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1.
A study of ether-linked moieties in macromolecular bound residues of polycyclic aromatic hydrocarbons (PAH) generated in bioremediation experiments was performed using high temperature hydrolysis degradation with subsequent analysis of the products by GC-MS. This hydrolysis reaction was specifically designed to cleave ether bonds including relatively stable diarylether structures. Among the reaction products, aromatic alcohols representing typical microbiologically derived metabolites of PAH were found in addition to natural compounds. Thus, parts of the bound residues appeared to be linked within the macromolecular material by ether bonds. Model experiments with an oxidoreductase enzyme and aromatic alcohols indicate the formation of these ether bonds to be an enzyme-catalysed process.  相似文献   
2.
Chemical degradations of coal resins, coal asphaltenes and coal residues have been performed with selective, non-oxidative reagents. The coal comprise samples a rank interval 0.30–1.21 %Rm. Degraded low-molecular-weight compounds were analyzed by GC-MS. The distributions of pentacyclic terpanes, isoprenoids, n-alkanes, acids and alcohols obtained as degradation products illustrate a considerable variability between the macromolecular coal fractions. A structural study on the molecular level of the degraded compounds from coal resins and coal asphaltenes show their potential to generate hydrocarbons during coalification process.  相似文献   
3.
Reactive tracer tests are performed to derive flow, transport and in situ biodegradation parameters. This paper describes the 3D simulation of a reactive tracer test using the transition probability geostatistical approach. Fifty different equally probable aquifer realizations were generated based on the geological information of 107 boreholes in an area of 62,500 m2. One realization was chosen for the reactive transport simulation based on the results of groundwater flow modeling and on particle tracking calculations for the site. Field velocities at the site vary between 0.4 and 3 m/d. The transport of the reactive tracers deuterium ring labeled toluene-d5 and fully deuterated toluene-d8 was simulated and first-order biodegradation rates of 0.017 d−1 for toluene-d5 and 0.012 d−1 for toluene-d8 were determined.  相似文献   
4.
Structural studies of a sulphur-rich kerogen and macromolecular oil fractions from the Monterey Formation were performed by selective sequential chemical degradation. The method provides low-molecular weight compounds as former building blocks of the network which allow detailed analyses on a molecular level. The degradation sequence is based on three subsequently performed reactions—a selective cleavage of sulphur bonds in the first step carried out with Ni(0)cene/LiAlD4, an ether and ester bond cleavage (BCl3), and an oxidation of aromatic entities by ruthenium tetroxide as a final step. Each step of this sequence afforded a considerable amount of low-molecular weight material which was separated chromatographically and studied by GC and GC/MS, while the high-molecular weight or insoluble fractions were subjected to the next reaction step.The chemical degradation products—hydrocarbons and carboxylic acids—are discussed in terms of incorporation into the macromolecular structure, distribution of heteroatomic bridges and the genetic relationships between the different macromolecular crude oil fractions and kerogen.Labelling experiments with deuterium provided evidence for a simultaneous linkage by oxygen and sulphur functionalities or by aromatic units and sulphur bonds of cross-linking macromolecular network constituents.The determination of sulphur positions in the macromolecule suggests early diagenetic sulphur incorporation into the biological precursor compounds and subsequent formation of a cross-linked network.  相似文献   
5.
In January 1989 we observed submarine eruptions on the summit of Macdonald volcano during a French-German diving programme with the IFREMER submersible Cyana. Gas-streaming of large amounts of CH4, CO2 and SO2 from summit vents, inferred from water column anomalies and observed by submersible, was accompanied on the sea surface by steam bursts, turbulence, red-glowing gases, and black bubbles comprising volcanic ash, sulphur and sulphides. Chloride depletion of water sampled on the floor of an actively degassing summit crater suggests either boiling and phase separation or additions of magmatic water vapour. Submersible observations, in-situ sampling and shipboard geophysical and hydrographic measurements show that the hydrothermal system of this hotspot volcano is distinguished by the influence of magmatic gases released from its shallow summit.  相似文献   
6.
We determined the stable carbon and hydrogen isotope fractionation factors for methane oxidation under oxic conditions using strains with known degradation pathways. The aerobic oxidation of methane can be initiated by two different forms of enzymes known as methane monooxygenases (MMO). The expression of these enzymes is type-specific and dependent upon the adjusted copper concentration in the medium (or environment). In this study, the expression of either the soluble MMO or the particulate MMO was supported by adjusting the copper concentrations in the growth medium. Taxonomically different aerobic methanotrophic strains, mainly belonging to the alpha- and gamma- classes of Proteobacteria, produced methane isotope enrichment factors (εbulk) ranging from −14.8 to −27.9‰ for carbon, and from −110.0 to −231.5‰ for hydrogen. The ratio of hydrogen versus carbon discrimination (Λ = (αH−1 − 1)/(αC−1 − 1) ≈ Δ(δ2H)/Δ(δ13C)) were similar for all tested cultures, and are also identical to values calculated from previously published enrichment factors for aerobic and anaerobic methane degradation. In contrast, Λ-values for the abiotic oxidation of methane with OH radicals (this process is considered as the main removal process for methane from the atmosphere) were significantly higher than the values derived from biotic oxidation. Due to the low variability of microbial methane isotope fractionation patterns, we propose that combined carbon and hydrogen isotope fractionation analyses can be used to monitor and assess the occurrence of microbial methane oxidation in marine or terrestrial environments. However, it is not possible to distinguish distinct aerobic or anaerobic methane-oxidation pathways by this approach.  相似文献   
7.
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8.
Compound specific stable isotope analysis (CSIA) has been established as a viable tool for proving, characterizing and assessing degradation of organic pollutants within contaminated aquifers. The fractionation of stable isotopes during contaminant degradation leads to observable shifts in stable isotope ratios which can serve as an indicator for in situ pollutant degradation and allow for a quantitative assessment by means of the so-called Rayleigh (distillation) equation.This review highlights the recent developments of the Rayleigh equation approach for quantifying in situ degradation of organic pollutants in contaminated aquifers. The advantages and limitations of the Rayleigh equation approach are discussed and suggestions for improvements are given. Concepts are provided to estimate the uncertainty due to errors or variability of input parameters and how to deal with such uncertainty. Moreover, the applicability of the Rayleigh equation approach is evaluated regarding the heterogeneity and complexity of groundwater systems. For such systems, the review discusses the relevance of non-destructive processes, which affect the concentration (e.g., dispersive mixing) and potentially also the stable isotope ratio of contaminants (e.g., sorption, volatilization), and the resulting implications for the Rayleigh equation approach.  相似文献   
9.
Soil organic matter (SOM) is important for soil fertility and for the global C cycle. Previous studies have shown that during SOM formation no new compound classes are formed and that it consists basically of plant- and microorganism-derived materials. However, little data on the contribution from microbial sources are available. Therefore, we investigated previously in a model study the fate of C from 13C-labelled Gram-negative bacteria in soil (Kindler, R., Miltner, A. Richnow, H.H., Kästner, M., 2006. Fate of gram negative bacterial biomass in soil – mineralization and contribution to SOM. Soil Biology and Biochemistry 38, 2860–2870) and showed that 44% of the bulk 13C remained in the soil. Here we present the corresponding data on the fate of amino acids hydrolysed from proteins, which are the most abundant components of microbial biomass. After 224 days incubation, the label in the total amino acids in the soil amended with 13C-labelled cells decreased only to >95%. The total amino acids therefore clearly showed a lower turnover than the bulk 13C and a surprisingly stable concentration. Proteins therefore have to be considered as being stabilised in soil in dead, non-extractable biomass or cell fragments by known general stabilisation mechanisms. The label in the amino acids in a fraction highly enriched in living microbial biomass decreased to a greater extent, i.e. to 25% of the initially added amount. The amino acids removed from this fraction were redistributed via the microbial food web to non-living SOM. All amino acids in the microbial biomass were degraded at similar rates without a change in isotopic signature. The nuclear magnetic resonance (NMR) spectra of the soils were very similar and indicate that the residues of the degraded microbial biomass were very similar to those of the SOM and are a significant source for the formation of the SOM.  相似文献   
10.
Radiolabelled assays and compound-specific stable isotope analysis (CSIA) were used to assess methyl tert-butyl ether (MTBE) biodegradation in an unleaded fuel plume in a UK chalk aquifer, both in the field and in laboratory microcosm experiments. The 14C-MTBE radiorespirometry studies demonstrated widespread potential for aerobic and anaerobic MTBE biodegradation in the aquifer. However, δ13C compositions of MTBE in groundwater samples from the plume showed no significant 13C enrichment that would indicate MTBE biodegradation at the field scale. Carbon isotope enrichment during MTBE biodegradation was assessed in the microcosms when dissolved O2 was not limiting, compared with low in situ concentrations (2 mg/L) in the aquifer, and in the absence of O2. The microcosm experiments showed ubiquitous potential for aerobic MTBE biodegradation in the aquifer within hundreds of days. Aerobic MTBE biodegradation in the microcosms produced an enrichment of 7‰ in the MTBE δ13C composition and an isotope enrichment factor (ε) of −1.53‰ when dissolved O2 was not limiting. However, for the low dissolved O2 concentration of up to 2 mg/L that characterizes most of the MTBE plume fringe, aerobic MTBE biodegradation produced an enrichment of 0.5-0.7‰, corresponding to an ε value of −0.22‰ to −0.24‰. No anaerobic MTBE biodegradation occurred under these experimental conditions. These results suggest the existence of a complex MTBE-biodegrading community in the aquifer, which may consist of different aerobic species competing for MTBE and dissolved O2. Under low O2 conditions, the lower fractionating species have been shown to govern overall MTBE C-isotope fractionation during biodegradation, confirming the results of previous laboratory experiments mixing pure cultures. This implies that significant aerobic MTBE biodegradation could occur under the low dissolved O2 concentration that typifies the reactive fringe zone of MTBE plumes, without producing detectable changes in the MTBE δ13C composition. This observed insensitivity of C isotope enrichment to MTBE biodegradation could lead to significant underestimation of aerobic MTBE biodegradation at field scale, with an unnecessarily pessimistic performance assessment for natural attenuation. Site-specific C isotope enrichment factors are, therefore, required to reliably quantify MTBE biodegradation, which may limit CSIA as a tool for the in situ assessment of MTBE biodegradation in groundwater using only C isotopes.  相似文献   
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