Résultat de la recherche
Intrinsic biodegradation potential of aromatic hydrocarbons in an alluvial aquifer - Potentials and limits of signature metabolite analysis and two stable isotope-based techniques
Three independent techniques were used to assess the biodegradation of monoaromatic hydrocarbons and low-molecular weight polyaromatic hydrocarbons in the alluvial aquifer at the site of a former cokery (Flémalle, Belgium).
Firstly, a stable carbon isotope-based field method allowed quantifying biodegradation of monoaromatic compounds in situ and confirmed the degradation of naphthalene. No evidence could be deduced from stable isotope shifts for the intrinsic biodegradation of larger molecules such as methylnaphthalenes or acenaphthene. Secondly, using signature metabolite analysis, various intermediates of the anaerobic degradation of (poly-) aromatic and heterocyclic compounds were identified. The discovery of a novel metabolite of acenaphthene in groundwater samples permitted deeper insights into the anaerobic biodegradation of almost persistent environmental contaminants. A third method, microcosm incubations with 13C-labeled compounds under in situ-like conditions, complemented techniques one and two by providing quantitative information on contaminant biodegradation independent of molecule size and sorption properties. Thanks to stable isotope labels, the sensitivity of this method was much higher compared to classical microcosm studies. The 13C-microcosm approach allowed the determination of first-order rate constants for 13C-labeled benzene, naphthalene, or acenaphthene even in cases when degradation activities were only small. The plausibility of the third method was checked by comparing 13C-microcosm-derived rates to field-derived rates of the first approach. Further advantage of the use of 13C-labels in microcosms is that novel metabolites can be linked more easily to specific mother compounds even in complex systems. This was achieved using alluvial sediments where 13C-acenaphthyl methylsuccinate was identified as transformation product of the anaerobic degradation of acenaphthene.
Deposition, persistence and turnover of pollutants: First results from the EU project AquaTerra for selected river basins and aquifers
Deposition, turnover and movement of persistent organic pollutants (POP) were investigated in the EU integrated project “AquaTerra”, which is among the first funded environmental projects within the 6th Framework Program by the European Commission. Project work integrates across various disciplines that range from biogeochemistry, environmental engineering, computer modelling and chemistry to socio-economic sciences. Field study areas are the river basins of the Ebro, the Meuse, the Elbe and the Danube as well as the 3-km2 French catchment of the Brévilles Spring. Within the first 2 years of the project more than 1700 samples of atmospherically deposited particles, sediments, and water have been collected in the above-mentioned systems. Results show clear spatial patterns of deposition of polyaromatic hydrocarbons (PAHs) with the highest rates in the Meuse Basin. For local inputs, in the Brévilles sandy aquifer, the contamination of the groundwater by the pesticides atrazine (AT) and deethylatrazine did not decrease even 5 years after their agricultural inputs were stopped. On the other hand, herbicides such as mecroprop (MCPP), and PAHs, were at least partially degraded microbiologically in laboratory studies with soils and aquifer material from selected sites. For sediment transport of contaminants, new flood sampling techniques revealed highest deposition rates of β-hexachlorocyclohexane (β−HCH) in river sediments at hotspot areas on the Mulde River in the Bitterfeld region (Elbe Basin, Germany). These selected preliminary results of AquaTerra help to improve fundamental understanding of persistent organic pollutants (POP) in the environment.
Bacterial contaminant degradation in the environment - a quantitative approach based on stable isotope analysis
Quantification of biodegradation for o-xylene and naphthalene using first order decay models, Michaelis–Menten kinetics and stable carbon isotopes
At a former wood preservation plant severely contaminated with coal tar oil, in situ bulk attenuation and biodegradation rate constants for several monoaromatic (BTEX) and polyaromatic hydrocarbons (PAH) were determined using (1) classical first order decay models, (2) Michaelis–Menten degradation kinetics (MM), and (3) stable carbon isotopes, for o-xylene and naphthalene. The first order bulk attenuation rate constant for o-xylene was calculated to be 0.0025 d−1 and a novel stable isotope-based first order model, which also accounted for the respective redox conditions, resulted in a slightly smaller biodegradation rate constant of 0.0019 d−1. Based on MM-kinetics, the o-xylene concentration decreased with a maximum rate of kmax=0.1 μg/L/d. The bulk attenuation rate constant of naphthalene retrieved from the classical first order decay model was 0.0038 d− 1. The stable isotope-based biodegradation rate constant of 0.0027 d−1 was smaller in the reduced zone, while residual naphthalene in the oxic part of the plume further downgradient was degraded at a higher rate of 0.0038 d−1. With MM-kinetics a maximum degradation rate of kmax=12 μg/L/d was determined. Although best fits were obtained by MM-kinetics, we consider the carbon stable isotope-based approach more appropriate as it is specific for biodegradation (not overall attenuation) and at the same time accounts for the dominant electron-accepting process. For o-xylene a field based isotope enrichment factor εfield of −1.4 could be determined using the Rayleigh model, which closely matched values from laboratory studies of o-xylene degradation under sulfate-reducing conditions.
Quantification of biodegradation for various organic compounds using first-order, Michaelis-Menten kinetics and stable carbon isotopes
Biodegradation of organic pollutants and molecular identification of responsible microorganisms in several European river basins
Evidence for in situ degradation of mono-and polyaromatic hydrocarbons in alluvial sediments based on microcosm experiments with 13C-labeled contaminants
A microcosm study was conducted to investigate the degradation of mono- and polyaromatic hydrocarbons under in situ-like conditions using alluvial sediments from the site of a former cokery. Benzene, naphthalene, or acenaphthene were added to the sediments as C-13-labeled substrates. Based on the evolution of C-13-CO2 determined by gas chromatography isotope-ratio mass spectrometry (GC-IRMS) it was possible to prove mineralization of the compound of interest in the presence of other unknown organic substances of the sediment material. This new approach was suitable to give evidence for the intrinsic biodegradation of benzene, naphthalene, and acenaphthene under oxic and also under anoxic conditions, due to the high sensitivity and reproducibility of C-13/C-12 stable isotope analysis. This semi-quantitative method can be used to screen for biodegradation of any slowly degrading, strongly sorbing compound in long-term experiments. (c) 2007 Elsevier Ltd. All rights reserved.
Evidence for in situ degradation of mono-and polyaromatic hydrocarbons in alluvial sediments based on microcosm experiments with 13C-labeled contaminants
A microcosm study was conducted to investigate the degradation of mono- and polyaromatic hydrocarbons under in situ-like conditions using alluvial sediments from the site of a former cokery. Benzene, naphthalene, or acenaphthene were added to the sediments as 13C-labeled substrates. Based on the evolution of 13C-CO2 determined by gas chromatography isotope-ratio mass spectrometry (GC-IRMS) it was possible to prove mineralization of the compound of interest in the presence of other unknown organic substances of the sediment material. This new approach was suitable to give evidence for the intrinsic biodegradation of benzene, naphthalene, and acenaphthene under oxic and also under anoxic conditions, due to the high sensitivity and reproducibility of 13C/12C stable isotope analysis. This semi-quantitative method can be used to screen for biodegradation of any slowly degrading, strongly sorbing compound in long-term experiments.
A method based on 13C-labeled substrates was developed to determine the intrinsic biodegradation potential of aromatic pollutants under oxic and under anoxic conditions.