4 Material und Umwelt
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- 4 Material und Umwelt (138) (entfernen)
The new OECD test guideline will address the following four main steps in the determination of the length and width distributions of fibers: sample preparation, image acquisition, data evaluation and uncertainty analysis. As the sample preparation has to be optimized for each material, general quality criteria will be given in the protocol. For full visibility of a fiber the appropriate resolution has to be chosen. In the data evaluation the length and diameter of each fiber will be determined concurrently to allow for application of different regulatory definitions. The quality of the results critically depends on the sample preparation as well as the data evaluation. In this step the classification rules have to be formulated and followed accurately in order to optimize reproducibility of the method. The SOP will be validated in an international round robin test, which is planned for 2018/2019.
Initial situation:
Aluminum is an often-used building material in modern architecture, not only for construction but as well for facades and decorative elements. In the 1950th and 1960th, after World War II, many buildings in Germany were constructed with aluminum or contain elements of colored anodized aluminum. In the last years a larger number of these buildings are increasingly in the sight of conservation works including the aluminum parts such as window frames or facade coverings.
Damaged Aluminum Surfaces:
Common damages are a change of color or gloss changes through weathering processes, drill holes or marks due to later modifications, scratches in the anodized layer due to extensive wear e.g. at handrails or door handles.
To repair damaged aluminum surfaces, there are usually two options: smaller damaged areas are repaired by using a touch-up pen. In case of larger damages, the complete re-anodization is necessary. This includes to de-anodize the surface with cleaning and grinding the whole aluminum object. Both possibilities are disadvantageous for the objects. The touch-up pen often does not match the color of the original surface together with an insufficient corrosion protection for outdoors. While the newly anodized surface differs in color and gloss from the originally applied color.
Research Approach:
The whole procedure contrasts with the principal approach in conservation which aims to intervene as less as possible, in case of the conservation of an object. To fulfill this approach in a more appropriate way the research project focuses on a mobile and partial application for colored, anodized aluminum parts.
To anodize aluminum the application of an electrolyte onto the surface together with sufficient voltage and current is necessary. Generally diluted sulfuric acid is used as electrolyte. Different possibilities are examined to enable the mobile application of the electrolyte, e. g. the application by producing a gel matrix or like in electroplating by pen or brush wrapped with a fleece fabric.
Experimental part:
First experiments are conducted to examine the structure of the anodized layer in relation with proper cleaning, anodization time with applied voltage and current and the coloring process. The aim was to reduce the preparation procedure and the anodization time as much as possible to facilitate the mobile application.
Examinations with Keyence microscope, Eddy current testing and REM are performed to characterize the layers. The results are shown in table 1. A clear connection between proper cleaning, anodization time, voltage and amperage and the achieved thickness of the anodized layer is significant. Cracks in the layer show that raising the voltage and amperage results in thicker layers but as well in a crumbled and less stable anodized surface.
Gel preparation:
In addition to the anodization process with a liquid e.g. sulfuric acid a gel application is tested to prevent the electrolyte from rinsing down during the mobile application. For this purpose, several gel-forming agents are tested together with their stability in acid systems. It was observed, that the consistency of the gels varies dependent of the time.
Conductivity:
The conductivity of sulfuric acid combined with different gel-systems was measured and compared in order to predict the possible growth of layers during anodic oxidation process.
Further steps:
Determination and optimization of application parameters like voltage, amperage and anodization-time to build up a preferably stable and sufficient thick anodized layer. Examination of gel preparation to guarantee a stable product, enforcing with textile tape for easy application.
Infections with multi-resistant Gram negative pathogens are a major threat to our health system. In order to serve the needs in antibiotics development we selected untapped bioresources and implemented high throughput approaches suitable for the discovery of strains producing antibiotics with anti-Gram negative activity.
Our approaches rely on the hypothesis that Termite associated bacteria are likely to produce potent antibiotics to defend their hosts against entomopathogenic microorganisms. Termite nests and guts harbor suitable, highly diverse microbiomes in which bacterial taxa are present known to potentially produce natural compounds. In
a first step the diversity of Coptotermes species nest microbiomes was assessed carefully by using 16S rDNA amplicon sequencing on the Illumina MiSeq platform and nest material was selected to retrieve viable cells by using Nycodenz density gradient centrifugation. In order to analyze the diversity of the culturable termite nest microbiome, bacterial cells were either distributed in 384-well plates
(approach 1) or encapsulated in small spheric agarose beads by an high throughput microfluidics technique (approach 2). Cultures obtained from approach 1 were scaled-up in 96-well Duetz-systems for characterization of diversity and for rapid supernatant screening using the bioluminescence-labeled E. coli pFU166. The generated
droplets of approach 2 simultaneously received a small population of GFP-tagged Gram negative screening cells and were sorted for low fluorescence using FACS. After elimination of redundancy we performed a fast scale-up of active strains.
Implementation of this pipeline allows us to prioritize antibiotics producing strains in a ultra-high throughput fashion and by cultivation of broad diversity in our approches.
Leachiing tests - a useful tool for the environmental impact assessment of construction products?
(2018)
Construction products and waste materials used for construction can be in contact with the environment and may release potential harmful compounds. Information on the total content of these substances in the product is not sufficient to assess its envrionmental impact since it does not consider realistic exposure conditions.The impact of these compounds is often assessed by using the total content in the product. This estimation lacks realistic exposure conditions.
Concerning the pathway to soil and groundwater by contact with rain or seepage water leaching tests, which were developed and standardized by the European Committee for Standardization, are available. While for secondary construction products and waste this investigation of the leaching behaviour is standard procedure and is already part of regulation in Germany (draft ordinance on reuse of mineral waste) and within Europe (landfill directive) the release from primary construction products got in the focus more recently. Several monitoring studies found unexpected high concentrations of substances used as herbicides and fungicides in surface water and stormwater originating from urban areas. As some of these compounds are even banned for the use in agricultural applications in Europe alternative sources as roof materials and façade coatings exposed to rain were suggested. Further field and laboratory tests confirmed construction products as sources of these substances in water.
The aim of this presentation is to show exemplary results of existing leaching methods and underline the strength and weaknesses of the test system with selected examples from our work. We especially draw the attention to the research which is still needed to close the gap between the results of leaching experiments and the subsequent risk assessment of the products.
Development of a methodical approach for in-situ analysis of modern reverse paintings on glass
(2018)
The technique of painting on the reverse side of glass was rediscovered by artists in the early 20th century and gained great popularity, especially in Germany. In contrast to other paint techniques (e.g. panel and mural painting), the paint layers are applied in reverse succession starting with the foremost paint layer and ending with the primer (backmost layer). The paintings are viewed in reflected light, thus revealing an impressive gloss, luminosity and depth of colour.
Scientific investigation of the material provides important information for appropriate conservation concepts. Transport of the precious and fragile objects to the lab is often not feasible. Therefore, in-situ, non-invasive analysis is necessary to analyse colorants and binders. However, some analytical problems need to be considered: due to the reverse paint stratigraphy in reverse paintings on glass, the measured layer is always the backmost one. The analytical possibilities are extremely reduced, when the back is covered by a metal foil (or by paper, carton etc.). However, measurements through the glass (using Raman and VIS) can still yield information on the colourants of the front layer.
When the paint layer is accessible, we start our procedure using X-ray fluorescence (Tracer III-SD, Bruker AXS Microanalysis GmbH, 40 kV, 15 μA) and VIS reflectance spectroscopy (SPM 100, Gretag-Imaging AG). Both techniques provide first information on the inorganic colourants. Raman measurements (i-Raman®Plus, Bwtek inc., 785 nm, 50× objective, resolution 4 cm-1) are then carried out to clarify uncertain XRF measurements and to identify synthetic organic pigments (SOP). Diffuse Reflection-Infrared-Fourier-Transform Spectroscopy (DRIFTS; ExoScan, Agilent GmbH, 4000–650 cm-1, 500 scans, spectral resolution 4 cm-1) is used for the classification of the binders. Moreover, it may help to identify SOP, when fluorescence dominates the Raman signal. This analytical sequence yields the best results, when time is the limiting factor.
We present two in-situ studies of the paintings “Kreuzabnahme” (1914-15) by Carlo Mense and “Stadt am Morgen” (1921) by Walter Dexel. The painting “Kreuzabnahme” is an outstanding piece in Mense’s ɶuvre, because the glass plate was painted on both sides (Fig. 1). The results of the back-side show mainly inorganic pigments: basic lead white, talc, red and brown ochre, cinnabar, chrome yellow, viridian, ultramarine blue, Prussian blue and bone black. The classification of binding media using DRIFTS yields positive results for drying oil. Acrylic resin could be identified in two areas, resulting from a previous restauration treatment. For the front side painting, Mense used basic lead white, cinnabar, chrome yellow and umbra as pigments and oil as binder.
Measurements of the abstract painting “Stadt am Morgen” by Walter Dexel show zinc white, basic lead white, chalk, cinnabar, red lead, strontium yellow, cadmium yellow, cobalt blue, Prussian blue, ultramarine blue, brown ochre and bone black as pigments. Moreover, synthetic alizarin (PR83) was identified as dark red colorant. The results of DRIFTS classify oil as binding media.
We conclude that, the use of complementary spectroscopic methods yields the best results for in-situ analysis of reverse paintings on glass.
Antimicrobial resistance is a major threat to human health. The prevalence of multi-drug resistant (MDR) bacteria is predicted to increase in the future requiring robust control strategies. One cornerstone to prevent the spread of MDR bacteria in clinical settings is the application of disinfectants to improve hygiene standards. However, bacteria can evolve resistance to disinfectants, which in turn can confer cross-resistance to antibiotics. Additionally, clonal bacterial populations can display phenotypic heterogeneity with respect to the tolerance of antibiotic stress leading to a prolonged survival of a sub-population; this phenomenon is termed persistence. Persistence to antibiotics is an evolvable trait and can serve as a stepping stone for the evolution of genetically encoded resistance. Until now, there is a lack of systematic studies that investigate if bacterial populations establish persister subpopulations that tolerate disinfectant stress longer than the majority of the population. Our results in E. coli indicate that persistence is a bacterial survival strategy against benzalkonium chloride, a widely used disinfectant.
In future experiments, we will investigate the evolution of persistence in the face of fluctuating exposure to disinfectants and whether persistence facilitates resistance against disinfectants. Lastly, we will test how tolerance and resistance against disinfectants affects susceptibility against antibiotics.
Zearalenone (ZEN) and its sulfate and glucoside conjugates have been detected in (a broad variety of) food and feed commodities1. Both conjugated derivatives are formed as part of fungal or plant secondary metabolism and thus, belong to the group of modified mycotoxins2. After consumption of contaminated foodstuff, the conjugates can be hydrolyzed by human intestinal microbiota leading to liberation of ZEN that implies an underestimation of the true ZEN exposure. In order to include ZEN conjugates in routine analysis, as well as for toxicological investigation reliable standards are needed.
The objective of the present study was to develop a simple and economic method for biosynthesis of ZEN conjugates. Preceding experiments on the biotransformation of ZEN by Rhizopus and Aspergillus species showed a mixed metabolite formation3. Therefore, these known ZEN conjugating fungal strains were screened for their potential to selectively synthesize the ZEN derivatives ZEN-14-sulfate (Z14S), ZEN-14-glucoside (Z14G) and ZEN-16-glucoside (Z16G). The screening was conducted by adding ZEN to liquid fungal cultures. Cultivation conditions and ZEN incubation time were varied. All media samples were analyzed for metabolite formation by HPLC-MS/MS. Z14S was exclusively formed by A. oryzae. Under optimized conditions a specific biosynthesis of Z14G by R. oryzae and Z16G by R. oligosporus was achieved. After liquid-liquid-extraction and preparative chromatographic cleanup 1H-NMR purities of ≥ 73% for Z14S, ≥ 82% for Z14G and ≥ 50% for Z16G were obtained. In addition, a consecutive biosynthesis was developed by first using Fusarium graminearum for ZEN biosynthesis on rice based liquid medium. After inactivation of Fusarium the subsequent conjugation reaction was conducted utilizing Aspergillus and Rhizopus species under the various optimized conditions.
In this study an easy and cost-efficient biosynthesis for Z14S, Z14G and Z16G was developed. The developed biosynthesis could be also used for other metabolites like ZEL conjugates. Our results of the in vitro screening indicate also the formation of a ZEL-glucoside and α ZEL-sulfate as major metabolites by R. oryzae. In sum, under optimized cultivation conditions fungi can be easily utilized for a targeted and stereospecific synthesis of ZEN conjugates.
Surface characterisation of biofilms by nearambient pressure X-ray photoelectron spectroscopy
(2018)
The XPS information depth of approximately 10 nm is in the same size range as the outer membrane of the gram-negative bacteria, which makes XPS a suitable tool for determining the elemental composition of the bacterial surface and monitor changes caused by outer stress like dehydration or exposure to antimicrobials. However, bacteria are inherently in a hydrated state, and therefore only compatible to ultra-high vacuum after extensive sample preparation, which may degrade the sample constituents. This issue is addressed by the development of near-ambient pressure (NAP)-XPS, which enables bacteria and biofilms to be characterised in their native wet state. Artificial biofilms, bacteria and biofilms of Escherichia coli have been characterised with the laboratory NAP-XPS instrument EnviroESCA from SPECS GmbH, at pressures ranging from high vacuum to 12 mbar, and in both humid and dry environment. By studying biological samples in their native wet state, new insight about composition and transport of drugs through cell membranes and the extracellular polymeric substance (EPS) of biofilms can be obtained.