Diffusivity and enzymatic activity control the exchange of carbonyl sulfide (COS) between soils and the atmosphere

Carbonylsulfid (COS) ist eines der stabilsten reduzierten schwefelhaltigen Spurengase in der Atmosphäre. In der gut durchmischten Troposphäre bewegt sich seine Konzentration um 500 ppt. COS spielt eine wichtige Rolle in der Produktion von stratosphärischem Aerosol und im Ozon Zyklus. Dieses Spurengas hat eine Vielfalt an natürlichen und anthropogenen Quellen, denen gleichstarke Senken, darunter die dominanten wie Vegetation und Boden, gegenüber stehen. Die Stärke der Senken ist trotz langjähriger Forschungen immer noch Gegenstand der Diskussionen. Daher ist es wichtig die kontrollierenden Parameter zu charakterisieren. Alle Austauschmessungen vor 1990 vermuteten Böden als Quelle von COS, was aber durch Castro and Galloway (1991) klar widerlegt wurde. Heute werden Böden in Ergänzung zur Vegetation grundsätzlich als Senke betrachtet. Vor diesem Hintergrund wurden Bodenproben auf den Austausch von Carbonylsulfid mit der Atmosphäre unter verschiedenen Umgebungsbedingungen untersucht. Drei Ackerböden aus Deutschland, China und Finnland und zwei Waldböden aus Sibirien und Surinam konnten parametrisiert werden in Relation zur atmosphärischen Umgebungskonzentration, Temperatur und Bodenfeuchte (WC). Neben Umgebungskonzentration und Bodenfeuchte, scheinen Bodenstruktur und enzymatische Aktivität die Richtung und Größe des Austauschflusses zu kontrollieren. Die übereinstimmenden Optima für boreale Böden in Relation zum wassergefüllten Porenvolumen des Bodens (WFPS) und die Linearität zwischen Depositionsgeschwindigkeit (Vd) und Bulk density lassen auf eine Dominanz der Abhängigkeit der COS-Aufnahme von der durch WFPS bestimmten Diffusionsfähigkeit schließen. WFPS ist abhängig von WC, Bodenstruktur und Bodenporosität. In Ergänzung zu diesen eher physikalischen Parametern konnte die Carboanhydrase (CA) als kontrollierendes Enzym in Böden identifiziert werden. Erste Versuche zur direkten Bestimmung der CA in den untersuchten Böden erlaubten eine erste, aber noch sehr ungenaue Abschätzung der Enzymaktivität.

Polycyclic aromatic hydrocarbons (PAHs) in river bank soils

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous and found in the atmosphere, aquatic environment, sediments and soils. For environmental risk assessments and the allocation of the polluter it is important to know the PAH sources. PAH contamination sites are usually the result of anthropogenic processes. Three major sources are known: i) petroleum, including crude oil and its refined products and coals (petrogenic PAHs), ii) burning of organic matter (pyrogenic PAHs) and iii) transformation products of natural organic precursors present in the environment (diagenetic processes). In one case elevated PAH concentrations were found in river bank soils when building a retention area along the Mosel River. The source of the PAHs in this area was unclear and required the investigation of possible sources. To evaluate the PAH distribution along the Mosel River, a section of ~ 160 km along the river and a short section along the Saar River were investigated within this study. Concentrations of the Σ16 EPA PAHs were as high as 81 mg kg-1 dry weight (dw). Additionally, coal particles were identified in some soils, which originated from mining activities in the Saarland region. PAH distribution patterns of the 16 EPA PAHs suggest a mainly pyrogenic origin and in some cases a mixture of pyrogenic and petrogenic origin. For a comprehensive investigation five sampling sites were selected. Two sites were located before the confluence of the Mosel and Saar River, one site at the confluence and two sites after the confluence. The examination included typical forensic methods such as PAH distribution patterns of 45 PAHs (including alkylated PAHs), calculation of PAH ratios, determination of PAH alkyl homologues, n-alkanes, principal component analysis (PCA) and coal petrography. The results revealed a mainly pyrogenic source at sampling sites before the confluence of the two rivers. At and after the confluence, a mixture of pyrogenic and petrogenic inputs were present. With the help of coal petrography, coal derived particles could be identified in these soils. Therefore, coal was suggested to be the petrogenic source. It could be shown that sites with diffuse sources of contaminants, like the bank soils of the Mosel River, are difficult to characterize. As previously mentioned for detailed source identifications, the use of various forensic methods is essential. Determination of PAH alkyl homologue series, biomarkers and isotopes are often recommended. Source identification was evaluated using three different methods (i.e. PAH distribution patterns of an extended PAH spectrum, PAH ratios and analyses of n-alkanes). It was assessed if these methods were sufficient for the initial steps in identifying sources of PAHs in selected samples, and if they could be used for decision-making purposes. Point- and non-point sources were identified by applying the three methods and it could be shown that these relatively simple methods are sufficient in determining the primary source. In a last step of this study two soils (one before the confluence of the Mosel and Saar rivers and one after the confluence), and one sediment of the Mosel River were evaluated by investigating the mutagenic potential of the soils and the sediment with a fluctuation version of the Ames-test. The study showed that coal bearing soils at the Mosel River do not exhibit a greater mutagenic potential than other soils or sediments without coal particles.