In the last decade, compound-specific stable isotopes analysis of groundwater pollutants became a... more In the last decade, compound-specific stable isotopes analysis of groundwater pollutants became an important tool to identify different sources of the same pollutant and for tracking natural attenuating processes in the sub-surface. It has been shown that trends in the isotopic composition of the target compounds can shed light on in-situ processes that are otherwise difficult to track. Analytical methods
Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) is a common contaminant at explosives production si... more Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) is a common contaminant at explosives production sites. Here, we report on the use of compound-specific isotope analysis of RDX to obtain delta(15)N and delta(18)O enrichment factors during biodegradation in batch cultures. A new preparation method has been developed based on RDX purification using thin-layer chromatography. RDX is then subjected to an elemental analyzer coupled with an isotope-ratio mass spectrometer (EA-IRMS). The precision of the method shows standard deviations of 0.13% per hundred and 1.18% per hundred for delta(15)N and delta(18)O, respectively, whereas the accuracy of the method has been checked routinely, adhering to external standards. The method was applied to RDX samples subjected to biodegradation under aerobic or anaerobic conditions. Enrichment factors under aerobic conditions were -2.1% per hundred and -1.7% per hundred for delta(15)N and delta(18)O, respectively, and under anaerobic conditions, -5.0% per hundred and -5.3% per hundred for delta(15)N and delta(18)O, respectively. The results of this study provide a tool for monitoring natural attenuation of RDX in a contaminated environment.
Compound-specific stable-isotope analysis (CSIA) has greatly facilitated assessment of sources an... more Compound-specific stable-isotope analysis (CSIA) has greatly facilitated assessment of sources and transformation processes of organic pollutants. Multielement isotope analysis is one of the most promising applications of CSIA because it even enables distinction of different transformation pathways. This review introduces the essential features of continuous-flow isotope-ratio mass spectrometry (IRMS) and highlights current challenges in environmental analysis as exemplified for the isotopes of nitrogen, hydrogen, chlorine, and oxygen. Strategies and recent advances to enable isotopic measurements of polar contaminants, for example pesticides or pharmaceuticals, are discussed with special emphasis on possible solutions for analysis of low concentrations of contaminants in environmental matrices. Finally, we discuss different levels of calibration and referencing and point out the urgent need for compound-specific isotope standards for gas chromatography-isotope-ratio mass spectrometry (GC-IRMS) of organic pollutants.
The increasing use of kinetic isotope effects for environmental studies has motivated the develop... more The increasing use of kinetic isotope effects for environmental studies has motivated the development of new compound-specific isotope analysis techniques for emerging pollutants. Recently, high-precision bromine isotope analysis in individual brominated organic compounds was proposed, by the coupling of gas chromatography to a multi-collector inductively coupled plasma mass spectrometer using strontium as an external spike for instrumental bias correction. The present study, for the first time, demonstrates an application of this technique for determining bromine kinetic isotope effects during biological reaction, focusing on the reductive debromination of brominated phenols under anaerobic conditions. Results show bromine isotope enrichment factors (ε) of -0.76 ± 0.08, -0.46 ± 0.19, and -0.20 ± 0.06 ‰ for the debromination of 4-bromophenol, 2,4-dibromophenol, and 2,4,6-tribromophenol, respectively. These values are rather low, yet still high enough to be obtained with satisfying certainty. This further implies that the analytical method may be also appropriate for future environmental applications.
... quantification assessment of in situ RDX biodegradation in the deep unsaturated zone. This wo... more ... quantification assessment of in situ RDX biodegradation in the deep unsaturated zone. This work is dedicated to the memory of Ronit Nativ who ... δ 15 N analysis was performed using a Flash EA 1112 (Thermo Finnigan, Milano, Italy) elemental analyzer (EA) interfaced to a Delta ...
Chlorinated ethenes are prevalent groundwater contaminants. To better constrain (bio)chemical rea... more Chlorinated ethenes are prevalent groundwater contaminants. To better constrain (bio)chemical reaction mechanisms of reductive dechlorination, the position-specificity of reductive trichloroethene (TCE) dehalogenation was investigated. Selective biotransformation reactions (i) of tetrachloroethene (PCE) to TCE in cultures of Desulfitobacterium sp. strain Viet1; and (ii) of TCE to cis-1,2-dichloroethene (cis-DCE) in cultures of Geobacter lovleyi strain SZ were investigated. Compound-average carbon isotope effects were -19.0‰ ± 0.9‰ (PCE) and -12.2‰ ± 1.0‰ (TCE) (95% confidence intervals). Using instrumental advances in chlorine isotope analysis by continuous flow isotope ratio mass spectrometry, compound-average chorine isotope effects were measured for PCE (-5.0‰ ± 0.1‰) and TCE (-3.6‰ ± 0.2‰). In addition, position-specific kinetic chlorine isotope effects were determined from fits of reactant and product isotope ratios. In PCE biodegradation, primary chlorine isotope effects were substantially larger (by -16.3‰ ± 1.4‰ (standard error)) than secondary. In TCE biodegradation, in contrast, the product cis-DCE reflected an average isotope effect of -2.4‰ ± 0.3‰ and the product chloride an isotope effect of -6.5‰ ± 2.5‰, in the original positions of TCE from which the products were formed (95% confidence intervals). A greater difference would be expected for a position-specific reaction (chloride would exclusively reflect a primary isotope effect). These results therefore suggest that both vicinal chlorine substituents of TCE were reactive (intramolecular competition). This finding puts new constraints on mechanistic scenarios and favours either nucleophilic addition by Co(I) or single electron transfer as reductive dehalogenation mechanisms.
In the last decade, compound-specific stable isotopes analysis of groundwater pollutants became a... more In the last decade, compound-specific stable isotopes analysis of groundwater pollutants became an important tool to identify different sources of the same pollutant and for tracking natural attenuating processes in the sub-surface. It has been shown that trends in the isotopic composition of the target compounds can shed light on in-situ processes that are otherwise difficult to track. Analytical methods
Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) is a common contaminant at explosives production si... more Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) is a common contaminant at explosives production sites. Here, we report on the use of compound-specific isotope analysis of RDX to obtain delta(15)N and delta(18)O enrichment factors during biodegradation in batch cultures. A new preparation method has been developed based on RDX purification using thin-layer chromatography. RDX is then subjected to an elemental analyzer coupled with an isotope-ratio mass spectrometer (EA-IRMS). The precision of the method shows standard deviations of 0.13% per hundred and 1.18% per hundred for delta(15)N and delta(18)O, respectively, whereas the accuracy of the method has been checked routinely, adhering to external standards. The method was applied to RDX samples subjected to biodegradation under aerobic or anaerobic conditions. Enrichment factors under aerobic conditions were -2.1% per hundred and -1.7% per hundred for delta(15)N and delta(18)O, respectively, and under anaerobic conditions, -5.0% per hundred and -5.3% per hundred for delta(15)N and delta(18)O, respectively. The results of this study provide a tool for monitoring natural attenuation of RDX in a contaminated environment.
Compound-specific stable-isotope analysis (CSIA) has greatly facilitated assessment of sources an... more Compound-specific stable-isotope analysis (CSIA) has greatly facilitated assessment of sources and transformation processes of organic pollutants. Multielement isotope analysis is one of the most promising applications of CSIA because it even enables distinction of different transformation pathways. This review introduces the essential features of continuous-flow isotope-ratio mass spectrometry (IRMS) and highlights current challenges in environmental analysis as exemplified for the isotopes of nitrogen, hydrogen, chlorine, and oxygen. Strategies and recent advances to enable isotopic measurements of polar contaminants, for example pesticides or pharmaceuticals, are discussed with special emphasis on possible solutions for analysis of low concentrations of contaminants in environmental matrices. Finally, we discuss different levels of calibration and referencing and point out the urgent need for compound-specific isotope standards for gas chromatography-isotope-ratio mass spectrometry (GC-IRMS) of organic pollutants.
The increasing use of kinetic isotope effects for environmental studies has motivated the develop... more The increasing use of kinetic isotope effects for environmental studies has motivated the development of new compound-specific isotope analysis techniques for emerging pollutants. Recently, high-precision bromine isotope analysis in individual brominated organic compounds was proposed, by the coupling of gas chromatography to a multi-collector inductively coupled plasma mass spectrometer using strontium as an external spike for instrumental bias correction. The present study, for the first time, demonstrates an application of this technique for determining bromine kinetic isotope effects during biological reaction, focusing on the reductive debromination of brominated phenols under anaerobic conditions. Results show bromine isotope enrichment factors (ε) of -0.76 ± 0.08, -0.46 ± 0.19, and -0.20 ± 0.06 ‰ for the debromination of 4-bromophenol, 2,4-dibromophenol, and 2,4,6-tribromophenol, respectively. These values are rather low, yet still high enough to be obtained with satisfying certainty. This further implies that the analytical method may be also appropriate for future environmental applications.
... quantification assessment of in situ RDX biodegradation in the deep unsaturated zone. This wo... more ... quantification assessment of in situ RDX biodegradation in the deep unsaturated zone. This work is dedicated to the memory of Ronit Nativ who ... δ 15 N analysis was performed using a Flash EA 1112 (Thermo Finnigan, Milano, Italy) elemental analyzer (EA) interfaced to a Delta ...
Chlorinated ethenes are prevalent groundwater contaminants. To better constrain (bio)chemical rea... more Chlorinated ethenes are prevalent groundwater contaminants. To better constrain (bio)chemical reaction mechanisms of reductive dechlorination, the position-specificity of reductive trichloroethene (TCE) dehalogenation was investigated. Selective biotransformation reactions (i) of tetrachloroethene (PCE) to TCE in cultures of Desulfitobacterium sp. strain Viet1; and (ii) of TCE to cis-1,2-dichloroethene (cis-DCE) in cultures of Geobacter lovleyi strain SZ were investigated. Compound-average carbon isotope effects were -19.0‰ ± 0.9‰ (PCE) and -12.2‰ ± 1.0‰ (TCE) (95% confidence intervals). Using instrumental advances in chlorine isotope analysis by continuous flow isotope ratio mass spectrometry, compound-average chorine isotope effects were measured for PCE (-5.0‰ ± 0.1‰) and TCE (-3.6‰ ± 0.2‰). In addition, position-specific kinetic chlorine isotope effects were determined from fits of reactant and product isotope ratios. In PCE biodegradation, primary chlorine isotope effects were substantially larger (by -16.3‰ ± 1.4‰ (standard error)) than secondary. In TCE biodegradation, in contrast, the product cis-DCE reflected an average isotope effect of -2.4‰ ± 0.3‰ and the product chloride an isotope effect of -6.5‰ ± 2.5‰, in the original positions of TCE from which the products were formed (95% confidence intervals). A greater difference would be expected for a position-specific reaction (chloride would exclusively reflect a primary isotope effect). These results therefore suggest that both vicinal chlorine substituents of TCE were reactive (intramolecular competition). This finding puts new constraints on mechanistic scenarios and favours either nucleophilic addition by Co(I) or single electron transfer as reductive dehalogenation mechanisms.
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