III. Ökotoxikologische Charakterisierung der Schwermetall-Immissionsmuster

The spatial variation of the immission patterns of Cr, Fe, Pb and V in the region Leipzig-Halle is dicussed in terms of similarities as well as dissimilarities. The representation by isopleths enables the identification of areas with high and low air pollution. The immission patterns can be used as criteria to select areas suitable for in-field testing so that possible effects on fauna und flora and xenobiotic fluxes can be studied at representative sites. The comparison with literature data yields a first characterization of the ecotoxic potential of the heavy-metal immission for the region. By the principal component analysis a comparative evaluation of the spatial structure of all element contents is performed, which leads to conclusions about emission sources and the physicochemical behaviour of the elements.     

Zinc accumulation potential and toxicity threshold determined for a metal-accumulating Populus canescens clone in a dose–response study

The effect of increasing soil Zn concentrations on growth and Zn tissue concentrations of a metal-accumulating aspen clone was examined in a dose–response study. Plants were grown in a soil with a low native Zn content which was spiked with Zn salt solutions and subsequently aged. Plant growth was not affected by NH₄NO₃-extractable soil Zn concentrations up to 60 μg Zn g^?1 soil, but it was completely inhibited at extractable concentrations above 90 μg Zn g^?1 soil. From these data an effective concentration of 68.5 μg extractable Zn g^?1 soil was calculated at which plant growth was reduced by 50%. The obtained information on toxicity threshold concentrations, and the relation between plant Zn accumulation and extractable soil Zn concentrations may be used to assess the suitability of the investigated Populus canescens clone for various phytoremediation strategies. The potential risk of metal transfer into food webs associated with P. canescens stands on Zn-polluted sites may also be estimated.     

A simple,explicit formula for the critical pressure of homogenous two-phase nozzle flows

The critical pressure ratio of the homogeneous two-phase nozzle flow model known as the Omega method is expressed in function of the Omega Parameter as the exact numerical solution of a transcendental equation. A well fitting, easy to use, explicit approximation for flashing and non-flashing flows is presented here. The validation against the exact numerical solution proves that this new formula is better fitting than the other ones in the technical literature for both single and two-component flows.     

TiO<Subscript><Emphasis Type="Bold">2</Emphasis></Subscript> nanoparticles – Relationship between dispersion preparation method and ecotoxicity in the algal growth test

PurposeLittle is known about the ecotoxicity of nanomaterials and there are no specific guidelines for sample preparation and testing. We set out to establish whether the method used to prepare TiO₂ dispersions had a significant impact on aquatic ecotoxicity. We also followed the formation of agglomerates during the incubation period.MethodsWe applied the algal growth inhibition test (OECD test guideline no. 201). Dispersions were prepared by stirring and/or ultrasonication for different durations, and by filtration according to an OECD procedure recommended for testing difficult substances.ResultsSamples stirred for 7?d were not toxic, but EC₂₀ values could be calculated for all the other treatments. Shorter treatments generated EC₂₀ values in the range 1–27?mg/L. Only the shortest treatment (1 min stirring, 1 min ultrasonication) produced an unusually high EC₂₀ value, indicating low toxicity. Development of agglomerate size and of toxicity depends on the nanoparticles. We found that ecotoxicity was predominantly caused by a fraction of nanoparticles and agglomerates obtained by passing dispersions through a 0.22-µm filter.ConclusionsWe propose a short treatment regime to generate the most relevant ecotoxicity data for TiO₂, for example stirring for 1?min followed by 3 min ultrasonication. Until more data concerning the ecotoxicity of different fractions are available, we recommend the testing of unfiltered dispersions rather than filtrates. Relating ecotoxicity to the total hydrodynamic surface of the nanomaterials rather than concentration does not seem to improve the accuracy of ecotoxicity assessments using the algal growth inhibition test.     

Integrated relief design for gas-generating reactions: predicted vessel pressure course in dependence on the phase separation model

Pressure relief of a hydrogen peroxide decomposition in a top-vented vessel is simulated numerically using six phase separation models. The results lead to the conclusion that generally a parameter study will be required for relief design by simulation when a gas-generating reaction is considered. None of the phase separation models can be expected to be always conservative in contrast to the case of tempered systems.