Martin Elsner - Academia.edu (original) (raw)

Papers by Martin Elsner

The Science of the total environment, Jan 15, 2017

cis-1,2-Dichloroethene (cis-DCE) and trichloroethene (TCE) are persistent, toxic and mobile pollu... more cis-1,2-Dichloroethene (cis-DCE) and trichloroethene (TCE) are persistent, toxic and mobile pollutants in groundwater systems. They are both conducive to reductive dehalogenation and to oxidation by permanganate. In this study, the potential of dual element (C, Cl) compound specific isotope analyses (CSIA) for distinguishing between chemical oxidation and anaerobic reductive dechlorination of cis-DCE and TCE was investigated. Well-controlled cis-DCE degradation batch tests gave similar carbon isotope enrichment factors εC (‰), but starkly contrasting dual element isotope slopes Δδ(13)C/Δδ(37)Cl for permanganate oxidation (εC=-26‰±6‰, Δδ(13)C/Δδ(37)Cl≈-125±47) compared to reductive dechlorination (εC=-18‰±4‰, Δδ(13)C/Δδ(37)Cl≈4.5±3.4). The difference can be tracked down to distinctly different chlorine isotope fractionation: an inverse isotope effect during chemical oxidation (εCl=+0.2‰±0.1‰) compared to a large normal isotope effect in reductive dechlorination (εCl=-3.3‰±0.9‰) (p≪0....

Environmental science & technology, Jan 16, 2017

Chlorinated ethenes (CEs) such as perchloroethylene, trichloroethylene and dichloroethylene are n... more Chlorinated ethenes (CEs) such as perchloroethylene, trichloroethylene and dichloroethylene are notorious groundwater contaminants. Although reductive dehalogenation is key to their environmental and engineered degradation, underlying reaction mechanisms remain elusive. Outer-sphere reductive single electron transfer (OS-SET) has been proposed for such different processes as Vitamin B12-dependent biodegradation and zerovalent metal-mediated dehalogenation. Compound-specific isotope effect ((13)C/(12)C, (37)Cl/(35)Cl) analysis offers a new opportunity to test these hypotheses. Defined OS-SET model reactants (CO2 radical anions, S(2-)-doped graphene oxide in water) caused strong carbon (εC = -7.9‰ to -11.9‰), but negligible chlorine isotope effects (εCl = -0.12‰ to 0.04‰) in CEs. Greater chlorine isotope effects were observed in CHCl3 (εC = -7.7‰, εCl = -2.6‰), and in CEs when the exergonicity of C-Cl bond cleavage was reduced in an organic solvent (reaction with arene radical anions ...

Environmental Science & Technology, 2016

Although diclofenac ranks among the most frequently detected pharmaceuticals in the urban water c... more Although diclofenac ranks among the most frequently detected pharmaceuticals in the urban water cycle, its environmental transformation reactions remain imperfectly understood. Biodegradation-induced changes in (15)N/(14)N ratios (εN = -7.1‰ ± 0.4‰) have indicated that compound-specific isotope analysis (CSIA) may detect diclofenac degradation. This singular observation warrants exploration for further transformation reactions. The present study surveys carbon and nitrogen isotope fractionation in other environmental and engineered transformation reactions of diclofenac. While carbon isotope fractionation was generally small, observed nitrogen isotope fractionation in degradation by MnO2 (εN = -7.3‰ ± 0.3‰), photolysis (εN = +1.9‰ ± 0.1‰), and ozonation (εN = +1.5‰ ± 0.2‰) revealed distinct trends for different oxidative transformation reactions. The small, secondary isotope effect associated with ozonation suggests an attack of O3 in a molecular position distant from the N atom. Model reactants for outer-sphere single electron transfer generated large inverse nitrogen isotope fractionation (εN = +5.7‰ ± 0.3‰), ruling out this mechanism for biodegradation and transformation by MnO2. In a river model, isotope fractionation-derived degradation estimates agreed well with concentration mass balances, providing a proof-of-principle validation for assessing micropollutant degradation in river sediment. Our study highlights the prospect of combining CSIA with transformation product analysis for a better assessment of transformation reactions within the environmental life of diclofenac.

Environmental microbiology, Jan 15, 2016

Biostimulation is widely used to enhance reductive dechlorination of chlorinated ethenes in conta... more Biostimulation is widely used to enhance reductive dechlorination of chlorinated ethenes in contaminated aquifers. However, the knowledge on corresponding biogeochemical responses is limited. In this study glycerol was injected in an aquifer contaminated with cis-dichloroethene (cDCE), and geochemical and microbial shifts were followed for 265 days. Consistent with anoxic conditions and sulfate reduction after biostimulation, MiSeq 16S rRNA gene sequencing revealed temporarily increased relative abundance of Firmicutes, Bacteriodetes and sulfate reducing Deltaproteobacteria. In line with (13) C cDCE enrichment and increased Dehalococcoides mccartyi (Dcm) numbers, dechlorination was observed towards the end of the field experiment, albeit being incomplete with accumulation of vinyl chloride. This was concurrent with i) decreased concentrations of dissolved organic carbon (DOC), reduced relative abundances of fermenting and sulfate reducing bacteria that have been suggested to promote...

Environmental Science & Technology, 2016

Unconventional natural gas development (UNGD) generates large volumes of wastewater, the detailed... more Unconventional natural gas development (UNGD) generates large volumes of wastewater, the detailed composition of which must be known for adequate risk assessment and treatment. In particular, transformation products of geogenic compounds and disclosed additives have not been described. This study investigated six Fayetteville Shale wastewater samples for organic composition using a suite of one- and two-dimensional gas chromatographic techniques to capture a broad distribution of chemical structures. Following the application of strict compound-identification-confidence criteria, we classified compounds according to their putative origin. Samples displayed distinct chemical distributions composed of typical geogenic substances (hydrocarbons and hopane biomarkers), disclosed UNGD additives (e.g., hydrocarbons, phthalates such as diisobutyl phthalate, and radical initiators such as azobis(isobutyronitrile)), and undisclosed compounds (e.g., halogenated hydrocarbons, such as 2-bromohexane or 4-bromoheptane). Undisclosed chloromethyl alkanoates (chloromethyl propanoate, pentanoate, and octanoate) were identified as potential delayed acids (i.e., those that release acidic moieties only after hydrolytic cleavage, the rate of which could be potentially controlled), suggesting they were deliberately introduced to react in the subsurface. In contrast, the identification of halogenated methanes and acetones suggested that those compounds were formed as unintended byproducts. Our study highlights the possibility that UNGD operations generate transformation products and underscores the value of disclosing additives injected into the subsurface.

Environmental Science Technology, 2010

Environmental Science and Technology, Feb 1, 2010

The fate of pesticides in the subsurface is of great interest to the public, industry, and regula... more The fate of pesticides in the subsurface is of great interest to the public, industry, and regulatory authorities. Compoundspecific isotope analysis (CSIA) is a promising tool complementary to existing methods for elucidating pesticide degradation reactions. Here, we address three different initial biotransformation reactions of the phenylurea herbicide isoproturon (3-(4isopropylphenyl)-1,1-dimethylurea) in pure culture experiments with bacterial and fungal strains. When analyzing isotopic changes in different parts of the isoproturon molecule, hydroxylation of the isopropyl group by fungi was found to be associated with C and H isotope fractionation. In contrast, hydrolysis by Arthrobacter globiformis D47 caused strong C and N isotope fractionation, albeit in a different manner than abiotic hydrolysis so that isotope measurements can distinguish between both modes of transformation. No significant isotope fractionation was observed during N-demethylation by Sphingomonas sp. SRS2. The observed isotope fractionation patterns were in agreement with the type of reactions and elements involved. Moreover, their substantially different nature suggests that isotope changes in natural samples may be uniquely attributed to either pathway, allowing even to distinguish the abiotic versus biotic nature of hydrolysis. Our investigations show how characteristic isotope patterns may significantly add to the present understanding of the environmental fate of pesticides.

"Compound specific isotope analysis can be used to quantify the in situ biodegradation of to... more "Compound specific isotope analysis can be used to quantify the in situ biodegradation of toxic chlorinated ethenes, such as trichloroethene (TCE), in groundwater. However, while the anaerobic biodegradation of TCE occurs via reductive dechlorination, the magnitude of observed kinetic isotope effects for carbon has varied widely for different bacteria and enrichment cultures [1]. This variability could indicate different initial transition states within the reaction mechanism or masking of the observed carbon kinetic isotope effect due to additional rate-limiting steps (e.g. substrate binding, mass transfer limitations) during the degradation of TCE. Here, we probe the details of the reductive dechlorination mechanism for different reductive dehalogenases in mixed enrichment cultures using dual element (Δδ13C/Δδ37Cl) isotope analysis. The slopes of dual element isotope plots remain largely constant even when masking suppresses observable kinetic isotope effects, so different slopes indicate a different initial transition state in the degradation mechanism [2]. Carbon and chlorine stable isotope ratios were observed during TCE biodegradation by a number of mixed enrichment cultures grown in microcosms with different chlorinated substrates to select for particular TCE-degrading reductive dehalogenases. This two-dimensional approach has the potential to elucidate whether different reductive dehalogenases use the same transition state in the rate-limiting step of TCE biodegradation. [1] Cichocka et al. (2008) Chemosphere 71, 639. [2] Elsner (2010) J. Environ. Monit. 12, 2005."

The degradation of pesticides in deeper soil layers and groundwater is of growing interest, becau... more The degradation of pesticides in deeper soil layers and groundwater is of growing interest, because they have repeatedly been found in drinking water supply wells and may pose a risk to future water resources. Current assessment schemes face a common problem, however: natural degradation often cannot be reliably assessed by concentration measurements alone, since mass balances are difficult to establish and transformation cannot be distinguished from sorption or dilution. Even detection of metabolites may only give an incomplete picture. When several transformation pathways occur, some metabolites may be degraded or form bound residues so that the associated pathways may be missed. Our research shows that dual isotope plots derived from compound specific isotope analysis offer a novel approach to give additional, complementary insight into the natural degradation of pesticides. Detection of metabolites is not required, since the isotope fractionation can be fully observed in the pesticide itself. Specifically, different initial biotransformation reactions of the phenylurea herbicide isoproturon (3-(4-isopropylphenyl)-1,1-dimethylurea) in pure culture experiments with bacterial and fungal strains showed strongly pathway-dependent isotope fractionation. When analyzing isotopic changes in different parts of the isoproturon molecule, hydroxylation of the isopropyl group by fungi was found to be associated with C and H isotope fractionation. In contrast, hydrolysis by Arthrobacter globiformis D47 caused strong C and N isotope fractionation, albeit in a different manner than abiotic hydrolysis so that isotope measurements can distinguish between both modes of transformation. Likewise, we observed highly pathway-dependent C and N isotope fractionation of atrazine (1-chloro-3-ethylamino-5-isopropylamino-2,4,6-triazine). Desalkylation of atrazine by Rhodococcus sp. strain NI86/21 resulted in enrichment of both 13-C and 15-N in atrazine, whereas hydrolysis to hydroxyatrazine by Chelatobacter heintzii, Pseudomonas sp. ADP and Arthrobacter aurescens TC1 gave enrichment of 13-C, but depletion of 15-N. Comparison with abiotic reference experiments provided novel insight into the underlying enzymatic transformation mechanisms. Our investigations show how characteristic isotope patterns may significantly add to the present understanding of the environmental fate of pesticides.

This study investigated C and, for the first time, Cl isotope fractionation of trichloroethene (T... more This study investigated C and, for the first time, Cl isotope fractionation of trichloroethene (TCE) and cisdichloroethene (cis-DCE) during reductive dechlorination by cast zero-valent iron (ZVI). Hydrogenolysis and b-dichloroelimination pathways occurred as parallel reactions, with ethene and ethane deriving from the b-dichloroelimination pathway. Carbon isotope fractionation of TCE and cis-DCE was consistent for different batches of Fe studied. Transformation of TCE and cis-DCE showed Cl isotopic enrichment factors (e Cl ) of À2.6‰ ± 0.1‰ (TCE) and À6.2‰ ± 0.8‰ (cis-DCE), with Apparent Kinetic Isotope Effects (AKIE Cl ) for Cl of 1.008 ± 0.001 (TCE) and 1.013 ± 0.002 (cis-DCE). This indicates that a C-Cl bond breakage is rate-determining in TCE and cis-DCE transformation by ZVI. Two approaches were investigated to evaluate if isotope fractionation analysis can distinguish the effectiveness of transformation by ZVI as opposed to natural biodegradation. (i) Dual isotope plots. This study reports the first dual (C, Cl) element isotope plots for TCE and cis-DCE degradation by ZVI. The pattern for cis-DCE differs markedly from that reported for biodegradation of the same compound by KB-1, a commercially available Dehalococcoidescontaining culture. The different trends suggest an expedient approach to distinguish abiotic and biotic transformation, but this needs to be confirmed in future studies. (ii) Product-related isotope fractionation. Carbon isotope ratios of the hydrogenolysis product cis-DCE differed consistently by 10‰ compared to the b-dichloroelimination products ethene and ethane providing a second line of evidence to differentiate abiotic or biotic degradation pathways.

Analytical Chemistry, Feb 1, 2010

Negatively charged analytes must be derivatized prior to gas chromatography-isotope ratio mass sp... more Negatively charged analytes must be derivatized prior to gas chromatography-isotope ratio mass spectrometry (GC-IRMS), with stringent control of isotope fractionation. Current methods require offline sample preparation. This study tests for the first time trimethylsulfonium hydroxide (TMSH) as online methylation agent prior to isotope analysis, addressing the herbicides bentazone and MCPA. Fully automated derivatization was achieved in a temperature-programmable GC injector, where reactants were injected into a packed liner, solvents were removed by split flow, and subsequent flash heating triggered the derivatization, thereby transferring derivatives onto the chromatographic column. Stoichiometric addition of TMSH resulted in complete conversion giving accurate and reproducible nitrogen isotope values of bentazone. In contrast, reproducible carbon isotope analysis required TMSH in g250-fold excess. Contrary to expectations, δ 13 C values became more negative at smaller TMSH excess. This indicates that elevated methyl group concentrations in the pore space of the injection liner facilitated close-to-equilibrium rather than kinetic isotope fractionation resulting in reproducible derivatization conditions. δ 13 C results under these conditions compared favorably with liquid chromatography-IRMS: low standard deviations (0.3‰ for GC-IRMS, 0.1‰ for LC-IRMS) and a comparable offset of 1‰ compared to elemental analyzer-IRMS demonstrate that both methods represent expedient ways for online isotope analysis of anionic target compounds.

Egu General Assembly Conference Abstracts, May 1, 2010

Site-specific quantitative 2H NMR: A new tool for the assessment of contaminant fate in the subsu... more Site-specific quantitative 2H NMR: A new tool for the assessment of contaminant fate in the subsurface

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 of carbon, nitrogen and hydrogen were established and are by now frequently used for a variety of organic pollutants. Yet, the motivation of introducing analytical methods for new isotopes is emerging. This motivation is further enhanced, as advantages of using two or more stable isotopes for gaining better insight on degradation pathways are well accepted. One important element which demands the development of appropriate analytical methods is chlorine, which is found in various groups of organic pollutants, among them the chlorinated ethylenes. Chlorinated ethylenes are considered as high priority environmental pollutants, and the development of suitable chlorine isotope methods for this group of pollutants is highly desired. Ideally, stable isotope techniques should have the capability to determine the isotopic composition of and individual target compound in a non-pure mixture, without the requirement of a laborious off-line treatment. Indeed, in the last years two different concepts for on-line chlorine isotope analysis methods were introduced, by using either a standard quadrapole GC/MS (Sakaguchi-Söder et al., 2007) or by using a GC/IRMS (Shouakar-Stash et al., 2006). We present a comparison of the performances of two concepts, carried out in five different laboratories: Waterloo (GC/IRMS), Neuchâtel (GC/MS), Darmstadt (GC/MS), Tübingen (GC/MS) and Munich (GC/IRMS). This comparison was performed on pure trichloroethylene and dichloroethylene products of different manufactures, as well as trichloroethylene and dichloroethylene samples that were exposed to biodegradation. This study sets standards for further application of these techniques to distinguish sources and track degradation processes in the sub-surface.

Environmental Science Technology, 2007

Despite widespread implementation of zero-valent iron remediation schemes, the manner and order o... more Despite widespread implementation of zero-valent iron remediation schemes, the manner and order of chemical bond cleavage in iron-mediated organohalide transformations remains imperfectly understood. We present insights from carbon isotope fractionation for the dehalogenation of 1,1,2,2-tetrachloroethane (1,1,2,2-TeCA) and 1,1,1-trichloroethane (1,1,1-TCA) by various reactants. Elimination of HCl by OH- gave isotope fractionation in 1,1,2,2-TeCA of Euro = -25.6 per thousand, KIE(c) = 1.02 to 1.03 per carbon center, consistentwith a concerted (E2) mechanism. In contrast, 1,1,1-TCA reduction by Cr(II), Fe(0), and Cu-plated iron (Cu/Fe) resulted in Euro = -13.6 per thousand to -15.8 per thousand indicating the initial involvement of a single C-Cl bond (KIE(c) approximately 1.03). 1,1,2,2-TeCA reduction by Cr(II), Fe(0), and Cu/Fe yielded Euro = -18.7 per thousand, -19.3 per thousand, and -17.0 per thousand, respectively. In the two latter cases, depletion of the minor product TCE by 26 per thousand indicated its formation via nonreductive dehydrohalogenation. The major 1,1,2,2-TeCA reduction products, cis- and trans-DCE, differed by 2.3 per thousand +/- 1.0 per thousand in Cr(II) systems, but were equivalent in Fe(0) and Cu/Fe systems. In contrast, the ratio of cis-DCE to trans-DCE concentration was 2.5 for reduction with Cr(II) and Fe(0), but -3.8 with Cu/Fe. Complementary isotope and concentration data therefore suggest differences in the transition state geometry and/ or reaction intermediates in each reductant system.

Environmental Science and Technology, Dec 1, 2008

Compound-specific stable isotope analysis by gas chromatography-isotope ratio mass spectrometry (... more Compound-specific stable isotope analysis by gas chromatography-isotope ratio mass spectrometry (GC-IRMS) is increasingly used to assess origin and fate of organic substances in the environment. Although analysis without isotopic discrimination is essential, it cannot be taken for granted for new target compounds. We developed and validated carbon isotope analysis of atrazine, a herbicide widely used in agriculture. Combustion was tested with reactors containing (i) CuO/NiO/ Pt operating at 940°C; (ii) CuO operating at 800°C; (iii) Ni/NiO operating at 1150°C and being reoxidized for 2 min during each gas chromatographic run. Accurate and precise carbon isotope measurements were only obtained with Ni/NiO reactors giving a mean deviation ∆δ 13 C from dual inlet measurements of -0.1-0.2‰ and a standard deviation (SD) of (0.4‰. CuO at 800°C gave precise, but inaccurate values (∆δ 13 C ) -1.3‰, SD (0.4‰), whereas CuO/NiO/Pt reactors at 940°C gave inaccurate and imprecise data. Accurate (∆δ 15 N ) 0.2‰) and precise (SD (0.3‰) nitrogen isotope analysis was accomplished with a Ni/NiO-reactor previously used for carbon isotope analysis. The applicability of the method was demonstrated for alkaline hydrolysis of atrazine at 20°C and pH 12 (nucleophilic aromatic substitution) giving carbon ) -5.6‰ ( 0.1‰ (SD) and nitrogen ) -1.2‰ ( 0.1‰ (SD).

Environmental Science and Technology, Sep 12, 2014

The role of the corrinoid cofactor in reductive dehalogenation catalysis by tetrachloroethene red... more The role of the corrinoid cofactor in reductive dehalogenation catalysis by tetrachloroethene reductive dehalogenase (PceA) of Sulfurospirillum multivorans was investigated using isotope analysis of carbon and chlorine. Crude extracts containing PceA--harboring either a native norpseudo-B12 or the alternative nor-B12 cofactor--were applied for dehalogenation of tetrachloroethene (PCE) or trichloroethene (TCE), and compared to abiotic dehalogenation with the respective purified corrinoids (norpseudovitamin B12 and norvitamin B12), as well as several commercially available cobalamins and cobinamide. Dehalogenation of TCE resulted in a similar extent of C and Cl isotope fractionation, and in similar dual-element isotope slopes (εC/εCl) of 5.0-5.3 for PceA enzyme and 3.7-4.5 for the corrinoids. Both observations support an identical reaction mechanism. For PCE, in contrast, observed C and Cl isotope fractionation was smaller in enzymatic dehalogenation, and dual-element isotope slopes (2.2-2.8) were distinctly different compared to dehalogenation mediated by corrinoids (4.6-7.0). Remarkably, εC/εCl of PCE depended in addition on the corrinoid type: εC/εCl values of 4.6 and 5.0 for vitamin B12 and norvitamin B12 were significantly different compared to values of 6.9 and 7.0 for norpseudovitamin B12 and dicyanocobinamide. Our results therefore suggest mechanistic and/or kinetic differences in catalytic PCE dehalogenation by enzymes and different corrinoids, whereas such differences were not observed for TCE.

Environmental Science & Technology, 2016

Compound-specific isotope analysis (CSIA) receives increasing interest for its ability to detect ... more Compound-specific isotope analysis (CSIA) receives increasing interest for its ability to detect natural degradation of pesticides and pharmaceuticals. Despite recent laboratory studies, CSIA investigations of such micropollutants in the environment are still rare. To explore the certainty of information obtainable by CSIA in a near-environmental setting, a pulse of the pesticide bentazone, the pesticide metabolite 2,6-dichlorobenzamide (BAM), and the pharmaceuticals diclofenac and ibuprofen was released into a mesoscale aquifer with quasi-two-dimensional flow. Concentration breakthrough curves (BTC) of BAM and ibuprofen demonstrated neither degradation nor sorption. Bentazone was transformed but did not sorb significantly, whereas diclofenac showed both degradation and sorption. Carbon and nitrogen CSIA could be accomplished in similar concentrations as for "traditional" priority pollutants (low μg/L range), however, at the cost of uncertainties (0.4-0.5‰ (carbon), 1‰ (nitrogen)). Nonetheless, invariant carbon and nitrogen isotope values confirmed that BAM was neither degraded nor sorbed, while significant enrichment of (13)C and in particular (15)N corroborated transformation of diclofenac and bentazone. Retardation of diclofenac was reflected in additional (15)N sorption isotope effects, whereas isotope fractionation of transverse dispersion could not be identified. These results provide a benchmark on the performance of CSIA to monitor the reactivity of micropollutants in aquifers and may guide future efforts to accomplish CSIA at even lower concentrations (ng/L range).

Environmental science & technology, Jan 9, 2016

Much interest is directed at the chemical structure of hydraulic fracturing (HF) additives in unc... more Much interest is directed at the chemical structure of hydraulic fracturing (HF) additives in unconventional gas exploitation. To bridge the gap between existing alphabetical disclosures by function/CAS number and emerging scientific contributions on fate and toxicity, we review the structural properties which motivate HF applications, and which determine environmental fate and toxicity. Our quantitative overview relied on voluntary U.S. disclosures evaluated from the FracFocus registry by different sources and on a House of Representatives ("Waxman") list. Out of over 1000 reported substances, classification by chemistry yielded succinct subsets able to illustrate the rationale of their use, and physicochemical properties relevant for environmental fate, toxicity and chemical analysis. While many substances were nontoxic, frequent disclosures also included notorious groundwater contaminants like petroleum hydrocarbons (solvents), precursors of endocrine disruptors like no...

Analytical chemistry, Jan 14, 2016

An international project developed, quality-tested, and determined isotope-δ values of 19 new org... more An international project developed, quality-tested, and determined isotope-δ values of 19 new organic reference materials (RMs) for hydrogen, carbon, and nitrogen stable isotope-ratio measurements, in addition to analyzing pre-existing RMs NBS 22 (oil), IAEA-CH-7 (polyethylene foil), and IAEA-600 (caffeine). These new RMs enable users to normalize measurements of samples to isotope-δ scales. The RMs span a range of δ2HVSMOW-SLAP values from -210.8 to +397.0 mUr or ‰, for δ13CVPDB-LSVEC from -40.81 to +0.49 mUr, and for δ15NAir from -5.21 to +61.53 mUr. Many of the new RMs are amenable to gas and liquid chromatography. The RMs include triads of isotopically contrasting caffeines, C16 n-alkanes, n-C20-fatty acid methyl esters (FAMEs), glycines, and L-valines, together with polyethylene powder and string, one n-C17-FAME, a vacuum oil (NBS 22a) to replace NBS 22 oil, and a 2H-enriched vacuum oil. Eleven laboratories from 7 countries used multiple analytical approaches and instrumentatio...

Environmental Science and Technology, Feb 1, 2004

Fe(II) present at surfaces of iron-containing minerals can play a significant role in the overall... more Fe(II) present at surfaces of iron-containing minerals can play a significant role in the overall attenuation of reducible contaminants in the subsurface. As the chemical environment, i.e., the type and arrangement of ligands, strongly affects the redox potential of Fe(II), the presence of various mineral sorbents is expected to modulate the reactivity of surficial Fe(II)-species in aqueous systems. In a comparative study we evaluated the reactivity of ferrous iron in aqueous suspensions of siderite (FeCO3), nontronite (ferruginous smectite SWa-1), hematite (alpha-Fe2O3), lepidocrocite (gamma-FeOOH), goethite (alpha-FeOOH), magnetite (Fe3O4), sulfate green rust (Fe(II)4Fe(III)2(OH)12SO4 x 4H2O), pyrite (FeS2), and mackinawite (FeS) under similar conditions (pH 7.2, 25 m2 mineral/L, 1 mM Fe(II)aq, O2 (aq) < 0.1 g/L). Surface-area-normalized pseudo first-order rate constants are reported for the reduction of hexachloroethane and 4-chloronitrobenzene representing two classes of environmentally relevant transformation reactions of pollutants, i.e., dehalogenation and nitroaryl reduction. The reactivities of the different Fe(II) mineral systems varied greatly and systematically both within and between the two data sets obtained with the two probe compounds. As a general trend, surface-area-normalized reaction rates increased in the order Fe(II) + siderite < Fe(II) + iron oxides < Fe(II) + iron sulfides. 4-Chloronitrobenzene was transformed by mineral-bound Fe(II) much more rapidly than hexachloroethane, except for suspensions of hematite, pyrite, and nontronite. The results demonstrate that abiotic reactions with surface-bound Fe(II) may affect or even dominate the long-term behavior of reducible pollutants in the subsurface, particularly in the presence of Fe(III) bearing minerals. As such reactions can be dominated by specific interactions of the oxidant with the surface, care must be taken in extrapolating reactivity data of surface-bound Fe(II) between different compound classes.

The Science of the total environment, Jan 15, 2017

cis-1,2-Dichloroethene (cis-DCE) and trichloroethene (TCE) are persistent, toxic and mobile pollu... more cis-1,2-Dichloroethene (cis-DCE) and trichloroethene (TCE) are persistent, toxic and mobile pollutants in groundwater systems. They are both conducive to reductive dehalogenation and to oxidation by permanganate. In this study, the potential of dual element (C, Cl) compound specific isotope analyses (CSIA) for distinguishing between chemical oxidation and anaerobic reductive dechlorination of cis-DCE and TCE was investigated. Well-controlled cis-DCE degradation batch tests gave similar carbon isotope enrichment factors εC (‰), but starkly contrasting dual element isotope slopes Δδ(13)C/Δδ(37)Cl for permanganate oxidation (εC=-26‰±6‰, Δδ(13)C/Δδ(37)Cl≈-125±47) compared to reductive dechlorination (εC=-18‰±4‰, Δδ(13)C/Δδ(37)Cl≈4.5±3.4). The difference can be tracked down to distinctly different chlorine isotope fractionation: an inverse isotope effect during chemical oxidation (εCl=+0.2‰±0.1‰) compared to a large normal isotope effect in reductive dechlorination (εCl=-3.3‰±0.9‰) (p≪0....

Environmental science & technology, Jan 16, 2017

Chlorinated ethenes (CEs) such as perchloroethylene, trichloroethylene and dichloroethylene are n... more Chlorinated ethenes (CEs) such as perchloroethylene, trichloroethylene and dichloroethylene are notorious groundwater contaminants. Although reductive dehalogenation is key to their environmental and engineered degradation, underlying reaction mechanisms remain elusive. Outer-sphere reductive single electron transfer (OS-SET) has been proposed for such different processes as Vitamin B12-dependent biodegradation and zerovalent metal-mediated dehalogenation. Compound-specific isotope effect ((13)C/(12)C, (37)Cl/(35)Cl) analysis offers a new opportunity to test these hypotheses. Defined OS-SET model reactants (CO2 radical anions, S(2-)-doped graphene oxide in water) caused strong carbon (εC = -7.9‰ to -11.9‰), but negligible chlorine isotope effects (εCl = -0.12‰ to 0.04‰) in CEs. Greater chlorine isotope effects were observed in CHCl3 (εC = -7.7‰, εCl = -2.6‰), and in CEs when the exergonicity of C-Cl bond cleavage was reduced in an organic solvent (reaction with arene radical anions ...

Environmental Science & Technology, 2016

Although diclofenac ranks among the most frequently detected pharmaceuticals in the urban water c... more Although diclofenac ranks among the most frequently detected pharmaceuticals in the urban water cycle, its environmental transformation reactions remain imperfectly understood. Biodegradation-induced changes in (15)N/(14)N ratios (εN = -7.1‰ ± 0.4‰) have indicated that compound-specific isotope analysis (CSIA) may detect diclofenac degradation. This singular observation warrants exploration for further transformation reactions. The present study surveys carbon and nitrogen isotope fractionation in other environmental and engineered transformation reactions of diclofenac. While carbon isotope fractionation was generally small, observed nitrogen isotope fractionation in degradation by MnO2 (εN = -7.3‰ ± 0.3‰), photolysis (εN = +1.9‰ ± 0.1‰), and ozonation (εN = +1.5‰ ± 0.2‰) revealed distinct trends for different oxidative transformation reactions. The small, secondary isotope effect associated with ozonation suggests an attack of O3 in a molecular position distant from the N atom. Model reactants for outer-sphere single electron transfer generated large inverse nitrogen isotope fractionation (εN = +5.7‰ ± 0.3‰), ruling out this mechanism for biodegradation and transformation by MnO2. In a river model, isotope fractionation-derived degradation estimates agreed well with concentration mass balances, providing a proof-of-principle validation for assessing micropollutant degradation in river sediment. Our study highlights the prospect of combining CSIA with transformation product analysis for a better assessment of transformation reactions within the environmental life of diclofenac.

Environmental microbiology, Jan 15, 2016

Biostimulation is widely used to enhance reductive dechlorination of chlorinated ethenes in conta... more Biostimulation is widely used to enhance reductive dechlorination of chlorinated ethenes in contaminated aquifers. However, the knowledge on corresponding biogeochemical responses is limited. In this study glycerol was injected in an aquifer contaminated with cis-dichloroethene (cDCE), and geochemical and microbial shifts were followed for 265 days. Consistent with anoxic conditions and sulfate reduction after biostimulation, MiSeq 16S rRNA gene sequencing revealed temporarily increased relative abundance of Firmicutes, Bacteriodetes and sulfate reducing Deltaproteobacteria. In line with (13) C cDCE enrichment and increased Dehalococcoides mccartyi (Dcm) numbers, dechlorination was observed towards the end of the field experiment, albeit being incomplete with accumulation of vinyl chloride. This was concurrent with i) decreased concentrations of dissolved organic carbon (DOC), reduced relative abundances of fermenting and sulfate reducing bacteria that have been suggested to promote...

Environmental Science & Technology, 2016

Unconventional natural gas development (UNGD) generates large volumes of wastewater, the detailed... more Unconventional natural gas development (UNGD) generates large volumes of wastewater, the detailed composition of which must be known for adequate risk assessment and treatment. In particular, transformation products of geogenic compounds and disclosed additives have not been described. This study investigated six Fayetteville Shale wastewater samples for organic composition using a suite of one- and two-dimensional gas chromatographic techniques to capture a broad distribution of chemical structures. Following the application of strict compound-identification-confidence criteria, we classified compounds according to their putative origin. Samples displayed distinct chemical distributions composed of typical geogenic substances (hydrocarbons and hopane biomarkers), disclosed UNGD additives (e.g., hydrocarbons, phthalates such as diisobutyl phthalate, and radical initiators such as azobis(isobutyronitrile)), and undisclosed compounds (e.g., halogenated hydrocarbons, such as 2-bromohexane or 4-bromoheptane). Undisclosed chloromethyl alkanoates (chloromethyl propanoate, pentanoate, and octanoate) were identified as potential delayed acids (i.e., those that release acidic moieties only after hydrolytic cleavage, the rate of which could be potentially controlled), suggesting they were deliberately introduced to react in the subsurface. In contrast, the identification of halogenated methanes and acetones suggested that those compounds were formed as unintended byproducts. Our study highlights the possibility that UNGD operations generate transformation products and underscores the value of disclosing additives injected into the subsurface.

Environmental Science Technology, 2010

Environmental Science and Technology, Feb 1, 2010

The fate of pesticides in the subsurface is of great interest to the public, industry, and regula... more The fate of pesticides in the subsurface is of great interest to the public, industry, and regulatory authorities. Compoundspecific isotope analysis (CSIA) is a promising tool complementary to existing methods for elucidating pesticide degradation reactions. Here, we address three different initial biotransformation reactions of the phenylurea herbicide isoproturon (3-(4isopropylphenyl)-1,1-dimethylurea) in pure culture experiments with bacterial and fungal strains. When analyzing isotopic changes in different parts of the isoproturon molecule, hydroxylation of the isopropyl group by fungi was found to be associated with C and H isotope fractionation. In contrast, hydrolysis by Arthrobacter globiformis D47 caused strong C and N isotope fractionation, albeit in a different manner than abiotic hydrolysis so that isotope measurements can distinguish between both modes of transformation. No significant isotope fractionation was observed during N-demethylation by Sphingomonas sp. SRS2. The observed isotope fractionation patterns were in agreement with the type of reactions and elements involved. Moreover, their substantially different nature suggests that isotope changes in natural samples may be uniquely attributed to either pathway, allowing even to distinguish the abiotic versus biotic nature of hydrolysis. Our investigations show how characteristic isotope patterns may significantly add to the present understanding of the environmental fate of pesticides.

"Compound specific isotope analysis can be used to quantify the in situ biodegradation of to... more "Compound specific isotope analysis can be used to quantify the in situ biodegradation of toxic chlorinated ethenes, such as trichloroethene (TCE), in groundwater. However, while the anaerobic biodegradation of TCE occurs via reductive dechlorination, the magnitude of observed kinetic isotope effects for carbon has varied widely for different bacteria and enrichment cultures [1]. This variability could indicate different initial transition states within the reaction mechanism or masking of the observed carbon kinetic isotope effect due to additional rate-limiting steps (e.g. substrate binding, mass transfer limitations) during the degradation of TCE. Here, we probe the details of the reductive dechlorination mechanism for different reductive dehalogenases in mixed enrichment cultures using dual element (Δδ13C/Δδ37Cl) isotope analysis. The slopes of dual element isotope plots remain largely constant even when masking suppresses observable kinetic isotope effects, so different slopes indicate a different initial transition state in the degradation mechanism [2]. Carbon and chlorine stable isotope ratios were observed during TCE biodegradation by a number of mixed enrichment cultures grown in microcosms with different chlorinated substrates to select for particular TCE-degrading reductive dehalogenases. This two-dimensional approach has the potential to elucidate whether different reductive dehalogenases use the same transition state in the rate-limiting step of TCE biodegradation. [1] Cichocka et al. (2008) Chemosphere 71, 639. [2] Elsner (2010) J. Environ. Monit. 12, 2005."

The degradation of pesticides in deeper soil layers and groundwater is of growing interest, becau... more The degradation of pesticides in deeper soil layers and groundwater is of growing interest, because they have repeatedly been found in drinking water supply wells and may pose a risk to future water resources. Current assessment schemes face a common problem, however: natural degradation often cannot be reliably assessed by concentration measurements alone, since mass balances are difficult to establish and transformation cannot be distinguished from sorption or dilution. Even detection of metabolites may only give an incomplete picture. When several transformation pathways occur, some metabolites may be degraded or form bound residues so that the associated pathways may be missed. Our research shows that dual isotope plots derived from compound specific isotope analysis offer a novel approach to give additional, complementary insight into the natural degradation of pesticides. Detection of metabolites is not required, since the isotope fractionation can be fully observed in the pesticide itself. Specifically, different initial biotransformation reactions of the phenylurea herbicide isoproturon (3-(4-isopropylphenyl)-1,1-dimethylurea) in pure culture experiments with bacterial and fungal strains showed strongly pathway-dependent isotope fractionation. When analyzing isotopic changes in different parts of the isoproturon molecule, hydroxylation of the isopropyl group by fungi was found to be associated with C and H isotope fractionation. In contrast, hydrolysis by Arthrobacter globiformis D47 caused strong C and N isotope fractionation, albeit in a different manner than abiotic hydrolysis so that isotope measurements can distinguish between both modes of transformation. Likewise, we observed highly pathway-dependent C and N isotope fractionation of atrazine (1-chloro-3-ethylamino-5-isopropylamino-2,4,6-triazine). Desalkylation of atrazine by Rhodococcus sp. strain NI86/21 resulted in enrichment of both 13-C and 15-N in atrazine, whereas hydrolysis to hydroxyatrazine by Chelatobacter heintzii, Pseudomonas sp. ADP and Arthrobacter aurescens TC1 gave enrichment of 13-C, but depletion of 15-N. Comparison with abiotic reference experiments provided novel insight into the underlying enzymatic transformation mechanisms. Our investigations show how characteristic isotope patterns may significantly add to the present understanding of the environmental fate of pesticides.

This study investigated C and, for the first time, Cl isotope fractionation of trichloroethene (T... more This study investigated C and, for the first time, Cl isotope fractionation of trichloroethene (TCE) and cisdichloroethene (cis-DCE) during reductive dechlorination by cast zero-valent iron (ZVI). Hydrogenolysis and b-dichloroelimination pathways occurred as parallel reactions, with ethene and ethane deriving from the b-dichloroelimination pathway. Carbon isotope fractionation of TCE and cis-DCE was consistent for different batches of Fe studied. Transformation of TCE and cis-DCE showed Cl isotopic enrichment factors (e Cl ) of À2.6‰ ± 0.1‰ (TCE) and À6.2‰ ± 0.8‰ (cis-DCE), with Apparent Kinetic Isotope Effects (AKIE Cl ) for Cl of 1.008 ± 0.001 (TCE) and 1.013 ± 0.002 (cis-DCE). This indicates that a C-Cl bond breakage is rate-determining in TCE and cis-DCE transformation by ZVI. Two approaches were investigated to evaluate if isotope fractionation analysis can distinguish the effectiveness of transformation by ZVI as opposed to natural biodegradation. (i) Dual isotope plots. This study reports the first dual (C, Cl) element isotope plots for TCE and cis-DCE degradation by ZVI. The pattern for cis-DCE differs markedly from that reported for biodegradation of the same compound by KB-1, a commercially available Dehalococcoidescontaining culture. The different trends suggest an expedient approach to distinguish abiotic and biotic transformation, but this needs to be confirmed in future studies. (ii) Product-related isotope fractionation. Carbon isotope ratios of the hydrogenolysis product cis-DCE differed consistently by 10‰ compared to the b-dichloroelimination products ethene and ethane providing a second line of evidence to differentiate abiotic or biotic degradation pathways.

Analytical Chemistry, Feb 1, 2010

Negatively charged analytes must be derivatized prior to gas chromatography-isotope ratio mass sp... more Negatively charged analytes must be derivatized prior to gas chromatography-isotope ratio mass spectrometry (GC-IRMS), with stringent control of isotope fractionation. Current methods require offline sample preparation. This study tests for the first time trimethylsulfonium hydroxide (TMSH) as online methylation agent prior to isotope analysis, addressing the herbicides bentazone and MCPA. Fully automated derivatization was achieved in a temperature-programmable GC injector, where reactants were injected into a packed liner, solvents were removed by split flow, and subsequent flash heating triggered the derivatization, thereby transferring derivatives onto the chromatographic column. Stoichiometric addition of TMSH resulted in complete conversion giving accurate and reproducible nitrogen isotope values of bentazone. In contrast, reproducible carbon isotope analysis required TMSH in g250-fold excess. Contrary to expectations, δ 13 C values became more negative at smaller TMSH excess. This indicates that elevated methyl group concentrations in the pore space of the injection liner facilitated close-to-equilibrium rather than kinetic isotope fractionation resulting in reproducible derivatization conditions. δ 13 C results under these conditions compared favorably with liquid chromatography-IRMS: low standard deviations (0.3‰ for GC-IRMS, 0.1‰ for LC-IRMS) and a comparable offset of 1‰ compared to elemental analyzer-IRMS demonstrate that both methods represent expedient ways for online isotope analysis of anionic target compounds.

Egu General Assembly Conference Abstracts, May 1, 2010

Site-specific quantitative 2H NMR: A new tool for the assessment of contaminant fate in the subsu... more Site-specific quantitative 2H NMR: A new tool for the assessment of contaminant fate in the subsurface

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 of carbon, nitrogen and hydrogen were established and are by now frequently used for a variety of organic pollutants. Yet, the motivation of introducing analytical methods for new isotopes is emerging. This motivation is further enhanced, as advantages of using two or more stable isotopes for gaining better insight on degradation pathways are well accepted. One important element which demands the development of appropriate analytical methods is chlorine, which is found in various groups of organic pollutants, among them the chlorinated ethylenes. Chlorinated ethylenes are considered as high priority environmental pollutants, and the development of suitable chlorine isotope methods for this group of pollutants is highly desired. Ideally, stable isotope techniques should have the capability to determine the isotopic composition of and individual target compound in a non-pure mixture, without the requirement of a laborious off-line treatment. Indeed, in the last years two different concepts for on-line chlorine isotope analysis methods were introduced, by using either a standard quadrapole GC/MS (Sakaguchi-Söder et al., 2007) or by using a GC/IRMS (Shouakar-Stash et al., 2006). We present a comparison of the performances of two concepts, carried out in five different laboratories: Waterloo (GC/IRMS), Neuchâtel (GC/MS), Darmstadt (GC/MS), Tübingen (GC/MS) and Munich (GC/IRMS). This comparison was performed on pure trichloroethylene and dichloroethylene products of different manufactures, as well as trichloroethylene and dichloroethylene samples that were exposed to biodegradation. This study sets standards for further application of these techniques to distinguish sources and track degradation processes in the sub-surface.

Environmental Science Technology, 2007

Despite widespread implementation of zero-valent iron remediation schemes, the manner and order o... more Despite widespread implementation of zero-valent iron remediation schemes, the manner and order of chemical bond cleavage in iron-mediated organohalide transformations remains imperfectly understood. We present insights from carbon isotope fractionation for the dehalogenation of 1,1,2,2-tetrachloroethane (1,1,2,2-TeCA) and 1,1,1-trichloroethane (1,1,1-TCA) by various reactants. Elimination of HCl by OH- gave isotope fractionation in 1,1,2,2-TeCA of Euro = -25.6 per thousand, KIE(c) = 1.02 to 1.03 per carbon center, consistentwith a concerted (E2) mechanism. In contrast, 1,1,1-TCA reduction by Cr(II), Fe(0), and Cu-plated iron (Cu/Fe) resulted in Euro = -13.6 per thousand to -15.8 per thousand indicating the initial involvement of a single C-Cl bond (KIE(c) approximately 1.03). 1,1,2,2-TeCA reduction by Cr(II), Fe(0), and Cu/Fe yielded Euro = -18.7 per thousand, -19.3 per thousand, and -17.0 per thousand, respectively. In the two latter cases, depletion of the minor product TCE by 26 per thousand indicated its formation via nonreductive dehydrohalogenation. The major 1,1,2,2-TeCA reduction products, cis- and trans-DCE, differed by 2.3 per thousand +/- 1.0 per thousand in Cr(II) systems, but were equivalent in Fe(0) and Cu/Fe systems. In contrast, the ratio of cis-DCE to trans-DCE concentration was 2.5 for reduction with Cr(II) and Fe(0), but -3.8 with Cu/Fe. Complementary isotope and concentration data therefore suggest differences in the transition state geometry and/ or reaction intermediates in each reductant system.

Environmental Science and Technology, Dec 1, 2008

Compound-specific stable isotope analysis by gas chromatography-isotope ratio mass spectrometry (... more Compound-specific stable isotope analysis by gas chromatography-isotope ratio mass spectrometry (GC-IRMS) is increasingly used to assess origin and fate of organic substances in the environment. Although analysis without isotopic discrimination is essential, it cannot be taken for granted for new target compounds. We developed and validated carbon isotope analysis of atrazine, a herbicide widely used in agriculture. Combustion was tested with reactors containing (i) CuO/NiO/ Pt operating at 940°C; (ii) CuO operating at 800°C; (iii) Ni/NiO operating at 1150°C and being reoxidized for 2 min during each gas chromatographic run. Accurate and precise carbon isotope measurements were only obtained with Ni/NiO reactors giving a mean deviation ∆δ 13 C from dual inlet measurements of -0.1-0.2‰ and a standard deviation (SD) of (0.4‰. CuO at 800°C gave precise, but inaccurate values (∆δ 13 C ) -1.3‰, SD (0.4‰), whereas CuO/NiO/Pt reactors at 940°C gave inaccurate and imprecise data. Accurate (∆δ 15 N ) 0.2‰) and precise (SD (0.3‰) nitrogen isotope analysis was accomplished with a Ni/NiO-reactor previously used for carbon isotope analysis. The applicability of the method was demonstrated for alkaline hydrolysis of atrazine at 20°C and pH 12 (nucleophilic aromatic substitution) giving carbon ) -5.6‰ ( 0.1‰ (SD) and nitrogen ) -1.2‰ ( 0.1‰ (SD).

Environmental Science and Technology, Sep 12, 2014

The role of the corrinoid cofactor in reductive dehalogenation catalysis by tetrachloroethene red... more The role of the corrinoid cofactor in reductive dehalogenation catalysis by tetrachloroethene reductive dehalogenase (PceA) of Sulfurospirillum multivorans was investigated using isotope analysis of carbon and chlorine. Crude extracts containing PceA--harboring either a native norpseudo-B12 or the alternative nor-B12 cofactor--were applied for dehalogenation of tetrachloroethene (PCE) or trichloroethene (TCE), and compared to abiotic dehalogenation with the respective purified corrinoids (norpseudovitamin B12 and norvitamin B12), as well as several commercially available cobalamins and cobinamide. Dehalogenation of TCE resulted in a similar extent of C and Cl isotope fractionation, and in similar dual-element isotope slopes (εC/εCl) of 5.0-5.3 for PceA enzyme and 3.7-4.5 for the corrinoids. Both observations support an identical reaction mechanism. For PCE, in contrast, observed C and Cl isotope fractionation was smaller in enzymatic dehalogenation, and dual-element isotope slopes (2.2-2.8) were distinctly different compared to dehalogenation mediated by corrinoids (4.6-7.0). Remarkably, εC/εCl of PCE depended in addition on the corrinoid type: εC/εCl values of 4.6 and 5.0 for vitamin B12 and norvitamin B12 were significantly different compared to values of 6.9 and 7.0 for norpseudovitamin B12 and dicyanocobinamide. Our results therefore suggest mechanistic and/or kinetic differences in catalytic PCE dehalogenation by enzymes and different corrinoids, whereas such differences were not observed for TCE.

Environmental Science & Technology, 2016

Compound-specific isotope analysis (CSIA) receives increasing interest for its ability to detect ... more Compound-specific isotope analysis (CSIA) receives increasing interest for its ability to detect natural degradation of pesticides and pharmaceuticals. Despite recent laboratory studies, CSIA investigations of such micropollutants in the environment are still rare. To explore the certainty of information obtainable by CSIA in a near-environmental setting, a pulse of the pesticide bentazone, the pesticide metabolite 2,6-dichlorobenzamide (BAM), and the pharmaceuticals diclofenac and ibuprofen was released into a mesoscale aquifer with quasi-two-dimensional flow. Concentration breakthrough curves (BTC) of BAM and ibuprofen demonstrated neither degradation nor sorption. Bentazone was transformed but did not sorb significantly, whereas diclofenac showed both degradation and sorption. Carbon and nitrogen CSIA could be accomplished in similar concentrations as for "traditional" priority pollutants (low μg/L range), however, at the cost of uncertainties (0.4-0.5‰ (carbon), 1‰ (nitrogen)). Nonetheless, invariant carbon and nitrogen isotope values confirmed that BAM was neither degraded nor sorbed, while significant enrichment of (13)C and in particular (15)N corroborated transformation of diclofenac and bentazone. Retardation of diclofenac was reflected in additional (15)N sorption isotope effects, whereas isotope fractionation of transverse dispersion could not be identified. These results provide a benchmark on the performance of CSIA to monitor the reactivity of micropollutants in aquifers and may guide future efforts to accomplish CSIA at even lower concentrations (ng/L range).

Environmental science & technology, Jan 9, 2016

Much interest is directed at the chemical structure of hydraulic fracturing (HF) additives in unc... more Much interest is directed at the chemical structure of hydraulic fracturing (HF) additives in unconventional gas exploitation. To bridge the gap between existing alphabetical disclosures by function/CAS number and emerging scientific contributions on fate and toxicity, we review the structural properties which motivate HF applications, and which determine environmental fate and toxicity. Our quantitative overview relied on voluntary U.S. disclosures evaluated from the FracFocus registry by different sources and on a House of Representatives ("Waxman") list. Out of over 1000 reported substances, classification by chemistry yielded succinct subsets able to illustrate the rationale of their use, and physicochemical properties relevant for environmental fate, toxicity and chemical analysis. While many substances were nontoxic, frequent disclosures also included notorious groundwater contaminants like petroleum hydrocarbons (solvents), precursors of endocrine disruptors like no...

Analytical chemistry, Jan 14, 2016

An international project developed, quality-tested, and determined isotope-δ values of 19 new org... more An international project developed, quality-tested, and determined isotope-δ values of 19 new organic reference materials (RMs) for hydrogen, carbon, and nitrogen stable isotope-ratio measurements, in addition to analyzing pre-existing RMs NBS 22 (oil), IAEA-CH-7 (polyethylene foil), and IAEA-600 (caffeine). These new RMs enable users to normalize measurements of samples to isotope-δ scales. The RMs span a range of δ2HVSMOW-SLAP values from -210.8 to +397.0 mUr or ‰, for δ13CVPDB-LSVEC from -40.81 to +0.49 mUr, and for δ15NAir from -5.21 to +61.53 mUr. Many of the new RMs are amenable to gas and liquid chromatography. The RMs include triads of isotopically contrasting caffeines, C16 n-alkanes, n-C20-fatty acid methyl esters (FAMEs), glycines, and L-valines, together with polyethylene powder and string, one n-C17-FAME, a vacuum oil (NBS 22a) to replace NBS 22 oil, and a 2H-enriched vacuum oil. Eleven laboratories from 7 countries used multiple analytical approaches and instrumentatio...

Environmental Science and Technology, Feb 1, 2004

Fe(II) present at surfaces of iron-containing minerals can play a significant role in the overall... more Fe(II) present at surfaces of iron-containing minerals can play a significant role in the overall attenuation of reducible contaminants in the subsurface. As the chemical environment, i.e., the type and arrangement of ligands, strongly affects the redox potential of Fe(II), the presence of various mineral sorbents is expected to modulate the reactivity of surficial Fe(II)-species in aqueous systems. In a comparative study we evaluated the reactivity of ferrous iron in aqueous suspensions of siderite (FeCO3), nontronite (ferruginous smectite SWa-1), hematite (alpha-Fe2O3), lepidocrocite (gamma-FeOOH), goethite (alpha-FeOOH), magnetite (Fe3O4), sulfate green rust (Fe(II)4Fe(III)2(OH)12SO4 x 4H2O), pyrite (FeS2), and mackinawite (FeS) under similar conditions (pH 7.2, 25 m2 mineral/L, 1 mM Fe(II)aq, O2 (aq) < 0.1 g/L). Surface-area-normalized pseudo first-order rate constants are reported for the reduction of hexachloroethane and 4-chloronitrobenzene representing two classes of environmentally relevant transformation reactions of pollutants, i.e., dehalogenation and nitroaryl reduction. The reactivities of the different Fe(II) mineral systems varied greatly and systematically both within and between the two data sets obtained with the two probe compounds. As a general trend, surface-area-normalized reaction rates increased in the order Fe(II) + siderite < Fe(II) + iron oxides < Fe(II) + iron sulfides. 4-Chloronitrobenzene was transformed by mineral-bound Fe(II) much more rapidly than hexachloroethane, except for suspensions of hematite, pyrite, and nontronite. The results demonstrate that abiotic reactions with surface-bound Fe(II) may affect or even dominate the long-term behavior of reducible pollutants in the subsurface, particularly in the presence of Fe(III) bearing minerals. As such reactions can be dominated by specific interactions of the oxidant with the surface, care must be taken in extrapolating reactivity data of surface-bound Fe(II) between different compound classes.