few previous studies. In addition, the role of factors driving process and potential sources are discussed with correlations between Ag-NPs concentrations and biogeochemical parameters, like dissolved organic carbon concentration and divalent cations concentrations. For the forested watershed NOM controls the stability (number and mass) of the Ag-NPs as recently observed in the field in lake water in Germany. In the case of the agricultural and urban watersheds major cations such as Ca would control the number and mass of Ag-NPs. Dilution processes are rejected as conductivity and Cl^- ions do not show significant correlations with Ag-NPs or other major geochemical parameters. The specific exportation rates of Ag-NPs for artificial, agricultural and forested areas were calculated based on the monthly data for the full year and are equal to 5.5 ± 3.0, 0.5 ± 0.3 and 0.2 ± 0.2 gy^-1km^-2, respectively. These data suggest a constant release of Ag-NPs from consumer products into freshwaters in artificial areas, for instance, from textiles, washing machines, domestic tap-water filters, outdoor paints. These first data of Ag-NPs fluxes in surface waters of France enlarge the very limited database of field measurements. Moreover, for the first time, the influence of time, land-use and aquatic geochemistry parameters on Ag-NPs in real natural water samples is reported. It is also helpful to further understand the fate and the process of Ag-NPs in natural waters, as well as to the ecotoxicity studies in real-world environment.

Removal of silver nanoparticles in aqueous solution by activated sludge: Mechanism and characteristics

The increasing production and use of silver nanoparticles (AgNPs) have attracted more and more attention due to their environmental and health risks. Municipal sewage biological treatment unit has been playing an important role in the removal of AgNPs. This study investigated the mechanism and characteristics of AgNPs and their removal from aqueous solution by activated sludge. Results from Scanning Electron Microscope and Energy Dispersive Spectrometer (SEM/EDS) showed that mixed AgNPs were immobilized by activated sludge. It was shown by X-ray photoelectron spectroscopy (XPS) that the fixed AgNPs had an oxidation state of +1. It was inferred by fourier transform infra-red (FTIR) spectra that AgNPs were adsorbed by activated sludge via binding with its primary amino (R-NH₂) radical groups on the surface. These results revealed that the major mechanism for the removal of AgNPs by activated sludge was adsorption. The experiment data were in agreement with the Langmuir and Redlich-Peterson isotherms. The maximum adsorption capacity ranged from 12-32 mg g^-1 at temperatures of 10-30 °C. Thermodynamic experiment showed that the adsorption of AgNPs by activated sludge was a spontaneous and endothermic reaction. The adsorption kinetics data were in good agreement with the pseudo-second-order model. The factor results indicated that the adsorption of AgNPs onto activated sludge was influenced by electrostatic repulsion, agglomeration, and the process of oxidation and sulfurization.

Health Impact of Silver Nanoparticles: A Review of the Biodistribution and Toxicity Following Various Routes of Exposure

Engineered nanomaterials (ENMs) have gained huge importance in technological advancements over the past few years. Among the various ENMs, silver nanoparticles (AgNPs) have become one of the most explored nanotechnology-derived nanostructures and have been intensively investigated for their unique physicochemical properties. The widespread commercial and biomedical application of nanosilver include its use as a catalyst and an optical receptor in cosmetics, electronics and textile engineering, as a bactericidal agent, and in wound dressings, surgical instruments, and disinfectants. This, in turn, has increased the potential for interactions of AgNPs with terrestrial and aquatic environments, as well as potential exposure and toxicity to human health. In the present review, after giving an overview of ENMs, we discuss the current advances on the physiochemical properties of AgNPs with specific emphasis on biodistribution and both in vitro and in vivo toxicity following various routes of exposure. Most in vitro studies have demonstrated the size-, dose- and coating-dependent cellular uptake of AgNPs. Following NPs exposure, in vivo biodistribution studies have reported Ag accumulation and toxicity to local as well as distant organs. Though there has been an increase in the number of studies in this area, more investigations are required to understand the mechanisms of toxicity following various modes of exposure to AgNPs.

Nanoparticle Tracking Analysis for Multiparameter Characterization and Counting of Nanoparticle Suspensions

Nanoparticle tracking analysis (NTA) provides direct and real time visualization, sizing and counting of particulate materials between 10 nm and 1 μm in liquid suspension. The technique works on a particle by particle basis, relating the degree of movement under Brownian motion to the sphere equivalent hydrodynamic diameter particle size, allowing for high-resolution particle size distributions to be obtained within minutes. NTA has been used in studying protein complexes and protein aggregates, protein nanoparticles, metal nanoparticles, silica nanoparticles, viruses, cellular vesicles and exosomes to name just a few. Here we describe application of NTA to the analysis of model nanospheres of ~100 nm in liquid suspension, the size being representative of the middle of the NTA working range. The technique described can be adapted for use with nearly all particulate materials with sizes between approximately 10 nm and 1 μm, with appropriate adjustments to instrument settings.

Transport and retention of engineered silver nanoparticles in carbonate-rich sediments in the presence and absence of soil organic matter

The transport and retention behavior of polymer- (PVP-AgNP) and surfactant-stabilized (AgPURE) silver nanoparticles in carbonate-dominated saturated and unconsolidated porous media was studied at the laboratory scale. Initial column experiments were conducted to investigate the influence of chemical heterogeneity (CH) and nano-scale surface roughness (NR) arising from mixtures of clean, positively charged calcium carbonate sand (CCS), and negatively charged quartz sands. Additional column experiments were performed to elucidate the impact of CH and NR arising from the presence and absence of soil organic matter (SOM) on a natural carbonate-dominated aquifer material. The role of the nanoparticle capping agent was examined under all conditions tested in the column experiments. Nanoparticle transport was well described using a numerical model that facilitated blocking on one or two retention sites. Results demonstrate that an increase in CCS content in the artificially mixed porous medium leads to delayed breakthrough of the AgNPs, although AgPURE was much less affected by the CCS content than PVP-AgNPs. Interestingly, only a small portion of the solid surface area contributed to AgNP retention, even on positively charged CCS, due to the presence of NR which weakened the adhesive interaction. The presence of SOM enhanced the retention of AgPURE on the natural carbonate-dominated aquifer material, which can be a result of hydrophobic or hydrophilic interactions or due to cation bridging. Surprisingly, SOM had no significant impact on PVP-AgNP retention, which suggests that a reduction in electrostatic repulsion due to the presence of SOM outweighs the relative importance of other binding mechanisms. Our findings are important for future studies related to AgNP transport in shallow unconsolidated calcareous and siliceous sands.

Is using nanosilver mattresses/pillows safe? A review of potential health implications of silver nanoparticles on human health

Human exposure to engineered nanoparticles has become inevitable in today's extensive commercial use and large-scale production of engineered nanoparticles. Even though several studies have characterised the exposure to nanomaterials during wakeful state (related to occupational exposures and exposures from commercially available particles), very few studies on human exposure during sleep exist. As the study of exposure to all possible nanomaterials during sleep is extensive, this study focuses on exposure to specifically silver nanoparticles which are present in beddings and mattresses. The reasoning behind the use of silver nanoparticles in bedding and related materials, possible routes of entry to various population groups in several sleep positions, exposure characterisation and toxicity potential of such silver nanoparticles are reviewed in this study. The toxicity potential of silver nanoparticles in vivo tests with relation to mammals and in vitro tests on human cells has been tabulated to understand the risks associated during oral, dermal and inhalation exposure to silver nanoparticles. The exposure to humans with regard to dermal absorption and oral intake has been summarised. Although potential inhalation exposure to silver nanoparticles is increasing, only a few studies address the possible toxic effect of inhaled silver particles. Determination of exposure to silver nanoparticles in beddings is a topic that has been less researched, and this review aims to provide background information for future research and help establish a comprehensive risk assessment during sleep in the times of increasing usage of nanoparticles in our daily activities. Despite the current limitations of our understanding, risk assessments must utilise the available data and apply extrapolation procedures in the face of uncertainty, in order to address the needs of regulatory programs. This would enable safe use of the antimicrobial properties of silver nanoparticles without negatively impacting human health. Until then, it would be better to adopt a conservative approach on the usage of silver nanoparticles in daily used commercial items.

Genetic and systemic toxicity induced by silver and copper oxide nanoparticles, and their mixture in Clarias gariepinus (Burchell, 1822)

Unanticipated increase in the use of silver (Ag) and copper oxide (CuO) nanoparticles (NPs) due to their antimicrobial properties is eliciting environmental health concern because of their coexistence in the aquatic environment. Therefore, we investigated the genetic and systemic toxicity of the individual NPs and their mixture (1:1) using the piscine micronucleus (MN) assay, haematological, histopathological (skin, gills and liver) and hepatic oxidative stress analyses [malondialdehyde (MDA), reduced glutathione (GSH), superoxide dismutase (SOD) and catalase (CAT)] in the African mud catfish, Clarias gariepinus. The fish were exposed to sublethal concentrations (6.25-100.00 mg/L) of each NP and their mixture for 28 days. Both NPs and their mixture induced significant (p < 0.05) increase in MN frequency and other nuclear abnormalities. There was significant decrease in haemoglobin concentration, red and white blood cell counts. Histopathological lesions observed include epidermal skin cells and gill lamellae hyperplasia and necrosis of hepatocytes. The levels of MDA, GSH and activities of SOD and CAT were impacted in C. gariepinus liver following the exposure to the NPs and their mixture. Interaction factor analysis of data indicates antagonistic genotoxicity and oxidative damage of the NPs mixture. These results suggest cytogenotoxic effects of Ag NPs, CuO NPs and their mixture via oxidative stress in Clarias gariepinus.

Phyllanthus emblica fruit extract stabilized biogenic silver nanoparticles as a growth promoter of wheat varieties by reducing ROS toxicity

The present study is focused on the biogenic synthesis of AgNPs (B-AgNPs) using fruit extract of Phyllanthus emblica L. and its effect (0, 5, 10, 25, 50 mg/L concentrations) on early seedling growth of two wheat varieties (HD-2967 and DBW-17). The prepared silver nanoparticles were characterized with several techniques such as UV-Vis spectroscopy, powder X-ray diffraction as well as high-resolution transmission electron microscopy. The capping of AgNPs by phytochemicals was confirmed by Fourier transforms infrared (FT-IR) spectroscopy. B-AgNPs, chemically synthesized AgNPs, chemically synthesized AgNPs+10% fruit extract and AgNO₃ salt were compared for phytotoxicity, based on growth parameters, ROS production, cytotoxicity assay and silver accumulation in two wheat varieties (HD-2967 and DBW-17). These effects were more pronounced in the variety HD-2967 over DBW-17 variety at 10 mg/L B-AgNPs exposure. Root cells viability of treated radicles was studied using Evans blue dye assay which suggest that 10 mg/L B-AgNPs was effective in promoting early seedling growth by decreasing ROS toxicity. Lower accumulation of Ag resulting in higher root cell viability than those of chemically synthesized AgNPs treated seedlings. The findings of the present study clearly indicate that phytochemicals capped AgNPs act as a growth promoter at lower concentrations by delivering a potent antioxidant during early seedling growth as compared to chemically synthesized AgNPs treated wheat seedlings.

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.

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.

Activated charcoal as a capture material for silver nanoparticles in environmental water samples

Silver nanoparticles (AgNPs), due to their antibacterial activity, have been incorporated into numerous consumer products. Their environmental impact however, is currently unclear. Uncertainties surround the concentration, fate, and effects of AgNPs in aquatic environments. This study examined the suitability of activated charcoal as a capture material for AgNPs from water. Samples of 100 ppb AgNPs were initially generated and exposed to activated charcoal for 24 h to examine the ability of charcoal to capture AgNPs. The decrease in Ag concentration was measured using ICP-MS. Following initial investigations, the surface area of the charcoal was increased firstly with a pestle and mortar and secondly by milling the charcoal using a ball mill. The increased surface area of the milled charcoal increased the capture of the AgNPs from 11.9% to 63.6% for the 100 ppb samples. Further investigations were carried out examining the effect on the capture of AgNP concentration (with concentration ranging from 10 to 100 ppb), particle coating and the effect of exposure time to the activated charcoal. The capture of AgNP increased with decreasing concentration. A hydrochloric acid (HCl) leaching procedure was also developed which successfully removed the captured silver allowing the fraction captured by the charcoal to be quantified with an average of 94.8% recovery. The results show that milled activated charcoal, can successfully capture AgNPs from water samples, and that therefore, activated charcoal may prove to be a cost effective material for the remediation of waters impacted by AgNP or other nano-wastes.

Occurrence, characterisation and fate of (nano)particulate Ti and Ag in two Norwegian wastewater treatment plants

Due to their widespread application in consumer products, elemental titanium (e.g., titanium dioxide, TiO₂) and silver (Ag), also in nanoparticulate form, are increasingly released from households and industrial facilities to urban wastewater treatment plants (WWTPs). A seven-day sampling campaign was conducted in two full-scale WWTPs in Trondheim (Norway) employing only primary treatment. We assessed the occurrence and elimination of Ti and Ag, and conducted size-based fractionation using sequential filtration of influent samples to separate particulate, colloidal and dissolved fractions. Eight-hour composite influent samples were collected to assess diurnal variations in total Ti and Ag influx. Measured influent Ti concentrations (up to 290 μg L^-1) were significantly higher than Ag (<0.15-2.1 μg L^-1), being mostly associated with suspended solids (>0.7 μm). Removal efficiencies ≥70% were observed for both elements, requiring for one WWTP to account for the high Ti content (∼2 g L^-1) in the flocculant. Nano- and micron-sized Ti particles were observed with scanning transmission electron microscopy (STEM) in influent, effluent and biosolids, while Ag nanoparticles were detected in biosolids only. Diurnal profiles of influent Ti were correlated to flow and pollutant concentration patterns (especially total suspended solids), with peaks during the morning and/or evening and minima at night, indicating household discharges as predominant source. Irregular profiles were exhibited by influent Ag, with periodic concentration spikes suggesting short-term discharges from one or few point sources (e.g., industry). Influent Ti and Ag dynamics were reproduced using a disturbance scenario generator model, and we estimated per capita loads of Ti (42-45 mg cap^-1 d^-1) and Ag (0.11 mg cap^-1 d^-1) from households as well as additional Ag load (14-22 g d^-1) from point discharge. This is the first study to experimentally and mathematically describe short-term release dynamics and dry-weather sources of emissions of Ti and Ag in municipal WWTPs and receiving environments.

The removal of silver nanoparticle by titanium tetrachloride and modified sodium alginate composite coagulants: floc properties, membrane fouling, and floc recycle

In this study, a modified sodium alginate (MSA) composited with TiCl₄ was used to treat the synthetic Ag nanoparticles (AgNPs) water in coagulation-ultrafiltration process. The floc properties and membrane fouling of TiCl₄ and MSA composite coagulants (TiCl₄ + MSA) were investigated by a laser diffraction instrument and ultrafiltration fouling model. The recycle of the AgNP-containing flocs was evaluated by XRD and photocatalytic experiments. The results showed that TiCl₄ + MSA could achieve better coagulation performance than TiCl₄ alone with AgNP and DOC removal up to 97 and 59% at the optimum condition (pH = 5 and dosage = 12 mg TiCl₄/L). TiCl₄ + MSA produced larger and looser flocs than TiCl₄ and TiCl₄ + SA composite coagulant (TiCl₄ + SA), which was benefit for the inhibition of subsequence membrane fouling. The strongly attached external fouling resistance (R_ef-s) and the reversible internal fouling resistance (R_if-r) of TiCl₄ + MSA were only 43 and 39.2% of those achieved by TiCl₄ at the optimal coagulation condition. Besides, the adopted AgCl-TiO₂ could be recycled from AgNP-containing flocs. And MSA could promote the form of TiO₂ anatase. It gives us a possible way for silver nanoparticle recycle.

Assessing the release of copper from nanocopper-treated and conventional copper-treated lumber into marine waters I: Concentrations and rates

Little is known about the release of metal engineered nanomaterials (ENMs) from consumer goods, including lumber treated with micronized copper. Micronized copper is a recent form of antifouling wood preservative containing nanosized copper particles for use in pressure-treated lumber. The present study investigated the concentrations released and the release rate of total copper over the course of 133 d under freshwater, estuarine, and marine salinity conditions (0, 1, 10, and 30‰) for several commercially available pressure-treated lumbers: micronized copper azole (MCA) at 0.96 and 2.4 kg/m3 , alkaline copper quaternary (ACQ) at 0.30 and 9.6 kg/m3 , and chromated copper arsenate (CCA) at 40 kg/m3 . Lumber was tested as blocks and as sawdust. Overall, copper was released from all treated lumber samples. Under leaching conditions, total release ranged from 2 to 55% of the measured copper originally in the lumber, with release rate constants from the blocks of 0.03 to 2.71 (units per day). Generally, measured release and modeled equilibrium concentrations were significantly higher in the estuarine conditions compared with freshwater or marine salinities, whereas rate constants showed very limited differences between salinities. Furthermore, organic carbon was released during the leaching and demonstrated a significant relationship with released copper concentrations as a function of salinity. The results indicate that copper is released into estuarine/marine waters from multiple wood treatments including lumber amended with nanoparticle-sized copper. Environ Toxicol Chem 2018;37:1956-1968. Published 2018 Wiley Periodicals Inc. on behalf of SETAC. This article is a US government work and, as such, is in the public domain in the United States of America.

Transport and retention of surfactant- and polymer-stabilized engineered silver nanoparticles in silicate-dominated aquifer material

Packed column experiments were conducted to investigate the transport and blocking behavior of surfactant- and polymer-stabilized engineered silver nanoparticles (Ag-ENPs) in saturated natural aquifer media with varying content of material < 0.063 mm in diameter (silt and clay fraction), background solution chemistry, and flow velocity. Breakthrough curves for Ag-ENPs exhibited blocking behavior that frequently produced a delay in arrival time in comparison to a conservative tracer that was dependent on the physicochemical conditions, and then a rapid increase in the effluent concentration of Ag-ENPs. This breakthrough behavior was accurately described using one or two irreversible retention sites that accounted for Langmuirian blocking on one site. Simulated values for the total retention rate coefficient and the maximum solid phase concentration of Ag-ENPs increased with increasing solution ionic strength, cation valence, clay and silt content, decreasing flow velocity, and for polymer-instead of surfactant-stabilized Ag-ENPs. Increased Ag-ENP retention with ionic strength occurred because of compression of the double layer and lower magnitudes in the zeta potential, whereas lower velocities increased the residence time and decreased the hydrodynamics forces. Enhanced Ag-ENP interactions with cation valence and clay were attributed to the creation of cation bridging in the presence of Ca²⁺. The delay in breakthrough was always more pronounced for polymer-than surfactant-stabilized Ag-ENPs, because of differences in the properties of the stabilizing agents and the magnitude of their zeta-potential was lower. Our results clearly indicate that the long-term transport behavior of Ag-ENPs in natural, silicate dominated aquifer material will be strongly dependent on blocking behavior that changes with the physicochemical conditions and enhanced Ag-ENP transport may occur when retention sites are filled.

Detection of nanoparticles in Dutch surface waters

Nano-enabled consumer products are a likely source of nanoparticles in the environment and a number of studies have shown the release of nanoparticles from commercial products. Predicted environmental concentrations have been calculated but there is a need for real measurement data to validate these calculations. However, the detection of engineered nanoparticles in environmental matrices is challenging because of the low predicted environmental concentrations which may be in the ng/L range. In this study nanosized Ag, CeO₂ and TiO₂ have been measured in multiple surface water samples collected along the rivers Meuse and IJssel in the Netherlands using single-particle ICP-MS as measurement technique. Validation of the analytical method showed its capability to quantitatively determine nanoparticles at low concentrations. Concentration mass detection limits for Ag, CeO₂ and TiO₂ were 0.1ng/L, 0.05ng/L and 10ng/L respectively. Size detection limits for Ag, CeO₂ and TiO₂ were 14, 10 and 100nm. The results of the study confirm the presence of nano-sized Ag and CeO₂ particles and micro-sized TiO₂ particles in these surface waters. n-Ag was present in all samples in concentrations ranging from 0.3 to 2.5ng/L with an average concentration of 0.8ng/L and an average particle size of 15nm. n-CeO₂ was found in all samples with concentrations ranging from 0.4 to 5.2ng/L with an average concentration of 2.7ng/L and an average particle size of 19nm. Finally, μ-TiO₂ was found in all samples with a concentration ranging from 0.2 to 8.1μg/L with an average concentration of 3.1μg/L and an average particle size of 300nm. The particle sizes that were found are comparable with the particle sizes that are used in nanomaterial applications and consumer products. The nanoparticle concentrations confirm the predicted environmental concentrations values in water for all three nanoparticles.

Phytotoxic effects of silver nanoparticles in tobacco plants

The small size of nanoparticles (NPs), with dimensions between 1 and 100 nm, results in unique chemical and physical characteristics, which is why they are implemented in various consumer products. Therefore, an important concern is the potential detrimental impact of NPs on the environment. As plants are a vital part of ecosystem, investigation of the phytotoxic effects of NPs is particularly interesting. This study investigated the potential phytotoxicity of silver nanoparticles (AgNPs) on tobacco (Nicotiana tabacum) plants and compared it with the effects of the same AgNO3 concentrations. Accumulation of silver in roots and leaves was equally efficient after both AgNP and AgNO3 treatment, with predominant Ag levels found in the roots. Exposure to AgNPs did not result in elevated values of oxidative stress parameters either in roots or in leaves, while AgNO3 induced oxidative stress in both plant tissues. In the presence of both AgNPs and AgNO3, root meristem cells became highly vacuolated, which indicates that vacuoles might be the primary storage target for accumulated Ag. Direct AgNP uptake by root cells was confirmed. Leaf ultrastructural studies revealed changes mainly in the size of chloroplasts of AgNP-treated and AgNO3-treated plants. All of these findings indicate that nano form of silver is less toxic to tobacco plants than silver ions.

Toxicity of silver nanoparticles to Arabidopsis: Inhibition of root gravitropism by interfering with auxin pathway

Impacts of polyvinylpyrrolidine-coated silver nanoparticles (AgNPs) on root gravitropism in Arabidopsis thaliana were investigated at the physiological, cellular, and molecular levels. Our results showed that AgNPs were taken up by the root and primarily localized at the cell wall and intercellular spaces. Root gravitropism was inhibited by exposure to AgNPs, and the inhibition in root gravitropism caused by exposure to AgNPs exhibited a dose-response relationship. Auxin accumulation was reduced in the root tips because of exposure to AgNPs. However, increased indole-3-acetic acid level could not rescue the inhibition of root gravitropism. Real-time polymerase chain reaction showed significant downregulation of expression of auxin receptor-related genes, which is the TIR1/AFB family of F-box proteins including AFB1, AFB2, AFB3, AFB5, and TIR1. Therefore, the present study suggests that AgNPs have toxicity to the model plant A. thaliana as shown by inhibition of root gravitropism along with a reduction in auxin accumulation and expression of auxin receptors. Environ Toxicol Chem 2017;36:2773-2780. © 2017 SETAC.

Exposure to silver nanoparticles produces oxidative stress and affects macromolecular and metabolic biomarkers in the goodeid fish Chapalichthys pardalis

Silver nanoparticles (AgNPs) are the most commercialized nanomaterial worldwide, mainly due to their microbicidal activity. Although, AgNPs have been shown to be toxic to aquatic species, their effect on endemic fish, like Goodeidae, has not been demonstrated. Endemic species are under strong pressures by anthropogenic contamination and destruction of their habitat; therefore, we studied adult Chapalichthys pardalis, an endemic fish of Mexico. We evaluated the toxic effect of AgNPs through oxidative stress, macromolecular and metabolic biomarkers. We determined the LC₅₀ (96h) and performed subchronic tests (21days) using sublethal AgNPs concentrations (equivalent to CL₁ and CL₁₀). At the end of the bioassay, we quantified 10 stress biomarkers in the liver, gills, and muscle, including the antioxidant enzymes (superoxide dismutase [SOD], catalase [CAT], and glutathione [GPx]), thiobarbituric acid reactive species (TBARS), protein oxidation (CO), macromolecules (proteins, lipids, and carbohydrates), and metabolites (glucose and lactate). In addition, we determined the integrated biomarkers response (IBR). LC₅₀ was of 10.32mgL^-1. Results of subchronic exposure (21days) revealed that AgNPs produce oxidative stress in C. pardalis adults, as evidenced by a diminution in antioxidant enzymes activity and an increase in TBARS and oxidized proteins. AgNPs also diminished levels of macromolecules and generated a high-energy consumption, reflected in the reduction of glucose levels, although lactate levels were not altered. The IBR analysis evidenced that the largest effect was produced in organisms exposed to LC₁₀, being the liver and gills the organs with the greatest damage. Results demonstrated that exposure to AgNPs induces acute and chronic toxic effects on C. pardalis and forewarns about the impact that these nanomaterials can exert on these ecologically relevant aquatic organisms.

Uptake, Accumulation and Toxicity of Silver Nanoparticle in Autotrophic Plants, and Heterotrophic Microbes: A Concentric Review

Nanotechnology is a cutting-edge field of science with the potential to revolutionize today's technological advances including industrial applications. It is being utilized for the welfare of mankind; but at the same time, the unprecedented use and uncontrolled release of nanomaterials into the environment poses enormous threat to living organisms. Silver nanoparticles (AgNPs) are used in several industries and its continuous release may hamper many physiological and biochemical processes in the living organisms including autotrophs and heterotrophs. The present review gives a concentric know-how of the effects of AgNPs on the lower and higher autotrophic plants as well as on heterotrophic microbes so as to have better understanding of the differences in effects among these two groups. It also focuses on the mechanism of uptake, translocation, accumulation in the plants and microbes, and resulting toxicity as well as tolerance mechanisms by which these microorganisms are able to survive and reduce the effects of AgNPs. This review differentiates the impact of silver nanoparticles at various levels between autotrophs and heterotrophs and signifies the prevailing tolerance mechanisms. With this background, a comprehensive idea can be made with respect to the influence of AgNPs on lower and higher autotrophic plants together with heterotrophic microbes and new insights can be generated for the researchers to understand the toxicity and tolerance mechanisms of AgNPs in plants and microbes.