Environmental Isotope Chemistry and Microbiology

Team members: Kleanthi Kourtaki, Anna Röhnelt, Philipp Martin, Dr. Daniel Buchner

Pollution of soils, surface waters and groundwater with organic contaminants is a major challenge of our time. The fate of contaminants in the environment is determined by a complex interplay of transport, sorption and abiotic or biotic transformation reactions. Thus, understanding the molecular mechanisms and effect of these processes on contaminant fate allows to develop appropriate remediation techniques and to predict the risk of compound introduction into the environment.

Analysis of compound isotope ratios using compound specific (stable) isotope analysis (CSIA) provides a unique tool to assess transformation reactions and to discern between processes determining contaminant removal. Compound isotope ratios of different elements (e.g. C, N, O) can be measured from complex sample matrices by gas chromatography (GC) coupled to isotope ratio mass spectrometry (IRMS). The coupling of IRMS with liquid chromatography (LC) expands the range of CSIA applications to highly polar compounds, but is restricted to analysis of C isotope ratios so far. For halogenated solvents and pesticides, isotope ratios of Cl and Br can also be determined by conventional quadrupole mass spectrometers (e.g. GC-(q)MS).

During transformation reactions, CSIA enables to measure shifts in compound isotope ratios that occur due to different chemical reaction rates between molecules containing the light or the heavy isotope at the reactive position (kinetic isotope effect). These shifts can be related to the prevailing reaction mechanism which allows to identify transformation pathways of organic contaminants in the environment. Simultaneous analysis of isotopic shifts of two different elements (e.g. C and Cl) and constraining the data in 2-D isotope plots aids the identification of different reaction mechanisms.

On the other hand, sorption or contaminant transport by diffusion show only minor kinetic isotope effects and may therefore diminish the kinetic isotope effect of transformation, if these processes limit degradation rates. This enables to evaluate potential bottlenecks during contaminant degradation in the environment by incorporating CSIA in well-designed experimental setups.

Ongoing research projects

Within the environmental isotope chemistry and microbiology group, we combine abiotic and biotic transformation experiments with CSIA and sorption experiments to gain process-based understanding on the environmental fate of different organic contaminant classes. Currently, our research focuses on:

sorption and abiotic degradation (Mn-catalyzed, photodegradation) of organophosphonate chelating agents (LC-IRMS)
physiology and bioavailability restrictions of microbial degradation of glyphosate and AMPA (LC-IRMS / GC-IRMS)
microbial transformation of chlorinated phenols and chlorinated ethenes (GC-IRMS / GC-MS)

In addition, in collaboration with the Geomicrobiology - Microbial Ecology group we apply molecular biological techniques (e.g. quantitative PCR of functional genes and mRNA) to assess molecular and physiological properties of bacteria and potential correlations thereof with the magnitude of measured isotope effects.