Interaction of iron species and colloids with dissolved organic matter (DOM), dissolved organic sulfur compounds (DOSC) and low-molecular weight acids (LMWA)
Final Report Abstract
Different LC-ESI-MS-MS methods have been applied successfully to identify and quantify various acidic microbial degradation products both in batch experiments and in field samples. The batch experiments demonstrated the complete toluene degradation and formation of the metabolite benzylsuccinate in the presence of other contaminants. The low concentration of benzylsuccinate in comparison to the amount of degraded toluene indicates that the metabolite is a typical intermediate which does not accumulate considerably. This could be verified with field samples in which other metabolites accumulated much higher than benzylsuccinate. Furthermore, it could be shown that even high concentrations of other contaminants had no toxic effects on the microbial activity. The finding of methylbenzylsuccinate demonstrates that also co-metabolic degradation processes occur. The influence of transport parameters on the degradation will be investigated in a 2-dimensional tank system, which is just under construction. Different anaerobic degradation pathways have been indicated in field samples by detecting typical anaerobic metabolites. In addition to metabolites of aromatic contaminants, like naphthyl-2-methyl-succinate, benzylsuccinate or acenaphthene-5-carboxylic, degradation products of heterocyclic compounds like 2-carboxybenzothiophene and 2-carboxybenzofurane could be identified. The degradation of heterocyclic contaminants is an important issue because they are often toxic and are regarded as relatively persistent compounds. The concentration profiles of metabolites comprise those of the original contaminants very well in samples of a high-resolution multi-level well from a contaminated aquifer. The steep gradients of the contaminants at the plume fringes could be well reproduced by either metabolites or by high microbial biomass. The various contaminant/metabolite pairs reveal their potential as indicators also of spatially highly resolved biodegradation activity in the field. Nearly no metabolites could be found in the samples of the downstream regions. This indicates that there is no relevant transport of the metabolites in the aquifer although they should be of higher mobility due to their more polar character compared to the parent compounds. For this reason the role of the metabolites as electron donors in other zones of the aquifer may be negligible for the sites considered so far. The analysis of fulvic acid fractions of a contaminated aquifer showed intensive signals of acidic degradafion products in the sample from the contaminant plume. An estimation shows that these compounds can make up a significant fraction of dissolved organic matter (DOM) in contaminated regions. Therefore it is expected that the effects of DOM on redox processes in the aquifer can be considerably influenced by acidic degradation products. Summarized we hypothesise that both components of DOM and of acidic degradation products affect iron based redox processes due to interaction of acidic (chelating) groups with iron species and minerals resulting in changed bioavailability or redox properties of iron species. The contribution of components of DOM and acidic degradation products may be quite different and have to be identified for a further understanding of the effects of DOM on iron based redox processes.
Publications
- Microbial degradation products of organic contaminants in anoxic aquifers: batch experiments with an iron reducing bacterial strain. Intern. Workshop on Biogeochemical Processes in Groundwater Systems, GSF, Munich, Germany, September 10-11, 2007
C. Jobelius, F.H. Frimmel, C. Zwiener
- Identifizierung von polaren Metaboliten in Huminstoffisolaten mit tandem-massenspektrometrischen Experimenten. Jahrestagung der Wasserchemischen Gesellschaft, Fachgruppe der GDCh, Trier, April 28 - 30, 2008
C. Jobelius, F.H. Frimmel, C. Zwiener
- Occurrence of metabolites and cometabolites during the anaerobic degradation of toluene in the presence of cosubstrates: Results from batch experiments and field samples. AXIOM-VIBE-eTRAP-HIGRADE Workshop "Electron transfer processes at biogeochemical gradients", Leipzig, March 4 - 7, 2008
C. Jobelius, F.H. Frimmel, C. Zwiener
