Monika Mortimer
National Institute of Chemical Physics and Biophysics
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Featured researches published by Monika Mortimer.
Environmental Pollution | 2010
Irina Blinova; Angela Ivask; Margit Heinlaan; Monika Mortimer; Anne Kahru
The acute toxicity of CuO and ZnO nanoparticles in artificial freshwater (AFW) and in natural waters to crustaceans Daphnia magna and Thamnocephalus platyurus and protozoan Tetrahymena thermophila was compared. The L(E)C(50) values of nanoCuO for both crustaceans in natural water ranged from 90 to 224 mg Cu/l and were about 10-fold lower than L(E)C(50) values of bulk CuO. In all test media, the L(E)C(50) values for both bulk and nanoZnO (1.1-16 mg Zn/l) were considerably lower than those of nanoCuO. The natural waters remarkably (up to 140-fold) decreased the toxicity of nanoCuO (but not that of nanoZnO) to crustaceans depending mainly on the concentration of dissolved organic carbon (DOC). The toxicity of both nanoCuO and nanoZnO was mostly due to the solubilised ions as determined by specific metal-sensing bacteria.
Toxicology | 2010
Monika Mortimer; Kaja Kasemets; Anne Kahru
The toxic effects of nanoparticles (NPs) of ZnO and CuO to particle-ingesting model organism protozoa Tetrahymena thermophila were evaluated. Nano-ZnO was remarkably more toxic than nano-CuO (EC(50) values approximately 5mg metal/l versus 128mg metal/l). Toxic effect of CuO depended on particle size: nano-CuO was about 10-20 times more toxic than bulk CuO. However, when calculated on basis of bioavailable copper (quantified using recombinant Cu-sensor bacteria) the 4-h EC(50) values of nano- and bulk formulations were comparable (2.7 and 1.9mg bioavailable Cu/l, respectively), and statistically different from the EC(50) value of Cu(2+) (1.1mg/l). Differently from CuO particles, bulk and nanosized ZnO as well as Zn(2+) were of similar toxicity (4-h EC(50) values 3.7 and 3.9mg bioavailable Zn/l, respectively, and 4.9mg Zn(2+)/l). Thus, the toxic effect of both, CuO and ZnO (nano)particles to protozoa was caused by their solubilised fraction. The toxic effects of the copper compounds were not dependent on exposure time (4 and 24h), whereas the toxicity of zinc compounds was about 1.5 times lower after 24h of exposure than after 4h, probably due to adaptation. In summary, we recommend T. thermophila as a simple eukaryotic particle-ingesting model organism for the toxicity screening of NPs. For the high throughput testing we suggest to use the 4-h assay on microplates using ATP and/or propidium iodide for the evaluation of cell viability.
Nanotoxicology | 2014
Angela Ivask; Katre Juganson; Olesja Bondarenko; Monika Mortimer; Villem Aruoja; Kaja Kasemets; Irina Blinova; Margit Heinlaan; Vera I. Slaveykova; Anne Kahru
Abstract Silver, ZnO and CuO nanoparticles (NPs) are increasingly used as biocides. There is however increasing evidence of their threat to “non-target” organisms. In such a context, the understanding of the toxicity mechanisms is crucial for both the design of more efficient nano-antimicrobials, i.e. for “toxic by design” and at the same time for the design of nanomaterials that are biologically and/or environmentally benign throughout their life-cycle (safe by design). This review provides a comprehensive and critical literature overview on Ag, ZnO and CuO NPs’ toxicity mechanisms on the basis of various environmentally relevant test species and mammalian cells in vitro. In addition, factors modifying the toxic effect of nanoparticles, e.g. impact of the test media, are discussed. Literature analysis revealed three major phenomena driving the toxicity of these nanoparticles: (i) dissolution of nanoparticles, (ii) organism-dependent cellular uptake of NPs and (iii) induction of oxidative stress and consequent cellular damages. The emerging information on quantitative structure–activity relationship modeling of nanomaterials’ toxic effects and the challenges of extrapolation of laboratory results to the environment are also addressed.
Toxicology in Vitro | 2008
Monika Mortimer; Kaja Kasemets; Margit Heinlaan; Imbi Kurvet; Anne Kahru
Despite of the growing production and use of nanoparticles (NPs) in various applications, current regulations, including EC new chemical policy REACH, fail to address the environmental, health, and safety risks posed by NPs. This paper shows that kinetic Vibrio fischeri luminescence inhibition test--Flash Assay--that up to now was mainly used for toxicity analysis of solid and colored environmental samples (e.g. sediments, soil suspensions), is a powerful tool for screening the toxic properties of NPs. To demonstrate that Flash Assay (initially designed for a tube luminometer) can also be adapted to a microplate format for high throughput toxicity screening of NPs, altogether 11 chemicals were comparatively analyzed. The studied chemicals included bulk and nanosized CuO and ZnO, polyethylenimine (PEI) and polyamidoamine dendrimer generations 2 and 5 (PAMAM G2 and G5). The results showed that EC50 values of 30-min Flash Assay in tube and microplate formats were practically similar and correlated very well (log-logR2=0.98), classifying all analyzed chemicals, except nano CuO (that was more toxic in cuvette format), analogously when compared to the risk phrases of the EC Directive 93/67/EEC for ranking toxicity of chemicals for aquatic organisms. The 30-min EC50 values of nanoscale organic cationic polymers (PEI and dendrimers) ranged from 215 to 775 mg/l. Thirty-minute EC50 values of metal oxides varied largely, ranging from approximately 4 mg/l (bulk and nano ZnO) to approximately 100 mg/l (nano CuO) and approximately 4000 mg/l (bulk CuO). Thus, considering an excellent correlation between both formats, 96-well microplate Flash Assay can be successfully used for high throughput evaluation of harmful properties of chemicals (including organic and inorganic NPs) to bacteria.
Environmental Science & Technology | 2012
Pengyu Chen; Brian A. Powell; Monika Mortimer; Pu Chun Ke
The effects of ZnO nanoparticles (NPs) interacting with single-celled green algae, Chlorella sp., have been found to be bilateral. Specifically, our electron microscopy, plant cell, and fluorescence assays showed that the adsorption and aggregation of ZnO NPs compromised algal cell morphology, viability, and membrane integrity, resulting from zinc ion dissolution as well as possible mechanical cell damage induced by the NPs. Conversely, algal cells displayed a remarkable capability of self-protection by minimizing their surface area through aggregation mediated by the oppositely charged metal ions and suppressing zinc ion release from the NPs through exudation, as evidenced by inductively coupled plasma mass spectrometry, zeta potential, and attenuated total reflectance-Fourier transform infrared spectroscopy. This study illustrates the adaptive nature and complexity in potential ecological response to discharged nanomaterials.
Environmental Science & Technology | 2011
Monika Mortimer; Kaja Kasemets; Maša Vodovnik; Romana Marinšek-Logar; Anne Kahru
In the current study, the toxicity mechanism of nanosized CuO (nCuO) to the freshwater ciliated protozoa Tetrahymena thermophila was studied. Changes in fatty acid profile, lipid peroxidation metabolites and reactive oxygen species (ROS) were measured. Bulk CuO and CuSO(4) served as controls for size and solubility and 3,5-dichorophenol (3,5-DCP) as a control for a chemical known to directly affect the membrane composition. Exposure to all copper compounds induced the generation of ROS, whereas nCuO was most potent. The latter effect was not solely explained by solubilized Cu-ions and was apparently particle-related. 24 h exposure of protozoa to 80 mg/L of nCuO (EC50) significantly decreased the proportion of two major unsaturated fatty acids (UFA) (C18:3 cis-6,9,12, C18:2 cis-9,12), while it increased the relative amount of two saturated fatty acids (SFA) (C18:0, C16:0). Analogous effect was not observed when protozoa were exposed to equitoxic suspensions of bulk CuO, Cu-ions or 3,5-DCP. As changes in the UFA:SFA upon exposure of protozoa to nCuO were not detected at 2 h exposure and no simultaneous dose- or time-dependent lipid peroxidation occurred, it is likely that one of the adaptation mechanisms of protozoa to nCuO was lowering membrane fluidity by the inhibition of de novo synthesis of fatty acid desaturases. This is the first study of the effects of nanoparticles on the membrane fatty acid composition.
Beilstein Journal of Nanotechnology | 2015
Katre Juganson; Angela Ivask; Irina Blinova; Monika Mortimer; Anne Kahru
Summary The increasing production and use of engineered nanomaterials (ENMs) inevitably results in their higher concentrations in the environment. This may lead to undesirable environmental effects and thus warrants risk assessment. The ecotoxicity testing of a wide variety of ENMs rapidly evolving in the market is costly but also ethically questionable when bioassays with vertebrates are conducted. Therefore, alternative methods, e.g., models for predicting toxicity mechanisms of ENMs based on their physico-chemical properties (e.g., quantitative (nano)structure-activity relationships, QSARs/QNARs), should be developed. While the development of such models relies on good-quality experimental toxicity data, most of the available data in the literature even for the same test species are highly variable. In order to map and analyse the state of the art of the existing nanoecotoxicological information suitable for QNARs, we created a database NanoE-Tox that is available as Supporting Information File 1. The database is based on existing literature on ecotoxicology of eight ENMs with different chemical composition: carbon nanotubes (CNTs), fullerenes, silver (Ag), titanium dioxide (TiO2), zinc oxide (ZnO), cerium dioxide (CeO2), copper oxide (CuO), and iron oxide (FeOx; Fe2O3, Fe3O4). Altogether, NanoE-Tox database consolidates data from 224 articles and lists altogether 1,518 toxicity values (EC50/LC50/NOEC) with corresponding test conditions and physico-chemical parameters of the ENMs as well as reported toxicity mechanisms and uptake of ENMs in the organisms. 35% of the data in NanoE-Tox concerns ecotoxicity of Ag NPs, followed by TiO2 (22%), CeO2 (13%), and ZnO (10%). Most of the data originates from studies with crustaceans (26%), bacteria (17%), fish (13%), and algae (11%). Based on the median toxicity values of the most sensitive organism (data derived from three or more articles) the toxicity order was as follows: Ag > ZnO > CuO > CeO2 > CNTs > TiO2 > FeOx. We believe NanoE-Tox database contains valuable information for ENM environmental hazard estimation and development of models for predicting toxic potential of ENMs.
Environmental Science & Technology | 2014
Monika Mortimer; Alexander Gogos; Nora Bartolomé; Anne Kahru; Thomas D. Bucheli; Vera I. Slaveykova
Hyperspectral imaging with enhanced darkfield microscopy (HSI-M) possesses unique advantages in its simplicity and non-invasiveness. In consideration of the urgent need for profound knowledge on the behavior and effects of engineered nanoparticles (NPs), here, we determined the capability of HSI-M for examining cellular uptake of different metal-based NPs, including nanosized metals (silver and gold, both citrate stabilized), metal oxides (copper oxide and titanium dioxide), and CdSe/ZnS core/shell quantum dots at subtoxic concentrations. Specifically, we demonstrated that HSI-M can be used to detect and semi-quantify these NPs in the ciliated protozoan Tetrahymena thermophila as a model aquatic organism. Detection and semi-quantification were achieved on the basis of spectral libraries for the NPs suspended in extracellular substances secreted by this single-celled organism, accounting for matrix effects. HSI-M was able to differentiate between NP types, provided that spectral profiles were significantly different from each other. This difference, in turn, depended upon NP type, size, agglomeration status, and position relative to the focal plane. As an exception among the NPs analyzed in this study, titanium dioxide NPs showed spectral similarities compared to cell material of unexposed control cells, leading to false positives. High biological variability resulted in highly variable uptake of NPs in cells of the same sample as well as between different exposures. We therefore encourage the development of techniques able to reduce the currently long analysis times that still hamper the acquisition of statistically strong data sets. Overall, this study demonstrates the potential and challenges of HSI-M in monitoring cellular uptake of synthetic NPs.
Environmental science. Nano | 2015
Villem Aruoja; Suman Pokhrel; Mariliis Sihtmäe; Monika Mortimer; Lutz Mädler; Anne Kahru
The use of metal-based nanoparticles (NPs) is increasing which leads to their release in water bodies via various waste streams, and thus warrants risk assessment. Consistent biological-effect data of NPs for environmentally relevant test species, which are accompanied by thorough characterization of NPs, are scarce but indispensable for understanding the possible risks of NPs. We composed and tested a library of 12 metal-based nanoparticles (Al2O3, Co3O4, CuO, Fe3O4, MgO, Mn3O4, Sb2O3, SiO2, ZnO, TiO2, WO3 and Pd) using the alga Pseudokirchneriella subcapitata, three bacterial species (Vibrio fischeri, Escherichia coli, Staphylococcus aureus) and the protozoa Tetrahymena thermophila. The NPs were characterized for their physico-chemical properties, solubility and abiotic reactive oxygen species (ROS) production. Also, respective soluble salts were analysed for toxic effects. The algal growth inhibition assay has proven to be the most sensitive and yielded EC50 values for 10 NPs ranging from 0.1 to 58 mg l−1. Algal toxicity correlated with abiotic ROS production of NPs, and the majority of the NPs formed agglomerates that entrapped algal cells. Despite the different sensitivities, there was a common trend in the toxicity of the NPs across different species and test formats: CuO and ZnO had the highest toxicity (EC50 values below 1 mg l−1) among all organism groups except for the protozoa. The high toxicity was mostly due to the shedding of toxic concentrations of Zn and Cu ions; for most of the test species, Al2O3, SiO2, WO3 and Sb2O3 were not toxic below 100 mg l−1 and MgO showed no adverse effects below 100 mg l−1 to any test species in any test setting.
Journal of Photochemistry and Photobiology B-biology | 2015
Urmas Joost; Katre Juganson; Meeri Visnapuu; Monika Mortimer; Anne Kahru; Ergo Nõmmiste; Urmeli Joost; Vambola Kisand; Angela Ivask
Titanium dioxide is a photocatalyst with well-known ability to oxidise a wide range of organic contaminants as well as to destroy microbial cells. In the present work TiO2 nanoparticles with high specific surface area (150m(2)/g) were used to prepare nanostructured films. The TiO2 nanoparticle-based film in combination with UV-A illumination with intensity (22W/m(2)) comparable to that of the sunlight in the UV-A region was used to demonstrate light-induced antibacterial effects. Fast and effective inactivation of Escherichia coli cells on the prepared thin films was observed. Visualization of bacterial cells under scanning electron microscopy (SEM) showed enlargement of the cells, distortion of cellular membrane and possible leakage of cytoplasm after 10min of exposure to photoactivated TiO2. According to the plate counts there were no viable cells as early as after 20min of exposure to UV-A activated TiO2. In parallel to effects on bacterial cell viability and morphology, changes in saturated and unsaturated fatty acids - important components of bacterial cell membrane-were studied. Fast decomposition of saturated fatty acids and changes in chemical structure of unsaturated fatty acids were detected. Thus, we suggest that peroxidation and decomposition of membrane fatty acids could be one of the factors contributing to the morphological changes of bacteria observed under SEM, and ultimately, cell death.