Daniel Buchner | Eberhard Karls Universität Tübingen (original) (raw)

Papers by Daniel Buchner

EGUGA, Apr 1, 2013

ABSTRACT Chloroethenes are commonly used in industrial applications, and detected as carcinogenic... more ABSTRACT Chloroethenes are commonly used in industrial applications, and detected as carcinogenic contaminants in the environment. Their dehalogenation is of environmental importance in remediation processes. However, a detailed understanding frequently accounted problem is the accumulation of toxic degradation products such as cis-dichloroethylene (cis-DCE) at contaminated sites. Several studies have addressed the reductive dehalogenation reactions using biotic and abiotic model systems, but a crucial question in this context has remained open: Do environmental transformations occur by the same mechanism as in their corresponding in vitro model systems? The presented study shows the potential to close this research gap using the latest developments in compound specific chlorine isotope analysis, which make it possible to routinely measure chlorine isotope fractionation of chloroethenes in environmental samples and complex reaction mixtures.1,2 In particular, such chlorine isotope analysis enables the measurement of isotope fractionation for two elements (i.e., C and Cl) in chloroethenes. When isotope values of both elements are plotted against each other, different slopes reflect different underlying mechanisms and are remarkably insensitive towards masking. Our results suggest that different microbial strains (G. lovleyi strain SZ, D. hafniense Y51) and the isolated cofactor cobalamin employ similar mechanisms of reductive dechlorination of TCE. In contrast, evidence for a different mechanism was obtained with cobaloxime cautioning its use as a model for biodegradation. The study shows the potential of the dual isotope approach as a tool to directly compare transformation mechanisms of environmental scenarios, biotic transformations, and their putative chemical lab scale systems. Furthermore, it serves as an essential reference when using the dual isotope approach to assess the fate of chlorinated compounds in the environment.

<div class="page" title="Page 1"> <div class="layou... more <div class="page" title="Page 1"> <div class="layoutArea"> <div class="column"> <p>Glyphosate (N-(phosphonomethyl)glycine) is the most applied herbicide in the world with an estimated annual application of 740 to 920 kt by 2025 extrapolating the current weed management strategy. Overuse of glyphosate in agriculture has led to frequent detection in terrestrial and aquatic environments. Concerns about glyphosate load and occurrence in the environment increase as its concentrations in water bodies tend to approach or exceed the EU drinking water threshold of 0.1 μg/L. Knowledge on the role of transformation processes on glyphosate fate in soil and water is critical to assess its impacts on the ecosystem. So far, the prevalent methods for the evaluation of glyphosate transformation include monitoring of concentration changes and detection of transformation products. However, in many cases concentration data cannot unequivocally distinguish actual elimination by transformation from other processes also reducing aqueous concentrations, such as sorption and dilution. The detection of transformation products is also often problematic due to either lack of suitable analytical methods or their fast metabolization and assimilation into the microbial biomass.<br />A promising complementary approach to concentration analysis is compound-specific stable isotope analysis (CSIA, e.g., <sup>13</sup>C/<sup>12</sup>C for carbon-CSIA), which can be used to study both the cause as well as the extent of transformation of organic contaminants such as glyphosate. A proof of a shift in the stable carbon isotope ratio (<sup>13</sup>C/<sup>12</sup>C) during transformation as well as its magnitude depend on the underlying reaction mechanism and thus can be indicative for a specific transformation pathway.<br />Microbially driven transformation is considered as the main process driving glyphosate elimination in the environment. Two main pathways have been reported for biotransformation of glyphosate depending on the specificity of the enzyme system involved. Catalysis of C—P bond cleavage occurs by a multienzyme complex known as C—P lyase resulting in the formation of sarcosine and phosphate as primary metabolites. The second pathway involves the cleavage of the C—N bond by the enzyme glyphosate oxidoreductase (GOX) yielding  aminomethylphosphonic acid (AMPA) and glyoxylate. Even though biotransformation of glyphosate has been frequently described and a carbon-CSIA method for it was established, isotope effects associated with the different microbial transformation pathways have scarcely been reported. Evidence of isotope fractionation related to its microbial transformation could elucidate the underlying transformation pathways that govern its removal from the environment. To this end, we applied isotope analysis during glyphosate transformation by different bacterial strains. The strains hold similar or different enzymes and are aerobically cultivated under P-limiting conditions. Preliminary results so far have showed no significant carbon-isotope fractionation (<1 ‰) during glyphosate transformation by two strains following the C—P pathway. An enrichment method for glyphosate compatible with subsequent CSIA analysis is under development to accomplish precise analysis also low concentrations due to extensive transformation (C<sub>min</sub>=20 mg/L).</p> </div> </div> </div>

Rapid Communications in Mass Spectrometry

Environmental Science & Technology, 2013

Chloroethenes like trichloroethene (TCE) are prevalent environmental contaminants, which may be d... more Chloroethenes like trichloroethene (TCE) are prevalent environmental contaminants, which may be degraded through reductive dechlorination. Chemical models such as cobalamine (vitamin B 12) and its simplified analogue cobaloxime have served to mimic microbial reductive dechlorination. To test whether in vitro and in vivo mechanisms agree, we combined carbon and chlorine isotope measurements of TCE. Degradation-associated enrichment factors ε carbon and ε chlorine (i.e., molecular-average isotope effects) were −12.2‰ ± 0.5‰ and −3.6‰ ± 0.1‰ with Geobacter lovleyi strain SZ; −9.1‰ ± 0.6‰ and −2.7‰ ± 0.6‰ with Desulf itobacterium haf niense Y51; −16.1‰ ± 0.9‰ and −4.0‰ ± 0.2‰ with the enzymatic cofactor cobalamin; −21.3‰ ± 0.5‰ and −3.5‰ ± 0.1‰ with cobaloxime. Dual element isotope slopes m = Δδ 13 C/ Δδ 37 Cl ≈ ε carbon / ε chlorine of TCE showed strong agreement between biotransformations (3.4 to 3.8) and cobalamin (3.9), but differed markedly for cobaloxime (6.1). These results (i) suggest a similar biodegradation mechanism despite different microbial strains, (ii) indicate that transformation with isolated cobalamin resembles in vivo transformation and (iii) suggest a different mechanism with cobaloxime. This model reactant should therefore be used with caution. Our results demonstrate the power of two-dimensional isotope analyses to characterize and distinguish between reaction mechanisms in whole cell experiments and in vitro model systems.

Environmental Science & Technology, 2022

Mn(II)-catalyzed oxidation by molecular oxygen is considered a relevant process for the environme... more Mn(II)-catalyzed oxidation by molecular oxygen is considered a relevant process for the environmental fate of aminopolyphosphonate chelating agents such as aminotrismethylene phosphonate (ATMP). However, the potential roles of Mn(III)ATMP-species in the underlying transformation mechanisms are not fully understood. We combined kinetic studies, compound-specific stable carbon isotope analysis, and equilibrium speciation modeling to shed light on the significance of such Mn-ATMP species for the overall ATMP oxidation by molecular oxygen. The fraction of ATMP complexed with Mn(II) inversely correlated with both (i) the Mn(II)-normalized transformation rate constants of ATMP and (ii) the observed carbon isotope enrichment factors (εc-values). These findings provide evidence for two parallel ATMP transformation pathways exhibiting distinctly different reaction kinetics and carbon isotope fractionation: (i) oxidation of ATMP present in Mn(III)ATMP complexes (εc ≈ -10 ‰) and (ii) oxidation of free ATMP by such Mn(III)ATMP species (εc ≈ -1 ‰) in a catalytic cycle. The higher reaction rate of the latter pathway implies that aminopolyphosphonates can be trapped in catalytic Mn-complexes before being transformed and suggests that Mn(III)ATMP might be a potent oxidant also for other reducible solutes in aqueous environments.

IAHS-AISH publication, 2011

The aim of the study was to demonstrate the stimulation of reductive dehalogenation of chlorinate... more The aim of the study was to demonstrate the stimulation of reductive dehalogenation of chlorinated ethenes in an oxic aquifer. Microcosms with aquifer material were amended with different organic substrates as electron donors in order to stimulate microbial reductive dechlorination. Next to molasses and lactate a commercial product was applied, which has been described as controlled-release carbon zero valent iron particles (EHC™). In addition, vitamins and bicarbonate buffer were added to the microcosms to further stimulate growth of halorespiring microorganisms. Reductive dechlorination was followed by measuring chlorinated ethene concentrations and their stable carbon isotope fractionation. The microbiological community was monitored by terminal restriction fragment length polymorphism (T-RFLP). The EHC amended microcosms showed only incomplete conversion of PCE, resulting in an accumulation of cis-DCE after incubation for 103 days. In the microcosms amended with molasses, comple...

Environmental Science & Technology, 2015

Environmental Science & Technology Letters

Although arsenic (As) groundwater contamination in South and Southeast Asia is a threat to human ... more Although arsenic (As) groundwater contamination in South and Southeast Asia is a threat to human health, mechanisms of its release from sediment to groundwater are still not fully understood. In many aquifers, Fe(III) minerals are often the main hosting phases for As and their stability is crucial for As mobility. Recently, a new mechanism for As mobilization into groundwater was proposed with methane (CH 4) serving as an electron donor for microbially mediated reductive dissolution of As-bearing Fe(III) minerals. To provide unequivocal evidence for the occurrence of Fe(III)-coupled methanotrophy, we incubated sediments from an As-contaminated aquifer in Hanoi (Vietnam) anoxically with isotopically labeled 13 CH 4. Up to 35% of the available Fe(III) was reduced within 232 days with simultaneous production of 13 CO 2 demonstrating anaerobic oxidation of 13 CH 4 with Fe(III) as the electron acceptor. The microbial community at the end of the incubation was dominated by archaea affiliating with Candidatus Methanoperedens, implying its involvement in Fe(III)-dependent CH 4 oxidation. These results suggest that methanotrophs can contribute to dissolution of As-bearing Fe(III) minerals, which eventually leads to As-release into groundwater.

Analytical Chemistry

Humic substances (HS) are important electron acceptors and donors in soils and aquifers. The coup... more Humic substances (HS) are important electron acceptors and donors in soils and aquifers. The coupling of anoxic nitrogen cycling to the function of HS as a redox battery, however, remains poorly understood. Mediated electrochemical analysis is an emerging tool to determine the redox properties (i.e., electron donating capacity (EDC), electron accepting capacity (EAC), and redox state) of HS. However, the presence of nitrite (NO2─), a central intermediate of the nitrogen cycle, interferes with the electrochemical determination of the EAC. To eliminate this interference, we developed a bioassay to remove nitrite in HS samples using the denitrifying bacterium Pseudomonas nitroreducens. Cell suspensions of P. nitroreducens completely removed NO2─ at various concentrations (1, 2 and 5 mM) from humic acid samples (1g HA/L) of different redox states. As P. nitroreducens is not able to exchange electrons with dissolved humic acids the procedure allows an accurate and reliable determination of the EAC of humic acid samples. The proposed method thus opens new perspectives in biogeochemistry to study interactions between humic substances and nitrogen cycling.

Analytical and Bioanalytical Chemistry

Compound-specific carbon isotope analysis (carbon CSIA) by liquid chromatography/isotope ratio ma... more Compound-specific carbon isotope analysis (carbon CSIA) by liquid chromatography/isotope ratio mass spectrometry (LC-IRMS) is a novel and promising tool to elucidate the environmental fate of polar organic compounds such as polyphosphonates, strong complexing agents for di- and trivalent cations with growing commercial importance over the last decades. Here, we present a LC-IRMS method for the three widely used polyphosphonates 1-hydroxyethane 1,1-diphosphonate (HEDP), amino tris(methylenephosphonate) (ATMP), and ethylenediamine tetra(methylenephosphonate) (EDTMP). Separation of the analytes, as well as ATMP and its degradation products, was carried out on an anion exchange column under acidic conditions. Quantitative wet chemical oxidation inside the LC-IRMS interface to CO 2 was achieved for all three investigated polyphosphonates at a comparatively low sodium persulfate concentration despite the described resilience of HEDP towards oxidative breakdown. The developed method has proven to be suitable for the determination of carbon isotope fractionation of ATMP transformation due to manganese-catalyzed reaction with molecular oxygen, as well as for equilibrium sorption of ATMP to goethite. A kinetic isotope effect was associated with the investigated reaction pathway, whereas no detectable isotope fractionation could be observed during sorption. Thus, CSIA is an appropriate technique to distinguish between sorption and degradation processes that contribute to a concentration decrease of ATMP in laboratory batch experiments. Our study highlights the potential of carbon CSIA by LC-IRMS to gain a process-based understanding of the fate of polyphosphonate complexing agents in environmental as well as technical systems.

Grundwasser

ZusammenfassungEine erfolgreiche biologische In-situ-Sanierung von PCE-kontaminierten Grundwasser... more ZusammenfassungEine erfolgreiche biologische In-situ-Sanierung von PCE-kontaminierten Grundwasserleitern erfordert hinreichend reduzierende Bedingungen sowie die Anwesenheit von molekularem Wasserstoff, der dehalogenierenden Bakterien als Elektronendonor dient. Durch Injektion eines biologisch gut abbaubaren Hilfsstoffs (Auxiliarsubstrat) können diese Faktoren gesteuert werden.Die vorliegende Fallstudie beschreibt die Verfahrensschritte für eine erfolgreiche Stimulierung des biologischen PCE-Abbaus in einem ursprünglich sauerstoffhaltigen Grundwasserleiter. Laboruntersuchungen in Mikrokosmen (Stufe I) verifizierten das standorteigene bakterielle Abbaupotenzial sowie die Eignung des Auxiliarsubstrats (hier: Melasse). Basierend auf hydrogeologischen und geochemischen Felddaten wurde die erforderliche Melassemenge abgeschätzt sowie deren Wirkungsbereich im Aquifer modelliert (Stufe II). Im Feldversuch erfolgten periodische Injektionen des Auxiliarsubstrats (hier: 170 Tage) begleitet von geochemischen und molekularbiologischen Analysen (Stufe III). Durch die Melasseinjektion konnten im PCE-kontaminiertem Bereich des Aquifers methanogene Bedingungen sowie eine massive Zunahme von Schlüsselbakterien der Gattung Dehalococcoides induziert werden. Der erfolgreiche In-situ-Bioabbau von PCE zu Ethen wurde durch substanzspezifische Kohlenstoff-Isotopenanalysen bestätigt.AbstractA successful biological in situ remediation of PCE contaminated aquifers requires suitable redox conditions as well as molecular hydrogen used by dehalogenating bacteria as the electron donor. Injecting an easily biodegradable auxiliary substrate allows to control both factors. The present study describes the procedural steps for a successful stimulation of biological PCE-degradation in a primary oxygen-containing aquifer. A microcosm study (level I) showed the bacterial potential of the site and the suitability of molasses as an auxiliary substrate. Using hydrogeological and geochemical field data, the amount of molasses was estimated and its zone of influence was modelled (level II). In a field test, molasses was periodically injected (170 days) accompanied by geochemical and molecular biological analysis (level III). Following the injection of molasses, methanogenic conditions as well as a significant increase of Dehalococcoides was observed. In situ biodegradation of PCE to ethene was verified by compound-specific carbon isotope analysis.

Earth and Environmental Science Transactions of the Royal Society of Edinburgh

ABSTRACTThe consequences of urbanisation for Earth's biogeochemical cycles are largely unexpl... more ABSTRACTThe consequences of urbanisation for Earth's biogeochemical cycles are largely unexplored. Copper (Cu) in urban soils is being accumulated mainly due to anthropogenic activities under rapid urbanisation. The increasing Cu concentrations may contribute to altering soil nitrogen (N) cycling in urban ecosystems through modulating denitrification processes. This research aims to identify how Cu impacts urban soil denitrification functions and denitrifier abundance. An urban park soil with a background total Cu concentration of 7.9μgg–1 was incubated anaerobically with different Cu amendments (10, 20, 40, 80 and 160μg Cu g–1 soil), similar to prevalent Cu contents in urban soils. We evaluated the soil denitrification functions using the acetylene (C2H2) inhibition method and assessed the denitrifier abundance by quantitative polymerase chain reaction (qPCR) analyses of denitrifying marker genes (nirK, nirS and nosZ). At the function level, we observed that both the potential ...

Environmental Science & Technology

Kinetic isotope effects have been used successfully to prove and characterize organic contaminant... more Kinetic isotope effects have been used successfully to prove and characterize organic contaminant transformation on various scales including field and laboratory studies. For tetrachloroethene (PCE) biotransformation, however, causes for the substantial variability of reported isotope enrichment factors (ε) are still not deciphered (εcarbon = -0.4‰ to -19.0‰). Factors such as different reaction mechanisms and masking of isotope fractionation by either limited intracellular mass transfer or rate-limitations within the enzymatic multi-step reaction are under discussion. This study evaluated the contribution of these factors to the magnitude of carbon and chlorine isotope fractionation of Desulfitobacterium strains harboring three different PCE-transforming enzymes (PCE-RdhA). Despite variable single element isotope fractionation (εC = -5.0‰ to -19.7‰; εCl = -1.9‰ to -6.3‰), similar slopes of dual element isotope plots (ΛC/Cl-values of 2.4 ± 0.1 to 3.6 ± 0.1) suggest a common reaction mechanism for the different PCE-RdhAs. Cell envelope properties of the Desulfitobacterium strains allowed to exclude masking effects due to PCE mass transfer limitation. Our results thus revealed that different rate-limiting steps (e.g. substrate channel diffusion) in the enzymatic multi-step reactions of individual PCE-RdhAs rather than different reaction mechanisms determine the extent of PCE isotope fractionation in the Desulfitobacterium genus.

Environmental Science & Technology, 2013

Chloroethenes like trichloroethene (TCE) are prevalent environmental contaminants, which may be d... more Chloroethenes like trichloroethene (TCE) are prevalent environmental contaminants, which may be degraded through reductive dechlorination. Chemical models such as cobalamine (vitamin B 12 ) and its simplified analogue cobaloxime have served to mimic microbial reductive dechlorination. To test whether in vitro and in vivo mechanisms agree, we combined carbon and chlorine isotope measurements of TCE. Degradation-associated enrichment factors ε carbon and ε chlorine (i.e., molecular-average isotope effects) were −12.2‰ ± 0.5‰ and −3.6‰ ± 0.1‰ with Geobacter lovleyi strain SZ; −9.1‰ ± 0.6‰ and −2.7‰ ± 0.6‰ with Desulf itobacterium haf niense Y51; −16.1‰ ± 0.9‰ and −4.0‰ ± 0.2‰ with the enzymatic cofactor cobalamin; −21.3‰ ± 0.5‰ and −3.5‰ ± 0.1‰ with cobaloxime. Dual element isotope slopes m = Δδ 13 C/ Δδ 37 Cl ≈ ε carbon / ε chlorine of TCE showed strong agreement between biotransformations (3.4 to 3.8) and cobalamin (3.9), but differed markedly for cobaloxime (6.1). These results (i) suggest a similar biodegradation mechanism despite different microbial strains, (ii) indicate that transformation with isolated cobalamin resembles in vivo transformation and (iii) suggest a different mechanism with cobaloxime. This model reactant should therefore be used with caution. Our results demonstrate the power of two-dimensional isotope analyses to characterize and distinguish between reaction mechanisms in whole cell experiments and in vitro model systems.

Environmental science & technology, Jan 7, 2017

Application of compound-specific stable isotope approaches often involves comparisons of isotope ... more Application of compound-specific stable isotope approaches often involves comparisons of isotope enrichment factors (ε). Experimental determination of ε-values is based on the Rayleigh equation, which relates the change in measured isotope ratios to the decreasing substrate fractions and is valid for closed systems. Even in well-controlled batch experiments, however, this requirement is not necessarily fulfilled, since repetitive sampling can remove a significant fraction of the analyte. For volatile compounds the need for appropriate corrections is most evident, and various methods have been proposed to account for mass removal and for volatilization into the headspace. In this study we use both synthetic and experimental data to demonstrate that the determination of ε-values according to current correction methods is prone to considerable systematic errors even in well-designed experimental setups. Application of inappropriate methods may lead to incorrect and inconsistent ε-value...

EGUGA, Apr 1, 2013

ABSTRACT Chloroethenes are commonly used in industrial applications, and detected as carcinogenic... more ABSTRACT Chloroethenes are commonly used in industrial applications, and detected as carcinogenic contaminants in the environment. Their dehalogenation is of environmental importance in remediation processes. However, a detailed understanding frequently accounted problem is the accumulation of toxic degradation products such as cis-dichloroethylene (cis-DCE) at contaminated sites. Several studies have addressed the reductive dehalogenation reactions using biotic and abiotic model systems, but a crucial question in this context has remained open: Do environmental transformations occur by the same mechanism as in their corresponding in vitro model systems? The presented study shows the potential to close this research gap using the latest developments in compound specific chlorine isotope analysis, which make it possible to routinely measure chlorine isotope fractionation of chloroethenes in environmental samples and complex reaction mixtures.1,2 In particular, such chlorine isotope analysis enables the measurement of isotope fractionation for two elements (i.e., C and Cl) in chloroethenes. When isotope values of both elements are plotted against each other, different slopes reflect different underlying mechanisms and are remarkably insensitive towards masking. Our results suggest that different microbial strains (G. lovleyi strain SZ, D. hafniense Y51) and the isolated cofactor cobalamin employ similar mechanisms of reductive dechlorination of TCE. In contrast, evidence for a different mechanism was obtained with cobaloxime cautioning its use as a model for biodegradation. The study shows the potential of the dual isotope approach as a tool to directly compare transformation mechanisms of environmental scenarios, biotic transformations, and their putative chemical lab scale systems. Furthermore, it serves as an essential reference when using the dual isotope approach to assess the fate of chlorinated compounds in the environment.

<div class="page" title="Page 1"> <div class="layou... more <div class="page" title="Page 1"> <div class="layoutArea"> <div class="column"> <p>Glyphosate (N-(phosphonomethyl)glycine) is the most applied herbicide in the world with an estimated annual application of 740 to 920 kt by 2025 extrapolating the current weed management strategy. Overuse of glyphosate in agriculture has led to frequent detection in terrestrial and aquatic environments. Concerns about glyphosate load and occurrence in the environment increase as its concentrations in water bodies tend to approach or exceed the EU drinking water threshold of 0.1 μg/L. Knowledge on the role of transformation processes on glyphosate fate in soil and water is critical to assess its impacts on the ecosystem. So far, the prevalent methods for the evaluation of glyphosate transformation include monitoring of concentration changes and detection of transformation products. However, in many cases concentration data cannot unequivocally distinguish actual elimination by transformation from other processes also reducing aqueous concentrations, such as sorption and dilution. The detection of transformation products is also often problematic due to either lack of suitable analytical methods or their fast metabolization and assimilation into the microbial biomass.<br />A promising complementary approach to concentration analysis is compound-specific stable isotope analysis (CSIA, e.g., <sup>13</sup>C/<sup>12</sup>C for carbon-CSIA), which can be used to study both the cause as well as the extent of transformation of organic contaminants such as glyphosate. A proof of a shift in the stable carbon isotope ratio (<sup>13</sup>C/<sup>12</sup>C) during transformation as well as its magnitude depend on the underlying reaction mechanism and thus can be indicative for a specific transformation pathway.<br />Microbially driven transformation is considered as the main process driving glyphosate elimination in the environment. Two main pathways have been reported for biotransformation of glyphosate depending on the specificity of the enzyme system involved. Catalysis of C—P bond cleavage occurs by a multienzyme complex known as C—P lyase resulting in the formation of sarcosine and phosphate as primary metabolites. The second pathway involves the cleavage of the C—N bond by the enzyme glyphosate oxidoreductase (GOX) yielding  aminomethylphosphonic acid (AMPA) and glyoxylate. Even though biotransformation of glyphosate has been frequently described and a carbon-CSIA method for it was established, isotope effects associated with the different microbial transformation pathways have scarcely been reported. Evidence of isotope fractionation related to its microbial transformation could elucidate the underlying transformation pathways that govern its removal from the environment. To this end, we applied isotope analysis during glyphosate transformation by different bacterial strains. The strains hold similar or different enzymes and are aerobically cultivated under P-limiting conditions. Preliminary results so far have showed no significant carbon-isotope fractionation (<1 ‰) during glyphosate transformation by two strains following the C—P pathway. An enrichment method for glyphosate compatible with subsequent CSIA analysis is under development to accomplish precise analysis also low concentrations due to extensive transformation (C<sub>min</sub>=20 mg/L).</p> </div> </div> </div>

Rapid Communications in Mass Spectrometry

Environmental Science & Technology, 2013

Chloroethenes like trichloroethene (TCE) are prevalent environmental contaminants, which may be d... more Chloroethenes like trichloroethene (TCE) are prevalent environmental contaminants, which may be degraded through reductive dechlorination. Chemical models such as cobalamine (vitamin B 12) and its simplified analogue cobaloxime have served to mimic microbial reductive dechlorination. To test whether in vitro and in vivo mechanisms agree, we combined carbon and chlorine isotope measurements of TCE. Degradation-associated enrichment factors ε carbon and ε chlorine (i.e., molecular-average isotope effects) were −12.2‰ ± 0.5‰ and −3.6‰ ± 0.1‰ with Geobacter lovleyi strain SZ; −9.1‰ ± 0.6‰ and −2.7‰ ± 0.6‰ with Desulf itobacterium haf niense Y51; −16.1‰ ± 0.9‰ and −4.0‰ ± 0.2‰ with the enzymatic cofactor cobalamin; −21.3‰ ± 0.5‰ and −3.5‰ ± 0.1‰ with cobaloxime. Dual element isotope slopes m = Δδ 13 C/ Δδ 37 Cl ≈ ε carbon / ε chlorine of TCE showed strong agreement between biotransformations (3.4 to 3.8) and cobalamin (3.9), but differed markedly for cobaloxime (6.1). These results (i) suggest a similar biodegradation mechanism despite different microbial strains, (ii) indicate that transformation with isolated cobalamin resembles in vivo transformation and (iii) suggest a different mechanism with cobaloxime. This model reactant should therefore be used with caution. Our results demonstrate the power of two-dimensional isotope analyses to characterize and distinguish between reaction mechanisms in whole cell experiments and in vitro model systems.

Environmental Science & Technology, 2022

Mn(II)-catalyzed oxidation by molecular oxygen is considered a relevant process for the environme... more Mn(II)-catalyzed oxidation by molecular oxygen is considered a relevant process for the environmental fate of aminopolyphosphonate chelating agents such as aminotrismethylene phosphonate (ATMP). However, the potential roles of Mn(III)ATMP-species in the underlying transformation mechanisms are not fully understood. We combined kinetic studies, compound-specific stable carbon isotope analysis, and equilibrium speciation modeling to shed light on the significance of such Mn-ATMP species for the overall ATMP oxidation by molecular oxygen. The fraction of ATMP complexed with Mn(II) inversely correlated with both (i) the Mn(II)-normalized transformation rate constants of ATMP and (ii) the observed carbon isotope enrichment factors (εc-values). These findings provide evidence for two parallel ATMP transformation pathways exhibiting distinctly different reaction kinetics and carbon isotope fractionation: (i) oxidation of ATMP present in Mn(III)ATMP complexes (εc ≈ -10 ‰) and (ii) oxidation of free ATMP by such Mn(III)ATMP species (εc ≈ -1 ‰) in a catalytic cycle. The higher reaction rate of the latter pathway implies that aminopolyphosphonates can be trapped in catalytic Mn-complexes before being transformed and suggests that Mn(III)ATMP might be a potent oxidant also for other reducible solutes in aqueous environments.

IAHS-AISH publication, 2011

The aim of the study was to demonstrate the stimulation of reductive dehalogenation of chlorinate... more The aim of the study was to demonstrate the stimulation of reductive dehalogenation of chlorinated ethenes in an oxic aquifer. Microcosms with aquifer material were amended with different organic substrates as electron donors in order to stimulate microbial reductive dechlorination. Next to molasses and lactate a commercial product was applied, which has been described as controlled-release carbon zero valent iron particles (EHC™). In addition, vitamins and bicarbonate buffer were added to the microcosms to further stimulate growth of halorespiring microorganisms. Reductive dechlorination was followed by measuring chlorinated ethene concentrations and their stable carbon isotope fractionation. The microbiological community was monitored by terminal restriction fragment length polymorphism (T-RFLP). The EHC amended microcosms showed only incomplete conversion of PCE, resulting in an accumulation of cis-DCE after incubation for 103 days. In the microcosms amended with molasses, comple...

Environmental Science & Technology, 2015

Environmental Science & Technology Letters

Although arsenic (As) groundwater contamination in South and Southeast Asia is a threat to human ... more Although arsenic (As) groundwater contamination in South and Southeast Asia is a threat to human health, mechanisms of its release from sediment to groundwater are still not fully understood. In many aquifers, Fe(III) minerals are often the main hosting phases for As and their stability is crucial for As mobility. Recently, a new mechanism for As mobilization into groundwater was proposed with methane (CH 4) serving as an electron donor for microbially mediated reductive dissolution of As-bearing Fe(III) minerals. To provide unequivocal evidence for the occurrence of Fe(III)-coupled methanotrophy, we incubated sediments from an As-contaminated aquifer in Hanoi (Vietnam) anoxically with isotopically labeled 13 CH 4. Up to 35% of the available Fe(III) was reduced within 232 days with simultaneous production of 13 CO 2 demonstrating anaerobic oxidation of 13 CH 4 with Fe(III) as the electron acceptor. The microbial community at the end of the incubation was dominated by archaea affiliating with Candidatus Methanoperedens, implying its involvement in Fe(III)-dependent CH 4 oxidation. These results suggest that methanotrophs can contribute to dissolution of As-bearing Fe(III) minerals, which eventually leads to As-release into groundwater.

Analytical Chemistry

Humic substances (HS) are important electron acceptors and donors in soils and aquifers. The coup... more Humic substances (HS) are important electron acceptors and donors in soils and aquifers. The coupling of anoxic nitrogen cycling to the function of HS as a redox battery, however, remains poorly understood. Mediated electrochemical analysis is an emerging tool to determine the redox properties (i.e., electron donating capacity (EDC), electron accepting capacity (EAC), and redox state) of HS. However, the presence of nitrite (NO2─), a central intermediate of the nitrogen cycle, interferes with the electrochemical determination of the EAC. To eliminate this interference, we developed a bioassay to remove nitrite in HS samples using the denitrifying bacterium Pseudomonas nitroreducens. Cell suspensions of P. nitroreducens completely removed NO2─ at various concentrations (1, 2 and 5 mM) from humic acid samples (1g HA/L) of different redox states. As P. nitroreducens is not able to exchange electrons with dissolved humic acids the procedure allows an accurate and reliable determination of the EAC of humic acid samples. The proposed method thus opens new perspectives in biogeochemistry to study interactions between humic substances and nitrogen cycling.

Analytical and Bioanalytical Chemistry

Compound-specific carbon isotope analysis (carbon CSIA) by liquid chromatography/isotope ratio ma... more Compound-specific carbon isotope analysis (carbon CSIA) by liquid chromatography/isotope ratio mass spectrometry (LC-IRMS) is a novel and promising tool to elucidate the environmental fate of polar organic compounds such as polyphosphonates, strong complexing agents for di- and trivalent cations with growing commercial importance over the last decades. Here, we present a LC-IRMS method for the three widely used polyphosphonates 1-hydroxyethane 1,1-diphosphonate (HEDP), amino tris(methylenephosphonate) (ATMP), and ethylenediamine tetra(methylenephosphonate) (EDTMP). Separation of the analytes, as well as ATMP and its degradation products, was carried out on an anion exchange column under acidic conditions. Quantitative wet chemical oxidation inside the LC-IRMS interface to CO 2 was achieved for all three investigated polyphosphonates at a comparatively low sodium persulfate concentration despite the described resilience of HEDP towards oxidative breakdown. The developed method has proven to be suitable for the determination of carbon isotope fractionation of ATMP transformation due to manganese-catalyzed reaction with molecular oxygen, as well as for equilibrium sorption of ATMP to goethite. A kinetic isotope effect was associated with the investigated reaction pathway, whereas no detectable isotope fractionation could be observed during sorption. Thus, CSIA is an appropriate technique to distinguish between sorption and degradation processes that contribute to a concentration decrease of ATMP in laboratory batch experiments. Our study highlights the potential of carbon CSIA by LC-IRMS to gain a process-based understanding of the fate of polyphosphonate complexing agents in environmental as well as technical systems.

Grundwasser

ZusammenfassungEine erfolgreiche biologische In-situ-Sanierung von PCE-kontaminierten Grundwasser... more ZusammenfassungEine erfolgreiche biologische In-situ-Sanierung von PCE-kontaminierten Grundwasserleitern erfordert hinreichend reduzierende Bedingungen sowie die Anwesenheit von molekularem Wasserstoff, der dehalogenierenden Bakterien als Elektronendonor dient. Durch Injektion eines biologisch gut abbaubaren Hilfsstoffs (Auxiliarsubstrat) können diese Faktoren gesteuert werden.Die vorliegende Fallstudie beschreibt die Verfahrensschritte für eine erfolgreiche Stimulierung des biologischen PCE-Abbaus in einem ursprünglich sauerstoffhaltigen Grundwasserleiter. Laboruntersuchungen in Mikrokosmen (Stufe I) verifizierten das standorteigene bakterielle Abbaupotenzial sowie die Eignung des Auxiliarsubstrats (hier: Melasse). Basierend auf hydrogeologischen und geochemischen Felddaten wurde die erforderliche Melassemenge abgeschätzt sowie deren Wirkungsbereich im Aquifer modelliert (Stufe II). Im Feldversuch erfolgten periodische Injektionen des Auxiliarsubstrats (hier: 170 Tage) begleitet von geochemischen und molekularbiologischen Analysen (Stufe III). Durch die Melasseinjektion konnten im PCE-kontaminiertem Bereich des Aquifers methanogene Bedingungen sowie eine massive Zunahme von Schlüsselbakterien der Gattung Dehalococcoides induziert werden. Der erfolgreiche In-situ-Bioabbau von PCE zu Ethen wurde durch substanzspezifische Kohlenstoff-Isotopenanalysen bestätigt.AbstractA successful biological in situ remediation of PCE contaminated aquifers requires suitable redox conditions as well as molecular hydrogen used by dehalogenating bacteria as the electron donor. Injecting an easily biodegradable auxiliary substrate allows to control both factors. The present study describes the procedural steps for a successful stimulation of biological PCE-degradation in a primary oxygen-containing aquifer. A microcosm study (level I) showed the bacterial potential of the site and the suitability of molasses as an auxiliary substrate. Using hydrogeological and geochemical field data, the amount of molasses was estimated and its zone of influence was modelled (level II). In a field test, molasses was periodically injected (170 days) accompanied by geochemical and molecular biological analysis (level III). Following the injection of molasses, methanogenic conditions as well as a significant increase of Dehalococcoides was observed. In situ biodegradation of PCE to ethene was verified by compound-specific carbon isotope analysis.

Earth and Environmental Science Transactions of the Royal Society of Edinburgh

ABSTRACTThe consequences of urbanisation for Earth's biogeochemical cycles are largely unexpl... more ABSTRACTThe consequences of urbanisation for Earth's biogeochemical cycles are largely unexplored. Copper (Cu) in urban soils is being accumulated mainly due to anthropogenic activities under rapid urbanisation. The increasing Cu concentrations may contribute to altering soil nitrogen (N) cycling in urban ecosystems through modulating denitrification processes. This research aims to identify how Cu impacts urban soil denitrification functions and denitrifier abundance. An urban park soil with a background total Cu concentration of 7.9μgg–1 was incubated anaerobically with different Cu amendments (10, 20, 40, 80 and 160μg Cu g–1 soil), similar to prevalent Cu contents in urban soils. We evaluated the soil denitrification functions using the acetylene (C2H2) inhibition method and assessed the denitrifier abundance by quantitative polymerase chain reaction (qPCR) analyses of denitrifying marker genes (nirK, nirS and nosZ). At the function level, we observed that both the potential ...

Environmental Science & Technology

Kinetic isotope effects have been used successfully to prove and characterize organic contaminant... more Kinetic isotope effects have been used successfully to prove and characterize organic contaminant transformation on various scales including field and laboratory studies. For tetrachloroethene (PCE) biotransformation, however, causes for the substantial variability of reported isotope enrichment factors (ε) are still not deciphered (εcarbon = -0.4‰ to -19.0‰). Factors such as different reaction mechanisms and masking of isotope fractionation by either limited intracellular mass transfer or rate-limitations within the enzymatic multi-step reaction are under discussion. This study evaluated the contribution of these factors to the magnitude of carbon and chlorine isotope fractionation of Desulfitobacterium strains harboring three different PCE-transforming enzymes (PCE-RdhA). Despite variable single element isotope fractionation (εC = -5.0‰ to -19.7‰; εCl = -1.9‰ to -6.3‰), similar slopes of dual element isotope plots (ΛC/Cl-values of 2.4 ± 0.1 to 3.6 ± 0.1) suggest a common reaction mechanism for the different PCE-RdhAs. Cell envelope properties of the Desulfitobacterium strains allowed to exclude masking effects due to PCE mass transfer limitation. Our results thus revealed that different rate-limiting steps (e.g. substrate channel diffusion) in the enzymatic multi-step reactions of individual PCE-RdhAs rather than different reaction mechanisms determine the extent of PCE isotope fractionation in the Desulfitobacterium genus.

Environmental Science & Technology, 2013

Chloroethenes like trichloroethene (TCE) are prevalent environmental contaminants, which may be d... more Chloroethenes like trichloroethene (TCE) are prevalent environmental contaminants, which may be degraded through reductive dechlorination. Chemical models such as cobalamine (vitamin B 12 ) and its simplified analogue cobaloxime have served to mimic microbial reductive dechlorination. To test whether in vitro and in vivo mechanisms agree, we combined carbon and chlorine isotope measurements of TCE. Degradation-associated enrichment factors ε carbon and ε chlorine (i.e., molecular-average isotope effects) were −12.2‰ ± 0.5‰ and −3.6‰ ± 0.1‰ with Geobacter lovleyi strain SZ; −9.1‰ ± 0.6‰ and −2.7‰ ± 0.6‰ with Desulf itobacterium haf niense Y51; −16.1‰ ± 0.9‰ and −4.0‰ ± 0.2‰ with the enzymatic cofactor cobalamin; −21.3‰ ± 0.5‰ and −3.5‰ ± 0.1‰ with cobaloxime. Dual element isotope slopes m = Δδ 13 C/ Δδ 37 Cl ≈ ε carbon / ε chlorine of TCE showed strong agreement between biotransformations (3.4 to 3.8) and cobalamin (3.9), but differed markedly for cobaloxime (6.1). These results (i) suggest a similar biodegradation mechanism despite different microbial strains, (ii) indicate that transformation with isolated cobalamin resembles in vivo transformation and (iii) suggest a different mechanism with cobaloxime. This model reactant should therefore be used with caution. Our results demonstrate the power of two-dimensional isotope analyses to characterize and distinguish between reaction mechanisms in whole cell experiments and in vitro model systems.

Environmental science & technology, Jan 7, 2017

Application of compound-specific stable isotope approaches often involves comparisons of isotope ... more Application of compound-specific stable isotope approaches often involves comparisons of isotope enrichment factors (ε). Experimental determination of ε-values is based on the Rayleigh equation, which relates the change in measured isotope ratios to the decreasing substrate fractions and is valid for closed systems. Even in well-controlled batch experiments, however, this requirement is not necessarily fulfilled, since repetitive sampling can remove a significant fraction of the analyte. For volatile compounds the need for appropriate corrections is most evident, and various methods have been proposed to account for mass removal and for volatilization into the headspace. In this study we use both synthetic and experimental data to demonstrate that the determination of ε-values according to current correction methods is prone to considerable systematic errors even in well-designed experimental setups. Application of inappropriate methods may lead to incorrect and inconsistent ε-value...