Evolution; international journal of organic evolution, 2016
We investigated the evolutionary response of an ecologically important freshwater crustacean, Dap... more We investigated the evolutionary response of an ecologically important freshwater crustacean, Daphnia, to a rapidly changing toxin environment. From the 1920s until the 1960s, the use of leaded gasoline caused the aquatic concentration of Pb to increase at least fivefold, presumably exerting rapid selective pressure on organisms for resistance. We predicted that Daphnia from this time of intense pollution would display greater resistance than those hatched from times of lower pollution. This question was addressed directly using the resurrection ecology approach, whereby dormant propagules from focal time periods were hatched and compared. We hatched several Daphnia genotypes from each of two Swiss lakes, during times of higher (1960s /1980s) and lower (2000s) lead stress, and compared their life histories under different laboratory levels of this stressor. Modern Daphnia had significantly reduced fitness, measured as the population growth rate (λ), when exposed to lead, whereas tho...
Nanoecotoxicology strives to understand the processes and mechanisms by which engineered nanopart... more 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 (CeO 2 NP) and titanium dioxide (TiO 2 NP), on aquatic organisms, including algae, biofilms, fish cells and fish embryos.
Nanopartikel tauchen in immer mehr Produkten auf. Damit wächst die Wahrscheinlichkeit, dass sie a... more Nanopartikel tauchen in immer mehr Produkten auf. Damit wächst die Wahrscheinlichkeit, dass sie auch in Gewässer eingetragen werden. Das kann bei der Produktion, Anwendung oder Entsor- gung direkt (z. B. aufgrund von Unfällen) oder über das Abwasser geschehen. Obwohl der Anteil synthetischer Nanopartikel in der Umwelt im Vergleich zu den natürlichen Partikeln bis jetzt noch gering ist (1), gilt es dennoch, die Risiken für die Umwelt abzuschätzen. Dafür braucht es einerseits analytische Systeme zur Quantifizierung und anderseits Informationen zu den Eintrags- wegen, Mengen und zum Verbleib der synthetischen Nanopar- tikel im Gewässer sowie zur Toxizität. Zwar gibt es inzwischen erste Studien, die negative Auswirkungen von Nanopartikeln auf verschiedene Gewässerorganismen beschreiben, insgesamt jedoch fehlt dieses Wissen heute noch weitestgehend. Dass das Spektrum der synthetischen Nanopartikel aufgrund ihrer unter- schiedlichen chemischen, physikalischen und morphologischen Eigenscha...
Phytochelatins are metal-binding polypeptides produced by algae under metal exposure. The aim of ... more Phytochelatins are metal-binding polypeptides produced by algae under metal exposure. The aim of this study was to investigate the effects of metal concentration variations in natural systems on periphyton at the biochemical level by analyzing its intracellular thiol content, in particular phytochelatins. To that purpose, two field campaigns were conducted in a stream subject to an increase of dissolved metal concentrations (particularly Cu and Zn) during rain events, which results in an increase of their accumulation in periphyton. At background metal concentrations, several thiols were detectable in periphyton, namely, glutathione (GSH), gamma-glutamylcysteine (gammaGluCys), phytochelatins (PC2), and some unidentified thiols, U1 and U2. Glutathione and gammaGluCys contents were found to vary independently of the rain, as well as U1 and U2, whereas the phytochelatin content increased during the rain events. To investigate whether Cu or Zn may be responsible for this increase, micro...
Environmental toxicology and chemistry / SETAC, 2005
Phytochelatins are small, intracellular, metal-binding polypeptides produced by algae on exposure... more Phytochelatins are small, intracellular, metal-binding polypeptides produced by algae on exposure to increased metal concentration in their environment. The aim of the present study was to examine the relationship between phytochelatin concentration, bioaccumulated metal, and sensitivity of algal growth on cadmium exposure. For that purpose, intracellular cadmium concentration and thiol (glutathione, gamma-glutamylcysteine [gammaGluCys], and phytochelatins [PCn]) content were determined in the freshwater green alga Scenedesmus vacuolatus exposed to growth-inhibitory and noninhibitory concentrations of free Cd2+ in the range from 10(-14) to 10(-7) M. The algal growth rate was optimal up to a free Cd2+ concentration of 10(-9) M and then decreased by 40% at higher concentrations. The intracellular cadmium content increased sharply from 0.22 to 746 amol/cell over this free Cd2+ range. At the lowest Cd2+ concentration (control), glutathione was the only detectable thiol (127 amol/cell). ...
Carbon nanotubes (CNT) are more and more likely to be present in the environment, where they, wil... more Carbon nanotubes (CNT) are more and more likely to be present in the environment, where they, will associate with organic micropollutants due to strong sorption. The toxic effects of these CNT-micropollutant mixtures on aquatic organisms are poorly characterized. Here, we systematically quantified the effects of the herbicide diuron on the photosynthetic activity of the green alga Chlorella vulgaris in presence of different multiwalled CNT (industrial, purified, pristine, and oxidized) or soot. The presence of carbonaceous nanoparticles reduced the adverse effect of diuron maximally by <78% (industrial CNT) and <34% (soot) at 10.0 mg CNT/L, 5.0 rug soot/L, and diuron concentrations in the range 0.73-2990 mu g/L. However, taking into account the measured dissolved instead of the nominal diuron concentration, the toxic effect of diuron was equal to or stronger in the presence of CNT by a factor of up to S. Sorbed diuron consequently remained partially bioavailable. The most pronounced increase in toxicity occurred after a 24 h exposure of algae and CNT. All results point to locally elevated exposure concentration (LEEC) in the proximity of algal cells associated with CNT as the cause for the increase in diuron toxicity.
Carbon nanotubes (CNT) are strong sorbents for organic micropollutants, but changing environmenta... more Carbon nanotubes (CNT) are strong sorbents for organic micropollutants, but changing environmental conditions may alter the distribution and bioavailability of the sorbed substances. Therefore, we investigated the effect of green algae (Chlorella vulgaris) on sorption of a model pollutant (diuron, synonyms: 3-(3,4-Dichlorophenyl)-1,1-dimethylurea, DCMU) to CNT (multi-walled purified, industrial grade, pristine, and oxidized; reference material: Diesel soot). In absence of algae, diuron sorption to CNT was fast, strong, and nonlinear (Freundlich coefficients: 105.79–106.24 μg/kgCNT·(μg/L)−n and 0.62–0.70 for KF and n, respectively). Adding algae to equilibrated diuron-CNT mixtures led to 15–20% (median) diuron re-dissolution. The relatively high amorphous carbon content slowed down ad-/desorption to/from the high energy sorption sites for both industrial grade CNT and soot. The results suggest that diuron binds readily, but – particularly in presence of algae – partially reversibly to CNT, which is of relevance for environmental exposure and risk assessment.
Transport into sediments of the trace elements Cu, Zn, Pb, Cd, Cr, and Sr by settling particles w... more Transport into sediments of the trace elements Cu, Zn, Pb, Cd, Cr, and Sr by settling particles was investigated in Lake Zurich; the concentrations of these elements in settling particles collected in sediment traps and in the water column were determined at different times of year. Correlations of trace element concentrations with the various main components of the settling particles (biological material, calcium carbonate, manganese and iron oxides, silicate minerals) and examination of seasonal variations both of these concentrations in particles and of particle fluxes to the sediments show that biological material is an important carrier phase (especially for Cu and Zn). Iron and manganese oxides also contribute to trace element transport; calcium carbonate is inefficient as a carrier material.
This study aims to investigate factors leading to agglomeration of citrate coated silver (AgNP-Ci... more This study aims to investigate factors leading to agglomeration of citrate coated silver (AgNP-Cit), polyvinylpyrrolidone coated AgNPPVP and titanium dioxide (TiO2) nanoparticles in surface waters and wastewater. ENPs (1 mg/L) were spiked to unfiltered, filtered, ultrafiltered (&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;10 kDa and &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;1 kDa) samples. Z-average particle sizes were measured after 1 h, 1 day and 1 week. AgNP-PVP was stable in all fractions of the samples and kept their original size around 60 nm over 1 week. Agglomeration of AgNP-Cit and TiO2 was positively correlated with Ca(2+) concentration, but dissolved organic carbon concentrations &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt; 2 mg/L contributed to stabilizing these NP. Moreover, agglomeration of AgNP-Cit in the various organic matter fractions showed that high molecular weight organic compounds such as biopolymers provide stabilization in natural water. A generalized scheme for the agglomeration behavior of AgNP-Cit, AgNP-PVP and TiO2 in natural waters was proposed based on their relation with Ca(2+), Mg(2+) and DOC concentration.
Developments in nanotechnology are leading to a rapid proliferation of new materials that are lik... more Developments in nanotechnology are leading to a rapid proliferation of new materials that are likely to become a source of engineered nanoparticles (ENPs) to the environment, where their possible ecotoxicological impacts remain unknown. The surface properties of ENPs are of essential importance for their aggregation behavior, and thus for their mobility in aquatic and terrestrial systems and for their interactions with algae, plants and, fungi. Interactions of ENPs with natural organic matter have to be considered as well, as those will alter the ENPs aggregation behavior in surface waters or in soils. Cells of plants, algae, and fungi possess cell walls that constitute a primary site for interaction and a barrier for the entrance of ENPs. Mechanisms allowing ENPs to pass through cell walls and membranes are as yet poorly understood. Inside cells, ENPs might directly provoke alterations of membranes and other cell structures and molecules, as well as protective mechanisms. Indirect effects of ENPs depend on their chemical and physical properties and may include physical restraints (clogging effects), solubilization of toxic ENP compounds, or production of reactive oxygen species. Many questions regarding the bioavailability of ENPs, their uptake by algae, plants, and fungi and the toxicity mechanisms remain to be elucidated.
Settling particles in the Lake Zrich were collected at different depths. Water samples and partic... more Settling particles in the Lake Zrich were collected at different depths. Water samples and particles have been analyzed for heavy metals and for organic matter elements. Samples were investigated by transmission electron microscopy, scanning electron microscopy, energy dispersive X ray and X ray. The elemental composition of the settling particles was found to be almost constant. Special remarks are made
The field measurement of dry deposition still represents a difficult task. In our approach, a 1 t... more The field measurement of dry deposition still represents a difficult task. In our approach, a 1 to 2 cm thick layer of water in a petri dish with a diameter of 22 cm, serves as a surrogate surface. The atmospheric constituents taken up by the water can be analyzed chemically by the same procedure as for the wet deposition samples. In contrast to solid surrogate surfaces, water exhibits the following advantageous properties: low and constant surface resistance, high sticking coefficient for aerosols, and predictable sorption behavior for gases. Consequently, the deposition rates measured to the wet surface are generally higher, by up to a factor of 4 for NH4 +, CI-, NO3-and SO42-, than those to a dry surface, but still smaller than the concurrent wet deposition rates. We observed the following average dry deposition rates in txmol m -2 d-l: NH4 + 48.3, Ca 2 § 40.7, Na + 15.8, Mg 2+ 8.4, K + 4.2, H-Aci 36.4; SO42-57.2, C1-39.2, NO 3-34.5, HSO 3-5.7, formate 4.0; acid soluble metals: Fe 2.8, Zn 0.60, Cu 0.11, Pb 0.073, Cd 0.0022. The soluble fraction of Zn, Cd, Cu, Pb and Fe in the dry deposition varied with the pH of the water phase corresponding to the adsorption tendency of these metals to oxide surfaces. The sampling method also allows tracing of regionally and locally emitted atmospheric pollutants. In our study the local pollution sources included road salting, construction work and a refuse incinerator. Finally, chemical reactions occurring in the atmosphere, such as the conversion of CI-to HC1 by HNO 3 or the oxidation of SO2, can be identified by evaluating the data. The method proposed is relevant to measure reproducibly the dry deposition of a variety of compounds to water bodies and moist vegetation.
The free ion activity model (FIAM) has already been confirmed under laboratory conditions for man... more The free ion activity model (FIAM) has already been confirmed under laboratory conditions for many trace metals but has still to be validated under natural conditions where the presence of natural organic ligands influences metal speciation and bioavailability. The goal of this study was to test if the FIAM is followed under natural conditions by measuring copper and zinc speciation as well as metal accumulation in periphyton. Periphyton was exposed in microcosms to natural river water with different added concentrations of copper (25-258 nM) or zinc (18-501 nM) and additions of a synthetic ligand (NTA). Free Cu2+ was in the range of 10(-16.5)-10(-14.5) M and Zn(2+) was in the range of 0.7-8.7 nM, as measured by competitive ligand exchange coupled with cathodic/anodic stripping voltammetry. Other metal complexes were either measured or computed. Bioaccumulation of zinc in periphyton appeared to be controlled by the free zinc ion concentration, confirming the FIAM. In contrast, bioaccumulation of copper was controlled by weakly complexed copper (including Cu2+ plus inorganic and weak organic complexes), which is in disagreement with the FIAM, and appears to be caused by limitation of copper diffusion due to very low free Cu2+ occurring in natural environments.
Although the free ion activity model (FIAM) has been well-established in laboratory studies, ther... more Although the free ion activity model (FIAM) has been well-established in laboratory studies, there remains the need for field data in order to validate the applicability of this model in natural systems. The objective of this study was to investigate the response of copper and zinc accumulation in periphyton to short-term variations in metal concentration and speciation in freshwater. During heavy rain events, dissolved Cu in the Furtbach stream increased from 40 to 118 nM, while dissolved Zn increased from 45 to 147 nM due to the release of metals from contaminated sediments. Increases in free copper and free zinc ions in the water (from 10(-14) to 10(-11.5) M for Cu2+; from 1 to 15 nM for Zn2+) were observed during the onset of heavy rain events. Periphytic algae collected from artificial substrates had an intracellular copper content (0.2-2.8 micromol/g dry weight (dw)) that varied as a function of the exchangeable copper in the water (labile form) rather than the free Cu2+. Intracellular zinc content (1.5-8.0 micromol/g dw) was found to follow the same trend as the free zinc ion concentration. Adsorbed Cu and Zn on periphyton showed a very dynamic response to variations in dissolved metal concentration. Different concentrations of dissolved manganese during the two time periods may affect the accumulation of zinc and copper by competition for metal uptake.
In situ measurements of copper and zinc using diffusive gradients in thin films (DGT) in two dist... more In situ measurements of copper and zinc using diffusive gradients in thin films (DGT) in two distinct natural water systems were compared to metal speciation assessed by competitive ligand exchange (CLE) and voltammetric measurements. In a dynamic river system, where dissolved metal concentrations vary significantly over short-time periods, DGT technique provided averaged values of the metal concentrations over time. In microcosms, at different total dissolved concentrations of copper and zinc, DGT technique measured a similar fraction as measurements of labile metal performed by voltammetry. The proportion of DGT and voltammetric-labile zinc to dissolved zinc was 61±4% and, respectively, 76±9%. DGT technique was measuring 81±8% of exchangeable copper (by exchange with catechol). These two fractions were similarly influenced by the addition of NTA. In the absence of NTA, copper measured by DGT represented 34±4% of dissolved copper whereas in the presence of NTA, this proportion raised to 57±2%. These measurements were compared to calculations performed with speciation programs using several models for the complexation by humic and fulvic substances, namely Model VI (WHAM), NICA-Donnan and SHM. The predicted speciation by these three models was similar. The prediction of free zinc ion and labile zinc concentrations were in agreement with experimental data. Calculated concentrations of free copper ion were overestimated because these models are not considering strong specific copper-binding ligands probably present in natural water.
Accumulation of Pb and induction of phytochelatin synthesis were observed in Chlamydomonas reinha... more Accumulation of Pb and induction of phytochelatin synthesis were observed in Chlamydomonas reinhardtii upon Pb(II) exposure. Our aim was to examine whether Pb(II) is bound by phytochelatins (PCs) in C. reinhardtii and to examine formed complexes for their stoichiometry and composition. Metal-phytochelatin (Me-PC) complexes induced by Pb were isolated by size-exclusion chromatography in 13 collected fractions, which were analyzed for their PC and metal content by high-performance liquid chromatography and inductively coupled plasma mass spectrometry. A recovery of more than 90% of Pb from standard Pb-PC₂ complexes within the total volume of the size-exclusion column indicated the adequacy of the method for Pb-PC(n) complex separation and characterization. Phytochelatins were detected mainly in a molecular weight ranging from 1,000 to 5,300 daltons (Da), indicating the formation of complexes with various stoichiometries. Approximately 72% of total PC₂ eluted in the range from 1,000 to 1,600 Da, and 80% of total PC₃ eluted in the molecular weight range from 1,600 to 2,300 Da. The distribution of Cu, Zn, and Pb showed that more than 70% of these metals were associated with the high-molecular-weight fractions. Copper, zinc, and lead were also observed in PC-containing fractions, suggesting the formation of various Me-PC complexes. The results of the present study indicate that the role of PCs in Pb detoxification is minor, because only 13% of total Pb was associated with PCs.
ABSTRACT The oxidation of SO2 in atmospheric water (cloud, rain, liquid aerosol and fog) is influ... more ABSTRACT The oxidation of SO2 in atmospheric water (cloud, rain, liquid aerosol and fog) is influenced by the presence of NH3. The enhancing effect of NH3 is especially pronounced if the oxidation occurs with an oxidant such as O3 for which the reaction rate increases strongly with increasing pH, because NH3 (i) codetermines the pH of the water and thus in turn the solubility of SO2, and (ii) provides acid neutralizing capacity as well as buffer intensity to the heterogeneous atmosphere-water system in counteracting the acidity produced by the oxidation of SO2. At low buffer intensity, the acidity production leads to the alleviation of further SO2-oxidation. A computer model is used to assess the influence of SO2, NH3 and other potential acids and bases, of aerosols and of the liquid water content on the composition and its temporal variation of closed or open atmospheric systems as a consequence of SO2 oxidation by O3. An essential corollary to this model is a definition of atmospheric alkalinity (or acidity). Model results are compared with field data obtained in measuring the temporal variation in urban/rural fog composition.
Various factors have been invoked to explain the toxicity of silver nanoparticles (AgNP) to micro... more Various factors have been invoked to explain the toxicity of silver nanoparticles (AgNP) to microorganisms including particle size and 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, polyvinylpyrrolidone, polyethelene glycol, gelatin, sodium dodecylbenzenesulfonate, citrate, dexpanthenol, and carbonate) and AgNO3 on the photosynthesis of the freshwater algae Chlamydomonas reinhardtii. We have thus examined how AgNP effects on 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 values similar to that of dissolved Ag, whereas other coated AgNP displayed lower EC50 values. 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 related neither 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 to or higher than measured Agd.
Evolution; international journal of organic evolution, 2016
We investigated the evolutionary response of an ecologically important freshwater crustacean, Dap... more We investigated the evolutionary response of an ecologically important freshwater crustacean, Daphnia, to a rapidly changing toxin environment. From the 1920s until the 1960s, the use of leaded gasoline caused the aquatic concentration of Pb to increase at least fivefold, presumably exerting rapid selective pressure on organisms for resistance. We predicted that Daphnia from this time of intense pollution would display greater resistance than those hatched from times of lower pollution. This question was addressed directly using the resurrection ecology approach, whereby dormant propagules from focal time periods were hatched and compared. We hatched several Daphnia genotypes from each of two Swiss lakes, during times of higher (1960s /1980s) and lower (2000s) lead stress, and compared their life histories under different laboratory levels of this stressor. Modern Daphnia had significantly reduced fitness, measured as the population growth rate (λ), when exposed to lead, whereas tho...
Nanoecotoxicology strives to understand the processes and mechanisms by which engineered nanopart... more 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 (CeO 2 NP) and titanium dioxide (TiO 2 NP), on aquatic organisms, including algae, biofilms, fish cells and fish embryos.
Nanopartikel tauchen in immer mehr Produkten auf. Damit wächst die Wahrscheinlichkeit, dass sie a... more Nanopartikel tauchen in immer mehr Produkten auf. Damit wächst die Wahrscheinlichkeit, dass sie auch in Gewässer eingetragen werden. Das kann bei der Produktion, Anwendung oder Entsor- gung direkt (z. B. aufgrund von Unfällen) oder über das Abwasser geschehen. Obwohl der Anteil synthetischer Nanopartikel in der Umwelt im Vergleich zu den natürlichen Partikeln bis jetzt noch gering ist (1), gilt es dennoch, die Risiken für die Umwelt abzuschätzen. Dafür braucht es einerseits analytische Systeme zur Quantifizierung und anderseits Informationen zu den Eintrags- wegen, Mengen und zum Verbleib der synthetischen Nanopar- tikel im Gewässer sowie zur Toxizität. Zwar gibt es inzwischen erste Studien, die negative Auswirkungen von Nanopartikeln auf verschiedene Gewässerorganismen beschreiben, insgesamt jedoch fehlt dieses Wissen heute noch weitestgehend. Dass das Spektrum der synthetischen Nanopartikel aufgrund ihrer unter- schiedlichen chemischen, physikalischen und morphologischen Eigenscha...
Phytochelatins are metal-binding polypeptides produced by algae under metal exposure. The aim of ... more Phytochelatins are metal-binding polypeptides produced by algae under metal exposure. The aim of this study was to investigate the effects of metal concentration variations in natural systems on periphyton at the biochemical level by analyzing its intracellular thiol content, in particular phytochelatins. To that purpose, two field campaigns were conducted in a stream subject to an increase of dissolved metal concentrations (particularly Cu and Zn) during rain events, which results in an increase of their accumulation in periphyton. At background metal concentrations, several thiols were detectable in periphyton, namely, glutathione (GSH), gamma-glutamylcysteine (gammaGluCys), phytochelatins (PC2), and some unidentified thiols, U1 and U2. Glutathione and gammaGluCys contents were found to vary independently of the rain, as well as U1 and U2, whereas the phytochelatin content increased during the rain events. To investigate whether Cu or Zn may be responsible for this increase, micro...
Environmental toxicology and chemistry / SETAC, 2005
Phytochelatins are small, intracellular, metal-binding polypeptides produced by algae on exposure... more Phytochelatins are small, intracellular, metal-binding polypeptides produced by algae on exposure to increased metal concentration in their environment. The aim of the present study was to examine the relationship between phytochelatin concentration, bioaccumulated metal, and sensitivity of algal growth on cadmium exposure. For that purpose, intracellular cadmium concentration and thiol (glutathione, gamma-glutamylcysteine [gammaGluCys], and phytochelatins [PCn]) content were determined in the freshwater green alga Scenedesmus vacuolatus exposed to growth-inhibitory and noninhibitory concentrations of free Cd2+ in the range from 10(-14) to 10(-7) M. The algal growth rate was optimal up to a free Cd2+ concentration of 10(-9) M and then decreased by 40% at higher concentrations. The intracellular cadmium content increased sharply from 0.22 to 746 amol/cell over this free Cd2+ range. At the lowest Cd2+ concentration (control), glutathione was the only detectable thiol (127 amol/cell). ...
Carbon nanotubes (CNT) are more and more likely to be present in the environment, where they, wil... more Carbon nanotubes (CNT) are more and more likely to be present in the environment, where they, will associate with organic micropollutants due to strong sorption. The toxic effects of these CNT-micropollutant mixtures on aquatic organisms are poorly characterized. Here, we systematically quantified the effects of the herbicide diuron on the photosynthetic activity of the green alga Chlorella vulgaris in presence of different multiwalled CNT (industrial, purified, pristine, and oxidized) or soot. The presence of carbonaceous nanoparticles reduced the adverse effect of diuron maximally by <78% (industrial CNT) and <34% (soot) at 10.0 mg CNT/L, 5.0 rug soot/L, and diuron concentrations in the range 0.73-2990 mu g/L. However, taking into account the measured dissolved instead of the nominal diuron concentration, the toxic effect of diuron was equal to or stronger in the presence of CNT by a factor of up to S. Sorbed diuron consequently remained partially bioavailable. The most pronounced increase in toxicity occurred after a 24 h exposure of algae and CNT. All results point to locally elevated exposure concentration (LEEC) in the proximity of algal cells associated with CNT as the cause for the increase in diuron toxicity.
Carbon nanotubes (CNT) are strong sorbents for organic micropollutants, but changing environmenta... more Carbon nanotubes (CNT) are strong sorbents for organic micropollutants, but changing environmental conditions may alter the distribution and bioavailability of the sorbed substances. Therefore, we investigated the effect of green algae (Chlorella vulgaris) on sorption of a model pollutant (diuron, synonyms: 3-(3,4-Dichlorophenyl)-1,1-dimethylurea, DCMU) to CNT (multi-walled purified, industrial grade, pristine, and oxidized; reference material: Diesel soot). In absence of algae, diuron sorption to CNT was fast, strong, and nonlinear (Freundlich coefficients: 105.79–106.24 μg/kgCNT·(μg/L)−n and 0.62–0.70 for KF and n, respectively). Adding algae to equilibrated diuron-CNT mixtures led to 15–20% (median) diuron re-dissolution. The relatively high amorphous carbon content slowed down ad-/desorption to/from the high energy sorption sites for both industrial grade CNT and soot. The results suggest that diuron binds readily, but – particularly in presence of algae – partially reversibly to CNT, which is of relevance for environmental exposure and risk assessment.
Transport into sediments of the trace elements Cu, Zn, Pb, Cd, Cr, and Sr by settling particles w... more Transport into sediments of the trace elements Cu, Zn, Pb, Cd, Cr, and Sr by settling particles was investigated in Lake Zurich; the concentrations of these elements in settling particles collected in sediment traps and in the water column were determined at different times of year. Correlations of trace element concentrations with the various main components of the settling particles (biological material, calcium carbonate, manganese and iron oxides, silicate minerals) and examination of seasonal variations both of these concentrations in particles and of particle fluxes to the sediments show that biological material is an important carrier phase (especially for Cu and Zn). Iron and manganese oxides also contribute to trace element transport; calcium carbonate is inefficient as a carrier material.
This study aims to investigate factors leading to agglomeration of citrate coated silver (AgNP-Ci... more This study aims to investigate factors leading to agglomeration of citrate coated silver (AgNP-Cit), polyvinylpyrrolidone coated AgNPPVP and titanium dioxide (TiO2) nanoparticles in surface waters and wastewater. ENPs (1 mg/L) were spiked to unfiltered, filtered, ultrafiltered (&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;10 kDa and &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;1 kDa) samples. Z-average particle sizes were measured after 1 h, 1 day and 1 week. AgNP-PVP was stable in all fractions of the samples and kept their original size around 60 nm over 1 week. Agglomeration of AgNP-Cit and TiO2 was positively correlated with Ca(2+) concentration, but dissolved organic carbon concentrations &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt; 2 mg/L contributed to stabilizing these NP. Moreover, agglomeration of AgNP-Cit in the various organic matter fractions showed that high molecular weight organic compounds such as biopolymers provide stabilization in natural water. A generalized scheme for the agglomeration behavior of AgNP-Cit, AgNP-PVP and TiO2 in natural waters was proposed based on their relation with Ca(2+), Mg(2+) and DOC concentration.
Developments in nanotechnology are leading to a rapid proliferation of new materials that are lik... more Developments in nanotechnology are leading to a rapid proliferation of new materials that are likely to become a source of engineered nanoparticles (ENPs) to the environment, where their possible ecotoxicological impacts remain unknown. The surface properties of ENPs are of essential importance for their aggregation behavior, and thus for their mobility in aquatic and terrestrial systems and for their interactions with algae, plants and, fungi. Interactions of ENPs with natural organic matter have to be considered as well, as those will alter the ENPs aggregation behavior in surface waters or in soils. Cells of plants, algae, and fungi possess cell walls that constitute a primary site for interaction and a barrier for the entrance of ENPs. Mechanisms allowing ENPs to pass through cell walls and membranes are as yet poorly understood. Inside cells, ENPs might directly provoke alterations of membranes and other cell structures and molecules, as well as protective mechanisms. Indirect effects of ENPs depend on their chemical and physical properties and may include physical restraints (clogging effects), solubilization of toxic ENP compounds, or production of reactive oxygen species. Many questions regarding the bioavailability of ENPs, their uptake by algae, plants, and fungi and the toxicity mechanisms remain to be elucidated.
Settling particles in the Lake Zrich were collected at different depths. Water samples and partic... more Settling particles in the Lake Zrich were collected at different depths. Water samples and particles have been analyzed for heavy metals and for organic matter elements. Samples were investigated by transmission electron microscopy, scanning electron microscopy, energy dispersive X ray and X ray. The elemental composition of the settling particles was found to be almost constant. Special remarks are made
The field measurement of dry deposition still represents a difficult task. In our approach, a 1 t... more The field measurement of dry deposition still represents a difficult task. In our approach, a 1 to 2 cm thick layer of water in a petri dish with a diameter of 22 cm, serves as a surrogate surface. The atmospheric constituents taken up by the water can be analyzed chemically by the same procedure as for the wet deposition samples. In contrast to solid surrogate surfaces, water exhibits the following advantageous properties: low and constant surface resistance, high sticking coefficient for aerosols, and predictable sorption behavior for gases. Consequently, the deposition rates measured to the wet surface are generally higher, by up to a factor of 4 for NH4 +, CI-, NO3-and SO42-, than those to a dry surface, but still smaller than the concurrent wet deposition rates. We observed the following average dry deposition rates in txmol m -2 d-l: NH4 + 48.3, Ca 2 § 40.7, Na + 15.8, Mg 2+ 8.4, K + 4.2, H-Aci 36.4; SO42-57.2, C1-39.2, NO 3-34.5, HSO 3-5.7, formate 4.0; acid soluble metals: Fe 2.8, Zn 0.60, Cu 0.11, Pb 0.073, Cd 0.0022. The soluble fraction of Zn, Cd, Cu, Pb and Fe in the dry deposition varied with the pH of the water phase corresponding to the adsorption tendency of these metals to oxide surfaces. The sampling method also allows tracing of regionally and locally emitted atmospheric pollutants. In our study the local pollution sources included road salting, construction work and a refuse incinerator. Finally, chemical reactions occurring in the atmosphere, such as the conversion of CI-to HC1 by HNO 3 or the oxidation of SO2, can be identified by evaluating the data. The method proposed is relevant to measure reproducibly the dry deposition of a variety of compounds to water bodies and moist vegetation.
The free ion activity model (FIAM) has already been confirmed under laboratory conditions for man... more The free ion activity model (FIAM) has already been confirmed under laboratory conditions for many trace metals but has still to be validated under natural conditions where the presence of natural organic ligands influences metal speciation and bioavailability. The goal of this study was to test if the FIAM is followed under natural conditions by measuring copper and zinc speciation as well as metal accumulation in periphyton. Periphyton was exposed in microcosms to natural river water with different added concentrations of copper (25-258 nM) or zinc (18-501 nM) and additions of a synthetic ligand (NTA). Free Cu2+ was in the range of 10(-16.5)-10(-14.5) M and Zn(2+) was in the range of 0.7-8.7 nM, as measured by competitive ligand exchange coupled with cathodic/anodic stripping voltammetry. Other metal complexes were either measured or computed. Bioaccumulation of zinc in periphyton appeared to be controlled by the free zinc ion concentration, confirming the FIAM. In contrast, bioaccumulation of copper was controlled by weakly complexed copper (including Cu2+ plus inorganic and weak organic complexes), which is in disagreement with the FIAM, and appears to be caused by limitation of copper diffusion due to very low free Cu2+ occurring in natural environments.
Although the free ion activity model (FIAM) has been well-established in laboratory studies, ther... more Although the free ion activity model (FIAM) has been well-established in laboratory studies, there remains the need for field data in order to validate the applicability of this model in natural systems. The objective of this study was to investigate the response of copper and zinc accumulation in periphyton to short-term variations in metal concentration and speciation in freshwater. During heavy rain events, dissolved Cu in the Furtbach stream increased from 40 to 118 nM, while dissolved Zn increased from 45 to 147 nM due to the release of metals from contaminated sediments. Increases in free copper and free zinc ions in the water (from 10(-14) to 10(-11.5) M for Cu2+; from 1 to 15 nM for Zn2+) were observed during the onset of heavy rain events. Periphytic algae collected from artificial substrates had an intracellular copper content (0.2-2.8 micromol/g dry weight (dw)) that varied as a function of the exchangeable copper in the water (labile form) rather than the free Cu2+. Intracellular zinc content (1.5-8.0 micromol/g dw) was found to follow the same trend as the free zinc ion concentration. Adsorbed Cu and Zn on periphyton showed a very dynamic response to variations in dissolved metal concentration. Different concentrations of dissolved manganese during the two time periods may affect the accumulation of zinc and copper by competition for metal uptake.
In situ measurements of copper and zinc using diffusive gradients in thin films (DGT) in two dist... more In situ measurements of copper and zinc using diffusive gradients in thin films (DGT) in two distinct natural water systems were compared to metal speciation assessed by competitive ligand exchange (CLE) and voltammetric measurements. In a dynamic river system, where dissolved metal concentrations vary significantly over short-time periods, DGT technique provided averaged values of the metal concentrations over time. In microcosms, at different total dissolved concentrations of copper and zinc, DGT technique measured a similar fraction as measurements of labile metal performed by voltammetry. The proportion of DGT and voltammetric-labile zinc to dissolved zinc was 61±4% and, respectively, 76±9%. DGT technique was measuring 81±8% of exchangeable copper (by exchange with catechol). These two fractions were similarly influenced by the addition of NTA. In the absence of NTA, copper measured by DGT represented 34±4% of dissolved copper whereas in the presence of NTA, this proportion raised to 57±2%. These measurements were compared to calculations performed with speciation programs using several models for the complexation by humic and fulvic substances, namely Model VI (WHAM), NICA-Donnan and SHM. The predicted speciation by these three models was similar. The prediction of free zinc ion and labile zinc concentrations were in agreement with experimental data. Calculated concentrations of free copper ion were overestimated because these models are not considering strong specific copper-binding ligands probably present in natural water.
Accumulation of Pb and induction of phytochelatin synthesis were observed in Chlamydomonas reinha... more Accumulation of Pb and induction of phytochelatin synthesis were observed in Chlamydomonas reinhardtii upon Pb(II) exposure. Our aim was to examine whether Pb(II) is bound by phytochelatins (PCs) in C. reinhardtii and to examine formed complexes for their stoichiometry and composition. Metal-phytochelatin (Me-PC) complexes induced by Pb were isolated by size-exclusion chromatography in 13 collected fractions, which were analyzed for their PC and metal content by high-performance liquid chromatography and inductively coupled plasma mass spectrometry. A recovery of more than 90% of Pb from standard Pb-PC₂ complexes within the total volume of the size-exclusion column indicated the adequacy of the method for Pb-PC(n) complex separation and characterization. Phytochelatins were detected mainly in a molecular weight ranging from 1,000 to 5,300 daltons (Da), indicating the formation of complexes with various stoichiometries. Approximately 72% of total PC₂ eluted in the range from 1,000 to 1,600 Da, and 80% of total PC₃ eluted in the molecular weight range from 1,600 to 2,300 Da. The distribution of Cu, Zn, and Pb showed that more than 70% of these metals were associated with the high-molecular-weight fractions. Copper, zinc, and lead were also observed in PC-containing fractions, suggesting the formation of various Me-PC complexes. The results of the present study indicate that the role of PCs in Pb detoxification is minor, because only 13% of total Pb was associated with PCs.
ABSTRACT The oxidation of SO2 in atmospheric water (cloud, rain, liquid aerosol and fog) is influ... more ABSTRACT The oxidation of SO2 in atmospheric water (cloud, rain, liquid aerosol and fog) is influenced by the presence of NH3. The enhancing effect of NH3 is especially pronounced if the oxidation occurs with an oxidant such as O3 for which the reaction rate increases strongly with increasing pH, because NH3 (i) codetermines the pH of the water and thus in turn the solubility of SO2, and (ii) provides acid neutralizing capacity as well as buffer intensity to the heterogeneous atmosphere-water system in counteracting the acidity produced by the oxidation of SO2. At low buffer intensity, the acidity production leads to the alleviation of further SO2-oxidation. A computer model is used to assess the influence of SO2, NH3 and other potential acids and bases, of aerosols and of the liquid water content on the composition and its temporal variation of closed or open atmospheric systems as a consequence of SO2 oxidation by O3. An essential corollary to this model is a definition of atmospheric alkalinity (or acidity). Model results are compared with field data obtained in measuring the temporal variation in urban/rural fog composition.
Various factors have been invoked to explain the toxicity of silver nanoparticles (AgNP) to micro... more Various factors have been invoked to explain the toxicity of silver nanoparticles (AgNP) to microorganisms including particle size and 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, polyvinylpyrrolidone, polyethelene glycol, gelatin, sodium dodecylbenzenesulfonate, citrate, dexpanthenol, and carbonate) and AgNO3 on the photosynthesis of the freshwater algae Chlamydomonas reinhardtii. We have thus examined how AgNP effects on 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 values similar to that of dissolved Ag, whereas other coated AgNP displayed lower EC50 values. 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 related neither 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 to or higher than measured Agd.
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Papers by Laura Sigg