Transfer of gold nanoparticles from the water column to the estuarine food web

Trophic transfer of nanomaterials and their effects on high-trophic-level predators

Nanotechnology offers great opportunities for numerous sectors in society. One important challenge in sustainable nanotechnology is the potential of trophic transfer of nanomaterials (NMs), which may lead to unintentional impacts on environmental and human health. Here, we highlight the key advances that have been made in recent 15 years with respect to trophic transfer of heterogeneous NMs, including metal-based NMs, carbon-based NMs and nanoplastics, across various aquatic and terrestrial food chains. Particle number-based trophic transfer factors (TTFs), rather than the variable mass-based TTFs, capture the particle-specific transfer, for which NMs exhibit dynamic and complex biotransformation (e.g., dissolution, sulfidation, reduction, and corona formation). Trophic transfer of NMs has toxicological significance to predators at molecular (e.g., increased oxidative stress and modified metabolites), physiological (e.g., feeding inhibition) and population (e.g., reproduction inhibition) levels. However, linking NM exposure and toxicity remains a challenge, partly due to the dynamic biotransformation along the food chain. Although NMs have been used to increase crop yield in agriculture, they can exert detrimental impacts on crop yield and modify crop quality, depending on NMs type, exposure dose, and crop species, with unknown consequences to human health via crop consumption. Given this information, we describe the challenges and opportunities in understanding the significance of NMs trophic transfer to develop more sustainable, effective and safer nanotechnology.

Seasonal Differences and Grazing Pressure Alter the Fate of Gold Nanoparticles in a Microcosm Experiment

Gold nanoparticles (AuNPs) are used as models to track and predict NP fates and effects in ecosystems. Previous work found that aquatic macrophytes and their associated biofilm primarily drove the fate of AuNPs within aquatic ecosystems and that seasonality was an important abiotic factor in the fate of AuNPs. Therefore, the present work aims to study if grazers, by feeding on these interfaces, modify the AuNP fate and if this is altered by seasonal fluctuations. Microcosms were dosed with 44.8 μg/L of AuNP weekly for 4 weeks and maintained in environmental chambers simulating Spring and Fall light and temperature conditions. We discovered that seasonal changes and the presence of grazers significantly altered the fate of Au. Higher temperatures in the warmer season increased dissolved organic carbon (DOC) content in the water column, leading to stabilization of Au in the water column. Additionally, snail grazing on biofilm growing on the Egeria densa surface led to a transfer of Au from macrophytes to the organic matter above the sediments. These results demonstrate that climate and grazers significantly impacted the fate of Au from AuNPs, highlighting the role that grazers might have in a large and biologically more complex ecosystem.

Gold Nanoparticles as Exquisite Colorimetric Transducers for Water Pollutant Detection

Gold nanoparticles (AuNPs) are useful nanomaterials as transducers for colorimetric sensors because of their high extinction coefficient and ability to change color depending on aggregation status. Therefore, over the past few decades, AuNP-based colorimetric sensors have been widely applied in several environmental and biological applications, including the detection of water pollutants. According to various studies, water pollutants are classified into heavy metals or cationic metal ions, toxins, and pesticides. Notably, many researchers have been interested in AuNP that detect water pollutants with high sensitivity and selectivity, while offering no adverse environmental issues in terms of AuNP use. This review provides a representative overview of AuNP-based colorimetric sensors for detecting several water pollutants. In particular, we emphasize the advantages of AuNP as colorimetric transducers for water pollutant detection in terms of their low toxicity, high stability, facile processability, and unique optical properties. Next, we discuss the status quo and future prospects of AuNP-based colorimetric sensors for the detection of water pollutants. We believe that this review will promote research and development of AuNP as next-generation colorimetric transducers for water pollutant detection.

The Toxic Effects of Cu and CuO Nanoparticles on Euplotes aediculatus

The single-celled eukaryote Euplotes aediculatus was chosen to test and compare the toxic effects of Cu and CuO nanoparticles (NPs). The antioxidant enzymatic activity, morphological changes, and functional groups on the membrane were determined using spectrophotometry, microscopy, and Fourier transform infrared spectroscopy after NPs treatment. The toxicity of the NPs to cells was dose-dependent, and the 24 h-LC₅₀ values of the CuNPs and CuONPs were 0.46 µg/L and 1.24 × 10³ µg/L, respectively. These NPs increased the activities of superoxide dismutase, glutathione peroxidase, and catalase and destroyed the cell structure; moreover, the CuNPs were more toxic than the CuONPs. In addition to the higher enzymatic activity, CuNPs also caused nucleoli disappearance, chromatin condensation, and mitochondrial and pellicle damage. The oxidization of the functional groups of the membrane (PO₂ - , C-O-C, and δ(COH) of carbohydrates) also confirmed the severe damage caused by CuNPs. Our study showed that oxidative stress and organelle destruction played important roles in the toxic effects of these NPs on this protozoan. Compared with other aquatic organisms, E. aediculatus can be considered a potential indicator at the preliminary stage of environmental pollution.

Metal transfer to sediments, invertebrates and fish following waterborne exposure to silver nitrate or silver sulfide nanoparticles in an indoor stream mesocosm

The fate of engineered nanomaterials in ecosystems is unclear. An aquatic stream mesocosm explored the fate and bioaccumulation of silver sulfide nanoparticles (Ag₂S NPs) compared to silver nitrate (AgNO₃). The aims were to determine the total Ag in water, sediment and biota, and to evaluate the bioavailable fractions of silver in the sediment using a serial extraction method. The total Ag in the water column from a nominal daily dose of 10 μg L^-1 of Ag for the AgNO₃ or Ag₂S NP treatments reached a plateau of around 13 and 12 μg L^-1, respectively, by the end of the study. Similarly, the sediment of both Ag-treatments reached ~380 μg Ag kg^-1, and with most of it being acid-extractable/labile. The biota accumulated 4-59 μg Ag g^-1 dw, depending on the type of Ag-treatment and organism. The oligochaete worm, Lumbriculus variegatus, accumulated Ag from the Ag₂S exposure over time, which was similar to the AgNO₃ treatment by the end of the experiment. The planarian, Girardia tigrina, and the chironomid larva, Chironomus riparius, showed much higher Ag concentrations than the oligochaete worms; and with a clearer time-dependent statistically significant Ag accumulation relative to the untreated controls. For the pulmonate snail, Physa acuta, bioaccumulation of Ag from AgNO₃ and Ag₂S NP exposures was observed, but was lower from the nano treatment. The AgNO₃ exposure caused appreciable Ag accumulation in the water flea, Daphnia magna, but accumulation was higher in the Ag₂S NP treatment (reaching 59 μg g^-1 dw). In the rainbow trout, Oncorhynchus mykiss, AgNO₃, but not Ag₂S NPs, caused total Ag concentrations to increase in the tissues. Overall, the study showed transfer of total Ag from the water column to the sediment, and Ag bioaccumulation in the biota, with Ag from Ag₂S NP exposure generally being less bioavailable than that from AgNO₃.

Fungicidal and antibiofilm activities of gold nanoparticles on Candida tropicalis

Aim: To investigate the antifungal activity of two different functionalized gold nanoparticles (AuNP), those stabilized with cetyltrimethylammonium bromide and those conjugated with cysteine, and their effects on the architecture of Candida tropicalis biofilms. Materials & methods: Biofilms were studied by crystal violet binding assay and scanning electron microscopy. We investigated the effects of AuNPs on reactive oxygen species, reactive nitrogen intermediates and enzymatic and nonenzymatic antioxidant defenses. Results/Conclusion: The fungicidal activity and cellular stress of both AuNPs affected biofilm growth through accumulation of reactive oxygen species and reactive nitrogen intermediates. However, cetyltrimethylammonium bromide-stabilized AuNPs revealed a higher redox imbalance. We correlated, for the first time, AuNP effects with the redox imbalance and alterations in the architecture of C. tropicalis biofilms.

Environmental Fate of Metal Nanoparticles in Estuarine Environments

In the last decade, metal engineered nanomaterials (ENMs) have seen an exponential use in many critical technologies and products, as well an increasing release into the environment. Coastal ecosystems worldwide may receive ENM-polluted waters and wastes, with a consequent alteration of habitats and contamination of aquatic biota. There is a scarcity of data regarding the fate of these emerging contaminants in such environments. Open issues include the determination of the sources, the quantification of the interactions with marine sediments, the bioaccumulation pathways, the ecotoxicology on marine fauna and the identification of the principal biotic and abiotic factors that may alter metal ENMs toxicity. Little is known about their potential transference into the food web, as well toxicity features and co-stressors of single or multiple ENMs under laboratory and real environmental conditions for various taxonomic phyla. This review reports current knowledge on the ecological impact of ENMs under the complex environmental conditions of estuary systems, identifies gaps in current knowledge and provides directions for future research.

Emerging trends in nanoparticle toxicity and the significance of using Daphnia as a model organism

Nanoparticle production is on the rise due to its many uses in the burgeoning nanotechnology industry. Although nanoparticles have growing applications, there is great concern over their environmental impact due to their inevitable release into the environment. With uncertainty of environmental concentration and risk to aquatic organisms, the microcrustacean Daphnia spp. has emerged as an important freshwater model organism for risk assessment of nanoparticles because of its biological properties, including parthenogenetic reproduction; small size and short generation time; wide range of endpoints for ecotoxicological studies; known genome, useful for providing mechanistic information; and high sensitivity to environmental contaminants and other stressors. In this review, we (1) highlight the advantages of using Daphnia as an experimental model organism for nanotoxicity studies, (2) summarize the impacts of nanoparticle physicochemical characteristics on toxicity in relation to Daphnia, and (3) summarize the effects of nanoparticles (including nanoplastics) on Daphnia as well as mechanisms of toxicity, and (4) highlight research uncertainties and recommend future directions necessary to develop a deeper understanding of the fate and toxicity of nanoparticles and for the development of safer and more sustainable nanotechnology.

Co-exposure of carbon nanotubes with carbofuran pesticide affects metabolic rate in Palaemon pandaliformis (shrimp)

Palaemon pandalirformis (shrimp) is a species widely distributed in the Brazilian coastal region and with an important economic role. In addition, this organism is considered an indicator of environmental pollution in estuaries; however, its physiological responses to toxic environmental pollutants, including pesticides and nanomaterials, are not well known, mainly, the effects of co-exposure. Thus, the purpose of this study was to evaluate the ecotoxicological effects of co-exposure between oxidized multiwalled carbon nanotubes (HNO₃-MWCNT) and carbofuran pesticide on the routine metabolism of P. pandalirformis. The shrimps were exposed to different concentrations of HNO₃-MWCNT (0; 10; 100; 500; 1000 μg L^-1), carbofuran (0; 0.1; 1.0; 5.0; 10 μg L^-1) and to co-exposure with 100 μg L^-1 of HNO₃-MWCNT + carbofuran (0; 0.1; 1.0; 5.0; 10 μg L^-1), to evaluate the effects on metabolic rate (O₂ consumption) and excretion of ammonia (NH₄+NH₃). Our results showed that the shrimps exposed to HNO₃-MWCNT (10 μg L^-1) increased the metabolic rate by 292% and the excretion of ammonia by 275%; those exposed to carbofuran (10 μg L^-1) increased their metabolic rate by 162% and the excretion of ammonia by 425%; and with the co-exposure of HNO₃-MWCNT + carbofuran there was also an increase in the metabolic rate by 317% and an excretion of ammonia by 433% when compared to control. These findings provides useful information toward better understanding the physiological responses of shrimps after combined exposure to nanomaterials and pesticides in aquatic environments.

Contribution, Composition, and Structure of EPS by In Vivo Exposure to Elucidate the Mechanisms of Nanoparticle-Enhanced Bioremediation to Metals

Bacterial extracellular polymeric substances (EPS) have been recently found to contribute most for metal removal in nanoenhanced bioremediation. However, the mechanism by which NPs affect EPS-metal interactions is not fully known. Here, Halomonas sp. was employed to explore the role of EPS after in vivo exposure to Cd/Pb and polyvinylpyrrolidone (PVP) coated iron oxide nanoparticles (IONPs, 20 mg L^-1) for 72 h. Cd-IONPs produced the highest concentrations of EPS proteins (136.3 mg L^-1), while Cd induced the most production of polysaccharides (241.0 mg L^-1). IONPs increased protein/polysaccharides ratio from 0.2 (Cd) to 1.2 (Cd-IONPs). The increased protein favors the formation of protein coronas on IONPs surface, which would promote Cd adsorption during NP-metal-EPS interaction. FTIR analysis indicated that the coexistence of Cd and IONPs interacted with proteins more strongly than with polysaccharides. Glycosyl monomer analyses suggested mannose and glucose as target sugars for EPS complexation with metals, and IONPs reduced metal-induced changes in monosaccharide profiles. Protein secondary structures changed in all treatments, but we could not distinguish stresses induced by metals from those by IONPs. These findings provide greater understanding of the role of EPS in NP-metal-EPS interaction, providing a better underpinning knowledge for the application of NP-enhanced bioremediation.

Aquatic Mesocosm Strategies for the Environmental Fate and Risk Assessment of Engineered Nanomaterials

In the past decade, mesocosms have emerged as a useful tool for the environmental study of engineered nanomaterials (ENMs) as they can mimic the relevant exposure scenario of contamination. Herein, we analyzed the scientific outcomes of aquatic mesocosm experiments, with regard to their designs, the ENMs tested, and the end points investigated. Several mesocosm designs were consistently applied in the past decade to virtually mimic various contamination scenarios with regard to ecosystem setting as well as ENMs class, dose, and dosing. Statistical analyses were carried out with the literature data to identify the main parameters driving ENM distribution in the mesocosms and the potential risk posed to benthic and planktonic communities as well as global ecosystem responses. These analyses showed that at the end of the exposure, mesocosm size (water volume), experiment duration, and location indoor/outdoor had major roles in defining the ENMs/metal partitioning. Moreover, a higher exposure of the benthic communities is often observed but did not necessarily translate to a higher risk due to the lower hazard posed by transformed ENMs in the sediments (e.g., aggregated, sulfidized). However, planktonic organisms were generally exposed to lower concentrations of potentially more reactive and toxic ENM species. Hence, mesocosms can be complementary tools to existing standard operational procedures for regulatory purposes and environmental fate and risk assessment of ENMs. To date, the research was markedly unbalanced toward the investigation of metal-based ENMs compared to metalloid- and carbon-based ENMs but also nanoenabled products. Future studies are expected to fill this gap, with special regard to high production volume and potentially hazardous ENMs. Finally, to take full advantage of mesocosms, future studies must be carefully planned to incorporate interdisciplinary approaches and ensure that the large data sets produced are fully exploited.

Transformation and release of micronized Cu used as a wood preservative in treated wood in wetland soil

Micronized Cu (μ-Cu) is used as a wood preservative, replacing toxic chromated copper arsenate (CCA). Micronized Cu is malachite [Cu₂CO₃(OH)₂] that has been milled to micron/submicron particles, with many particle diameters less than 100 nm, mixed with biocides and then used to treat wood. In addition to concerns about the fate of the Cu from μ-Cu, there is interest in the fate of the nano-Cu (n-Cu) constituents. We examined movement of Cu from μ-Cu-treated wood after placing treated-wood stakes into model wetland ecosystems. Release of Cu into surface and subsurface water was monitored. Surface water Cu reached maximum levels 3 days after stake installation and remained elevated if the systems remained inundated. Subsurface water Cu levels were 10% of surface water levels at day 3 and increased gradually thereafter. Sequential filtering indicated that a large portion of the Cu in solution was associating with soluble organics, but there was no evidence for n-Cu in solution. After 4 months, Cu in thin-sections of treated wood and adjacent soil were characterized with micro X-ray absorption fine structure spectroscopy (μ-XAFS). Localization and speciation of Cu in the wood and adjacent soil using μ-XAFS clearly indicated that Cu concentrations decreased over time in the treated wood and increased in the adjacent soil. However, n-Cu from the treated wood was not found in the adjacent soil or plant roots. The results of this study indicate that Cu in the μ-Cu-treated wood dissolves and migrates into adjacent soil and waters primarily in ionic form (i.e., Cu²⁺) and not as nano-sized Cu particles. A reduced form of Cu (Cu₂S) was identified in deep soil proximal to the treated wood, indicating strong reducing conditions. The formation of the insoluble Cu₂S effectively removes some portion of dissolved Cu from solution, reducing movement of Cu²⁺ to the water column and diminishing exposure.

Comprehensive Interrogation of Metabolic and Bioenergetic Responses of Early-Staged Zebrafish (Danio rerio) to a Commercial Copper Hydroxide Nanopesticide

The use of copper hydroxide nanopesticide can pose exposure risks to aquatic organisms. In this study, the toxicity of a copper hydroxide nanopesticide, compared to conventional copper sulfate at environmentally relevant doses, was evaluated using metabolomics and bioenergetic assays in embryonic zebrafish. At a copper concentration of 100 μg/L, the nanopesticide caused higher mortality and deformity compared to copper ions alone; despite higher copper accumulation, increased metallothionein and elevated ATP-binding cassette (ABC) transporter activity in zebrafish exposed to copper ions were observed. Both nanopesticide and copper ions reduced the abundance of metabolites of glycolysis and induced energetic stress in zebrafish. The nanopesticide also increased concentrations of several organic acids involved in the tricarboxylic acid (TCA) cycle and elevated the activity of isocitrate dehydrogenase and α-ketoglutarate dehydrogenase, suggesting enhanced TCA cycle activity. Nanopesticide exposure depleted both glutamate and glutamine parallel to the upregulation of the TCA cycle. In addition, zebrafish exposed to the nanopesticide appeared to shift metabolism toward amino acid catabolism and lipid accumulation based upon altered expression profiles of glutaminase, glutamate dehydrogenase, fatty acid synthase, and acetyl-CoA carboxylase. Lastly, the ability of the ions to increase oxidative phosphorylation to alleviate energetic stress was reduced in the case of the nanopesticide. We hypothesize that, unlike copper ions alone, the nanopesticide induces higher toxicity to zebrafish because of increased protein catabolism. This study provides a comprehensive understanding of the risks of copper hydroxide nanopesticide exposure in relation to metabolic activity and mitochondrial function.

Eradication of Mature Bacterial Biofilms with Concurrent Improvement in Chronic Wound Healing Using Silver Nanoparticle Hydrogel Treatment

Biofilm-associated infections are a major cause of impaired wound healing. Despite the broad spectrum of anti-bacterial benefits provided by silver nanoparticles (AgNPs), these materials still cause controversy due to cytotoxicity and a lack of efficacy against mature biofilms. Herein, highly potent ultrasmall AgNPs were combined with a biocompatible hydrogel with integrated synergistic functionalities to facilitate elimination of clinically relevant mature biofilms in-vivo combined with improved wound healing capacity. The delivery platform showed a superior release mechanism, reflected by high biocompatibility, hemocompatibility, and extended antibacterial efficacy. In vivo studies using the S. aureus wound biofilm model showed that the AgNP hydrogel (200 µg/g) was highly effective in eliminating biofilm infection and promoting wound repair compared to the controls, including silver sulfadiazine (Ag SD). Treatment of infected wounds with the AgNP hydrogel resulted in faster wound closure (46% closure compared to 20% for Ag SD) and accelerated wound re-epithelization (60% for AgNP), as well as improved early collagen deposition. The AgNP hydrogel did not show any toxicity to tissue and/or organs. These findings suggest that the developed AgNP hydrogel has the potential to be a safe wound treatment capable of eliminating infection and providing a safe yet effective strategy for the treatment of infected wounds.

Nanotargeting of Resistant Infections with a Special Emphasis on the Biofilm Landscape

Bacterial resistance to antimicrobial compounds is a growing concern in medical and public health circles. Overcoming the adaptable and duplicative resistance mechanisms of bacteria requires chemistry-based approaches. Engineered nanoparticles (NPs) now offer unique advantages toward this effort. However, most in situ infections (in humans) occur as attached biofilms enveloped in a protective surrounding matrix of extracellular polymers, where survival of microbial cells is enhanced. This presents special considerations in the design and deployment of antimicrobials. Here, we review recent efforts to combat resistant bacterial strains using NPs and, then, explore how NP surfaces may be specifically engineered to enhance the potency and delivery of antimicrobial compounds. Special NP-engineering challenges in the design of NPs must be overcome to penetrate the inherent protective barriers of the biofilm and to successfully deliver antimicrobials to bacterial cells. Future challenges are discussed in the development of new antibiotics and their mechanisms of action and targeted delivery via NPs.

In silico nanosafety assessment tools and their ecosystem-level integration prospect

Engineered nanomaterials (ENMs) have tremendous potential in many fields, but their applications and commercialization are difficult to widely implement due to their safety concerns. Recently, in silico nanosafety assessment has become an important and necessary tool to realize the safer-by-design strategy of ENMs and at the same time to reduce animal tests and exposure experiments. Here, in silico nanosafety assessment tools are classified into three categories according to their methodologies and objectives, including (i) data-driven prediction for acute toxicity, (ii) fate modeling for environmental pollution, and (iii) nano-biological interaction modeling for long-term biological effects. Released ENMs may cross environmental boundaries and undergo a variety of transformations in biological and environmental media. Therefore, the potential impacts of ENMs must be assessed from a multimedia perspective and with integrated approaches considering environmental and biological effects. Ecosystems with biodiversity and an abiotic environment may be used as an excellent integration platform to assess the community- and ecosystem-level nanosafety. In this review, the advances and challenges of in silico nanosafety assessment tools are carefully discussed. Furthermore, their integration at the ecosystem level may provide more comprehensive and reliable nanosafety assessment by establishing a site-specific interactive system among ENMs, abiotic environment, and biological communities.

Toxicity of gold nanorods on Ceriodaphnia dubia and Danio rerio after sub-lethal exposure and recovery

Gold nanorods (AuNRs) are rod-shaped nanoparticles (NPs) with special optical properties that allow their application in several areas including photothermal therapy, diagnosis, drug and gene delivery, cellular imaging, and biosensors. Their high potential for many applications increases the possibility of release in aquatic environments, which can cause risks to organisms. In this study, we evaluated toxic effects of AuNRs on cladoceran and fish (Ceriodaphnia dubia and Danio rerio) and their recovery after post-exposure periods. The EC₅₀ of 0.03 mg L^-1 was found for C. dubia in the acute exposure. There was a significant decrease in the number of neonates produced and in the filtration rate of C. dubia after sub-lethal exposure to AuNRs. The toxic mechanism of these NPs to cladocerans was attributed to increases in the reactive oxygen species (ROS) generation. After 4 h of recovery in clean medium, C. dubia were able to reestablish the filtration rate. Enzymatic biomarkers for D. rerio showed significant increases in the activity of superoxide dismutase, catalase, and lipid peroxidation after sub-lethal exposure to AuNRs. These biomarkers were recovered after 168 h in clean water. These results are pivotal on the comprehension of AuNR toxicity to aquatic organisms and are useful in assessing this novel nanomaterial impacts on aquatic biota.

Monitoring chemically and green-synthesized silver nanoparticles in maize seedlings via surface-enhanced Raman spectroscopy (SERS) and their phytotoxicity evaluation

The emergence of nanomaterials in consumer products has increased concern for their potential hazards in the environment and biological systems. Therefore, the monitoring of nanoparticles in biological systems is of great importance. Despite the numerous attempts, the methods to evaluate the uptake, translocation, and accumulation of nanomaterials inside the plant tissue are still limited. In this study, for the first time, we proposed the monitoring of the silver nanoparticles (AgNPs) in different tissues of the plant through surface-enhanced Raman spectroscopy (SERS) approach. For this, chemically (Che-AgNPs) and green-synthesized AgNPs (Gr-AgNPs) were prepared properly and their surfaces were functionalized with Raman-active molecule. With the contribution of electromagnetic enhancement, our NP systems provided high signal-to-noise SERS spectra. After exposure to NPs to maize seedlings as a model plant, we detected that AgNPs were accumulated mainly in the epidermis and cortex of the root and phloem parts of the shoot. Highly distinctive SERS spectra were collected from the root and shoot cross-section of each NP system. Also, the accumulation of the AgNPs was furtherly confirmed through inductively-coupled mass spectrometry and scanning electron microscopy analysis. Moreover, the exposure of AgNPs to maize seedlings led to remarkable alterations in both phytotoxic and biomolecular indicators including chlorophyll, protein and, antioxidant enzymes.

Particle number-based trophic transfer of gold nanomaterials in an aquatic food chain

Analytical limitations considerably hinder our understanding of the impacts of the physicochemical properties of nanomaterials (NMs) on their biological fate in organisms. Here, using a fit-for-purpose analytical workflow, including dosing and emerging analytical techniques, NMs present in organisms are characterized and quantified across an aquatic food chain. The size and shape of gold (Au)-NMs are shown to control the number of Au-NMs attached to algae that were exposed to an equal initial concentration of 2.9 × 10¹¹ particles mL^-1. The Au-NMs undergo size/shape-dependent dissolution and agglomeration in the gut of the daphnids, which determines the size distribution of the NMs accumulated in fish. The biodistribution of NMs in fish tissues (intestine, liver, gills, and brain) also depends on NM size and shape, although the highest particle numbers per unit of mass are almost always present in the fish brain. The findings emphasize the importance of physicochemical properties of metallic NMs in their biotransformations and tropic transfers.

FEAST of biosensors: Food, environmental and agricultural sensing technologies (FEAST) in North America

We review the challenges and opportunities for biosensor research in North America aimed to accelerate translational research. We call for platform approaches based on: i) tools that can support interoperability between food, environment and agriculture, ii) open-source tools for analytics, iii) algorithms used for data and information arbitrage, and iv) use-inspired sensor design. We summarize select mobile devices and phone-based biosensors that couple analytical systems with biosensors for improving decision support. Over 100 biosensors developed by labs in North America were analyzed, including lab-based and portable devices. The results of this literature review show that nearly one quarter of the manuscripts focused on fundamental platform development or material characterization. Among the biosensors analyzed for food (post-harvest) or environmental applications, most devices were based on optical transduction (whether a lab assay or portable device). Most biosensors for agricultural applications were based on electrochemical transduction and few utilized a mobile platform. Presently, the FEAST of biosensors has produced a wealth of opportunity but faces a famine of actionable information without a platform for analytics.

Transfer and Transcriptomic Profiling in Liver and Brain of European Eels (Anguilla anguilla) After Diet-borne Exposure to Gold Nanoparticles

A nanometric revolution is underway, promising technical innovations in a wide range of applications and leading to a potential boost in environmental discharges. The propensity of nanoparticles (NPs) to be transferred throughout trophic chains and to generate toxicity was mainly assessed in primary consumers, whereas a lack of knowledge for higher trophic levels persists. The present study focused on a predatory fish, the European eel (Anguilla anguilla) exposed to gold NPs (AuNPs; 10 nm, polyethylene glycol-coated) for 21 d at 3 concentration levels in food: 0 (NP0), 1 (NP1), and 10 (NP10) mg Au kg^-1 . Transfer was assessed by Au quantification in eel tissues, and transcriptomic responses in the liver and brain were revealed by a high-throughput RNA-sequencing approach. Eels fed at NP10 presented an erratic feeding behavior, whereas Au quantification only indicated transfer to intestine and kidney of NP1-exposed eels. Sequencing of RNA was performed in NP0 and NP1 eels. A total of 258 genes and 156 genes were significantly differentially transcribed in response to AuNP trophic exposure in the liver and brain, respectively. Enrichment analysis highlighted modifications in the immune system-related processes in the liver. In addition, results pointed out a shared response of both organs regarding 13 genes, most of them being involved in immune functions. This finding may shed light on the mode of action and toxicity of AuNPs in fish. Environ Toxicol Chem 2020;39:2450-2461. © 2020 SETAC.

Heterogenous Internalization of Nanoparticles at Ultra-Trace Concentration in Environmental Individual Unicellular Organisms Unveiled by Single-Cell Mass Cytometry

The application and consumption of nanoparticles (NPs) inevitably result in the contamination of environmental water. The internalized NPs in unicellular organisms could travel to human bodies along food chains and raise health concerns. Current research failed to determine the characteristics of cellular uptake of NPs by unicellular organisms at extremely low concentration in the real environment. We here developed a label-free high-throughput mass cytometry method to investigate gold NP (AuNP) uptake in a unicellular organism (Tetrahymena thermophila) at the single-cell level. The limit of detection for Au is as low as to 6.67 × 10^-18 g/cell, which equals ∼5.3 5 nm AuNPs. We demonstrated that active engulfment pathways were responsible for the cellular accumulation of AuNPs and T. thermophila could also eliminate the cellular AuNPs rapidly. The interaction between AuNPs and T. thermophila is highly dependent on the sizes of nanoparticles; i.e., the population of T. thermophila containing AuNPs decreased with the increment of the diameters of AuNPs when exposed to the same mass concentration. For each type of AuNP, distinct heterogeneous cellular uptake of AuNPs by T. thermophila was observed. Intriguingly, for 5 nm AuNP, even at 0.001 ng/mL, some T. thermophila cells could concentrate AuNPs, indicating a real environmental concern even when water was contaminated by only trace level of NPs. This method represents a promising tool for simultaneous determination of physiological status of cells together with the intracellular level of heavy metal or metallic NPs in study of biological effects.

Metal Oxide Nanoparticles Against Bacterial Biofilms: Perspectives and Limitations

At present, there is an urgent need in medicine and industry to develop new approaches to eliminate bacterial biofilms. Considering the low efficiency of classical approaches to biofilm eradication and the growing problem of antibiotic resistance, the introduction of nanomaterials may be a promising solution. Outstanding antimicrobial properties have been demonstrated by nanoparticles (NPs) of metal oxides and their nanocomposites. The review presents a comparative analysis of antibiofilm properties of various metal oxide NPs (primarily, CuO, Fe3O4, TiO2, ZnO, MgO, and Al2O3 NPs) and nanocomposites, as well as mechanisms of their effect on plankton bacteria cells and biofilms. The potential mutagenicity of metal oxide NPs and safety problems of their wide application are also discussed.

The Known and Unknown about the Environmental Safety of Nanomaterials in Commerce

The widespread nanomaterial use in commercial products has fed significant concern over environmental health and safety ramifications. Initially, little was known as to how these highly reactive particulates interacted with biological systems. Nanomaterials have introduced complexities not normally considered in traditional safety assessments of chemicals and therefore have generated uncertainty in the reliability of standard tests of safety. Advances in understanding the potential impacts of nanomaterials have occurred since their introduction, particularly for those used in the greatest quantities in commerce. The impact of characteristics such as charge, size, surface functionalization, chemical composition, and certain transformations on the potential effect of nanomaterials in the environment continue to move the field forward. However, generalizations of risk based on any one factor across nanomaterials is not possible. Estimating risk also remains difficult due to the introduction of materials that are new and more complex, minimal information on the specific molecular interactions of nanomaterials and organisms, and the need for more tools for measuring the dynamics of nanomaterial state and fate in complex matrices. Finally, exposure estimates are difficult due to difficulty of environmental monitoring which may be exacerbated by lack of information on nanomaterials in products and new uses in the marketplace.

Copper and Gold Nanoparticles Increase Nutrient Excretion Rates of Primary Consumers

Freshwater ecosystems are exposed to engineered nanoparticles through municipal and industrial wastewater-effluent discharges and agricultural nonpoint source runoff. Because previous work has shown that engineered nanoparticles from these sources can accumulate in freshwater algal assemblages, we hypothesized that nanoparticles may affect the biology of primary consumers by altering the processing of two critical nutrients associated with growth and survivorship, nitrogen and phosphorus. We tested this hypothesis by measuring the excretion rates of nitrogen and phosphorus of Physella acuta, a ubiquitous pulmonate snail that grazes heavily on periphyton, exposed to either copper or gold engineered nanoparticles for 6 months in an outdoor wetland mesocosm experiment. Chronic nanoparticle exposure doubled nutrient excretion when compared to the control. Gold nanoparticles increased nitrogen and phosphorus excretion rates more than copper nanoparticles, but overall, both nanoparticles led to higher consumer excretion, despite contrasting particle stability and physiochemical properties. Snails in mesocosms enriched with nitrogen and phosphorus had overall higher excretion rates than ones in ambient (no nutrients added) mesocosms. Stimulation patterns were different between nitrogen and phosphorus excretion, which could have implications for the resulting nutrient ratio in the water column. These results suggest that low concentrations of engineered nanoparticles could alter the metabolism of consumers and increase consumer-mediated nutrient recycling rates, potentially intensifying eutrophication in aquatic systems, for example, the increased persistence of algal blooms as observed in our mesocosm experiment.

Phytoremediation of engineered nanoparticles using aquatic plants: Mechanisms and practical feasibility

Certain plants have demonstrated the capability to take up and accumulate metals, thus offering the potential to remediate metal-contaminated water and sediment. Several aquatic species have further been identified which can take up metal and metal oxide engineered nanoparticles (ENPs). It is important to evaluate if aquatic plants exhibiting potential for metal phytoremediation can be applied to remediation of metallic ENPs. Understanding the interactions between ENPs and aquatic plants, and evaluating possible influences on metal uptake and phytoremediation processes is therefore essential. This review article will address the feasibility of green plants for treatment of ENP-affected aquatic ecosystems. Discussion will include common types of ENPs in current use; transformations of ENPs in aquatic systems; the importance of microorganisms in supporting plant growth; ENP entry into the plant; the influence of microorganisms in promoting plant uptake; and recent findings in phytoremediation of ENP-affected water, including applications to constructed wetlands.

A high throughput method to investigate nanoparticle entrapment efficiencies in biofilms

The commercial use of nanoparticles has increased in recent years due to their unique characteristics, including high surface area, modifiable shape and surface charge and size-dependent properties. Consequently, a greater number of nanomaterials are now being released into the environment and inevitably interact with the natural ecosystem. Bacterial biofilms have the potential to capture and retain nanoparticles, however the factors determining the specific nanoparticle entrapment efficiencies of biofilms are not yet fully understood. Based on fluorescent intensity measurements we developed a simple and straightforward method that allowed the entrapment of different silica nanoparticles by two Pseudomonas strains to be quantified. It was determined that, regardless of nanoparticle size or surface functionalisation, Pseudomonas putida biofilms showed enhanced entrapment efficiencies compared to Pseudomonas fluorescens biofilms. It was also noted that both biofilms showed a higher entrapment capacity towards positively charged NPs. The method developed has the potential to be utilized for high throughput biofilm screening studies in order to develop a new understating of the relationship between nanoparticle characteristics and its uptake by bacterial biofilms.

Heterogeneous Diffusion of Polystyrene Nanoparticles through an Alginate Matrix: The Role of Cross-linking and Particle Size

Most bacteria in natural and engineered environments grow and exist in biofilms. Recent investigations have shown that nanoparticles (NPs) interact with environmental biofilms, but these interactions are still not well characterized. Extracellular polymeric substances (EPS) are polymers secreted by bacteria to establish the functional and structural integrity of biofilms, and EPS porosity is a major contributor to NP access to and diffusion in biofilms. We used a synergistic combination of total internal reflection fluorescence microscopy and image correlation spectroscopy to monitor and map diffusion of fluorescent NPs in alginate yielding a detailed picture of the heterogeneous structure and connectivity of pores within a model EPS polymer. Using different sizes (20, 100, and 200 nm) of carboxylated polystyrene NPs, we examined how NP diffusive behaviors change as a result of calcium-induced cross-linking of the alginate matrix. This study reveals that cross-linking decreases NP diffusion coefficients and pore accessibility in an NP size-dependent manner and that NP movement through alginate matrices is anisotropic and heterogeneous. These results on heterogeneous and size-dependent movement within biofilms have important implications for future studies and simulations of NP-biofilm interactions.

Molecular mechanisms in phytoremediation of environmental contaminants and prospects of engineered transgenic plants/microbes

Concerns about emerging environmental contaminants have been growing along with industrialization and urbanization around the globe. Among various options for remediating these contaminants, phytotechnology is suggested as a feasible option to maintain the environmental sustainability. The recent advances in phytoremediation, genetic/molecular/omics/metabolic engineering, and nanotechnology are opening new paths for efficient treatment of emerging organic/inorganic contaminants. In this respect, elucidation of molecular mechanisms and genetic engineering of hyperaccumulator plants is expected to enhance remediation of environmental contaminants. This review was organized to offer valuable insights into the molecular mechanisms of phytoremediation and the prospects of transgenic hyperaccumulators with enhanced stress tolerance to diverse contaminants such as heavy metals and metalloids, xenobiotics, explosives, poly aromatic hydrocarbons (PAHs), petroleum hydrocarbons, pesticides, and nanoparticles. The roles of genoremediation and nanoparticles in augmenting the phytoremediation technology are also described in an interrelated framework with biotechnological prospects (e.g., plant molecular nano-farming). Finally, political debate on the preferential use of crops versus non-crop hyperaccumulators in genoremediation, limitations of transgenics in phytotechnologies, and their public acceptance issues are discussed in the policy framework.

Cellular Uptake of Few-Layered Black Phosphorus and the Toxicity to an Aquatic Unicellular Organism

With the potential continuous application of mono- or few-layered black phosphorus (BP) in electronic, photonic, therapeutic, and environmental fields, the possible side effects of BP on aquatic organisms after release into natural water are of great concern. We investigated the potential toxicity of BP on the unicellular organism, Tetrahymena thermophila. After the exposure for 8 h at 10 μg/mL, the reproduction of T. thermophila significantly decreased by 46.3%. Severe cell membrane and cilium damage were observed by scanning electron microscopy (SEM) upon treatment with BP. Based on bright-field microscopy and three-dimensional Raman imaging, we investigated the cellular uptake and translocation of BP within T. thermophila. It was observed that the engulfment of BP by T. thermophila was oral apparatus dependent, through which intracellular BP was then transported to the posterior end of T. thermophila by food vacuole packaging. Our study also revealed that BP induced the increase of intracellular reactive oxidant species and formed oxidative stress-dependent toxicity to T. thermophila. Our findings paved a way for better understanding the BP toxicityon aquatic organisms and its potential ecological risks.

Differential Reactivity of Copper- and Gold-Based Nanomaterials Controls Their Seasonal Biogeochemical Cycling and Fate in a Freshwater Wetland Mesocosm

Reliable predictions of the environmental fate and risk of engineered nanomaterials (ENMs) require a better understanding of ENM reactivity in complex, biologically active systems for chronic low-concentration exposure scenarios. Here, simulated freshwater wetland mesocosms were dosed with ENMs to assess how their reactivity and seasonal changes in environmental parameters influence ENM fate in aquatic systems. Copper-based ENMs (Kocide), known to dissolve in water, and gold nanoparticles (AuNPs), stable against dissolution in the absence of specific ligands, were added weekly to mesocosm waters for 9 months. Metal accumulation and speciation changes in the different environmental compartments were assessed over time. Copper from Kocide rapidly dissolved likely associating with organic matter in the water column, transported to terrestrial soils and deeper sediment where it became associated with organic or sulfide phases. In contrast, Au accumulated on/in the macrophytes where it oxidized and transferred over time to surficial sediment. A dynamic seasonal accumulation and metal redox cycling were found between the macrophyte and the surficial sediment for AuNPs. These results demonstrate the need for experimental quantification of how the biological and chemical complexity of the environment, combined with their seasonal variations, drive the fate of metastable ENMs.

Engineered nanomaterials: From their properties and applications, to their toxicity towards marine bivalves in a changing environment

As a consequence of their unique characteristics, the use of Engineered Nanomaterials (ENMs) is rapidly increasing in industrial, agricultural products, as well as in environmental technology. However, this fast expansion and use make likely their release into the environment with particular concerns for the aquatic ecosystems, which tend to be the ultimate sink for this type of contaminants. Considering the settling behaviour of particulates, benthic organisms are more likely to be exposed to these compounds. In this way, the present review aims to summarise the most recent data available from the literature on ENMs behaviour and fate in aquatic ecosystems, focusing on their ecotoxicological impacts towards marine and estuarine bivalves. The selection of ENMs presented here was based on the OECD's Working Party on Manufactured Nanomaterials (WPMN), which involves the safety testing and risk assessment of ENMs. Physical-chemical characteristics and properties, applications, environmental relevant concentrations and behaviour in aquatic environment, as well as their toxic impacts towards marine bivalves are discussed. Moreover, it is also identified the impacts derived from the simultaneous exposure of marine organisms to ENMs and climate changes as an ecologically relevant scenario.

Nanoparticles transported from aquatic to terrestrial ecosystems via emerging aquatic insects compromise subsidy quality

Nanoparticle contaminants enter aquatic ecosystems and are transported along the stream network. Here, we demonstrate a novel pathway for the return of nanoparticles from aquatic to terrestrial ecosystems via cross-boundary subsidies. During their emergence, trichopteran caddisflies carried titanium dioxide and gold nanoparticles into their terrestrial life stages. Moreover, their emergence was delayed by ≤30 days, and their energy reserves were depleted by ≤25%. Based on worst case estimates, it is suggested that terrestrial predators, such as bats feeding on aquatic prey, may ingest up to three orders of magnitude higher gold levels than anticipated for humans. Additionally, terrestrial predator species may suffer from alterations in the temporal availability and nutritional quality of their prey. Considering the substantial transfer of insect biomass to terrestrial ecosystems, nanoparticles may decouple aquatic and terrestrial food webs with important (meta-)ecosystem level consequences.

Are gold nanoparticles and microplastics mixtures more toxic to the marine microalgae Tetraselmis chuii than the substances individually?

The widespread use of microplastics and nanomaterials resulting in environmental contamination is of high concern. Microplastics have been found to modulate the toxicity of other environmental contaminants. Thus, the hypothesis that microplastics increase the toxicity of gold nanoparticles to the marine microalgae Tetraselmis chuii was tested. In a laboratory bioassay, T. chuii cultures were exposed for 96 h to ∼5 nm diameter gold nanoparticles (AuNP) and to virgin 1-5 μm diameter microplastics (MP), alone and in mixture. The treatments were: control; citrate-control; AuNP alone (0.1, 0.3 and 3 mg/L); MP alone (0.3, 0.9 and 4 mg/L) and mixture of the two substances in three different concentrations (0.1 mg/L AuNP + 0.3 mg/L MP; 0.3 mg/L AuNP + 0.9 mg/L MP; 3 mg/l AuNP + 4 mg/L MP). The effect criterion was the inhibition of the average specific growth rate. AuNP alone and MP alone did not cause significant decrease of T. chui average specific growth rate up to 3 mg/L and 4 mg/L, respectively. The mixture containing 3 mg/L AuNP + 4 mg/L MP significantly reduced the average specific growth rate of the microalgae. Therefore, this mixture was more toxic to T. chuii than its components individually. Overall, the results of the present study indicated that the MP and AuNP tested have a relatively low toxicity to T. chuii, but the toxicity increases when they are in mixtures containing high concentrations of both substances. These proof-of-concept findings stress the need of more research on the toxicity of mixtures containing microplastics and nanomaterials.

Virus-Sized Gold Nanorods: Plasmonic Particles for Biology

Plasmons, collective oscillations of conduction-band electrons in nanoscale metals, are well-known phenomena in colloidal gold and silver nanocrystals that produce brilliant visible colors in these materials that depend on the nanocrystal size and shape. Under illumination at or near the plasmon bands, gold and silver nanocrystals exhibit properties that enable fascinating biological applications: (i) the nanocrystals elastically scatter light, providing a straightforward way to image them in complex aqueous environments; (ii) the nanocrystals produce local electric fields that enable various surface-enhanced spectroscopies for sensing, molecular diagnostics, and boosting of bound fluorophore performance; (iii) the nanocrystals produce heat, which can lead to chemical transformations at or near the nanocrystal surface and can photothermally destroy nearby cells. While all the above-mentioned applications have already been well-demonstrated in the literature, this Account focuses on several other aspects of these nanomaterials, in particular gold nanorods that are approximately the size of viruses (diameters of ∼10 nm, lengths up to 100 nm). Absolute extinction, scattering, and absorption properties are compared for gold nanorods of various absolute dimensions, and references for how to synthesize gold nanorods with four different absolute dimensions are provided. Surface chemistry strategies for coating nanocrystals with smooth or rough shells are detailed; specific examples include mesoporous silica and metal-organic framework shells for porous (rough) coatings and polyelectrolyte layer-by-layer wrapping for "smooth" shells. For self-assembled-monolayer molecular coating ligands, the smoothest shells of all, a wide range of ligand densities have been reported from many experiments, yielding values from less than 1 to nearly 10 molecules/nm2 depending on the nanocrystal size and the nature of the ligand. Systematic studies of ligand density for one particular ligand with a bulky headgroup are highlighted, showing that the highest ligand density occurs for the smallest nanocrystals, even though these ligand headgroups are the most mobile as judged by NMR relaxation studies. Biomolecular coronas form around spherical and rod-shaped nanocrystals upon immersion into biological fluids; these proteins and lipids can be quantified, and their degree of adsorption depends on the nanocrystal surface chemistry as well as the biophysical characteristics of the adsorbing biomolecule. Photothermal adsorption and desorption of proteins on nanocrystals depend on the enthalpy of protein-nanocrystal surface interactions, leading to light-triggered alteration in protein concentrations near the nanocrystals. At the cellular scale, gold nanocrystals exert genetic changes at the mRNA level, with a variety of likely mechanisms that include alteration of local biomolecular concentration gradients, changes in mechanical properties of the extracellular matrix, and physical interruption of key cellular processes-even without plasmonic effects. Microbiomes, both organismal and environmental, are the likely first point of contact of nanomaterials with natural living systems; we see a major scientific frontier in understanding, predicting, and controlling microbe-nanocrystal interactions, which may be augmented by plasmonic effects.

Species-Specific (Hyalella azteca and Lymnea stagnalis) Dietary Accumulation of Gold Nano-particles Associated with Periphyton

Ecological effects of gold nano-particles (AuNP) are examined due to growing use in consumer and industrial materials. This study investigated uptake and movement of AuNPs through an aquatic food chain. Simple (single-species) and diverse (multi-species) periphyton communities were exposed to AuNP (0, 100, 500 µg L^-1 treatments). AuNP quickly aggregated and precipitated from the water column, suggesting it is an insignificant route of AuNP exposure even at elevated concentrations. Gold was measured in 100 and 500 µg L^-1 periphyton treatments. Gold accumulation was similar between periphyton treatments, suggesting physical processes were important for AuNP basal accumulation. Hyalella azteca and Lymnea stagnalis whole body tissue analysis indicated gold accumulation may be attributed to different feeding mechanisms, general versus selective grazing, respectively. Results suggest trophic transfer of AuNP is organism specific and aggregation properties of AuNP are important when considering fate of nano-particles in the environment and movement through aquatic food webs.

Photothermal-Induced Antibacterial Activity of Gold Nanorods Loaded into Polymeric Hydrogel against Pseudomonas aeruginosa Biofilm

In this study, the photothermal-induced bactericidal activity of phospholipid-decorated gold nanorods (DSPE-AuNR) suspension against Pseudomonas aeruginosa planktonic and biofilm cultures was investigated. We found that the treatment of planktonic culture of Pseudomonas aeruginosa with DSPE-AuNR suspension (0.25-0.03 nM) followed by a continuous laser beam exposure resulted in ~6 log cycle reduction of the bacterial viable count in comparison to the control. The percentage reduction of Pseudomonas aeruginosa biofilm viable count was ~2.5-6.0 log cycle upon laser excitation with different concentrations of DSPE-AuNR as compared to the control. The photothermal ablation activity of DSPE-AuNR (0.125 nM) loaded into poloxamer 407 hydrogel against Pseudomonas aeruginosa biofilm resulted in ~4.5-5 log cycle reduction in the biofilm viable count compared to the control. Moreover, transmission electron microscope (TEM) images of the photothermally-treated bacteria revealed a significant change in the bacterial shape and lysis of the bacterial cell membrane in comparison to the untreated bacteria. Furthermore, the results revealed that continuous and pulse laser beam modes effected a comparable photothermal-induced bactericidal activity. Therefore, it can be concluded that phospholipid-coated gold nanorods present a promising nanoplatform to eradicate Pseudomonas aeruginosa biofilm responsible for common skin diseases.

Graphene oxide as a tool for antibiotic-resistant gene removal: a review

Environmental pollutants, including antibiotics (ATBs), have become an increasingly common health hazard in the last several decades. Overdose and abuse of ATBs led to the emergence of antibiotic-resistant genes (ARGs), which represent a serious health threat. Moreover, water bodies and reservoirs are places where a wide range of bacterial species with ARGs originate, owing to the strong selective pressure from presence of ATB residues. In this regard, graphene oxide (GO) has been utilised in several fields including remediation of the environment. In this review, we present a brief overview of resistant genes of frequently used ATBs, their occurrence in the environment and their behaviour. Further, we discussed the factors influencing the binding of nucleic acids and the response of ARGs to GO, including the presence of salts in the water environment or water pH, because of intrinsic properties of GO of not only binding to nucleic acids but also catalysing their decomposition. This would be helpful in designing new types of water treatment facilities.

A hydrofluoric acid-free method to dissolve and quantify silica nanoparticles in aqueous and solid matrices

As the commercial use of synthetic amorphous silica nanomaterials (SiO2-NPs) increases, their effects on the environment and human health have still not been explored in detail. An often-insurmountable obstacle for SiO2-NP fate and hazard research is the challenging analytics of solid particulate silica species, which involves toxic and corrosive hydrofluoric acid (HF). We therefore developed and validated a set of simple hydrofluoric acid-free sample preparation methods for the quantification of amorphous SiO2 micro- and nanoparticles. To circumvent HF, we dissolved the SiO2-NPs by base-catalyzed hydrolysis at room temperature or under microwave irradiation using potassium hydroxide, replacing the stabilizing fluoride ions with OH-, and exploiting the stability of the orthosilicic acid monomer under a strongly basic pH. Inductively coupled plasma - optical emission spectroscopy (ICP-OES) or a colorimetric assay served to quantify silicon. The lowest KOH: SiO2 molar ratio to effectively dissolve and quantify SiO2-NPs was 1.2 for colloidal Stöber SiO2-NPs at a pH >12. Fumed SiO2-NPs (Aerosil®) or food grade SiO2 (E551) containing SiO2-NPs were degradable at higher KOH: SiO2 ratios >8000. Thus, hydrofluoric acid-free SiO2-NP digestion protocols based on KOH present an effective (recoveries of >84%), less hazardous, and easy to implement alternative to current methods.

The influence of simulated global ocean acidification on the toxic effects of carbon nanoparticles on polychaetes

Ocean acidification events are recognized as important drivers of change in biological systems. Particularly, the impacts of acidification are more severe in estuarine systems than in surface ocean due to their shallowness, low buffering capacity, low salinity and high organic matter from land drainage. Moreover, because they are transitional areas, estuaries can be seriously impacted by a vast number of anthropogenic activities and in the last decades, carbon nanomaterials (CNMs) are considered as emerging contaminants in these ecosystems. Considering all these evidences, chronic experiment was carried out, trying to understand the possible alteration on the chemical behaviour of two different CNMs (functionalized and pristine) in predicted climate change scenarios and consequently, how these alterations could modify the sensitivity of one the most common marine and estuarine organisms (the polychaeta Hediste diversicolor) assessing a set of biomarkers related to polychaetes oxidative status as well as the metabolic performance and neurotoxicity. Our results demonstrated that all enzymes worked together to counteract seawater acidification and CNMs, however oxidative stress in the exposed polychaetes to both CNMs, especially under ocean acidification conditions, was enhanced. In fact, although the antioxidant enzymes tried to cope as compensatory response of cellular defense systems against oxidative stress, the synergistic interactive effects of pH and functionalized CNMs indicated that acidified pH significantly increased the oxidative damage (in terms of lipid peroxidation) in the cotaminated organisms. Different responses were observed in organisms submitted to pristine CNMs under pH control, where the lipid peroxidation did not increase along with the increasing exposure concentrations. The present results further demonstrated neurotoxicity caused by both CNMs, especially noticeable at acidified conditions. The mechanism of enhanced toxicity could be attributed to slighter aggregation and more suspended NMs in acidified seawater (as demonstrated by the DLS analysis). Therefore, ocean acidification may cause a higher risk of CNMs to marine ecosystems.

Functional sustainability of periphytic biofilms in organic matter and Cu2+ removal during prolonged exposure to TiO2 nanoparticles

Responses of microbial communities to nanotoxicity in aquatic ecosystems are largely unknown, particularly with respect to relationship between community dynamics and functions. Here, periphytic biofilms were selected as a model of species-rich microbial communities to elucidate their responses when exposed to titanium dioxide nanoparticles (TiO₂-NPs). Especially, the relationships between the functions (e.g. organic matter and Cu²⁺ removal) and community dynamics after long-term exposure to TiO₂-NPs were assessed systematically. After 5days exposure to TiO₂-NPs (5mgL^-1), periphytic biofilms showed sustainable functions in pollutant removal and strong plasticity in defensing the toxic disturbance of TiO₂-NPs, including photosynthesis and carbon metabolic diversity. The sustainable pollutant removal functions of periphytic biofilms were attributed to their functional redundancy. Specifically, periphytic biofilms altered their composition with cyanobacteria, Sphingobacteriia and Spirochaetes being the newly dominant taxa, and changed the carbon substrate utilization pattern to maintain high photosynthesis and metabolic rates. Moreover, extracellular polymeric substances (EPS) especially proteins were overproduced to bind the NPs and thereby reduce the nanotoxicity. The information obtained in this study may greatly help to understand the interactions between microbial community dynamics and function under NPs exposure conditions and functional redundancy is an important mechanism of periphytic biofilms to maintain sustainable functions.

High-Level Extraction of Recyclable Nanocatalysts by Using Polyphosphazene Microparticles

Improper disposal of metal nanoparticles has caused serious environmental and pathological problems because of their active nanotoxicity. Therefore, there is an urgent need to develop a strategy for efficiently removing redundant metal nanoparticles from water, while also permitting restoration of their catalytic activities to those of pristine particles for reapplication. Herein, we present intrinsically nitrogen-rich cross-linked polyphosphazene microparticles to capture silver nanoparticles (AgNPs) from aqueous media by a simple one-step method. The described microparticles exhibit an outstanding adsorption capacity for AgNPs of approximately 59.35 mg/g, exceeding those of other adsorbents. The adsorption kinetics of AgNPs on these microparticles obeyed a pseudo-second-order kinetic model. More importantly, the recovered AgNPs maintained good catalytic activity in the reduction of methylene blue by sodium borohydride. Based on their simple preparation, high adsorption efficiency, and nondestructive effect on the catalytic activity of the recovered AgNPs, the described polyphosphazene microparticles display promising potential for the removal and recovery of AgNPs from water.

Conserved Microbial Toxicity Responses for Acute and Chronic Silver Nanoparticle Treatments in Wetland Mesocosms

Most studies of bacterial exposure to environmental contaminants focus on acute treatments; however, the impacts of single, high-dose exposures on microbial communities may not readily be extended to the more likely scenario of chronic, low-dose contaminant exposures. Here, in a year-long, wetland mesocosm experiment, we compared microbial community responses to pulse (single 450 mg dose of silver) and chronic (weekly 8.7 mg doses of silver for 1 year) silver nanoparticle (Ag⁰ NP) treatments, as well as a chronic treatment of "aged" sulfidized silver nanoparticles (Ag₂S NPs). While mesocosms exposed to Ag₂S NPs never differed significantly from the controls, both Ag⁰ NP treatments exhibited reduced microbial diversity and altered community composition; however, the effects differed in timing, duration, and magnitude. Microbial community-level impacts in the acute Ag⁰ NP treatment were apparent only within the first weeks and then converged on the control mesocosm composition, while chronic exposure effects were observed several months after exposures began, likely due to interactive effects of nanoparticle toxicity and winter environmental conditions. Notably, there was a high level of overlap in the taxa which exhibited significant declines (>10×) in both treatments, suggesting a conserved toxicity response for both pulse and chronic exposures. Thus, this research suggests that complex, but short-term, acute toxicological studies may provide critical, cost-effective insights into identifying microbial taxa sensitive to long-term chronic exposures to Ag NPs.

Protection Mechanisms of Periphytic Biofilm to Photocatalytic Nanoparticle Exposure

Researchers are devoting great effort to combine photocatalytic nanoparticles (PNPs) with biological processes to create efficient environmental purification technologies (i.e., intimately coupled photobiocatalysis). However, little information is available to illuminate the responses of multispecies microbial aggregates against PNP exposure. Periphytic biofilm, as a model multispecies microbial aggregate, was exposed to three different PNPs (CdS, TiO₂, and Fe₂O₃) under xenon lamp irradiation. There were no obvious toxic effects of PNP exposure on periphytic biofilm as biomass, chlorophyll content, and ATPase activity were not negatively impacted. Enhanced production of extracellular polymetric substances (EPS) is the most important protection mechanism of periphytic biofilm against PNPs exposure. Although PNP exposure produced extracellular superoxide radicals and caused intracellular reactive oxygen species (ROS) accumulation in periphytic biofilm, the interaction between EPS and PNPs could mitigate production of ROS while superoxide dismutase could alleviate biotic ROS accumulation in periphytic biofilm. The periphytic biofilms changed their community composition in the presence of PNPs by increasing the relative abundance of phototrophic and high nutrient metabolic microorganisms (families Chlamydomonadaceae, Cyanobacteriacea, Sphingobacteriales, and Xanthomonadaceae). This study provides insight into the protection mechanisms of microbial aggregates against simultaneous photogenerated and nanoparticle toxicity from PNPs.

Biogenic Cyanide Production Promotes Dissolution of Gold Nanoparticles in Soil

Gold nanoparticles (Au NPs) are often used to study the physiochemical behavior and distribution of nanomaterials in natural systems because they are assumed to be inert under environmental conditions, even though Au can be oxidized and dissolved by a common environmental compound: cyanide. We used the cyanogenic soil bacterium, Chromobacterium violaceum, to demonstrate that quorum-sensing-regulated cyanide production could lead to a high rate of oxidative dissolution of Au NPs in soil. After 7 days of incubation in a pH 7.0 soil inoculated with C. violaceum, labile Au concentration increased from 0 to 15%. There was no observable dissolution when Au NPs were incubated in abiotic soil. In the same soil adjusted to pH 7.5, labile Au concentration increased up to 29% over the same time frame. Furthermore, we demonstrated that Au dissolution required quorum-sensing-regulated cyanide production in soil by inoculating the soil with different cell densities and using a quorum-sensing-deficient mutant of C. violaceum, CV026. Au NP dissolution experiments in liquid media coupled with mass spectrometry analysis confirmed that biogenic cyanide oxidized Au NPs to soluble Au(CN)₂^-. These results demonstrate under which conditions biologically enhanced metal dissolution can contribute to the overall geochemical transformation kinetics of nanoparticle in soils, even though the materials may be inert in abiotic environments.

Strategies for robust and accurate experimental approaches to quantify nanomaterial bioaccumulation across a broad range of organisms

One of the key components for environmental risk assessment of engineered nanomaterials (ENMs) is data on bioaccumulation potential. Accurately measuring bioaccumulation can be critical for regulatory decision making regarding material hazard and risk, and for understanding the mechanism of toxicity. This perspective provides expert guidance for performing ENM bioaccumulation measurements across a broad range of test organisms and species. To accomplish this aim, we critically evaluated ENM bioaccumulation within three categories of organisms: single-celled species, multicellular species excluding plants, and multicellular plants. For aqueous exposures of suspended single-celled and small multicellular species, it is critical to perform a robust procedure to separate suspended ENMs and small organisms to avoid overestimating bioaccumulation. For many multicellular organisms, it is essential to differentiate between the ENMs adsorbed to external surfaces or in the digestive tract and the amount absorbed across epithelial tissues. For multicellular plants, key considerations include how exposure route and the role of the rhizosphere may affect the quantitative measurement of uptake, and that the efficiency of washing procedures to remove loosely attached ENMs to the roots is not well understood. Within each organism category, case studies are provided to illustrate key methodological considerations for conducting robust bioaccumulation experiments for different species within each major group. The full scope of ENM bioaccumulation measurements and interpretations are discussed including conducting the organism exposure, separating organisms from the ENMs in the test media after exposure, analytical methods to quantify ENMs in the tissues or cells, and modeling the ENM bioaccumulation results. One key finding to improve bioaccumulation measurements was the critical need for further analytical method development to identify and quantify ENMs in complex matrices. Overall, the discussion, suggestions, and case studies described herein will help improve the robustness of ENM bioaccumulation studies.

Copper Bioaccumulation Kinetics in Swan Mussel, Anodonta cygnea (Linnaeus, 1758) During Waterborne Exposure to CuO Nanoparticles

This study was conducted to investigate bioaccumulation of copper in two internal organs (mantle and foot) of swan mussel, Anodonta cygnea (Linnaeus, 1758) in exposure to copper oxide nanoparticles (CuO NPs). Basal concentration of Cu in the mantle (3.15 ± 1.09 µg g^-1 DW) was significantly (p < 0.05) lower than the foot (5.43 ± 1.54 µg g^-1 DW). At the end of the exposure period, the highest concentration of Cu in both organs belonged to the highest exposure concentration. Calculated bioconcentration factor (BCF) values showed significant (p < 0.05) higher values for the mantle in each day and each exposure concentration (except the lowest exposure concentration) than the foot. For both organs, the highest and lowest BCFs occurred at the lowest and highest exposure concentrations, respectively. Cu concentration in both organs was significantly (p < 0.05) decreased after day 4. Based on the results, it was obvious that exposure to sub-lethal concentrations of CuO NPs would lead to the significant accumulation of copper in mantle and foot that may have adverse effects on this organism.