| Abstract
| - To evaluate the intrinsic bioremediation potential in ananoxic tar oil-contaminated aquifer at a former gasworkssite, groundwater samples were qualitatively andquantitatively analyzed by compound-specific isotopeanalysis (CSIA) and signature metabolites analysis (SMA).13C/12C fractionation data revealed conclusive evidencefor in situ biodegradation of benzene, toluene, o-xylene,m/p-xylene, naphthalene, and 1-methylnaphthalene. Inlaboratory growth studies, 13C/12C isotope enrichment factorsfor anaerobic degradation of naphthalene (ε = −1.1 ±0.4) and 2-methylnaphthalene (ε = −0.9 ± 0.1) weredetermined with the sulfate-reducing enrichment cultureN47, which was isolated from the investigated test site. Onthe basis of these and other laboratory-derived enrichmentfactors from the literature, in situ biodegradation couldbe quantified for toluene, o-xylene, m/p-xylene, andnaphthalene. Stable carbon isotope fractionation in thefield was also observed for ethylbenzene, 2-methylnaphthalene, and benzothiophene but without providing conclusiveresults. Further evidence for the in situ turnover ofindividual BTEX compounds was provided by the presenceof acetophenone, o-toluic acid, and p-toluic acid, threeintermediates in the anaerobic degradation of ethylbenzene,o-xylene, and p-xylene, respectively. A number ofgroundwater samples also contained naphthyl-2-methylsuccinic acid, a metabolite that is highly specific for theanaerobic degradation of 2-methylnaphthalene. Additionalmetabolites that provided evidence on the anaerobic insitu degradation of naphthalenes were 1-naphthoic acid,2-naphthoic acid, 1,2,3,4-tetrahydronaphthoic acid, and 5,6,7,8-tetrahydronaphthoic acid. 2-Carboxybenzothiophene,5-carboxybenzothiophene, a putative further carboxybenzothiophene isomer, and the reduced derivative dihydrocarboxybenzothiophene indicated the anaerobicconversion of the heterocyclic aromatic hydrocarbonbenzothiophene. The combined application of CSIA andSMA, as two reliable and independent tools to collect directevidence on intrinsic bioremediation, leads to a substantiallyimproved evaluation of natural attenuation in situ.
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