Report and evaluation of the redox potential measurements during the Intercomparison Exercise of ReCosy

The redox potential measurements were performed in systems with simple organics, near-natural, and natural ground- and porewater samples (NAT) and in microbial systems (MIC). As an example the results of the natural ground- and porewater samples (NAT), which were obtained by 10 to 19 groups or redox sensors, were interpreted in detail. Nine groups or redox sensors, including FZD, showed similar results. In most cases the measurements varied insignificantly. In some samples a difference of approximately 100 mV between the lowest and the highest value was determined. Accepting the measurement ranges, the results will give a good overview of the redox conditions in the near-natural, and natural ground- and porewater samples. However, in special cases further studies are needed for the interpretation of the measured redox potential, e.g. Extended X-ray Absorption Fine Structure (EXAFS), TEM in combination with Electron Energy Loss Spectroscopy (EELS) and Confocal Laser Scanning Microscopy (CLSM)/Laser Induced Fluorescence Spectroscopy (LIFS).
Unfortunately, only one of the microbial system samples was studied. The results showed clearly that redox potential measurements of microbial systems need much more time for getting a stable signal due to microbially influenced processes.