Compound-specific Isotope Analysis Research Articles

Integrated approach for the isotope trophic position of black-tailed gull (Larus crassirostris) eggs over a decade: Combining stable isotopes of amino acids and fatty acids composition

Recently, compound-specific isotope analysis (CSIA) using the amino acid nitrogen stable isotope ratio (δ15NAAs) has been widely used for accurate estimation of trophic position (TP). In addition, a quantitative fatty acid signature analysis (QFASA) offers insights into diet sources. In this study, we used these techniques to estimate the TP for seabirds that rely on diverse food sources across multiple ecosystems. This allows for the proper combination of factors used in TP calculation which are different for each ecosystem. The approach involved the application of a multi-mixing trophic discrimination factor (TDF) and mixing β which is a Δδ15N between trophic and source amino acid of primary producer. Since the black-tailed gulls (BTGs) are income-breeding seabirds, which rely on energy sources obtained around their breeding sites, they and their eggs could be useful bioindicators for environmental monitoring. However, the ecological properties of BTGs such as habitats, diets, and TP are not well known due to their large migration range for wintering or breeding and their feeding habits on both aquatic and terrestrial prey. In this study, the eggs were used for estimating TP and for predicting TP of mother birds to overcome difficulties such as capturing birds and collecting non-invasive tissue samples. Eggs, sampled over a decade from three Korean islands, showed spatial differences in diet origin. Considering both the food chain and physiology of BTG, the TP of eggs was estimated to be 3.3–4.0. Notably, the TP was significantly higher at site H (3.8 ± 0.1) than at site B (3.5 ± 0.2), which indicated a higher contribution of marine diet as confirmed by QFASA. Using a reproductive shift of δ15NAAs, the TP of the mother birds was predicted to be 3.6–4.3, positioning them as the top predator in the food web. The advanced integration of multiple approaches provides valuable insights into bird ecology.

Turning a 3D Printer into a HPLC Fraction Collector: A Tool for Compound-Specific Stable Isotope Measurements

Compound-specific isotope analysis (CSIA) can provide unique insights into the cycling of elements including carbon and nitrogen. One approach for CSIA is the use of high-performance liquid chromatography (HPLC) to separate compounds of interest, followed by analysis of these compounds using an elemental analyser coupled to an isotope ratio mass spectrometer. A key component of this technique is the fraction collector, which automatically collects compounds as they are separated by HPLC. Here, we present a fraction collector that is a simple adaptation of a 3D printer, and, thus, can be easily adopted by any laboratory already equipped for HPLC. In addition to the much lower cost compared to commercial alternatives, this adaptation has the advantage for CSIA that the 3D printer is able to heat the collected fractions, which is not true for many commercial fraction collectors. Heating allows faster evaporation of the solvent, so that the dried compounds can be measured by EA–IRMS immediately. The procedure can be repeated consecutively so that diluted solutions can have the compounds concentrated for analysis. Any computer-controlled HPLC can be integrated to the fraction collector used here by means of AutoIt.

The biological source and paleoenvironment implication of rare short-chain lanostanes in alkaline lacustrine sediments

Highly mature organic-rich source rocks in the Early Permian Fengcheng Formation, Mahu Sag, Junggar Basin, northwestern China, were deposited in an alkaline lacustrine environment. Analysis of extracts of eight core samples by gas chromatography–mass spectrometry detected a series of short-chain lanostanes (C23–C25) lanostanes. The relative abundance of short-chain lanostanes has a strong positive correlation with those of long chain (C30–C32) homologues, indicating a possible common biological origin and genesis. Compound specific isotopic analyses of phytane, steranes, hopanes and C30 lanostane from the core extracts reflect input from primary photosynthetic producers including cyanobacteria. Abundant lamalginite was observed in the samples from the study area. A well-defined positive relationship is also evident between the relative abundance of lanostanes and the ratios of 7-+8-methyl heptadecanes/Cmax and 2-methyl hopanes/C30-hopanes. Given that 7-+8-methyl heptadecanes and 2-methyl hopanes are considered to be diagnostic molecular biomarkers for organic matter derived from cyanobacteria, it is possible that cyanobacteria may serve as a possible biological precursor for lanostanes in the Fengcheng Formation. The influence of maturity on the lanostanes is considered to be minor, as no significant relationship is found between lanostanes and thermal maturity parameters, although this may be due to a limited maturity range of the samples. The co-existence of high contents of phytane, β-carotanes, and gammacerane, and their correlations in abundance with lanostanes, indicates a strongly reducing sedimentary environment.

Assessing Biodegradation Processes of Atrazine in Constructed Wetland Using Compound-Specific Stable Isotope Analysis

To bridge the gap between lab-scale microcosm research and field application in the compound-specific stable isotope analysis (CSIA) of atrazine, we studied the characteristics of carbon and nitrogen isotope fractionation in the atrazine degradation processes within a constructed wetland. In the wetland, we observed multiple element (C, N) isotope fractionation parameters, such as kinetic isotope effects and dual isotope slopes. These parameters are very consistent with those observed in the cultivation of AtzA- or TrzN-harboring strains, suggesting a similarity in the pathway and reaction mechanism of atrazine biodegradation between the two settings. However, we recorded variable carbon (εC: −3.2 ± 0.6‰ to −4.3 ± 0.6‰) and nitrogen isotope fractionation (εN: 1.0 ± 0.3‰ to 2.2 ± 0.3‰) across different phases. This variance could lead to an over- or underestimation of the biodegradation extent of atrazine when employing the large or small enrichment factor of the carbon isotope. Intriguingly, the estimation accuracy improved considerably when using the enrichment factor (−4.6‰) derived from the batch cultivation of the pore water. This study advances the application of CSIA in tracking atrazine biodegradation processes in ecosystems, and it also underlines the importance of the careful selection and application of the enrichment factor in quantifying the intrinsic biodegradation of atrazine in ecosystems.

Blood and tissue docosahexaenoic acid (DHA, 22:6n-3) turnover rates from Ahiflower® oil are not different than from DHA ethyl ester oil in a diet switch mouse model

Ahiflower® oil is high in α-linolenic and stearidonic acids, however, tissue/blood docosahexaenoic acid (DHA, 22:6n-3) turnover from dietary Ahiflower oil has not been investigated. In this study, we use compound-specific isotope analysis to determine tissue DHA synthesis/turnover from Ahiflower, flaxseed and DHA oils. Pregnant BALB/c mice (13–17 days) were placed on a 2 % algal DHA oil diet of high carbon-13 content (δ13C) and pups (n = 132) were maintained on the diet until 9 weeks old. Mice were then randomly allocated to a low δ13C-n-3 PUFA diet of either: 1) 4 % Ahiflower oil, 2) 4.35 % flaxseed oil or 3) 1 % fish DHA ethyl ester oil for 1, 3, 7, 14, 30, 60 or 120 days (n = 6). Serum, liver, adipose and brains were collected and DHA levels and δ13C were determined. DHA concentrations were highest (p < 0.05) in the liver and adipose of DHA-fed animals with no diet differences in serum or brain (p > 0.05). Based on the presence or absence of overlapping 95 % C.I.'s, DHA half-lives and synthesis/turnover rates were not different between Ahiflower and DHA diets in the liver, adipose or brain. DHA half-lives and synthesis/turnover rates from flaxseed oil were significantly slower than from the DHA diet in all serum/tissues. These findings suggest that the distinct Ahiflower oil n-3 PUFA composition could support tissue DHA needs at a similar rate to dietary DHA, making it a unique plant-based dietary option for maintaining DHA turnover comparably to dietary DHA.

Using compound-specific isotope analysis to identify the mechanism of acetochlor degradation during oxygenation of hyporheic zone sediment

Biodegradation is recognized as the main pathway for acetochlor attenuation in aquatic environments. However, the potential abiotic degradation of acetochlor by hydroxyl radicals (•OH) generated during oxygenation of hyporheic zone sediments has not been investigated. This study aims to examine the production of •OH during oxygenation of hyporheic zone sediments and its effects on acetochlor attenuation. A significant decrease of acetochlor, ranging from 77.9% to 100%, was observed in the water-sediment systems with extensive •OH production. The primary sources of •OH production were found to be the oxidation of Fe(II) and reduced humic acids. Furthermore, a •OH quenching experiment suggests that •OH driven oxidation is the dominant pathway for acetochlor attenuation. Carbon isotope fractionation of acetochlor degradation during oxygenation of sediments (εbulk,C ranged from −1.5‰ to −0.5 ± 0.3‰) was close to that during acetochlor degradation by •OH in a H2O2–Fe3O4 Fenton system (εbulk,C = −0.5 ± 0.1‰), but significantly smaller than that during acetochlor biodegradation (εbulk,C = −5.8 ± 0.9‰). Compound-specific isotope analysis (CSIA) further suggests that •OH produced by sediment oxygenation plays a critical role in acetochlor attenuation in aquatic environments. Results of calculated apparent kinetic isotope effect of carbon (AKIEC) and transformation products indicate that SN1 and SN2-type nucleophilic substitution are the first steps in acetochlor attenuation through •OH driven oxidation (AKIEC = 1.007 ± 0.001) and aerobic biodegradation (AKIEC = 1.088 ± 0.013), respectively. Our findings highlight the potential of CSIA to assess the acetochlor degradation in water-sediment system, which can help to elucidate the fate of herbicide in aquatic environments.

Identification of microbial exopolymer producers in sandy and muddy intertidal sediments by compound-specific isotope analysis

Identification of microbial exopolymer producers in sandy and muddy intertidal sediments by compound-specific isotope analysis

Compound-specific stable isotopes of amino acids reveal influences of trophic level and primary production sources on mercury concentrations in fishes from the Aleutian Islands, Alaska

Total mercury concentrations ([THg]) exceed thresholds of concern in some Steller sea lion (Eumetopias jubatus) tissues from certain portions of the Aleutian Islands, Alaska. We applied compound-specific stable isotope analyses of both carbon and nitrogen in amino acids from fish muscle tissue to quantify the proportional contributions of primary production sources and trophic positions of eight prey species (n = 474 total) that are part of Steller sea lion diets. Previous THg analyses of fish muscle, coupled with monomethylmercury analyses of a subset of samples, substantiated previous findings that fishes from the west of Amchitka Pass, a discrete oceanographic boundary of the Aleutian Archipelago, have higher muscle Hg concentrations relative to fishes from the east. The δ13C values of essential amino acids (EAAs) in fish muscle demonstrated that although most fishes obtained their EAAs primarily from algae, some species varied in the extent to which they relied on this EAA source. The δ15N values of phenylalanine (0.9 to 7.8 ‰), an indicator of the isotopic baseline of a food web, varied widely within and among fish species. Trophic position estimates, accounting for this baseline variation, were higher from the west relative to the east of the pass for some fish species. Trophic magnification slopes using baseline-corrected trophic position estimates indicated similar rates of Hg biomagnification to the east and west of Amchitka Pass. Multiple linear regression models revealed that trophic position was the most important driver of fish muscle [THg] with less variation explained by other parameters. Thus, higher trophic positions but not the rate of Hg biomagnification to the west of Amchitka Pass may play a role in the regional differences in both fish and Steller sea lion [THg]. Although, differences in Hg contamination and uptake at the base of the east and west food webs could not be excluded.

A Novel Multi-ion Evaluation Scheme to Determine Stable Chlorine Isotope Ratios (37Cl/35Cl) of Chlordecone by LC-QTOF.

Organochlorinated pesticides are highly persistent organic pollutants having important adverse effects in the environment. To study their fate, compound-specific isotope analysis (CSIA) may be used to investigate their degradation pathways and mechanisms but is currently limited to 13C isotope ratios. The assessment of 37Cl isotope ratios from mass spectra is complicated by the large number of isotopologues of polychlorinated compounds. For method development, chlordecone (C10Cl10O2H2; hydrate form), an organochlorine insecticide that led to severe contamination of soils and aquatic ecosystems of the French West Indies, was taken as a model analyte. Chlorine isotope analysis of chlordecone hydrate was evaluated using high-resolution liquid chromatography quadrupole time-of-flight mass spectrometry (LC-QTOF-MS), enabling smooth ionization to detect the molecular ion. First, a new evaluation scheme is presented to correct for multiple isotope presence in polychlorinated compounds. The scheme is based on probability calculations of the most frequent isotopologues, distributions by binomial probability functions, and corrections for the presence of nonchlorine heavy isotopes. Second, mobile-phase modifiers, ionization energy (sampling cone tension) and scan time were optimized for accurate chlorine isotope ratios. Chlordecone standard samples were measured up to 10-fold and bracketed with a second chlordecone external standard. δ37Cl values were obtained after conversion to the SMOC scale by a two-point calibration. The robustness of the analysis method and evaluation scheme were tested and gave satisfactory results with standard errors (σm) of ±0.34‰ for precision and ±0.89‰ for long-term accuracy of chlorine isotope ratios of chlordecone hydrate. This work opens perspectives for applications of the C-Cl CSIA approach to investigate the fate of highly toxic and low reactive polychlorinated compounds in the environment.

Compound-specific stable nitrogen isotope analysis of amino acids shows that bulk methods provide higher estimates of mercury biomagnification in the Gulf of St. Lawrence

Compound-specific stable isotope analysis of amino acids (CSIA-AA) provides a method to estimate baseline δ15N values of food chains, allowing less biased estimates of trophic positions for organisms. Greater accuracy in trophic positions can improve estimates of contaminant biomagnification. We calculated trophic positions with various CSIA-AA equations for four species of fish and northern gannets (Morus bassanus) from the Gulf of St. Lawrence. We examined the effect of CSIA-AA-derived trophic positions on mercury biomagnification metrics (trophic magnification factors (TMF) and biomagnification factors) and compared these with trophic position estimates and metrics obtained from traditional bulk stable isotope analysis. The TMFs for the CSIA-AA equations ranged from 10 to 19, and bulk stable isotope analysis produced TMFs of 43, one of the highest TMFs recorded yet in the literature. Biomagnification factors between prey and northern gannets ranged from 20 to 42 using dietary observations and stable isotope mixing models. Our study demonstrates that discrepancies in biomagnification assessed using different approaches may go undetected when using a single approach.

Carbon and hydrogen isotope fractionation of phthalates during photocatalysis reactions in aqueous solution containing Fe(III) complexes or iron minerals

The hydrogen and carbon isotope fractionation factor (ε2H, ε13C) of dimethyl-, diethyl‑ and dibutyl phthalic acid ester during photosensitized degradation by artificial sunlight with Fe(III) ions and iron minerals (hematite, goethite and magnetite) in aqueous solution were examined by compound-specific isotope analysis (CSIA) in order to analyze the degradation mechanism. Hematite does not catalyze photosensitized degradation of phthalates. The correlation of 2H and 13C isotope fractionation (Λ = Δδ2H/Δδ13C) of phthalates with increasing chain length (dimethyl-; diethyl‑; and dibutyl-) were compared with values of the ∙OH radical model reaction with the aromatic ring as well as acidic and alkaline hydrolysis. The Λ values of die photosensitized reaction of diethyl phthalate with goethite (-5.1 ± 1.8) and magnetite (-18.9 ± 3.9) show a large difference compared to Fe(III) solutions (4.7 ± 0.9 to 4.8 ± 1.0) suggesting specific reaction mechanisms. The fractionation factors determined here have potential to characterize the degradation of phthalates catalyzed by photo-induced reaction of Fe(III), goethite and magnetite in natural system and in remediation approaches.

Compatibility of polar organic chemical integrative sampler (POCIS) with compound specific isotope analysis (CSIA) of substituted chlorobenzenes

Compound specific isotope analysis (CSIA) is a powerful technique to demonstrate in situ degradation of traditional groundwater contaminants when concentrations are typically in the mg/L range. Currently, an efficient preconcentration method is lacking to expand CSIA to low aqueous concentration environmental samples. Specially for the H- and N-CSIA of heteroatom-bearing non-traditional compounds, the CSIA analytical detection limits are significantly higher than that of the C-CSIA. This work demonstrates the compatibility of polar organic chemical integrative sampler (POCIS) with C-, H-, and N-CSIA using four nitro- and amino-substituted chlorobenzenes that are common industrial feedstocks for numerous applications and are commonly detected in the environment at mg/L to μg/L range. Using lab experiments, we showed isotopic equilibrium in POCIS was achieved after 30 days with either a negligible (<0.5 ‰) or a constant shift for C (<1 ‰) and N (<2 ‰). Similar negligible (<5 ‰) or constant shift (<20 ‰) was evident for H isotope except for 3,4-dichloroaniline. The method quantification limits for the combined sorbent and membrane of one POCIS were comparable to that of the solid phase extraction (SPE) using 10 L water. Next, we demonstrated the field applicability of POCIS for C- and N-CSIA after a 60-day deployment in a pilot constructed wetland by showing <1 ‰ difference between the δ13C and δ15N obtained from POCIS and SPE. Finally, we evaluated whether the biofilm development on POCIS membrane could affect the isotope signature of the sampled compounds during field deployment. Although a diverse microbial community was identified on the membrane after a 60-day deployment, we did not observe significant isotope fractionation. This was likely due to either slower diffusion in the biofilm or microbial degradation of the sampled compounds. This work demonstrates the potential of using POCIS-CSIA as a simple, fast, and sensitive method for low-concentration contaminants, such as pesticides, pharmaceuticals, and flame-retardants.

Efficient atrazine removal in bioaugmentation constructed wetland: Insight from stable isotope fractionation analysis

Constructed wetlands (CW) provides a sustainable approach to remove pesticides from agricultural or urban runoff, while the low efficiency of the herbicide atrazine remains a challenge. Focused on improving atrazine removal in CW, a bioaugmentation strategy was implemented using the mixed culture of atrazine-degrading bacteria. The results shown a significant increase in atrazine removal from 26.2 ± 6.9% to 60.9 ± 8.7–90.6 ± 4.1% during the bioaugmentation phases. To investigate in-situ degradation processes of atrazine, compound-specific stable isotope analysis (CSIA) was conducted. The carbon and nitrogen isotope fractionation pattern revealed atrazine was primarily degraded via a hydrolysis pathway mediated by microorganisms. The biodegradation extent of atrazine calculated from δ13C signatures suggested that 90% of atrazine was removed via the hydrolysis pathway, with only a small portion being removed abiotically. This was additionally supported by an increase in microbial diversity and the abundance of specific bacteria (such as Rhizobium sp. and Pseudomonas sp.) capable of degrading atrazine. Altogether, this study demonstrated the effectiveness of atrazine-degrading mixed culture and its feasibility on bioaugmentation atrazine removal in CW. This work highlights the potential of bioaugmentation in sustainable pesticide removal approaches and CSIA can contribute to an understanding of in-situ pesticide transformation processes in wetland systems.

Novel Insights into Uptake, Translocation, and Transformation Mechanisms of 2,2',4,4'-Tetra Brominated Diphenyl Ether (BDE-47) in Wheat (Triticum aestivum L.): Implication by Compound-Specific Stable Isotope and Transcriptome Analysis.

The uptake, translocation, and transformation of 2,2',4,4'-tetra brominated diphenyl ether (BDE-47) in wheat (Triticum aestivum L.) were comprehensively investigated by hydroponic experiments using compound-specific stable isotope analysis (CSIA) and transcriptome analysis. The results indicated that BDE-47 was quickly adsorbed on epidermis of wheat roots and then absorbed in roots via water and anion channels as well as an active process dependent on energy. A small fraction of BDE-47 in roots was subjected to translocation acropetally, and an increase of δ13C values in shoots than roots implied that BDE-47 in roots had to cross at least one lipid bilayer to enter the vascular bundle via transporters. In addition, accompanied by the decreasing concentrations, δ13C values of BDE-47 showed the increasing trend with time in shoots, indicating occurrence of BDE-47 transformation. OH-PBDEs were detected as transformation products, and the hydroxyl group preferentially substituted at the ortho-positions of BDE-47. Based on transcriptome analysis, genes encoding polybrominated diphenyl ether (PBDE)-metabolizing enzymes, including cytochrome P450 enzymes, nitrate reductases, and glutathione S-transferases, were significantly upregulated after exposure to BDE-47 in shoots, further evidencing BDE-47 transformation. This study first reported the stable carbon isotope fractionation of PBDEs during translocation and transformation in plants, and application of CSIA and transcriptome analysis allowed systematically characterize the environmental behaviors of pollutants in plants.

Carbon and hydrogen stable isotope fractionation due to monooxygenation of short-chain alkanes by butane monooxygenase of Thauera butanivorans Bu-B1211.

Multi element compound-specific stable isotope analysis (ME-CSIA) is a tool to assess (bio)chemical reactions of molecules in the environment based on their isotopic fingerprints. To that effect, ME-CSIA concepts are initially developed with laboratory model experiments to determine the isotope fractionation factors specific for distinct (bio)chemical reactions. Here, we determined for the first time the carbon and hydrogen isotope fractionation factors for the monooxygenation of the short-chain alkanes ethane, propane, and butane. As model organism we used Thauera butanivorans strain Bu-B1211 which employs a non-haem iron monooxygenase (butane monooxygenase) to activate alkanes. Monooxygenation of alkanes was associated with strong carbon and hydrogen isotope effects: εbulkC = -2.95 ± 0.5 ‰ for ethane, -2.68 ± 0.1 ‰ for propane, -1.19 ± 0.18 ‰ for butane; εbulkH = -56.3 ± 15 ‰ for ethane, -40.5 ± 2.3 ‰ for propane, -14.6 ± 3.6 ‰ for butane. This resulted in lambda (Λ ≈ εHbulk/εCbulk) values of 16.2 ± 3.7 for ethane, 13.2 ± 0.7 for propane, and 11.4 ± 2.8 for butane. The results show that ME-CSIA can be used to track the occurrence and impact of monooxygenase-dependent aerobic processes converting short-chain alkanes in natural settings like marine and terrestrial seeps, gas reservoirs, and other geological formations impacted by natural gas.

New insights into the use of Neolithic pottery in Guangxi of South China: organic residue analysis of experimental and archaeological pottery

As one of the world’s earliest pottery origins in Eurasia, the role of pottery during Neolithic period in South China remains unclear. Here, we present a new understanding on the utilization pattern of early pottery from the Neolithic sites of Dayan, Dingsishan and Zengpiyan in Guangxi province, China. Compound-specific stable isotope analysis of pottery and bone lipids show that a persistent use of terrestrial C3 and C4 resources throughout the pottery utilization history highlight the culinary practice and terrestrial exploitation during Neolithic period. Contrary to the traditional view that the primary use of these pottery was closely linked with aquatic resource processing, no aquatic biomarkers were found in the potsherds, yet these compounds were detected in the cooking experiments in this study, indicating that aquatic resources in these sites were probably processed or consumed in other ways. Moreover, a remarkable diachronic change from extensive use of C3 and C4 resources to the intensive use of certain kinds of C3 resources in different Neolithic stages, further indicating that an ecological tradition rooted in the subtropical and tropical environments as well as the Neolithic social evolution exerted great influence upon the initial production and the subsequent utilization of early pottery in prehistoric South China.

Use of molecular composition and compound-specific isotope analysis for source appointment of PAHs in sediments of a highly industrialized area

This study utilized both conventional molecular analysis and compound-specific isotopic techniques to identify the sources of polycyclic aromatic hydrocarbons (PAHs) in sediments of Ulsan Bay, South Korea. The concentrations of 15 traditional and 11 emerging PAHs were determined in sediments from 21 source sites and 26 bay sites. The concentrations and compositions of traditional and emerging PAHs varied significantly, even at sites close to the source areas. The results obtained from diagnostic ratios and the positive matrix factorization model for source identification were inconsistent in adjacent source areas. The δ13C profiles of PAHs, such as phenanthrene (Phe), fluoranthene (Fl), pyrene (Py), and benz[a]anthracene (BaA) in the sediments showed distinct features depending on the surrounding sources. In urban sediments, lighter δ13CPhe values were observed (mean: −25.1‰), whereas relatively heavier values of δ13CPy were found in petroleum industry areas (mean: −23.4‰). The Bayesian isotope mixing model indicates that the predominant source of PAHs in Ulsan Bay sediments was the petroleum industry (45%), followed by the non-ferrous metals industry (30%), automobile industry (18%), and urban areas (6.3%). These results demonstrated the utility of stable isotopes in assessing the sources and contributions of PAHs in small-scale regions. However, there are still limitations in compound-specific isotope analysis of PAHs, including insufficient end-members for each source, difficulty in analysis, and the influence of non-point sources; thus, further study is needed to expand its application.

Carbon isotope fractionation of di-(2-ethylhexyl)-phthalate during photosensitized degradation by •OH and [formula omitted] for characterization of reaction mechanisms

Compound specific isotope analysis (CSIA) has been used to explore the degradation pathways of di-(2-ethylhexyl)-phthalate (DEHP) in photosensitization experiments with H2O2, TiO2, Fe(III) and PMS. The reaction kinetics could be described by first order rate constants [k (h−1)]. The highest degradation rates of DEHP were observed in UV/TiO2 catalyzed reactions.Carbon isotope fractionation factors (εC) and metabolite patterns were examined to analyze the radical reaction. Similar carbon isotope fractionation factors have been found in experiments dominated by OH radical reactions (UV/H2O2, −1.2 ± 0.3‰; UV/TiO2, −1.2 ± 0.5‰). An inverse carbon isotope fractionation has been found for UV/Fe(III) (0.8 ± 0.2‰) and SO4− (0.6 ± 0.2‰ at pH 3) catalyzed reactions indicating that these reactions preferentially taking place at the H atom bond at tert-butyl carbon of the side chain. This hypothesis is further supported by an experiment with isobutyl acetate (εC = 1.8 ± 0.2‰ for UV/Fe(III) at pH 7; εC = -1.1 ± 0.2‰ for UV/PMS at pH 6 and εC = 0.9 ± 0.3‰ for UV/PMS at pH 3).Quenching experiments in the UV/PMS catalyzed reaction indicated a coexistence of SO4− and OH at pH 7. SO4− was the predominant radical at pH 3. OH was found to be the predominant radical in UV/H2O2 and UV/TiO2 reactions. CSIA indicated that the addition of OH to the aromatic ring of DEHP by the RAF pathway is the main reaction mechanism in UV/H2O2 and UV/TiO2 experiments. The SO4− attacks preferentially the C-H bond at the tert-butyl carbon position of the side chain of DEHP which causes an inverse carbon isotope effect. Thus, carbon isotope enrichment factors can be used to distinguish different radical reaction mechanisms with DEHP as a substrate.

Tracking the origin of Ordovician natural gas in the Ordos basin using volatile sulfur compounds

Molecular and compound specific isotope analysis of volatile organic sulfur compounds (VOSC), alkanes and CO2 in natural gases from the Ordovician Majiagou Formation of the Daniudi field (Ordos basin, China) was performed. The analysis of VOSC demonstrated abundant thiols, sulfides and thiophenes in several samples while others had low concentrations of sulfides only. Molecular analysis of main alkanes and non-hydrocarbons showed the samples vary by the nitrogen and H2S concentrations. Thiols in the gas were at isotopic equilibrium with H2S bearing isotopic signature similar to that of Ordovician anhydrites within the reservoirs, hence the source of H2S was likely thermochemical sulfate reduction (TSR) of these anhydrites. In contrast, gas samples that lacked thiols also lacked H2S. Since all gases came from the same formation and similar thermal regime, the lack of thiols and H2S indicates that the occurrence of TSR in the field was limited, likely by contact between hydrocarbons to the anhydrites. The isotopic signature (δ34S) of thiophenes in the gas samples suggests the source of the gas is unlikely to be Carboniferous or Permian coals which were previously suggested as the source rocks for the gas. The δ13C and δ2H of alkanes further supports this suggestion as it demonstrates Carboniferous and Permian gases are unlikely to undergo TSR and generate the gas present in the Ordovician reservoirs. Instead, the δ13C and δ2H of alkanes hint that the gas source is shale rather than coal.This study demonstrates the applicability of compound specific sulfur isotope analysis of VOSC in identification of H2S sources, performing gas-source rock correlation and acting as a complementary proxy in case where routine analysis of hydrocarbons (δ13C and δ2H) is insufficient for identification of the gas source.

Analysis of omega-3 and omega-6 polyunsaturated fatty acid metabolism by compound-specific isotope analysis in humans

Natural variations in the 13C:12C ratio (carbon-13 isotopic abundance [δ13C]) of the food supply have been used to determine the dietary origin and metabolism of fatty acids, especially in the n-3 PUFA biosynthesis pathway. However, n-6 PUFA metabolism following linoleic acid (LNA) intake remains under investigation. Here, we sought to use natural variations in the δ13C signature of dietary oils and fatty fish to analyze n-3 and n-6 PUFA metabolism following dietary changes in LNA and eicosapentaenoic acid (EPA) + DHA in adult humans. Participants with migraine (aged 38.6 ± 2.3 years, 93% female, body mass index of 27.0 ± 1.1 kg/m2) were randomly assigned to one of three dietary groups for 16 weeks: 1) low omega-3, high omega-6 (H6), 2) high omega-3, high omega-6 (H3H6), or 3) high omega-3, low omega-6 (H3). Blood was collected at baseline, 4, 10, and 16 weeks. Plasma PUFA concentrations and δ13C were determined. The H6 intervention exhibited increases in plasma LNA δ13C signature over time; meanwhile, plasma LNA concentrations were unchanged. No changes in plasma arachidonic acid δ13C or concentration were observed. Participants on the H3H6 and H3 interventions demonstrated increases in plasma EPA and DHA concentration over time. Plasma δ13C-EPA increased in total lipids of the H3 group and phospholipids of the H3H6 group compared with baseline. Compound-specific isotope analysis supports a tracer-free technique that can track metabolism of dietary fatty acids in humans, provided that the isotopic signature of the dietary source is sufficiently different from plasma δ13C.