Cl Isotope Research Articles

A chlorine isotope effect for enzyme-catalyzed chlorination.

Several chlorinated organic compounds (COCs) that have been detected in a wide range of human, animal, and environmental samples may be derived from natural or anthropogenic sources. To determine whether the Cl isotope ratios of these compounds could be used to differentiate sources, we investigated the chlorine isotope effect for enzyme-catalyzed chlorination. Two aromatic substrates, 1,3,5-trimethylbenzene (TMB) and 3,5-dimethylphenol (DMP), were treated with a chloroperoxidase isolated from the fungus Caldariomyces fumago. A kinetic isotope effect (KIE) (in terms of k35/k37) was calculated to be 1.012 for TMB and 1.011 for DMP. A similar reaction, but not catalyzed, with hypochlorite yielded a much smaller KIE. These results indicate that a substantial KIE exists for this process. Furthermore, natural COCs synthesized by this enzymatic pathway may have Cl isotope ratios that will be easily distinguished from anthropogenic COCs.

Measurements of the interaction cross sections for Ar and Cl isotopes

We have measured the interaction cross sections (σI) of 31–40Ar and 31–37Cl on carbon targets at energies of around 950 AMeV. The effective matter radii for these nuclei were deduced by a Glauber-model analysis. Combining our matter radii with measured charge radii for Ar isotopes, we could deduce the proton-skin thicknesses for the 32–40Ar isotopes, which were found to increase monotonically with decreasing neutron number. The larger radius of the proton drip-line nucleus 31Ar suggests an anomalous structure for this nucleus. In addition, using NaI(Tl) arrays surrounding the carbon target, we measured γ-rays emitted from excited states in these isotopes. In this way we could deduce the upper limits for the inelastic cross sections (σinela) on carbon targets at energies of around 950 AMeV.

Transport modeling applied to the interpretation of groundwater 36Cl age

We use reactive transport modeling to consider how diffusion and hydrodynamic dispersion, cross‐formational flow, and subsurface production affect the steady state distribution in flow regimes of the radioactive isotope 36Cl, and the relationship of the isotope distribution to groundwater residence time, or “age.” The isotope forms naturally in the atmosphere, dissolves in rainwater, and then decays in the subsurface with a half‐life of ∼301,000 years; hence it is important for age dating very old groundwater. In a simple flow regime composed of an aquifer confined above and below by aquitards, isotopic age may correspond rather well with a groundwater's “piston flow” age. This correspondence is favored where the aquifer is thick, cross‐formational flow is insignificant, salinity is low, and the diffusion coefficient within the aquitards is small. The maximum dateable age, however, is somewhat smaller than expected from the isotope's half‐life. Owing to the effect of “dead” chloride, dating based on isotope abundance (the 36Cl/Cl ratio) may be less accurate than that based on 36Cl concentration. Cross‐formational flow can strongly affect the 36Cl distribution and abundance, preventing the rates and even direction of flow within an aquifer from being interpreted using the piston flow model. Where salinity is moderate or high, the isotope distribution is controlled by subsurface production, and dating on the basis of the decay of atmospheric 36Cl is not possible. In models of simple flow regimes the 36Cl method fails to predict groundwater age accurately where groundwater chlorinity exceeds ∼75–150 mg kg−1. Reactive transport models hold considerable promise for improving interpretation of the rates and patterns of groundwater flow from radioisotope distributions.

Halogens of Bushveld Complex, South Africa: δ37Cl and Cl/F evidence for hydration melting of the source region in a back-arc setting

The Bushveld Complex is one of only a few layered intrusions anomalously enriched in chlorine. This study presents the first chlorine stable isotope analyses of Bushveld and associated rocks designed to constrain the source of Bushveld Cl. Most samples overlap the range of values for pristine MORB and altered seafloor samples ( δ 37Cl ∼+4‰ relative to sea water). This contrasts with distal metasedimentary floor rocks ( δ 37Cl ∼+0‰), with little evidence of contamination away from the marginal rocks. The Cl isotope composition and high Cl/F ratio is therefore a fundamental characteristic of the Lower and Critical Zone magmas and not derived from infiltration from the country rock. These results, the high Cl/F ratio and the boninitic arc-like character of Bushveld magma, are consistent with hydration partial melting of a depleted source in a subduction-related setting with Cl supplied either by the dehydration of a subducted slab with a heavy Cl signature or an overridden “wet” mantle hotspot.

Chlorine stable isotope measurements of chlorinated aliphatic hydrocarbons by thermal ionization mass spectrometry

An improved method for chlorine isotopic analysis using thermal ionization mass spectrometry (TIMS) of Cs 2Cl + has been investigated. The δ 37 Cl values (parts per mil deviations from the standard seawater 37 Cl/ 35 Cl ratio) for 10 commercial chlorinated aliphatic hydrocarbons (CAHs), provided by six suppliers are presented. The CAHs were treated with a sodiumbiphenyl reagent. The liberated chloride ions were converted to CsCl and their isotopic compositions were determined by TIMS. Replicate analysis of the CAHs gave an external precision of 0.1–0.4‰ (1 σ S.D.). As each compound and each supplier has a distinctive δ 37 Cl value ( δ 37 Cl values: −5.0 to +2.9‰), Cl isotope data can be used to trace a specific source of pollutants in the subsurface environment. Trichloroethene (TCE) and tetrachloroethene (PCE) were extracted from aqueous solutions with toluene and their chlorine isotope compositions were analyzed. The solvent extraction method presented here may be applicable to the analysis of actual contaminated water samples. Chlorine atoms were recovered as inorganic chloride from unsaturated chlorinated aliphatic compounds (TCE and PCE) by KMnO 4 oxidation. However, the saturated compounds were resistant to KMnO 4 oxidation. The isotopic compositions of the recovered chloride ion were then determined by TIMS. It is suggested that such compound-specific isotopic analyses may give information about the past record of each contaminant.

13C NMR spectra of halocarbons

Abstract13C NMR chemical shifts and 13C–19F and 13C–1H coupling constants are reported for 103 halocarbons. Methods used for analyzing complex spectra (e.g. simultaneous 1H and 19F broadband decoupling, 2D INADEQUATE/FRED, HMQC, 35,37Cl isotope effects) are briefly illustrated. Longitudinal relaxation times for CF3CCl2CH2CHClF are reported. Copyright © 2001 John Wiley & Sons, Ltd.

Extraction of chlorinated aliphatic hydrocarbons from groundwater at micromolar concentrations for isotopic analysis of chlorine

A method is described for near-quantitative extraction of micromolar concentrations of chlorinated aliphatic hydrocarbons (CAHs) from water for determination of chlorine (Cl) isotope ratios. A low pressure, carrier-gas procedure of extraction was proven to be applicable to CH 2Cl 2, CCl 4, C 2H 2Cl 2, and C 2HCl 3. The pH of the water was adjusted with NaOH to prevent extraction of CO 2 from air and/or dissolved inorganic carbonate species. Recoveries of CAH samples (∼15 μmol), added to and extracted from ∼340 ml of water, averaged ∼96%. Average changes in the δ 37Cl values of the CAHs, attributable to the extraction process, were −0.01±0.06‰. Significant isotopic fractionation of Cl was measured during partial extraction of C 2CHCl 3 from water, indicating that near-quantitative extraction is required for reliable stable Cl isotope analysis of CAHs. This method is also suitable for the extraction of dissolved CAH for gas chromatography-combustion-isotope ratio mass spectrometric measurements of hydrogen and carbon.

37,35Cl isotope effects on 19F and 13C chemical shifts of chlorofluoro‐ and hydrochlorofluorocarbons

Chlorine isotope effects on 19F and 13C NMR chemical shifts can be used for the indirect determination of the number of geminal and vicinal chlorine atoms in fluorinated molecules. Two- and three-bond 37,35Cl isotope effects on the 19F chemical shifts of 29 and eight compounds, respectively, are reported. One-bond isotope effects on the 13C chemical shifts of four compounds are also reported. The usefulness of these isotope-induced shifts in the identification of chlorofluoro- and hydrochlorofluorocarbons is discussed. Copyright © 2000 John Wiley & Sons, Ltd.

The Hyperfine Structures of ScCl and ScF

The Fourier transform microwave spectra of gaseous ScF and ScCl have been measured in their 1Σ+ ground electronic states. Transitions have been observed for ScF (J = 1–0) and for both Sc35Cl and Sc37Cl (J = 1–0 and J = 2–1) in the ground vibrational state, and for Sc35Cl (J = 1–0 and J = 2–1) in the first excited vibrational state. The nuclear quadrupole coupling constants of Sc and of both isotopes of Cl, the spin–rotation constants for all the nuclei and the nuclear spin–nuclear spin constants for both molecules, have been determined. From these hyperfine constants, the electronic structures of ScF and ScCl have been investigated and comparisons have been made to similar molecules. ScCl has been found to be highly ionic. For Sc35Cl, the equilibrium bond length has been reevaluated and the vibration frequency and dissociation energy have been estimated. A simple approach to account for the Sc quadrupole coupling constants has been shown to be flawed.

Gas chromatography/mass spectrometry identification and quantification of isazophos in a famphur pour-on and in bovine tissues after a toxic exposure.

A sample identified as "Warbex pour-on," expected to contain 13.2% famphur, and bovine tissue samples from 2 heifers that died after exhibiting signs of organophosphate intoxication were analyzed by gas chromatography/mass spectrometry (GC/MS). A product formulation problem was suspected because brain cholinesterase activities were depressed in both animals. Electron impact (EI) GC/MS of the pour-on revealed 9.7% famphur and an unidentified peak with approximately 76% of the peak area of the famphur. The unidentified peak showed a molecular ion at m/z 313, with a single Cl isotope cluster. Methane chemical ionization (MeCI) MS confirmed the molecular weight at 313 (1 Cl). A search on the molecular formula C9H17N3O3PSCl yielded a single match, isazophos. EI and MeCI GC/MS of reference isazophos confirmed the identity of the suspect peak. The concentration of isazophos in the pour-on was determined to be 6.0%. Famphur and isazophos were identified by their EI spectra and GC retention times in extracts of liver and brain from the 2 deceased animals. A GC/MS procedure utilizing selected ion monitoring (SIM) was developed for quantification of isazophos in liver, kidney, muscle, and fat of additional affected animals sacrificed at various times after exposure. Isazophos remained in animal tissues for as long as 94 days after topical exposure. Isazophos was present in fetal liver 70 days after exposure of the dam. High levels (6-3,500 ppm) of isazophos and famphur remained on the skin at 39 days postexposure.

37,35Cl isotope effects on19F and13C chemical shifts of chlorofluoro- and hydrochlorofluorocarbons

Chlorine isotope effects on 19F and 13C NMR chemical shifts can be used for the indirect determination of the number of geminal and vicinal chlorine atoms in fluorinated molecules. Two- and three-bond 37,35Cl isotope effects on the 19F chemical shifts of 29 and eight compounds, respectively, are reported. One-bond isotope effects on the 13C chemical shifts of four compounds are also reported. The usefulness of these isotope-induced shifts in the identification of chlorofluoro- and hydrochlorofluorocarbons is discussed. Copyright © 2000 John Wiley & Sons, Ltd.

Strong absorption radii from reaction cross section measurements for neutron-rich nuclei

Energy-integrated reaction cross sections have been measured at energies ranging from 38 to 80 MeV/nucleon for various exotic neutron-rich isotopes of Al, Si, P, S, Cl, Ar, K, Ca, Sc, and Ti stopping in Si. An experimental technique is employed where Si detectors are used for both particle identification and to serve as the target material. The reduced strong absorption radii r[sub 0][sup 2] are deduced and compared with other experimental results. The radius dependence on the neutron number was studied and a trend of increasing reduced radius with neutron excess was found. This behavior is similar to that seen in lighter systems, although less pronounced than found there. The implications of this result on the conjectured existence of neutron halo or skin nuclei is discussed. [copyright] [ital 1999] [ital The American Physical Society]

Salinization and dilution history of ground water discharging into the Sea of Galilee, the Dead Sea Transform, Israel

The mechanism governing salinization of ground water discharging into the Sea of Galilee in Israel has been the subject of debate for several decades. Because the lake provides 25% of the water consumed annually in Israel, correct identification of the salt sources is essential for the establishment of suitable water-management strategies for the lake and the ground water in the surrounding aquifers. Existing salinization models were evaluated in light of available and newly acquired data including general chemistry, and O, H, C and Cl isotopes. Based on the chemical and isotopic observations, the proposed salt source is an ancient, intensively evaporated brine (21- to 33-fold seawater) which percolated through the valley formations from a lake which had formed in the Rift Valley following seawater intrusion during the late Miocene. Low Na:Cl and high Br:Cl values support the extensive evaporation, whereas high Ca:Cl and low Mg:Cl values indicate the impact of dolomitization of the carbonate host rock on the residual solution. Based on radiocarbon and other isotope data, the dilution of the original brine occurred in two stages: the first took place ∼30 000 a ago by slightly evaporated fresh-to-brackish lake water to form the Sea of Galilee Brine. The second dilution phase is associated with the current hydrological regime as the Sea of Galilee Brine migrates upward along the Rift faults and mixes with the actively circulating fresh ground water to form the saline springs. The spatially variable chemical and isotopic features of the saline springs suggest not only differential dilution by fresh meteoric water, but also differential percolation timing of the original brine into the tectonically disconnected blocks, registering different evaporation stages in the original brine. Consequently, various operations to reduce the brine contribution to the lake may be differentially effective in the various areas.

Cl-37 in the Dead Sea system---preliminary results

This study presents the first set of δ 37Cl measurements in the Dead Sea environment. δ 37Cl values for the meromictic (long term stratified) Dead Sea water column prior to its complete overturn in 1979 were −0.47‰ SMOC for the UWM (Upper Water Mass) and +0.55‰ SMOC for the LWM (Lower Water Mass). The δ 37Cl values for the pre-overturn Dead Sea cannot be explained by the prevailing model on the evolution of the Dead Sea during the last few centuries and require corroboration by more measurements. The 1979 overturn wiped out almost completely the isotopic differences between the UWM and LWM. Even so, Cl isotope data could be used to decipher physical processes related to the overturn such as incomplete homogenization of the deep water mass. Inputs into the lake, comprising freshwaters (springs and the Jordan River) and saline springs gave a range of −0.37‰ to +1.0‰ with the freshwater sources being more enriched in δ 37Cl. Based on the δ 37Cl measurements of the End-Brine (the effluent from Dead Sea evaporation ponds) and of recent Dead Sea halite, the Cl isotopic composition of the originating brines have been estimated. They gave a narrow isotopic spread, +0.01‰ and +0.07‰ and fall within the same range with Dead Sea pore water (+0.13‰) and with the post-overturn Dead Sea (−0.03‰ and +0.16‰). Rock salt from Mount Sdom gave a value of −0.59‰ indicating its formation at the last stages of halite deposition from evaporating sea water. The hypersaline En Ashlag spring gave a depleted δ 37Cl value of −0.32‰, corresponding to a residual brine formed in the very latest stages (including bishofite deposition) of seawater evaporation.

Noble gases, stable isotopes, and radiocarbon as tracers of flow in the Dakota aquifer, Colorado and Kansas

A suite of chemical and isotope tracers (dissolved noble gases, stable isotopes of water, radiocarbon, and Cl) have been analyzed along a flow path in the Dakota aquifer system to determine likely recharge sources, ground water residence times, and the extent of mixing between local and intermediate flow systems, presumably caused by large well screens. Three water types were distinguished with the tracers, each having a very different history. Two of the water types were found in south-eastern Colorado where the Dakota is poorly confined. The tracer data suggest that the first group recharged locally during the last few thousand years and the second group was composed of ground water that recharged earlier during a cooler climate, presumably during the last glacial period (LGP) and mixed aged water. The paleotemperature record archived in this groundwater system indicates that south-eastern Colorado was about 5°C cooler during the LGP than during the late Holocene. Similar temperature changes derived from dissolved noble gases in other aquifer systems have been reported earlier for the south-western United States. The third water type was located down gradient of the first two in the confined Dakota in western and central Kansas. Groundwater residence time of this water mass is on the order of 104–105yrs and its recharge location is near the Colorado and Kansas border down gradient of the other water types. The study shows the importance of using multiple tracers when investigating ground water systems.

Stable chlorine-isotope analysis of rock samples: New aspects of chlorine extraction

This paper presents refinements of the chlorine-extraction technique which allows to measure stable chlorine-isotope compositions ( δ 37Cl: per-mil deviation relative to standard mean ocean chloride, SMOC) of rock samples by isotope-ratio mass spectrometry (IRMS) with a precision of 0.12‰ (2 σ). HF (17 M, 4 ml) was used for decomposition of gram amounts of several rock standard samples containing 220–16200 ppm Cl. Excess amount of F − was precipitated and removed as CaF 2 by neutralizing with Ca(OH) 2 and by cation-exchange chromatography with strongly acidic resin (Ca 2+ form). Extracted Cl dissolved in 50–250 ml of water was concentrated on a strongly basic anion-exchange resin bed (OH − form) and was quantitatively recovered into 4.0 ml of 0.5 M KNO 3 and then converted to CH 3Cl. This CH 3Cl was used for Cl isotope analysis by IRMS. Recovery yield of the Cl-extraction from standard rocks agreed well with Cl contents reported for them. Reproducibility of the measured δ 37Cl values through the whole process of the Cl extraction was better than 0.10‰.

Measurement of elastic recoil cross sections of light nuclei by 35Cl using inverse scattering

The elastic recoil cross sections of 6Li, 12C, 16O and 19F by 35Cl below the incident energy of 10 MeV have been measured by the inverse scattering method. About 10 17 Cl/cm 2 BaCl 2 vacuum-deposited on 1 μm DLC (Diamond Like Carbon) was used as a target. During the irradiation the target showed good stability. The Cl isotope effect has an influence on the recoil cross section of less than 0.5%. In the useful energy region for quantitative analysis by elastic recoil detection, the measured recoil cross sections agree with the Rutherford's values within a few percent.

Conversion of Chlorinated Volatile Organic Compounds to Carbon Dioxide and Methyl Chloride for Isotopic Analysis of Carbon and Chlorine

A nonaqueous, high-temperature method is described for converting micromole quantities of chlorinated volatile organic compounds to CO2 and CH3Cl for C and Cl isotope ratio determinations. This method provides an improved analytical approach for using C and Cl isotope ratios in studies of the biodegradation of chlorinated volatile organic compounds in the environment. Conversion of reagent CH3Cl to CO2 + CuCl and then conversion of the CuCl back to CH3Cl by the present method gives typical yields of 99 ± 1% for CO2 and 91 ± 1% for CH3Cl, both products of >99% purity. An offset of −0.23 ± 0.05‰ is observed between the 37Cl/35Cl ratios of product and initial CH3Cl. Precision of the isotopic ratio measurements is better than ± 0.1‰ for a variety of chlorinated volatile organic compounds.

Slit jet infrared absorption spectroscopy of N2-HCl complexes

The vibration–rotation spectra of the weakly bound complexes N2-HCl have been studied in the 3·5 μm region of the υ1 fundamental band correlated with the HCl stretch, using a pulsed slit jet expansion and a tunable diode laser spectrometer. For the first time the υ1 band for the N2-H37 Cl isotope has been analysed and the rotational constants determined. The υ1 band was observed previously for the N2– H35 Cl isotope using a cooled long path cell and a Fourier transform spectrometer. This band has been re-examined to confirm and extend this analysis, with new lines corresponding to low J values observed and assigned. The rotational molecular constants are in agreement with those determined already, but for the band centre the value found was slightly greater than those obtained previously. For both isotopes, the observed spectra confirm the quasilinear geometry of the complex.

Stable Cl isotopes and origin of high-Cl magmas of the Stillwater Complex, Montana

The first Cl isotopic determinations on biotite from the Ultramafic series and from the J-M reef of the Lower Banded series of the Stillwater Complex, Montana, have δ 37 Cl values (normalized to seawater, 95% confidence limit error is 0.2‰) ranging from 0.27‰ to −0.93‰; the average is −0.18‰. Assuming minimal fractionation on incorporation into biotite, these data imply an ultimate crustal source for the Cl. However, field, petrographic, and isotopic evidence suggests that high-Cl fluids did not infiltrate from the country rocks after emplacement of the Stillwater magma, nor was the Cl-isotopic signature the result of assimilation of Cl-rich crustal rocks. Stillwater parent magmas have boninitic affinities and can be modeled as second-stage melts from a metasomatically enriched, depleted mantle. We propose that the early melt-extraction event depleted the mantle in F and Cl. Subsequent metasomatism by a Cl-rich agent with a crustal Cl isotopic signature, probably a fluid, produced a source rock with a high Cl/F ratio. In modern magmas, high Cl/F weight ratios are associated with high overall volatile contents, suggesting that the Stillwater Complex and other high-Cl layered intrusions crystallized from magmas that may have contained in excess of 1 wt% water.