Vacancies
PhD
There are unfortunately no open PhD positions at the moment.
Master thesis topics
- Fate of CeO2 NPs in stream biofilms (periphyton)
Contact: Dr. Alexandra Kroll
CeO2 based nanoparticles (NPs) are used for example as catalytic additive to fuel and to enhance UV stability of wood preservatives. They have become potential environmental contaminants that may be transported in surface waters. CeO2 NPs in the water column may stay dispersed or agglomerate depending on water chemistry and NP properties. Natural biofilms formed by algae, bacteria, and fungi in the benthic zone, known as periphyton, may be exposed to dispersed and sedimenting NPs. Periphyton is an essential element of aquatic ecosystems as main producer of oxygen and biomass.
As of now there are no reports on the visualization and characterization of engineered NPs in periphyton. Both are a challenge due to the small size of the particles, low environmentally relevant concentrations, and the background of natural particles. Available methods are limited regarding sample background, method detection limits, or artifacts generated during sample preparation.
We have explored the possibility of visualizing and characterizing NPs in periphyton using confocal laser scanning microscopy (CLSM) and nanoparticle tracking analysis (NTA). Data analysis by NTA is faster and easier, while CLSM allows the use of different laser lines. This provides additional information on the number of particles reflecting at different wavelengths. In this way we were able to determine the size of silver-based NPs in periphyton samples. In the frame of this project, the methodology is to be refined and extended to CeO2 NPs with different surface properties. Apart from investigating physico-chemical properties of NPs in situ, this project is aimed at tracking the bioaccumulation and distribution of NP in intact biofilms.
Questions:
Are CeO2 NPs accumulated by periphytic organisms or cumulated in the extracellular space?
How do the physico-chemical properties of CeO2 NPs change in in periphyton?
Which parameters influence this process (CeO2 NP surface properties, time, flow rate, light, and temperature)?
Timeframe: earliest start June 2013
- Transformation of silver-based
nanoparticles by organic matter from stream biofilms
Contact: Dr. Alexandra Kroll
Silver-based nanoparticles (Ag NPs) are used in diverse products due to their antibacterial properties. They have become potential environmental contaminants that may be transported in surface waters. Depending on water chemistry and NP properties, Ag NPs may stay dispersed or agglomerate and sediment. Natural biofilms formed by algae, bacteria, and fungi in the benthic zone, known as periphyton, may be exposed to dispersed and sedimenting NPs. Periphyton is an essential element of aquatic ecosystems as main producer of oxygen and biomass. NPs reaching periphyton from the water column will first encounter the extracellular matrix of periphytic organisms made up of extracellular polymeric substances (EPS). This interaction will determine the fate of Ag NPs in periphyton.
Thus, to understand the fate of Ag NPs in streams and periphyton in particular, it is essential to study their interaction with the periphytic EPS.
In previous studies we analyzed the effect of EPS on carbonate coated Ag NPs. Our results showed that light and EPS induced a pH-dependent increase in Ag NP size over time, however, NPs remained stable after several days. Furthermore, we found de novo formation of elemental Ag NPs from silver nitrate in the presence of EPS by photoreduction.
Ag NPs may thus constantly change their size and surface properties due to redox processes.
We want to further investigate these processes with respect to different Ag NP chemistry and surface properties.
Questions:
How do the physico-chemical properties of Ag NPs change in the presence of EPS extracts?
Which parameters influence these processes (Ag NP surface properties, NP concentration, DOC concentration, EPS composition, light intensity, pH, time, temperature)?
Timeframe: earliest start April 2013
- Potential toxic effects of TiO2 nanoparticles on benthic food chains
Contact: Dr Carl Isaacson or Prof Kristin Schirmer
To date most of the aquatic ecotoxicological studies of the environmental effects of TiO2 nanomaterials have focused on pelagic organisms; however, many studies show that when TiO2 nanomaterials enter the environment, they readily aggregate and settle from the water column. This indicates that benthic systems may be more exposed to TiO2 nanoparticles than pelagic organisms. As benthic biofilms are composed of many different types of organisms, including primary producers and predacious organisms, this Masters thesis will focus on the effects of nanoparticles to these two broad groups of test organisms. By using heterotrophic biofilms we aim to determine if nanoparticles can be taken up by heterotrophic biofilms or become trapped in the extracellular matrix of these biofilms, and do these interactions result in toxic effects to the biofilms. By using predacious organisms we aim to determine if titanium dioxide nanoparticles can be transferred through a benthic food chain, from benthic biofilms to biofilm predators. Then we aim to determine what effects this food chain transfer has on these higher level predators. By determining the toxicity of titanium dioxide nanoparticles to heterotrophic biofilms and the ability for trophic transfer of nanoparticles through a benthic food chain, this Masters thesis will provide much needed information for assessing the environmental implications of our growing use of TiO2 nanoparticles.
If you are enthusiastic about conducting research with a well-equipped, international team consisting environmental toxicologists, biochemists and molecular biologists, EAWAG, within the ETH domain, is the place for you
- Development of a multiplex-PCR method to assess chemical
toxicity towards fish cells
Contact: Prof Kristin Schirmer
In environmental risk assessment fish is the most widely used vertebrate species. Within an international research project we aim to develop a fish cell-based test system to replace or reduce the use of fish needed for Acute Fish toxicity tests (OECD test guideline 203). One possibility to determine the toxic potential of chemicals is the measurement of cytotoxicity using different fluorescent dyes. Another way to assess chemical toxicity is to quantify the expression or repression of stress-responsive genes. By establishing a multiplex-PCR method it is possible to determine the expression/repression of up to 15 genes simultaneously. This will further allow us to identify expression patterns depending on the chemicals toxic mode of action. The proposed master project combines cell culture (working under sterile conditions with fish cell lines) and molecular biology techniques (RNA isolation, PCR, primer design, gel electrophoresis, working with chip technique).
- Development of a fish intestinal barrier
model using a novel rainbow trout cell line
Contact: Prof Kristin Schirmer
The fish intestine is an important site of nutrient absorption, ion regulation and pathogen defense. At the same time, it may serve as an entry port for contaminants by means of transfer from the fish diet. Little is known thus far about the intestinal cells’ function, in part because of a lack of an appropriate in vitro cell culture model. We therefore have established a cell line from rainbow trout intestine, to our knowledge the first of its kind. The goal of this project is to develop culture and exposure conditions that closely mimic the physiological conditions in fish and to explore how these specifically adapted cells take up and respond to a model toxicant. Thus, work is a combination of cell biology (sterile cell culture techniques; biochemical and cell physiological characterisations) and toxicology (exposure, cellular uptake and response to model contaminant).
- Time- and concentration-dependent uptake
and distribution of benzo(a)pyrene in a liver cell line
Contact: Prof Kristin Schirmer
In an integrated project of experimental and theoretical biologists, we are investigating time- and concentration dependent responses elicited by benzo(a)pyrene, a polycyclic aromatic hydrocarbon and common environmental contaminant, in a well characterized liver cell line from mouse. Cellular responses, genome and proteome-wide expression are analyzed and linked by different computational tools. In order to link the presence of the chemical to the biological responses observed, it is important to understand the uptake kinetics of benzo(a)pyrene and its cellular distribution. This project therefore aims to quantify the uptake and distribution of the chemical into cells and organelles using radiolabelled benzo(a)pyrene in combination with scintillation counting and potentially radio-HPLC.
- Glucocorticoid-like activity screening of municipal and hospital wastewater
Contact: Dr Marc Suter
The natural agonists of the glucocorticoid receptor (GR) are cortisol and other glucocorticoids. They regulate immune and stress response, and exert other wide ranging effects on animal physiology. Hence GR signaling pathways could be a prime target for endocrine disruptors. A recent Dutch study found significant glucocorticoid-like activity in raw industrial and hospital effluents, as well as in municipal waste water treatment plant (WWTP) effluents. The levels ranged up to 16 ng cortisol equivalents/L for surface waters, and up to 2'900 ng/L in effluents. The exact causes for this very high activity are unknown, but it may likely be due to synthetic glucocorticoids used as immunosuppressives and anti-inflammatories.
In view of the physiological importance of glucocorticoid signaling and the negative effects of chronic exposure, the glucocorticoid-like activity in Swiss WWTP effluents will be assessed using a bioanalytical tool, a reporter cell line stably transfected with the human glucocorticoid receptor.