Silver nanoparticles in aquatic environments: Physiochemical behavior and antimicrobial mechanisms

Advancing groundwater quality predictions: Machine learning challenges and solutions

Machine learning (ML) is revolutionizing groundwater quality research by enhancing predictive accuracy and management strategies for contamination. This comprehensive review explores the evolution of ML technologies and their integration into environmental science, assessing 230 papers to understand the advancements and challenges in groundwater quality research. It reveals that a substantial portion of the research neglects critical preprocessing steps, crucial for model accuracy, with 83 % of the studies overlooking this phase. Furthermore, while model optimization is more commonly addressed, being implemented in 65 % of the papers, there is a noticeable gap in model interpretability, with only 15 % of the research providing explanations for model outcomes. Comparative evaluation of ML algorithms and careful selection of evaluation metrics are deemed essential for determining model fitness and reliability. The review underscores the need for interdisciplinary collaboration, methodological rigor, and continuous innovation to advance ML in groundwater management. By addressing these challenges and implementing solutions, the full potential of ML can be harnessed to tackle complex environmental issues and ensure sustainable groundwater management. This comprehensive and critical review paper can serve as a guiding framework to establish minimum standards for developing ML in groundwater quality studies.

Silver nanoparticles alter planktonic community structure and promote ecosystem respiration in freshwater mesocosms

The widespread use of silver nanoparticles (AgNPs) has resulted in their release into the aquatic environment, which threatens the health of aquatic ecosystems. Although the ecotoxicological effects of AgNPs have been widely reported at individual and population levels, the impact of long-term exposure to AgNPs on community structure and ecosystem function in aquatic ecosystems remains poorly understood. Herein, the present study investigated the effects of long-term exposure (28 d) to environmentally relevant concentrations (1 μg/L and 10 μg/L) of AgNPs on the community structure and function of freshwater ecosystems by artificially constructed 28 mesocosms freshwater ecosystem in experimental greenhouses, using plastic water tanks and food web manipulation. The results showed that long-term exposure to AgNPs significantly altered the community structure of zooplankton, phytoplankton, and bacterioplankton in the aquatic ecosystem. Exposure to 10 μg/L AgNPs significantly reduced the zooplankton density (70.3%, p < 0.05) and increased the phytoplankton biomass and bacterial richness and diversity via a "top-down effect." With regards to ecosystem function, AgNPs exposure significantly increased the respiration in freshwater ecosystems but did not have a significant effect on decomposition. The partial least squares path modeling (PLS-PM) further revealed that AgNPs may have a negative impact on ecosystem functions by reducing zooplankton community density and thus increasing phytoplankton biomass. This study is the first to show that long-term exposure to environmentally relevant concentrations of AgNPs leads to alterations in plankton community structure and promotes respiration in freshwater ecosystems. It emphasizes the need for assessing the environmental risk of long-term exposure to AgNPs at the ecosystem level.

Graphitic Carbon Nitride Enters the Scene: A Promising Versatile Tool for Biomedical Applications

Graphitic carbon nitride (g-C3N4), since the pioneering work on visible-light photocatalytic water splitting in 2009, has emerged as a highly promising advanced material for environmental and energetic applications, including photocatalytic degradation of pollutants, photocatalytic hydrogen generation, and carbon dioxide reduction. Due to its distinctive two-dimensional structure, excellent chemical stability, and distinctive optical and electrical properties, g-C3N4 has garnered a considerable amount of interest in the field of biomedicine in recent years. This review focuses on the fundamental properties of g-C3N4, highlighting the synthesis and modification strategies associated with the interfacial structures of g-C3N4-based materials, including heterojunction, band gap engineering, doping, and nanocomposite hybridization. Furthermore, the biomedical applications of these materials in various domains, including biosensors, antimicrobial applications, and photocatalytic degradation of medical pollutants, are also described with the objective of spotlighting the unique advantages of g-C3N4. A summary of the challenges faced and future prospects for the advancement of g-C3N4-based materials is presented, and it is hoped that this review will inspire readers to seek further new applications for this material in biomedical and other fields.

Enhanced Antimicrobial Activity of AgCu Nanoparticles: The Role of Particle Size and Alloy Composition

AgCu bimetallic· nanoparticles (NPs) represent a novel class of inorganic, broad-spectrum antimicrobial agents that offer enhanced antimicrobial effectiveness and reduced cytotoxicity compared to conventional Ag NP antibacterial materials. This study examines the antimicrobial performance and structural characteristics of AgCu nanoparticles (NPs) synthesized via two distinct chemical reduction processes using PVP-PVA as stabilizers. Despite identical chemical elements and sphere-like shapes in both synthesis methods, the resulting AgCu nanoparticles exhibited significant differences in size and antimicrobial properties. Notably, AgCu NPs with smaller average particle sizes demonstrated weaker antimicrobial activity, as assessed by the minimum inhibitory concentration (MIC) measurement, contrary to conventional expectations. However, larger average particle-sized AgCu NPs showed superior antimicrobial effectiveness. High-resolution transmission electron microscopy analysis revealed that nearly all larger particle-sized nanoparticles were AgCu nanoalloys. In contrast, the smaller particle-sized samples consisted of both AgCu alloys and monometallic Ag and Cu NPs. The fraction of Ag ions (relative to the total silver amount) in the larger AgCu NPs was found to be around 9%, compared to only 5% in that of the smaller AgCu NPs. This indicates that the AgCu alloy content significantly contributes to enhanced antibacterial efficacy, as a higher AgCu content results in the increased release of Ag ions. These findings suggest that the enhanced antimicrobial efficacy of AgCu NPs is primarily attributed to their chemical composition and phase structures, rather than the size of the nanoparticles.

Effects of sliver nanoparticles on nitrogen removal by the heterotrophic nitrification-aerobic denitrification bacteria Zobellella sp. B307 and their toxicity mechanisms

Due to the widespread use of sliver nanoparticles (AgNPs), a large amount of AgNPs has inevitably been released into the environment, and there is growing concern about the toxicity of AgNPs to nitrogen-functional bacteria. In addition to traditional anaerobic denitrifying bacteria, heterotrophic nitrification-aerobic denitrification (HNAD) bacteria are also important participants in the nitrogen cycle. However, the mechanisms by which AgNPs influence HNAD bacteria have yet to be explicitly demonstrated. In this study, the inhibitory effects of different concentrations of AgNPs on a HNAD bacteria Zobellella sp. B307 were investigated, and the underlying mechanism was explored by analyzing the antioxidant system and the activities of key denitrifying enzymes. Results showed that AgNPs could inhibit the growth and the HNAD ability of Zobellella sp. B307. AgNPs could accumulate on the surface of bacterial cells and significantly destroyed the cell membrane integrity. Further studies demonstrated that the presence of high concentration of AgNPs could result in the overproduction of reactive oxygen species (ROS) and related oxidative stress in the cells. Furthermore, the catalytic activities of key denitrifying enzymes (nitrate reductase (NAR), nitrite reductase (NIR), and nitrous oxide reductase (N2OR)) were significantly suppressed under exposure to a high concentration of AgNPs (20 mg·L-1), which might be responsible for the inhibited nitrogen removal performance of strain B307. This work could improve our understanding of the inhibitory effect and underlying mechanism of AgNPs on HNAD bacteria.

Recent advances and potential applications for metal-organic framework (MOFs) and MOFs-derived materials: Characterizations and antimicrobial activities

Microbial infections, particularly those caused by antibiotic-resistant pathogens, pose a critical global health threat. Metal-Organic Frameworks (MOFs), porous crystalline structures built from metal ions and organic linkers, initially developed for gas adsorption, have emerged as promising alternatives to traditional antibiotics. This review, covering research up to 2023, explores the potential of MOFs and MOF-based materials as broad-spectrum antimicrobial agents against bacteria, viruses, fungi, and even parasites. It delves into the historical context of antimicrobial agents, recent advancements in MOF research, and the diverse synthesis techniques employed for their production. Furthermore, the review comprehensively analyzes the mechanisms of action by which MOFs combat various microbial threats. By highlighting the vast potential of MOFs, their diverse synthesis methods, and their effectiveness against various pathogens, this study underscores their potential as a novel solution to the growing challenge of antibiotic resistance.

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.

In Situ Reduction of Silver Nanoparticles/Urushiol-Based Polybenzoxazine Composite Coatings with Enhanced Antimicrobial and Antifouling Performances

Marine anti-fouling coatings represent an efficient approach to prevent and control the marine biofouling. However, a significant amount of antifouling agent is added to improve the static antifouling performance of the coatings, which leads to an issue whereby static antifouling performance conflicts with eco-friendly traits. Herein, this work reports an in situ reduction synthesis of silver nanoparticles (AgNPs) within polymers to produce composite coatings, aiming to solve the aforementioned issue. Firstly, urushiol-based benzoxazine monomers were synthesized by the Mannich reaction, using an eco-friendly natural product urushiol and n-octylamine and paraformaldehyde as the reactants. Additionally, AgNPs were obtained through the employment of free radicals formed by phenolic hydroxyl groups in the urushiol-based benzoxazine monomers, achieved by the in situ reduction of silver nitrate in benzoxazine. Then, the urushiol-based benzoxazine/AgNPs composite coatings were prepared by the thermosetting method. AgNPs exhibit broad-spectrum and highly efficient antimicrobial properties, with a low risk to human health and a minimal environmental impact. The composite coating containing a small amount of AgNPs (≤1 wt%) exhibits effective inhibition against various types of bacteria and marine microalgae in static immersion, thereby displaying outstanding antifouling properties. This organic polymer and inorganic nanoparticle composite marine antifouling coating, with its simple preparation method and eco-friendliness, presents an effective solution to the conflict between static antifouling effectiveness and environmental sustainability in marine antifouling coatings.

Environmental behavior of silver nanomaterials in aquatic environments: An updated review

The increasing applications of silver nanomaterials (nano-Ag) and their inevitable release posed great potential risks to aquatic organisms and ecosystems. Considerable attention has been attracted on their behaviors and transformations, which were critically important for their subsequent biological toxicities and ecological effects. Therefore, the summary of the recent efforts on the environmental behavior of nano-Ag would be beneficial for understanding the environmental fate and accurate risk assessment. This review summarized the studies on various physical, chemical and biological transformations of nano-Ag, meanwhile, the influencing factors (including the intrinsic properties and environmental conditions) and related mechanisms were highlighted. Surface structure and facets of nano-Ag, abiotic conditions and natural freeze-thaw cycle processes could affect the transformations of nano-Ag under different environmental scenarios (including freshwater, seawater and wastewater). The interactions with co-present components, such as chemicals and other particles, impacted the multiple processes of nano-Ag. Besides, the contradictory effects and mechanisms by several environmental factors were summarized. Lastly, the key knowledge gaps and some aspects that deserve further investigation were also addressed. Therefore, the current review aimed to provide an overall analysis of transformation processes of nano-Ag, which will provide more available information and pave the way for the future research areas.

Potential role of AgNPs within wastewater in deteriorating sludge floc structure and settleability during activated sludge process: Filamentous bacteria and quorum sensing

Excellent sludge floc structure and settleability are essential to maintain the process stability and excellent effluent quality during the activated sludge process. The underlying effect of silver nanoparticles (AgNPs) within wastewater on sludge floc structure and settleability is still unclear. The potential role of AgNPs in promoting filamentous bacterial proliferation and deteriorating sludge floc structure and settleability based on quorum sensing (QS) were investigated in this study. The results indicated that N-acyl homoserine lactose (AHL) concentration sharply increased from 23.56 to 108.41 ng/g VSS in the sequencing batch reactor with 1 mg/L AgNPs. AgNPs strengthened communication between filamentous bacteria, which triggered the filamentous bacterial QS system involving the synthetic gene hdtS and sensing genes traR and lasR. Filamentous bacterial proliferation was promoted by the triggered QS via positively regulating its cell cycle progression including chromosomal replication and divisome formation. In addition, extracellular protein production was obviously increased from 43.56 to 97.91 mg/g VSS through QS by regulating arginine and tyrosine secretion during filamentous bacterial proliferation under 1 mg/L AgNPs condition, which led to an increase in the negative charge and hydrophily at the cell surface. AgNPs resulted in an obvious increase in the surface energy barrier (WT) between bacteria. The change in the physicochemical properties of extracellular polymeric substance (EPS) induced by QS among filamentous bacteria obviously inhibited bacterial aggregation between filamentous bacteria and floc-forming bacteria under AgNPs condition, thus resulting in serious deterioration of the sludge floc structure and settleability. This study provided new insights into the microcosmic mechanism for the effect of AgNPs on sludge floc structure and settleability.

The combined contamination of nano-polystyrene and nanoAg: Uptake, translocation and ecotoxicity effects on willow saplings

Nanoplastics (NPLs) and nanoAg (AgNPs) are emerging contaminants commonly detected in aquatic and terrestrial environments due to their widespread use in various domains. However, their uptake, translocation, and toxic effects on plants in cooccurrence environments remain largely unexplored. Therefore, a hydroponic experiment was conducted using 100 nm NPLs (1 mg/L and 10 mg/L), AgNPs (100 μg/L and 1000 μg/L) and saplings of willow (Salix matsudana 'J172') to investigate absorption, translocation and the physio-biochemical responses of the plants. The results indicated that NPLs and AgNPs were agglomerated with each other in solutions. NPLs not only penetrated the roots of the saplings but also translocated to the branches and leaves through xylem ducts. However, AgNPs was only detected in the roots, suggesting that the internalization of nanoparticles in plants depends on the properties and types of particles themselves. The combined exposure to NPLs and AgNPs selectively affected the absorption and distribution of K, Ca, Mg and Fe, resulting in inhibited saplings growth and photosynthesis. Furthermore, the presence of NPLs and AgNPs induced oxidative damage and stimulated the antioxidant stress system in the plants. This study provides novel insights into the internalization and ecotoxicological mechanisms of NPLs and AgNPs in woody vascular plants.

Reveal molecular mechanism on the effects of silver nanoparticles on nitrogen transformation and related functional microorganisms in an agricultural soil

Silver nanoparticles (AgNPs) are widely present in aquatic and soil environment, raising significant concerns about their impacts on creatures in ecosystem. While the toxicity of AgNPs on microorganisms has been reported, their effects on biogeochemical processes and specific functional microorganisms remain relatively unexplored. In this study, a 28-day microcosmic experiment was conducted to investigate the dose-dependent effects of AgNPs (10 mg and 100 mg Ag kg-1 soil) on nitrogen transformation and functional microorganisms in agricultural soils. The molecular mechanisms were uncovered by examining change in functional microorganisms and metabolic pathways. To enable comparison, the toxicity of positive control with an equivalent Ag+ dose from CH3COOAg was also included. The results indicated that both AgNPs and CH3COOAg enhanced nitrogen fixation and nitrification, corresponding to increased relative abundances of associated functional genes. However, they inhibited denitrification via downregulating nirS, nirK, and nosZ genes as well as reducing nitrate and nitrite reductase activities. In contrast to high dose of AgNPs, low levels increased bacterial diversity. AgNPs and CH3COOAg altered the activities of associated metabolic pathways, resulting in the enrichment of specific taxa that demonstrated tolerance to Ag. At genus level, AgNPs increased the relative abundances of nitrogen-fixing Microvirga and Bacillus by 0.02 %-629.39 % and 14.44 %-30.10 %, respectively, compared with control group (CK). The abundances of denitrifying bacteria, such as Rhodoplanes, Pseudomonas, and Micromonospora, decreased by 19.03 % to 32.55 %, 24.73 % to 50.05 %, and 15.66 % to 76.06 %, respectively, compared to CK. CH3COOAg reduced bacterial network complexity, diminished the symbiosis mode compared to AgNPs. The prediction of genes involved in metabolic pathways related to membrane transporter and cell motility showed sensitive to AgNPs exposure in the soil. Further studies involving metabolomics are necessary to reveal the essential effects of AgNPs and CH3COOAg on biogeochemical cycle of elements in agricultural soil.

Fabrication of Au-Ag Bimetallic Nanoparticles Using Pulsed Laser Ablation for Medical Applications: A Review

In recent years, the synthesis of Au-Ag bimetallic nanoparticles has garnered immense attention due to their potential applications in diverse fields, particularly in the realm of medicine and healthcare. The development of efficient synthesis methods is crucial in harnessing their unique properties for medical applications. Among the synthesis methods, pulsed laser ablation in a liquid environment has emerged as a robust and versatile method for precisely tailoring the synthesis of bimetallic nanoparticles. This manuscript provides an overview of the fundamentals of the pulsed laser ablation in a liquid method, elucidating the critical factors involved. It comprehensively explores the pivotal factors influencing Au-Ag bimetallic nanoparticle synthesis, delving into the material composition, laser parameters, and environmental conditions. Furthermore, this review highlights the promising strides made in antibacterial, photothermal, and diagnostic applications. Despite the remarkable progress, the manuscript also outlines the existing limitations and challenges in this advanced synthesis technique. By providing a thorough examination of the current state of research, this review aims to pave the way for future innovations in the field, driving the development of novel, safe, and effective medical technologies based on Au-Ag bimetallic nanoparticles.

A Review of the Aquatic Environmental Transformations of Engineered Nanomaterials

Once released into the environment, engineered nanomaterials (ENMs) undergo complex interactions and transformations that determine their fate, exposure concentration, form, and likely impact on biota. Transformations are physical, chemical, or biological changes that occur to the ENM or the ENM coating. Over time, these transformations have an impact on their behaviour and properties. The interactions and transformations of ENMs in the environment depend on their pristine physical and chemical characteristics and the environmental or biological compartment into which they are released. The uniqueness of each ENM property or lifecycle results in a great deal of complexity. Even small changes may have a significant impact on their potential transformations. This review outlines the key influences and outcomes of ENM evolution pathways in aquatic environments and provides an assessment of potential environmental transformations, focusing on key chemical, physical, and biological processes. By obtaining a comprehensive understanding of the potential environmental transformations that nanomaterials can undergo, more realistic models of their probable environmental behaviour and potential impact can be developed. This will, in turn, be crucial in supporting regulatory bodies in their efforts to develop environmental policy in the field of nanotechnology.

Exposure to silver and titanium dioxide nanoparticles at supra-environmental concentrations decreased sperm motility and affected spermatozoa subpopulations in gilthead seabream, Sparus aurata

Marine pollution by nanoparticles (NPs) can be reprotoxic for fish and disturb successful reproduction of wild populations. In gilthead seabream (Sparus aurata), a mild effect on sperm motility was observed after exposure to high concentrations of silver NPs. Considering the great heterogeneity traits within a sperm sample, it is possible that NPs affect spermatozoa accordingly, modulating subpopulation profile. Thus, this work aimed to analyse NP effects in sperm motility in general and considering spermatozoa population structure, using a subpopulation approach. Seabream sperm samples from mature males were exposed for 1 h to increasing concentrations of titanium dioxide (1, 10, 100, 1000 and 10,000 μg L^-1) and silver (0.25, 25 and 250 μg L^-1) NPs, including Ag NP and Ag⁺, dissolved in a non-activating medium (0.9 % NaCl). Concentrations chosen include realistic (10-100 and 0.25 μg L^-1, respectively, for TiO₂ and Ag) and supra-environmental values. The mean particle diameter was determined as 19.34 ± 6.72 and 21.50 ± 8.27 nm in the stock suspension, respectively, for titanium dioxide and silver. After the ex vivo exposure, sperm motility parameters were determined using computer-assisted sperm analysis, and sperm subpopulations were later identified using a two-step cluster analysis. Results revealed a significant reduction in total motility after exposure to the 2 highest concentrations of titanium dioxide NPs, while curvilinear and straight-line velocities were not altered. Exposure to silver NPs (Ag NP and Ag⁺) lowered significantly total and progressive motilities at all concentrations, while curvilinear and straight-line velocities were significantly lower only at the highest concentration. Sperm subpopulations were also affected by the exposure to both titanium dioxide and silver NPs. In both cases, the highest levels of NPs triggered a decrease in the percentage of fast sperm subpopulations (38.2% in TiO₂ 1000 μg L^-1, 34.8.% in Ag NP 250 μg L^-1, and 45.0% in Ag⁺ 250 μg L^-1 vs 53.4% in the control), while an increase on slow sperm subpopulations. A reprotoxic effect was proven for both NPs, but only at supra-environmental concentrations.

Silver nanoparticles loaded on lactose/alginate: in situ synthesis, catalytic degradation, and pH-dependent antibacterial activity

We present the in situ synthesis of silver nanoparticles (AgNPs) through ionotropic gelation utilizing the biodegradable saccharides lactose (Lac) and alginate (Alg). The lactose reduced silver ions to form AgNPs. The crystallite structure of the nanocomposite AgNPs@Lac/Alg, with a mean size of 4-6 nm, was confirmed by analytical techniques. The nanocomposite exhibited high catalytic performance in degrading the pollutants methyl orange and rhodamine B. The antibacterial activity of the nanocomposite is pH-dependent, related to the alterations in surface properties of the nanocomposite at different pH values. At pH 6, the nanocomposite demonstrated the highest antibacterial activity. These findings suggest that this nanocomposite has the potential to be tailored for specific applications in environmental and medicinal treatments, making it a highly promising material.

Comparison of toxicity of silver nanomaterials and silver nitrate on developing zebrafish embryos: Bioavailability, osmoregulatory and oxidative stress

The mechanisms of toxicity of engineered nanomaterials (ENMs) to the early life stages of freshwater fish, and the relative hazard compared to dissolved metals, is only partially understood. In the present study, zebrafish (Danio rerio) embryos were exposed to lethal concentrations of silver nitrate (AgNO₃) or silver (Ag) ENMs (primary size 42.5 ± 10.2 nm). The 96 h-LC₅₀ for AgNO₃ was 32.8 ± 0.72 μg Ag L^-1 (mean ± 95% CI) compared to 6.5 ± 0.4 mg L^-1 of the whole material for Ag ENMs; with the ENMs being orders of magnitude less toxic than the metal salt. The EC₅₀ for hatching success was 30.5 ± 1.4 μg Ag L^-1 and 6.04 ± 0.4 mg L^-1 for AgNO₃ and Ag ENMs, respectively. Further sub-lethal exposures were performed with the estimated LC₁₀ concentrations for both AgNO₃ or Ag ENMs over 96 h where about 3.7% of the total Ag as AgNO₃ was internalised, as measured by Ag accumulation in the dechorionated embryos. However, for the ENMs exposures, nearly all (99.8%) of the total Ag was associated with chorion; indicating the chorion as an effective barrier to protect the embryo in the short term. Calcium (Ca²⁺) and sodium (Na⁺) depletion was induced in embryos by both forms of Ag, but hyponatremia was more pronounced in the nano form. Total glutathione (tGSH) levels declined in embryos exposed to both Ag forms, but a superior depletion occurred with the nano form. Nevertheless, oxidative stress was mild as superoxide dismutase (SOD) activity stayed uniform and the sodium pump (Na⁺/K⁺-ATPase) activity had no appreciable inhibition compared to the control. In conclusion, AgNO₃ was more toxic to the early life stage zebrafish than the Ag ENMs, still differences were found in the exposure and toxic mechanisms of both Ag forms.

Multifunctional O-phenanthroline silver(I) complexes for antitumor activity against colorectal adenocarcinoma cells and antimicrobial properties by multiple mechanisms

A series of O-phenanthroline silver(I) complexes were synthesized and characterized by infrared (IR) spectroscopy, mass spectrometry (MS), ¹H nuclear magnetic resonance (NMR) spectroscopy and single-crystal X-ray crystallography. The cytotoxicity of the silver(I) complex (P-131) was evaluated in the cancer cell lines HCT-116, HeLa, and MDA-MB-231 and the normal cell line LO2 via MTT assays. The 50% inhibition concentration (IC₅₀) of P-131 on HCT116 cell line is 0.86 ± 0.03 μM. It is far lower than the IC₅₀ value of cisplatin (9.08 ± 1.10 μM), the IC₅₀ value of normal cell LO2 (76.20 ± 0.48 μM) is much higher than that of cisplatin (3.99 ± 0.74 μM), indicating that its anticancer effect is stronger than that of cisplatin, and its biological safety is greater than that of cisplatin. Furthermore, anticancer mechanistic studies showed that P-131 inhibited cell proliferation by blocking DNA synthesis and acted temporally on the nucleus in dividing HCT-116 cells. Moreover, P-131 increased intracellular reactive oxygen species (ROS) levels in a dose-dependent manner. Notably, 10 mg/kg P-131 showed better antitumor effects than oxaliplatin in an HCT116 human colorectal xenograft mouse model without inducing toxicity. Moreover, the microdilution broth method was used to evaluate the antimicrobial properties of P-131 against Pseudomonas aeruginosa and Candida albicans. A biofilm eradication study was also performed using the crystal violet method and confocal laser scanning microscopy.

Enhanced Anti-Biofouling Properties of BWRO Membranes via the Deposition of Poly (Catechol/Polyamine) and Ag Nanoparticles

The surface modification of reverse osmosis (RO) membranes to improve their anti-biofouling properties is gaining increased attention. Here, we modified the polyamide brackish water reverse osmosis (BWRO) membrane via the biomimetic co-deposition of catechol (CA)/tetraethylenepentamine (TEPA) and in situ growth of Ag nanoparticles. Ag ions were reduced into Ag nanoparticles (AgNPs) without extraneous reducing agents. The hydrophilic property of the membrane was improved, and the zeta potential was also increased after the deposition of poly (catechol/polyamine) and AgNPs. Compared with the original RO membrane, the optimized PCPA3-Ag10 membrane showed a slight reduction in water flux, and the salt rejection declined, but enhanced anti-adhesion and anti-bacterial activities were observed. The FDR_t of the PCPA3-Ag10 membranes during the filtration of BSA, SA and DTAB solution were 5.63 ± 0.09%, 18.34 ± 0.33% and 34.12 ± 0.15%, respectively, much better than those of the original membrane. Moreover, the PCPA3-Ag10 membrane exhibited a 100% reduction in the number of viable bacteria (B. subtilis and E. coli) inoculated on the membrane. The stability of the AgNPs was also high enough, and these results verify the effectiveness of poly (catechol/polyamine) and the AgNP-based modification strategy for the control of fouling.

In situ surface modification of forward osmosis membrane by polydopamine/polyethyleneimine-silver nanoparticle for anti-fouling improvement in municipal wastewater treatment

In this work, we demonstrate the surface functionalization of cellulose triacetate membrane with co-deposition of polydopamine (PDA)/polyethyleneimine (PEI) and silver nanoparticles (AgNPs) for antifouling property in municipal wastewater treatment. PDA/PEI was first coated on the membrane surface by single-step co-deposition, while AgNPs were formed in situ through catechol groups of PDA immobilizing silver ions and subsequently reducing. The successful surface modification was verified by different membrane characterization techniques. The modified PDA/PEI-nAg CTA membrane exhibits enhanced hydrophilicity and improved antiadhesion and antimicrobial activity. Furthermore, the functional layer had an indistinctive effect on the membrane transport parameters. In addition, dynamic forward osmosis (FO) fouling experiment with raw municipal wastewater as feed solution indicated that the PDA/PEI-nAg CTA membrane exhibited notably lower water flux decrease compared to the nascent CTA membrane. The results of confocal laser scanning microscopy (CLSM) showed that PDA/PEI-nAg CTA membranes effectively reduced the adsorption of organic foulants (proteins and polysaccharides) and inhibited the formation and development of the fouling layer. The membrane surface modification of the CTA membrane with PDA/PEI and AgNPs efficiently mitigated membrane fouling in municipal wastewater treatment.

Metatranscriptome deciphers the effects of non-antibiotic antimicrobial agents on antibiotic resistance and virulence factors in freshwater microcosms

The emergence and transmission of antibiotic resistance genes (ARGs) and virulence factors (VFs) pose health risks to the ecosystem and humans. Understanding how non-antibiotic antimicrobial agents drive the expression of ARGs and VFs in freshwater ecosystems, however, remains large challenges. Here, we employed freshwater microcosms and performed metatranscriptomic analysis to investigate the expression profiles of ARGs and VFs in response to pollutants of non-antibiotic antimicrobial agents, including silver nanoparticles (AgNPs) and azoxystrobin. Results showed that AgNPs significantly inhibited the total expression of ARGs and VFs and decreased the number of pathogenic microorganisms expressing these genes. Azoxystrobin increased the total expression of ARGs and VFs, as well as the number of pathogens expressing VFs, but concomitantly reduced the number of pathogens expressing ARGs. Two tested pollutants dramatically changed the expression profiles of ARGs and VFs, with distinct patterns: AgNPs displayed a negative effect, while azoxystrobin showed a positive effect on their expression profiles. Our findings provided a systematical insight to demonstrate that non-antibiotic antimicrobial agents with different mechanisms of action showed various effects on ARGs and VFs, and therefore represented different ecological risks.

Form-Dependent Toxicity of Silver Nanomaterials in Rainbow Trout Gills

The toxicity of the form of nanoparticles is presently not well understood. The purpose of this study consists in comparing the toxicity of various forms of silver nanoparticles (nAg) in juvenile rainbow trout Oncorhynchus mykiss. Juveniles were exposed to various forms of polyvinyl-coated nAg of similar size for 96 h at 15 °C. After the exposure period, the gills were isolated and analyzed for Ag uptake/distribution, oxidative stress, glucose metabolism, and genotoxicity. Higher levels of Ag were detected in gills in fish exposed to dissolved Ag followed by spherical, cubic, and prismatic nAg. Size-exclusion chromatography of gill fractions revealed that the dissolution of nAg was observed for all forms of nAg where prismatic nAg released more important levels of Ag in the protein pool as in fish exposed to dissolved Ag as well. The aggregation of nAg was more important for cubic nAg in respect of the other forms of nAg. The data revealed that lipid peroxidation was closely associated with protein aggregation and viscosity. Biomarkers revealed changes in lipid/oxidative stress and genotoxicity, which were related to the loss of protein aggregation and inflammation (NO₂ levels), respectively. In general, the observed effects were found for all forms of nAg where the effects from prismatic nAg were generally higher than for spherical and cubic nAg. The strong relationship between genotoxicity and inflammation response suggests the participation of the immune system in the observed responses of juvenile fish gills.

Ambivalent effects of dissolved organic matter on silver nanoparticles/silver ions transformation: A review

The numerous applications of silver nanoparticles (AgNPs) lead to their spread in aquatic systems and the release of silver ions (Ag⁺), which brings potential risks to environment and human health. Owing to the different toxicity, the mutual transformations between AgNPs and Ag⁺ has been a hot topic of research. Dissolved organic matter (DOM) is ubiquitous on the earth and almost participates in all the reactions in the nature. The previous studies have reported the roles of DOM played in the transformation between AgNPs and Ag⁺. However, different experiment conditions commonly caused contradictory results, leading to the difficulty to predict the fate of AgNPs in specific reactions. Here we summarized mechanisms of DOM-mediated AgNPs oxidation and Ag⁺ reduction, and analyzed the effects of environmental parameters. Moreover, the knowledge gaps, challenges, and new opportunities for research in this field are discussed. This review will promote the understanding of the fate and risk assessments of AgNPs in natural water systems.

Assessing the effects of silver nanoparticles on the ecophysiology of Gammarus roeseli

Being part of the macrobenthic fauna, gammarids are efficient indicators of contamination of aquatic ecosystems by nanoparticles that are likely to sediment on the bottom. The present study investigates the effects of silver nanoparticles (nAg) on ecophysiological functions in Gammarus roeseli by using a realistic scenario of contamination. Indeed, an experiment was conducted during 72 h, assessing the effects of 5 silver nAg from 10 to 100 nm diluted at concentrations of maximum 5 µg L^-1 in a natural water retrieved from a stream and supplemented with food. The measured endpoints in gammarids were survival, silver concentrations in tissues, consumption of oxygen and ventilation of gills. Additionally, a set of biomarkers of the energetic metabolism was measured. After a 72-h exposure, results showed a concentration-dependent increase of silver levels in G. roeseli that was significant for the smallest nAg size (10 nm). Ecophysiological responses in G. roeseli were affected and the most striking effect was a concentration-dependent increase in oxygen consumption especially for the smallest nAg (10 to 40 nm), whereas ventilation of gills by gammarids was not changed. The potential mechanisms underlying these findings are discussed. Thus, we demonstrated the very low exposure concentration of 0.5 µg L^-1 for the small nAg size led to significant ecophysiological effects reinforcing the need to further investigate subtle effects on nanoparticles on aquatic organisms.

Autophagy and lipid droplets are a defense mechanism against toxic copper oxide nanotubes in the eukaryotic microbial model Tetrahymena thermophila

The widespread use of inorganic nanomaterials of anthropogenic origin has significantly increased in the last decade, being now considered as emerging pollutants. This makes it necessary to carry out studies to further understand their toxicity and interactions with cells. In the present work we analyzed the toxicity of CuO nanotubes (CuONT) in the ciliate Tetrahymena thermophila, a eukaryotic unicellular model with animal biology. CuONT exposure rapidly induced ROS generation in the cell leading to oxidative stress and upregulation of genes encoding antioxidant enzymes (catalase, superoxide dismutase, glutathione peroxidase), metal-chelating metallothioneins and cytochrome P450 monooxygenases. Comet assays and overexpression of genes involved in DNA repair confirmed oxidative DNA damage in CuONT-treated cells. Remarkably, both electron and fluorescent microscopy revealed numerous lipid droplets and autophagosomes containing CuONT aggregates and damaged mitochondria, indicating activation of macroautophagy, which was further confirmed by a dramatic upregulation of ATG (AuTophaGy related) genes. Treatment with autophagy inhibitors significantly increased CuONT toxicity, evidencing the protective role of autophagy towards CuONT-induced damage. Moreover, increased formation of lipid droplets appears as an additional mechanism of CuONT detoxification. Based on these results, we present a hypothetical scenario summarizing how T. thermophila responds to CuONT toxicity. This study corroborates the use of this ciliate as an excellent eukaryotic microbial model for analyzing the cellular response to stress caused by toxic metal nanoparticles.

Ecotoxicity assessment for environmental risk and consideration for assessing the impact of silver nanoparticles on soil earthworms

Silver nanoparticles (AgNPs) are found in a range of commercial products due to their proven antibacterial properties. The unused silver nanoparticles (AgNPs) may make its way into the soil via biosolids that come from wastewater treatment or the effluent that comes from industrialisation processes, where it could be harmful to the organism that live in terrestrial ecosystems. In addition, silver ions are one of the most toxic forms of heavy metal released from dissolved silver nitrate (AgNO₃) and AgNPs through dissolution or oxidation. The study examined the effect of engineered AgNPs, and AgNO₃ on earthworms which are one of the most important bioindicator for determining toxicity in soil environment. Epigeic earthworm, Eudrilus eugeniae was exposed to soils spiked with equivalent concentrations of AgNPs or AgNO₃ at 0, 10, 100, and 200 mg kg⁻¹ in soil for 56 days of experiments. The survival and growth rate was recorded at 7^th, 14^th, 21^st, 28^th days and accumulation of Ag in earthworm tissue at 14^th and 28^th days, antioxidant enzymes at 28^th days and reproduction at 56^th days of experiment. Further, a short-term exposure of AgNPs and AgNO₃ was conducted to observe avoidance behaviour after 48 h of exposure. The result indicated that survivability was relatively low on exposure of AgNO₃ (83.3%) than AgNPs (86.7%) in 200 mg kg⁻¹ spiked soils, besides the growth was inhibited in both AgNPs (3.68%) and AgNO₃ (3.25%) at 28^th days. The uptake of Ag from AgNO₃ in the earthworm tissue was slightly higher than uptake of Ag from AgNPs and it showed concentration-dependent inhibitory effects on reproduction. In AgNO₃ spiked soil, a high level of the Malondialdehyde (MDA) based lipid peroxidation and increased activity of antioxidant enzyme catalase (CAT) was observed than AgNPs spiked soil. Similarly, glutathione (GSH), a cofactor for GPx and GST enzymes, was lower in AgNO₃-spiked soil than in AgNPs-spiked soil. In terms of avoidance behaviour, there was no discernible difference between the distribution of earthworms in AgNPs and AgNO₃ after 48 h. The study found E. eugeniae exhibits concentration-dependent alterations in its competence to survive, antioxidant enzymes, and reproduction. AgNO₃ was found to be more sensitive than AgNPs in the study. The research investigates the effect of AgNPs on earthworms in the soil ecosystem since this understanding is crucial for a comprehensive evaluation of AgNPs' environmental consequences.

The Effects of Seven-Day Exposure to Silver Nanoparticles on Fertility and Homeostasis of Zebrafish (Danio rerio)

Silver nanoparticles (AgNPs) are found in open waters, but the effect of their low concentrations on an organism’s homeostasis is not fully understood. The aim of the study was to determine the short-term exposure effects of AgNPs coated by PvP (polyvinylpyrrolidone) on the homeostasis of livers and gonads in zebrafish. Sexually mature zebrafish were exposed for seven days to silver ions (0.01 mg/dm³) or AgNPs (0.01; 0.05; 0.1; 0.5; 1.0 mg/dm³). On the last day, the liver, testes, and ovaries were subjected to a histology analysis. In the liver, we analyzed the expression of the cat, gpx1a, gsr, sod1, and cyp1a genes. On the last day of the experiment, the lowest survival rate was found in the AgNPs 0.05 mg/dm³ group. The histological analysis showed that AgNPs and silver ions cause an increase in the area of hepatocytes. The highest proliferation index of hepatocytes was found in the AgNP 0.05 mg/dm³ group. Furthermore, AgNPs were found to interfere with spermatogenesis and oogonesis as well as reduce the expression levels of the cat, gpx1a, and sod1 genes in the liver compared with the control group. Based on the results, it can be concluded that exposure to AgNPs causes cytotoxic changes in zebrafish, activates the immune system, negatively affects the process of meiosis in the gonads, and generates oxidative stress.

In situ facile green synthesis of Ag-ZnO nanocomposites using Tetradenia riperia leaf extract and its antimicrobial efficacy on water disinfection

In this work, Ag–ZnO nanocomposites were prepared by a green synthesis route using aqueous leaf extract of Tetradenia riperia and investigated for antibacterial activity against Escherichia coli and Staphylococcus aureus. To optimize the synthesis of the Ag–ZnO, the effects of precursor concentrations, pH, and temperatures were studied. The Ag–ZnO nanocomposites were characterized by XRD, ATR-FTIR, FESEM, and TEM. Results show that the concentration of 8% Ag, the temperature of 80 °C, and a pH of 7–8 were optimal for the synthesis of Ag–ZnO nanocomposites. The XRD analysis showed the decrease in particle size of Ag–ZnO from 23.6 to 14.8 nm with an increase in Ag concentrations, which was further supported by FESEM analysis. TEM image of 8% Ag provides more information on the coexistence of Ag on ZnO where an average particle size of 14.8 nm was determined. The ATR-FTIR analysis confirmed the presence of phenolic compounds, which work as reducing and stabilizing agents. The antimicrobial activity results show that Ag–ZnO nanocomposite demonstrated a higher antimicrobial potency on E. coli than on S. aureus. Therefore, Tetradenia riperia leaf extract is a viable route for the synthesis of Ag–ZnO nanocomposites to be used for various applications, including water disinfection.

Shape-Dependent Toxicity of Silver Nanoparticles on Freshwater Cnidarians

Silver nanoparticles (AgNPs) are increasingly used in various consumer products, leading to their inadvertent release in aquatic ecosystems. The toxicity of AgNPs could be associated with the leaching of ionic Ag but also with the size, shape and surface properties. The purpose of this study was to test the null hypothesis that toxicity of AgNPs was independent of shape in the invertebrate Hydra vulgaris. The hydranths were exposed to increasing concentrations of ionic Ag and AgNPs of three different shapes (spherical, cubic and prismatic) with the same size and coating (polyvinylpyrrolidone). The data revealed that between 68% and 75% of total Ag remained in solution after the 96 h exposure period, while 85−90% of ionic Ag remained in solution. The 96 h lethal concentration (LC50) was lower with ionic (4 µg/L) and spherical AgNPs (56 µg/L), based on irreversible morphological changes such as loss of tentacles and body disintegration. Cubic and prismatic AgNPs were not toxic at a concentration of <100 µg/L. The sublethal toxicity was also determined at 96 h based on characteristic morphological changes (clubbed and/or shortened tentacles) and showed the following toxicity: ionic (2.6 µg/L), spherical (22 µg/L) and prismatic (32.5 µg/L) AgNPs. The nanocube was not toxic at this level. The data indicated that toxicity was shape-dependent where nanoparticles with a low aspect ratio in addition to high circularity and elongation properties were more toxic at both the lethal and sublethal levels. In conclusion, the shape of AgNPs could influence toxicity and warrants further research to better understand the mechanisms of action at play.

Toxicity and modulation of silver nanoparticles synthesized using abalone viscera hydrolysates on bacterial community in aquatic environment

Polysaccharide decorated silver nanoparticles (AgNPs) are a new type of antibacterial agent in aquaculture, but their effects on the bacterial community structure in aquaculture water are still unknown. In this study, the primary hydrolysate from abalone (Haliotis discus hannai) viscera (AVH) was used to biosynthesize AVH-AgNPs by in situ reduction, and the crystallinity nature, size, morphology, and chemical composition were analyzed by high-resolution characterization techniques such as Ultraviolet–visible spectroscopy (UV–vis), X-rays diffraction (XRD), Transmission Electron Microscope (TEM), Dynamic light scattering (DLS), Zeta potential, inductively coupled plasma-optical emission spectrometry (ICP-OES) and Turbiscan stability index (TSI) values. Furthermore, the acute toxicity of AVH-AgNPs to zebrafish (Danio rerio) and their effects on bacterial community structure in fish culture water at low concentrations were studied. The results showed that the spherical AVH-AgNPs with an average diameter of 54.57 ± 12.96 nm had good stability, low toxicity, and good in vitro antibacterial activity. Within the experimental concentration range, all AVH-AgNPs treatments had decreased the bacterial diversity in zebrafish culture water to varying degrees. The bacteria with significantly decreased abundances were pathogenic or potential pathogenic, such as Aeromonas veronii, Flavobacterium columnare, and genera Flectobacillus and Bosea. The abundance of Haliscomenobacter sp. JS224, which might cause sludge swelling, also decreased significantly. On the other hand, the relative abundance of some bacterial taxa could remove xenobiotics (e.g., Runella defluvii and Phenylobacterium), control water eutrophication (Sediminibacterium), and reduce toxic algae proliferation (Candidatus Intestinusbacter nucleariae and Candidatus Finniella), increased significantly. Thus, the application of AVH-AgNPs in aquaculture water at low concentrations is relatively safe and has positive significance for improving the aquaculture environment. Also, AVH-AgNPs have good prospects in aquaculture.

The Aggregation and Dissolution of Citrate-Coated AgNPs in High Ammonia Nitrogen Wastewater and Sludge from UASB-Anammox Reactor

Silver nanoparticles (AgNPs) are released into the sewage pipes and ultimately wastewater treatment plants during manufacturing, use, and end-life disposal. AgNPs in wastewater treatment plants aggregate or dissolve, and may affect the microbial community and subsequent pollutant removal efficiency. This study aims to quantitatively investigate the fate of AgNPs in synthetic high ammonia nitrogen wastewater (SW) and sludge from an up-flow anaerobic sludge blanket (UASB) anammox reactor using a nanoparticle tracking analysis (NTA), dynamic light scattering (DLS), transmission electron microscope (TEM), and atomic absorption spectroscopy (AAS). Results showed that 18.1 mM NH4+, 2.11 mM Mg2+ in SW caused less negative zeta potential (ζ-potential, -18.4 vs. -37.4 mV), aggregation (388.8 vs. 21.5 nm), and settlement (80%) of citrate-coated AgNPs (cit-AgNPs) in 220 min. The presence of 18.5 mM Cl- in SW formed AgCl2-, AgCl(aq) and eventually promoted the dissolution (9.3%) of cit-AgNPs. Further exposure of SW-diluted AgNPs to sludge (42 mg L-1 humic acid) and induced a more negative ζ-potential (-22.2 vs. -18.4 mV) and smaller aggregates (313.4 vs. 388.8 nm) due to the steric and hindrance effect. The promoted Ag dissolution (34.4% vs. 9.3%) was also observed after the addition of sludge and the possible reason may be the production of Ag(NH3)2+ by the coexistence of HA from sludge and NH4+ from SW. These findings on the fate of AgNPs can be used to explain why AgNPs had limited effects on the sludge-retained bacteria which are responsible for the anammox process.

Lung Models to Evaluate Silver Nanoparticles’ Toxicity and Their Impact on Human Health

Nanomaterials (NMs) solve specific problems with remarkable results in several industrial and scientific areas. Among NMs, silver nanoparticles (AgNPs) have been extensively employed as drug carriers, medical diagnostics, energy harvesting devices, sensors, lubricants, and bioremediation. Notably, they have shown excellent antimicrobial, anticancer, and antiviral properties in the biomedical field. The literature analysis shows a selective cytotoxic effect on cancer cells compared to healthy cells, making its potential application in cancer treatment evident, increasing the need to study the potential risk of their use to environmental and human health. A large battery of toxicity models, both in vitro and in vivo, have been established to predict the harmful effects of incorporating AgNPs in these numerous areas or those produced due to involuntary exposure. However, these models often report contradictory results due to their lack of standardization, generating controversy and slowing the advances in nanotoxicology research, fundamentally by generalizing the biological response produced by the AgNP formulations. This review summarizes the last ten years’ reports concerning AgNPs’ toxicity in cellular respiratory system models (e.g., mono-culture models, co-cultures, 3D cultures, ex vivo and in vivo). In turn, more complex cellular models represent in a better way the physical and chemical barriers of the body; however, results should be used carefully so as not to be misleading. The main objective of this work is to highlight current models with the highest physiological relevance, identifying the opportunity areas of lung nanotoxicology and contributing to the establishment and strengthening of specific regulations regarding health and the environment.

Effects of Heavy Metals on the Performance and Mechanism of Anaerobic Ammonium Oxidation for Treating Wastewater

Persistence of ammonium nitrogen and heavy metals in wastewater still remains a challenge, and many wastewater treatment plants face the challenge of removing nitrogen under heavy metal stresses. There is no preferred method for the biological treatment of wastewater containing nitrogen and heavy metals with the possible exception of the anaerobic ammonium oxidation (anammox), since it has shown promise for removing nitrogen under heavy metal stresses. This article reviews the recent research results of the nitrogen-removal performance and mechanism by the anammox process under heavy metal stresses, mainly discussing the enhancing and inhibition effects of heavy metals on the performance of the Anammox reactor. The influencing mechanism of heavy metals on the microbial community and extracellular polymeric substances is also presented, and examples are given for explanation. The main problems of the present research are pointed out, and it is proposed that unifying the metal ion concentrations of inhibiting or promoting anammox activity is necessary for the development and industrial application of the anammox process. The information of this review can offer a great possibility for achieving desired nitrogen removal in wastewater treatment under heavy metal stresses and with significant energy savings.

Focus on using nanopore technology for societal health, environmental, and energy challenges

With an increasing global population that is rapidly ageing, our society faces challenges that impact health, environment, and energy demand. With this ageing comes an accumulation of cellular changes that lead to the development of diseases and susceptibility to infections. This impacts not only the health system, but also the global economy. As the population increases, so does the demand for energy and the emission of pollutants, leading to a progressive degradation of our environment. This in turn impacts health through reduced access to arable land, clean water, and breathable air. New monitoring approaches to assist in environmental control and minimize the impact on health are urgently needed, leading to the development of new sensor technologies that are highly sensitive, rapid, and low-cost. Nanopore sensing is a new technology that helps to meet this purpose, with the potential to provide rapid point-of-care medical diagnosis, real-time on-site pollutant monitoring systems to manage environmental health, as well as integrated sensors to increase the efficiency and storage capacity of renewable energy sources. In this review we discuss how the powerful approach of nanopore based single-molecule, or particle, electrical promises to overcome existing and emerging societal challenges, providing new opportunities and tools for personalized medicine, localized environmental monitoring, and improved energy production and storage systems.

Absorption and Resonance Rayleigh Scattering Spectra of Ag(I) and Erythrosin System and Their Analytical Application in Food Safety

In pH 4.4∼4.6 weakly acidic media, erythrosine (Ery) can react with Ag(I) to form hydrophobic ion-association complex, which can further aggregate to form nanoparticles with an average particle size of about 45 nm under the action of water phase extrusion and van der Waals force. As a result, it could lead to a decrease of absorbance, a significant enhancement of resonance Rayleigh scattering (RRS) and the appearance of a new emission spectrum. Based on these Phenomena, two new methods (spectrophotometry and RRS) were established for the determination of trace Ag(I). The detection limits for Ag(I) by spectrophotometry and RRS are 9.74 and 0.12 ng/ml, respectively. In this paper, we have investigated the formation of nanoparticles, the optimum reaction conditions, the influence factors, explored the reason for enhancement of the scattering intensity and the effect of coexisting substance. This research shows that RRS method not only has good selectivity and high sensitivity, but also is simple and rapid. Analyzing of actual samples and standard samples, the determination result of this method is consistent with that of standard methods (Flame atomic absorption spectroscopy). Thus the method had potential feasibility to analysis for Ag(I) in the environmental water samples, pharmaceutical, and food industries.

Hypothetical Mechanism of Skin Argyria

Introduction. Argyria is an acquired skin condition that appears after the exposure or consumption of silver, leading to blue or grey coloration of the skin and mucosa. The aim of the present work was to draw researchers’ attention to two aspects of the argyria that until now have not received enough consideration. They are: (1) the process of delivering silver compound from the gastrointestinal tract to the skin and (2) the possibility for silver chloride to participate in this process along with the silver proteinates. Methodology. Illustrative experiments included the observation of color change (visual and using UV-Vis spectrometry) under different light exposure conditions of silver chloride sol in a sweat-simulating solution, in vials and under pig skin (in direct contact). Results and Discussion. A hypothetical mechanism based on a perspiration system for delivering the silver compounds from the gastrointestinal tract to the skin for argyria was proposed. It was also proposed not to completely exclude the partial participation of silver chloride along with the silver proteinates in this process.

Ex vivo exposure to titanium dioxide and silver nanoparticles mildly affect sperm of gilthead seabream (Sparus aurata) - A multiparameter spermiotoxicity approach

Nanoparticles (NP) are potentially reprotoxic, which may compromise the success of populations. However, the reprotoxicity of NP is still scarcely addressed in marine fish. Therefore, we evaluated the impacts of environmentally relevant and supra environmental concentrations of titanium dioxide (TiO₂: 10 to 10,000 μg·L^-1) and silver NP (Ag: 0.25 to 250 μg·L^-1) on the sperm of gilthead seabream (Sparus aurata). We performed short-term direct exposures (ex vivo) and evaluated sperm motility, head morphometry, mitochondrial function, antioxidant responses and DNA integrity. No alteration in sperm motility (except for supra environmental Ag NP concentration), head morphometry, mitochondrial function, and DNA integrity occurred. However, depletion of all antioxidants occurred after exposure to TiO₂ NP, whereas SOD decreased after exposure to Ag NP (lowest and intermediate concentration). Considering our results, the decrease in antioxidants did not indicate vulnerability towards oxidative stress. TiO₂ NP and Ag NP induced low spermiotoxicity, without proven relevant ecological impacts.

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

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

A review on silver-mediated DNA base pairs: methodology and application

The investigation of the interaction between metal ions and DNA has always attracted much attention in the fields of bioinorganic chemistry, supramolecular coordination chemistry, and DNA nanotechnology. Its mode of action can be simply divided into two aspects. On the one hand, it is non-specific electrostatic adsorption, mainly including Na⁺, K⁺, Mg²⁺, Ca²⁺ and other physiologically regulating ions; on the other hand, it is specific covalent binding, such as Pt²⁺, Hg²⁺, Ag⁺ and other heavy metal ions. This article focuses on the mechanism of action between Ag⁺ and DNA mismatch pair C-C, and summarizes its main characterization methods and various applications. It aims to provide a certain reference for the field of biological devices. With the development of cryo-electron microscopy and liquidcell TEM, the structure of C-Ag⁺-C is expected to be further characterized, which will be more widely used.

The Influence of Silver Nanoparticle Form on the Toxicity in Freshwater Mussels

The contribution of the form of silver nanomaterials (nAg) towards toxicity in aquatic organisms is not well understood. The purpose of this study was to examine the toxicity of various structures (sphere, cube and prism) of nAg in Dreissena bugensis mussels. Mussels were exposed to increasing concentrations of polyvinyl-coated nAg of the same size for 96 h at 15 °C. They were then analyzed for biophysical changes in the cytoplasm (viscosity, protein aggregation and lipids), neuro-activity (fractal kinetics of acetylcholinesterase (AChE)), oxidative stress (labile zinc (Zn) and lipid peroxidation) and inflammation (arachidonate cyclooxygenase). Although some decreasing effects in protein aggregation were observed, viscosity was more strongly decreased in mussels exposed to spheric and prismatic nAg. The activity of AChE was significantly decreased in the following form-dependent manner: prismatic > cubic > spheric nAg. The fractal dimension of AChE reactions was reduced by all geometries of nAg, while dissolved Ag had no effects. For nanoparticles with the same coating and relative size, spheric nAg produced more significant changes towards the fractal dimension of AChE, while prismatic nAg increased both protein aggregation and viscosity, whereas cubic nAg decreased protein aggregation in the cytoplasm. It is concluded that the geometries of nanoparticles could influence toxicity in aquatic organisms.

The impact of silver nanoparticles on microbial communities and antibiotic resistance determinants in the environment

Nanosilver (NAg) is currently one of the major alternative antimicrobials to control microorganisms. With its broad-spectrum efficacy and lucrative commercial values, NAg has been used in medical devices and increasingly, in consumer products and appliances. This widespread use has inevitably led to the release and accumulation of the nanoparticle in water and sediment, in soil and even, wastewater treatment plants (WWTPs). This Article describes the physical and chemical transformations of NAg as well as the impact of the nanoparticle on microbial communities in different environmental settings; how the nanoparticle shifts not only the diversity and abundance of microbes, including those that are important in nitrogen cycles and decomposition of organic matters, but also their associated genes and in turn, the key metabolic processes. Current findings on the microbiological activity of the leached soluble silver, solid silver particulates and their respective transformed products, which underpin the mechanism of the nanoparticle toxicity in environmental microbes, is critically discussed. The Article also addresses the emerging evidence of silver-driven co-selection of antibiotic resistance determinants. The mechanism has been linked to the increasing pools of many antibiotic resistance genes already detected in samples from different environmental settings, which could ultimately find their ways to animals and human. The realized ecological impact of NAg calls for more judicial use of the nanoparticle. The generated knowledge can inform strategies for a better 'risks versus benefits' assessment of NAg applications, including the disposal stage.

Aquatic macrophytes mitigate the short-term negative effects of silver nanoparticles on denitrification and greenhouse gas emissions in riparian soils

Silver nanoparticles (AgNPs) are increasingly released into the aquatic environments because of their extensive use in consumer products and industrial applications. Some researchers have explored the toxicity of AgNPs to nitrogen (N) and carbon (C) cycles, but little is known about the role of aquatic plants in regulating the impact of AgNPs on these biogeochemical processes and related microorganisms. Here, two 90-day pot experiments were conducted to determine the effect of AgNPs on denitrification rates and greenhouse gas emissions in riparian wetland soils, with or without emergent plants (Typha minima Funck). As a comparison, the toxicity of equal concentration of AgNO₃ was also determined. The results showed that AgNPs released a great quantity of free Ag⁺, most of which was accumulated in soils, while little (less than 2%) was absorbed by plant shoots and roots. Both AgNPs and AgNO₃ could increase the soil redox potential and affect the growth and nutrient (N and phosphorus) uptake of plants. In soils with plants, there was no significant difference in denitrification rates and emissions of N₂O and CH₄ between control and AgNPs or AgNO₃ treatments at all tested concentrations (0.5, 1 and 10 mg kg^-1). However, low levels of AgNPs (0.5 mg kg^-1) significantly enhanced CO₂ emission throughout the experiment. Interestingly, in the absence of plants, a high dosage (10 mg kg^-1) of AgNPs generally inhibited soil denitrification and stimulated the emissions of CO₂, CH₄ and N₂O in the short-term. Meanwhile, the abundance of key denitrifying genes (nirS and nirK) was significantly increased by exposure to 10 mg kg^-1 AgNPs or AgNO₃. Our results suggest that emergent plants can alleviate the short-term negative effects of AgNPs on N and C cycling processes in wetland soils through different pathways.

Ab initio modeling of H2S dissociative chemisorption on Ag(100)

Natural sulfidation of silver nanomaterials can passivate the surface, while preserving desirable optical and electrical properties, which is beneficial for limiting Ag+ release and cytotoxicity. But little is known at...

Legionella: A Promising Supplementary Indicator of Microbial Drinking Water Quality in Municipal Engineered Water Systems

Opportunistic pathogens (OPs) are natural inhabitants and the predominant disease causative biotic agents in municipal engineered water systems (EWSs). In EWSs, OPs occur at high frequencies and concentrations, cause drinking-water-related disease outbreaks, and are a major factor threatening public health. Therefore, the prevalence of OPs in EWSs represents microbial drinking water quality. Closely or routinely monitoring the dynamics of OPs in municipal EWSs is thus critical to ensuring drinking water quality and protecting public health. Monitoring the dynamics of conventional (fecal) indicators (e.g., total coliforms, fecal coliforms, and Escherichia coli) is the customary or even exclusive means of assessing microbial drinking water quality. However, those indicators infer only fecal contamination due to treatment (e.g., disinfection within water utilities) failure and EWS infrastructure issues (e.g., water main breaks and infiltration), whereas OPs are not contaminants in drinking water. In addition, those indicators appear in EWSs at low concentrations (often absent in well-maintained EWSs) and are uncorrelated with OPs. For instance, conventional indicators decay, while OPs regrow with increasing hydraulic residence time. As a result, conventional indicators are poor indicators of OPs (the major aspect of microbial drinking water quality) in EWSs. An additional or supplementary indicator that can well infer the prevalence of OPs in EWSs is highly needed. This systematic review argues that Legionella as a dominant OP-containing genus and natural inhabitant in EWSs is a promising candidate for such a supplementary indicator. Through comprehensively comparing the behavior (i.e., occurrence, growth and regrowth, spatiotemporal variations in concentrations, resistance to disinfectant residuals, and responses to physicochemical water quality parameters) of major OPs (e.g., Legionella especially L. pneumophila, Mycobacterium, and Pseudomonas especially P. aeruginosa), this review proves that Legionella is a promising supplementary indicator for the prevalence of OPs in EWSs while other OPs lack this indication feature. Legionella as a dominant natural inhabitant in EWSs occurs frequently, has a high concentration, and correlates with more microbial and physicochemical water quality parameters than other common OPs. Legionella and OPs in EWSs share multiple key features such as high disinfectant resistance, biofilm formation, proliferation within amoebae, and significant spatiotemporal variations in concentrations. Therefore, the presence and concentration of Legionella well indicate the presence and concentrations of OPs (especially L. pneumophila) and microbial drinking water quality in EWSs. In addition, Legionella concentration indicates the efficacies of disinfectant residuals in EWSs. Furthermore, with the development of modern Legionella quantification methods (especially quantitative polymerase chain reactions), monitoring Legionella in ESWs is becoming easier, more affordable, and less labor-intensive. Those features make Legionella a proper supplementary indicator for microbial drinking water quality (especially the prevalence of OPs) in EWSs. Water authorities may use Legionella and conventional indicators in combination to more comprehensively assess microbial drinking water quality in municipal EWSs. Future work should further explore the indication role of Legionella in EWSs and propose drinking water Legionella concentration limits that indicate serious public health effects and require enhanced treatment (e.g., booster disinfection).

Nano-QTTR development for interspecies aquatic toxicity of silver nanoparticles between daphnia and fish

Limited studies of quantitative toxicity-toxicity relationship (QTTR) modeling have been conducted to predict interspecies toxicity of engineered nanomaterials (ENMs) between aquatic test species. A meta-analysis of 66 publications providing acute toxicity data of silver nanoparticles (AgNPs) to daphnia and fish was performed, and the toxicity data, physicochemical properties, and experimental conditions were collected and curated. Based on Euclidean distance (ED) grouping, a meaningful correlation of logarithmic lethal concentrations between daphnia and fish was derived for bare (R²_bare = 0.47) and coated AgNPs (R²_coated = 0.48) when a distance of 10 was applied. The correlation of coated AgNPs was improved (R²_coated = 0.55) by the inclusion of descriptors of the coating materials. The correlations were further improved by R²_bare = 0.57 and R²_coated = 0.81 after additionally considering particle size only, and by R²_bare = 0.59 and R²_coated = 0.92 after considering particle size and zeta potential simultaneously. The developed ED-based nano-QTTR model demonstrated that inclusion of the coating material descriptors and physicochemical properties improved the goodness-of-fit to predict interspecies aquatic toxicity of AgNPs between daphnia and fish. This study provides insight for future in silico research on QTTR model development in ENM toxicology.

Stability and Microbial Toxicity of Silver Nanoparticles under Denitrifying Conditions

While the antibacterial effect of silver nanoparticles (AgNPs) on environmentally beneficial microbes has drawn considerable attention, the stability and microbial toxicity of AgNPs in a system where nitrate reduction is the dominant terminal electron-accepting process remain understudied. Here, we explore the impact of citrate-coated AgNPs (cit-AgNPs) on the growth and metabolism of two metal-sensitive and one nonsensitive bacterial strains under denitrifying conditions. Dose-response analysis revealed that in contrast to the bacteriostatic effect exhibited at 1 ppm, 5 ppm cit-AgNPs were bactericidal to the metal-sensitive strains. It was observed that the growth of the cells initiated Ag(I) formation, and the supplement of chloride (2.7 mM) to the cultures substantially mitigated the bactericidal capacity of cit-AgNPs, indicating that AgNP dissolution to ionic Ag(I) played a key role in AgNP toxicity. Abiotic experiments confirmed that nitrite, not nitrate, had the capacity to oxidize cit-AgNPs. Transcriptomic analysis revealed that (i) the gene encoding for membrane stress was upregulated proportionally to cit-AgNP concentrations; (ii) cit-AgNPs and Ag(I) at higher levels upregulated genes involved in oxidative stress and iron-sulfur clusters, whereas expressions of the genes responsible for electron transport, ATP synthesis, and denitrification were substantially repressed; (iii) the addition of chloride significantly altered the level of transcriptional profiles of all of the genes. These results not only provide evidence of abiotic AgNP oxidation by metabolic intermediate nitrogen species but also suggest that AgNPs and Ag(I) may induce differential toxicity modes to prokaryotes. Our findings reinforce the importance of evaluating the potential ecological toxicity and risks associated with the transformation of nanomaterials.