Dosing, Not the Dose: Comparing Chronic and Pulsed Silver Nanoparticle Exposures

Silver nanoparticles induce formation of multi-protein aggregates that contain cadherin but do not colocalize with nanoparticles

Silver nanoparticles (AgNPs) are increasingly incorporated in diverse products to confer antimicrobial properties. They are released into the environment during manufacture, after disposal, and from the products during use. Because AgNPs bioaccumulate in brain, it is important to understand how they interact with neural cell physiology. We found that the focal adhesion (FA)-associated protein cadherin aggregated in a dose-dependent response to AgNP exposure in differentiating cultured B35 neuroblastoma cells. These aggregates tended to colocalize with F-actin inclusions that form in response to AgNP and also contain β-catenin. However, using hyperspectral microscopy, we demonstrate that these multi-protein aggregates did not colocalize with the AgNPs themselves. Furthermore, expression and organization of the FA protein vinculin did not change in cells exposed to AgNP. Our findings suggest that AgNPs activate an intermediate mechanism which leads to formation of aggregates via specific protein-protein interactions. Finally, we detail the changes in hyperspectral profiles of AgNPs during different stages of cell culture and immunocytochemistry processing. AgNPs in citrate-stabilized solution present mostly blue with some rainbow spectra and these are maintained upon mounting in Prolong Gold. Exposure to tissue culture medium results in a uniform green spectral shift that is not further altered by fixation and protein block steps of immunocytochemistry.

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.

Biotic and Abiotic Interactions in Freshwater Mesocosms Determine Fate and Toxicity of CuO Nanoparticles

Transformation, dissolution, and sorption of copper oxide nanoparticles (CuO-NP) play an important role in freshwater ecosystems. We present the first mesocosm experiment on the fate of CuO-NP and the dynamics of the zooplankton community over a period of 12 months. Increasingly low (0.08-0.28 mg Cu L-1) and high (0.99-2.99 mg Cu L-1) concentrations of CuO-NP and CuSO4 (0.10-0.34 mg Cu L-1) were tested in a multiple dosing scenario. At the high applied concentration (CuO-NP_H) CuO-NP aggregated and sank onto the sediment layer, where we recovered 63% of Cu applied. For the low concentration (CuO-NP_L) only 41% of applied copper could be recovered in the sediment. In the water column, the percentage of initially applied Cu recovered was on average 3-fold higher for CuO-NP_L than for CuO-NP_H. Zooplankton abundance was substantially compromised in the treatments CuSO4 (p < 0.001) and CuO-NP_L (p < 0.001). Community analysis indicated that Cladocera were most affected (bk = -0.49), followed by Nematocera (bk = -0.32). The abundance of Cladocera over time and of Dixidae in summer was significantly reduced in the treatment CuO-NP_L (p < 0.001; p < 0.05) compared to the Control. Our results indicate a higher potential for negative impacts on the freshwater community when lower concentrations of CuO-NP (<0.1 mg Cu L-1) enter the ecosystem.

Long-term effects of Ag NPs on denitrification in sediment: Importance of Ag NPs exposure ways in aquatic ecosystems

The widespread use of silver nanoparticles (Ag NPs) inevitably leads to their increasing release into aquatic systems, with studies indicating that the mode of Ag NPs entry into water significantly affects their toxicity and ecological risks. However, there is a lack of research on the impact of different exposure ways of Ag NPs on functional bacteria in sediment. This study investigates the long-term influence of Ag NPs on denitrification process in sediments by comparing denitrifies responses to single (pulse injection of 10 mg/L) and repetitive (1 mg/L × 10 times) Ag NPs treatments over 60-day incubation. Results showed that a single exposure of 10 mg/L Ag NPs caused an obvious toxicity on activity and abundance of denitrifying bacteria on the first 30 days, reflecting by the decreased NADH amount, ETS activity, NIR and NOS activity, and nirK gene copy number, which resulted in a significant decline of denitrification rate in sediments (from 0.59 to 0.64 to 0.41-0.47 μmol15N L-1 h-1). While inhibition was mitigated with time and denitrification process recovered to the normal at the end of the experiment, the accumulated nitrate generated in the system showed that the recovery of microbial function did not mean the restoration of aquatic ecosystem after pollution. Differently, the repetitive exposure of 1 mg/L Ag NPs exhibited the evident inhibition on metabolism, abundance, and function of denitrifiers on Day 60, due to the accumulated amount of Ag NPs with the increased dosing number, indicating that the accumulated toxicity on functional microorganic community of repetitive exposure in less toxic concentration. Our study highlights the importance of Ag NPs entry pathways into aquatic ecosystem on their ecological risks, which affected dynamic responses of microbial function to Ag NPs.

Chronic Engineered Nanoparticle Additions Alter Insect Emergence and Result in Metal Flux from Aquatic Ecosystems into Riparian Food Webs

Freshwater ecosystems are exposed to engineered nanoparticles (NPs) through discharge from wastewater and agricultural runoff. We conducted a 9-month mesocosm experiment to examine the combined effects of chronic NP additions on insect emergence and insect-mediated contaminant flux to riparian spiders. Two NPs (copper, gold, plus controls) were crossed by two levels of nutrients in 18 outdoor mesocosms open to natural insect and spider colonization. We collected adult insects and two riparian spider genera, Tetragnatha and Dolomedes, for 1 week on a monthly basis. We estimated a significant decrease in cumulative insect emergence of 19% and 24% after exposure to copper and gold NPs, irrespective of nutrient level. NP treatments led to elevated copper and gold tissue concentrations in adult insects, which resulted in terrestrial fluxes of metals. These metal fluxes were associated with increased gold and copper tissue concentrations for both spider genera. We also observed about 25% fewer spiders in the NP mesocosms, likely due to reduced insect emergence and/or NP toxicity. These results demonstrate the transfer of NPs from aquatic to terrestrial ecosystems via emergence of aquatic insects and predation by riparian spiders, as well as significant reductions in insect and spider abundance in response to NP additions.

Responses of cyanobacterium Microcystis aeruginosa under single and repeated ofloxacin exposure

Antibiotics are omnipresent and pseudo-persistent in the environment. Yet, their potential ecological risks under repeated exposure, which is more environmentally relevant, are understudied. Therefore, this study used ofloxacin (OFL) as the probe chemical to investigate the toxic effects of different exposure scenarios-single dose of high concentration (4.0 µg/L) and multiple additions of low concentrations-towards the cyanobacterium Microcystis aeruginosa. Flow cytometry was employed to measure a collection of biomarkers, including endpoints related with biomass, single cell properties and physiological status. Results showed that the single dose of the highest OFL level inhibited cellular growth, chl-a content and cell size of M. aeruginosa. In contrast, OFL induced stronger chl-a autofluorescence and higher doses tended to have more remarkable effects. Repeated low OFL doses can more significantly increase the metabolic activity of M. aeruginosa than a single high dose. Viability and cytoplasmic membrane were not affected by OFL exposure. Oxidative stress was observed for the different exposure scenarios, with fluctuating responses. This study demonstrated the different physiological responses of M. aeruginosa under different OFL exposure scenarios, providing novel insights into the toxicity of antibiotics under repeated exposure.

Utility of Diffusive Gradient in Thin-Film Passive Samplers for Predicting Mercury Methylation Potential and Bioaccumulation in Freshwater Wetlands

Mercury is a risk in aquatic ecosystems when the metal is converted to methylmercury (MeHg) and subsequently bioaccumulates in aquatic food webs. This risk can be difficult to manage because of the complexity of biogeochemical processes for mercury and the need for accessible techniques to navigate this complexity. Here, we explored the use of diffusive gradient in thin-film (DGT) passive samplers as a tool to simultaneously quantify the methylation potential of inorganic Hg (IHg) and the bioaccumulation potential of MeHg in freshwater wetlands. Outdoor freshwater wetland mesocosms were amended with four isotopically labeled and geochemically relevant IHg forms that represent a range of methylation potentials (²⁰²Hg²⁺, ²⁰¹Hg-humic acid, ¹⁹⁹Hg-sorbed to FeS, and ²⁰⁰HgS nanoparticles). Six weeks after the spikes, we deployed DGT samplers in the mesocosm water and sediments, evaluated DGT-uptake rates of total Hg, MeHg, and IHg (calculated by difference) for the Hg isotope spikes, and examined correlations with total Hg, MeHg, and IHg concentrations in sediment, water, and micro and macrofauna in the ecosystem. In the sediments, we observed greater relative MeHg concentrations from the initially dissolved IHg isotope spikes and lower MeHg levels from the initially particulate IHg spikes. These trends were consistent with uptake flux of IHg into DGTs deployed in surface sediments. Moreover, we observed correlations between total Hg-DGT uptake flux and MeHg levels in periphyton biofilms, submergent plant stems, snails, and mosquitofish in the ecosystem. These correlations were better for DGTs deployed in the water column compared to DGTs in the sediments, suggesting the importance of vertical distribution of bioavailable MeHg in relation to food sources for macrofauna. Overall, these results demonstrate that DGT passive samplers are a relatively simple and efficient tool for predicting IHg methylation and MeHg bioaccumulation potentials without the need to explicitly delineate IHg and MeHg speciation and partitioning in complex ecosystems.

Insights into the lower trophic transfer of silver ions than silver containing nanoparticles along an aquatic food chain

Silver nanoparticles (AgNPs) released into the environment are subject to environmental transformation processes before accumulating in aquatic organisms and transferring along the food chain. Lack of understanding on how environmental transformation affects trophic transfer of AgNPs hinders accurate prediction of the environmental risks of these widely present nanomaterials. Here we discover that pristine AgNPs as well as their sulfidation products (Ag₂S-NPs) and dissolution products (Ag⁺) tend to be accumulated in Daphnia magna and subsequently transferred to zebrafish. In D. magna, Ag⁺ exhibits the highest bioaccumulation potential whereas Ag₂S-NPs show the lowest bioaccumulation. Surprisingly, the biomagnification factor of Ag⁺ along the D. magna-zebrafish food chain appears to be significantly lower relative to AgNPs and Ag₂S-NPs, likely due to the limited release of Ag from D. magna to zebrafish during digestion. Moreover, AgNPs and their transformation products mainly accumulate in the internal organs, particularly intestine, of zebrafish. Adsorption of AgNPs on the surface of the intestinal cell membrane mitigates depuration of AgNPs and, at least in part, leads to the larger biomagnification factor of AgNPs, relative to their transformation products. This research highlights the necessity of considering environmental transformation processes of nanomaterials in assessing their bioavailability and risk.

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.

Akt and MAPK/ERK signaling regulate neurite extension in adult neural progenitor cells but do not directly mediate disruption of cytoskeletal structure and neurite dynamics by low-level silver nanoparticles

Silver nanoparticles (AgNPs) are an environmental contaminant of emerging concern. Ionic and colloidal silver has long been used for its antimicrobial properties, but with the development of engineered AgNPs, these are increasingly incorporated in the manufacture of nano-enhanced products. AgNPs are released into the environment from manufacturing plants and they can be shed from products during use and after disposal. This can lead to chronic low-level environmental exposure in animals. Unlike traditional forms of silver, the unique physical properties of AgNPs allow them to bypass biological barriers and enter tissues, like the brain, where they can bioaccumulate. Thus, it is important to understand if low-level AgNPs induce physiological changes in brain cells. Previously we found that 1.0 μg/mL AgNP exposure resulted in disruption of f-actin organization and neurite collapse in cultured differentiating adult neural stem cells, and that interaction with β-catenin signaling was involved. Here, we report that AgNP exposure may interact with pAkt signaling irreversibly or indirectly to disrupt cytoskeleton and inhibit neurite extension. Furthermore, the MAPK/ERK signaling pathway is not a target for AgNP-mediated dysregulation. Environmental exposure to low-level AgNPs therefore appears to target specific cellular mechanisms to alter brain cell physiology. Understanding these underlying mechanisms is important for decisions regulating the use and disposal of manufactured AgNPs.

The impacts of metal-based engineered nanomaterial mixtures on microbial systems: A review

The last decade has witnessed tremendous growth in the commercial use of metal-based engineered nanomaterials (ENMs) for a wide range of products and processes. Consequently, direct and indirect release into environmental systems may no longer be considered negligible or insignificant. Yet, there is an active debate as to whether there are real risks to human or ecological health with environmental exposure to ENMs. Previous research has focused primarily on the acute effects of individual ENMs using pure cultures under controlled laboratory environments, which may not accurately reveal the ecological impacts of ENMs under real environmental conditions. The goal of this review is to assess our current understanding of ENM effects as we move from exposure of single to multiple ENMs or microbial species. For instance, are ENMs' impacts on microbial communities predicted by their intrinsic physical or chemical characteristics or their effects on single microbial populations; how do chronic ENM interactions compare to acute toxicity; does behavior under simplified laboratory conditions reflect that in environmental media; finally, is biological stress modified by interactions in ENM mixtures relative to that of individual ENM? This review summarizes key findings and our evolving understanding of the ecological effects of ENMs under complex environmental conditions on microbial systems, identifies the gaps in our current knowledge, and indicates the direction of future research.

Transformations of Ag2S nanoparticles in simulated human gastrointestinal tract: Impacts of the degree and origin of sulfidation

Engineered silver sulfide nanoparticles (e-Ag₂S-NPs) are used in industry and can be released into the environment. Besides e-Ag₂S-NPs, transformed silver sulfide nanoparticles (t-Ag₂S-NPs) from silver nanoparticles are more likely to be the form that is widely distributed in the environment. Both e-Ag₂S-NPs and t-Ag₂S-NPs may be ingested and get into human gastrointestinal tract (GIT) through trophic transfer, posing a potential threat to human health. Nevertheless, knowledge of chemical stability of t-Ag₂S-NPs and e-Ag₂S-NPs in the human GIT is very limited. Herein e-Ag₂S-NPs and a series of t-Ag₂S-NPs with different degrees of sulfidation were selected as models for exposure to the simulated human GIT including mouth, stomach and small intestine phases under fed and fasted conditions. Silver ions were detected in the simulated saliva, gastric and small intestine fluids when t-Ag₂S-NPs or e-Ag₂S-NPs were incubated in the simulated GIT, but the amount (e.g., < 20 μg) of silver ion in each phase accounted for < 0.2‰ (w/w) of the silver added (i.e., 100 mg). Silver species of the residual particulate from each phase of the simulated GIT with t-Ag₂S-NPs or e-Ag₂S-NPs were thus analyzed through a developed analytical method that could selectively, successively and efficiently dissolve and quantify AgCl, Ag(0), and Ag₂S in particulates. Both e-Ag₂S-NPs and fully sulfidized t-Ag₂S-NPs were shown to be highly stable in the simulated human GIT. Conversely, partially sulfidized t-Ag₂S-NPs primarily underwent transformations in the mouth phase relative to stomach and small intestine phases regardless of fed or fasted status, wherein AgCl and Ag₂S were observed besides Ag(0). The amount of Ag₂S in the mouth phase negatively (r = -0.99, p <  0.001) correlated with the sulfidation degree of initial t-Ag₂S-NPs. This work improved our understanding of potential transformations of t-Ag₂S-NPs in the simulated human GIT, providing valuable information for future researches on evaluating health risks of ingested Ag₂S-NPs.

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.

Copper(I) Promotes Silver Sulfide Dissolution and Increases Silver Phytoavailability

Metal sulfides, including acanthite (Ag₂S), are persistent in the environment. In colloidal form, however, they can serve as a "Trojan horse", facilitating the mobility of trace metal contaminants. The natural processes that lead to the in situ dissolution of colloidal metal sulfides in soil are largely unknown. In this study, the dissolution of colloidal Ag₂S in topsoil and Ag phytoavailability to wheat were examined in Ag₂S-Cu(II)-thiosulfate systems. Cu(II) and thiosulfate strongly increased silver release (up to 83% of total Ag) from Ag₂S in the dark. Electron paramagnetic resonance, X-ray photoelectron spectroscopy, and Cu K-edge X-ray absorption spectroscopy identified Cu(I) as the driving force of Ag₂S dissolution. Density functional theory calculations further demonstrated the ability of Cu(I) to substitute for surface Ag on Ag₂S in an energetically favorable manner. However, excess Cu(II) could enhance the formation of precipitates containing Cu(I), Ag, and S. Our results indicate that at ambient temperature and in the dark, Cu(I) can promote the dissolution of Ag₂S and act as a precipitating agent. These findings reveal previously unrecognized biogeochemical processes of colloidal Ag₂S and their importance in determining the fate of metal sulfides in the environment and probably also in vivo.

Contrasting effects of iron plaque on the bioavailability of metallic and sulfidized silver nanoparticles to rice

Interaction between silver nanoparticles (AgNPs) and iron plaque, which forms at the root surface of wetland plants under waterlogging conditions, is a critical process that controls the bioavailability of AgNPs. In this study, we comparatively evaluated how and to what extent iron plaque affected silver uptake sourced from metallic (Ag⁰NPs) and sulfidized (Ag₂S-NPs) silver nanoparticles under hydroponic conditions. After the formation of iron plaque at the root surface upon exposure to Fe²⁺ at 0-100 μg mL^-1, rice (Oryza sativa L.) seedlings were transferred to AgNP suspensions. Silver uptake depended on the amount of iron plaque and AgNP species (Ag⁰NPs vs. Ag₂S-NPs): Ag₂S-NP exposure had lower or comparable Ag uptake to that of Ag⁰NP exposure at low levels of Fe²⁺ (0-80 μg mL^-1), but significantly higher Ag uptake at 100 μg Fe²⁺ mL^-1. Such contrasting effects of iron plaque on the bioavailability of Ag⁰NPs and Ag₂S-NPs were attributed to their influences on AgNP dissolution. However, the translocation factors (TFs) and particle size distribution of NPs in planta (as determined by single-particle inductively coupled plasma-mass spectrometry analysis) were not affected by the amount of iron plaque. These results reveal contrasting effects of iron plaque on the bioavailability of Ag⁰NPs and Ag₂S-NPs, and raise concerns about the exposure of wetland plants to Ag₂S-NPs in Fe-rich environments, where high Fe levels may facilitate Ag₂S-NP bioavailability.

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.

Assessment of Cu and CuO nanoparticle ecological responses using laboratory small-scale microcosms

Copper based nanoparticles (NPs) are used extensively in industrial and commercial products as sensors, catalysts, surfactants, antimicrobials, and for other purposes. The high production volume and increasing use of copper-based NPs make their ecological risk a concern. Commonly used copper-based NPs are composed of metallic copper or copper oxide (Cu and CuO NPs); however, their environmental toxicity can vary dramatically depending on their physico-chemical properties, such as dissolution, aggregation behavior, and the generation of reactive oxygen species. Here, we investigated the NP dissolution, organismal uptake and aquatic toxicity of Cu and CuO NPs at 0, 0.1, 1, 5 or 10 mg Cu/L using a previously developed multi-species microcosm. This 5-day microcosm assay was comprised of C. reinhardtti, E. coli, D. magna, and D. rerio. We hypothesized that Cu and CuO NPs can elicit differential toxicity to the organisms due to alterations in particle dissolution and variations in organismal uptake. The actual concentrations of dissolved Cu released from the NPs were compared to ionic copper controls (CuCl₂) at the same concentrations to determine the relative contribution of particulate and dissolved Cu on organism uptake and toxicity. We found that both NPs had higher uptake in D. magna and zebrafish than equivalent ionic exposures, suggesting that both Cu-based NPs are taken up by organisms. Cu NP exposures significantly inhibited algal growth rate, D. magna survival, and zebrafish hatching while exposure to equivalent concentrations of CuCl₂ (dissolved Cu fraction) and CuO NPs did not. This indicates that Cu NPs themselves likely elicited a particle-specific mechanism of toxicity to the test organisms, or a combination effect from ionic Cu and the Cu NPs. Overall, this work was the first study to utilize a small-scale rapid assay designed to evaluate the fate and ecotoxicological impacts of Cu and CuO NPs in a mixed aquatic community.

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.