9 research outputs found

    Stability of Citrate, PVP, and PEG Coated Silver Nanoparticles in Ecotoxicology Media

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    Silver nanoparticles (AgNPs) are present in the environment and a number of ecotoxicology studies have shown that AgNPs might be highly toxic. Nevertheless, there are little data on their stability in toxicology media. This is an important issue as such dynamic changes affect exposure dose and the nature of the toxicant studied and have a direct impact on all (eco)­toxicology data. In this study, monodisperse citrate, PVP, and PEG coated AgNPs with a core size of approximately 10 nm were synthesized and characterized; their behavior was examined in standard OECD media used for <i>Daphnia</i> sp. acute and chronic tests (in the absence of Daphnia). Surface plasmon resonance, size, aggregation, and shape were monitored over 21 days, comparable to a chronic exposure period. Charge stabilized particles (citrate) were more unstable than sterically stabilized particles. Replacement of chloride in the media (due to concerns over chloride-silver interactions) with either nitrate or sulfate resulted in increased shape and dissolution changes. PVP-stabilized NPs in a 10-fold diluted OECD media (chloride present) were found to be the most stable, with only small losses in total concentration over 21 days, and no shape, aggregation, or dissolution changes observed and are recommended for exposure studies

    Synthesis and Characterization of Polyvinylpyrrolidone Coated Cerium Oxide Nanoparticles

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    There is a pressing need for the development of standard and reference nanomaterials for environmental nanoscience and nanotoxicology. To that aim, suspensions of polyvinylpyrrolidone (PVP)-coated ceria nanoparticles (NPs) were produced. Four differently sized monodispersed samples were produced by using different PVP chain lengths. The chemical and physical properties of these NPs were characterized as prepared and in different ecotoxicology exposure media. Dynamic light scattering analysis showed that the samples were monodispersed, with an unchanged size when suspended in the different media over a 72 h period. Electron microscopy confirmed this and revealed that the larger (ca. 20 nm) particles were aggregates composed of the smaller individual particles (4–5 nm). Electron energy loss spectroscopy (EELS) showed that the smallest and largest samples were composed almost entirely of cerium­(III) oxide, with only small amounts of cerium­(IV) present in the largest sample. Dissolved cerium concentrations in media were low and constant, showing that the NPs did not dissolve over time. The simple synthesis of the these NPs and their physical and chemical stability in different environmental conditions make them potentially suitable for use as reference materials for (eco)­toxicology and surface water environmental studies

    A High Resolution Study of Dynamic Changes of Ce<sub>2</sub>O<sub>3</sub> and CeO<sub>2</sub> Nanoparticles in Complex Environmental Media

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    Ceria nanoparticles (NPs) rapidly and easily cycle between Ce­(III) and Ce­(IV) oxidation states, making them prime candidates for commercial and other applications. Increased commercial use has resulted in increased discharge to the environment and increased associated risk. Once in complex media such as environmental waters or toxicology exposure media, the same redox transformations can occur, causing altered behavior and effects compared to the pristine NPs. This study used high resolution scanning transmission electron microscopy and electron energy loss spectroscopy to investigate changes in structure and oxidation state of small, polymer-coated ceria suspensions in complex media. NPs initially in either the III or IV oxidation states, but otherwise identical, were used. Ce­(IV) NPs were changed to mixed (III, IV) NPs at high ionic strengths, while the presence of natural organic macromolecules (NOM) stabilized the oxidation state and increased crystallinity. The Ce­(III) NPs remained as Ce­(III) at high ionic strengths, but were modified by the presence of NOM, causing reduced crystallinity and degradation of the NPs. Subtle changes to NP properties upon addition to environmental or ecotoxicology media suggest that there may be small but important effects on fate and effects of NPs compared to their pristine form

    Characterization of Suboxic Groundwater Colloids Using a Multi-method Approach

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    Anoxic groundwater colloid properties were measured using a minimally perturbing procedure for sampling, processing, and analysis. Analytical methods included atomic force microscopy (AFM), flow field flow fractionation (FlFFF), and transmission and scanning electron microscopy (TEM and SEM). Shallow groundwater samples showed abundant iron rich nanoparticles (NP) with diameters of 10–30 nm as well as a smaller heterogeneous polydisperse dissolved organic matter (DOM) fraction. AFM results showed NP with average heights of 10 ± 2 nm, which was corroborated by high-resolution TEM and SEM. FlFFF with UV254 nm detection found particles with number average diffusion coefficients of 2–3 × 10<sup>–10</sup> m<sup>2</sup> s<sup>–1</sup> and hydrodynamic diameters between 1.5 and 2 nm probably representing smaller organic macromolecules. Aeration of the samples resulted in extensive agglomeration of NP to form larger (>50 nm) colloids, and a reduction of UV-absorbing material in the 0.5–4 nm range. The complementary methods described have potential applications for investigating the fate and transport of NP in suboxic hotspots such as leachate plumes, wastewater treatment plants, and within the hyporheic mixing zone

    Influence of hardness on the bioavailability of silver to a freshwater snail after waterborne exposure to silver nitrate and silver nanoparticles

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    <div><p></p><p>The release of Ag nanoparticles (AgNPs) into the aquatic environment is likely, but the influence of water chemistry on their impacts and fate remains unclear. Here, we characterize the bioavailability of Ag from AgNO<sub>3</sub> and from AgNPs capped with polyvinylpyrrolidone (PVP AgNP) and thiolated polyethylene glycol (PEG AgNP) in the freshwater snail, <i>Lymnaea stagnalis,</i> after short waterborne exposures. Results showed that water hardness, AgNP capping agents, and metal speciation affected the uptake rate of Ag from AgNPs. Comparison of the results from organisms of similar weight showed that water hardness affected the uptake of Ag from AgNPs, but not that from AgNO<sub>3</sub>. Transformation (dissolution and aggregation) of the AgNPs was also influenced by water hardness and the capping agent. Bioavailability of Ag from AgNPs was, in turn, correlated to these physical changes. Water hardness increased the aggregation of AgNPs, especially for PEG AgNPs, reducing the bioavailability of Ag from PEG AgNPs to a greater degree than from PVP AgNPs. Higher dissolved Ag concentrations were measured for the PVP AgNPs (15%) compared to PEG AgNPs (3%) in moderately hard water, enhancing Ag bioavailability of the former. Multiple drivers of bioavailability yielded differences in Ag influx between very hard and deionized water where the uptake rate constants (<i>k</i><sub>uw</sub>, l g<sup>−1</sup> d<sup>−1</sup> ± SE) varied from 3.1 ± 0.7 to 0.2 ± 0.01 for PEG AgNPs and from 2.3 ± 0.02 to 1.3 ± 0.01 for PVP AgNPs. Modeling bioavailability of Ag from NPs revealed that Ag influx into <i>L. stagnalis</i> comprised uptake from the NPs themselves and from newly dissolved Ag.</p></div

    Molecular toxicity of cerium oxide nanoparticles to the freshwater alga <i>Chlamydomonas reinhardtii</i> is associated with supra-environmental exposure concentrations

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    <p>Ceria nanoparticles (NPs) are widely used as fuel catalysts and consequently are likely to enter the environment. Their potential impacts on. biota at environmentally relevant concentrations, including uptake and toxicity, remain to be elucidated and quantitative data on which to assess risk are sparse. Therefore, a definitive assessment of the molecular and phenotypic effects of ceria NPs was undertaken, using well-characterised mono-dispersed NPs as their toxicity is likely to be higher, enabling a conservative hazard assessment. Unbiased transcriptomics and metabolomics approaches were used to investigate the potential toxicity of tightly constrained 4–5 nm ceria NPs to the unicellular green alga, <i>Chlamydomonas reinhardtii</i>, a sentinel freshwater species. A wide range of exposure concentrations were investigated from predicted environmental levels, to support hazard assessment, to supra-environmental levels to provide insight into molecular toxicity pathways. Ceria NPs were internalised into intracellular vesicles within <i>C. reinhardtii</i>, yet caused no significant effect on algal growth at any exposure concentration. Molecular perturbations were only detected at supra-environmental ceria NP-concentrations, primarily down-regulation of photosynthesis and carbon fixation with associated effects on energy metabolism. For acute exposures to small mono-dispersed particles, it can be concluded there should be little concern regarding their dispersal into the environment for this trophic level.</p

    Citrate-Coated Silver Nanoparticles Growth-Independently Inhibit Aflatoxin Synthesis in <i>Aspergillus parasiticus</i>

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    Manufactured silver nanoparticles (Ag NPs) have long been used as antimicrobials. However, little is known about how these NPs affect fungal cell functions. While multiple previous studies reveal that Ag NPs inhibit secondary metabolite syntheses in several mycotoxin producing filamentous fungi, these effects are associated with growth repression and hence need sublethal to lethal NP doses, which besides stopping fungal growth, can potentially accumulate in the environment. Here we demonstrate that citrate-coated Ag NPs of size 20 nm, when applied at a selected nonlethal dose, can result in a >2 fold inhibition of biosynthesis of the carcinogenic mycotoxin and secondary metabolite, aflatoxin B<sub>1</sub> in the filamentous fungus and an important plant pathogen, <i>Aspergillus parasiticus</i>, without inhibiting fungal growth. We also show that the observed inhibition was not due to Ag ions, but was specifically associated with the mycelial uptake of Ag NPs. The NP exposure resulted in a significant decrease in transcript levels of five aflatoxin genes and at least two key global regulators of secondary metabolism, <i>laeA</i> and <i>veA,</i> with a concomitant reduction of total reactive oxygen species (ROS). Finally, the depletion of Ag NPs in the growth medium allowed the fungus to regain completely its ability of aflatoxin biosynthesis. Our results therefore demonstrate the feasibility of Ag NPs to inhibit fungal secondary metabolism at nonlethal concentrations, hence providing a novel starting point for discovery of custom designed engineered nanoparticles that can efficiently prevent mycotoxins with minimal risk to health and environment

    Accumulation Dynamics and Acute Toxicity of Silver Nanoparticles to <i>Daphnia magna</i> and <i>Lumbriculus variegatus</i>: Implications for Metal Modeling Approaches

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    Frameworks commonly used in trace metal ecotoxicology (e.g., biotic ligand model (BLM) and tissue residue approach (TRA)) are based on the established link between uptake, accumulation and toxicity, but similar relationships remain unverified for metal-containing nanoparticles (NPs). The present study aimed to (i) characterize the bioaccumulation dynamics of PVP-, PEG-, and citrate-AgNPs, in comparison to dissolved Ag, in <i>Daphnia magna</i> and <i>Lumbriculus variegatus</i>; and (ii) investigate whether parameters of bioavailability and accumulation predict acute toxicity. In both species, uptake rate constants for AgNPs were ∼2–10 times less than for dissolved Ag and showed significant rank order concordance with acute toxicity. Ag elimination by <i>L. variegatus</i> fitted a 1-compartment loss model, whereas elimination in <i>D. magna</i> was biphasic. The latter showed consistency with studies that reported daphnids ingesting NPs, whereas <i>L. variegatus</i> biodynamic parameters indicated that uptake and efflux were primarily determined by the bioavailability of dissolved Ag released by the AgNPs. Thus, principles of BLM and TRA frameworks are confounded by the feeding behavior of <i>D. magna</i> where the ingestion of AgNPs perturbs the relationship between tissue concentrations and acute toxicity, but such approaches are applicable when accumulation and acute toxicity are linked to dissolved concentrations. The uptake rate constant, as a parameter of bioavailability inclusive of all available pathways, could be a successful predictor of acute toxicity

    Sensory systems and ionocytes are targets for silver nanoparticle effects in fish

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    <p>Some nanoparticles (NPs) may induce adverse health effects in exposed organisms, but to date the evidence for this in wildlife is very limited. Silver nanoparticles (AgNPs) can be toxic to aquatic organisms, including fish, at concentrations relevant for some environmental exposures. We applied whole mount <i>in-situ</i> hybridisation (<i>WISH</i>) in zebrafish embryos and larvae for a suite of genes involved with detoxifying processes and oxidative stress, including metallothionein (<i>mt2</i>), glutathionine <i>S</i>-transferase pi (<i>gstp</i>), glutathionine <i>S</i>-transferase mu (<i>gstm1</i>), haem oxygenase (<i>hmox1</i>) and ferritin heavy chain 1 (<i>fth1</i>) to identify potential target tissues and effect mechanisms of AgNPs compared with a bulk counterpart and ionic silver (AgNO<sub>3</sub>). AgNPs caused upregulation in the expression of <i>mt2, gstp</i> and <i>gstm1</i> and down regulation of expression of both <i>hmox1</i> and <i>fth1</i> and there were both life stage and tissue-specific responses. Responding tissues included olfactory bulbs, lateral line neuromasts and ionocytes in the skin with the potential for effects on olfaction, behaviour and maintenance of ion balance. Silver ions induced similar gene responses and affected the same target tissues as AgNPs. AgNPs invoked levels of target gene responses more similar to silver treatments compared to coated AgNPs indicating the responses seen were due to released silver ions. In the <i>Nrf2</i> zebrafish mutant, expression of <i>mt2</i> (24 hpf) and <i>gstp</i> (3 dpf) were either non-detectable or were at lower levels compared with wild type zebrafish for exposures to AgNPs, indicating that these gene responses are controlled through the Nrf2-Keap pathway.</p