Mechanismen der physikochemischen Alterung der organischen Bodensubstanz

Die dynamischen Veränderungen der organische Bodensubstanz, die durch Änderungen der Umweltbedingungen hervorgerufen werden, haben einen wichtigen Einfluss auf die Sorptions- und Transportvorgängen von organischen Schadstoffen. Das Verständnis der Veränderungen innerhalb der organischen Bodensubstanz ist wichtig für die Aufklärung der Mechanismen der Sorptions- und Transportvorgänge. Die organische Bodensubstanz wird hier basierend auf einer Modellvorstellung als amorphe Matrix angesehen. Untersuchungen mit der Dynamischen Differenz Kalorimetrie (DSC) zeigten für ausgewählte Bodenproben ein thermisches Verhalten ähnlich dem eines Glasüberganges. Da nicht alle untersuchten Bodenproben einen solchen Übergang aufweisen, stellt sich die Frage, welche Mechanismen zu diesen Übergängen führen und inwiefern ein Zusammenhang mit der chemischen Zusammensetzung der Böden besteht. Zu diesem Zweck wurden ausgewählte Bodenproben mit der 13C-Festkörper-NMR und der DSC charakterisiert

Ausbringung von Abwasser aus der Olivenölproduktion auf Böden - Eine Screening studie

Olivenplantagen sind von großer Bedeutung für die Israelische und Palestinensische Agrarwirtschaft. Bei der continuierlichen 3-Phasen-Extraktion wird der Olivenpresskuchen mit Wasser versetzt. Nach Abtrennung des Öls fallen große Mengen Abwasser an. Es ist stark sauer, besitzt eine hohe Konzentration an organischen Stoffen und ist aufgrund toxischer Effekte durch überwiegend phenolische Verbindungen nur schwer mikrobiologisch abbaubar. Augrund dieser Eigenschaften kann es sich negative auf den wasseraufbereitenden Vorgang in Kläranlagen auswirken. Alternative Entsorgungsmethoden sind kaum vorhanden, weshalb es oft zu einer unkontrollierten Entsorgung des Abwassers kommt. Wir untersuchten verschiedenen Böden im Westjordanland und Israel, die in der Vergangenheit unkontrolliert mit Abwasser aus der Olivenölproduktion versetzt wurden in einer Screening Studie. Alle contaminierten Böden enthielten signifant mehr Nährstoffe, wie z.B. Chlorid, Kalium, organischen Kohlenstoff und Stickstoff. Allerdings waren die Mehrzahl der contaminierten Proben hydrophober als vergleichbare unkontaminierte Proben. Dies konnte durch Kontaktwinkelmessungen und die Bestimmung der Water Drop Penetration Time gezeigt werden. Vielversprechend wäre es, das Abwasser als Dünger einzusetzen und gleichzeitig hydrophobisierenden Auswirkungen zu reduzieren

Biological Surface Coating and Molting Inhibition as Mechanisms of TiO2 Nanoparticle Toxicity in Daphnia magna

The production and use of nanoparticles (NP) has steadily increased within the last decade; however, knowledge about risks of NP to human health and ecosystems is still scarce. Common knowledge concerning NP effects on freshwater organisms is largely limited to standard short-term (≤48 h) toxicity tests, which lack both NP fate characterization and an understanding of the mechanisms underlying toxicity. Employing slightly longer exposure times (72 to 96 h), we found that suspensions of nanosized (∼100 nm initial mean diameter) titanium dioxide (nTiO2) led to toxicity in Daphnia magna at nominal concentrations of 3.8 (72-h EC50) and 0.73 mg/L (96-h EC50). However, nTiO2 disappeared quickly from the ISO-medium water phase, resulting in toxicity levels as low as 0.24 mg/L (96-h EC50) based on measured concentrations. Moreover, we showed that nTiO2 (∼100 nm) is significantly more toxic than non-nanosized TiO2 (∼200 nm) prepared from the same stock suspension. Most importantly, we hypothesized a mechanistic chain of events for nTiO2 toxicity in D. magna that involves the coating of the organism surface with nTiO2 combined with a molting disruption. Neonate D. magna (≤6 h) exposed to 2 mg/L nTiO2 exhibited a “biological surface coating” that disappeared within 36 h, during which the first molting was successfully managed by 100% of the exposed organisms. Continued exposure up to 96 h led to a renewed formation of the surface coating and significantly reduced the molting rate to 10%, resulting in 90% mortality. Because coating of aquatic organisms by manmade NP might be ubiquitous in nature, this form of physical NP toxicity might result in widespread negative impacts on environmental health

Historical Irrigated Meadows at the River Queich, Rhineland-Palatinate

For centuries the meadows at the river Queich in southern Rhineland-Palatinate were irrigated to enhance the quantity and quality of hay. With the introduction of fertili-zers irrigation was stopped in most areas but partly reactivated within the last few years. Today we find a small-scaled mosaic of (non-) irrigated and (un-) fertilized meadows. The Institute for Environmental Sciences Landau at the University of Koblenz - Landau conducts interdisciplinary research on the meadows to investigate the effects of irrigation and the interactions between the involved terrestrial and aquatic systems

Hypertonic stress induced changes of Pseudomonas fluorescens adhesion towards soil minerals studied by AFM

Studying bacterial adhesion to mineral surfaces is crucial for understanding soil properties. Recent research suggests that minimal coverage of sand particles with cell fragments significantly reduces soil wettability. Using atomic force microscopy (AFM), we investigated the influence of hypertonic stress on Pseudomonas fluorescens adhesion to four different minerals in water. These findings were compared with theoretical XDLVO predictions. To make adhesion force measurements comparable for irregularly shaped particles, we normalized adhesion forces by the respective cell-mineral contact area. Our study revealed an inverse relationship between wettability and the surface-organic carbon content of the minerals. This relationship was evident in the increased adhesion of cells to minerals with decreasing wettability. This phenomenon was attributed to hydrophobic interactions, which appeared to be predominant in all cell–mineral interaction scenarios alongside with hydrogen bonding. Moreover, while montmorillonite and goethite exhibited stronger adhesion to stressed cells, presumably due to enhanced hydrophobic interactions, kaolinite showed an unexpected trend of weaker adhesion to stressed cells. Surprisingly, the adhesion of quartz remained independent of cell stress level. Discrepancies between measured cell–mineral interactions and those calculated by XDLVO, assuming an idealized sphere-plane geometry, helped us interpret the chemical heterogeneity arising from differently exposed edges and planes of minerals. Our results suggest that bacteria may have a significant impact on soil wettability under changing moisture condition

Interactions of Dissolved Organic Matter with Natural and Engineered Inorganic Colloids: A Review

This contribution critically reviews the state of knowledge on interactions of natural colloids and engineered nanoparticles with natural dissolved organic materials (DOM). These interactions determine the behavior and impact of colloids in natural system. Humic substances, polysaccharides, and proteins present in natural waters adsorb onto the surface of most colloids. We outline major adsorption mechanisms and structures of adsorption layers reported in the literature and discuss their generality on the basis of particle type, DOM type, and media composition. Advanced characterization methods of both DOM and colloids are needed to address insufficiently understood aspects as DOM fractionation upon adsorption, adsorption reversibility, and effect of capping agent. Precise knowledge on adsorption layer helps in predicting the colloidal stability of the sorbent. While humic substances tend to decrease aggregation and deposition through electrostatic and steric effects, bridging-flocculation can occur in the presence of multivalent cations. In the presence of DOM, aggregation may become reversible and aggregate structure dynamic. Nonetheless, the role of shear forces is still poorly understood. If traditional approaches based on the DLVO-theory can be useful in specific cases, quantitative aggregation models taking into account DOM dynamics, bridging, and disaggregation are needed for a comprehensive modeling of colloids stability in natural media

HDC-UVD-ICP-MS chromatograms of sunscreens extracts.

<p>HDC chromatograms of the colloids extracted from S1 (a and b) and S2 (c, d, and e). a and c: Titanium signal (three isotopes); b and e: UV-signal (absorption wavelength: 200 nm); d: Zinc signal (three isotopes). The time delay between the UVD and the ICP-MS detector was around 4 s.</p

Eluent composition effect.

<p>Retention factors of polystyrene standards measured using HDC in three different eluents (column type 2, three replicates).</p

Effective diameters of silver nanoparticles in synthetic surface water.

<p>Estimated effective diameter using HDC-ICP-MS of citrate-stabilised silver nanoparticles (nominal diameter 40 nm) in different media: MQW and MSW containing X mg L⁻¹ of humic acid (HAX) after three hours of incubation at room temperature. The error bars represent the confidence intervals at 95% calculated using three measurements.</p