Department Environmental Toxicology

Interactions of nanoparticles with algae

The present projects aim at gathering scientific information on the environmental fate and effects of silver- and cerium oxide nanoparticles. AgNP belong to the most important materials incorporated in consumer products and used because of their toxicity to microorganisms. Cerium oxide is industrially exploited because of its catalytic properties also as diesel fuel additive.

In the MeNanoqa project (SNSF, NRP 64) we are examining interactions between the algae Euglena gracilis and citrate coated AgNP. Toxicity experiments with AgNP show a concentration dependent inhibition of algal photosynthesis and effects on cell morphology. However, AgNP toxicity is not detectable in presence of the strong silver ligand cysteine, indicating Ag+  ions as major contributors to AgNP toxicity. Uptake experiments with AgNP indicated silver being associated with E. gracilis cells. Analysis of cells by TOF SIMS showed AgNP to be adsorbed onto the algal surface, suggesting that particles are not internalized in algae cells (PhD thesis X. Li; Li et al. 2015).

In case of CeO2NP, long-term exposures of C. reinhardtii did not evidence any toxicity to photosynthesis, growth or cellular ATP content. Slight toxicity of these particles was detected when phosphate was omitted from exposure media which was shown to be caused by Ce3+ ions present in particles suspensions. There was no evidence that the CeO2NP are internalized in algae cells (PhD thesis L. Röhder).

The NanoMILE project (Engineered nanomaterials mechanisms of interaction with living systems and the environment: a universal framework for safe nanotechnology, http://www.nanomile.eu-vri.eu) aims to investigate the mechanism of interaction and the effects of the same nanoparticles on a selected range of target organisms, which represent a variety of wildlife taxa. The nanoparticles used in the NanoMILE project are selected according to their industrial relevance and include zinc oxide, silver, cerium oxide, iron oxides, titanium oxide, gold, graphene and carbon based nanoparticles. As a partner in NanoMILE project, Dr. Smitha Pillai at Utox intend to obtain a mechanistic and systematic understanding of the toxicity of manufactured nanomaterials in the alga Chlamydomonas reinhardtii at the molecular and physiological level. The toxic effects observed, at several physiological endpoints, in C. reinhardtii on exposure to metal nanoparticles are due the dissolved metals. Moreover, the effects co-relate to the bioaccumulated metal in C. reinhardtii. A systems biology approach which elucidates the response at the transcriptome, proteome and metabolite levels will provide a mechanistic insight into the toxicity in and response of C. reinhardtii (Dr. S. Pillai, A. Tierbach).

Contact

Prof. Dr. Kristin Schirmer Head of department Tel. +41 58 765 5266 Send Mail

Publications

Silver nanoparticle toxicity and association with the alga Euglena gracilis

The impact of silver nanoparticles (AgNPs) on aquatic algae has largely been studied with model species that possess a rigid cell wall. Here, we explored the interactions of AgNPs with Euglena gracilis, a green alga having no cell wall but a pellicle. The toxicity and silver uptake upon 1–2 h of exposure to various concentrations of AgNO3 and AgNPs, having a mean size of 47 nm measured in the exposure medium, were examined. The photosynthetic yield decreased in a concentration-dependent manner and AgNPs were less toxic than AgNO3 based on the total silver added. The cell morphology was significantly altered by AgNPs and AgNO3. The damaging effects of AgNPs on the photosynthesis and morphology were completely prevented by cysteine, suggesting that the toxicity of AgNPs was mediated by dissolved Ag. Indeed, the maximal quantity of cell-associated silver was higher upon exposure to AgNPs compared to that upon AgNO3 exposure, amounting to 5.1 × 10−4 mol Lcell−1 and 1.4 × 10−4 mol Lcell−1 for AgNPs and AgNO3, respectively. However, the difference was not caused by the cellular uptake of AgNPs, but by the strong sorption of AgNPs onto the pellicle.
Li, X.; Schirmer, K.; Bernard, L.; Sigg, L.; Pillai, S.; Behra, R. (2015) Silver nanoparticle toxicity and association with the alga Euglena gracilis, Environmental Science: Nano, 2(6), 594-602, doi:10.1039/c5en00093a, Institutional Repository

Effect of ozone treatment on nano-sized silver sulfide in wastewater effluent

Silver nanoparticles used in consumer products are likely to be released into municipal wastewater. Transformation reactions, most importantly sulfidation, lead to the formation of nanoscale silver sulfide (nano-Ag2S) particles. In wastewater treatment plants (WWTP), ozonation can enhance the effluent quality by eliminating organic micropollutants. The effect of ozonation on the fate of nano-Ag2S, however, is currently unknown. In this study, we investigate the interaction of ozone with nano-Ag2S and evaluate the effect of ozonation on the short-term toxicity of WWTP effluent spiked with nano-Ag2S. The oxidation of nano-Ag2S by ozone resulted in a stoichiometric factor (number of moles of ozone required to oxidize one mole of sulfide to sulfate) of 2.91, which is comparable to the results obtained for the reaction of bisulfide (HS–) with ozone. The second-order rate constant for the reaction of nano-Ag2S with ozone (k = 3.1 × 104 M–1 s–1) is comparable to the rate constant of fast-reacting micropollutants. Analysis of the ozonation products of nano-Ag2S by transmission electron microscopy (TEM) and X-ray absorption spectroscopy (XAS) revealed that ozonation dominantly led to the formation of silver chloride in WWTP effluent. After ozonation of the Ag2S-spiked effluent, the short-term toxicity for the green algae Chlamydomonas reinhardtii increased and reached EC50 values comparable to Ag+. This study thus reveals that ozone treatment of WWTP effluent results in the oxidation of Ag2S and, hence, an increase of the Ag toxicity in the effluent, which may become relevant at elevated Ag concentrations.
Thalmann, B.; Voegelin, A.; von Gunten, U.; Behra, R.; Morgenroth, E.; Kaegi, R. (2015) Effect of ozone treatment on nano-sized silver sulfide in wastewater effluent, Environmental Science and Technology, 49(18), 10911-10919, doi:10.1021/acs.est.5b02194, Institutional Repository

Colloidal stability and toxicity of gold nanoparticles and gold chloride on Chlamydomonas reinhardtii

Here we have examined interactions of gold nanoparticles differing in primary particle size and coating with the green algae Chlamydomonas reinhardtii as function of the colloidal stability of the particles in the experimental media used for toxicity studies. Interactions of dissolved Au3+ ions with algae were also examined. Included endpoints were photosynthetic yield and algal growth. Morphological and structural effects were examined microscopically and by flow cytometry. The results indicate no significant toxicity of gold nanoparticles to C. reinhardtii. Analysis of published data suggests toxicity of gold nanoparticles on algal growth to relate rather to particular coatings than to the gold core.
Behra, R.; Wagner, B.; Sgier, L.; Kistler, D. (2015) Colloidal stability and toxicity of gold nanoparticles and gold chloride on Chlamydomonas reinhardtii, Aquatic Geochemistry, 21(2), 331-342, doi:10.1007/s10498-015-9255-1, Institutional Repository

Influence of agglomeration of cerium oxide nanoparticles and speciation of cerium(III) on short term effects to the green algae Chlamydomonas reinhardtii

Cerium oxide nanoparticles (CeO2 NP) are increasingly used in industrial applications and may be released to the aquatic environment.
The fate of CeO2 NP and effects on algae are largely unknown. In this study, the short term effects of CeO2 NP in two different agglomeration states on the green algae Chlamydomonas reinhardtii were examined. The role of dissolved cerium(III) on toxicity, its speciation and the dissolution of CeO2 NP were considered. The role of cell wall of C. reinhardtii as a barrier and its influence on the sensitivity to CeO2 NP and cerium(III) was evaluated by testing both, the wild type and the cell wall free mutant of C. reinhardtii.
Characterization showed that CeO2 NP had a surface charge of ∼0 mV at physiological pH and agglomerated in exposure media. Phosphate stabilized CeO2 NP at pH 7.5 over 24 h. This effect was exploited to test CeO2 NP dispersed in phosphate with a mean size of 140 nm and agglomerated in absence of phosphate with a mean size of 2000 nm. The level of dissolved cerium(III) in CeO2 NP suspensions was very low and between 0.1 and 27 nM in all tested media.
Exposure of C. reinhardtii to Ce(NO3)3 decreased the photosynthetic yield in a concentration dependent manner with EC50 of 7.5 ± 0.84 μM for wild type and EC50 of 6.3 ± 0.53 μM for the cell wall free mutant. The intracellular level of reactive oxygen species (ROS) increased upon exposure to Ce(NO3)3 with effective concentrations similar to those inhibiting photosynthesis. The agglomerated CeO2 NP caused a slight decrease of photosynthetic yield at the highest concentrations (100 μM), while no effect was observed for dispersed CeO2 NP. The low toxicity of agglomerated CeO2 NP was attributed quantitatively to Ce3+ ions co-occurring in the nanoparticle suspension whereas for dispersed CeO2 NP, dissolved Ce3+ was precipitated with phosphate and not bioavailable. Furthermore CeO2 NP did not affect the intracellular ROS level. The cell wall free mutant and wild type of C. reinhardtii showed the same sensitivity to CeO2 NP and Ce(NO3)3, indicating a minor role of the cell wall on toxicity. For both algae strains, a flocculation of cells was observed upon exposure to agglomerated CeO2 NP and Ce(NO3)3, only algae exposed to agglomerated CeO2 NP were tightly packed in exopolymeric substances.
Röhder, L. A.; Brandt, T.; Sigg, L.; Behra, R. (2014) Influence of agglomeration of cerium oxide nanoparticles and speciation of cerium(III) on short term effects to the green algae Chlamydomonas reinhardtii, Aquatic Toxicology, 152, 121-130, doi:10.1016/j.aquatox.2014.03.027, Institutional Repository

Bioavailability of silver nanoparticles and ions: from a chemical and biochemical perspective

Owing to their antimicrobial properties, silver nanoparticles (NPs) are the most commonly used engineered nanomaterial for use in a wide array of consumer and medical applications. Many discussions are currently ongoing as to whether or not exposure of silver NPs to the ecosystem (i.e. plants and animals) may be conceived as harmful or not. Metallic silver, if released into the environment, can undergo chemical and biochemical conversion which strongly influence its availability towards any biological system. During this process, in the presence of moisture, silver can be oxidized resulting in the release of silver ions. To date, it is still debatable as to whether any biological impact of nanosized silver is relative to either its size, or to its ionic constitution. The aim of this review therefore is to provide a comprehensive, interdisciplinary overview—for biologists, chemists, toxicologists as well as physicists—regarding the production of silver NPs, its (as well as in their ionic form) chemical and biochemical behaviours towards/within a multitude of relative and realistic biological environments and also how such interactions may be correlated across a plethora of different biological organisms.
Behra, R.; Sigg, L.; Clift, M. J. D.; Herzog, F.; Minghetti, M.; Johnston, B.; Petri-Fink, A.; Rothen-Rutishauser, B. (2013) Bioavailability of silver nanoparticles and ions: from a chemical and biochemical perspective, Journal of the Royal Society Interface, 10(87), 1-15, doi:10.1098/rsif.2013.0396, Institutional Repository