Carbon, Hydrogen and Chlorine Stable Isotope Fingerprinting for Forensic Investigations of Hexachlorocyclohexanes.

Multielemental stable isotope analysis of persistent organic pollutants (POPs) has the potential to characterize sources, sinks, and degradation processes in the environment. To verify the applicability of this approach for source identification of hexachlorocyclohexane (HCHs), we provide a data set of carbon, hydrogen, and chlorine stable isotope ratios (δ13C, δ2H, δ37Cl) of its main stereoisomers (α-, ß-, δ- and γ-HCHs) from a sample collection based on worldwide manufacturing. This sample collection comprises production stocks, agricultural and pharmaceutical products, chemical waste dumps, and analytical-grade material, covering the production time period from the late 1960s until now. Stable isotope ratios of HCHs cover the ranges from -233‰ to +1‰, from -35.9‰ to -22.7‰, and from -6.69‰ to +0.54‰ for δ2H, δ13C, and δ37Cl values, respectively. Four groups of samples with distinct multielemental stable isotope fingerprints were differentiated, most probably as a result of purification and isolation processes. No clear temporal trend in the isotope compositions of HCHs was found at the global scale. The multielemental stable isotope fingerprints facilitate the source identification of HCHs at the regional scale and can be used to assess transformation processes. The data set and methodology reported herein provide basic information for the assessment of environmental field sites contaminated with HCHs.

Organic Reference Materials for Hydrogen, Carbon, and Nitrogen Stable Isotope-Ratio Measurements: Caffeines, n-Alkanes, Fatty Acid Methyl Esters, Glycines, L-Valines, Polyethylenes, and Oils.

An international project developed, quality-tested, and determined isotope-δ values of 19 new organic reference materials (RMs) for hydrogen, carbon, and nitrogen stable isotope-ratio measurements, in addition to analyzing pre-existing RMs NBS 22 (oil), IAEA-CH-7 (polyethylene foil), and IAEA-600 (caffeine). These new RMs enable users to normalize measurements of samples to isotope-δ scales. The RMs span a range of δ(2)H(VSMOW-SLAP) values from -210.8 to +397.0 mUr or ‰, for δ(13)C(VPDB-LSVEC) from -40.81 to +0.49 mUr and for δ(15)N(Air) from -5.21 to +61.53 mUr. Many of the new RMs are amenable to gas and liquid chromatography. The RMs include triads of isotopically contrasting caffeines, C16 n-alkanes, n-C20-fatty acid methyl esters (FAMEs), glycines, and l-valines, together with polyethylene powder and string, one n-C17-FAME, a vacuum oil (NBS 22a) to replace NBS 22 oil, and a (2)H-enriched vacuum oil. A total of 11 laboratories from 7 countries used multiple analytical approaches and instrumentation for 2-point isotopic normalization against international primary measurement standards. The use of reference waters in silver tubes allowed direct normalization of δ(2)H values of organic materials against isotopic reference waters following the principle of identical treatment. Bayesian statistical analysis yielded the mean values reported here. New RMs are numbered from USGS61 through USGS78, in addition to NBS 22a. Because of exchangeable hydrogen, amino acid RMs currently are recommended only for carbon- and nitrogen-isotope measurements. Some amino acids contain (13)C and carbon-bound organic (2)H-enrichments at different molecular sites to provide RMs for potential site-specific isotopic analysis in future studies.

Coupling of a headspace autosampler with a programmed temperature vaporizer for stable carbon and hydrogen isotope analysis of volatile organic compounds at microgram per liter concentrations.

One major challenge for the environmental application of compound-specific stable isotope analysis (CSIA) is the necessity of efficient sample treatment methods, allowing isolation of a sufficient mass of organic contaminants needed for accurate measurement of the isotope ratios. Here, we present a novel preconcentration technique--the coupling of a headspace (HS) autosampler with a programmed temperature vaporizer (PTV)--for carbon (δ(13)C) and hydrogen (δ(2)H) isotope analysis of volatile organic compounds in water at concentrations of tens of micrograms per liter. The technique permits large-volume injection of headspace samples, maintaining the principle of simple static HS extraction. We developed the method for multielement isotope analysis (δ(13)C and δ(2)H) of methyl tert-butyl ether (MTBE), benzene, toluene, ethylbenzene, and o-xylene (BTEX), and analysis of δ(13)C for chlorinated benzenes and ethenes. Extraction and injection conditions were optimized for maximum sensitivity and minimum isotope effects. Injection of up to 5 mL of headspace sample from a 20 mL vial containing 13 mL of aqueous solution and 5 g of NaCl (10 min of incubation at 90 °C) resulted in accurate δ(13)C and δ(2)H values. The method detection limits (MDLs) for δ(13)C were from 2 to 60 µg/L (MTBE, BTEX, chlorinated ethenes, and benzenes) and 60-97 µg/L for δ(2)H (MTBE and BTEX). Overall, the HS-PTV technique is faster, simpler, isotope effect-free, and requires fewer treatment steps and less sample volume than other extraction techniques used for CSIA. The environmental applicability was proved by the analysis of groundwater samples containing BTEX and chlorinated contaminants at microgram per liter concentrations.

Investigation of humic substance photosensitized reactions via carbon and hydrogen isotope fractionation.

Humic substances (HS) acting as photosensitizers can generate a variety of reactive species, such as OH radicals and excited triplet states ((3)HS*), promoting the degradation of organic compounds. Here, we apply compound-specific stable isotope analysis (CSIA) to characterize photosensitized mechanisms employing fuel oxygenates, such as methyl tert-butyl ether (MTBE) and ethyl tert-butyl ether (ETBE), as probes. In oxygenated aqueous media, Λ (Δδ(2)H/Δδ(13)C) values of 23 ± 3 and 21 ± 3 for ETBE obtained by photosensitization by Pahokee Peat Humic Acid (PPHA) and Suwannee River Fulvic Acid (SRFA), respectively, were in the range typical for H-abstraction by OH radicals generated by photolysis of H2O2 (Λ = 24 ± 2). However, (3)HS* may become a predominant reactive species upon the quenching of OH radicals (Λ = 14 ± 1), and this process can also play a key role in the degradation of ETBE by PPHA photosensitization in deoxygenated media (Λ = 11 ± 1). This is in agreement with a model photosensitization by rose bengal (RB(2-)) in deoxygenated aqueous solutions resulting in one-electron oxidation of ETBE (Λ = 14 ± 1). Our results demonstrate that the use of CSIA could open new avenues for the assessment of photosensitization pathways.

Origin of VC-only plumes from naturally enhanced dechlorination in a peat-rich hydrogeologic setting.

The occurrence of vinyl chloride (VC) is often a main concern at sites contaminated with chlorinated solvents due to its high degree of toxicity and carcinogenicity. VC occurrence in aquifers is most often related to the degradation of higher chlorinated ethenes or ethanes and it is generally detected in plumes along with parent contaminants. However, specific combination of stratigraphic, hydrogeologic and geochemical conditions can enhance the degradation of parents and lead to the formation of plumes almost entirely composed of VC (i.e. VC-only plumes). This paper investigates the causes of VC-only plumes in the aquifers below the city of Ferrara (northern Italy) by combining multiple lines of evidence. The City of Ferrara is located on an alluvial lowland, built by the River Po, and is made up of alternating unconsolidated sandy aquifer and silt-clay aquitard deposits of fluvial origin. This region has been strongly impacted by prior industrial activities, with the occurrence of chlorinated compounds at several sites. VC-only plumes with uncertain source location were found at two contaminated sites. The source zone of a third plume composed of chloroethenes from PCE to VC was investigated for high resolution depositional facies architecture and contaminant distribution (contaminant concentration and Compound Specific Isotope Analysis - CSIA). The investigation suggested that degradation of PCE and TCE takes place during contaminant migration through peat-rich (swamp) layers related to the Holocene transgression, which locally act as a "reactor" for stimulating degradation with the accumulation of VC in the strongly reducing environment of the peat. Regional-scale stratigraphic architecture showed the ubiquitous occurrence of swamp layers at distinct stratigraphic levels in the investigated system and their apparent linkage to the in situ creation of the VC-only plumes.

Validation of user- and environmentally friendly extraction and clean-up methods for compound-specific stable carbon isotope analysis of organochlorine pesticides and their metabolites in soils.

In order to evaluate the potential of compound-specific stable carbon isotope analysis (CSIA) for tracking organochlorine pesticides in soil systems, sample pre-treatment methods have to be developed, which can provide recoveries sufficient for low detection limits without altering the isotope ratio of the target compounds. In this study we tested the compatibility of CSIA with user- and environmentally friendly extraction methods, including the Quick, Easy, Cheap, Effective, Rugged and Safe procedure (QuEChERS), Ultrasonic Assisted Extraction (USE) and Focused Ultrasonic Extraction (FUSE), as well as clean-up methods, including sulfuric acid clean-up and Florisil(®) column chromatography for hexachlorocyclohexanes (HCHs), p,p'-dichlorodiphenyltrichloroethane (DDT) and their environmental metabolites (chlorinated benzenes, dichlorodiphenyldichloroethylene - DDE and dichlorodiphenyldichloroethane - DDD) in soils. We optimized the extraction methods for maximum recovery and pre-concentration. At optimal conditions, all extraction methods and clean-up procedures, as well as the pre-concentration of the extract by solvent evaporation, led to insignificant changes in carbon isotope ratios of the target compounds. We modified the USE procedure to increase the volume of withdrawn organic extract, resulting in a higher pre-concentration of the target compounds by the subsequent solvent evaporation step. This Modified Ultrasonic Assisted Extraction (MUSE) was the most suitable procedure, and it was validated for the determination of carbon isotope ratios of the target compounds using two different types of soil matrices. The method could be applied to analyze carbon isotope ratios of HCHs, DDT, and their chlorinated metabolites in soil samples with concentrations ranging from 0.3 to 0.8mg/kg. The analytical uncertainty of MUSE, incorporating both accuracy and precision, was ≤0.4‰.

A simplified Quick, Easy, Cheap, Effective, Rugged and Safe approach for the determination of trihalomethanes and benzene, toluene, ethylbenzene and xylenes in soil matrices by fast gas chromatography with mass spectrometry detection.

A method based on simplified QuEChERS (Quick, Easy, Cheap, Effective, Rugged and Safe) extraction followed by large-injection volume-fast gas chromatography and mass spectrometry detection has been developed for the determination of trihalomethanes (chloroform, bromodichloromethane, dibromochloromethane and bromoform) and BTEX (benzene, toluene, ethylbenzene and xylenes) in soil samples. The simplified version of QuEChERS used meets the requirements of the "green chemistry" and provides reliable results with high sample throughput, low solvent consumption, little labour and the use of materials commonly employed in laboratories. The GC device used is equipped with a programmable temperature vaporizer (PTV), with a liner packed with Tenax-TA(®). Using the solvent-vent mode, the PTV allows the injection of large volumes of sample, affording an improvement in the sensitivity of the method. The chromatographic conditions used here allowed the separation of the compounds in less than 5.50 min. Good linearity was obtained for all the target compounds, with highly satisfactory repeatability and reproducibility values. The limits of detection were in the 0.2 to 15 µg kg(-1) range. The method was validated by the analysis of two certified reference materials.

Determination of trihalomethanes in soil matrices by simplified quick, easy, cheap, effective, rugged and safe extraction and fast gas chromatography with electron capture detection.

A method based on QuEChERS extraction is proposed for the determination of trihalomethanes (chloroform, bromodichloromethane, dibromocloromethane and bromoform) in soil samples. The new version of QuEChERS adapted to soil samples consists of liquid extraction with ethyl acetate, the addition of water to moisten the samples, salting-out partitioning of the water with anhydrous MgSO4, and direct injection of the organic extract, obtained after the centrifugation step, into the gas chromatograph. This simplified extraction procedure maintains the advantages of the original method and avoids some steps, making the final procedure simpler, faster, and cheaper, with the consequent reduction in errors associated with sample manipulation. The experimental conditions of the analytical method, based on fast gas chromatography (FGC) and micro-electron capture detection (microECD), were optimized. The column and oven program used allowed fast separation of the compounds in less than 4 min and the total analysis cycle time was as short as 10 min. The existence of a matrix effect was checked and the analytical conditions of the method were studied in a fortified garden soil sample. The highly sensitive and selective detector used afforded to detection limits in the order of ng/kg for the target compounds. To validate the proposed method two certified reference materials (CRMs) were analyzed.

Determination of trihalomethanes in water samples: a review.

This article reviews the most recent literature addressing the analytical methods applied for trihalomethanes (THMs) determination in water samples. This analysis is usually performed with gas chromatography (GC) combined with a preconcentration step. The detectors most widely used in this type of analyses are mass spectrometers (MS) and electron capture detectors (ECD). Here, we review the analytical characteristics, the time required for analysis, and the simplicity of the optimised methods. The main difference between these methods lies in the sample pretreatment step; therefore, special emphasis is placed on this aspect. The techniques covered are direct aqueous injection (DAI), liquid-liquid extraction (LLE), headspace (HS), and membrane-based techniques. We also review the main chromatographic columns employed and consider novel aspects of chromatographic analysis, such as the use of fast gas chromatography (FGC). Concerning the detection step, besides the common techniques, the use of uncommon detectors such as fluorescence detector, pulsed discharge photoionization detector (PDPID), dry electrolytic conductivity detector (DELCD), atomic emission detector (AED) and inductively coupled plasma-mass spectrometry (ICP-MS) for this type of analysis is described.