Abstract:The potential influence of pH on water repellency in soils has already been mentioned in some studies, but no clear correlation between these parameters has been found to date. In addition, although correlations of water content and water repellency have been found in numerous studies, the influence of drying and subsequent storage conditions on water repellency are still unclear. In this study, a series of samples showing water repellent and wettable conditions respectively at field moist states from two urban locations were compared regarding two main aspects: (i) the influence of artificial pH-changes on their wetting behaviour and (ii) sample wettability changes during drying for different drying temperatures. The assumption made in a study by Hurraß and Schaumann (2006) on the same sample site, that differences in wettability of closely neighboured samples from one sample location can be interrelated with differences in pH, was confirmed. However, in contrast to the assumption that rising pH will improve the wettability and decreasing pH will intensify water repellency, we found a maximum in water repellency at a pH above the initial pH. The results from drying samples at different temperatures confirmed the dependence of water repellency development on the drying temperature. Additionally, we could confirm the conclusion from previous studies that the water content alone cannot explain the water content-WDPT (water drop penetration time) relationship. The results from drying and pH changes show that some location specific factors, like the number of pH active functional groups, may be relevant for sample wettability. As additional mechanism, which may be partly antagonistic to the influence of the water content, we assume temperature-dependent conformational changes in SOM (Soil Organic Matter). It seems that aspects of these conformational changes may additionally be governed by pH in one of our two locations.

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Proton NMR relaxometry is a very powerful tool for investigating porous media and their interaction with water or other liquids and the mobility and interaction of organic molecules in solution. It is commonly used in material science or earth science. However, it is only scarcely applied in soil science although it shows great potential for helping to understand water uptake into the soil matrix and processes occurring at the solid-liquid interface at soil particle surfaces. This review introduces proton NMR relaxometry in the context of soil science and discusses the most important applications of the method in this field. Relevant results from different applications of NMR relaxometry in soils are described and research gaps identified. Some original data is presented concerning biofilm formation in soils, which was investigated using proton NMR relaxometry. NMR relaxometry is a sensitive, informative and promising method to study pore size distribution in soils as well as many kinds of soil physicochemical processes, among which are wetting, swelling or changes in macromolecular status. It is further a very helpful method to study interactions between molecules in soil organic matter and can serve to study the state of binding of water or organic chemicals to soil organic matter. Relaxation times determined by NMR relaxometry are sensitive to various factors that play a role in soil-water interaction which is both an advantage and shortcoming of the method: NMR relaxometry can be applied to numerous investigations in soil science, but at the same time interpretation of the results may be very difficult in such complex and heterogeneous systems like soils.

The demand to quantify the elemental composition of very small sample amounts and/or of samples which form artefacts during conventional sample preparations is increasing. Example applications are the quantification of engineered metal(loid) based nanomaterials in environmental samples, e.g. (i) the direct analyses of engineered nanoparticle (ENP) suspensions showing broad particle size distributions which are not suitable to be applied via the spray chamber in ICP-MS analyses, (ii) measurements of single invertebrates and tissue of selected organs which were exposed to ENPs, and (iii) whole plants or plant parts e.g. from Lemna sp. The use of imaging based high resolution methods like atomic force microscopy or environmental scanning electron microscopy creates the need to quantify the elemental composition of the visualised objects as directly and exactly as possible, at very low limits of detection. With this study the authors present a method/concept for the multi-element quantification of analytes from ENPs in complex matrices with different degrees of complexity by graphite furnace electrothermal vaporisation coupled to inductively coupled plasma quadrupole mass spectrometry equipped with collision/reaction cell (GF-ETV-ICP-QMS).

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