Silver nanoparticle behaviour in lake water depends on their surface coating

Human health risk assessment and uncertainty analysis of silver nanoparticles in water

Despite frequent detection in environmental waters, literature which quantifies the health risk of silver nanoparticles (Ag NPs) through oral ingestion is scarce. This study compiled literature data to find the removal of Ag NPs from different treatment schemes (i.e., natural, engineered, or hybrid). Ag NP concentrations were found either in surface water or in groundwater based on where the effluent of treatment schemes was discharged, i.e., either in surface water or in groundwater. Monte-Carlo simulation was carried out for probabilistic assessment of health risks for children for two hypothetical exposure scenarios: (a) ingesting river water while swimming and (b) drinking groundwater. Bio-accessible fraction, dietary metal adsorption factor, and concentrations of silver ions were incorporated to simulate realistic situations. Different treatment schemes were ranked for their nanoparticles' removal efficiency with respect to (i) exceedance probability from guideline value and (ii) health risk to children. Hybrid treatment combinations, i.e., conventional primary and secondary treatment units followed by nature-based units (constructed wetlands and soil aquifer treatment), were ranked the best. The health risk value was found to be less than 1, with the 99th percentile value less than 10-3 in all cases. The maximum allowable concentration of Ag NPs was found to be as low as 1.43 mg/L for groundwater, suggesting probable potential for risk. Uncertainty analysis revealed that the uncertainty of the influent NPs concentration in raw wastewater contributes > 99% to the variance of the hazard index. The results of this work indicate that the use of natural treatment technologies with existing engineered treatments provides higher nanoparticle removal from wastewater without the requirement of any tertiary treatment unit.

Transformation of Mercuric Ions to Mercury Nanoparticles in Diatom Chaetoceros curvisetus

Particulate HgS play crucial roles in the mercury (Hg) cycle. Approximately 20-90% of dissolved Hg can be transformed into particulate HgS by algae. However, detailed knowledge regarding these particles, including sizes and distribution, remains unknown. The present study explored the formation, distribution, and excretion of mercury nanoparticles (HgNPs) in diatom Chaetoceros curvisetus. The results demonstrated that HgNPs (HgS nanoparticles, 29.6-66.2 nm) formed intracellularly upon exposure to 5.0-100.0 μg L-1 Hg(II), accounting for 12-27% of the total Hg. HgNP concentrations significantly increased with increasing intracellular Hg(II) concentrations, while their sizes remained unaffected. HgNPs formed intracellularly and partly accumulated inside the cells (7-11%). Subsequently, the sizes of intracellular HgNPs gradually decreased to facilitate expulsion, 21-50% of which were excreted. These suggested the vital roles of HgNPs in comprehending marine Hg fate. Their unique physicochemical properties and bioavailability would influence Hg biotransformation in the ocean. Additionally, both intracellular and extracellular HgNPs contributed to Hg settling with cells, ultimately leading to Hg burial in sediments. Overall, these findings further deepened our understanding of Hg biotransformation and posed challenges in accurately estimating marine Hg flux and Hg burial.

Metagenomic analysis reveals the short-term influences on conjugation of blaNDM-1 and microbiome in hospital wastewater by silver nanoparticles at environmental-related concentration

Hospital wastewater contains large amounts of antibiotic-resistant bacteria and serves as an important reservoir for horizontal gene transfer (HGT). However, the response of the microbiome in hospital wastewater to silver remains unclear. In this study, the short-term impacts of silver on the microbiome in hospital wastewater were investigated by metagenome next-generation sequencing. The influence of silver on the conjugation of plasmid carrying bla_NDM-1 was further examined. Our results showed that in hospital wastewater, high abundances of antibiotic resistance genes (ARGs) were detected. The distribution tendencies of certain ARG types on chromosomes or plasmids were different. Clinically important ARGs were identified in phage-like contigs, indicating potential transmission via transduction. Pseudomonadales, Enterobacterales, and Bacteroidales were the major ARG hosts. Mobile genetic elements were mainly detected in plasmids and associated with various types of ARGs. The binning approach identified 29 bins that were assigned to three phyla. Various ARGs and virulence factors were identified in 14 and 11 bins, respectively. MetaCHIP identified 49 HGT events. The transferred genes were annotated as ARGs, mobile genetic elements, and functional genes, and they mainly originated from donors belonging to Bacteroides and Pseudomonadales. In addition, 20 nm AgNPs reduced microbial diversity and enhanced the relative abundance of Acinetobacter. The changes induced by 20 nm AgNPs included increases in the abundances of ARGs and genes involved lipid metabolism pathway. Conjugation experiments showed that Ag⁺ and 20 nm AgNPs caused 2.38-, 3.31-, 4.72-, and 4.57-fold and 1.46-, 1.61-, 3.86-, and 2.16-fold increases in conjugation frequencies of plasmid with bla_NDM-1 at 0.1, 1, 10, and 100 μg/L, respectively. Our findings provide insight into the response of the microbiome in hospital wastewater to silver, emphasize the adaptation capability of Acinetobacter inhabiting hospitals against adverse environments, and highlight the promotion of silver for antibiotic resistance.

Interaction of silver nanoparticles with marine/lake snow in early formation stage

Marine and lake snows play an important ecological role in aquatic systems, and recent researches have also revealed their interactions with various pollutants. In this paper, the interaction of silver nanoparticles (Ag-NPs), a typical nano-pollutant, with marine/lake snow in the early formation stage was investigated by roller table experiments. Results indicated Ag-NPs promoted the accumulation of larger marine snow flocs while inhibited the development of lake snow. The promotion effect of AgNPs might be attributed to their oxidative dissolution into low-toxic silver chloride complexes in seawater, and the subsequent incorporation into marine snow, which would enhance the rigidity and strength of larger flocs and favor the development of biomass. Conversely, Ag-NPs mainly existed in the form of colloidal nanoparticles in lake water and their strong antimicrobial effect suppressed the growths of biomass and lake snow. In addition, Ag-NPs could also affect the microbial community of marine/lake snow, including impact on microbial diversity, and elevation on abundances of extracellular polymeric substances (EPS) synthesis genes and silver resistance genes. This work has deepened our understanding of the fate and ecological effect of Ag-NPs via the interaction with marine/lake snow in aquatic environments.

Assessment by a multi-technique approach of PtNPs' transformations in waters under relevant environmental concentrations and conditions

Once released to the environment, platinum nanoparticles (PtNPs) can undergo different transformations and are affected by several environmental conditions. An only analytical technique cannot provide all the information required to understand those complex processes, so new analytical developments are demanded. In the present work, the potential of asymmetric flow field flow fractionation hyphenated to inductively coupled plasma mass spectrometry (AF4-ICP-MS) for these studies, has been investigated, and classical dynamic and electrophoretic light scattering (DLS & ELS) have been used as complementary techniques. The role of ionic strength, ionic water composition, and natural organic matter (NOM) in the behaviour of PtNPs of different sizes (5 and 50 nm) has been specifically studied. Dynamic and electrophoretic light scattering have been used to track changes in the hydrodynamic diameters (d_h) and polydispersity index (PdI) for 50 nm PtNPs (5 nm cannot be studied by DLS) and Z-potential values (for all sizes) to monitor aggregation. AF4-ICP-MS has been also employed to have a solid insight of aggregation at low environmental concentrations for different sizes of PtNPs simultaneously. The information gathered with those techniques was useful to observe changes as the ionic strength increases, which induces aggregation. Also, it was observed that this aggregation process was attenuated in the presence of organic matter. This approach, based on complementary analytical techniques, is needed for a comprehensive study of such complex interactions of NPs in the environment. AF4-ICP-MS is still under-exploited but shows a great potential for this purpose, especially low size NPs and concentrations.

Aquatic organisms modulate the bioreactivity of engineered nanoparticles: focus on biomolecular corona

The increased use of nanoparticle (NP)-enabled materials in everyday-life products have raised concerns about their environmental implications and safety. This motivated the extensive research in nanoecotoxicology showing the possibility that NPs could cause harm to the aquatic organisms if present at high concentrations. By contrast, studies dealing with influence that organisms could exert on the fate and thus effects of NPs are still very rare. Drawing on the existing up-to-date knowledge we critically discuss the formation of biomolecular corona as one of the mechanisms by which organisms exerted control on the NPs fate in the aquatic and biotic environments. We focused the formation of corona by exogeneous and endogenous biomolecules and illustrated the discussion with the specific example of phytoplankton and aquatic invertebrate species. We highlighted the necessity to incorporate the concept of biomolecular corona within more general framework considering the feedback of aquatic organisms and the control they exert in shaping the fate and impact of NPs in the aquatic and biological environment. In our view such broader perspective will contribute to get novel insights into the drivers of environmental transformations of NPs and their mechanisms, which are important in environmental risk assessment.

Self-defense mechanisms of microorganisms from the antimicrobial effect of silver nanoparticles: Highlight the role of extracellular polymeric substances

Silver nanoparticles (AgNPs) are nowadays widely utilized in various fields due to their unique antimicrobial properties. Extracellular polymeric substances (EPS) excreted by microorganisms might affect the transformations and antibacterial efficacy of AgNPs. In the present study, the effects of EPS released by Escherichia coli (E. coli) on the dissolution and sulfidation of AgNPs as well as the associated growth inhibition to E. coli were systematically investigated. The formation of EPS-corona caused the reduced exposure of (111) facets of AgNPs due to the preferential binding with aromatic protein components in EPS. The EPS inhibited AgNPs dissolution, while facilitated reductive transformation of the released Ag⁺ to Ag⁰ under simulated sunlight. Additionally, EPS enhanced the colloidal stability and reduced electrostatic repulsive of AgNPs, which favored the access of sulfide and significantly promoted the sulfidation of AgNPs under simulated sunlight, further reducing the available dissolved Ag⁺ ions. Consequently, the EPS relieved the antibacterial activity of AgNPs to E. coli. These findings highlight the importance of microbial EPS in the transformations and bactericidal effect of AgNPs, which provide clues for the development of AgNPs-based antibacterial strategies.

A critical review on the role of abiotic factors on the transformation, environmental identity and toxicity of engineered nanomaterials in aquatic environment

Engineered nanomaterials (ENMs) are at the forefront of many technological breakthroughs in science and engineering. The extensive use of ENMs in several consumer products has resulted in their release to the aquatic environment. ENMs entering the aquatic ecosystem undergo a dynamic transformation as they interact with organic and inorganic constituents present in aquatic environment, specifically abiotic factors such as NOM and clay minerals, and attain an environmental identity. Thus, a greater understanding of ENM-abiotic factors interactions is required for an improved risk assessment and sustainable management of ENMs contamination in the aquatic environment. This review integrates fundamental aspects of ENMs transformation in aquatic environment as impacted by abiotic factors, and delineates the recent advances in bioavailability and ecotoxicity of ENMs in relation to risk assessment for ENMs-contaminated aquatic ecosystem. It specifically discusses the mechanism of transformation of different ENMs (metals, metal oxides and carbon based nanomaterials) following their interaction with the two most common abiotic factors NOM and clay minerals present within the aquatic ecosystem. The review critically discusses the impact of these mechanisms on the altered ecotoxicity of ENMs including the impact of such transformation at the genomic level. Finally, it identifies the gaps in our current understanding of the role of abiotic factors on the transformation of ENMs and paves the way for the future research areas.

Emerging investigator series: metal nanoparticles in freshwater: transformation, bioavailability and effects on invertebrates

MNPs may undergo different environmental transformations in aquatic systems, consequently changing their mobility, bioavailability and toxicity to freshwater invertebrates.

Silver Nanoparticles and Ionic Silver Separation Using a Cation-Exchange Resin. Variables Affecting Their Separation and Improvements of AgNP Characterization by SP-ICPMS

Silver nanoparticles (AgNPs) are frequently found in everyday products and, as a consequence, their release into the environment cannot be avoided. Once in aquatic systems, AgNPs interact with natural constituents and undergo different transformation processes. Therefore, it is important to characterize and quantify AgNPs in environmental waters in order to understand their behavior, their transformation, and their associated toxicological risks. However, the coexistence of ionic silver (Ag⁺) with AgNPs in aquatic systems is one of the greatest challenges for the determination of nanosilver. Ion-exchange resins can be used to separate Ag⁺ from AgNPs, taking advantage of the different charges of the species. In this work, Dowex 50W-X8 was used to separate Ag⁺ and AgNPs in order to easily determine AgNP concentrations using inductively coupled plasma optical emission spectroscopy. The separation methodology was successfully applied to river water samples with different ratios of Ag⁺ and AgNPs. However, the methodology is not useful for wastewater samples. The described methodology also demonstrated an improvement in the determination of the particle size of AgNPs present in river waters by single particle inductively coupled plasma mass spectrometry when a significant amount of Ag⁺ is also present.

Assessment of Nanopollution from Commercial Products in Water Environments

The use of nano-enabled products (NEPs) can release engineered nanomaterials (ENMs) into water resources, and the increasing commercialisation of NEPs raises the environmental exposure potential. The current study investigated the release of ENMs and their characteristics from six commercial products (sunscreens, body creams, sanitiser, and socks) containing nTiO2, nAg, and nZnO. ENMs were released in aqueous media from all investigated NEPs and were associated with ions (Ag+ and Zn2+) and coating agents (Si and Al). NEPs generally released elongated (7-9 × 66-70 nm) and angular (21-80 × 25-79 nm) nTiO2, near-spherical (12-49 nm) and angular nAg (21-76 × 29-77 nm), and angular nZnO (32-36 × 32-40 nm). NEPs released varying ENMs' total concentrations (ca 0.4-95%) of total Ti, Ag, Ag+, Zn, and Zn2+ relative to the initial amount of ENMs added in NEPs, influenced by the nature of the product and recipient water quality. The findings confirmed the use of the examined NEPs as sources of nanopollution in water resources, and the physicochemical properties of the nanopollutants were determined. Exposure assessment data from real-life sources are highly valuable for enriching the robust environmental risk assessment of nanotechnology.

Silver nanoparticles in aquatic sediments: Occurrence, chemical transformations, toxicity, and analytical methods

Sediments represent the major sink for released silver nanoparticles (AgNPs) in aquatic environments. It is well known that the environmental behavior and toxicity of AgNPs in sediments are governed by their specific chemical species instead of their total concentration. This review focuses on various chemical transformations of AgNPs in sediments, which have not been well outlined before. We first outline the concentrations of AgNPs in sediments. The predicted concentrations are 1-5 µg kg^-1 in most model studies. Once enter sediments, AgNPs are transformed to different species (e.g., Ag₂S, Ag-humic substance complexes, AgCl, and Ag⁺) during multiple chemical transformations, such as oxidative dissolution, sulfidation, chlorination, and complexation. Those chemical behaviors mitigate the toxicity of AgNPs by reducing their availability and decreasing Ag⁺ release. Benthic invertebrates and microbes are prone to be affected by AgNPs. AgNPs are found to be accumulated in sediment-dwelling organisms and transferred to higher trophic levels along the food web. Besides X-ray absorption spectroscopy, reliable separation procedures coupled with detection techniques, are powerful tools that characterize the speciation of AgNPs in sediments. More research is needed to investigate diverse chemical transformations in various sediments through development of novel techniques and mathematical models.

Simple Method for the Extraction and Determination of Ti-, Zn-, Ag-, and Au-Containing Nanoparticles in Sediments Using Single-Particle Inductively Coupled Plasma Mass Spectrometry

The quantitative analysis of nanoparticles (NPs) in the environment is significantly important for the exploration of the occurrence, fate, and toxicological behaviors of NPs and their subsequent environmental risks. Some protocols have been recommended for the separation and extraction of NPs that are potentially dispersed in complex environmental matrixes, e.g. sediments and soils, but they remain limited. However, certain factors that may significantly affect extraction efficiency have not been comprehensively explored. In this study, on the basis of the single-particle inductively coupled plasma mass spectrometry (SP-ICP-MS) technique, a simple standardized protocol for separating and analyzing metal-containing NPs in sediment samples was developed. On consideration of the extraction efficiencies of indigenous NPs (Ti- and Zn-NPs) and spiked NPs (Ag- and Au-NPs) in sediments, sedimentation with a settling time of 6 h is recommended for the separation of NPs and large particles, and the optimal sediment to water ratio, ultrasonication power, time, and temperature are 0.4 mg/mL, 285 W, 20 min, and 15-25 °C, respectively. On the basis of the optimized method, the recoveries of spiked Ag and Au-NPs were 71.4% and 81.1%, respectively. The applicability of the optimal protocols was verified, and TOC was proved to be an important factor controlling the separation and extraction of NPs in environmental samples. The separation and extraction of NPs in elevated TOC samples can be improved by increasing the ultrasonication power, time, and temperature.

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

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

Emission of (chlorinated) reclaimed water into a Mediterranean River and its related effects to the dissolved organic matter fingerprint

High resolution mass spectrometry (HRMS) was used to investigate the dissolved organic matter (DOM) profile of a reclamation water trial performed in the Llobregat River (Spain) during summer 2019. 23 water samples (including tertiary effluents, surface river and drinking water), taken during five sampling campaigns, were analyzed and their van Krevelen diagrams were compared. The reclaimed water fingerprint was substantially different from the natural profile of the river, showing a higher number of heteroatomic signals (i.e. CHON, CHOS and CHONS) and the presence of high-intensity S-containing features. As a result, reclaimed water discharge introduced substantial changes in the signature of the lignin-like and soot-like compositional-spaces of the river DOM fingerprint. However, the effect on the drinking water fingerprint was, ultimately, very limited. Only a limited number of features (up to 34) were detected as exclusively emitted with the reclaimed water. During the second phase of the trial, the tertiary effluent was chlorinated for disinfection purposes. This process triggered the unexpected formation of a myriad of new features along the Llobregat River. Notably, 109 brominated/chlorinated features were detected, probably generated as a consequence of the photochemical decay of the emitted chloramines and their free-radical reaction with DOM, and three of them persisted in the final drinking water. The formation of halogenated species in situ in the Llobregat River entails uncertainty at ecological and water treatment levels and should be studied carefully to fully disclose the risks associated to wastewater effluent disinfection.

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.

A method based on asymmetric flow field flow fractionation hyphenated to inductively coupled plasma mass spectrometry for the monitoring of platinum nanoparticles in water samples

An analytical methodology based on asymmetric flow field flow fractionation hyphenated to inductively coupled plasma mass spectrometry (AF4-ICP-MS) has been developed for monitoring citrate coated platinum nanoparticles (PtNPs) of different sizes (5, 30, and 50 nm) in water samples. Several factors have been optimized, such as carrier composition, AF4 separation program, focusing step or cross flow values. Under the optimum conditions, PtNPs can be fractionated in about 30 min in a single run with quantitative recoveries of the membrane (100 ± 7%, n = 5). The optimized method has been successfully applied to study transformations, not only in size but also surface modifications, of PtNPs in synthetic and natural water samples over time. The effect of organic matter was specifically studied, and it was found to be a critical parameter. The analytical strategy followed in this work can be very useful to develop further environmental studies involving PtNPs.

A modified coagulation-ultrafiltration process for silver nanoparticles removal and membrane fouling mitigation: The role of laminarin

Silver nanoparticles (AgNPs) in surface water are highly toxic to humans and difficult to remove due to their adsorption to humic acid (HA). In this study, laminarin (LA) was used as a coagulant aid in a coagulation-ultrafiltration (C-UF) system to improve AgNPs-HA removal efficiency. C-UF efficiency, membrane flux, and flocs properties were investigated to explore the AgNPs-HA removal mechanism and membrane fouling. Results showed that when poly aluminum chloride (PAC) was dosed with LA, AgNPs-HA removal was 10-15% higher than when using PAC alone. The C-UF system using only PAC improved the AgNPs-HA removal efficiency through increased coagulation but resulted in membrane fouling. LA application helped mitigate membrane fouling, and the highest normalized permeate flux and smallest resistance values (0.573 and 2.180 × 10¹⁰ m^-1, respectively) were achieved when 0.1 mg/L of LA was applied with 5 mg/L of PAC. The alleviating mechanism was related to flocs with large sizes and small fractal dimension (D_f) values, generating a cake layer with porous morphology. This cake layer was easily removed by flushing and backwashing, which resulted in minimal resistance and fouling of the UF membrane.

Roles of pH, cation valence, and ionic strength in the stability and aggregation behavior of zinc oxide nanoparticles

The effects of pH, cation valence, and ionic strength (IS) on the stability and aggregation behavior of zinc oxide nanoparticles (ZnO NPs) were investigated in this study. Results showed that ZnO NPs were most prone to aggregation at the isoelectric point (pH = 8.7), with an aggregation rate (ΔD/Δt) of 30.1. ZnO NPs showed a greater propensity for dissolution at lower pH (pH < 7), and Zn²⁺ was more rapidly released into the aqueous phase in acidic solutions than neutral or alkaline conditions. The C/C₀ of ZnO NPs was about 21.56% and remained stable in acidic solution of pH 4.0. Additionally, slow sedimentation with a C/C₀ ratio of 95.0% was observed due to an increase in repulsive interactions between nanoparticles under pH = 10. The effect of cations on the ΔD/Δt of ZnO NPs decreased in strength as follows: Ca²⁺ > Mg²⁺ > K⁺ > Na⁺. High-valence metal cations (Ca²⁺, Mg²⁺) were more competitively adsorbed onto the surface of ZnO NPs with a hydrogen atom due to Coulomb's law, increasing the zeta potential and stabilizing the suspension of ZnO NPs at IS < 10 mM. Furthermore, compression of the electric double layer (EDL) became stronger than electrostatic adsorption with increasing IS, reaching a maximum ΔD/Δt of 23.3 (Ca²⁺, pH = 7, IS = 1 M). The C/C₀ ratio of ZnO NPs decreased from 100% to 56.5% (Na⁺), 52.2% (K⁺), 45.2% (Mg²⁺), and 40.1% (Ca²⁺) at pH = 7 and an IS of 0.5 M. In addition to the cation valence, the hydration forces and ionic radii of the metal cations might be other factors that affected the interactions of metal cations with ZnO NPs. Finally, the total interaction energy between ZnO NPs was calculated using the Derjaguin-Landau-Verwey-Overbeek (DLVO) theoretical formula, and the calculated results were in agreement with the experimental outcomes under various aquatic environmental conditions.

A voltammetric investigation of the sulfidation of silver nanoparticles by zinc sulfide

Silver nanoparticles (Ag NPs) are among the most common forms of nanoparticles in consumer products, yet the environmental implications of their widespread use remain unclear due to uncertainties about their fate. Because sulfidation of Ag NPs results in the formation of a stable silver sulfide (Ag₂S) product, it is likely an important removal mechanism of bioavailable silver in natural waters. In addition to sulfide, the complete conversion of Ag NPs to Ag₂S will require dissolved oxygen or some other oxidant so dispersed metal sulfides may be an important pool of reactive sulfide for such reactions in oxygenated systems. The reaction of Ag NPs with zinc sulfide (ZnS) was investigated using a voltammetric method, anodic stripping voltammetry (ASV). ASV provided sensitive, in situ measurements of the release of zinc (Zn²⁺) cations resulting from the cation exchange reaction between Ag NPs and ZnS. The effects of Ag NP size and surface coatings on the initial rates of sulfidation by ZnS were examined. Sulfidation of smaller Ag NPs generally occurred faster and to a greater extent due to their larger relative surface areas. Sulfidation of Ag NPs capped by citrate and lipoic acid occurred more rapidly relative to polyvinylpyrrolidone (PVP) and branched polyethylene (BPEI). This study demonstrates the utility of voltammetry for such investigations and provides insights into important factors controlling Ag NP sulfidation such as availability of dissolved oxygen, Ag NP size and Ag NP surface coating. Furthermore, this work demonstrates the importance of cation exchange reactions between silver and metal sulfides, and how the environmental release of Ag NPs could alter the speciation of other metals of environmental significance.

The toxicity of non-aged and aged coated silver nanoparticles to the freshwater shrimp Paratya australiensis

Nanoparticles (NPs) transform in the environment which result in alterations to their physicochemical properties. However, the effects of aging on the toxicity of NPs to aquatic organisms remain to be determined. Further the reports that have been published present contradictory results. The aim of this study was to examine the stability of differently coated silver nanoparticles (AgNPs) in media and the influence of aging of these NP on potential toxicity to freshwater shrimp Paratya australiensis. Coating-dependent changes in the stability of AgNP were observed with aging. Curcumin (C) coated AgNPs were stable, while tyrosine (T) coated AgNPs and epigallocatechin gallate (E) coated AgNPs aggregated in the P. australiensis medium. Increased lipid peroxidation and catalase activity was noted in P. australiensis exposed to AgNPs, suggesting oxidative stress was associated with NP exposure. The enhanced oxidative stress initiated by aged C-AgNPs suggests that aging of these NPs produced different toxicological responses. In summary, data suggest that coating-dependent alterations in NPs, together with aging affect both persistence and subsequent toxicity of NPs to freshwater organisms. Thus, the coating-dependent fate and toxicity of AgNPs together with the effect of their aging need to be considered in assessing the environmental risk of AgNPs to aquatic organisms.

Lipoic acid capped silver nanoparticles: a facile route to covalent protein capping and oxidative stability within biological systems

Covalent attachment of human serum albumin protein to the surface of spherical lipoic acid capped silver nanoparticles results in the generation of stable nanoparticle–protein hybrids with well defined surface composition. Enhanced stability towards oxidation and in the presence of complex media with high ionic strength, holds promise towards the use of these conjugates as therapeutics in biomedical applications and sensing.

Covalent attachment of human serum albumin protein to the surface of spherical lipoic acid capped silver nanoparticles results in the generation of stable nanoparticle–protein hybrids with well defined surface composition.

A brief overview on nano-sized materials used in the topical treatment of skin and soft tissue bacterial infections

Introduction: Skin and soft tissue infections are a significant clinical problem that can happen anywhere on the body. Bacteria are the most common cause of skin and soft tissue infections in humans. Despite the fact that there is a lot of antimicrobial agents and antibiotics for elucidating bacterial infections, the prevention and control of infectious diseases continue to be one of the greatest challenges for public health worldwide. At the present time, an alarming increase in multidrug resistance instantly requests to find suitable alternatives to current antibiotics. Therefore, drug resistance has been attempted to be resolved by the development of new classes of antimicrobial agents or targeted delivery systems for antibacterial drugs using nanotechnology.Area covered: The present review summarizes the emerging topical efforts to support the use of nano-sized materials as a new opportunity to combat today's skin infectious diseases.Expert opinion: Nano-sized materials can overcome the stratum corneum barrier and deliver drugs specifically to bacterial skin infections with trivial side effects. Depending on the physicochemical characteristics of nano-scaled materials, they can specifically be selected to target bacterial pathogens and also to get into the skin layers. These systems can overcome the antibiotic-resistance mechanisms and help us to the design of novel topical formulations that will make administration of antibacterial compounds safer, easier and more convenient.

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.

Behavior, remediation effect and toxicity of nanomaterials in water environments

In recent years, nanotechnology has been developing continuously. Due to their advantageous huge specific surface areas, microinterface characteristics, remediation ability and potential environmental risks, nanomaterials have become a hot topic in the field of environmental research. With the mass production and use of nanomaterials, they will inevitably be discharged or leaked into the water environment. In this paper, we will describe some typical nanomaterials, such as nanoscale zero valent iron (nZVI), graphene nanomaterials (GNMs), TiO₂ nanoparticles (NPs), ZnO NPs, Fe₃O₄ NPs, carbon nanotubes (CNTs), Ag NPs, and other nanomaterials in water environments, focusing on the positive and negative effects of some nanomaterials in water environments. The remediation function and the impact of nanomaterials in water environments, including behavior of nanomaterials and their toxicity to aquatic organisms will be discussed. This will be of great significance for our subsequent research on nanomaterials.

Soil dissolved organic matter affects mercury immobilization by biogenic selenium nanoparticles

Molecular weight (MW) heterogeneity is a fundamental property of dissolved organic matter (DOM) in soil, which has been demonstrated to influence the binding behaviour between DOM and engineered nanoparticles. In the present study, DOM, extracted from black soil, was dialyzed into four fractions: above 10,000 Da, 3500-10,000 Da, 1000-3500 Da and 100-1000 Da. Homoaggregation and fluorescence quenching titration of selenium nanoparticles (SeNPs) was examined in the presence of the different DOM fractions, as well as the consequences for immobilization of elemental mercury. It was found that the intermediate MW fraction (3500-10,000 Da) rather than the high MW DOM fraction was likely to adsorb to SeNPs. Generally, low MW DOM was expected to adsorb initially due to faster diffusion and these compounds would be displaced by high MW DOM over longer time period. However, the electrostatic barrier imparted by adsorbed DOM limited such displacement, leading to preferential adsorption of the intermediate MW fraction over the high MW fraction. Adsorbed DOM fractions, especially that of intermediate MW, enhanced the stability of SeNPs which favoured immobilization of elemental mercury. These findings show that MW exerts an important impact on DOM binding with SeNPs which, in consequence, governs the fate of SeNPs and mercury bioremediation performance.

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.

Effect of silver sulfide nanoparticles on photochemical degradation of dissolved organic matter in surface water

Silver sulfide nanoparticles (Ag₂SNPs) have shown photocatalytic activity, yet little is known about the effect of Ag₂SNPs on the photochemical degradation of dissolved organic matter (DOM) in surface water, which seriously impairs understanding of Ag₂SNPs' environmental risks. Herein, this study on the basis of electrospray ionization coupled with Fourier-transform ion cyclotron resonance mass spectrometry (ESI-FTICR-MS) showed for the first time that photodegradation of natural organic matter (NOM, 2R101 N) could be accelerated by both bared and polyvinylpyrrolidone (PVP)-coated Ag₂SNPs; the NOM with Ag₂SNPs (e.g., 500 μg/L) exposed to light irradiation for 96 h showed molecular formulas with lower O/C ratios as compared to the NOM alone. Also, added number of points (ranging from 1 to 2 carboxyl groups) having the same Kendrick mass defect (KMD) (COO) values and higher intensity in smaller Kendrick mass (KM) (COO) values were observed in NOM with Ag₂SNPs compared to NOM alone. However, negligible effects of Ag₂SNPs on photodegradation of humic acid (HA, 2S101H) were observed, even when the concentration of Ag₂SNPs was as high as 5 mg/L. Besides molecular characteristics, a great reduction in organic carbon content of NOM within 96 h was only observed in the presence of Ag₂SNPs under light condition. More importantly, the enhanced photodegradation of DOM by Ag₂SNPs even at a concentration of 100 μg/L was also validated in surface water. These findings suggest that Ag₂SNPs have the potential to accelerate the photochemical degradation of DOM in surface water.

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.

Synthesis and Structural Characterization of Silver Nanoparticles Stabilized with 3-Mercapto-1-Propansulfonate and 1-Thioglucose Mixed Thiols for Antibacterial Applications

The synthesis, characterization and assessment of the antibacterial properties of hydrophilic silver nanoparticles (AgNPs) were investigated with the aim to probe their suitability for innovative applications in the field of nanobiotechnology. First, silver nanoparticles were synthetized and functionalized with two capping agents, namely 3-mercapto-1-propansulfonate (3MPS) and 1-β-thio-d-glucose (TG). The investigation of the structural and electronic properties of the nano-systems was carried out by means of X-ray Photoelectron Spectroscopy (XPS) and X-ray Absorption Spectroscopy (XAS). XPS data provided information about the system stability and the interactions between the metallic surface and the organic ligands. In addition, XPS data allowed us to achieve a deep understanding of the influence of the thiols stoichiometric ratio on the electronic properties and stability of AgNPs. In order to shed light on the structural and electronic local properties at Ag atoms sites, XAS at Ag K-Edge was successfully applied; furthermore, the combination of Dynamic Light Scattering (DLS) and XAS results allowed determining AgNPs sizes, ranging between 3 and 13 nm. Finally, preliminary studies on the antibacterial properties of AgNPs showed promising results on four of six multidrug-resistant bacteria belonging to the ESKAPE group (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter sp.).