Toxizität von Aluminium

The concentration of solubilized aluminium in soils and waters increases due to environmental influences. To obtain information on the types of Al species occuring under these conditions, aluminium chloride solutions were prepared in a wide range of concentrations (10^?1–10^?5 mol·l^?1 Al) and basicity (OH/Al=0,5–2,5), respectively, and then structurally characterized using the ferron method. For the freshly prepared solutions, a decrease in the portion of monomeric Al species is observed, with an increasing OH/Al-ratio; the formation of polymeric cations decreases to lower OH/Al-ratios with diminishing concentration. The portion of tridecameric cations (Al₁₃) decreases with diminishing concentration, but so called transition polymers occur in these solutions. The transition polymers are instable under ageing; by inreasing the ageing time, a disproportion of these cations into monomeric and polymeric species can be observed. At extremly low Al concentrations (10^?5 mol·l^?1 Al), a condensation of the transition polymers into polymeric species occurs, after only a short ageing. The influence of admixtures of Mg²⁺-and Ca²⁺-ions, respectively, on the specification of the Al cations are only observed after longer ageing times; in this case, the formation of polymeric Al species is forced. The polymeric Al species therefore, seem to be especially preferred alongside the monomeric ones under biologically relevant concentrations.     

Abiotic hydrogen production in fresh and altered MSWI-residues: Texture and microstructure investigation

Long-term hydrogen generation was observed in a Bavarian mono-landfill for municipal solid waste incineration (MSWI) residues. Hydration reactions of non-noble metals, especially aluminum, predominantly produce hydrogen at alkaline reaction conditions. Microscopic investigations show that aluminum metal may occur in different forms: as larger single grains, as small particles embedded in a vitrified matrix or less frequently in blowholes together with metallic silica.Four types of corrosion texture were observed, indicating different reaction mechanisms: aluminum hydroxide rims caused by hydration reactions at alkaline reaction conditions (reaction type 1) and multiphase rims with ettringite and hydrocalumite due to the reaction of aluminum hydroxide with sulfate and chloride ions which are solved in the pore water (reaction type 2). Galvanic corrosion textures due to the electric potential difference between aluminum and embedded intermetallic Fe- or Cu-rich exsolution phases lead to two further corrosion textures: Strong hydration effects of aluminum except a border of aluminum remnant directly beside the Fe- or Cu-rich segregations were only observed in fresh samples (reaction type 3). The reaction type 4 shows a network of Al-hydroxide veins occurring along the embedded intermetallic Fe- or Cu-rich exsolution segregation pattern within the metallic aluminum grain. Metal particles enclosed in vitrified particles offers the potential for future corrosion processes.The occurrence of corrosion types 1, 2 and 3 in fresh bottom ashes indicates that these reaction mechanisms predominate during the first reaction period in the presence of chlorine in an alkaline solution. Corrosion type 4, however, was additionally observed in aged samples. Here aluminum acts as sacrificed anode implying electrochemical reaction due to electrolytic pore water. Chloride in the system keeps the reaction alive as Al-hydroxide is solved which normally builds a protection shield around the aluminum metal particles.Due to field observations and experimental results we have reasonable indications that after an initial strong formation of hydrogen the reaction time for hydrogen production in the landfill is lengthened for several decades by the presence of chloride in the alkaline pore water.     

A comparison of relative abundance versus class data in diatom-based quantitative reconstructions

Relative species abundances are the most frequently applied data type used for modern or paleolimnological diatom studies. In contrast, plant ecologists save time by commonly using ordinal scale data (class data), where the abundance of a species is estimated using dominance classes, instead of relative abundance data. This study compares the performance of models based on ordinal diatom species class data (class 1: sporadic (<0–1%) up to class 6: dominant (>60%)) with similar model types based on relative abundance data for different regional training sets and sediment cores. First, relative diatom abundances were converted into ordinal classes. Species response to total phosphorous (TP) was modelled using both types of data - relative abundance and ordinal class data. Secondly, TP was reconstructed for six sediment cores from North-East Germany, Switzerland, and Denmark using WA and WA-PLS based on both types of data. Thirdly, 20 lake sediment surface samples with known relative diatom abundances and known water TP concentrations were recounted using an ordinal data scale to create an independent test set. No significant differences were found between relative abundance and class data for (1) explained species variance, (2) reconstructed TP values, and (3) inferred TP values of the 20 recounted samples. This approach demonstrates that past TP concentrations may also be reliably reconstructed using class data instead of relative diatom abundances. Thus, by using class data lake managers may not only obtain more long-term records past water quality, but this approach is also quicker and therefore more cost effective. Moreover, the findings of this study may also advance the use of automatic diatom identification with digital image recognition, as we demonstrate that not every damaged diatom valve needs to be identified.