Temperaturgrenzen der Bildsamkeit von Bronze mit 20% Zinn

The Science of Nature -     

Partitioning radiolabeled thymidine uptake by bacteria and meiofauna using metabolic blocks and poisons in benthic feeding studies

Techniques exist which allow for the measurement of in situ grazing rates of meiobenthos on sedimentary bacteria and microalgae. Radiolabeled substrates are incorporated into microbes which serve as food for meiofauna and which themselves also become labeled during feeding. However, during in situ grazing experiments, meiofauna may become radiolabeled by a variety of non-feeding processes. Proper controls to correct for these extraneous routes of labeling have been developed in the present study. The use of [methyl-³H] thymidine (³HTdR) in studies of meiofaunal grazing on bacteria has two unique advantages: (1) it is incorporated only into prokaryotic macromolecules, and (2) bacterial incorporation of ³HTdR may be selectively blocked by several inhibitors which are non-toxic to meiofaunal grazers. Coupled with formalin-killed control treatments, the use of these inhibitors makes it possible to accurately determine the partitioning of radiolabel into meiofauna during grazing into adsorptive, absorptive and grazing components. A saturated solution of nalidixic acid and 5-deoxythymidine was found to be most effective in inhibiting water-column bacterial uptake and incorporation of ³HTdR, and had no toxic effects on meiofauna. The inhibitor was found to immediately block bacterial incorporation of ³HTdR and was as effective at 20% saturation as at 100%. The presence of sediment reduced the effectiveness of this inhibitor by 50%. Solutions of the inhibitor with excess undissolved material, however, completely blocked sediment bacterial uptake of ³HTdR. Employing these techniques during in situ grazing experiments showed that up to 83% of total meiofaunal uptake of ³H-label may be attributable to non-grazing processes. Experiments conducted in slurried sediments yielded grazing rates which were the same as those from intact cores. Furthermore, meiofaunal grazing rates on multiple food sources (e.g. bacteria and diatoms) may be determined synoptically by adding isotopically-distinct substrates (e.g. ³HTdR and H¹⁴CO₃) to the same experimental incubation.University of Texas Marine Science Contribution No. 698.     

Field evaluation of two diffusive samplers and two adsorbent media to determine 1,3-butadiene and benzene levels in air

Two types of diffusive samplers, both of which are compatible with thermal desorption, but differ in their geometry—SKC-Ultra (badge-type) and Radiello (radial symmetry-type)—were evaluated indoors and outdoors under varying temperature, humidity and wind speed conditions, using the graphitized adsorbents Carbopack X or Carbograph 5 to measure 1,3-butadiene and benzene in ambient air. The results obtained by diffusive sampling were compared with results obtained using a conventional active sampling method over both long (1 week) and shorter periods (6–24 h). Analysis and detection were performed using an automatic thermal desorber (ATD) connected to a gas chromatograph-flame ionization detector (GC/FID). Results from each sampler and adsorbent combination were examined using ordinary or multiple linear regression analysis. The overall uncertainty (OU) was also determined. In general, the results obtained with both samplers showed good agreement with those obtained by active sampling. Carbopack X appeared to be a more efficient adsorbent than Carbograph 5 for 1,3-butadiene, but the two adsorbents were equivalent for benzene. No effects of either humidity or air velocity were observed. Minor temperature effects were observed for both samplers for 1,3-butadiene. In summary, the results confirmed the accuracy of sampling rates previously determined for the two samplers and adsorbents. We consider the two samplers to be suitable for stationary and personal monitoring for the general population of 1,3-butadiene and benzene in various environments, indoors and outdoors. They are almost independent of meteorological conditions and may be suitable for monitoring industrial atmospheres.     

The effect of wastewater treatment on antibiotic resistance in Escherichia coli and Enterococcus sp.

The effects of wastewater treatment on the proportion of Escherichia coli and Enterococcus sp. resistant to specific antibiotics were investigated at two facilities in Davis County, Utah, one of which received hospital waste. Samples were taken from the influent, effluent before disinfection, and secondary anaerobic sludge digester effluent. There was very little difference in antibiotic resistance among E. coli in the inflow waters of the plants but the plant receiving hospital waste had a significantly higher proportion of antibiotic resistant Enterococcus. The effect of wastewater treatment on antibiotic resistance was more pronounced on enterococci than E. coli. Although some increases in antibiotic resistance were observed, the general trend seemed to be a decrease in resistance, especially in the proportion of multidrug resistant Enterococcus sp.     

Heterogeneous photocatalytic oxidation of organics for air purification by near UV irradiated titanium dioxide

The photocatalytic degradation of high concentrations of various organic pollutants (acetone, 2-propanol and toluene) in dry and humid air streams was carried out using a specially designed photoreactor based on the UV-TiO2 principle. The influence of several parameters which control the destruction efficiency (flow rate, initial contaminant and water vapour concentration, temperature and light intensity) has been studied. The conversion was maximal at room temperature, low flow rates and low initial contaminant concentrations. The presence of water in the inlet stream strongly affected the performance of the catalyst. The primary oxidation product of 2-propanol was acetone.