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Abiotic and biotic influences on silver nanoparticle fate and effects in aquatic model ecosystems
Abstract
Silver nanoparticles (AgNP) are used dominantly for disinfection purposes due to their high toxicity against bacteria. Even though this property is desired during use, it may become unwanted, if AgNP are released into the environment. As the toxicity of AgNP is not limited to bacteria, also other taxonomic groups may suffer from release of AgNP into the environment. Release of silver ions from the AgNP represents an important source for toxicity, however, also AgNP themselves can act toxic. In aquatic systems, toxicity of AgNP is highly affected by their colloidal stability (dissolution and agglomeration) in the medium, which is in turn closely related to the coating of the used AgNP. As also the test conditions, such as pH, medium composition, light intensity, or test duration interact with the coating, generalizations on the mode of action or toxicity of AgNP to aquatic organisms can only be made for a single coating or a certain test design. Still, the high number of studies using AgNP provide a good reference for investigating the relation between colloidal stability in the test medium and toxicity in more detail. For this dissertation, two rarely considered aspects of this relation were chosen 1) the influence of surface area and surface properties on colloidal stability and actual concentrations of AgNP in the test medium, and 2) the effect of resource reduction on AgNP toxicity. By using these two topics, biological as well as chemical influences on AgNP toxicity could be investigated. For this purpose, an aquatic model system was used including two differently coated AgNP, two green algae, Raphidocelis subcapitata and Desmodesmus subspicatus, and the big water flea, Daphnia magna, in varying compositions. The investigation of surface-related effects revealed that differences in surface area were of minor importance for AgNP colloidal stability and fate compared to surface properties. Higher hydrophobicity increased the attachment of detergent stabilized AgNP to the test vessela s surface, thus reducing the actual exposure concentrations and causing lower levels of toxicity in this test vessel. In case of variation of the AgNP surface itself, the coating, higher degrees of attachment of the AgNP to each other, so a higher degree of agglomeration, increased uptake of the corresponding AgNP and caused higher levels of toxicity. These results support the importance of surface properties for the fate of AgNP in a given test system and identified hydrophobicity as well as surface charge as most important properties for the attachment of AgNP to surfaces. In addition, the interactions between biological surfaces and citrate coated AgNP were identified as most probable link between colloidal stability and observed toxicity, suggesting further investigations on this topic. The reduction of resources had a close connection to the other topic of research, as changes in media composition, as required for changes in nutrient supply for algae, highly affected colloidal stability of the AgNP. By the use of intensive analytics, however, effects resulting from changes in colloidal stability could be separated from changes caused by differences nutrient reduction. Resource reduction caused an increase in AgNP toxicity in both trophic levels with the response also differing between the two algae species. Consequently, AgNP toxicity can be expected to be higher for various taxa when resource provision is low, but the intensity of this change is likely to vary between species.
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Ecotoxicological testing of new chemicals is being performed under controlled laboratory conditions, following standardised procedures such as OECD and ISO guidelines. One of the most common test guidelines is growth inhibition of algae (OECD 201, 2011).
The test medium in OECD 201 is hypertrophic (Ongley, 1996), i.e. both N and P are available in excess. This might underestimate potential risks of new substances like silver nanoparticles (AgNP), for in the natural environment nutrients can frequently be limiting.
The main objectives of the study were,
1. to observe the growth and survival of two algae species Desmodesmus subspicatus (DS) and Raphidocelis subcapitata (RS) (Formerly Pseudokirchneriella subcapitata (PS)) against different AgNP concentrations;
2. to watch the AgNP toxicity in different nutrient conditions for DS and PS;
3. to compare the sensitivity of algae at different P and N limited condition with and without the application of AgNP; and
4. to observe the survival strategy of two algae species cultured together, against AgNP in different nutrient conditions.
The relation between test conditions such as medium composition or pH on silver nanoparticle (AgNP) behavior and its link to toxicity is one of the major topics in nanoecotoxicological research in the last years. In addition, the adaptation of the ecotoxicological standard tests for nanomaterials is intensely discussed to increase comparability and reliability of results. Due to the limitation of test material production volumes and the need for high-throughput screening, miniaturization has been proposed for several test designs. In the present study, the effect of a miniaturization of the acute Daphnia immobilization test on AgNP behavior was investigated. For this purpose, available, adsorbed, and dissolved silver fractions were measured using AgNP and silver nitrate in the following two test designs: a standard test (ST) design and a miniaturized test (MT) design with reduced test volume and less animals. Despite the increase in surface area in relation to the test volume in MT, more AgNP attached to the ST vessel surface, so that in this case, exposure concentrations were significantly lower compared to the MT assessment. Ionic silver concentrations resulting from AgNP dissolution were similar in both test designs. The same was observed for ionic silver concentrations in silver nitrate (AgNO3) treatments, but adsorbed silver was also higher in ST treatments. Assessing the structure-activity relationships revealed that surface properties such as hydrophobicity, potential binding sites, or surface roughness were of higher importance than surface:volume ratios for both test substances.
It remains unclear which kinds of nanoproducts are available on the European market, although this information is a prerequisite for any kind of exposure and risk assessment. In order to address this lack of information, we have established The Nanodatabase (http://www.nanodb.dk), which is an online inventory of products claimed by manufacturers to contain nanomaterials (NMs) or be based on nanotechnology. The database currently entails 2231 products. The database is unique and includes basic information about the product (name, NM used, location of NM, product category, etc.) as well as a safety evaluation of each individual product according to the NanoRiskCat-framework. Our analysis of products that are currently present in the database shows that most products fall into “personal care” and “clothing” categories (≥300), followed by “sporting goods” and “cleaning” (>200). Silver and titanium dioxide are the most used NMs, but it is not possible to identify the NMs used for almost 60% of the products in the database. The data analysis shows that for most product categories the dominant route of exposure is dermal, and that the exposure potential as well as human and environmental hazard potential of most products is either “high” or “unknown”. In order to address the current lack of reporting by manufacturers when it comes to nanoproducts, we recommend that it is made mandatory to disclose and report any nanomaterials used in a consumer product and it becomes illegal to advertise and market products as “nano” when they have no content of nanomaterials.
The knowledge regarding the effects of metal or metal oxide nanoparticles on soil microbial metabolic activity and key ecological functions is limited, relative to the information about their species diversity. For this reason, the responses of soil microbial metabolic activity to silver (AgNPs) and iron oxide (FeONPs) nanoparticles, along concentration gradients of each, were evaluated by microcalorimetry and soil nitrification potential. The changes in abundances of bacteria, eukaryotes and ammonia-oxidizing bacteria were measured by real time quantitative PCR. It was found that AgNP (at 0.1, 1 and 10 mg kg−1 soil) amendments decreased soil microbial metabolic activity, nitrification potential and the abundances of bacteria and ammonia-oxidizing bacteria; on the contrary, FeONPs had the positive effects on soil microbial metabolic activity (at 1 and 10 mg kg−1 soil) and soil nitrification potential (at 0.1 and 1 mg kg−1 soil). Specific microbial metabolic activity and specific nitrification potential further revealed that metal or metal oxide nanoparticles could change the C and N cycles of the agricultural soil through influencing soil microbial metabolism. These findings could deepen the understanding of the influence of NPs on soil microorganisms and their driven soil ecology process.
Silver nanoparticles, endowed with powerful antimicrobial property, are the most widely used nanomaterial in consumer products, with associated risk of their easy access to environment and freshwater ecosystems by surface runoff. Although toxic effects of nanosilver on bacterial, fungal and mammalian cells have been documented, its impact on algal growth remains unknown. Pithophora oedogonia and Chara vulgaris are predominant members of photosynthetic eukaryotic algae, which form major component of global aquatic ecosystem. Here we report for the first time that nanosilver has significant adverse effects on growth and morphology of these filamentous green algae in a dose-dependent manner. Exposure of algal thalli to increasing concentrations of silver nanoparticles resulted in progressive depletion in algal chlorophyll content, chromosome instability and mitotic disturbance, associated with morphological malformations in algal filaments. SEM micrographs revealed dramatic alterations in cell wall in nanoparticle-treated algae, characterized with cell wall rupture and degradation in Pithophora. Although these observations underscore severe deleterious effects of nanosilver on aquatic environment, the information can also be exploited as a bioengineering strategy to control unwanted and persistent growth of noxious algal weeds that clog the municipal water supply and water channels and produce fouling of water bodies.
The European Commission Joint Research Centre (JRC) provides scientific support to European Union policy regarding nanotechnology and public health in a sustainable environment. Over the last three years, the JRC has focused part of its work on establishing and applying a priority list (NM-Series) of representative manufactured nanomaterials (RMNs) in support of one of the most comprehensive nanomaterial research programmes that is currently being carried out: the Organisation for Economic Co-operation and Development’s (OECD) Working Party on Manufactured Nanomaterials (WPMN) Sponsorship Programme. The JRC’s provision of NM-Series RMNs to the OECD WPMN Sponsorship Programme ultimately enables the development and collection of data on characterisation, measurement, toxicological and eco-toxicological testing, and risk assessment or safety evaluation of nanomaterials. Representative nanomaterials are of utmost importance to be made available to the international scientific community to enable innovation and development of safe materials and products. This report describes the characterisation of NM-300, a RMN nano-silver dispersion containing nanoparticles (NPs) of < 20 nm, originating from a single batch of manufactured nano-silver, used for measurement and testing for hazard identification, risk and exposure assessment studies. The first series of sub-samples created from the batch is labelled NM-300, while the further processed series of NM 300 is labelled with an additional 'K' as NM 300K, in order to signify a continued processed number of sub-samples from the same batch of raw material. This NM-Series material was produced in the frame of the JRC programme on nanomaterials. It was studied by a number of international laboratories including the JRC IES analytical laboratory. Inorganic chemical characterisation of the total silver content and the homogeneity of the silver distribution were performed using photometry and ICP-OES. To this end, a dedicated method was developed and validated according to the principles of ISO 17025. Key properties of size and size distribution were studied in an inter-laboratory comparative study using SEM as well as TEM and nanoparticle tracking analysis. Furthermore, the release of silver ions from the NM-300 was studied after embedding in an acrylic matrix. The NM-300 silver <20 nm was found to contain silver particles of about 15 nm size with a narrow size distribution of 99 % of the particle number concentration exhibiting a diameter of below 20 nm. A second, much smaller abundance of particles was identified by TEM to have narrow diameter distribution of around 5 nm. The silver content and particle number of NM-300 was shown to be stable over the time of examination, lasting up to 12 months. Silver-ions were released from NM-300 silver nanomaterial, which was embedded in a poly-acrylic matrix up to a defined concentration level. The properties of NM-300 studied and described in this report demonstrate its relevance for use in measurement and testing studies, such as for hazard identification, related to the safety of nanomaterials. The studies were performed in close collaboration with the Fraunhofer Institute for Molecular and Applied Ecology (Fh-IME), German Institute of Energy and Environmental Technology e.V. (IUTA), the Swiss Federal Laboratories for Materials Science and Technology (EMPA), RAS Material Science GmbH, Germany, and the Veterinary and Agrochemical Research Centre (VAR) in Belgium.
Biological significance:
Daphnia magna are an important environmental indicator species who may be especially sensitive to nanoparticles (NPs) as a result of being filter-feeders. This paper demonstrates for the first time that proteins released by Daphnia magna create an eco-corona around polystyrene NPs which causes heightened uptake of the NPs and consequently increases toxicity. The secreted protein eco-corona also causes the NPs to be less efficiently removed from the gut of D. magna and NPs remaining in the gut of D. magna affected the rate of subsequent feeding. Thus, fate of NPs in the environment should be evaluated and monitored under more realistic exposure scenarios.
Exposure to silver nanoparticles (AgNPs) may alter the structure and function of freshwater ecosystems. However, there remains a paucity of studies investigating the effects of AgNP exposure on freshwater communities in the natural environment where interactions with the ambient environment may modify AgNP toxicity. We used nutrient diffusing substrates to determine the interactive effects of AgNP exposure and phosphorus (P) enrichment on natural assemblages of periphyton in three Canadian Shield lakes. The lakes were all phosphorus poor and spanned a gradient of dissolved organic carbon availability. Ag slowly accumulated in the exposed periphyton, which decreased periphyton carbon and chlorophyll a content and increased periphyton C:P and N:P in the carbon rich lakes. We found significant interactions between AgNP and P treatments on periphyton carbon, autotroph standing crop and periphyton stoichiometry in the carbon poor lake such that P enhanced the negative effects of AgNPs on chlorophyll a and lessened the impact of AgNP exposure on periphyton stoichiometry. Our results contrast with those of other studies demonstrating that P addition decreases metal toxicity for phytoplankton, suggesting that benthic and pe-lagic primary producers may react differently to AgNP exposure and highlighting the importance of in situ assays when assessing potential effects of AgNPs in fresh waters.
The toxicity of silver nanoparticles (AgNPs) to green alga
Pseudokirchneriella subcapitata was evaluated in standard nutrient medium
(ISO 8692), lake water samples from an oligotrophic and an eutrophic
lake, and in lake waters supplemented with the standard nutrient medium.
Prior to toxicity testing the agglomeration of polyvinylpyrrolidone (PVP) and
starch-coated AgNPs was studied in each test medium. Agglomeration
was studied by determining the hydrodynamic diameter (HDD). The HDDs
for the PVP- and starch-capped AgNP dispersions in deionized water were
40 and 175 nm respectively, indicating the presence of agglomerates. The
HDDs of AgNPs remained stable throughout the exposure time in all media
used for the toxicity tests. The algae growth inhibition test was performed
as a microplate modification of the ISO method using fluorescence
detection. The effect of concentration at a 50% inhibition value for PVPcoated
AgNPs in standard medium was 115 ± 3 μg/L, and for starchcoated
AgNPs 51 ± 32 μg/L. The eutrophic freshwater conditions
suppressed the toxicity of the PVP- coated AgNPs, but not the starchcoated
NPs. This finding emphasizes the importance of using different
AgNPs and natural waters in assessing the environmental risks of silver
nanoparticles.
Nanosilver and other forms ofof silver are widely used nowadays for their antibacterial activity.
The characteristics and the use of different forms of silver (including silver salts, silver oxides and silver materials appearing as silver wires, silver nanoparticles (Ag-NP) and others) are used in consumer and medical products may have different physico-chemical properties such as distinct solubility and surface-to-volume ratio, which all may affect their fate and biological activity.
In medical care forms of (nano)silver are used, for example in: wound dressings and catheters to reduce infections. In consumer products, forms of (nano)silver are used, for example in: sports and other textiles, washing powders and deodorants, where (nano)silver should reduce odours producing bacteria.
In view of the increasing use of (nano)silver compounds several questions were raised: Are these consumer and health care products hazardous for the environment and/or for human health; can micro-organisms become resistant against silver (including nanosilver and silver-based compounds); and is there any risk of an increased bacterial resistance with regard to their pervasive and widespread use.
Currently, products that contain forms of (nano)silver are difficult to track since they are marketed under numerous brand names, and, with a few exceptions, current labelling regulations do not specifically require listing nanomaterials as a constituent.
Consumer exposure depends on the location of the nanomaterial in consumer/medical products and/or the manipulation of the product. To determine the level of exposure, more information is needed on the concentrations of silver in products, the size and the form in which it is present and the probability of release of Ag-NP or Ag ions from the products.
When evaluating the end-of-life phase of Ag-NP containing products it is assumed that their waste management (recycling, wastewater treatment, landfilling, and incineration) is similar to conventional products. Consequently, silver content in non-recycled waste will ultimately end up in the environment, either as solid waste in landfills, emission from wastewater treatment plants, or as residual waste from incineration plants.
In humans, bioavailability of silver after oral and pulmonary administration of Ag-NPs has been shown. The main target organs for Ag-NP deposition after systemic availability are spleen, liver and kidney while there is less distribution to other organs. Additionally, high levels of silver were sometimes found in the testes.
The best-described adverse effects in humans of chronic exposure to silver are a permanent bluish-grey discoloration (argyria or argyrosis) of the skin and/or eyes. In several animal toxicity studies an increase of various liver enzymes was observed, indicating liver toxicity after a silver nanoparticle administration. However, liver toxicity could not be observed by histopathology. In vivo, oral exposure to silver nanoparticles did not consistently result in alterations of the non-specific immune responses. However, for iv exposure it was shown that the immune system is the most sensitive target for Ag-NP toxicity. In vitro, genotoxic effect of nanosilver has been reported. As the studies available on the in vivo genotoxicity of Ag-NPs are few, it was concluded that further studies are required to draw final conclusions.
It should be stressed that, in many studies, the release of ionic silver has been found to be the main cause of toxicity (in humans, in the environment and in hygienic applications), nevertheless an increasing number of studies found that this release cannot alone account for the toxic effects observed.
Current human risk assessments are mainly based on the development of argyria. In workers the threshold limit value for metallic silver is 0.1 mg/m³ and 0.01 mg/m3 for silver salts. For the general population the WHO did set a No Observable Adverse Effect Level (NOAEL) related to the sum of all exposure routes of 5 µg/kg bw/d. A detailed risk assessment of nanosilver has not been performed since too little information is available.
Ag-NP undergoes several transformations when it is released into the environment. Apart from aggregation and agglomeration, the important ones are dissolution and subsequent speciation, such as the formation of silver chloride and silver sulphide. Silver sulphide is particularly important because it is highly stable; sulphide is available in wastewater treatment plants and also in many freshwater bodies. The chemical species that are actually present determine the bioavailability and toxicity of silver in the environment. Bioavailability of Ag-NP in soils depends on both particle and soil properties. In general, the mobility of ionic silver in soil and sediments is very limited; however, particles may behave differently.
There is an effect of Ag-NP on the composition of bacterial flora and on the bacterial adaptation associated with certain conditions and uses. However, evidence is often fragmentary and focused on few specific cases. There is a paucity of information on potential resistance mechanisms to Ag-NP. Some of the genetic basis of bacterial resistance to ionic silver has been well documented, notably the expression of well-characterised efflux systems. Recent transcriptomic and proteomic data suggest that a decrease in oxidative damage by regulation of anaerobic respiration may be important. Exposure to ionic silver and Ag-NP produces a stress-response and affects gene expression. More data is needed to better understand bacterial response to ionic silver and Ag-NP exposure.
Regarding the hazard associated with the dissemination of resistance mechanism following the use of Ag-NP, no documentation is available at this moment. This represents a serious gap in knowledge.
The growing use of nanoparticles in a wide range of products has resulted in their release into the aquatic environment; therefore, an understanding of the toxic effects of nanoparticles on aquatic organisms is of permanent importance. The aim of this study was to evaluate the toxicity of silver and platinum nanoparticles toward the freshwater microalga, Pseudokirchneriella subcapitata. Algal growth and photosynthetic pigments were determined to quantitate the effects of varying concentrations of Ag and Pt nanoparticles. The silver nanoparticles were much more toxic than the platinum ones. The concentrations causing total inhibition of algal growth were 5.0 and 22.2 mg L(-1), respectively. Similar results were obtained by analyzing the concentration of photosynthetic pigments in P. subcapitata exposed to nanoparticles. Thus, simple spectrophotometric determination of chlorophyll is a convenient tool for the analysis of nanoparticle toxicity to algae.
Engineered nanomaterials (ENM) offer enhanced or new functionalities and properties that are used in various products. This also entails potential environmental risks in terms of hazard and exposure. However, hazard and exposure assessment for ENM still suffer from insufficient knowledge particularly for product-related releases and environmental fate and behavior. This study therefore analyzes the multiple impacts of the product use, the properties of the matrix material, and the related waste management system (WMS) on the predicted environmental concentration (PEC) by applying nine prospective life cycle release scenarios based on reasonable assumptions. The products studied here are clothing textiles treated with silver nanoparticles (AgNPs), since they constitute a controversial application. Surprisingly, the results show counter-intuitive increases by a factor of 2.6 in PEC values for the air compartment in minimal AgNP release scenarios. Also, air releases can shift from washing to wearing activity; their associated release points may shift accordingly, potentially altering release hot spots. Additionally, at end-of-life, the fraction of AgNP-residues contained on exported textiles can be increased by 350% when assuming short product lifespans and globalized WMS. It becomes evident that certain combinations of use activities, matrix material characteristics, and WMS can influence the regional PEC by several orders of magnitude. Thus, in the light of the findings and expected ENM market potential, future assessments should consider these aspects to derive precautionary design alternatives and to enable prospective global and regional risk assessments.
Copyright © 2015 Elsevier B.V. All rights reserved.
Abstract Silver nanoparticles (Ag-NPs) are used in a wide variety of products, prompting concerns regarding their potential environmental impacts. To accurately determine the toxicity of Ag-NPs it is necessary to differentiate between the toxicity of the nanoparticles themselves and the toxicity of ionic silver (Ag) released from them. This is not a trivial task given the reactive nature of Ag in solution, and its propensity for both adsorption and photoreduction. In the experiments reported here, we quantified the loss of silver from test solutions during standard ecotoxicity testing conducted using a variety of different test container materials and geometries. This sensitive (110m)Ag isotope tracing method revealed a substantial underestimation of the toxicity of dissolved Ag to the green algae Pseudokirchneriella subcapitata when calculated only on the basis of the initial test concentrations. Furthermore, experiments with surface-functionalized Ag-NPs under standard algal growth inhibition test conditions also demonstrated extensive losses of Ag-NPs from the solution due to adsorption to the container walls, and the extent of loss was dependent on Ag-NP surface-functionality. These results hold important messages for researchers engaged in both environmental and human nanotoxicology testing, not only for Ag-NPs but also for other NPs with various tailored surface chemistries, where these phenomena are recognized but are also frequently disregarded in the experimental design and reporting.
Silver nanoparticles (AgNPs) are prominent group of nanomaterials and are recognized for their diverse applications in various health sectors. This study aimed to synthesize the AgNPs using the leaf extract of Artemisia princeps as a bio-reductant. Furthermore, we evaluated the multidimensional effect of the biologically synthesized AgNPs in Helicobacter pylori, Helicobacter felis, and human lung (L132) and lung carcinoma (A549) cells. UV-visible (UV-vis) spectroscopy confirmed the synthesis of AgNPs. X-ray diffraction (XRD) indicated that the AgNPs are specifically indexed to a crystal structure. The results from Fourier transform infrared spectroscopy (FTIR) indicate that biomolecules are involved in the synthesis and stabilization of AgNPs. Dynamic light scattering (DLS) studies showed the average size distribution of the particle between 10 and 40 nm, and transmission electron microscopy (TEM) confirmed that the AgNPs were significantly well separated and spherical with an average size of 20 nm. AgNPs caused dose-dependent decrease in cell viability and biofilm formation and increase in reactive oxygen species (ROS) generation and DNA fragmentation in H. pylori and H. felis. Furthermore, AgNPs induced mitochondrial-mediated apoptosis in A549 cells; conversely, AgNPs had no significant effects on L132 cells. The results from this study suggest that AgNPs could cause cell-specific apoptosis in mammalian cells. Our findings demonstrate that this environmentally friendly method for the synthesis of AgNPs and that the prepared AgNPs have multidimensional effects such as anti-bacterial and anti-biofilm activity against H. pylori and H. felis and also cytotoxic effects against human cancer cells. This report describes comprehensively the effects of AgNPs on bacteria and mammalian cells. We believe that biologically synthesized AgNPs will open a new avenue towards various biotechnological and biomedical applications in the near future.
We investigated the interspecific variation of silver nanoparticle (SNP) sensitivity in common cladocerans (Daphnia magna, D. galeata, and Bosmina longirostris) and the exact cause of both acute and chronic toxicity focusing on the form of silver (NPs and ions). Materials tested were non-surface-coated silver nanocolloids (SNCs) and AgNO3. The results of the acute toxicity tests support the theory that the effects of SNPs on aquatic organisms is mainly due to Ag+ released from SNPs. Among the three cladocerans, D. galeata was more sensitive to silver (as Ag+) than both D. magna and B. longirostris. Moreover, the chronic toxicity of SNCs was also derived from dissolved silver (especially Ag+). SNCs (as total silver concentration) showed far lower chronic compared with acute toxicity to daphnids because the amount of dissolved silver decreased in the presence of prey algae. The chronic end-point values (EC10 values for net reproductive rate and the probability of survival to maturation) did not differ largely from acute ones (48-h EC50 obtained from acute toxicity tests and 48-h LC50 estimated by the biotic ligand model) when the values were calculated based on Ag+ concentration. The α value (concentration at which intrinsic population growth rate is decreased to zero) estimated by a power function model was a reliable parameter for assessing the chronic toxicity of silver.
Nanoecotoxicology strives to understand the processes and mechanisms by which engineered nanoparticles (ENP) may exert toxic effects on aquatic organisms. Detailed knowledge of the chemical reactions of nanoparticles in the media and of their interactions with organisms is required
to understand these effects. The processes of agglomeration of nanoparticles, of dissolution and release of toxic metal ions, and of production of reactive oxygen species (ROS) are considered in this article. Important questions concern the role of uptake of nanoparticles in various organisms,
in contrast to uptake of ions released from nanoparticles and to nanoparticle attachment to organism surfaces. These interactions are illustrated for effects of silver nanoparticles (AgNP), cerium oxide (CeO2 NP) and titanium dioxide (TiO2 NP), on aquatic organisms, including
algae, biofilms, fish cells and fish embryos.
Over the years there has been a significant increase in the manufacturing of silver nanoparticles-based products, mainly due to their antimicrobial activity, with application in medicine and textile and food industry. However, the inappropriate use and disposal of these materials can allow the entry of silver nanoparticles (AgNP) compounds into the aquatic environment, with potential toxicological effects. In this study we have used Pseudokirchneriella subcapitata, Artemia salina and Daphnia similis as model organisms to investigate the toxicity of PVA-stabilized AgNP at several concentration levels. AgNP were physico-chemically characterized by UV-Vis spectroscopy, particle size distribution, zeta potential analyzes and Transmission Electron Microscopy (TEM). AgNP presented a maximum absorption at 400 nm and size range between 2 and 18 nm. Each specific organism was exposed to AgNP concentrations through standardized protocol. For P. subcapitata and Artemia salina the EC50 value found, 1.09 mgL-1 and 5.5×10-2 mg⧸L, respectively, were in accordance to previous results reported in the literature. However, for D. similis, the EC50 24-48 h values indicate a higher toxicity than other results reported for other daphnids.
The development and application of products containing engineered nanoparticles (ENP) has dramatically increased over the past decade, whereas the assessment of potential hazards to humans and especially to the environment substantially falls behind. The UFT Centre for Environmental Research and Sustainable Technology at the University of Bremen focuses on environmentally benign nanomaterials. Here we present some results from two ongoing large project networks. Using examples from ecotoxicological tests and numerical speciation we demonstrate the necessity of interdisciplinary cooperation for the hazard assessment of silver nanoparticles.
We have carried out surface and zeta-potential measurements on AgCl and AgBr single crystals. As for particle systems we find that, surprisingly and previously unnoted, the zeta-potential exhibits pH-dependence, while the surface potential does not. A possible interpretation of these observations is the involvement of water ions in the interfacial equilibria and in particular, stronger affinity of the hydroxide ion compared to the proton. The pH-dependence of the zeta-potential can be suppressed at sufficiently high silver concentrations, which agrees with previous measurements in particle systems where no pH-dependence was found at high halide ion concentrations. The results suggest a subtle interplay between the surface potential determining the halide and silver ion concentrations, and the water ions. Whenever the charge due to the halide and silver ions is sufficiently high, the influence of the proton/hydroxide ion on the zeta-potential vanishes. This might be related to the water structuring at the relevant interfaces which should be strongly affected by the surface potential. Another interesting observation is accentuation of the assumed water ion effect on the zeta-potential at the flat single crystal surfaces compared to the corresponding silver halide colloids. Previous generic MD simulations have indeed predicted that hydroxide ion adsorption is accentuated on flat/rigid surfaces. A thermodynamic model for AgI single crystals was developed to describe the combined effects of iodide, silver and water ions, based on two independently previously published models for AgI (that only consider constituent and background electrolyte ions) and inert surfaces (that only consider water and background electrolyte ions). The combined model correctly predicts all the experimentally observed trends.
An extractive procedure for detection of surplus‐stored phosphorus (luxury consumption) in algae and an enzymatic analysis for conditions of P‐limited growth in algae have been evaluated. A simple 60‐min boiling water extraction of algae known to contain surplus P separates essential P compounds and surplus‐stored P compounds. Surplus P compounds can be measured in the extract as orthophosphate. Extracts of algae limited in their growth by the amount of available P contain little or no orthophosphate. Limitation of algal growth by P supply induces the enzyme alkaline phosphatase. The activity of this enzyme can be measured at pH 9 using p‐nitro‐phenylphosphate as substrate. Algae which were P‐limited and contained no extractable orthophosphate have as much as 25 times more alkaline phosphatase activity than algae with surplus available P.
While differences in silver nanoparticle (AgNP) colloidal stability, surface potential, or acute aquatic toxicity for differently stabilized AgNP have often been reported, these have rarely been studied in long-term ecotoxicity tests. In the current study, we investigated the chronic toxicity of AgNP to Daphnia magna over a 21-day period with two different stabilizers (citrate and detergent), representative for charge and sterical stabilizers, respectively. This was coupled with a series of short-term experiments, such as mass balance and uptake/depuration testing, to investigate the behavior of both types of AgNP during a typical media exchange period in the D. magna test for chronic toxicity. As expected, the sterically stabilized AgNP were more stable in the test medium, also in the presence of food; however, a higher uptake of silver after 24 h exposure of the charge stabilized AgNP was found compared to the detergent-stabilized AgNP (0.046 ± 0.006 μg Ag μg DW−1 and 0.023 ± 0.005 μg Ag μg DW−1, respectively). In accordance with this, the higher reproductive effects and mortality were found for the charge-stabilized than for the sterically-stabilized silver nanoparticles in 21-d tests for chronic toxicity. LOEC was 19.2 μg Ag L−1 for both endpoints for citrate-coated AgNP and >27.5 μg Ag L−1 (highest tested concentration for detergent-stabilized AgNP). This indicates a link between uptake and toxicity. The inclusion of additional short-term experiments on uptake and depuration is recommended when longer-term chronic experiments with nanoparticles are conducted.
As use and emission of metal-based engineered nanomaterials (MENM) is steadily increasing, concern of adverse effects on soil communities is rising. MENM are not only toxic to various organisms in soil, but can bioaccumulate, trophically transfer and even biomagnify in some systems. Negative effects of MENM on plant-fungi and plant-bacteria interactions have been shown in various studies, while further research on other forms of interactions (e.g. competition, predation) is needed to assess potential risks. Negative effects of MENM on nitrogen turnover and increased carbon emissions have been shown in numerous studies, and other biogeochemical cycles potentially at risk are addressed here. Most data to date has been collected on the consequences of MENM exposure for microorganisms and particle dependent changes in their community composition have been shown; data on other organism communities is however not available. In this review we summarize community interactions and soil ecosystem processes affected by MENM exposure and show how soil organisms influence MENM properties. Based on short- and long-term toxic effects, multiple inter- and intraspecific interactions and chemical processes we develop a conceptual framework. We postulate that cascading and potentially catalytic effects of MENM in soil might explain toxic effects at low concentration after longer exposure. Therefore, risk assessment of MENM relying solely on acute single species tests might be insufficient, and major research efforts are still needed in the area of soil communities and MENM exposure.
The vadose zone is a critical region controlling fate and transport of contaminants in soils and, ultimately, groundwater. It is therefore important to understand the behavior of engineered nanoparticles (ENPs) in this zone, as a potential group of emerging contaminants. Soil is a significant sink for ENPs; however, only a few studies have considered the fate and transport of ENPs in partially saturated systems, representative of the vadose zone. Here, transport behavior of three commonly used ENPs − gold (Au-NPs), silver (Ag-NPs) and zinc oxide (ZnO-NPs) − is investigated in partially saturated sand columns. High mobilities of Au-NPs and Ag-NPs under different water saturation levels and concentrations were observed. The presence of CaCl2 reduces Ag-NP mobility through chemical interactions, similar to behavior reported in saturated systems. Furthermore, transformation of Ag-NPs in the environment may influence their mobility; aging of Ag-NPs following sulfidation was investigated. The silver sulfide (Ag2S-NPs) remained stable in aqueous suspension, and mobile in the partially saturated sand column. In contrast, the positively-charged ZnO-NPs were completely immobilized in the sand column. Significantly, though, addition of humic acid (HA) to the ZnO-NP suspension reverses particle surface charge and thus increases their mobility. Moreover, remobilization of entrapped ZnO-NPs by HA was demonstrated.
Die vakuumtechnische Metallisierung von Kunststoffen und Polymeren bietet neue Möglichkeiten zur Gestaltung elektronischer Komponenten sowie in Anwendungsgebieten wie z.B. in der Automobilindustrie für Reflektoren oder dekorative Elemente im Fahrzeuginnenraum. Die Haftung einer vakuumtechnisch abgeschiedenen Metallisierung auf Polymeren ist dabei eine wichtige Voraussetzung für den Einsatz des metallisierten Bauteils. Zur Verbesserung der Haftfestigkeit vakuumtechnischer Schichten wird in industriell genutzten Beschichtungsanlagen häufig eine Plasmabehandlung z.B. durch Anregung mittels Gleichspannung (DC) eingesetzt. Ziel der Arbeit war es, ausgehend vom Haftverhalten vakuumtechnisch abgeschiedener Metallschichten auf unterschiedlichen Kunststoffen, einen Beitrag zum Verständnis des Haftungsmechanismus zu leisten. Fokus der Untersuchungen war dabei das Haftverhaltens der am häufigsten vakuumtechnisch abgeschiedenen Schichten (Aluminium und Kupfer) auf drei unterschiedlichen Polymeren verschiedener Kunststoffklassen. Die Metallisierung erfolgte mittels thermischer Verdampfung in einer industriell eingesetzten Beschichtungsanlage. Oberflächenanalytische Untersuchungen der Polymere in Korrelation zum Haftverhalten der metallischen Schichten ergaben, dass bei vergleichbarer Topografie der untersuchten Polymeroberflächen hohe Haftfestigkeiten der Metallschichten auf metalloxidische Wechselwirkungen der Metallatome mit polaren funktionalen Gruppen der Polymere zurückzuführen sind. Durch das unterschiedliche Oxidationsverhalten der Metalle kann das variierende Haftverhalten erklärt werden. Ausgehend von diesem grundlegenden Ansatz, der auch schon in der Literatur beschrieben wird, lag der Schwerpunkt der Arbeit auf der Untersuchung der Haftfestigkeit der beiden Metallschichten in Abhängigkeit variierter Prozessparameter der Plasmabehandlung. Aufgrund der Ergebnisse des Haftverhaltens sowie der topografischen und chemischen Oberflächencharakterisierung der Polymere nach variierten Plasmabehandlungen stellt sich als die wesentliche Größe für die Haftfestigkeit der Metallschichten die chemische Zusammensetzung der Polymeroberflächen dar. Die Bildung polarer funktionaler Gruppen wird durch die chemische Struktur der Polymere sowie durch die Prozessparameter der Plasmabehandlung beeinflusst und trägt durch den Einfluss auf die Bildung metalloxidisch gebundener Keime der metallischen Schicht wesentlich zur Haftfestigkeit der metallischen Schicht bei. Mit diesen Erklärungen für das Haftverhaltens zweier Metallschichten auf drei Polymeren tragen die Untersuchungen durch eine Modellvorstellung und deren experimenteller Untermauerung zum Verständnis der Haftung vakuumtechnisch abgeschiedener Metallisierungen bei. Die Erkenntnisse zum Einfluss variierter Prozessparameter der Plasmabehandlung auf das Haftverhalten erlauben die Optimierung vakuumtechnischer Metallisierungsprozesse für die Entwicklung neuer Polymer-Metall-Verbunde.
In aquatic toxicity testing of engineered nanoparticles (ENPs) the process of agglomeration is very important as it may alter bioavailability and toxicity. In the present study, we aimed to identify test conditions that are favorable for maintaining stable ENP suspensions. We evaluated the influence of key environmental parameters: pH (2–12) and ionic strength using M7, Soft EPA (S EPA) medium, and Very Soft EPA (VS EPA) medium; and observed the influence of these parameters on zeta potential, zeta average, and acute immobilization of Daphnia magna for three different ENPs. Despite being sterically stabilized, test suspensions of silver (Ag) ENPs formed large agglomerates in both VS EPA and M7 media; and toxicity was found to be higher in VS EPA medium due to increased dissolution. Low-agglomerate suspensions for zinc oxide (ZnO) could be obtained at pH 7 in VS EPA medium, but the increase in dissolution caused higher toxicity than in M7 medium. Titanium dioxide (TiO2) ENPs had a point of zero charge in the range of pH 7–8. At pH 7 in VS EPA, agglomerates with smaller hydrodynamic diameters (~200 nm) were present compared to the high ionic strength M7 medium where hydrodynamic diameters reached micrometer range. The stable suspensions of TiO2 ENPs caused immobilization of D. magna, 48-h EC50 value of 13.7 mg L−1 (95% CI, 2.4 mg–79.1 mg L−1); whereas no toxicity was seen in the unstable, highly agglomerated M7 medium suspensions, 48-h EC50 >100 mg L−1. The current study provides a preliminary approach for methodology in testing and assessing stability and toxicity of ENPs in aquatic toxicity tests of regulatory relevance.
The extraordinary chemical diversity seen in the cyanobacteria (blue-green algae) is especially pronounced in the ubiquitous tropical marine species, Lyngbya majuscula. The gene clusters responsible for the production of some of the secondary metabolites have recently been elucidated. The clinoflagellates, which are lower eukaryotic algae, also demonstrate chemical diversity and produce unique polycyclic ethers of polyketide origin. A new mechanism for the formation of the truncated polyketide backbones has recently been proposed. The toxicogenicity of clinoflagellates of the genus Pfiesteria has been the focus of controversy - are they 'killer organisms', as alleged? A recent investigation of Pfiesteria genes seems to rule out the presence of polyketide synthase, which is the gene responsible for the production of most dinoflagellate toxins.
The permeability of the peritrophic membranes of some crustaceans was investigated by using dextran fractions unlabelled or labelled with the fluorescent dye FITC, colloidal gold particles with a diameter of 17 nm coupled with BSA, and unisphere latex particles as markers. The peritrophic membranes of Daphnia magna are permeable to dextrans with a molecular weight up to 2.000 kDa (ESR 31 nm), and to latex beads with a diameter of 130 nm. Latex beads with a diameter of 327 nm did not penetrate. The peritrophic membranes of metanauplii of Artemia salina are fully permeable for latex beads with a diameter of 70 nm, less permeable for those of 130 nm, and completely impermeable for beads with a diameter of 327 nm. Adults have nearly the same effective pore size of the peritrophic membranes as the metanauplii. The peritrophic membranes of Cyclops strenuus were permeable only to latex beads with a diameter of 70 nm. The peritrophic membranes of Gammarus pulex were permeated by latex beads with a diameter of 327 nm, whereas latex beads with a diameter of 542 nm were retained. The results demonstrated that the permeability of the peritrophic membranes of crustaceans is considerably greater than that of Diptera.
Here, we evaluate the extent of sorption of silver nanoparticles (AgNPs) with different primary sizes (30 and 70 nm) and surface properties (branched polyethylene imine, "bPEI" and citrate coating) to laboratory plastic during (eco)toxicological testing. Under conditions of algal growth inhibition assay, up to 97% of the added AgNPs were sorbed onto the test vessels whereas under conditions of in vitro toxicological assay with mammalian cells, the maximum loss of AgNPs was 15%. We propose that the high concentration of proteins and biomolecules in the in vitro toxicological assay originating from serum-containing cell culture medium prevented NP sorption due to steric stabilisation. The sorption of AgNPs to test vessels was clearly concentration dependent. In the conditions of algal growth inhibition assay at 10 ng AgNPs/mL, up to 97% of AgNPs were lost from the test while at higher concentrations (1000 ng AgNPs/mL), the loss of AgNPs was remarkably smaller, up to 64%. Sorption of positively charged bPEI-coated AgNPs was more extensive than the sorption of negatively charged citrate-coated AgNPs and, when calculated on a mass basis, more 70 nm-sized Ag than 30 nm Ag sorbed to plastic surfaces. In summary, this study demonstrates that the loss of AgNPs during (eco)toxicological tests due to sorption on test vessel surfaces is significant, especially in diluted media (e.g. in algal growth medium) and at low NP concentrations. Thus, to ensure the accurate interpretation of (eco)toxicological results, the loss of AgNPs due to adsorption to test vessels should not be overlooked and considered for each specific case.
This PhD thesis focuses on the investigation of iron oxide nanoparticles (IONP). Due to the increasing application of iron nanomaterials (NM) in environmental remediation of contaminated sites, tons of these NM will consequently be released to the environment with unknown risks to biota. For assessing effects of IONP, Daphnia magna was used since there are several standardized test protocols available. Due to its sensitivity against most pollutants and its filter-feeding way of life Daphnia is a preferred organism for testing NM in aquatic ecotoxicology. The presented studies show the influence of coating materials and colloidal properties on the effects of IONP on Daphnia in acute and chronic tests. In a further study, the use of IONP for remediation applications and the risk/benefit for the environment from this technique was studied in combinatory exposure acute tests. Furthermore, the Daphnia acute test was critically revised and possible miniaturizations and prolongations are shown.
Due to the unique antibacterial activities, silver nanoparticles (AgNPs) have been extensively used in commercial products. Anthropogenic activities have released considerable AgNPs as well as highly toxic silver ion (Ag+) into the aquatic environment. Our recent study revealed that ubiquitous natural organic matter (NOM) could reduce Ag+ to AgNP under natural sunlight. However, the toxic effect of this process is not well understood. In this work, we prepared mixture solution of Ag+ and AgNPs with varied Ag+% through the sunlight-driven reduction of Ag+ by NOM and investigated the acute toxicity of the solutions on Daphnia magna. Formation of AgNPs was demonstrated and characterized by comprehensive techniques and the fraction of unconverted Ag+ was determined by ultrafiltration-inductively coupled plasma mass spectrometry determination. The formation of AgNPs enhanced significantly with the increasing of solution pH and cumulative photosynthetically active radiation of sunlight. The toxicity of the resulting solution was further investigated by using freshwater crustacean D. magna as a model and an 8 hr-median lethal concentration (LC50) demonstrated that the reduction of Ag+ by NOM to AgNPs significantly mitigated the acute toxicity of silver. These results highlight the importance of sunlight and NOM in the fate, transformation and toxicity of Ag+ and AgNPs, and further indicate that the acute toxicity of AgNPs should be mainly ascribed to the dissolved Ag+ from AgNPs.
Various factors have been invoked to explain the toxicity of silver nanoparticles (AgNP) to microorganisms including particle size, the nature of stabilizing coatings as well as the amount of dissolved silver occurring in AgNP suspensions. In this study we have assessed the effects of nine differently coated AgNP (chitosan, lactate, polyvinyl pyrrolidone, polyetheleneglycol, gelatin, sodium-dodecyl-benzenesulfonate, citrate, dexpanthenol and carbonate) and AgNO3 on the photosynthesis of the freshwater algae Chlamydomonas reinhardtii. We have thus examined how AgNP effects to algae relate to particle size, measured dissolved silver (Agd) and bioavailable silver (Agbioav). Agbioav was indirectly estimated in toxicity experiments by cysteine-silver complexation at the EC50. The EC50 calculated as a function of measured Agd concentrations showed for some coatings similar values to that of dissolved Ag, while other coated AgNP displayed lower EC50. In all cases, excess cysteine completely prevented effects on photosynthetic yield, confirming the role of Agd as a cause of the observed effect on the photosynthesis. Toxicity was neither related to particle size nor to the coatings. For all differently coated AgNP suspensions, the EC50 values calculated as a function of Agbioav were comparable to the value of AgNO3. Depending on the coatings Agbioav was comparable or higher than measured Agd.
Engineered nanomaterials (ENMs) are a relatively new strain of materials for which little is understood about their impacts. A species sensitivity distribution (SSDs) is a cumulative probability distribution of a chemical's toxicity measurements obtained from single-species bioassays of various species that can be used to estimate the ecotoxicological impacts of a chemical. The recent increase in the availability of acute toxicity data for ENMs enabled the construction of 10 ENM-specific SSDs, with which we analyzed (1) the range of toxic concentrations, (2) whether ENMs cause greater hazard to an ecosystem than the ionic or bulk form, and (3) the key parameters that affect variability in toxicity. The resulting estimates for hazardous concentrations at which 5% of species will be harmed ranged from < 1 ug/L for PVP-coated n-Ag to >3.5 mg/L for CNTs. The results indicated that size, formulation, and the presence of a coating can alter toxicity, and thereby corresponding SSDs. Few statistical differences were observed between SSDs of an ENM and its ionic counterpart. However, we did find a significant correlation between the solubility of ENMs and corresponding SSD. Uncertainty in SSD values can be reduced through greater consideration of ENM characteristics and physiochemical transformations in the environment.
Concern has been raised regarding the current and future release of engineered nanomaterials into aquatic environments from industry and other sources. However, not all nanomaterials may cause an environmental impact and identifying which nanomaterials may be of greatest concern has been difficult. It is thought that the surface groups of a functionalized nanoparticles (NPs) may play a significant role in determining their interactions with aquatic organisms, but the way in which surface properties of NPs impact their toxicity in whole organisms has been minimally explored. A major point of interaction of NPs with aquatic organisms is in the gastrointestinal tract as they ingest particulates from the water column or from the sediment. The main goal of this study was to use model gold NP (AuNPs) to evaluate the potential effects of the different surfaces groups on NPs on the gut of an aquatic model organism, Daphnia magna. In this study, we exposed daphnids to a range of AuNPs concentrations and assessed the impact of AuNP exposure in the daphnid gut by measuring reactive oxygen species (ROS) production and expression of genes associated with oxidative stress and general cellular stress: glutathione S-transferase (gst), catalase (cat), heat shock protein 70 (hsp70), and metallothionein1 (mt1). We found ROS formation and gene expression were impacted by both charge and the specific surface ligand used. We detected some degree of ROS production in all NP exposures, but positively charged AuNPs induced a greater ROS response. Similarly, we observed that, compared to controls, both positively charged AuNPs and only one negatively AuNP impacted expression of genes associated with cellular stress. Finally, ligand-AuNP exposures showed a different toxicity and gene expression profile than the ligand alone, indicating a NP specific effect.
Copyright © 2015 Elsevier B.V. All rights reserved.
Despite substantial information on the acute toxicity of silver nanoparticles (AgNP) to aquatic organisms,little is known about their potential chronic effects and the applicability of current test guidelines fortesting nanomaterials. The purpose of this study was to study the influence of food availability on toxicity.This was done through a series of Daphnia magna 21-day reproduction tests (OECD 211) using 30 nm citricacid stabilized AgNP aimed at studying the influence of food abundance on the reproductive toxicity ofAgNP in D. magna. The experiments were carried out as static renewal tests with exposure concentrationsfrom 10 to 50 µg Ag/L, and test animals were fed green algae Pseudokirchneriella subcapitata in low andhigh food treatments. The endpoints recorded were survival, growth of parent animals and number oflive neonates produced. Detrimental effects of AgNP on survival, growth and reproduction were observedin concentrations higher than 10 µg Ag/L, whereas the animals exposed to 10 µg Ag/L had larger bodylength and produced more offspring than controls at both food treatments. High food treatment resultedin higher animal survival, growth and reproduction compared to result found for low food treatment.
Food dependence in growth, development, reproduction and survivorship are important components in modelling the interaction between an organism and its food supply, and may help to explain demographic patterns observed in laboratory and field populations. In the field, the freshwater zooplankter Daphnia appears to live for extended periods at very low food levels. While Daphnia is one of the most well-studied organisms, there are few data on the performance of individuals receiving food supplies that resemble field levels. We present results from experiments on a single clone of D. pulex Leydig that illustrate the food dependence in growth, development, reproduction, and survivorship. These results show that allocation among competing processes of reproduction and growth can be modified by the pattern of food supply and that food dependence in maturation delays provide support for the hypothesis that cycles in the abundance of Daphnia field populations are `single-generation' cycles.
In this study, we investigated the influence of pH and ionic strength on the deposition of silver nanoparticles (AgNPs) on cellulous acetate microfiltration membranes. Results indicated that flux and total silver concentration in the permeate increased with increasing pH. AgNPs and membrane zeta potential measurements suggest the increased flux and particle breakthrough with increasing pH were a result of more repulsive particle-particle and particle-membrane interactions. The greater repulsive interactions under these conditions resulted in less AgNP deposition, greater particle breakthrough, and higher water flux. Increasing ionic strength, on the other hand, increased deposition and reduced total silver in the permeate, at least at pH 4. This lower silver concentration observed in the permeate presumably was a result of the screening of repulsive electrostatic particle-particle and particle-membrane interactions and the resulting steric exclusion caused by membrane fouling. At higher pH values (7.6 and 10), however, no difference in flux decline was observed at different ionic strengths and significant breakthrough of silver occurred. These results at higher pH values suggest that sodium chloride facilitated the dissolution of AgNPs and the formation of AgCl, AgCl2- and AgCl32- on the particle surface, which enabled soluble silver complexes and AgNPs to penetrate the membrane.
Large quantities of engineered nanoparticles (NP), such as nanosilver (AgNP), have been widely applied, leading to an increased exposure and potential health concerns. Herein, we have examined the ability of AgNP to induce reactive oxygen species (ROS), their role in genotoxic effects and the involvement of mitogen-activated protein kinases (MAPK). AgNP exposure induced ROS production in human epithelial embryonic cells which could be decreased by diphenyleneiodonium (DPI), an inhibitor of NADPH oxidases. Extracellular signal-regulated kinase (ERK) and c-Jun N-terminal kinase (JNK) phosphorylation, induced by AgNP, was an early response but not sustained in time. Furthermore, JNK and ERK activation could be inhibited by both DPI and a free radicals scavenger N-acetyl cysteine. We also investigated the role of MAPK in the DNA damage. Using a modified comet assay for the specific detection of hOGG1 sensitive sites, we showed that AgNP induced DNA oxidation after 30-min treatment, whereas no response was observed after 2h. In conclusion, AgNP seem to induce DNA damage via a mechanism involving ROS formation. The oxidative DNA damage observed was transient, likely due to DNA repair; furthermore, higher damage was achieved upon inhibition of ERK activation by pre-treatment with U0126, suggesting a role for ERK in DNA damage repair. Activation of different MAPK might play an important role in the NP toxicity outcomes; understanding this process may be helpful for the identification of NP toxicity.
© The Author 2014. Published by Oxford University Press on behalf of the UK Environmental Mutagen Society. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.
Silver nanoparticles (AgNP) are increasingly used as antimicrobials in consumer products. Subsequently released into aquatic environments, they are likely to come in contact with microbial communities like periphyton, which plays a key role as a primary producer in stream ecosystems. At present, however, very little is known about the effects of nanoparticles on processes mediated by periphyton communities. We assessed the effects of citrate-coated silver nanoparticles and silver ions (dosed as AgNO3) on five functional endpoints reflecting community and ecosystem-level processes in periphyton: photosynthetic yield, respiration potential, and the activity of three extracellular enzymes. After two hours of exposure in experimental microcosms, AgNP and AgNO3 inhibited respiration and photosynthesis of periphyton and the activities of two of the three extracellular enzymes. Addition of a chelating ligand that complexes free silver ions indicated that, in most cases, toxicity of AgNP suspensions was caused by Ag(I) dissolved from the particles. However, these suspensions inhibited one of the extracellular enzymes (leucine aminopeptidase), pointing to a specific nanoparticle effect independent of the dissolved Ag(I). Thus, our results show that both silver nanoparticles and silver ions have potential to disrupt basic metabolic functions and enzymatic resource acquisition of stream periphyton.
A simple modification of the Rosenzweig-MacArthur predator (zooplankton)-prey (phytoplankton) model with the interference of the predators by adding the effect of nanoparticles is proposed and analyzed. It is assumed that the effect of these particles has a potential to reduce the maximum physiological per-capita growth rate of the prey. The dynamics of nanoparticles is assumed to follow a simple Lotka-Volterra uptake term. Our study suggests that nanoparticle induce growth suppression of phytoplankton population can destabilize the system which leads to limit cycle oscillation. We also observe that if the contact rate of nanoparticles and phytoplankton increases, then the equilibrium densities of phytoplankton as well as zooplankton decrease. Furthermore, we observe that the depletion/removal of nanoparticles from the aquatic system plays a crucial role for the stable coexistence of both populations. Our investigation with various types of functional response suggests that Beddington functional response is the most appropriate representation of the interaction of phytoplankton-nanoparticles in comparison to other widely used functional responses.
Copyright © 2014 Elsevier Ireland Ltd. All rights reserved.
The potential uptake and trophic transfer of nanoparticles (NP) is not well understood so far and for ZnO NP the data presented in peer-reviewed literature is limited. In this paper the influence of surface functionalization on the uptake and depuration behavior of ZnO NP, ZnO-OH NP and ZnO-octyl NP in D. magna was studied. Bulk ZnO particles (≤5 μm) and ZnCl2 were used as references for uptake of particles and dissolved species of Zn, respectively. Furthermore, the trophic transfer of ZnO NP and ZnO-octyl NP from daphnids (Daphnia magna) to zebra fish (Danio rerio) was studied. For ZnO NP and ZnO-octyl NP fast uptakes in D. magna were observed, whereas no measurable uptake took place for ZnO-OH NP. Lower body burden of ZnCl2 was found compared to both ZnO NP and ZnO-octyl. Contrary, the body burden for bulk ZnO was higher than that of ZnO NP but lower than ZnO-octyl. The higher body burdens found for functionalized ZnO-octyl NP than for non-functionalized ZnO NP showed that that the functionalization of the NP has a high influence on the uptake and depuration behavior. Though no mortality was observed, the resulting body burdens were 9.6 times (ZnO NP) and 47 times (ZnO-octyl NP) higher than toxic levels reported for zinc in D. magna. Consequently, the zinc recovered in the animals was not solely due to soluble zinc, but agglomerates/aggregates of ZnO NP or ZnO-octyl NP contributed to the body burdens. The trophic transfer study showed uptake of both ZnO NP and ZnO-octyl NP reaching more than tenfold higher levels than those obtained through aqueous exposure in other studies. This study contributes to expand the available data on uptake behavior of differently functionalized ZnO NP in D. magna and the potential trophic transfer from zooplankton to fish.
Increasing amounts of silver nanoparticles (AgNPs) are expected to enter the aquatic ecosystems where their effects on natural phytoplankton communities are poorly understood. We investigated the effects of AgNPs and its interactions with phosphorus (P) supply on the growth kinetics and stoichiometry of natural phytoplankton. Lake water was dosed with AgNPs (carboxy-functionalized capping agent; ~10-nm particle size; ~20% Ag w/w) at four different concentrations and five P concentrations and incubated in situ for 3 days. A treatment with ionic silver (AgNO3) was used as a positive control. We found that growth rates, calculated from changes in seston carbon and chlorophyll, responded significantly and interactively (p<0.0001) to both AgNPs and P. AgNPs reduced the maximum phytoplankton growth rates by 11-85%. In the positive control, no or very little growth was observed. Inhibition of growth rates after exposure to Ag might be related to the reduction in chlorophyll and the inhibition of C and N acquisition rather than P uptake mechanisms. AgNPs, P supply and their interactions also significantly (p<0.0001) reduced sestonic C:P and N:P ratios and increased C:N, C:Chl and cell-bound Ag stoichiometry. Our results indicate that fate and toxicity of AgNP will vary with phosphorus pollution level in aquatic ecosystems.
Nano–bio interfacial interactions that can likely regulate the potential toxicity of nanoparticles (NPs) toward aquatic organisms are receiving increasing research interest worldwide and warrant more investigation. This review presents an overview of already-known nano–bio interactions and some speculations on the interfaces between NPs and aquatic organisms, in order to gain a new insight into the biological effects of NPs in the aquatic environment. The fundamental interfaces between NPs and organism cells and the main biophysicochemical interactions that occur at the nano–bio interfaces are described. The interfacial interactions, focused on adsorption and internalization, during the contact of NPs with microorganisms, hydrophytes, invertebrates and fish were reviewed. The effects of NP properties and suspending states as well as environmental conditions including pH, ionic strength, natural organic matter and other factors on the interfacial interactions were elucidated. Furthermore, the analytical methods employed in the interfacial interaction investigations were also briefly introduced. Future research directions of nano–bio interactions were prospected.
