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Transformation of Chlorofluorocarbons Investigated via Stable Carbon Compound-Specific Isotope Analysis
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  • Elizabeth Phillips
    Elizabeth Phillips
    Department of Earth Sciences, University of Toronto, Toronto, Ontario M5S 3B1, Canada
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    Orcidhttp://orcid.org/0000-0002-3412-5480
  • Tetyana Gilevska
    Tetyana Gilevska
    Department of Earth Sciences, University of Toronto, Toronto, Ontario M5S 3B1, Canada
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  • Axel Horst
    Axel Horst
    Department of Earth Sciences, University of Toronto, Toronto, Ontario M5S 3B1, Canada
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    Orcidhttp://orcid.org/0000-0002-3475-2425
  • Jesse Manna
    Jesse Manna
    Department of Earth Sciences, University of Toronto, Toronto, Ontario M5S 3B1, Canada
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  • Edward Seger
    Edward Seger
    The Chemours Company, Wilmington, Delaware 19899, United States
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    Edward J. Lutz
    The Chemours Company, Wilmington, Delaware 19899, United States
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    AECOM, Deepwater, New Jersey 08023, United States
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    AECOM, Deepwater, New Jersey 08023, United States
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    AECOM, Deepwater, New Jersey 08023, United States
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    Corporate Remediation Group, E. I. DuPont de Nemours and Company, Wilmington, Delaware 19805, United States
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    SiREM, Guelph, Ontario N1G 3Z2, Canada
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    Jennifer Webb
    SiREM, Guelph, Ontario N1G 3Z2, Canada
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  • Barbara Sherwood Lollar*
    Barbara Sherwood Lollar
    Department of Earth Sciences, University of Toronto, Toronto, Ontario M5S 3B1, Canada
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Environmental Science & Technology

Cite this: Environ. Sci. Technol. 2020, 54, 2, 870–878
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https://doi.org/10.1021/acs.est.9b05746
Published December 2, 2019

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Abstract

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Compound-specific isotope analysis (CSIA) is a valuable tool in contaminant remediation studies. Chlorofluorocarbons (CFCs) are ozone-depleting substances previously thought to be persistent in groundwater under most geochemical conditions but more recently have been found to (bio)transform in some laboratory experiments. To date, limited applications of CSIA to CFCs have been undertaken. Here, biotransformation-associated carbon isotope enrichment factors, εC,bulk for CFC-113 (εC,bulk = −8.5 ± 0.4‰) and CFC-11 (εC,bulk = −14.5 ± 1.9‰), were determined. δ13C signatures of pure-phase CFCs and hydrochlorofluorocarbons were measured to establish source signatures. These findings were applied to investigate potential in situ CFC transformation in groundwater at a field site, where carbon isotope fractionation of CFC-11 suggests naturally occurring biotransformation by indigenous microorganisms. The maximum extent of CFC-11 transformation is estimated to be up to 86% by an approximate calculation using the Rayleigh concept. CFC-113 δ13C values in contrast were not resolvably different from pure-phase sources measured to date, demonstrating that CSIA can aid in identifying which compounds may, or may not, be undergoing reactive processes at field sites. Science and public attention remains focused on CFCs, as unexplained source inputs to the atmosphere have been recently reported, and the potential for CFC biotransformation in surface and groundwaters remains unclear. This study proposes δ13C CSIA as a novel application to study the fate of CFCs in groundwater.

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Introduction

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Chlorofluorocarbons (CFCs) are manmade aliphatic compounds fully saturated in chlorine or fluorine atoms. CFCs were historically used worldwide as aerosol propellants, refrigerants, foaming agents, solvents, and intermediates for the synthesis of fluorinated polymers. (1) In the mid-1970s, the critical role of CFCs in the destruction of ozone was discovered, whereby CFC photodissociation in the stratosphere released chlorine atoms that participated in a chain reaction with ozone. (2,3) CFCs contribute approximately 61% of total tropospheric chlorine from ozone-depleting substances (ODS). (4) In 1987, the Montreal Protocol on substances that deplete the ozone layer (5) was ratified by 197 countries, resulting in gradual elimination of production and consumption of ODS. However, recent work (6) highlights a slowdown in declining rates of trichlorofluoromethane (CFC-11) atmospheric concentrations, suggesting a sustained increase in the net flux of CFC-11 to the atmosphere because of unreported production. (6) A detailed understanding of the sources and sinks of CFCs is required to constrain estimates of fluxes to investigate the extent and potential causes for this increase. As a result of widespread atmospheric CFC contamination and dissolution in groundwater according to Henry’s Law, (7) CFCs are prevalent in groundwater at background concentrations at equilibrium with modern air. (1) These background groundwater concentrations are on the order of 690, 360, and 130 pg L–1 for CFC-11, dichlorodifluoromethane (CFC-12), and 1,1,2-trichloro-1,2,2-trifluoroethane (CFC-113), respectively. (7) Squillace et al. (8) analyzed volatile organic contaminants (VOCs) in groundwater with no known point sources of contamination using United States Geological Survey (USGS) data, and a reporting level of 0.2 μg L–1. CFC-11, CFC-12, and CFC-113 were detected in 3.1, 2.8, and 1.3% of ambient groundwater from wells in urban areas across the United States, respectively. (8) Additionally, CFCs persist as common groundwater contaminants throughout North America as a legacy of production, spills, and improper disposal, (1) underscoring the importance of point source contamination.
Until recently, CFCs were thought to be chemically and biologically inert and in fact are used to date groundwater based on that assumption. (9) More recently, anaerobic biotransformation of CFC-11, (10−13) CFC-12, (10,11,13) and CFC-113 (11,13−15) to hydrochlorofluorocarbons (HCFCs) via reductive dechlorination has been observed in various anaerobic environments. Although anaerobic microbial breakdown in reducing environments is now acknowledged by practitioners using CFCs to date groundwater, (7) the potential and implications for dating have not yet been fully evaluated as the prevalence and extent of biotransformation of CFCs in groundwaters is still under-investigated. Horneman et al. (16) showed that CFC degradation occurs over a range of redox conditions, further suggesting an underestimation of the importance of microbial biotransformation in this field. Anaerobic reactions can occur via different types of reductive dechlorination, including reductive α-elimination, reductive β-elimination, and hydrogenolysis. The main anaerobic biotransformation pathway of CFCs is hydrogenolysis, whereby a chlorine atom is replaced by a hydrogen atom. Further hydrogenolysis of HCFCs is often observed. (10,11,15) CFC-113 can also degrade biotically via simultaneous reductive β-elimination and hydrogenolysis. (11) In aerobic environments, co-oxidation has been reported only for chlorotrifluoroethene (CFC-1113) and 1,1-dichloro-difluoroethene (CFC-1112a). (17) Aerobic co-oxidation of CFC-113 and CFC-11 has also been suggested. (18)
Abiotic dechlorination of CFC-113 and CFC-11 by zero valent iron (ZVI) and zinc also occur via hydrogenolysis and reductive β-elimination (CFC-113 only). (15,19,20) The results from a column study (20) suggest reductive α-elimination as a possible minor pathway for CFC-11. (20) Furthermore, abiotic defluorination of CFCs catalyzed by corrinoids has been demonstrated with titanium(III) citrate, a strong reductant, as an electron donor. (21) Although CFCs have been shown to degrade abiotically, (15,19−22) these experiments were conducted with a very strong reductant or saturated metal content (>200 000 mg L–1) that is unlikely to occur in natural environments. For comparison, the maximum iron and zinc concentrations at the field site in this study are 155 and 0.024 mg L–1, respectively. Because in situ abiotic CFC transformation has yet to be demonstrated in natural environments, biotransformation via dechlorination is the main mechanism generally considered for natural CFC transformation processes. (7) In situ biotransformation is a desirable strategy for contaminant transformation as it is generally less intrusive and can be more cost- and time-effective than other strategies. (23,24)
In contrast to CFCs, transformation of HCFCs, products of CFC dechlorination, can occur in aerobic environments as well as anaerobic abiotic and biotic transformation. (1) Complete mineralization of HCFCs involving bacterial defluorination in aerobic conditions has also been reported. (25,26) Additionally, the presence of hydrogen makes HCFCs susceptible to tropospheric oxidation to nonvolatile products in the lower atmosphere, a major sink for HCFCs. (27)
The identification of contaminant transformation at field sites is complicated by the fact that contaminant concentrations can decrease because of physical nondegradative processes and reactive processes that break bonds. While daughter products can provide a line of evidence for transformation at field sites, this approach is complicated when reaction products are present at field sites both as original (primary) contaminants and as daughter products (secondary contaminants). In a study by Lesage et al., (14) both CFC-113 and 1,2-dichloro-1,1,2-trifluoroethane (HCFC-123a), the product of CFC-113 hydrogenolysis, were present at a site. This study could not discern whether HCFC-123a was an impurity in the original contaminant source or a product of CFC-113 hydrogenolysis using concentration analysis. (14) In many cases, if daughter products are below the detection limit, or their record of release as primary contaminants makes their presence alone not a definitive line of evidence for transformation, additional lines of evidence are required. Compound-specific isotope analysis (CSIA) is a tool to identify and quantitatively estimate the extent of transformation (EoT) in the field for a wide variety of VOCs (28) and to provide insight into transformation mechanisms of organic compounds. (29−32) An extensive overview of the principles and applications of CSIA is given in the EPA Best Practice Guide. (28) Briefly, because of differences in activation energy, molecules containing exclusively light isotopes of an element (e.g., 12C) react at a slightly faster rate than molecules containing a heavy atom in a reactive position or its vicinity (e.g., 13C). The magnitude of isotope fractionation involved (expressed as an isotope enrichment factor, ε) is often a constant and reproducible parameter for many contaminants investigated to date (for a given mechanism or pathway). (28) A caveat to this is that additional complications in mechanistic interpretations can arise if the transformation step is not rate-limiting in the overall reaction, which is known as a “masking effect” and is reviewed elsewhere. (33) Notwithstanding, in many cases, the amount of residual contaminant can be related to the stable isotope ratio of a compound (R) by the Rayleigh model
(1)
where Ro is the initial isotopic ratio and f is the fraction of the original contaminant remaining. To date in hundreds of papers, CSIA has been successfully applied to various priority pollutants, including chlorinated alkanes, chlorinated alkenes, BTEX, alkanes, and MTBE to identify and quantify transformation in the field, differentiate between contaminant sources, and/or to quantify transformation rates. (28) Recent literature has emphasized the role of the multi-element isotope analysis (typically C–Cl, or C–H) in delineating mechanisms of chlorohydrocarbon degradation in subsurface environments. (34) To date, this has been done most successfully for cholorohydrocarbons such as chlorinated alkanes and alkenes (35,36) and once methods and fractionation factors have been established for chlorine or hydrogen for CFCs, such studies will provide the interpretation frameworks to extend such investigations to CFCs. The main focus of this initial study was to determine for the first time the carbon isotope effects occurring during biotransformation of two major CFC contaminants and to investigate the implications for field studies, while the study of the detailed reaction mechanisms remains for future work.
The application of CSIA to investigate transformation of CFCs, however, in laboratory experiments and in the field has been hindered by the incompatibility of CFCs with traditional preconcentration methods such as purge-and-trap and solid phase microextraction combined with low environmental CFC concentrations. A major step forward was the development of a method for extracting and preconcentrating CFCs from water that does not cause an isotope effect, as has been recently demonstrated by Horst et al. (37) for carbon CSIA of CFC-11 and CFC-113 for aqueous concentrations down to 190 and 270 μg L–1, respectively. While this work opened the field to carbon isotope analysis of CFCs at concentrations in the range typically found at contaminated field sites, to date the corresponding techniques to apply CSIA for other elements (e.g., H, Cl) have yet to be demonstrated in the literature. To date, only one laboratory study has used carbon CSIA to investigate the abiotic transformation of CFC-11 and CFC-113 at aqueous concentrations >30 mg L–1 with ZVI and reported carbon εbulk = −17.8 ± 4.8‰ and εbulk = −5.0 ± 0.3‰, respectively. (19)
The current study applies CSIA to (1) establish ranges of isotopic compositions of pure-phase CFC material to distinguish between different sources, (2) determine the first carbon biotransformation-associated εC for two CFC compounds, CFC-113 and CFC-11, by a mixed microbial culture derived from a contaminated field site, and (3) apply these calculated εC’s to a CFC-113 and CFC-11 contaminated field site to investigate and estimate the EoT.

Materials and Methods

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Microcosm Setup

For CFC-113 experiments, triplicate 240 mL glass bottles were prepared in an anaerobic glovebox (Labconco) with a CO2/H2/N2 atmosphere (10%/10%/80%). The triplicate bottles were then filled with 240 mL of an enriched anaerobic microbial culture, SC01, in a defined mineral medium with a composition as described in Edwards and Grbić-Galić. (38) SC01 is an enriched microbial culture derived from sediment and groundwater from a TCE- and CFC-113-contaminated site that is maintained and marketed by SiREM as part of its KB-1 Plus line of bioaugmentation cultures. Microorganisms from this site can completely degrade CFC-113 in increasing concentrations up to 8 mg L–1. Prior to this work, this culture was not fed with CFC-11. Two abiotic controls containing 240 mL of mineral medium and two sterile controls containing 240 mL of the autoclaved culture were prepared to ensure that the isotopic compositions were not affected by experimental design or sampling procedure. Subsequently, 18.5 mL of culture or medium was removed to create 18.5 mL of headspace. Each bottle was amended with high performance liquid chromatography grade methanol, ethanol, and lactate (2.6, 3.7, and 12 μL, respectively) and 1.4 μL of CFC-113, characterized using offline preparation and dual inlet measurement (δ13C = −29.93 ± 0.06‰ based on Vienna Pee-Dee-Belemnite, V-PDB), to produce a 5 mg L–1 aqueous concentration. Bottles were then capped with Mininert valves. Triplicate bottles were stored on their side on an orbital shaker in the anaerobic chamber for 3 h to achieve equilibrium between the aqueous and gaseous phases, as determined in laboratory protocol tests, before analysis.
For CFC-11 experiments, triplicate sets of 6–7 30 mL anaerobic vials (Chemglass Life Sciences) were prepared anaerobically. Each vial was filled with 20 mL of SC01 culture in defined mineral medium. (38) Each set of vials was treated as a single replicate (“sample bottle”). Ten abiotic control vials containing 20 mL of mineral medium and ten sterile controls containing autoclaved culture were prepared. A 160 mL stock solution containing 39.5 μL of methanol, 43.0 μL of ethanol, 41.3 μL of lactate, and 17.2 μL of isotopically characterized CFC-11 (δ13C = −33.36 ± 0.04‰ based on V-PDB and offline preparation and dual inlet measurements as above) in mineral medium was prepared in a 160 mL glass serum bottle (Wheaton) without headspace, sealed with a blue butyl stopper (Bellco Glass, Inc.), and placed in the anaerobic chamber overnight to produce an aqueous CFC-11 concentration of 160 mg L–1 with methanol, ethanol, and lactate at 10× the electron donor demand. Each vial was amended with 1 mL of stock solution to reach a final CFC-11 aqueous concentration of 3 mg L–1. Aqueous phase and headspace concentrations of CFC-113 and CFC-11 were calculated using Henry’s Law and dimensionless constants 12.8 and 3.6, respectively. (39)

Field Study

The study area is located in New Jersey, USA and covers approximately 0.2 km2. CFC-113 and CFC-11 are present dissolved in groundwater and as dense nonaqueous phase liquids (DNAPLs), resulting from past manufacturing and storage operations at the site beginning in 1930. Groundwater samples containing CFC-113 and CFC-11 were collected following the standard 40 mL volatile organic analyses vial method, (40) which is the standard protocol for groundwater sample collection. A schematic of the field site location is given in the Supporting Information Figure S1. Additional site detail including co-contaminant distributions (41) and hydrogeology (42) are included in previous publications. This site provided an opportunity to investigate the CFC source and fate as multiple CFC and HCFC compounds are present in groundwater at 0.25–65 mg L–1 concentrations. At the field site, there is a legacy source DNAPL and groundwater plume of fluoroproducts in the area where CFCs were previously produced and stored (Figure S1). However, accidental smaller releases may have occurred over the history of operations.
There are three main hydrogeological formations sampled in this study. Units B (<6 m thickness), C (<5 m thickness), and D (<6 m thickness), are predominantly sandy (quartz) gravel with some clayey silt. The hydraulic conductivity of B, C, and D units are all ≥10–3 to 10–5 cm/s. (42) Throughout the site a thin lower permeability lens with higher clay content (B/C ≈ 0.5–1.5 m thick) separates units B and C. At only one location (well D13-CMT), an additional thin lower permeability clayey lens (C/D) C (<2 m thick) separates units C and D. Elsewhere units C and D are in direct contact. The results of hydraulic head tests show that the entire vertical sequence is hydraulically connected as even the less permeable, more clay-rich layers are leaky. See the Results section and ref (42) for full details. The average water table depth is 1.8 m.
Figure S1 shows the horizontal location of the wells. Lateral hydraulic flow under natural conditions was historically westward. As a standard hydrogeologic containment practice at contaminated sites, pumping in the northeast corner of the site now predominantly controls the lateral direction of groundwater flow toward the northeast. Groundwater samples were taken in the autumn of 2015 from well nests with wells in the B, C, and D units (screen lengths between 1.5 and 3 m) and from one continuous multichannel tube (CMT) 7-port well (0.6 m screen lengths), D13-CMT. The pH at the site is slightly acidic (ranging from 4.7 to 6.5) and redox conditions range from oxidizing in upper layers to slightly reducing, with measured redox potential ranging from −32.4 to 139 mV.

Analytical Methods

Detailed analytical methods are presented in the Supporting Information. Briefly, δ13C of pure-phase CFCs were determined using offline preparation and dual inlet measurement. For biotransformation experiments, CFC-113 and CFC-11 concentrations were quantified using a Varian 3400 gas chromatograph (GC) equipped with a flame ionization detector (FID). Four-point CFC-113 and CFC-11 standard curves were injected daily. Reproducibility of daily standard measurements was used to quantify uncertainty, which was less than or equal to the typical uncertainty of GC/FID, ±5%. Field sample concentrations were measured commercially using GC/mass spectrometry (GC/MS). (43) Carbon isotope analyses were performed on a Finnigan MAT 252 isotope-ratio mass spectrometer interfaced with a Hewlett-Packard 6890 GC and a combustion oven. Samples were introduced either using headspace analysis (44) or the cryo-refocusing method of Horst et al. (37) Isotopically characterized CFC-113 and CFC-11 standards (described above) were injected daily. Total uncertainty of δ13C measurements incorporating both accuracy and reproducibility is ±0.5‰. (37,45)

Results and Discussion

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Pure-Phase δ13C Signatures

δ13C signatures for the aliquots of pure compounds measured in this study are presented in Table 1 and where applicable, compared to other studies that characterized some pure-phase CFCs. Measured δ13C for CFC-11, CFC-113, dichlorotetrafluoroethane (CFC-114), and HCFC-123a are fairly similar, within 3.4‰ of each other. δ13C ranges for these compounds (−29.93 to −33.36‰) are comparable to petroleum feedstocks, which typically vary from approximately −22 to −32‰ (46) and are the feedstock material for CFC production. (47) In contrast, CFC-12 (−45.27 ± 0.04‰) and chlorodifluoromethane (HCFC-22, −49.51 ± 0.07) measured here and HCFC-21 (−50.1 ± 0.5‰) measured in a previous study have δ13C signatures much more depleted in 13C than the range for CFC-11, CFC-113, CFC-114, and HCFC-123a. The depleted signatures of CFC-12, HCFC-22, and HCFC-21 may result from different manufacturing processes (47) or different feedstock materials. This depletion was also reported by Ertl (48) and Archbold et al. (49) for CFC-12 and HCFC-22. Overall, measured CFC and HCFC δ13C signatures in this study are within ranges of previously reported δ13C signatures for pure-phase samples of each compound, but Table 1 significantly expands the database on baseline δ13C signatures for CFCs. These ranges are not dissimilar to those reported for a pure-phase material of other priority hydrocarbon pollutants, but the measured ranges for CFC-12, HCFC-22, and HCFC-21 here and in previous studies are among the δ13C signatures most depleted in 13C reported to date for pure-phase hydrocarbons.
Table 1. Source δ13C for Pure-Phase CFC and HCFC Compounds Measured in This Study Compared to Values Reported in the Literaturea
   δ13C (‰) ± 1σ (n = 3)published pure-phase values, δ13C (‰)
compound nameshort namechemical formula(this study)Horst et al. (37)Ertl (48)Thompson et al. (50)Archbold et al. (49)Archbold et al. (19)
trichlorofluoromethaneCFC-11CCl3F–33.36 ± 0.04–33.34 ± 0.08–35 to −25-–26.2 ± 0.6–39.8 ± 1.0‰
    –28.93 ± 0.05    
1,1,2-trichloro-1,2,2-trifluoroethaneCFC-113C2Cl3F3–29.93 ± 0.06–28.07 ± 0.07-–31.3 ± 0.5–26.5 ± 0.8–30.4 ± 0.5‰
1,2-dichlorotetra-fluoroethaneCFC-114C2Cl2F4–32.57 ± 0.01-----
1,2-dichloro-1,1,2-trifluoroethaneHCFC-123aC2HCl2F3–31.67 ± 0.07-----
dichlorodifluoromethaneCFC-12CCl2F2–45.27 ± 0.04-–45 to −33-–46.8 ± 0.2-
chlorodifluoromethaneHCFC-22CHClF2–49.51 ± 0.07–49.71 ± 0.13–48 to −45---
dichlorofluoromethaneHCFC-21CHCl2F-–50.1 ± 0.5----
a

The σ represents external reproducibility for n individually prepared combustion tube samples (n = 3). Internal precision for dual inlet measurements is typically better than 0.04‰. A dash (-) indicates that a δ13C value has not been reported for a given compound.

Isotopic signatures of daughter products may also be considered during isotope data interpretation for evidence of contaminant transformation, as enrichment of 13C in the remaining pool of parent compounds as they undergo transformation is typically accompanied by the formation of daughter products more depleted in 13C relative to parent compounds. (28) It is important to note that without an investigation of pure-phase δ13C signatures reported in Table 1, the highly depleted source δ13C signatures of HCFC-22 (in this study and previous studies (37,48)) and of HCFC-21 (published in one previous study (37)) measured in the field may be misinterpreted as evidence for reductive dechlorination of CFC-12 and CFC-11, respectively. This emphasizes the importance of a database of pure-phase δ13C signatures when using carbon isotope data for the interpretation of transformation.

Laboratory Experiment-Derived ε Values

No significant variation in contaminant concentrations or δ13C was observed in the abiotic and sterile controls throughout CFC-113 and CFC-11 biotransformation experiments (Figures S2–S5). For CFC-113, biotransformation of ∼85% of original contaminant concentrations occurred in all replicate bottles after 40 h. For CFC-11, biotransformation of ∼65% of original contaminant concentrations occurred in all replicate bottles after 76 days. The faster rate of CFC-113 degradation in this study is likely due to the culture history, as discussed in the Materials and Methods. Anaerobic CFC-113 and CFC-11 biotransformation produced significant isotopic fractionation, with enrichment in 13C (Δδ13C) of up to 14.8 ± 0.7‰ with 20 ± 7% of the original contaminant remaining and 15.3 ± 0.7‰ with 32 ± 7% of the original contaminant remaining, respectively. These substantial carbon isotope effects for CFC-113 and CFC-11 demonstrate that CSIA may be used as a tool for evaluation of these compounds.
Equation 2 was used to calculate εbulk values for biotransformation of CFC-113 and CFC-11 from the data in Figure 1,
(2)
where δ13Ct is the carbon isotopic composition at time t, δ13Co is the initial carbon isotopic composition, and f is the fraction of original contaminant remaining. εbulk values for each sample bottle were calculated by plotting 1000 × ln[(δ13Ct + 1000)/(δ13Co + 1000)] versus ln f and determining the slope of the linear regression (m), where m = εbulk after ref (28) (Figure 1A,B). Data points at later stages of the reaction progress (i.e., f < 0.20) were not included in the εbulk calculation as increasing uncertainty in f with decreasing concentration measurements can significantly impact the calculated εbulk as established in prior works. (51,52) To determine the effects of mass removal by repetitive sampling, εbulk was calculated (i) without correcting for mass removal, (ii) correcting for cumulative mass removal at each time point (referred to as “Henry + CSR”, (53)eq S1), and (iii) using the “stepwise” (SW) correction method from Buchner et al. (53) for volatile compounds (eqs S2 and S3). The three calculations did not result in a significant difference in εbulk for CFC-113 or CFC-11 for individual sample bottles or for combined εbulk values (Tables S1 and S2), indicating that the calculated εbulk are robust with respect to mass removal because of repetitive sampling. Although the calculated εbulk values are within uncertainty regardless of approach, the values calculated using the SW correction method were used for further calculation following most recent best practice recommendations of Buchner et al. (53)

Figure 1

Figure 1. Plot of 1000 × ln[(δ13Ct + 1000)/(δ13Co + 1000)/)] vs ln f for the biotransformation of CFC-113 (a) and CFC-11 (b) by SC01 for all three replicate bottles. The solid line represents a linear regression giving the isotope enrichment factor, εbulk. Error bars on the x- and y-axes represent propagated error of ±7 and ±0.7‰, respectively (eq S4).

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Fit to the Rayleigh model was evaluated based on the correlation coefficients (R2 values) of linear plots. Data from CFC-113 and CFC-11 experiments showed excellent fit (i.e., R2 > 0.95) to the Rayleigh model (Figure 1), with R2 values of 0.99 and 0.97, respectively. Uncertainty of εbulk is reported as 95% confidence intervals. The εbulk for each replicate for the CFC-113 and CFC-11 experiments were within confidence intervals, and thus a combined value of εbulk was calculated by combining the data for all sample bottles and determining the slope of the linear regression. (54) Using the Rayleigh model, the calculated εbulk for CFC-113 and CFC-11 are −8.5 ± 0.4 and −14.5 ± 1.9‰, respectively. The smaller R2 values and larger confidence intervals for CFC-11 are likely due to the somewhat fewer data points for this experiment.
Position-specific ε (εreactive position) were calculated to correct for dilution of the isotope effect (32) by converting changes in the bulk isotopic signature (Δδ13C) to position-specific changes (Δδ13Cposition specific) using eq 3 and determining the slope of the linear regression using these corrected values in eq 2, following the standard practice outlined by Elsner et al (32)
(3)
n is the total number of carbon atoms in the molecule, x is the number of atoms in the reactive position, and Δδ13C is the change in the isotopic ratio from t = 0 to a given time, t. An apparent kinetic isotope effect (AKIE) was calculated to correct for intramolecular competition effects for atoms in equally reactive positions. (32)Equation 4 was used for the calculation of the AKIE value from εreactive position
(4)
where z is the number of atoms in equivalent reactive positions. Details of these calculations (n, x, z) are presented in Scheme S1 of the Supporting Information. The calculated εreactive position and AKIEC are presented in Table 2. Accumulation of daughter products (HCFCs) was not identified in the CFC-11 experiment, possibly due to low initial concentrations of CFC-11 required for the experiment and low volatility of HCFCs relative to CFCs or simultaneous HCFC degradation. Calculations of εreactive position and AKIEC for CFC-113 can be used to consider two potential reaction pathways, hydrogenolysis and reductive β-elimination (see Scheme S1, Table 2).
Table 2. Comparison of Calculated εbulk, εreactive position, and AKIEC for the Biotransformation of CFC-113 and CFC-11 Calculated with Eq 2, Eqs 2 and 3, and Eq 4, respectivelya
compoundεbulk (‰)hypothesized pathwayεreactive position (‰)AKIEC
CFC-113–8.5 ± 0.4hydrogenolysis–17.0 ± 0.7a1.017 ± 0.001a
  reductive β-elimination–8.5 ± 0.4b1.0086 ± 0.0004b
CFC-11–14.5 ± 1.9hydrogenolysisεbulk = εreactive position1.015 ± 0.002
a

For CFC-113, εreactive position and AKIEC are calculated for ahydrogenolysis and breductive β-elimination.

The CFC-11 AKIEC in this study is within uncertainty of the abiotic AKIEC, where hydrogenolysis was the sole reported degradation pathway, (19) which is consistent with the results from previous biotransformation studies with HCFC-21 as the major daughter product. (10−12) For CFC-113, the AKIEC calculated for hydrogenolysis (Table 2; CFC-113 hypothesis a) is within uncertainty of the AKIEC of CFC-11, suggesting hydrogenolysis as a common biotransformation pathway for CFC-113 and CFC-11 by SC01. However, for the biotransformation of CFC-113, minor contribution of reductive β-elimination cannot be ruled out. (19) HCFC-123a (product via hydrogenolysis) was identified as a daughter product in preliminary CFC-113 experiments. However, like CFCs, HCFCs are controlled substances, making it difficult to obtain and store quantities of these compounds. HCFC-123a was not quantified in later experiments because of the lack of an HCFC-123a standard. Overall the AKIEC values for CFC-11 and CFC-113 transformation are consistent with the theoretical maximum kinetic isotope effect (KIE) for the cleavage of a C–Cl bond via reductive dechlorination, with a maximum value of ∼1.03 based on the semiclassical Streitwieser limit assuming 50% cleavage in the transition state. (32,55)

Field δ13C Measurements

The laboratory microcosm biotransformation experiments in this study provide estimates of CFC-113 and CFC-11 biotransformation-associated εbulk. As per the standard practice in the literature these results were integrated with field measurements of these contaminants to investigate potential in situ transformation at the contaminated site. Applying laboratory-derived εbulk at the field scale is an equivalent assumption to those in laboratory studies where microcosm data and rate estimates are applied to predict plume behavior at field sites. (28) Nonetheless, the standard practice in the literature is to apply these laboratory-derived εbulk estimates, and hence this approach as outlined in the EPA Best Practice Guidance provides a means to estimate the EoT. (28) An additional caveat is that the effects of physical processes in the field will lead to an overestimation of transformation and therefore an underestimation of εbulk derived from field data, but through following best practice guidance, (28) this approach has nonetheless become common and used in literature worldwide to explore the EoT.
δ13C results of field data measurements are shown in Figure 2. Horst et al. (56) demonstrated that the volatilization of CFCs dissolved in water does not produce an isotope effect outside of analytical uncertainty of CSIA. Carbon isotope effects produced from other physical processes such as sorption, diffusion, and dissolution are also typically small or insignificant relative to the analytical uncertainty of carbon CSIA, (28) which is 0.5‰ after Sherwood Lollar et al. (45) Therefore, significant variations in δ13C of CFCs dissolved in groundwater are not attributed to physical processes and are more likely representative of transformation or source variation.

Figure 2

Figure 2. Projected cross section showing measured concentrations and δ13C values of CFC-113 at D13-CMT, E14-M01, and D15-M01 (a), G12-M01 (b) and of CFC-11 at D13-CMT, E14-M01, and D15-M01 (c), and G12-M01 (d). Note the difference in the concentration scale for D13-CMT (CFC-113), E14-M01 (CFC-113), and D15-M01 (CFC-11). (B–D) Are permeable sand and gravel units with some silt. Throughout the site, a lower permeability layer with a higher clay content (B/C ≈ 1 m thick) separates units B and C. At only one location (well D13-CMT), an additional thin lower permeability clay lens (C/D) separates units C and D. The results of hydraulic head tests show that the entire vertical sequence is in hydraulic connection as even the less permeable more clay-rich layers are leaky. An approximate transect line for the projected cross section (A–A′) is shown in Figure S1. Depth is given as meters below ground surface (mbgs).

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At each of the four locations, measured CFC-113 δ13C are consistent within all three units (Figure 2A,B). Mean δ13C values are −29.1 ± 0.4, −31.6 ± 0.2, and −30.6 ± 0.5‰ at D13-CMT, E14-M01, and D15-M01, respectively. Only two values were measured at G12-M01, however these values are within 0.5‰. In contrast, significant variation is observed in δ13C of CFC-113 at different well locations (Figure 2A,B). With the exception of one measurement (G12-M01C), all field CFC-113 δ13C values are within the range of the reported CFC-113 pure-phase δ13C signatures (Figure 3; Table S3). The differences in CFC-113 δ13C at each well location are below the criterion recommended for the positive identification of transformation (2‰) (28) and are within analytical uncertainty for δ13C measurement and thus are analytically unresolvable. (45) The uniformity in CFC-113 δ13C values at each well location and their similarity to pure-phase (nondegraded) CFC-113 δ13C signatures (Figure 3) suggest that the transformation of CFC-113 is not occurring at the field site because CFC-113 transformation is associated with significant isotope fractionation based on the results of this study (εC,bulk = −8.5 ± 0.4) and Archbold et al. (19) (εC,bulk = −5.0 ± 0.3). Differences between CFC-113 δ13C at different well locations may be due to different CFC-113 sources, potentially corresponding to different source zones from the previous manufacturing area and operations at this large and complex site.

Figure 3

Figure 3. Comparison of δ13C values from the current study as well as previously published studies for pure-phase CFC and HCFC compounds with the δ13C of the field samples measured in this study. The solid bars represent pure-phase δ13C measurements and the hatched bars represent field measurements.

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In contrast, CFC-11 δ13C varies significantly between units and between well locations (Figure 2C,D; Table S3). As shown in Figure 3, CFC-11 δ13C values (hatched bars) overlap but fall well outside range reported to date for pure product (solid bars). The variation of measured CFC-11 δ13C values between well locations is also significant, from −46.9‰ at E14-M01B to −30.8‰ at D15M01B, which may reflect multiple original contaminant sources, as for CFC-113. Measured δ13C for well location D13-CMT increased with a depth from −31.7 to −24.9‰ (Figure 2C), as the concentration decreased from 12 to 0.25 mg L–1 (Table S3), a pattern consistent with transformation and isotopic enrichment of the remaining CFC-11. Increasing δ13C of CFC-11, corresponding to enrichment in 13C, and decreasing CFC-11 concentration with depth at D13-CMT and G12-M01 at this site provide evidence for in situ CFC-11 transformation. The interpretation of CFC-11 is complicated by the possibility of two controls on CFC-11 isotope signatures: transformation and source variation. Nonetheless, a preliminary assessment of transformation can be undertaken to estimate the maximum possible extent of CFC-11 transformation, that is, if transformation is the only cause of δ13C variation. Consistent with this approach, Hunkeler et al. (28) has recommended that when it is not feasible to measure the δ13C of the primary contaminant that was spilled at the site, δ13Csource can be estimated in a preliminary way based on the literature or based on the most negative value at the site. Values of f were calculated for each well location using eq 2 and the laboratory-derived εbulk for anaerobic biotransformation of CFC-11, −14.5 ± 1.9‰. The site has not been augmented with a ZVI permeable barrier or other metal treatment, and thus this transformation is likely biotic as discussed earlier. Most importantly, whether transformation is abiotic or biotic would not significantly affect calculations of f as εbulk for biotic (−14.5 ± 1.9‰) and abiotic transformation (−17.8 ± 4.8‰) are not statistically different. The most depleted δ13C value, which was consistently in the near surface and the stratigraphically highest hydrogeological unit and had the highest measured CFC-11 concentration, with the exception of E14-M01B, at each well location, was taken as δ13Co as recommended by Hunkeler et al. (28) The δ13C value in the stratigraphically lowest hydrogeological unit was taken as δ13Ct based on the inferred connectivity between units. The EoT was then calculated for each well location using eq 5. (28)
(5)
At D13-CMT, the maximum possible EoT between D13-CMT-Port3 (i.e., δ13Co) and D13-CMT-Port6 (δ13Ct), is between 62 and 52%. The range for EoT corresponds to the propagated uncertainty through eqs 2 and 5 (using eq S4). The same calculation for the other two well locations showing a significant difference in δ13C values yields a preliminary estimate of EoT between 77 and 86% (location E14-M01) and 52–62% (location G12-M01).
Depth profiles were only available for CFC-113 and CFC-11 at this site as the majority of the other compounds were below CSIA detection limits. Of those that could be measured, δ13C values for HCFC-21 (well E14-M01) and CFC-114 (well G12-M01) are enriched in 13C relative to measured pure-phase signatures (Figure 3; Table S3). This enrichment in 13C relative to available pure-phase δ13C data may be indicative of some transformation of these compounds at the field site. However, more pure-phase δ13C data is required for both compounds to differentiate between the source and degraded δ13C in the field before any reliable interpretation of these limited HCFC-21 and CFC-114 data points can be undertaken. Furthermore, the measured δ13C of one field sample of CFC-11 (E14-M01B, δ13C = −46.9 ± 0.5‰; Figure 3, Table S3) was much more depleted in 13C than the range of pure-phase CFC-11 signatures (Table 1, Figure 3), suggesting that pure-phase δ13C signatures of CFC-11 may not be fully constrained.

Environmental Significance and Implications for Field Investigations

The results of this study demonstrate the potential for a novel application of CSIA to CFCs. Findings reported here lay the foundation for future applications of CSIA to CFC-contaminated field sites in providing baseline pure-phase δ13C signatures for comparison to measured field δ13C values and the first estimation of biotransformation-associated εbulk. The field δ13C measurements provide preliminary evidence for naturally occurring transformation of CFC-11 at this field site, which is likely biotic, indicating that in situ transformation may play a more significant role in the CFCs’ fate than has previously been recognized. The evidence for anaerobic dechlorination of CFC-11 to HCFC-21 at the field site suggests that in situ transformation may be a feasible strategy to provide the first step for complete degradation leading to full destruction of these compounds.

Supporting Information

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The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.est.9b05746.

  • Field site schematic, full analytical methods, control data, mass removal calculations, dechlorination mechanisms, error propagation, and tabulated field results (PDF)

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Author Information

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  • Corresponding Author
  • Authors
    • Elizabeth Phillips - Department of Earth Sciences, University of Toronto, Toronto, Ontario M5S 3B1, Canada;  Orcidhttp://orcid.org/0000-0002-3412-5480
    • Tetyana Gilevska - Department of Earth Sciences, University of Toronto, Toronto, Ontario M5S 3B1, Canada
    • Axel Horst - Department of Earth Sciences, University of Toronto, Toronto, Ontario M5S 3B1, Canada;  Present Address: Helmholtz Centre for Environmental Research, UFZ, Permoserstrasse 15, 04318, Leipzig;  Orcidhttp://orcid.org/0000-0002-3475-2425
    • Jesse Manna - Department of Earth Sciences, University of Toronto, Toronto, Ontario M5S 3B1, Canada
    • Edward Seger - The Chemours Company, Wilmington, Delaware 19899, United States
    • Edward J. Lutz - The Chemours Company, Wilmington, Delaware 19899, United States
    • Scott Norcross - AECOM, Deepwater, New Jersey 08023, United States
    • Scott A. Morgan - AECOM, Deepwater, New Jersey 08023, United States
    • Kathryn A. West - AECOM, Deepwater, New Jersey 08023, United States
    • E. Erin Mack - Corporate Remediation Group, E. I. DuPont de Nemours and Company, Wilmington, Delaware 19805, United States
    • Sandra Dworatzek - SiREM, Guelph, Ontario N1G 3Z2, Canada
    • Jennifer Webb - SiREM, Guelph, Ontario N1G 3Z2, Canada
  • Notes
    The authors declare no competing financial interest.

Acknowledgments

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Funding for this study was provided by NSERC Collaborative Research and Development Grant 497236. Additional funding was provided by the Canada Research Chair Program 104559, NSERC Discovery 453949, E.I. DuPont Canada Co. 492441, and DuPont Corporate Remediation Group (CRG) 501935.

References

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    Denovan, B. A.; Strand, S. E. Biological Degradation of Chlorofluorocarbons in Anaerobic Environments. Chemosphere 1992, 24, 935– 940,  DOI: 10.1016/0045-6535(92)90012-g
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    Biological degradation of chlorofluorocarbons in anaerobic environments
    Denovan, Barbara A.; Strand, Stuart E.
    Chemosphere (1992), 24 (7), 935-40CODEN: CMSHAF; ISSN:0045-6535.
    In lab. studies, CCl3F (F-11), CCl2F2 (F-12), and 1,1,2-trichlorotrifluoroethane (F-113) were degraded by microbial activity in anaerobic sludges and F-11 and F-113 were degraded in sediments. Biomass acclimated to chlorinated orgs. degraded chlorofluorocarbons faster than unacclimated biomass. Up to 9% of all CFCs may ultimately be susceptible to biol. degrdn. before release to the atm.
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  14. 14
    Lesage, S.; Jackson, R. E.; Priddle, M. W.; Riemann, P. G. Occurrence and fate of organic solvent residues in anoxic groundwater at the Gloucester landfill, Canada. Environ. Sci. Technol. 1990, 24, 559– 566,  DOI: 10.1021/es00074a016
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    Occurrence and fate of organic solvent residues in anoxic groundwater at the Gloucester landfill, Canada
    Lesage, Suzanne; Jackson, Richard E.; Priddle, Mark W.; Riemann, Peter G.
    Environmental Science and Technology (1990), 24 (4), 559-66CODEN: ESTHAG; ISSN:0013-936X.
    The disposal of org. chems. in trenches at a waste disposal site near Ottawa, Ontario, resulted in the contamination of the underlying aquifer. The org. residues measured in groundwater samples are reported and the mechanisms of contaminant transport in the aquifer discussed. Groundwater samples from monitoring wells and multilevel samplers were analyzed by gas chromatog.-mass spectrometry. Ultratrace quantities of chlorinated dibenzodioxins and -furans were found in groundwaters directly beneath the trenches. A wide variety of volatile compds. were identified and quantitated in samples from the aquifer. The compd. of greatest concern was 1,4-dioxane, because of its toxicity and mobility, while that present in greatest concn. was a Freon, F113, which appeared to be very persistent, although 3 transformation products were identified.
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  15. 15
    Lesage, S.; Brown, S.; Hosler, K. R. Degradation of Chlorofluorocarbon-113 under Anaerobic Conditions. Chemosphere 1992, 24, 1225– 1243,  DOI: 10.1016/0045-6535(92)90049-w
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    Degradation of chlorofluorocarbon-113 under anaerobic conditions
    Lesage, Suzanne; Brown, Susan; Hosler, Kevin R.
    Chemosphere (1992), 24 (9), 1225-43CODEN: CMSHAF; ISSN:0045-6535.
    A series of microcosms were set up to verify the degrdn. pathway of CFC-113 in water under anaerobic conditions and to measure its half-life and that of its major degrdn. products HCFC-123a and C2ClF3. Anaerobic landfill leachate was used as a source of bacteria acclimated to chlorinated solvents. The rate of reaction in methanogenic leachate was also compared to that obtained in a buffer contg. reduced hematin. In methanogenic landfill leachate, CFC-113 was transformed to HCFC-123a with a half-life of 5 days at 20°. The same reaction occurred in Na2S/cysteine buffers contg. hematin, but at a much slower rate. The prodn. of C2ClF3 was independent of the presence of HCFC-123a and occurred abiotically. Under methanogenic conditions, HCFC-123a was further dechlorinated to HCFC-133 and HCFC-133b. C2ClF3 was relatively stable in methanogenic landfill leachate but was decompd. rapidly in a buffer contg. S2-.
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  16. 16
    Horneman, A.; Stute, M.; Schlosser, P.; Smethie, W.; Santella, N.; Ho, D. T.; Mailloux, B.; Gorman, E.; Zheng, Y.; van Geen, A. Degradation rates of CFC-11, CFC-12 and CFC-113 in anoxic shallow aquifers of Araihazar, Bangladesh. J. Contam. Hydrol. 2008, 97, 27– 41,  DOI: 10.1016/j.jconhyd.2007.12.001
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    16
    Degradation rates of CFC-11, CFC-12 and CFC-113 in anoxic shallow aquifers of Araihazar, Bangladesh
    Horneman, A.; Stute, M.; Schlosser, P.; Smethie, W.; Santella, N.; Ho, D. T.; Mailloux, B.; Gorman, E.; Zheng, Y.; van Geen, A.
    Journal of Contaminant Hydrology (2008), 97 (1-2), 27-41CODEN: JCOHE6; ISSN:0169-7722. (Elsevier B.V.)
    Chlorofluorocarbons CFC-11 (CCl3F), CFC-12 (CCl2F2), and CFC-113 (CCl2F-CClF2) are used in hydrol. as transient tracers under the assumption of conservative behavior in the unsatd. and satd. soil zones. However, lab. and field studies have shown that these compds. are not stable under anaerobic conditions. To det. the degrdn. rates of CFCs in a tropical environment, atm. air, unsatd. zone soil gas, and anoxic groundwater samples were collected in Araihazar upazila, Bangladesh. Obsd. CFC concns. in both soil gas and groundwater were significantly below those expected from atm. levels. The CFC deficits in the unsatd. zone can be explained by gas exchange with groundwater undersatd. in CFCs. The CFC deficits obsd. in 3H/3He dated groundwater were used to est. degrdn. rates in the satd. zone. The results show that CFCs are degraded to the point where practically no (<5%) CFC-11, CFC-12, or CFC-113 remains in groundwater with 3H/3He ages >10 yr. In groundwater sampled at our site CFC-11 and CFC-12 appear to degrade at similar rates with estd. degrdn. rates ranging from ∼0.25 to ∼6/yr. Degrdn. rates increased as a function of reducing conditions. This indicates that CFC dating of groundwater in regions of humid tropical climate has to be carried out with great caution.
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    Field, J. A.; Sierra-Alvarez, R. Biodegradability of Chlorinated Solvents and Related Chlorinated Aliphatic Compounds. Rev. Environ. Sci. Biotechnol. 2004, 3, 185– 254,  DOI: 10.1007/s11157-004-4733-8
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    Biodegradability of chlorinated solvents and related chlorinated aliphatic compounds
    Field, J. A.; Sierra-Alvarez, R.
    Reviews in Environmental Science and Bio/Technology (2004), 3 (3), 185-254CODEN: RESBC6; ISSN:1569-1705. (Kluwer Academic Publishers)
    A review concerning biodegradability of chlorinated solvents and related chlorinated aliph. compds. in 7 compd. categories (chlorinated methanes, ethanes, ethenes, acetic acids, propanoids, butadienes, and chlorofluorocarbons [CFC]) is given. Topics discussed include: sources; biodegrdn. principles; dehalogenation mechanisms; chloromethanes (biodegrdn. of lower and higher); chloroethanes (biodegrdn. of lower and higher chlorinated ethanes); chloroethenes (biodegrdn. of lower and higher chlorinated ethenes); chlorofluorocarbons (biodegrdn. of CFC and HCFC); chloroacetic acids; chloropropanes, chloropropenes, and epichlorohydrin; chlorobutadienes; and summary and conclusions (scope of different physiol. approaches to biodegrdn., biodegrdn. per chlorinated compd. category).
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    Weidhaas, J.; Dupont, R. R. Aerobic Biotransformation of N-Nitrosodimethylamine and N-Nitrodimethylamine in Methane and Benzene Amended Soil Columns. J. Contam. Hydrol. 2013, 150, 45– 53,  DOI: 10.1016/j.jconhyd.2013.04.004
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    Aerobic biotransformation of N-nitrosodimethylamine and N-nitrodimethylamine in methane and benzene amended soil columns
    Weidhaas, Jennifer; Dupont, R. Ryan
    Journal of Contaminant Hydrology (2013), 150 (), 45-53CODEN: JCOHE6; ISSN:0169-7722. (Elsevier B.V.)
    Aerobic biotransformation of N-nitrosodimethylamine (NDMA), an emerging contaminant of concern, and its structural analog N-nitrodimethylamine (DMN), was evaluated in benzene and methane amended groundwater passed through lab. scale soil columns. Competitive inhibition models were used to model the kinetics for NDMA and DMN cometabolism accounting for the concurrent degrdn. of the growth and cometabolic substrates. Transformation capacities for NDMA and DMN with benzene (13 and 23 μg (mg cells)-1) and methane (0.14 and 8.4 μg (mg cells)-1) grown cultures, resp. are comparable to those presented in the literature, as were first order endogenous decay rates estd. to be 2.1 × 10-2 ± 1.7 × 10-3 d-1 and 6.5 × 10-1 ± 7.1 × 10-1 d-1 for the methane and benzene amended cultures, resp. These studies highlight possible attenuation mechanisms and rates for NDMA and DMN biotransformation in aerobic aquifers undergoing active remediation, natural attenuation or managed aquifer recharge with treated wastewater (i.e., reclaimed water).
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    Archbold, M. E.; Elliot, T.; Kalin, R. M. Carbon Isotopic Fractionation of CFCs during Abiotic and Biotic Degradation. Environ. Sci. Technol. 2012, 46, 1764– 1773,  DOI: 10.1021/es203386a
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    Carbon Isotopic Fractionation of CFCs during Abiotic and Biotic Degradation
    Archbold, Marie E.; Elliot, Trevor; Kalin, Robert M.
    Environmental Science & Technology (2012), 46 (3), 1764-1773CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
    Carbon stable isotope (13C) fractionation in chlorofluorocarbon (CFC) compds. arising from abiotic (chem.) degrdn. using zero-valent iron (ZVI) and biotic (landfill gas attenuation) processes is investigated. Batch tests (at 25 °C) for CFC-113 and CFC-11 using ZVI show quant. degrdn. of CFC-113 to HCFC-123a and CFC-1113 following pseudo-first-order kinetics corresponding to a half-life (τ1/2) of 20.5 h, and a ZVI surface-area normalized rate const. (kSA) of -(9.8 ± 0.5) × 10-5 L m-2 h-1. CFC-11 degraded to trace HCFC-21 and HCFC-31 following pseudo-first-order kinetics corresponding to τ1/2 = 17.3 h and kSA = -(1.2 ± 0.5) × 10-4 L m-2 h-1. Significant kinetic isotope effects of ε(‰) = -5.0 ± 0.3 (CFC-113) and -17.8 ± 4.8 (CFC-11) were obsd. Compd.-specific carbon isotope analyses also have been used here to characterize source signatures of CFC gases (HCFC-22, CFC-12, HFC-134a, HCFC-142b, CFC-114, CFC-11, CFC-113) for urban (UAA), rural/remote (RAA), and landfill (LAA) ambient air samples, as well as in situ surface flux chamber (FLUX; NO FLUX) and landfill gas (LFG) samples at the Dargan Road site, Northern Ireland. The latter values reflect biotic degrdn. and isotopic fractionation in LFG prodn., and local atm. impact of landfill emissions through the cover. Isotopic fractionations of Δ13C ∼ -13‰ (HCFC-22), Δ13C ∼ -35‰ (CFC-12) and Δ13C ∼ -15‰ (CFC-11) were obsd. for LFG in comparison to characteristic solvent source signatures, with the magnitude of the isotopic effect for CFC-11 apparently similar to the kinetic isotope effect for (abiotic) ZVI degrdn.
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    Jeen, S.-W.; Lazar, S.; Gui, L.; Gillham, R. W. Degradation of Chlorofluorocarbons Using Granular Iron and Bimetallic Irons. J. Contam. Hydrol. 2014, 158, 55– 64,  DOI: 10.1016/j.jconhyd.2014.01.002
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    Degradation of chlorofluorocarbons using granular iron and bimetallic irons
    Jeen, Sung-Wook; Lazar, Snezana; Gui, Lai; Gillham, Robert W.
    Journal of Contaminant Hydrology (2014), 158 (), 55-64CODEN: JCOHE6; ISSN:0169-7722. (Elsevier B.V.)
    Degrdn. of trichlorofluoromethane (CFC11) and 1,1,2-trichloro-1,2,2-trifluoroethane (CFC113) by granular iron and bimetallic (nickel- or palladium-enhanced) irons was studied in flow-through column tests. Both compds. were rapidly degraded, following pseudo-first-order kinetics with respect to the parent compds. The av. pseudo-first-order rate consts. for CFC11 were similar among different materials, except for palladium-enhanced iron (PdFe), in which the rate of degrdn. was about two times faster than for the other materials. In the case of CFC113, the rate consts. for bimetallic irons were about two to three times greater than for the regular iron material. The smaller than expected differences in degrdn. rate consts. of chlorofluorocarbons (CFCs) between regular iron and bimetallic irons suggested little, if any, catalytic effect of the bimetallic materials in the initial degrdn. step. Subsequent degrdn. steps involved catalytic hydrogenation, however, playing a significant role in further degrdn. of reaction intermediates. The degrdn. intermediates and final products of CFC11 and CFC113 suggested that degrdn. proceeded through hydrogenolysis and α/β-elimination in the presence of regular iron (Fe) and nickel-enhanced iron (NiFe). Even though there is only minor benefit in the use of bimetallic iron in terms of degrdn. kinetics of the parent CFCs, enhanced degrdn. rates of intermediates such as chlorotriflouroethene (CTFE) in subsequent reaction steps could be beneficial.
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    Krone, U. E.; Thauer, R. K.; Hogenkamp, H. P. C.; Steinbach, K. Reductive formation of carbon monoxide from carbon tetrachloride and FREONS 11, 12, and 13 catalyzed by corrinoids. Biochemistry 1991, 30, 2713– 2719,  DOI: 10.1021/bi00224a020
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    Reductive formation of carbon monoxide from carbon tetrachloride and FREONS 11, 12, and 13 catalyzed by corrinoids
    Krone, Ute E.; Thauer, Rudolf K.; Hogenkamp, Harry P. C.; Steinbach, Klaus
    Biochemistry (1991), 30 (10), 2713-19CODEN: BICHAW; ISSN:0006-2960.
    CCl4 was converted to CO via corrinoid-catalyzed reductive dehalogenation with Ti(III) citrate as the electron donor. Corrinoids catalyzed the redn. of CFCl3, CF2Cl2, and CF3Cl to CO and, in the case of CFCl3, to a lesser extent, to formate. CF4 was not reduced. The rate of CO and formate formation paralleled that of fluoride release. Both rates decreased in the series CFCl3, CF2Cl2, CCl4, and CF3Cl. The redn. of CFCl3 gave, in addn. to CO and formate, CHFCl2, CH2FCl, CH3F, CH4, C2F2Cl2, and C2F2Cl4. The product pattern indicates that the corrinoid-mediated redn. of halogenated C1-hydrocarbons involves the intermediacy of dihalocarbenes, which may be a reason why these compds. are highly toxic for anaerobic bacteria.
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    Scheutz, C.; Winther, K.; Kjeldsen, P. Removal of Halogenated Organic Compounds in Landfill Gas by Top Covers Containing Zero-Valent Iron. Environ. Sci. Technol. 2000, 34, 2557– 2563,  DOI: 10.1021/es991301f
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    Removal of Halogenated Organic Compounds in Landfill Gas by Top Covers Containing Zero-Valent Iron
    Scheutz, Charlotte; Winther, Klaus; Kjeldsen, Peter
    Environmental Science and Technology (2000), 34 (12), 2557-2563CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
    Transformation of gaseous CCl3F and CCl4 by zero-valent Fe was studied in systems unsatd. with water under anaerobic conditions in N2 gas and landfill gas atms. Transformation was studied using batch and flow-through column tests; in both systems, the transformation process of the compds. was pseudo-first-order. Transformation rate consts., referring to the water phase and normalized to 1 m2 Fe surface/mL, of up to 1100 mL/m2-h (batch) and 200 mL/m2-h (flow-through) were obsd. Transformation strongly depended on pH and the presence of O2. During continuous aerobic conditions, CCl3F transformation decreased toward zero. Model calcns. showed that using zero-valent Fe in landfill top covers is a potential treatment technol. to reduce halogenated trace compd. emissions from landfills.
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    Committee on In Situ Bioremediation. The Current Practice of Bioremediation. In Situ Bioremediation: When Does it Work?; National Academies Press: Washington, DC, 1993; pp 47– 62.
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    Malla, M. A.; Dubey, A.; Yadav, S.; Kumar, A.; Hashem, A.; Abd-Allah, E. F. Understanding and Designing the Strategies for the Microbe-Mediated Remediation of Environmental Contaminants Using Omics Approaches. Front. Microbiol. 2018, 9, 1– 18,  DOI: 10.3389/fmicb.2018.01132
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    Streger, S. H.; Condee, C. W.; Togna, A. P.; Deflaun, M. F. Degradation of Hydrohalocarbons and Brominated Compounds by Methane- and Propane-Oxidizing Bacteria. Environ. Sci. Technol. 1999, 33, 4477– 4482,  DOI: 10.1021/es9907459
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    Degradation of Hydrohalocarbons and Brominated Compounds by Methane- and Propane-Oxidizing Bacteria
    Streger, Sheryl H.; Condee, Charles W.; Togna, A. Paul; DeFlaun, Mary F.
    Environmental Science and Technology (1999), 33 (24), 4477-4482CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
    Concern over the use of chems. that potentially contribute to O3 depletion and the greenhouse effect has led to a ban on chlorofluorocarbons (CFC) and potential limitations on the use of Me bromide and other brominated fumigants. This work tested naturally-occurring aerobic microorganisms for their ability to degrade brominated fumigants and the hydrohalocarbons developed to replace CFC. Bacterial strains used degraded a significant percentage of hydrohalocarbons and brominated fumigants tested, which were present at high substrate levels. Degrdn. was often rapid and complete. Ion chromatog. results indicated the stoichiometric release of halogens for several compds. tested. Many compds. were readily biodegradable at high concns. and were metabolized by all strains tested, while others were more recalcitrant. The presence of these microorganisms in the environment may represent a natural sink for some of these compds.; however, the high substrate and bacterial concns. used in this study were chosen for bioreactor development. Information about the biodegradability of these compds. may make it easier to choose the most ecol. safe CFC replacements and fumigants.
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    DeFlaun, M. F.; Ensley, B. D.; Steffan, R. J. Biological Oxidation of Hydrochlorofluorocarbons (HCFCs) by a Methanotrophic Bacterium. Biotechnology 1992, 10, 1576– 1578,  DOI: 10.1038/nbt1292-1576
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    Key, B. D.; Howell, R. D.; Criddle, C. S. Fluorinated Organics in the Biosphere. Environ. Sci. Technol. 1997, 31, 2445– 2454,  DOI: 10.1021/es961007c
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    Fluorinated organics in the biosphere
    Key, Blake D.; Howell, Robert D.; Criddle, Craig S.
    Environmental Science and Technology (1997), 31 (9), 2445-2454CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
    A review with 144 refs. The use of organofluorine compds. has increased throughout this century, and they are now ubiquitous environmental contaminants. Although generally viewed as recalcitrant because of their lack of chem. reactivity, many fluorinated orgs. are biol. active. Several questions surround their distribution, fate, and effects. Of particular interest is the fate of perfluoroalkyl substituents, such as the trifluoromethyl group. Most evidence to date suggest that such groups resist defluorination, yet they can confer significant biol. activity. Certain volatile fluorinated compds. can be oxidized in the troposphere yielding nonvolatile compds., such as trifluoroacetic acid. In addn., certain nonvolatile fluorinated compds. can be transformed in the biosphere to volatile compds. Research is needed to assess the fate and effects of nonvolatile fluorinated orgs., the fluorinated impurities present in com. formulations, and the transformation products generated by biochem. processes and/or oxidn. in the troposphere.
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    Hunkeler, D.; Meckenstock, R. U.; Sherwood Lollar, B.; Schmidt, T. C.; Wilson, J. T. A Guide for Assessing Biodegradation and Source Identification of Organic Ground Water Contaminants Using Compound Specific Isotope Analysis (CSIA); USEPA Publ., 2008, EPA 600/R-(December); pp 1– 82.
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    Hirschorn, S. K.; Dinglasan, M. J.; Elsner, M.; Mancini, S. A.; Lacrampe-Couloume, G.; Edwards, E. A.; Sherwood Lollar, B. Pathway Dependent Isotopic Fractionation during Aerobic Biodegradation of 1,2-Dichloroethane. Environ. Sci. Technol. 2004, 38, 4775– 4781,  DOI: 10.1021/es049920y
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    Pathway Dependent Isotopic Fractionation during Aerobic Biodegradation of 1,2-Dichloroethane
    Hirschorn, Sarah K.; Dinglasan, M. Joyce; Elsner, Martin; Mancini, Silvia A.; Lacrampe-Couloume, Georges; Edwards, Elizabeth A.; Lollar, Barbara Sherwood
    Environmental Science and Technology (2004), 38 (18), 4775-4781CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
    1,2-Dichloroethane (1,2-DCA) is a widespread groundwater contaminant known to be biodegradable under aerobic conditions via enzymic oxidn. or hydrolytic dehalogenation reactions. Current literature reports that stable carbon isotope fractionation of 1,2-DCA during aerobic biodegrdn. is large and reproducible (-27 to -33‰). In this study, a significant variation in the magnitude of stable carbon isotope fractionation during aerobic biodegrdn. was obsd. Biodegrdn. in expts. involving microcosms, enrichment cultures, and pure microbial cultures produced a consistent bimodal distribution of enrichment factors (ε) with one mean ε centered on -3.9 ± 0.6‰ and the other on -29.2 ± 1.9‰. Reevaluation of ε in terms of kinetic isotope effects 12k/13k gave values of 12k/13k = 1.01 and 1.06, which are typical of oxidn. and hydrolytic dehalogenation (SN2) reactions, resp. The bimodal distribution is therefore consistent with the microbial degrdn. of 1,2-DCA by two sep. enzymic pathways. This interpretation is further supported in this study by expts. with pure strains of Xanthobacter autotrophicus GJ10, Ancylobacter aquaticus AD20, and Pseudomonas sp. Strain DCA1 for which the enzymic degrdn. pathways are well-known. A small fractionation of -3.0‰ was measured for 1,2-DCA degrdn. by Pseudomonas sp. Strain DCA1 (monooxygenase enzyme), while degrdn. by the hydrolytic dehalogenase enzyme by the other two pure strains was characterized by fractionation of -32.3‰.
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    Hirschorn, S. K.; Dinglasan-Panlilio, M. J.; Edwards, E. A.; Lacrampe-Couloume, G.; Sherwood Lollar, B. Isotope analysis as a natural reaction probe to determine mechanisms of biodegradation of 1,2-dichloroethane. Environ. Microbiol. 2007, 9, 1651– 1657,  DOI: 10.1111/j.1462-2920.2007.01282.x
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    Isotope analysis as a natural reaction probe to determine mechanisms of biodegradation of 1,2-dichloroethane
    Hirschorn, Sarah K.; Dinglasan-Panlilio, M. Joyce; Edwards, Elizabeth A.; Lacrampe-Couloume, Georges; Lollar, Barbara Sherwood
    Environmental Microbiology (2007), 9 (7), 1651-1657CODEN: ENMIFM; ISSN:1462-2912. (Blackwell Publishing Ltd.)
    1,2-Dichloroethane (1,2-DCA), a chlorinated aliph. hydrocarbon, is a well-known groundwater contaminant. In this study, fractionation of stable carbon isotope values of 1,2-DCA during biodegrdn. was used as a novel reaction probe to provide information about the mechanism of 1,2-DCA biodegrdn. under both aerobic (O2-reducing) and anaerobic (NO3-reducing) conditions. Under O2-reducing conditions, an isotopic enrichment value (ε) of -25.8 ± 1.1‰ (±95% confidence intervals) was measured for the enrichment culture. Under NO3-reducing conditions, an ε-value of -25.8 ± 3.5‰ was measured. The microbial culture produced isotopic enrichment values (ε) that are not only large and reproducible, but also are the same whether O2 or NO3 was used as an electron acceptor. Combining data measured under both O2- and NO3-reducing conditions, an isotopic enrichment value (ε) of -25.8 ± 1.6‰ is measured for the microbial culture during 1,2-DCA degrdn. The ε-value can be converted into a kinetic isotope effect (KIE) value to relate the obsd. isotopic fractionation to the mechanism of degrdn. This KIE value (1.05) is consistent with degrdn. via hydrolytic dehalogenation under both electron-accepting conditions. This study demonstrates the added value of compd.-specific isotope anal. not only as a technique to verify the occurrence and extent of biodegrdn. in the field, but also as a natural reaction probe to provide insight into the enzymic mechanism of contaminant degrdn.
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  31. 31
    Vanstone, N.; Elsner, M.; Lacrampe-Couloume, G.; Mabury, S.; Sherwood Lollar, B. Potential for Identifying Abiotic Chloroalkane Degradation Mechanisms using Carbon Isotopic Fractionation. Environ. Sci. Technol. 2008, 42, 126– 132,  DOI: 10.1021/es0711819
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    Potential for Identifying Abiotic Chloroalkane Degradation Mechanisms using Carbon Isotopic Fractionation
    VanStone, Nancy; Elsner, Martin; Lacrampe-Couloume, Georges; Mabury, Scott; Sherwood Lollar, Barbara
    Environmental Science & Technology (2008), 42 (1), 126-132CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
    Degrdn. of 1,1- and 1,2-dichloroethane (1,1-DCA, 1,2-DCA) and carbon tetrachloride (CCl4) on Zn was investigated using compd. specific isotope anal. (CSIA) to measure isotopic fractionation factors for chloroalkane degrdn. by hydrogenolysis, by α-elimination, and by β-elimination. Significant differences in enrichment factors (ε) and assocd. apparent kinetic isotope effects (AKIE) were measured for these different reaction pathways, suggesting that carbon isotope fractionation by β-elimination is substantially larger than fractionation by hydrogenolysis or by α-elimination. Specifically, for 1,1-DCA, the isotopic compn. of the reductive α-elimination product (ethane) and the hydrogenolysis product (chloroethane) were the same, indicating that cleavage of a single C-Cl bond was the rate-limiting step in both cases. In contrast, for 1,2-DCA, ε = εreactive position = -29.7 ± 1.5‰, and the calcd. AKIE (1.03) indicated that β-elimination was likely concerted, possibly involving two C-Cl bonds simultaneously. Compared to 1,1-DCA hydrogenolysis, the AKIE of 1.01 for hydrogenolysis of CCl4 was much lower, indicating that, for this highly reactive organohalide, mass transfer to the surface was likely partially rate-limiting. These findings are a first step toward delineating the relative contribution of these competing pathways in other abiotic systems such as the degrdn. of chlorinated ethenes on zerovalent iron (ZVI), iron sulfide, pyrite, or magnetite, and, potentially, toward distinguishing between degrdn. of chlorinated ethenes by abiotic vs. biotic processes.
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  32. 32
    Elsner, M.; Zwank, L.; Hunkeler, D.; Schwarzenbach, R. P. A New Concept Linking Observable Stable Isotope Fractionation to Transformation Pathways of Organic Pollutants. Environ. Sci. Technol. 2005, 39, 6896– 6916,  DOI: 10.1021/es0504587
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    A New Concept Linking Observable Stable Isotope Fractionation to Transformation Pathways of Organic Pollutants
    Elsner, Martin; Zwank, Luc; Hunkeler, Daniel; Schwarzenbach, Rene P.
    Environmental Science and Technology (2005), 39 (18), 6896-6916CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
    A review. Measuring stable isotope fractionation of carbon, hydrogen, and other elements by Compd. Specific Isotope Anal. (CSIA) is a new, innovative approach to assess org. pollutant degrdn. in the environment. Central to this concept is the Rayleigh equation which relates degrdn.-induced decreases in concns. directly to concomitant changes in bulk (= av. over the whole compd.) isotope ratios. The extent of in situ transformation may therefore be inferred from measured isotope ratios in field samples, provided that an appropriate enrichment factor (εbulk) is known. This εbulk value, however, is usually only valid for a specific compd. and for specific degrdn. conditions. Therefore, a direct comparison of εbulk values for different compds. and for different types of reactions has in general not been feasible. In addn., it is often uncertain how robust and reproducible εbulk values are and how confidently they can be used to quantify contaminant degrdn. in the field. To improve this situation and to achieve a more in-depth understanding, this crit. review aims to relate fundamental insight about kinetic isotope effects (KIE) found in the physico(bio)chem. literature to apparent kinetic isotope effects (AKIE) derived from εbulk values reported in environmentally oriented studies. Starting from basic rate laws, a quite general derivation of the Rayleigh equation is given, resulting in a novel set of simple equations that take into account the effects of (1) nonreacting positions and (2) intramol. competition and that lead to position-specific AKIE values rather than bulk enrichment factors. Reevaluation of existing εbulk literature values result in consistent ranges of AKIE values that generally are in good agreement with previously published data in the (bio)chem. literature and are typical of certain degrdn. reactions (subscripts C and H indicate values for carbon and hydrogen): AKIEC = 1.01-1.03 and AKIEH = 2-23 for oxidn. of C-H bonds; AKIEC = 1.03-1.07 for SN2-reactions; AKIEC = 1.02-1.03 for reductive cleavage of C-Cl bonds; AKIEC = 1.00-1.01 for C:C bond epoxidn.; AKIEC = 1.02-1.03 for C:C bond oxidn. by permanganate. Hence, the evaluation scheme presented bridges a gap between basic and environmental (bio)chem. and provides insight into factors that control the magnitude of bulk isotope fractionation factors. It also serves as a basis to identify degrdn. pathways using isotope data. It is shown how such an anal. may be even possible in complex field situations and/or in cases where AKIE values are smaller than intrinsic KIE values, provided that isotope fractionation is measured for two elements simultaneously ("two-dimensional isotope anal."). Finally, the procedure is used (1) to point out the possibility of estg. approx. εbulk values for new compds. and (2) to discuss the moderate, but non-negligible variability that may quite generally be assocd. with εbulk values. Future research is suggested to better understand and take into account the various factors that may cause such variability.
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    Elsner, M. Stable Isotope Fractionation to Investigate Natural Transformation Mechanisms of Organic Contaminants: Principles, Prospects and Limitations. J. Environ. Monit. 2010, 12, 2005– 2031,  DOI: 10.1039/c0em00277a
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    Stable isotope fractionation to investigate natural transformation mechanisms of organic contaminants: principles, prospects and limitations
    Elsner, Martin
    Journal of Environmental Monitoring (2010), 12 (11), 2005-2031CODEN: JEMOFW; ISSN:1464-0325. (Royal Society of Chemistry)
    A review. Gas chromatog.-isotope ratio mass spectrometry (GC-IRMS) has made it possible to analyze natural stable isotope ratios (e.g., 13C/12C, 15N/14N, 2H/1H) of individual org. contaminants in environmental samples. They may be used as fingerprints to infer contamination sources, and may demonstrate, and even quantify, the occurrence of natural contaminant transformation by the enrichment of heavy isotopes that arises from degrdn.-induced isotope fractionation. This review highlights an addnl. powerful feature of stable isotope fractionation: the study of environmental transformation mechanisms. Isotope effects reflect the energy difference of isotopologues (i.e., mols. carrying a light vs. a heavy isotope in a particular mol. position) when moving from reactant to transition state. Measuring isotope fractionation, therefore, essentially allows a glimpse at transition states! It is shown how such position-specific isotope effects are "dild. out" in the compd. av. measured by GC-IRMS, and how a careful evaluation in mechanistic scenarios and by dual isotope plots can recover the underlying mechanistic information. The math. framework for multistep isotope fractionation in environmental transformations is reviewed. Case studies demonstrate how isotope fractionation changes in the presence of mass transfer, enzymic commitment to catalysis, multiple chem. reaction steps or limited bioavailability, and how this gives information about the individual process steps. Finally, it is discussed how isotope ratios of individual products evolve in sequential or parallel transformations, and what mechanistic insight they contain. A concluding session gives an outlook on current developments, future research directions and the potential for bridging the gap between lab. and real world systems.
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  34. 34
    Elsner, M.; Hofstetter, T. B. Current Perspectives on the Mechanisms of Chlorohydrocarbon Degradation in Subsurface Environments : Insight from Kinetics, Product Formation, Probe Molecules, and Isotope Fractionation. ACS Symp. Ser. 2011, 1071, 407,  DOI: 10.1021/bk-2011-1071.ch019
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    Current perspectives on the mechanisms of chlorohydrocarbon degradation in subsurface environments- insight from kinetics, product formation, probe molecules, and isotope fractionation
    Elsner, Martin; Hofstetter, Thomas B.
    ACS Symposium Series (2011), 1071 (Aquatic Redox Chemistry), 407-439CODEN: ACSMC8; ISSN:0097-6156. (American Chemical Society)
    A review. Degrdn. of chlorinated org. contaminants by natural and engineered reductive dechlorination reactions can occur via numerous biotic and abiotic transformation pathways giving rise to either benign or more toxic products. To assess whether dechlorination processes may lead to significant detoxification (a) the thermodn. feasibility of a reaction, (b) rates of transformation, and (c) product formation routes need to be understood. To this end, fundamental knowledge of chlorohydrocarbon (CHC) reaction mechanisms is essential. The authors review insight from reaction thermodn., structure-reactivity relations, and applications of radical and carbene traps, and of synthetic probe mols. The authors summarize the state-of-knowledge about intermediates and reductive dechlorination pathways of vicinal and geminal haloalkanes, and of chlorinated ethenes. Transformation conditions are identified under which problematic products may be avoided. In an outlook, the potential of stable C and Cl isotope fractionation to identify initial transformation mechanisms, competing transformation pathways, and common branching points are discussed.
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  35. 35
    Hofstetter, T. B.; Bolotin, J.; Skarpeli-liati, M.; Wijker, R.; Kurt, Z.; Nishino, S. F.; Spain, J. C. Tracking transformation processes of organic micropollutants in aquatic environments using multi-element isotope fractionation analysis. Geochemistry 2011, 26, S334– S336,  DOI: 10.1016/j.apgeochem.2011.03.068
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    Tracking transformation processes of organic micropollutants in aquatic environments using multi-element isotope fractionation analysis
    Hofstetter, Thomas B.; Bolotin, Jakov; Skarpeli-Liati, Marita; Wijker, Reto; Kurt, Zohre; Nishino, Shirley F.; Spain, Jim C.
    Applied Geochemistry (2011), 26 (Supplement), S334-S336CODEN: APPGEY; ISSN:0883-2927. (Elsevier Ltd.)
    The quant. description of enzymic or abiotic transformations of man-made org. micropollutants in rivers, lakes, and groundwaters is one of the major challenges assocd. with the risk assessment of water resource contamination. Compd.-specific isotope anal. enables one to identify (bio)degrdn. pathways based on changes in the contaminants' stable isotope ratios even if multiple reactive and non-reactive processes cause concns. to decrease. Here, we investigated how the magnitude and variability of isotope fractionation in some priority pollutants is detd. by the kinetics and mechanisms of important enzymic and abiotic redox reactions. For nitroarom. compds. and substituted anilines, we illustrate that competing transformation pathways can be assessed via trends of N and C isotope signatures.
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    Elsner, M.; Jochmann, M. A.; Hofstetter, T. B.; Hunkeler, D.; Bernstein, A.; Schmidt, T. C.; Schimmelmann, A. Current Challenges in Compound-Specific Stable Isotope Analysis of Environmental Organic Contaminants. Anal Bioanal Chem 2012, 403, 2471– 2491,  DOI: 10.1007/s00216-011-5683-y
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    Current challenges in compound-specific stable isotope analysis of environmental organic contaminants
    Elsner, Martin; Jochmann, Maik A.; Hofstetter, Thomas B.; Hunkeler, Daniel; Bernstein, Anat; Schmidt, Torsten C.; Schimmelmann, Arndt
    Analytical and Bioanalytical Chemistry (2012), 403 (9), 2471-2491CODEN: ABCNBP; ISSN:1618-2642. (Springer)
    A review. Compd.-specific stable-isotope anal. (CSIA) has greatly facilitated assessment of sources and transformation processes of org. pollutants. Multielement isotope anal. is one of the most promising applications of CSIA because it even enables distinction of different transformation pathways. This review introduces the essential features of continuous-flow isotope-ratio mass spectrometry (IRMS) and highlights current challenges in environmental anal. as exemplified for the isotopes of nitrogen, hydrogen, chlorine, and oxygen. Strategies and recent advances to enable isotopic measurements of polar contaminants, for example pesticides or pharmaceuticals, are discussed with special emphasis on possible solns. for anal. of low concns. of contaminants in environmental matrixes. Finally, discuss different levels of calibration and referencing are discussed and the urgent need for compd.-specific isotope stds. for gas chromatog.-isotope-ratio mass spectrometry (GC-IRMS) of org. pollutants is pointed out.
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    Horst, A.; Lacrampe-Couloume, G.; Sherwood Lollar, B. Compound-Specific Stable Carbon Isotope Analysis of Chlorofluorocarbons in Groundwater. Anal. Chem. 2015, 87, 10498– 10504,  DOI: 10.1021/acs.analchem.5b02701
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    Compound-Specific Stable Carbon Isotope Analysis of Chlorofluorocarbons in Groundwater
    Horst, Axel; Lacrampe-Couloume, Georges; Sherwood Lollar, Barbara
    Analytical Chemistry (Washington, DC, United States) (2015), 87 (20), 10498-10504CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)
    Chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs), controlled substances due to their role in stratospheric ozone loss, also occur as dissolved contaminants in groundwaters. Stable carbon isotopic signatures may provide valuable new information on the fate of these compds. as has been seen for other priority hydrocarbon contaminants, but to date no method for extn. and isotopic anal. of dissolved CFCs from groundwaters was developed. We describe a cryogenic purge and trap system coupled to continuous flow compd.-specific stable C isotope anal. mass spectrometry for concns. as low as 35 μg/L. The method is validated by comparing isotopic signatures from water extd. CFCs against a new suite of isotopic CFC stds. Fractionation of CFCs in volatilization expts. from pure-phase CFC-11 and CFC-113 resulted in enrichment factors (ε) of +1.7±0.1 and +1.1±0.1‰, resp., indicating that such volatile loss, if significant, would produce a more 13C depleted signature in the remaining CFCs. Importantly, no significant fractionation was obsd. during volatile extn. of dissolved CFCs from aq. solns. δ13C values for groundwaters from a CFC-contaminated site were, on av., more enriched than δ13C values for pure compds. Such enriched δ13C values have been seen in other hydrocarbon contaminants such as chlorinated ethenes and ethanes due to in situ degrdn., but definitive interpretation of such enriched signatures in field samples requires addnl. expts. to characterize fractionation of CFCs during biodegrdn. The establishment of a robust and sensitive method of extn. and anal., as described here, provides the foundation for such future directions.
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    Anaerobic degradation of toluene and o-xylene by a methanogenic consortium
    Edwards, Elizabeth A.; Grbic-Galic, Dunja
    Applied and Environmental Microbiology (1994), 60 (1), 313-22CODEN: AEMIDF; ISSN:0099-2240.
    Toluene and o-xylene were completely mineralized to stoichiometric amts. of carbon dioxide, methane, and biomass by aquifer-derived microorganisms under strictly anaerobic conditions. The source of the inoculum was creosote-contaminated sediment from Pensacola, Fla. The adaptation periods before the onset of degrdn. were long (100 to 120 days for toluene degrdn. and 200 to 255 days for o-xylene). Successive transfers of the toluene- and o-xylene-degrading cultures remained active. Cell d. in the cultures progressively increased over 2 to 3 yr to stabilize at approx. 109 cells per mL. Degrdn. of toluene and o-xylene in stable mixed methanogenic cultures followed Monod kinetics, with inhibition noted at substrate concns. above 700 μM for o-xylene and 1800 μM for toluene. The cultures degraded toluene or o-xylene but did not degrade m-xylene, p-xylene, benzene, ethylbenzene, or naphthalene. The degradative activity was retained after pasteurization or after starvation for 1 yr. Degrdn. of toluene and o-xylene was inhibited by the alternate electron acceptors oxygen, nitrate, and sulfate. Degrdn. was also inhibited by the addn. of preferred substrates such as acetate, H2, propionate, methanol, acetone, glucose, amino acid, fatty acids, peptone, and yeast ext. These data suggest that the presence of natural org. substrates or cocontaminants may inhibit anaerobic degrdn. of pollutants such as toluene and o-xylene at contaminated sites.
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    Capozzi, S. L.; Rodenburg, L. A.; Krumins, V.; Fennell, D. E.; Mack, E. E. Using Positive Matrix Factorization to Investigate Microbial Dehalogenation of Chlorinated Benzenes in Groundwater at a Historically Contaminated Site. Chemosphere 2018, 211, 515– 523,  DOI: 10.1016/j.chemosphere.2018.07.180
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    Using positive matrix factorization to investigate microbial dehalogenation of chlorinated benzenes in groundwater at a historically contaminated site
    Capozzi, Staci L.; Rodenburg, Lisa A.; Krumins, Valdis; Fennell, Donna E.; Mack, E. Erin
    Chemosphere (2018), 211 (), 515-523CODEN: CMSHAF; ISSN:0045-6535. (Elsevier Ltd.)
    Chlorinated benzenes are common groundwater contaminants in the United States, so demonstrating whether they undergo degrdn. in the subsurface is important in detg. the best remedy for this contamination. The purpose of this work was to use a new data mining approach to investigate chlorinated benzene degrdn. pathways in the subsurface. Pos. Matrix Factorization (PMF) was used to analyze long-term measurements of chlorinated benzene concns. in groundwater at a contaminated site in New Jersey. A dataset contg. 597 groundwater samples and 5 chlorinated benzenes and benzene collected from 144 wells over 20 years was investigated using PMF2 software. Despite the heterogeneity of this dataset, PMF anal. revealed patterns indicative of microbial dechlorination in the groundwater and provided insight about where dechlorination is occurring, to what extent, and under which geochem. conditions. PMF resolved a factor indicative of a source of 1,2,4-trichlorobenzene and 1,2-dichlorobenzene and two factors representing stages of dechlorination, one more advanced than the other. The PMF results indicated that virtually all of the 1,2-dichlorobenzene at the site arises from its use onsite, not from the dechlorination of trichlorobenzenes. Factors were further interpreted using ancillary data such as geochem. indicators and field parameters also measured in the samples. Anal. suggested that the partial and advanced dechlorination signals occur under different subsurface phys. conditions. The results provided field validation of the current understanding of anaerobic dechlorination of chlorinated benzenes in the subsurface developed from lab. studies. PMF is thereby shown to be a useful tool for investigating chlorinated benzene dechlorination.
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    Slater, G. F.; Dempster, H. S.; Sherwood Lollar, B.; Ahad, J. Headspace Analysis: A New Application for Isotopic Characterization of Dissolved Organic Contaminants. Environ. Sci. Technol. 1999, 33, 190– 194,  DOI: 10.1021/es9803254
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    Headspace Analysis: A New Application for Isotopic Characterization of Dissolved Organic Contaminants
    Slater, Gregory F.; Dempster, Helen S.; Lollar, Barbara Sherwood; Ahad, Jason
    Environmental Science and Technology (1999), 33 (1), 190-194CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
    Petroleum products and industrial solvents are among the most ubiquitous contaminants of soil and groundwater and the source of several common and hazardous volatile org. chems. (VOCs). Volatilization is a key determinant of the fate of VOCs in the subsurface environment, impacting contaminant partitioning between the aq., gaseous, and nonaq. liq. phases. This study uses stable C isotope anal. to investigate the isotopic effects involved in volatilization of trichloroethylene (TCE) and toluene from both free product (or pure phase) and aq. solns. Results indicate that, during volatilization from the aq. phase and from free product, the isotopic compn. of TCE and toluene remains unchanged within reproducibility limits. These results have 2 important implications for contaminant hydrogeol. First, they suggest that C isotopic signatures may be useful in tracking contaminant transport between the vapor, aq., and NAPL phases since they remain conservative during phase changes. Second, they demonstrate the utility of headspace extn. (sampling of the vapor phase or headspace above an aq. soln.) as a preparatory technique for isotopic anal. of dissolved VOCs. Headspace isotopic anal. provides a straightforward and rapid technique for δ13C anal. of dissolved org. contaminants at concns. as low as hundreds of ppb.
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    Sherwood Lollar, B.; Hirschorn, S. K.; Chartrand, M. M. G.; Lacrampe-Couloume, G. An Approach for Assessing Total Instrumental Uncertainty in Compound-Specific Carbon Isotope Analysis: Implications for Environmental Remediation Studies. Anal. Chem. 2007, 79, 3469– 3475,  DOI: 10.1021/ac062299v
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    An Approach for Assessing Total Instrumental Uncertainty in Compound-Specific Carbon Isotope Analysis: Implications for Environmental Remediation Studies
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    Analytical Chemistry (Washington, DC, United States) (2007), 79 (9), 3469-3475CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)
    Detn. of compd.-specific carbon isotope values by continuous flow isotope ratio mass spectrometry is impacted by variation in several routine operating parameters of which one of the most important is signal size, or linearity. Expts. were carried out to evaluate the implications of these operating parameters on both reproducibility and accuracy of δ13C measurements. A new method is described for assessing total instrumental uncertainty of routine compd.-specific δ13C anal., incorporating both accuracy and reproducibility. These findings have important implications for application of compd.-specific isotope anal. in environmental geochem. and in particular for the rapidly developing field of isotopic investigation of biodegrdn. and remediation of org. chems. in contaminant hydrogeol.
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    Archbold, M. E.; Redeker, K. R.; Davis, S.; Elliot, T.; Kalin, R. M. A Method for Carbon Stable Isotope Analysis of Methyl Halides and Chlorofluorocarbons at Pptv Concentrations. Rapid Commun. Mass Spectrom. 2005, 19, 337– 342,  DOI: 10.1002/rcm.1791
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    A method for carbon stable isotope analysis of methyl halides and chlorofluorocarbons at pptv concentrations
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    Samples of background air were collected in the lower troposphere of the Northern (high Arctic, northern Ontario, Vancouver and Houston) and Southern (Baring Head, New Zealand) Hemispheres over the period July 1999 until Mar. 2001. These samples were analyzed for the stable carbon isotope ratios of 1,1,1-trichlorotrifluoroethane (CFC113) and CH3Cl using a gas chromatog.-continuous flow online combustion isotope ratio mass spectrometry combination. For CH3Cl the global av. of the stable carbon isotope ratio is -36.2 ± 0.3‰ (error of mean). The av. is based on 78 data points, std. deviation for all measurements is 2.3‰, and the 90% confidence interval is -35.8 to -36.6‰. However, the no. of data points from the Southern Hemisphere is rather limited and thus this observation is not necessarily representative for the entire Southern Hemisphere. A simple isotopic budget of CH3Cl shows the most important parameters needing to be defined are the kinetic isotope effect of CH3Cl destruction by OH radicals and the source compn. of CH3Cl emitted by the oceans and biomass burning of C-4 plants. Present budgets of atm. CH3Cl show a significant deficit in the source strength. We est. that the av. stable carbon isotope ratio of the addnl. CH3Cl emissions required to balance the budget is -41.9 ± 7.8‰. The av. CFC113 isotopic compn. based on 38 measurements is -23.3 ± 1.6‰ (error of mean), σ = 9.6‰ with no significant difference between the hemispheres.
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    The interpretation of stable isotope values hinges on precise, accurate ests. of kinetic isotope effects (α), which are equal to 1k/2k, where 1k and 2k are the reaction rate consts. for the two isotopes. Kinetic isotope effects are commonly detd. by monitoring the reactant concn. (C) and isotope ratio (R) relative to their initial values (C1 and R1, resp.). Values of α are estd. from the C and R values by using the Rayleigh distn. equation (RDE). (R/R1)=(C/C1)1/α-1 We conducted simulation expts. to evaluate the precision of the many different published approaches of estg. α from linearized versions of the RDE and reached the following conclusions: (a) kinetic isotope effects estd. from the slope of the line ln(R) vs. ln(C) were accurate and precise; (b) regressing ln(Ri/Rj) on ln(Ci/Cj), where all i datapoints were compared to all preceding datapoints j resulted in inflated 95% confidence intervals; (c) forcing the regression of ln(R/R1) on ln(C/C1) through the origin resulted in 95% confidence intervals for α that covered the true value less than 90% of the time; and (d) regression methods that compensate for errors in both x and y values need to be used with caution. When combining multiple datasets, values of α were sensitive to the form of the equation and the level of error. If all datasets had the same level of error, the optimal est. of α was achieved by a linear regression with dummy variables. However, when the three datasets had different levels of error, the optimal est. of α and much narrower 95% confidence intervals were obtained by using the Pitman estimator. The study demonstrates that some of the other methods jeopardize the accuracy and precision of empirically detd. kinetic isotope effects, thus confounding the interpretation of stable isotope values in the environment.
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    Volatilization causes changes in the isotopic compn. of org. compds. as a result of different vapor pressures of mols. contg. heavy and light isotopes. Both normal and inverse vapor pressure isotope effects (VPIE) have been obsd., depending on mol. interactions in the liq. phase and the investigated element. Previous studies have focused mostly on pure compd. volatilization or on compds. dissolved in org. liqs. Environmentally relevant scenarios, such as isotope fractionation during volatilization of orgs. from open water surfaces, have largely been neglected. In the current study, open-system volatilization expts. (focusing thereby on kinetic/-nonequil. effects) were carried out at ambient temps. for trichloromethane, trichloroethene, trichlorofluoromethane, trichlorotrifluoroethane, methanol, and ethanol dissolved in water and, if not previously reported in the literature for these compds., for volatilization from pure liqs. Stable carbon isotopic signatures were measured using continuous flow isotope ratio mass spectrometry. The results demonstrate that volatilization of the four halogenated compds. from water does not cause a measurable change in the carbon isotopic compn., whereas for pure-phase evapn., significant inverse isotope effects are consistently obsd. (+0.3 ‰< ε < + 1.7 ‰). In contrast, methanol and ethanol showed normal isotope effects for evapn. of pure org. liqs. (-3.9 ‰ and -1.9 ‰) and for volatilization of compds. dissolved in water (-4.4 ‰ and -2.9 ‰), resp. This absence of measurable carbon isotope fractionation considerably facilitates the application of isotopic techniques for extn. of field samples and preconcn. of organohalogens-known to be important pollutants in groundwater and in the atm.
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  • Abstract

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    Figure 1

    Figure 1. Plot of 1000 × ln[(δ13Ct + 1000)/(δ13Co + 1000)/)] vs ln f for the biotransformation of CFC-113 (a) and CFC-11 (b) by SC01 for all three replicate bottles. The solid line represents a linear regression giving the isotope enrichment factor, εbulk. Error bars on the x- and y-axes represent propagated error of ±7 and ±0.7‰, respectively (eq S4).

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    Figure 2

    Figure 2. Projected cross section showing measured concentrations and δ13C values of CFC-113 at D13-CMT, E14-M01, and D15-M01 (a), G12-M01 (b) and of CFC-11 at D13-CMT, E14-M01, and D15-M01 (c), and G12-M01 (d). Note the difference in the concentration scale for D13-CMT (CFC-113), E14-M01 (CFC-113), and D15-M01 (CFC-11). (B–D) Are permeable sand and gravel units with some silt. Throughout the site, a lower permeability layer with a higher clay content (B/C ≈ 1 m thick) separates units B and C. At only one location (well D13-CMT), an additional thin lower permeability clay lens (C/D) separates units C and D. The results of hydraulic head tests show that the entire vertical sequence is in hydraulic connection as even the less permeable more clay-rich layers are leaky. An approximate transect line for the projected cross section (A–A′) is shown in Figure S1. Depth is given as meters below ground surface (mbgs).

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    Figure 3

    Figure 3. Comparison of δ13C values from the current study as well as previously published studies for pure-phase CFC and HCFC compounds with the δ13C of the field samples measured in this study. The solid bars represent pure-phase δ13C measurements and the hatched bars represent field measurements.

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      Montzka, Stephen A.; Dutton, Geoff S.; Yu, Pengfei; Ray, Eric; Portmann, Robert W.; Daniel, John S.; Kuijpers, Lambert; Hall, Brad D.; Mondeel, Debra; Siso, Carolina; Nance, J. David; Rigby, Matt; Manning, Alistair J.; Hu, Lei; Moore, Fred; Miller, Ben R.; Elkins, James W.
      Nature (London, United Kingdom) (2018), 557 (7705), 413-417CODEN: NATUAS; ISSN:0028-0836. (Nature Research)
      The Montreal Protocol was designed to protect the stratospheric ozone layer by enabling redns. in the abundance of ozone-depleting substances such as chlorofluorocarbons (CFCs) in the atm.1-3. The redn. in the atm. concn. of trichlorofluoromethane (CFC-11) has made the second-largest contribution to the decline in the total atm. concn. of ozone-depleting chlorine since the 1990s1. However, CFC-11 still contributes one-quarter of all chlorine reaching the stratosphere, and a timely recovery of the stratospheric ozone layer depends on a sustained decline in CFC-11 concns.1. Here we show that the rate of decline of atm. CFC-11 concns. obsd. at remote measurement sites was const. from 2002 to 2012, and then slowed by about 50 per cent after 2012. The obsd. slowdown in the decline of CFC-11 concn. was concurrent with a 50 per cent increase in the mean concn. difference obsd. between the Northern and Southern Hemispheres, and also with the emergence of strong correlations at the Mauna Loa Observatory between concns. of CFC-11 and other chems. assocd. with anthropogenic emissions. A simple model anal. of our findings suggests an increase in CFC-11 emissions of 13 ± 5 Gg per yr (25 ± 13 per cent) since 2012, despite reported prodn. being close to zero4 since 2006. Our three-dimensional model simulations confirm the increase in CFC-11 emissions, but indicate that this increase may have been as much as 50 per cent smaller as a result of changes in stratospheric processes or dynamics. The increase in emission of CFC-11 appears unrelated to past prodn.; this suggests unreported new prodn., which is inconsistent with the Montreal Protocol agreement to phase out global CFC prodn. by 2010.
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    7. 7
      Chambers, L. A.; Gooddy, D. C.; Binley, A. M. Use and Application of CFC-11, CFC-12, CFC-113 and SF 6 as Environmental Tracers of Groundwater Residence Time : A Review. Geosci. Front. 2018, 10, 1643,  DOI: 10.1016/j.gsf.2018.02.017
      There is no corresponding record for this reference.
    8. 8
      Squillace, P. J.; Moran, M. J.; Lapham, W. W.; Price, C. V.; Clawges, R. M.; Zogorski, J. S. Volatile Organic Compounds in Untreated Ambient Groundwater of the United States, 1985–1995. Environ. Sci. Technol. 1999, 33, 4176– 4187,  DOI: 10.1021/es990234m
      8
      Volatile Organic Compounds in Untreated Ambient Groundwater of the United States, 1985-1995
      Squillace, Paul J.; Moran, Michael J.; Lapham, Wayne W.; Price, Curtis V.; Clawges, Rick M.; Zogorski, John S.
      Environmental Science and Technology (1999), 33 (23), 4176-4187CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
      As part of the National Water-Quality Assessment Program of the US Geol. Survey, an assessment of 60 volatile org. compds. (VOCs) in untreated, ambient groundwater of the conterminous USA was conducted based on samples collected from 2948 wells between 1985 and 1995. The samples represent urban and rural areas and drinking-water and nondrinking-water wells. A reporting level of 0.2 μg/L was used with the exception of 1,2-dibromo-3-chloropropane, which had a reporting level of 1.0 μg/L. Because ambient groundwater was targeted, areas of known point-source contamination were excluded from this assessment. VOC concns. generally were low; 56% of the concns. were less than 1 μg/L. In urban areas, 47% of the sampled wells had at least one VOC, and 29% had two or more VOCs; furthermore, US Environmental Protection Agency drinking-water criteria were exceeded in 6.4% of all sampled wells and in 2.5% of the sampled drinking-water wells. In rural areas, 14% of the sampled wells had at least one VOC; furthermore, drinking-water criteria were exceeded in 1.5% of all sampled wells and in 1.3% of the sampled drinking-water wells. Solvent compds. and the fuel oxygenate Me tert-Bu ether were among the most frequently detected VOCs in urban and rural areas. It was detd. that the probability of finding VOCs in untreated groundwater can be estd. on the basis of a logistic regression model by using population d. as an explanatory variable. Although there are limitations to this national scale model, it fitted the data from 2354 wells used for model development and adequately estd. the VOC presence in samples from 589 wells used for model validation. Model ests. indicate that 7% (6-9% on the basis of one std. error) of the ambient groundwater resources of the USA probably contain at least one VOC at a reporting level of 0.2 μg/L. Groundwater is used in these areas by 42 million people (35-50 million based on one std. error); however, human exposure to VOCs from this ambient groundwater is uncertain because the quality of the finished drinking water is generally unknown.
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    9. 9
      Plummer, L. N.; Busenberg, E. Chlorofluorocarbons: Tools for Dating and Tracing Young Groundwater. In Environmental Tracers in Subsurface Hydrology; Cook, P.Herczeg, A., Eds.; Kluwer: Boston, 1999; pp 441– 478.
      There is no corresponding record for this reference.
    10. 10
      Scheutz, C.; Dote, Y.; Fredenslund, A. M.; Kjeldsen, P.; Kjeldsen, P. Attenuation of Fluorocarbons Released from Foam Insulation in Landfills. Environ. Sci. Technol. 2007, 41, 7714– 7722,  DOI: 10.1021/es0707409
      10
      Attenuation of Fluorocarbons Released from Foam Insulation in Landfills
      Scheutz, Charlotte; Dote, Yutaka; Fredenslund, Anders M.; Mosbk, Hans; Kjeldsen, Peter
      Environmental Science & Technology (2007), 41 (22), 7714-7722CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
      Chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), and hydrofluorocarbons (HFCs) have been used as blowing agents (BAs) for foam insulation in home appliances and building materials, which after the end of their useful life are disposed of in landfills. The objective of this project was to evaluate the potential for degrdn. of BAs in landfills, and to develop a landfill model, which could simulate the fate of BAs in landfills. The investigation was performed by use of anaerobic microcosm studies using different types of org. waste and anaerobic digested sludge as inoculum. The BAs studied were CFC-11, CFC-12, HCFC-141b, HFC-134a, and HFC-245fa. Expts. considering the fate of some of the expected degrdns. products of CFC-11 and CFC-12 were included like HCFC-21, HCFC-22, HCFC-31, HCFC-32, and HFC-41. Degrdn. of all studied CFCs and HCFCs was obsd. regardless the type of waste used. In general, the degrdn. followed first-order kinetics. CFC-11 was rapidly degraded from 590 μg L-1 to less than 5 μg L-1 within 15-20 days. The degrdn. pattern indicated a sequential prodn. of HCFC-21, HCFC-31, and HFC-41. However, the prodn. of degrdn. products did not correlate with a stoichiometric removal of CFC-11 indicating that other degrdn. products were produced. HCFC-21 and HCFC-31 were further degraded whereas no further degrdn. of HFC-41 was obsd. The degrdn. rate coeff. was directly correlated with the no. of chlorine atoms attached to the carbon. The highest degrdn. rate coeff. was obtained for CFC-11, whereas lower rates were seen for HCFC-21 and HCFC-31. Equivalent results were obtained for CFC-12. HCFC-141b was also degraded with rates comparable to HCFC-21 and CFC-12. Anaerobic degrdn. of the studied HFCs was not obsd. in any of the expts. within a run time of up to 200 days. The obtained degrdn. rate coeffs. were used as input for an extended version of an existing landfill fate model incorporating a time dependent BA release from co-disposed foam insulation waste. Predictions with the model indicate that the emission of foam released BAs may be strongly attenuated by microbial degrdn. reactions. Sensitivity anal. suggests that there is a need for detn. of degrdn. rates under more field realistic scenarios.
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    11. 11
      Balsiger, C.; Holliger, C.; Höhener, P. Reductive Dechlorination of Chlorofluorocarbons and Hydrochlorofluorocarbons in Sewage Sludge and Aquifer Sediment Microcosms. Chemosphere 2005, 61, 361– 373,  DOI: 10.1016/j.chemosphere.2005.02.087
      11
      Reductive dechlorination of chlorofluorocarbons and hydrochlorofluorocarbons in sewage sludge and aquifer sediment microcosms
      Balsiger, Christian; Holliger, Christof; Hoehener, Patrick
      Chemosphere (2005), 61 (3), 361-373CODEN: CMSHAF; ISSN:0045-6535. (Elsevier B.V.)
      The reductive transformation of the 10 most-widely distributed fluorinated volatile compds. and of tetrachloroethene was examd. for ≤177 days under anaerobic conditions in wastewater sludge and aquifer sediment slurries. Parent compd. and degrdn. product concns. were identified by gas chromatog.-mass spectrometry. Transformation of CFC-11 to HCFC-21 and HCFC-31; CFC-113 to HCFC-123a, chlorotrifluoroethene, and trifluoroethene; CFC-12 to HCFC-22; HCFC-141b to HCFC-151b; and tetrachloroethene to vinyl chloride and ethene were obsd. CFC-114, CFC-115, HCFC-142b, HFC-134, and HCFC-22 were not transformed. Results suggested that for both studied inocula, hydrogenolysis was the primary reductive dechlorination reaction. CFC-113 was the only compd. where a dichloro-elimination was obsd., leading to the formation of chlorotrifluoroethene as temporal intermediate and trifluoroethene as end product. Relative redn. rates of chlorofluoromethanes compared reasonably well with theor. rates calcd. based on thermochem. data using the Marcus theory. Some accumulating hydrochlorofluorocarbons and haloethenes obsd. are toxic and may be of practical relevance in anaerobic environments.
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    12. 12
      Sonier, D. N.; Duran, N. L.; Smith, G. B. Dechlorination of trichlorofluoromethane (CFC-11) by sulfate-reducing bacteria from an aquifer contaminated with halogenated aliphatic compounds. Appl. Environ. Microbiol. 1994, 60, 4567– 4572
      12
      Dechlorination of trichlorofluoromethane (CFC-11) by sulfate-reducing bacteria from an aquifer contaminated with halogenated aliphatic compounds
      Sonier, Dyane N.; Duran, Norma L.; Smith, Geoffrey B.
      Applied and Environmental Microbiology (1994), 60 (12), 4567-72CODEN: AEMIDF; ISSN:0099-2240. (American Society for Microbiology)
      Groundwater samples were obtained from a deep aquifer contaminated with halogenated aliph. compds. One-milliliter samples contained 9.2 × 105 total bacteria (by acridine orange microscopic counts) and 2.5 × 103 SO42--reducing bacteria (by most probable no. anal.). Samples were incubated anaerobically in a basal salts medium with OAc- as the electron donor and NO3- and SO42- as the electron acceptors. Residual levels of CFC-11 in samples were biotically degraded, while trichloroethylene was not. When successively higher levels of CFC-11 were added, increasingly rapid degrdn. rates were obsd. Concomitant with CFC-11 degrdn. was the near stoichiometric prodn. of fluorodichloromethane (HCFC-21); the prodn. of HCFC-21 was verified by mass spectrometry. CFC-11 degrdn. was dependent on the presence of OAc- (or butyrate) and SO42- but was independent of NO3-. Other C sources, such as lactate and iso-PrOH did not support the degrdn. The addn. of 1 mM Na2S completely inhibited CFC-11 degrdn.; however, degrdn. occurred in the presence of 2mM 2-bromoethanesulfonic acid. These results indicate that the anaerobic dechlorination of CFC-11 is carried out by SO42--reducing bacteria and not by denitrifying or methanogenic bacteria.
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    13. 13
      Denovan, B. A.; Strand, S. E. Biological Degradation of Chlorofluorocarbons in Anaerobic Environments. Chemosphere 1992, 24, 935– 940,  DOI: 10.1016/0045-6535(92)90012-g
      13
      Biological degradation of chlorofluorocarbons in anaerobic environments
      Denovan, Barbara A.; Strand, Stuart E.
      Chemosphere (1992), 24 (7), 935-40CODEN: CMSHAF; ISSN:0045-6535.
      In lab. studies, CCl3F (F-11), CCl2F2 (F-12), and 1,1,2-trichlorotrifluoroethane (F-113) were degraded by microbial activity in anaerobic sludges and F-11 and F-113 were degraded in sediments. Biomass acclimated to chlorinated orgs. degraded chlorofluorocarbons faster than unacclimated biomass. Up to 9% of all CFCs may ultimately be susceptible to biol. degrdn. before release to the atm.
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    14. 14
      Lesage, S.; Jackson, R. E.; Priddle, M. W.; Riemann, P. G. Occurrence and fate of organic solvent residues in anoxic groundwater at the Gloucester landfill, Canada. Environ. Sci. Technol. 1990, 24, 559– 566,  DOI: 10.1021/es00074a016
      14
      Occurrence and fate of organic solvent residues in anoxic groundwater at the Gloucester landfill, Canada
      Lesage, Suzanne; Jackson, Richard E.; Priddle, Mark W.; Riemann, Peter G.
      Environmental Science and Technology (1990), 24 (4), 559-66CODEN: ESTHAG; ISSN:0013-936X.
      The disposal of org. chems. in trenches at a waste disposal site near Ottawa, Ontario, resulted in the contamination of the underlying aquifer. The org. residues measured in groundwater samples are reported and the mechanisms of contaminant transport in the aquifer discussed. Groundwater samples from monitoring wells and multilevel samplers were analyzed by gas chromatog.-mass spectrometry. Ultratrace quantities of chlorinated dibenzodioxins and -furans were found in groundwaters directly beneath the trenches. A wide variety of volatile compds. were identified and quantitated in samples from the aquifer. The compd. of greatest concern was 1,4-dioxane, because of its toxicity and mobility, while that present in greatest concn. was a Freon, F113, which appeared to be very persistent, although 3 transformation products were identified.
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    15. 15
      Lesage, S.; Brown, S.; Hosler, K. R. Degradation of Chlorofluorocarbon-113 under Anaerobic Conditions. Chemosphere 1992, 24, 1225– 1243,  DOI: 10.1016/0045-6535(92)90049-w
      15
      Degradation of chlorofluorocarbon-113 under anaerobic conditions
      Lesage, Suzanne; Brown, Susan; Hosler, Kevin R.
      Chemosphere (1992), 24 (9), 1225-43CODEN: CMSHAF; ISSN:0045-6535.
      A series of microcosms were set up to verify the degrdn. pathway of CFC-113 in water under anaerobic conditions and to measure its half-life and that of its major degrdn. products HCFC-123a and C2ClF3. Anaerobic landfill leachate was used as a source of bacteria acclimated to chlorinated solvents. The rate of reaction in methanogenic leachate was also compared to that obtained in a buffer contg. reduced hematin. In methanogenic landfill leachate, CFC-113 was transformed to HCFC-123a with a half-life of 5 days at 20°. The same reaction occurred in Na2S/cysteine buffers contg. hematin, but at a much slower rate. The prodn. of C2ClF3 was independent of the presence of HCFC-123a and occurred abiotically. Under methanogenic conditions, HCFC-123a was further dechlorinated to HCFC-133 and HCFC-133b. C2ClF3 was relatively stable in methanogenic landfill leachate but was decompd. rapidly in a buffer contg. S2-.
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    16. 16
      Horneman, A.; Stute, M.; Schlosser, P.; Smethie, W.; Santella, N.; Ho, D. T.; Mailloux, B.; Gorman, E.; Zheng, Y.; van Geen, A. Degradation rates of CFC-11, CFC-12 and CFC-113 in anoxic shallow aquifers of Araihazar, Bangladesh. J. Contam. Hydrol. 2008, 97, 27– 41,  DOI: 10.1016/j.jconhyd.2007.12.001
      16
      Degradation rates of CFC-11, CFC-12 and CFC-113 in anoxic shallow aquifers of Araihazar, Bangladesh
      Horneman, A.; Stute, M.; Schlosser, P.; Smethie, W.; Santella, N.; Ho, D. T.; Mailloux, B.; Gorman, E.; Zheng, Y.; van Geen, A.
      Journal of Contaminant Hydrology (2008), 97 (1-2), 27-41CODEN: JCOHE6; ISSN:0169-7722. (Elsevier B.V.)
      Chlorofluorocarbons CFC-11 (CCl3F), CFC-12 (CCl2F2), and CFC-113 (CCl2F-CClF2) are used in hydrol. as transient tracers under the assumption of conservative behavior in the unsatd. and satd. soil zones. However, lab. and field studies have shown that these compds. are not stable under anaerobic conditions. To det. the degrdn. rates of CFCs in a tropical environment, atm. air, unsatd. zone soil gas, and anoxic groundwater samples were collected in Araihazar upazila, Bangladesh. Obsd. CFC concns. in both soil gas and groundwater were significantly below those expected from atm. levels. The CFC deficits in the unsatd. zone can be explained by gas exchange with groundwater undersatd. in CFCs. The CFC deficits obsd. in 3H/3He dated groundwater were used to est. degrdn. rates in the satd. zone. The results show that CFCs are degraded to the point where practically no (<5%) CFC-11, CFC-12, or CFC-113 remains in groundwater with 3H/3He ages >10 yr. In groundwater sampled at our site CFC-11 and CFC-12 appear to degrade at similar rates with estd. degrdn. rates ranging from ∼0.25 to ∼6/yr. Degrdn. rates increased as a function of reducing conditions. This indicates that CFC dating of groundwater in regions of humid tropical climate has to be carried out with great caution.
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    17. 17
      Field, J. A.; Sierra-Alvarez, R. Biodegradability of Chlorinated Solvents and Related Chlorinated Aliphatic Compounds. Rev. Environ. Sci. Biotechnol. 2004, 3, 185– 254,  DOI: 10.1007/s11157-004-4733-8
      17
      Biodegradability of chlorinated solvents and related chlorinated aliphatic compounds
      Field, J. A.; Sierra-Alvarez, R.
      Reviews in Environmental Science and Bio/Technology (2004), 3 (3), 185-254CODEN: RESBC6; ISSN:1569-1705. (Kluwer Academic Publishers)
      A review concerning biodegradability of chlorinated solvents and related chlorinated aliph. compds. in 7 compd. categories (chlorinated methanes, ethanes, ethenes, acetic acids, propanoids, butadienes, and chlorofluorocarbons [CFC]) is given. Topics discussed include: sources; biodegrdn. principles; dehalogenation mechanisms; chloromethanes (biodegrdn. of lower and higher); chloroethanes (biodegrdn. of lower and higher chlorinated ethanes); chloroethenes (biodegrdn. of lower and higher chlorinated ethenes); chlorofluorocarbons (biodegrdn. of CFC and HCFC); chloroacetic acids; chloropropanes, chloropropenes, and epichlorohydrin; chlorobutadienes; and summary and conclusions (scope of different physiol. approaches to biodegrdn., biodegrdn. per chlorinated compd. category).
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    18. 18
      Weidhaas, J.; Dupont, R. R. Aerobic Biotransformation of N-Nitrosodimethylamine and N-Nitrodimethylamine in Methane and Benzene Amended Soil Columns. J. Contam. Hydrol. 2013, 150, 45– 53,  DOI: 10.1016/j.jconhyd.2013.04.004
      18
      Aerobic biotransformation of N-nitrosodimethylamine and N-nitrodimethylamine in methane and benzene amended soil columns
      Weidhaas, Jennifer; Dupont, R. Ryan
      Journal of Contaminant Hydrology (2013), 150 (), 45-53CODEN: JCOHE6; ISSN:0169-7722. (Elsevier B.V.)
      Aerobic biotransformation of N-nitrosodimethylamine (NDMA), an emerging contaminant of concern, and its structural analog N-nitrodimethylamine (DMN), was evaluated in benzene and methane amended groundwater passed through lab. scale soil columns. Competitive inhibition models were used to model the kinetics for NDMA and DMN cometabolism accounting for the concurrent degrdn. of the growth and cometabolic substrates. Transformation capacities for NDMA and DMN with benzene (13 and 23 μg (mg cells)-1) and methane (0.14 and 8.4 μg (mg cells)-1) grown cultures, resp. are comparable to those presented in the literature, as were first order endogenous decay rates estd. to be 2.1 × 10-2 ± 1.7 × 10-3 d-1 and 6.5 × 10-1 ± 7.1 × 10-1 d-1 for the methane and benzene amended cultures, resp. These studies highlight possible attenuation mechanisms and rates for NDMA and DMN biotransformation in aerobic aquifers undergoing active remediation, natural attenuation or managed aquifer recharge with treated wastewater (i.e., reclaimed water).
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    19. 19
      Archbold, M. E.; Elliot, T.; Kalin, R. M. Carbon Isotopic Fractionation of CFCs during Abiotic and Biotic Degradation. Environ. Sci. Technol. 2012, 46, 1764– 1773,  DOI: 10.1021/es203386a
      19
      Carbon Isotopic Fractionation of CFCs during Abiotic and Biotic Degradation
      Archbold, Marie E.; Elliot, Trevor; Kalin, Robert M.
      Environmental Science & Technology (2012), 46 (3), 1764-1773CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
      Carbon stable isotope (13C) fractionation in chlorofluorocarbon (CFC) compds. arising from abiotic (chem.) degrdn. using zero-valent iron (ZVI) and biotic (landfill gas attenuation) processes is investigated. Batch tests (at 25 °C) for CFC-113 and CFC-11 using ZVI show quant. degrdn. of CFC-113 to HCFC-123a and CFC-1113 following pseudo-first-order kinetics corresponding to a half-life (τ1/2) of 20.5 h, and a ZVI surface-area normalized rate const. (kSA) of -(9.8 ± 0.5) × 10-5 L m-2 h-1. CFC-11 degraded to trace HCFC-21 and HCFC-31 following pseudo-first-order kinetics corresponding to τ1/2 = 17.3 h and kSA = -(1.2 ± 0.5) × 10-4 L m-2 h-1. Significant kinetic isotope effects of ε(‰) = -5.0 ± 0.3 (CFC-113) and -17.8 ± 4.8 (CFC-11) were obsd. Compd.-specific carbon isotope analyses also have been used here to characterize source signatures of CFC gases (HCFC-22, CFC-12, HFC-134a, HCFC-142b, CFC-114, CFC-11, CFC-113) for urban (UAA), rural/remote (RAA), and landfill (LAA) ambient air samples, as well as in situ surface flux chamber (FLUX; NO FLUX) and landfill gas (LFG) samples at the Dargan Road site, Northern Ireland. The latter values reflect biotic degrdn. and isotopic fractionation in LFG prodn., and local atm. impact of landfill emissions through the cover. Isotopic fractionations of Δ13C ∼ -13‰ (HCFC-22), Δ13C ∼ -35‰ (CFC-12) and Δ13C ∼ -15‰ (CFC-11) were obsd. for LFG in comparison to characteristic solvent source signatures, with the magnitude of the isotopic effect for CFC-11 apparently similar to the kinetic isotope effect for (abiotic) ZVI degrdn.
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    20. 20
      Jeen, S.-W.; Lazar, S.; Gui, L.; Gillham, R. W. Degradation of Chlorofluorocarbons Using Granular Iron and Bimetallic Irons. J. Contam. Hydrol. 2014, 158, 55– 64,  DOI: 10.1016/j.jconhyd.2014.01.002
      20
      Degradation of chlorofluorocarbons using granular iron and bimetallic irons
      Jeen, Sung-Wook; Lazar, Snezana; Gui, Lai; Gillham, Robert W.
      Journal of Contaminant Hydrology (2014), 158 (), 55-64CODEN: JCOHE6; ISSN:0169-7722. (Elsevier B.V.)
      Degrdn. of trichlorofluoromethane (CFC11) and 1,1,2-trichloro-1,2,2-trifluoroethane (CFC113) by granular iron and bimetallic (nickel- or palladium-enhanced) irons was studied in flow-through column tests. Both compds. were rapidly degraded, following pseudo-first-order kinetics with respect to the parent compds. The av. pseudo-first-order rate consts. for CFC11 were similar among different materials, except for palladium-enhanced iron (PdFe), in which the rate of degrdn. was about two times faster than for the other materials. In the case of CFC113, the rate consts. for bimetallic irons were about two to three times greater than for the regular iron material. The smaller than expected differences in degrdn. rate consts. of chlorofluorocarbons (CFCs) between regular iron and bimetallic irons suggested little, if any, catalytic effect of the bimetallic materials in the initial degrdn. step. Subsequent degrdn. steps involved catalytic hydrogenation, however, playing a significant role in further degrdn. of reaction intermediates. The degrdn. intermediates and final products of CFC11 and CFC113 suggested that degrdn. proceeded through hydrogenolysis and α/β-elimination in the presence of regular iron (Fe) and nickel-enhanced iron (NiFe). Even though there is only minor benefit in the use of bimetallic iron in terms of degrdn. kinetics of the parent CFCs, enhanced degrdn. rates of intermediates such as chlorotriflouroethene (CTFE) in subsequent reaction steps could be beneficial.
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    21. 21
      Krone, U. E.; Thauer, R. K.; Hogenkamp, H. P. C.; Steinbach, K. Reductive formation of carbon monoxide from carbon tetrachloride and FREONS 11, 12, and 13 catalyzed by corrinoids. Biochemistry 1991, 30, 2713– 2719,  DOI: 10.1021/bi00224a020
      21
      Reductive formation of carbon monoxide from carbon tetrachloride and FREONS 11, 12, and 13 catalyzed by corrinoids
      Krone, Ute E.; Thauer, Rudolf K.; Hogenkamp, Harry P. C.; Steinbach, Klaus
      Biochemistry (1991), 30 (10), 2713-19CODEN: BICHAW; ISSN:0006-2960.
      CCl4 was converted to CO via corrinoid-catalyzed reductive dehalogenation with Ti(III) citrate as the electron donor. Corrinoids catalyzed the redn. of CFCl3, CF2Cl2, and CF3Cl to CO and, in the case of CFCl3, to a lesser extent, to formate. CF4 was not reduced. The rate of CO and formate formation paralleled that of fluoride release. Both rates decreased in the series CFCl3, CF2Cl2, CCl4, and CF3Cl. The redn. of CFCl3 gave, in addn. to CO and formate, CHFCl2, CH2FCl, CH3F, CH4, C2F2Cl2, and C2F2Cl4. The product pattern indicates that the corrinoid-mediated redn. of halogenated C1-hydrocarbons involves the intermediacy of dihalocarbenes, which may be a reason why these compds. are highly toxic for anaerobic bacteria.
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    22. 22
      Scheutz, C.; Winther, K.; Kjeldsen, P. Removal of Halogenated Organic Compounds in Landfill Gas by Top Covers Containing Zero-Valent Iron. Environ. Sci. Technol. 2000, 34, 2557– 2563,  DOI: 10.1021/es991301f
      22
      Removal of Halogenated Organic Compounds in Landfill Gas by Top Covers Containing Zero-Valent Iron
      Scheutz, Charlotte; Winther, Klaus; Kjeldsen, Peter
      Environmental Science and Technology (2000), 34 (12), 2557-2563CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
      Transformation of gaseous CCl3F and CCl4 by zero-valent Fe was studied in systems unsatd. with water under anaerobic conditions in N2 gas and landfill gas atms. Transformation was studied using batch and flow-through column tests; in both systems, the transformation process of the compds. was pseudo-first-order. Transformation rate consts., referring to the water phase and normalized to 1 m2 Fe surface/mL, of up to 1100 mL/m2-h (batch) and 200 mL/m2-h (flow-through) were obsd. Transformation strongly depended on pH and the presence of O2. During continuous aerobic conditions, CCl3F transformation decreased toward zero. Model calcns. showed that using zero-valent Fe in landfill top covers is a potential treatment technol. to reduce halogenated trace compd. emissions from landfills.
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    23. 23
      Committee on In Situ Bioremediation. The Current Practice of Bioremediation. In Situ Bioremediation: When Does it Work?; National Academies Press: Washington, DC, 1993; pp 47– 62.
      There is no corresponding record for this reference.
    24. 24
      Malla, M. A.; Dubey, A.; Yadav, S.; Kumar, A.; Hashem, A.; Abd-Allah, E. F. Understanding and Designing the Strategies for the Microbe-Mediated Remediation of Environmental Contaminants Using Omics Approaches. Front. Microbiol. 2018, 9, 1– 18,  DOI: 10.3389/fmicb.2018.01132
      There is no corresponding record for this reference.
    25. 25
      Streger, S. H.; Condee, C. W.; Togna, A. P.; Deflaun, M. F. Degradation of Hydrohalocarbons and Brominated Compounds by Methane- and Propane-Oxidizing Bacteria. Environ. Sci. Technol. 1999, 33, 4477– 4482,  DOI: 10.1021/es9907459
      25
      Degradation of Hydrohalocarbons and Brominated Compounds by Methane- and Propane-Oxidizing Bacteria
      Streger, Sheryl H.; Condee, Charles W.; Togna, A. Paul; DeFlaun, Mary F.
      Environmental Science and Technology (1999), 33 (24), 4477-4482CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
      Concern over the use of chems. that potentially contribute to O3 depletion and the greenhouse effect has led to a ban on chlorofluorocarbons (CFC) and potential limitations on the use of Me bromide and other brominated fumigants. This work tested naturally-occurring aerobic microorganisms for their ability to degrade brominated fumigants and the hydrohalocarbons developed to replace CFC. Bacterial strains used degraded a significant percentage of hydrohalocarbons and brominated fumigants tested, which were present at high substrate levels. Degrdn. was often rapid and complete. Ion chromatog. results indicated the stoichiometric release of halogens for several compds. tested. Many compds. were readily biodegradable at high concns. and were metabolized by all strains tested, while others were more recalcitrant. The presence of these microorganisms in the environment may represent a natural sink for some of these compds.; however, the high substrate and bacterial concns. used in this study were chosen for bioreactor development. Information about the biodegradability of these compds. may make it easier to choose the most ecol. safe CFC replacements and fumigants.
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    26. 26
      DeFlaun, M. F.; Ensley, B. D.; Steffan, R. J. Biological Oxidation of Hydrochlorofluorocarbons (HCFCs) by a Methanotrophic Bacterium. Biotechnology 1992, 10, 1576– 1578,  DOI: 10.1038/nbt1292-1576
      There is no corresponding record for this reference.
    27. 27
      Key, B. D.; Howell, R. D.; Criddle, C. S. Fluorinated Organics in the Biosphere. Environ. Sci. Technol. 1997, 31, 2445– 2454,  DOI: 10.1021/es961007c
      27
      Fluorinated organics in the biosphere
      Key, Blake D.; Howell, Robert D.; Criddle, Craig S.
      Environmental Science and Technology (1997), 31 (9), 2445-2454CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
      A review with 144 refs. The use of organofluorine compds. has increased throughout this century, and they are now ubiquitous environmental contaminants. Although generally viewed as recalcitrant because of their lack of chem. reactivity, many fluorinated orgs. are biol. active. Several questions surround their distribution, fate, and effects. Of particular interest is the fate of perfluoroalkyl substituents, such as the trifluoromethyl group. Most evidence to date suggest that such groups resist defluorination, yet they can confer significant biol. activity. Certain volatile fluorinated compds. can be oxidized in the troposphere yielding nonvolatile compds., such as trifluoroacetic acid. In addn., certain nonvolatile fluorinated compds. can be transformed in the biosphere to volatile compds. Research is needed to assess the fate and effects of nonvolatile fluorinated orgs., the fluorinated impurities present in com. formulations, and the transformation products generated by biochem. processes and/or oxidn. in the troposphere.
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    28. 28
      Hunkeler, D.; Meckenstock, R. U.; Sherwood Lollar, B.; Schmidt, T. C.; Wilson, J. T. A Guide for Assessing Biodegradation and Source Identification of Organic Ground Water Contaminants Using Compound Specific Isotope Analysis (CSIA); USEPA Publ., 2008, EPA 600/R-(December); pp 1– 82.
      There is no corresponding record for this reference.
    29. 29
      Hirschorn, S. K.; Dinglasan, M. J.; Elsner, M.; Mancini, S. A.; Lacrampe-Couloume, G.; Edwards, E. A.; Sherwood Lollar, B. Pathway Dependent Isotopic Fractionation during Aerobic Biodegradation of 1,2-Dichloroethane. Environ. Sci. Technol. 2004, 38, 4775– 4781,  DOI: 10.1021/es049920y
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      Pathway Dependent Isotopic Fractionation during Aerobic Biodegradation of 1,2-Dichloroethane
      Hirschorn, Sarah K.; Dinglasan, M. Joyce; Elsner, Martin; Mancini, Silvia A.; Lacrampe-Couloume, Georges; Edwards, Elizabeth A.; Lollar, Barbara Sherwood
      Environmental Science and Technology (2004), 38 (18), 4775-4781CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
      1,2-Dichloroethane (1,2-DCA) is a widespread groundwater contaminant known to be biodegradable under aerobic conditions via enzymic oxidn. or hydrolytic dehalogenation reactions. Current literature reports that stable carbon isotope fractionation of 1,2-DCA during aerobic biodegrdn. is large and reproducible (-27 to -33‰). In this study, a significant variation in the magnitude of stable carbon isotope fractionation during aerobic biodegrdn. was obsd. Biodegrdn. in expts. involving microcosms, enrichment cultures, and pure microbial cultures produced a consistent bimodal distribution of enrichment factors (ε) with one mean ε centered on -3.9 ± 0.6‰ and the other on -29.2 ± 1.9‰. Reevaluation of ε in terms of kinetic isotope effects 12k/13k gave values of 12k/13k = 1.01 and 1.06, which are typical of oxidn. and hydrolytic dehalogenation (SN2) reactions, resp. The bimodal distribution is therefore consistent with the microbial degrdn. of 1,2-DCA by two sep. enzymic pathways. This interpretation is further supported in this study by expts. with pure strains of Xanthobacter autotrophicus GJ10, Ancylobacter aquaticus AD20, and Pseudomonas sp. Strain DCA1 for which the enzymic degrdn. pathways are well-known. A small fractionation of -3.0‰ was measured for 1,2-DCA degrdn. by Pseudomonas sp. Strain DCA1 (monooxygenase enzyme), while degrdn. by the hydrolytic dehalogenase enzyme by the other two pure strains was characterized by fractionation of -32.3‰.
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    30. 30
      Hirschorn, S. K.; Dinglasan-Panlilio, M. J.; Edwards, E. A.; Lacrampe-Couloume, G.; Sherwood Lollar, B. Isotope analysis as a natural reaction probe to determine mechanisms of biodegradation of 1,2-dichloroethane. Environ. Microbiol. 2007, 9, 1651– 1657,  DOI: 10.1111/j.1462-2920.2007.01282.x
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      Isotope analysis as a natural reaction probe to determine mechanisms of biodegradation of 1,2-dichloroethane
      Hirschorn, Sarah K.; Dinglasan-Panlilio, M. Joyce; Edwards, Elizabeth A.; Lacrampe-Couloume, Georges; Lollar, Barbara Sherwood
      Environmental Microbiology (2007), 9 (7), 1651-1657CODEN: ENMIFM; ISSN:1462-2912. (Blackwell Publishing Ltd.)
      1,2-Dichloroethane (1,2-DCA), a chlorinated aliph. hydrocarbon, is a well-known groundwater contaminant. In this study, fractionation of stable carbon isotope values of 1,2-DCA during biodegrdn. was used as a novel reaction probe to provide information about the mechanism of 1,2-DCA biodegrdn. under both aerobic (O2-reducing) and anaerobic (NO3-reducing) conditions. Under O2-reducing conditions, an isotopic enrichment value (ε) of -25.8 ± 1.1‰ (±95% confidence intervals) was measured for the enrichment culture. Under NO3-reducing conditions, an ε-value of -25.8 ± 3.5‰ was measured. The microbial culture produced isotopic enrichment values (ε) that are not only large and reproducible, but also are the same whether O2 or NO3 was used as an electron acceptor. Combining data measured under both O2- and NO3-reducing conditions, an isotopic enrichment value (ε) of -25.8 ± 1.6‰ is measured for the microbial culture during 1,2-DCA degrdn. The ε-value can be converted into a kinetic isotope effect (KIE) value to relate the obsd. isotopic fractionation to the mechanism of degrdn. This KIE value (1.05) is consistent with degrdn. via hydrolytic dehalogenation under both electron-accepting conditions. This study demonstrates the added value of compd.-specific isotope anal. not only as a technique to verify the occurrence and extent of biodegrdn. in the field, but also as a natural reaction probe to provide insight into the enzymic mechanism of contaminant degrdn.
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    31. 31
      Vanstone, N.; Elsner, M.; Lacrampe-Couloume, G.; Mabury, S.; Sherwood Lollar, B. Potential for Identifying Abiotic Chloroalkane Degradation Mechanisms using Carbon Isotopic Fractionation. Environ. Sci. Technol. 2008, 42, 126– 132,  DOI: 10.1021/es0711819
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      Potential for Identifying Abiotic Chloroalkane Degradation Mechanisms using Carbon Isotopic Fractionation
      VanStone, Nancy; Elsner, Martin; Lacrampe-Couloume, Georges; Mabury, Scott; Sherwood Lollar, Barbara
      Environmental Science & Technology (2008), 42 (1), 126-132CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
      Degrdn. of 1,1- and 1,2-dichloroethane (1,1-DCA, 1,2-DCA) and carbon tetrachloride (CCl4) on Zn was investigated using compd. specific isotope anal. (CSIA) to measure isotopic fractionation factors for chloroalkane degrdn. by hydrogenolysis, by α-elimination, and by β-elimination. Significant differences in enrichment factors (ε) and assocd. apparent kinetic isotope effects (AKIE) were measured for these different reaction pathways, suggesting that carbon isotope fractionation by β-elimination is substantially larger than fractionation by hydrogenolysis or by α-elimination. Specifically, for 1,1-DCA, the isotopic compn. of the reductive α-elimination product (ethane) and the hydrogenolysis product (chloroethane) were the same, indicating that cleavage of a single C-Cl bond was the rate-limiting step in both cases. In contrast, for 1,2-DCA, ε = εreactive position = -29.7 ± 1.5‰, and the calcd. AKIE (1.03) indicated that β-elimination was likely concerted, possibly involving two C-Cl bonds simultaneously. Compared to 1,1-DCA hydrogenolysis, the AKIE of 1.01 for hydrogenolysis of CCl4 was much lower, indicating that, for this highly reactive organohalide, mass transfer to the surface was likely partially rate-limiting. These findings are a first step toward delineating the relative contribution of these competing pathways in other abiotic systems such as the degrdn. of chlorinated ethenes on zerovalent iron (ZVI), iron sulfide, pyrite, or magnetite, and, potentially, toward distinguishing between degrdn. of chlorinated ethenes by abiotic vs. biotic processes.
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    32. 32
      Elsner, M.; Zwank, L.; Hunkeler, D.; Schwarzenbach, R. P. A New Concept Linking Observable Stable Isotope Fractionation to Transformation Pathways of Organic Pollutants. Environ. Sci. Technol. 2005, 39, 6896– 6916,  DOI: 10.1021/es0504587
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      A New Concept Linking Observable Stable Isotope Fractionation to Transformation Pathways of Organic Pollutants
      Elsner, Martin; Zwank, Luc; Hunkeler, Daniel; Schwarzenbach, Rene P.
      Environmental Science and Technology (2005), 39 (18), 6896-6916CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
      A review. Measuring stable isotope fractionation of carbon, hydrogen, and other elements by Compd. Specific Isotope Anal. (CSIA) is a new, innovative approach to assess org. pollutant degrdn. in the environment. Central to this concept is the Rayleigh equation which relates degrdn.-induced decreases in concns. directly to concomitant changes in bulk (= av. over the whole compd.) isotope ratios. The extent of in situ transformation may therefore be inferred from measured isotope ratios in field samples, provided that an appropriate enrichment factor (εbulk) is known. This εbulk value, however, is usually only valid for a specific compd. and for specific degrdn. conditions. Therefore, a direct comparison of εbulk values for different compds. and for different types of reactions has in general not been feasible. In addn., it is often uncertain how robust and reproducible εbulk values are and how confidently they can be used to quantify contaminant degrdn. in the field. To improve this situation and to achieve a more in-depth understanding, this crit. review aims to relate fundamental insight about kinetic isotope effects (KIE) found in the physico(bio)chem. literature to apparent kinetic isotope effects (AKIE) derived from εbulk values reported in environmentally oriented studies. Starting from basic rate laws, a quite general derivation of the Rayleigh equation is given, resulting in a novel set of simple equations that take into account the effects of (1) nonreacting positions and (2) intramol. competition and that lead to position-specific AKIE values rather than bulk enrichment factors. Reevaluation of existing εbulk literature values result in consistent ranges of AKIE values that generally are in good agreement with previously published data in the (bio)chem. literature and are typical of certain degrdn. reactions (subscripts C and H indicate values for carbon and hydrogen): AKIEC = 1.01-1.03 and AKIEH = 2-23 for oxidn. of C-H bonds; AKIEC = 1.03-1.07 for SN2-reactions; AKIEC = 1.02-1.03 for reductive cleavage of C-Cl bonds; AKIEC = 1.00-1.01 for C:C bond epoxidn.; AKIEC = 1.02-1.03 for C:C bond oxidn. by permanganate. Hence, the evaluation scheme presented bridges a gap between basic and environmental (bio)chem. and provides insight into factors that control the magnitude of bulk isotope fractionation factors. It also serves as a basis to identify degrdn. pathways using isotope data. It is shown how such an anal. may be even possible in complex field situations and/or in cases where AKIE values are smaller than intrinsic KIE values, provided that isotope fractionation is measured for two elements simultaneously ("two-dimensional isotope anal."). Finally, the procedure is used (1) to point out the possibility of estg. approx. εbulk values for new compds. and (2) to discuss the moderate, but non-negligible variability that may quite generally be assocd. with εbulk values. Future research is suggested to better understand and take into account the various factors that may cause such variability.
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    33. 33
      Elsner, M. Stable Isotope Fractionation to Investigate Natural Transformation Mechanisms of Organic Contaminants: Principles, Prospects and Limitations. J. Environ. Monit. 2010, 12, 2005– 2031,  DOI: 10.1039/c0em00277a
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      Stable isotope fractionation to investigate natural transformation mechanisms of organic contaminants: principles, prospects and limitations
      Elsner, Martin
      Journal of Environmental Monitoring (2010), 12 (11), 2005-2031CODEN: JEMOFW; ISSN:1464-0325. (Royal Society of Chemistry)
      A review. Gas chromatog.-isotope ratio mass spectrometry (GC-IRMS) has made it possible to analyze natural stable isotope ratios (e.g., 13C/12C, 15N/14N, 2H/1H) of individual org. contaminants in environmental samples. They may be used as fingerprints to infer contamination sources, and may demonstrate, and even quantify, the occurrence of natural contaminant transformation by the enrichment of heavy isotopes that arises from degrdn.-induced isotope fractionation. This review highlights an addnl. powerful feature of stable isotope fractionation: the study of environmental transformation mechanisms. Isotope effects reflect the energy difference of isotopologues (i.e., mols. carrying a light vs. a heavy isotope in a particular mol. position) when moving from reactant to transition state. Measuring isotope fractionation, therefore, essentially allows a glimpse at transition states! It is shown how such position-specific isotope effects are "dild. out" in the compd. av. measured by GC-IRMS, and how a careful evaluation in mechanistic scenarios and by dual isotope plots can recover the underlying mechanistic information. The math. framework for multistep isotope fractionation in environmental transformations is reviewed. Case studies demonstrate how isotope fractionation changes in the presence of mass transfer, enzymic commitment to catalysis, multiple chem. reaction steps or limited bioavailability, and how this gives information about the individual process steps. Finally, it is discussed how isotope ratios of individual products evolve in sequential or parallel transformations, and what mechanistic insight they contain. A concluding session gives an outlook on current developments, future research directions and the potential for bridging the gap between lab. and real world systems.
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    34. 34
      Elsner, M.; Hofstetter, T. B. Current Perspectives on the Mechanisms of Chlorohydrocarbon Degradation in Subsurface Environments : Insight from Kinetics, Product Formation, Probe Molecules, and Isotope Fractionation. ACS Symp. Ser. 2011, 1071, 407,  DOI: 10.1021/bk-2011-1071.ch019
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      Current perspectives on the mechanisms of chlorohydrocarbon degradation in subsurface environments- insight from kinetics, product formation, probe molecules, and isotope fractionation
      Elsner, Martin; Hofstetter, Thomas B.
      ACS Symposium Series (2011), 1071 (Aquatic Redox Chemistry), 407-439CODEN: ACSMC8; ISSN:0097-6156. (American Chemical Society)
      A review. Degrdn. of chlorinated org. contaminants by natural and engineered reductive dechlorination reactions can occur via numerous biotic and abiotic transformation pathways giving rise to either benign or more toxic products. To assess whether dechlorination processes may lead to significant detoxification (a) the thermodn. feasibility of a reaction, (b) rates of transformation, and (c) product formation routes need to be understood. To this end, fundamental knowledge of chlorohydrocarbon (CHC) reaction mechanisms is essential. The authors review insight from reaction thermodn., structure-reactivity relations, and applications of radical and carbene traps, and of synthetic probe mols. The authors summarize the state-of-knowledge about intermediates and reductive dechlorination pathways of vicinal and geminal haloalkanes, and of chlorinated ethenes. Transformation conditions are identified under which problematic products may be avoided. In an outlook, the potential of stable C and Cl isotope fractionation to identify initial transformation mechanisms, competing transformation pathways, and common branching points are discussed.
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    35. 35
      Hofstetter, T. B.; Bolotin, J.; Skarpeli-liati, M.; Wijker, R.; Kurt, Z.; Nishino, S. F.; Spain, J. C. Tracking transformation processes of organic micropollutants in aquatic environments using multi-element isotope fractionation analysis. Geochemistry 2011, 26, S334– S336,  DOI: 10.1016/j.apgeochem.2011.03.068
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      Tracking transformation processes of organic micropollutants in aquatic environments using multi-element isotope fractionation analysis
      Hofstetter, Thomas B.; Bolotin, Jakov; Skarpeli-Liati, Marita; Wijker, Reto; Kurt, Zohre; Nishino, Shirley F.; Spain, Jim C.
      Applied Geochemistry (2011), 26 (Supplement), S334-S336CODEN: APPGEY; ISSN:0883-2927. (Elsevier Ltd.)
      The quant. description of enzymic or abiotic transformations of man-made org. micropollutants in rivers, lakes, and groundwaters is one of the major challenges assocd. with the risk assessment of water resource contamination. Compd.-specific isotope anal. enables one to identify (bio)degrdn. pathways based on changes in the contaminants' stable isotope ratios even if multiple reactive and non-reactive processes cause concns. to decrease. Here, we investigated how the magnitude and variability of isotope fractionation in some priority pollutants is detd. by the kinetics and mechanisms of important enzymic and abiotic redox reactions. For nitroarom. compds. and substituted anilines, we illustrate that competing transformation pathways can be assessed via trends of N and C isotope signatures.
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    36. 36
      Elsner, M.; Jochmann, M. A.; Hofstetter, T. B.; Hunkeler, D.; Bernstein, A.; Schmidt, T. C.; Schimmelmann, A. Current Challenges in Compound-Specific Stable Isotope Analysis of Environmental Organic Contaminants. Anal Bioanal Chem 2012, 403, 2471– 2491,  DOI: 10.1007/s00216-011-5683-y
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      Current challenges in compound-specific stable isotope analysis of environmental organic contaminants
      Elsner, Martin; Jochmann, Maik A.; Hofstetter, Thomas B.; Hunkeler, Daniel; Bernstein, Anat; Schmidt, Torsten C.; Schimmelmann, Arndt
      Analytical and Bioanalytical Chemistry (2012), 403 (9), 2471-2491CODEN: ABCNBP; ISSN:1618-2642. (Springer)
      A review. Compd.-specific stable-isotope anal. (CSIA) has greatly facilitated assessment of sources and transformation processes of org. pollutants. Multielement isotope anal. is one of the most promising applications of CSIA because it even enables distinction of different transformation pathways. This review introduces the essential features of continuous-flow isotope-ratio mass spectrometry (IRMS) and highlights current challenges in environmental anal. as exemplified for the isotopes of nitrogen, hydrogen, chlorine, and oxygen. Strategies and recent advances to enable isotopic measurements of polar contaminants, for example pesticides or pharmaceuticals, are discussed with special emphasis on possible solns. for anal. of low concns. of contaminants in environmental matrixes. Finally, discuss different levels of calibration and referencing are discussed and the urgent need for compd.-specific isotope stds. for gas chromatog.-isotope-ratio mass spectrometry (GC-IRMS) of org. pollutants is pointed out.
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    37. 37
      Horst, A.; Lacrampe-Couloume, G.; Sherwood Lollar, B. Compound-Specific Stable Carbon Isotope Analysis of Chlorofluorocarbons in Groundwater. Anal. Chem. 2015, 87, 10498– 10504,  DOI: 10.1021/acs.analchem.5b02701
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      Compound-Specific Stable Carbon Isotope Analysis of Chlorofluorocarbons in Groundwater
      Horst, Axel; Lacrampe-Couloume, Georges; Sherwood Lollar, Barbara
      Analytical Chemistry (Washington, DC, United States) (2015), 87 (20), 10498-10504CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)
      Chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs), controlled substances due to their role in stratospheric ozone loss, also occur as dissolved contaminants in groundwaters. Stable carbon isotopic signatures may provide valuable new information on the fate of these compds. as has been seen for other priority hydrocarbon contaminants, but to date no method for extn. and isotopic anal. of dissolved CFCs from groundwaters was developed. We describe a cryogenic purge and trap system coupled to continuous flow compd.-specific stable C isotope anal. mass spectrometry for concns. as low as 35 μg/L. The method is validated by comparing isotopic signatures from water extd. CFCs against a new suite of isotopic CFC stds. Fractionation of CFCs in volatilization expts. from pure-phase CFC-11 and CFC-113 resulted in enrichment factors (ε) of +1.7±0.1 and +1.1±0.1‰, resp., indicating that such volatile loss, if significant, would produce a more 13C depleted signature in the remaining CFCs. Importantly, no significant fractionation was obsd. during volatile extn. of dissolved CFCs from aq. solns. δ13C values for groundwaters from a CFC-contaminated site were, on av., more enriched than δ13C values for pure compds. Such enriched δ13C values have been seen in other hydrocarbon contaminants such as chlorinated ethenes and ethanes due to in situ degrdn., but definitive interpretation of such enriched signatures in field samples requires addnl. expts. to characterize fractionation of CFCs during biodegrdn. The establishment of a robust and sensitive method of extn. and anal., as described here, provides the foundation for such future directions.
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    38. 38
      Edwards, E. A.; Grbić-Galić, D. Anaerobic degradation of toluene and o-xylene by a methanogenic consortium. Appl Environ Microbiol 1994, 60, 313– 322
      38
      Anaerobic degradation of toluene and o-xylene by a methanogenic consortium
      Edwards, Elizabeth A.; Grbic-Galic, Dunja
      Applied and Environmental Microbiology (1994), 60 (1), 313-22CODEN: AEMIDF; ISSN:0099-2240.
      Toluene and o-xylene were completely mineralized to stoichiometric amts. of carbon dioxide, methane, and biomass by aquifer-derived microorganisms under strictly anaerobic conditions. The source of the inoculum was creosote-contaminated sediment from Pensacola, Fla. The adaptation periods before the onset of degrdn. were long (100 to 120 days for toluene degrdn. and 200 to 255 days for o-xylene). Successive transfers of the toluene- and o-xylene-degrading cultures remained active. Cell d. in the cultures progressively increased over 2 to 3 yr to stabilize at approx. 109 cells per mL. Degrdn. of toluene and o-xylene in stable mixed methanogenic cultures followed Monod kinetics, with inhibition noted at substrate concns. above 700 μM for o-xylene and 1800 μM for toluene. The cultures degraded toluene or o-xylene but did not degrade m-xylene, p-xylene, benzene, ethylbenzene, or naphthalene. The degradative activity was retained after pasteurization or after starvation for 1 yr. Degrdn. of toluene and o-xylene was inhibited by the alternate electron acceptors oxygen, nitrate, and sulfate. Degrdn. was also inhibited by the addn. of preferred substrates such as acetate, H2, propionate, methanol, acetone, glucose, amino acid, fatty acids, peptone, and yeast ext. These data suggest that the presence of natural org. substrates or cocontaminants may inhibit anaerobic degrdn. of pollutants such as toluene and o-xylene at contaminated sites.
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    39. 39
      Mackay, D.; Shiu, W. Y.; Ma, K. C.; Lee, S. C. Halogenated Aliphatic Hydrocarbons. Handbook of Physical-Chemical Properties and Environmental Fate for Organic Chemicals ; 2006; pp 1199– 1205.
      There is no corresponding record for this reference.
    40. 40
      Vail, J.; France, D.; Lewis, B. U.S. Environmental Protection Agency Science and Ecosystem Support Division Standard Operating Procedure: Groundwater Sampling: Athens, Georgia, 2013.
      There is no corresponding record for this reference.
    41. 41
      Capozzi, S. L.; Rodenburg, L. A.; Krumins, V.; Fennell, D. E.; Mack, E. E. Using Positive Matrix Factorization to Investigate Microbial Dehalogenation of Chlorinated Benzenes in Groundwater at a Historically Contaminated Site. Chemosphere 2018, 211, 515– 523,  DOI: 10.1016/j.chemosphere.2018.07.180
      41
      Using positive matrix factorization to investigate microbial dehalogenation of chlorinated benzenes in groundwater at a historically contaminated site
      Capozzi, Staci L.; Rodenburg, Lisa A.; Krumins, Valdis; Fennell, Donna E.; Mack, E. Erin
      Chemosphere (2018), 211 (), 515-523CODEN: CMSHAF; ISSN:0045-6535. (Elsevier Ltd.)
      Chlorinated benzenes are common groundwater contaminants in the United States, so demonstrating whether they undergo degrdn. in the subsurface is important in detg. the best remedy for this contamination. The purpose of this work was to use a new data mining approach to investigate chlorinated benzene degrdn. pathways in the subsurface. Pos. Matrix Factorization (PMF) was used to analyze long-term measurements of chlorinated benzene concns. in groundwater at a contaminated site in New Jersey. A dataset contg. 597 groundwater samples and 5 chlorinated benzenes and benzene collected from 144 wells over 20 years was investigated using PMF2 software. Despite the heterogeneity of this dataset, PMF anal. revealed patterns indicative of microbial dechlorination in the groundwater and provided insight about where dechlorination is occurring, to what extent, and under which geochem. conditions. PMF resolved a factor indicative of a source of 1,2,4-trichlorobenzene and 1,2-dichlorobenzene and two factors representing stages of dechlorination, one more advanced than the other. The PMF results indicated that virtually all of the 1,2-dichlorobenzene at the site arises from its use onsite, not from the dechlorination of trichlorobenzenes. Factors were further interpreted using ancillary data such as geochem. indicators and field parameters also measured in the samples. Anal. suggested that the partial and advanced dechlorination signals occur under different subsurface phys. conditions. The results provided field validation of the current understanding of anaerobic dechlorination of chlorinated benzenes in the subsurface developed from lab. studies. PMF is thereby shown to be a useful tool for investigating chlorinated benzene dechlorination.
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    42. 42
      Army Corps of Engineers. U. S. Feasibility Study: DuPont Chambers Works FUSRAP Site: Philadelphia, 2012.
      There is no corresponding record for this reference.
    43. 43
      US EPA. METHOD 8260B: Volatile Organic Compounds by Gas Chromatography/Mass Spectrometry (GC/MS), Part of Test Methods for Evaluating Solid Waste, Physical/Chemical Methods , 1996.
      There is no corresponding record for this reference.
    44. 44
      Slater, G. F.; Dempster, H. S.; Sherwood Lollar, B.; Ahad, J. Headspace Analysis: A New Application for Isotopic Characterization of Dissolved Organic Contaminants. Environ. Sci. Technol. 1999, 33, 190– 194,  DOI: 10.1021/es9803254
      44
      Headspace Analysis: A New Application for Isotopic Characterization of Dissolved Organic Contaminants
      Slater, Gregory F.; Dempster, Helen S.; Lollar, Barbara Sherwood; Ahad, Jason
      Environmental Science and Technology (1999), 33 (1), 190-194CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
      Petroleum products and industrial solvents are among the most ubiquitous contaminants of soil and groundwater and the source of several common and hazardous volatile org. chems. (VOCs). Volatilization is a key determinant of the fate of VOCs in the subsurface environment, impacting contaminant partitioning between the aq., gaseous, and nonaq. liq. phases. This study uses stable C isotope anal. to investigate the isotopic effects involved in volatilization of trichloroethylene (TCE) and toluene from both free product (or pure phase) and aq. solns. Results indicate that, during volatilization from the aq. phase and from free product, the isotopic compn. of TCE and toluene remains unchanged within reproducibility limits. These results have 2 important implications for contaminant hydrogeol. First, they suggest that C isotopic signatures may be useful in tracking contaminant transport between the vapor, aq., and NAPL phases since they remain conservative during phase changes. Second, they demonstrate the utility of headspace extn. (sampling of the vapor phase or headspace above an aq. soln.) as a preparatory technique for isotopic anal. of dissolved VOCs. Headspace isotopic anal. provides a straightforward and rapid technique for δ13C anal. of dissolved org. contaminants at concns. as low as hundreds of ppb.
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    45. 45
      Sherwood Lollar, B.; Hirschorn, S. K.; Chartrand, M. M. G.; Lacrampe-Couloume, G. An Approach for Assessing Total Instrumental Uncertainty in Compound-Specific Carbon Isotope Analysis: Implications for Environmental Remediation Studies. Anal. Chem. 2007, 79, 3469– 3475,  DOI: 10.1021/ac062299v
      45
      An Approach for Assessing Total Instrumental Uncertainty in Compound-Specific Carbon Isotope Analysis: Implications for Environmental Remediation Studies
      Sherwood Lollar, Barbara; Hirschorn, Sarah K.; Chartrand, Michelle M. G.; Lacrampe-Couloume, Georges
      Analytical Chemistry (Washington, DC, United States) (2007), 79 (9), 3469-3475CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)
      Detn. of compd.-specific carbon isotope values by continuous flow isotope ratio mass spectrometry is impacted by variation in several routine operating parameters of which one of the most important is signal size, or linearity. Expts. were carried out to evaluate the implications of these operating parameters on both reproducibility and accuracy of δ13C measurements. A new method is described for assessing total instrumental uncertainty of routine compd.-specific δ13C anal., incorporating both accuracy and reproducibility. These findings have important implications for application of compd.-specific isotope anal. in environmental geochem. and in particular for the rapidly developing field of isotopic investigation of biodegrdn. and remediation of org. chems. in contaminant hydrogeol.
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    46. 46
      Fontes, J.; Fritz, P. Handbook of Environmental Isotope Geochemistry, 1st ed.; Elsevier: New York, 1980.
      There is no corresponding record for this reference.
    47. 47
      Siegemund, G.; Schwertfeger, W.; Feiring, A.; Smart, B.; Behr, F.; Vogel, H.; McKusick, B.; Kirsch, P. Fluorine Compounds, Organic. Ullmann’s Encyclopedia of Industrial Chemistry; John Wiley & Sons, 2016; Vol. 15, pp 1– 56.
      There is no corresponding record for this reference.
    48. 48
      Etrl, S. J. Herkunftsbestimmung Organischer Shadstoffe Durch Untersuchung Des Natürlichen Isotopengehalts. Ph.D. Thesis, Technische Universität München, 1997.
      There is no corresponding record for this reference.
    49. 49
      Archbold, M. E.; Redeker, K. R.; Davis, S.; Elliot, T.; Kalin, R. M. A Method for Carbon Stable Isotope Analysis of Methyl Halides and Chlorofluorocarbons at Pptv Concentrations. Rapid Commun. Mass Spectrom. 2005, 19, 337– 342,  DOI: 10.1002/rcm.1791
      49
      A method for carbon stable isotope analysis of methyl halides and chlorofluorocarbons at pptv concentrations
      Archbold, Marie E.; Redeker, Kelly R.; Davis, Simon; Elliot, Trevor; Kalin, Robert M.
      Rapid Communications in Mass Spectrometry (2005), 19 (3), 337-342CODEN: RCMSEF; ISSN:0951-4198. (John Wiley & Sons Ltd.)
      A pre-concn. system was validated for use with a gas chromatog./mass spectrometry/isotope ratio mass spectrometer (GC/MS/IRMS) to det. ambient air 13C/12C ratios for Me halides (MeCl and MeBr) and chlorofluorocarbons (CFCs). The isotopic compn. of specific compds. can provide useful information on their atm. budgets and biogeochem. that cannot be ascertained from abundance measurements alone. Although pre-concn. systems were previously used with a GC/MS/IRMS for atm. trace gas anal., this is the 1st study also to report system validation tests. Validation results indicate that the pre-concn. system and subsequent sepn. technologies do not significantly alter the stable isotopic ratios of the target Me halides, CFC-12 (CCl2F2) and CFC-113 (C2Cl3F3). Significant, but consistent, isotopic shifts of -27.5‰ to -25.6‰ do occur within the system for CFC-11 (CCl3F), although the shift is correctable. The method presented has the capacity to sep. these target halocarbons from >50 other compds. in ambient air samples. Sepn. allows for the detn. of stable carbon isotope ratios of five of these six target trace atm. constituents within ambient air for large vol. samples ( ≤ 10 L). Representative urban air analyses from Belfast City are also presented which give carbon isotope results similar to published values for 13C/12C anal. of MeCl (-39.1‰) and CFC-113 (-28.1‰). However, this is the 1st paper reporting stable carbon isotope signatures for CFC-11 (-29.4‰) and CFC-12 (-37.0‰).
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    50. 50
      Thompson, A. E.; Anderson, R. S.; Rudolph, J.; Huang, L. Stable Isotope Signatures of Background Tropospheric Chloromethane and CFC-113. Biogeochemistry 2002, 60, 191– 211,  DOI: 10.1023/a:1019820208377
      50
      Stable carbon isotope signatures of background tropospheric chloromethane and CFC113
      Thompson, Alexandra E.; Anderson, Rebecca S.; Rudolph, Jochen; Huang, Lin
      Biogeochemistry (2002), 60 (2), 191-211CODEN: BIOGEP; ISSN:0168-2563. (Kluwer Academic Publishers)
      Samples of background air were collected in the lower troposphere of the Northern (high Arctic, northern Ontario, Vancouver and Houston) and Southern (Baring Head, New Zealand) Hemispheres over the period July 1999 until Mar. 2001. These samples were analyzed for the stable carbon isotope ratios of 1,1,1-trichlorotrifluoroethane (CFC113) and CH3Cl using a gas chromatog.-continuous flow online combustion isotope ratio mass spectrometry combination. For CH3Cl the global av. of the stable carbon isotope ratio is -36.2 ± 0.3‰ (error of mean). The av. is based on 78 data points, std. deviation for all measurements is 2.3‰, and the 90% confidence interval is -35.8 to -36.6‰. However, the no. of data points from the Southern Hemisphere is rather limited and thus this observation is not necessarily representative for the entire Southern Hemisphere. A simple isotopic budget of CH3Cl shows the most important parameters needing to be defined are the kinetic isotope effect of CH3Cl destruction by OH radicals and the source compn. of CH3Cl emitted by the oceans and biomass burning of C-4 plants. Present budgets of atm. CH3Cl show a significant deficit in the source strength. We est. that the av. stable carbon isotope ratio of the addnl. CH3Cl emissions required to balance the budget is -41.9 ± 7.8‰. The av. CFC113 isotopic compn. based on 38 measurements is -23.3 ± 1.6‰ (error of mean), σ = 9.6‰ with no significant difference between the hemispheres.
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    51. 51
      Mundle, S. O. C.; Vandersteen, A. A.; Lacrampe-Couloume, G.; Kluger, R.; Sherwood Lollar, B. Pressure-monitored headspace analysis combined with compound-specific isotope analysis to measure isotope fractionation in gas-producing reactions. Rapid Commun. Mass Spectrom. 2013, 27, 1778– 1784,  DOI: 10.1002/rcm.6625
      51
      Pressure-monitored headspace analysis combined with compound-specific isotope analysis to measure isotope fractionation in gas-producing reactions
      Mundle, Scott O. C.; Vandersteen, Adelle A.; Lacrampe-Couloume, Georges; Kluger, Ronald; Sherwood Lollar, Barbara
      Rapid Communications in Mass Spectrometry (2013), 27 (15), 1778-1784CODEN: RCMSEF; ISSN:0951-4198. (John Wiley & Sons Ltd.)
      Processes that lead to pressure changes in closed exptl. systems can dramatically increase the total uncertainty in enrichment factors (ε) based on headspace anal. and compd.-specific isotope anal. (CSIA). We report: (1) A new technique to det. ε values for non-isobaric processes, and (2) a general approach to evaluate the exptl. error in calcd. ε values. The ε values were detd. by monitoring the change in headspace pressure from the prodn. of CO2 in a decarboxylation reaction using a pressure gauge and measuring the δ13C values using CSIA. The statistical error was assessed over shorter reaction progress intervals to evaluate the impact of exptl. error on the total uncertainty assocd. with calcd. ε values. As an alternative to conventional compositional anal., calcn. of CO2 produced during the reaction monitored with a pressure gauge resulted in rate consts. and ε values with improved correlation coeffs. and confidence intervals for a non-isobaric process in a closed system. Further, statistical evaluation of the ε values as a function of reaction progress showed that uncertainty in data points for reaction progress (f) at late stages of the reaction can have a significant impact on the reported ε value. Pressure-monitored headspace anal. reduces the uncertainty assocd. with monitoring the reaction progress (f) based on estg. substrate removal and headspace diln. during sampling. Statistical calcns. over shorter intervals should be used to evaluate the total error for reported ε values.
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    52. 52
      Bigeleisen, J.; Allen, T. L. Fractionation of the Carbon Isotopes in Decarboxylation Reactions. IV. The Relative Rates of Decomposition of 1-C12and 1-C13Trichloracetate Ions. J. Chem. Phys. 1951, 19, 760– 764,  DOI: 10.1063/1.1748348
      52
      Fractionation of the carbon isotopes in decarboxylation reactions. IV. The relative rates of decomposition of 1-C12 and 1-C13 trichloroacetate ions
      Bigeleisen, Jacob; Allen, Thomas L.
      Journal of Chemical Physics (1951), 19 (), 760-4CODEN: JCPSA6; ISSN:0021-9606.
      A precise detn. of the relative rates of decompn. of 1-C12 and 1-C13 trichloroacetate ions has been made. The 1-C12 ion decomps. 1.0338 times as fast as the 1-C13 ion into CHCl3 and bicarbonate at 70.4°. Trichloroacetate undergoes a decompn. reaction which gives Cl- but no CO2, OH-, or H+. The ratio of the rate consts. for the production of Cl- and bicarbonate is 0.078. The errors in the detn. of the effect of isotopic substitution on the rates of chem. reactions are discussed. Studies of the isotopes of C by mass-spectrometric analyses of C13 at the natural abundance level are capable of a precision of 1 order of magnitude better than ones in which the sp. activity of C14 is detd. by counting.
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    53. 53
      Buchner, D.; Jin, B.; Ebert, K.; Rolle, M.; Elsner, M.; Haderlein, S. B. Experimental Determination of Isotope Enrichment Factors - Bias from Mass Removal by Repetitive Sampling. Environ. Sci. Technol. 2017, 51, 1527– 1536,  DOI: 10.1021/acs.est.6b03689
      53
      Experimental Determination of Isotope Enrichment Factors - Bias from Mass Removal by Repetitive Sampling
      Buchner, Daniel; Jin, Biao; Ebert, Karin; Rolle, Massimo; Elsner, Martin; Haderlein, Stefan B.
      Environmental Science & Technology (2017), 51 (3), 1527-1536CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
      Application of compd.-specific stable isotope approaches often involves comparisons of isotope enrichment factors (ε). Exptl. detn. 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 expts., however, this requirement is not necessarily fulfilled, since repetitive sampling can remove a significant fraction of the analyte. For volatile compds. 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 exptl. data to demonstrate that the detn. of ε-values according to current correction methods is prone to considerable systematic errors even in well-designed exptl. setups. Application of inappropriate methods may lead to incorrect and inconsistent ε-values entailing misinterpretations regarding the processes underlying isotope fractionation. In fact, our results suggest that artifacts arising from inappropriate data evaluation might contribute to the variability of published ε-values. In response, we present novel, adequate methods to eliminate systematic errors in data evaluation. A model-based sensitivity anal. serves to reveal the most crucial exptl. parameters and can be used for future exptl. design to obtain correct ε-values allowing mechanistic interpretations.
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    54. 54
      Scott, K. M.; Lu, X.; Cavanaugh, C. M.; Liu, J. S. Optimal Methods for Estimating Kinetic Isotope Effects from Different Forms of the Rayleigh Distillation Equation. Geochim. Cosmochim. Acta 2004, 68, 433– 442,  DOI: 10.1016/s0016-7037(03)00459-9
      54
      Optimal methods for estimating kinetic isotope effects from different forms of the Rayleigh distillation equation
      Scott, K. M.; Lu, X.; Cavanaugh, C. M.; Liu, J. S.
      Geochimica et Cosmochimica Acta (2004), 68 (3), 433-442CODEN: GCACAK; ISSN:0016-7037. (Elsevier Science Inc.)
      The interpretation of stable isotope values hinges on precise, accurate ests. of kinetic isotope effects (α), which are equal to 1k/2k, where 1k and 2k are the reaction rate consts. for the two isotopes. Kinetic isotope effects are commonly detd. by monitoring the reactant concn. (C) and isotope ratio (R) relative to their initial values (C1 and R1, resp.). Values of α are estd. from the C and R values by using the Rayleigh distn. equation (RDE). (R/R1)=(C/C1)1/α-1 We conducted simulation expts. to evaluate the precision of the many different published approaches of estg. α from linearized versions of the RDE and reached the following conclusions: (a) kinetic isotope effects estd. from the slope of the line ln(R) vs. ln(C) were accurate and precise; (b) regressing ln(Ri/Rj) on ln(Ci/Cj), where all i datapoints were compared to all preceding datapoints j resulted in inflated 95% confidence intervals; (c) forcing the regression of ln(R/R1) on ln(C/C1) through the origin resulted in 95% confidence intervals for α that covered the true value less than 90% of the time; and (d) regression methods that compensate for errors in both x and y values need to be used with caution. When combining multiple datasets, values of α were sensitive to the form of the equation and the level of error. If all datasets had the same level of error, the optimal est. of α was achieved by a linear regression with dummy variables. However, when the three datasets had different levels of error, the optimal est. of α and much narrower 95% confidence intervals were obtained by using the Pitman estimator. The study demonstrates that some of the other methods jeopardize the accuracy and precision of empirically detd. kinetic isotope effects, thus confounding the interpretation of stable isotope values in the environment.
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    55. 55
      Huskey, W. P. Enzyme Mechanism from Isotope Effects; Cook, P. F., Ed.; CRC Press: Boca Raton, 1991.
      There is no corresponding record for this reference.
    56. 56
      Horst, A.; Lacrampe-Couloume, G.; Sherwood Lollar, B. Vapor Pressure Isotope Effects in Halogenated Organic Compounds and Alcohols Dissolved in Water. Anal. Chem. 2016, 88, 12066– 12071,  DOI: 10.1021/acs.analchem.6b02597
      56
      Vapor Pressure Isotope Effects in Halogenated Organic Compounds and Alcohols Dissolved in Water
      Horst, Axel; Lacrampe-Couloume, Georges; Sherwood Lollar, Barbara
      Analytical Chemistry (Washington, DC, United States) (2016), 88 (24), 12066-12071CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)
      Volatilization causes changes in the isotopic compn. of org. compds. as a result of different vapor pressures of mols. contg. heavy and light isotopes. Both normal and inverse vapor pressure isotope effects (VPIE) have been obsd., depending on mol. interactions in the liq. phase and the investigated element. Previous studies have focused mostly on pure compd. volatilization or on compds. dissolved in org. liqs. Environmentally relevant scenarios, such as isotope fractionation during volatilization of orgs. from open water surfaces, have largely been neglected. In the current study, open-system volatilization expts. (focusing thereby on kinetic/-nonequil. effects) were carried out at ambient temps. for trichloromethane, trichloroethene, trichlorofluoromethane, trichlorotrifluoroethane, methanol, and ethanol dissolved in water and, if not previously reported in the literature for these compds., for volatilization from pure liqs. Stable carbon isotopic signatures were measured using continuous flow isotope ratio mass spectrometry. The results demonstrate that volatilization of the four halogenated compds. from water does not cause a measurable change in the carbon isotopic compn., whereas for pure-phase evapn., significant inverse isotope effects are consistently obsd. (+0.3 ‰< ε < + 1.7 ‰). In contrast, methanol and ethanol showed normal isotope effects for evapn. of pure org. liqs. (-3.9 ‰ and -1.9 ‰) and for volatilization of compds. dissolved in water (-4.4 ‰ and -2.9 ‰), resp. This absence of measurable carbon isotope fractionation considerably facilitates the application of isotopic techniques for extn. of field samples and preconcn. of organohalogens-known to be important pollutants in groundwater and in the atm.
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  • Supporting Information

    Supporting Information

    The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.est.9b05746.

    • Field site schematic, full analytical methods, control data, mass removal calculations, dechlorination mechanisms, error propagation, and tabulated field results (PDF)


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