Our research interests cover a wide range of areas in molecular environmental sciences including biogeochemical processes in soils and groundwater, reactions and phase transfer processes of pollutants and development and application of in situ methods to characterize and quantify processes in pristine and polluted subsurface environments. As surface mediated processes play a key role in determining the transport and transformation of natural and xenobiotic compounds in the subsurface we are interested in a process-based understanding of the factors that control the formation of reactive surfaces, in particular at minerals, and how such surfaces interact with natural and anthropogenic compounds. To this end our work interfaces aquatic and environmental chemistry with geomicrobiology and geochemistry. For our laboratory and field studies we apply a wide array of modern instrumentation and techniques, including compound specific stable isotope analysis (CSIA) as well as Mössbauer spectroscopy.

Sketch illustrating the significance of surface mediated processes for speciation, reactivity, bioavailability, and biodegradation of natural and anthropogenic organic compounds in the subsurface.

The overall objective of our research is to provide through an improved understanding of biogeochemical key processes the scientific basis for assessment, management and remediation options of soil and groundwater environments

We are active in the following fields of research:

Environmental Isotope Chemistry and Microbiology

In environmental sciences, compound specific stable isotope analysis (CSIA) is applied for source identification, detection and quantification of in situ biodegradation and identification of reaction mechanisms or other processes related to isotope fractionation of organic contaminants.

Nowadays online-coupling of chromatographic systems to isotope ratio mass spectrometers (GC-IRMS, LC-IRMS) is well established. This allows analyzing the compound-specific isotope composition of organic analytes with regard to carbon (13C/12C), hydrogen (2H/1H) and nitrogen (15N/14N). Recently developed approaches also enable measuring chlorine isotope ratios (37Cl/35Cl), - a breakthrough for evaluating degradation processes of chlorinated ethenes. The availability of δ37Cl- CSIA will enable us to determine chlorine isotope fractionation factors for microbial dehalogenation processes; where the database is still lacking. Most importantly it will open the enormous prospects of 2-dimensional isotope analysis for process identification for halogenated organic compounds. To evaluate a compound´s transformation processes the kinetic isotope effect(s) (KIE) accompanying (bio)chemical reactions can be used. In general, organic contaminants consist of a mixture of “heavy” and “light” molecules (isotopologues). During the breakdown, typically molecules exhibiting a heavy isotope (e.g. 13C) in the reactive position are discriminated from those exhibiting a light isotope, as a higher activation energy is needed to break the bonds with the heavy isotope. This leads to gradual enrichment of the lighter isotopologues in the product, while the heavier ones remain in the substrate.

Using cultivation-based approaches we investigate pure and mixed cultures of organohalide respiring organisms that utilizes organohalides (e.g. tetrachlorethene) as the terminal electron acceptor to gain energy. In collaboration with the Geomicrobiology - Microbial Ecology group, we use molecular techniques like qPCR, cDNA synthesis or Western blot analysis to investigate the response of the cells to defined growth conditions. These techniques enable us to monitor e.g. total cell numbers, the abundance and transcriptions of specific genes as well as the detection of processed enzymes like reductive dehalogenases (the key enzmyes in organohalide respiration where the carbon-chlorine bond is cleaved).

Combining molecular techniques with 2D isotope analysis will improve our understanding of microbe driven contaminant degradation and therefore the approach of engineered bioremediation using microorganisms to clean up contaminated sites.

Current Projects