Visualization and localization of bromotoluene distribution in Hedera helix using NanoSIMS

Some plants are known as indoor air purifiers. A large number of studies report kinetic purification results for an extensive panel of plants, i.e. the pollutant concentration (volatile organic compounds, as known as VOC, most of the time) is continuously monitored by gas chromatography. However, only a few papers describe the mechanisms involved in such processes. This study deals with the use of secondary ion mass spectrometry imaging as an efficient tool to locate atmospheric pollutant as bromotoluene within the Hedera helix plant (leaf, roots) and the substrate on which it was previously grown. Hedera helix plants have been placed in a pollution chamber with control of the exposure parameters. Plant and soil samples excised were transferred into a fixative solution of glutaraldehyde and paraformaldehyde for a few days, were dehydrated using ethanol and were embedded with resin. Cross sections were made from the pale brown solids obtained. Then, a device using a cathodic pulverization device capable of depositing a few nanometers of gold atoms over the sample was used to make the surface electronically conductive for the NanoSIMS. Hence, polluted and unpolluted samples of Hedera helix and substrates were obtained following a careful procedure that allowed for the discrimination between polluted and nonpolluted ones. Nanoscale spatial resolution was an invaluable tool (NanoSIMS) to achieve this, and proved that VOCs, such as bromotoluene, were actually trapped by plants such as Hedera helix.     

Facing Hazardous Matter in Atmospheric Particles with NanoSIMS (2 pp)

Background, Aim and Scope Current scientific studies and evaluations clearly show that an increase of urban dust loads, alone or combined with other pollutants und certain meteorological conditions lead to different significant health effects. Premature death, increased hospital admissions and increased respiratory symptoms and diseases as well as decreased lung function can be observed in combination with high pollutant levels. Sensitive groups like elderly people or children and persons with cardiopulmonary diseases such as asthma are more strongly affected. Because of the direct contact between fine particles and lung tissue more information concerning the surface structure (mapping of toxic elements) is required. Materials and Methods: The NanoSims50 ion microprobe images the element composition at the surface of sub-micrometer air dust particles and documents hot spots of toxic elements as a possible threat for human health. Results: The atmospheric fine dust consists of a complex mixture of organic and inorganic compounds. Heavy metals are fixed on airborn particles in the form of hot spots in a nanometer scale. From a sanitary point of view, the hot spots consisting of toxic elements are particularly relevant as they react directly with the lung tissues. Discussion: To what extent particles can penetrate the various areas of the lungs and be deposited there depends on the one hand on their physical characteristics and on the other on breathing patterns and the anatomy of the lung, which is subject to change as the result of growth, ageing or illness. Once inhaled, some particles can reach the pulmonary alveoli and thus directly expose the lung tissues to toxic elements. Conclusions: Especially the mapping of toxic arsenic or heavy metals like copper on the dust particles shows local hot spots of pollution in the dimension of only 50 nanometers. Recommendations and Perspectives: Imaging of elements in atmospheric particles with NanoSIMS will help to identify the material sources.     

Equation for isotope accumulation in products and biomass as a way to reveal the pathways in mesophilic methanol methanization by microbial community

Isotope-labelling of substrate is used to reveal the methabolic pathways of substrate transformation by microbial community. In this paper, in order to describe the batch mesophilic anaerobic methanization of ¹³C-labelled methanol and microbial ecology analysis (Li et al., 2008), an equation for the isotope accumulation in products and biomass was included into the basic mathematical model based on stoichiometric chemical reactions. The higher was the isotope level in substrate, the larger fraction of ¹³C accumulated in products and biomass. Acetate, total organic and inorganic carbon (TOC, TIC) concentrations and methane production were used for the model calibration, whereas ¹³C enrichment of acetate, TIC and biomass were used for model validation. In the model, chemical transformations including methanol and acetate oxidation, homoacetogenesis, hydrogenotrophic and aceticlastic methanogenesis were considered. The rate-limiting reactions were methanol and acetate consumption. According to the model, homoacetogens performing acetate formation and oxidation were competed with hydrogenotrophic methanogens for hydrogen. Biphasic methane production was due to hydrogenotrophic methanogenesis in the first phase and due to acetiticlastic and hydrogenotrophic methanogenesis following acetate oxidation in the second phase.