Compound-specific Stable Carbon Isotope Research Articles

Purity Assessment of Honey Based on Compound Specific Stable Carbon Isotope Ratios Obtained by LC-IRMS.

The use of stable carbon isotope ratios (δ13C) of sugar fractions of honey is a powerful tool to detect adulteration with sugar syrups. This is accomplished by calculating differences of the δ13C values between individual honey saccharides and comparing them to published purity criteria. A liquid chromatography-isotope ratio mass spectrometry (LC-IRMS) method for the determination of δ13C values of sugars in honey was previously validated by an interlaboratory comparison but no further guidance was given how to include the obtained precision figures of the compound specific δ13C values in the purity assessment of honey. To use existing data to estimate the standard deviation of the repeatability (sr) and reproducibility (sR) of differences (Δ δ13C) between the δ13C values of individual honey saccharides. Previously published δ13C values were used to calculate differences (Δ δ13C values) between δ13C fructose-δ13C glucose, δ13C glucose-δ13C disaccharides, etc in a honey sample; sr and sR of Δ δ13C values were calculated according to ISO 5725-2:2019. The Δ δ13C sr and sR values were essentially of the same magnitude as the sr and sR values of δ13C values of the sugar fractions. The precision of the Δ δ13C values was used to estimate the critical difference for comparing a test result with a reference value according to ISO 5725-6:1994. This varied between 0.02 ‰ and 0.40 ‰. The estimated critical differences can be used to determine whether a honey test result complies with published Δ δ13C purity criteria. The proposed procedure will increase the confidence in decisions based on compound specific δ13C values regarding the conformity of honey with published purity criteria.

Geochemistry and petrology of Early Permian lacustrine shales in the Lodève Basin, Southern France: Depositional history, organic matter accumulation and thermal maturity

The lacustrine shales in the Lodève Basin, southern France, serve as excellent archives of paleo-lake development as well as climatic evolution during the Early Permian. In this study, an extensive dataset is presented encompassing organic petrographic data, major and trace element quantification, bulk and molecular organic geochemical proxies, as well as compound-specific stable carbon isotope data derived from the analysis of 36 black shale outcrop samples originating from the Usclas-St. Privat Formation (USPF), Tuilières-Loiras Formation (TLF), and Viala Formation (VF). All sample are thermally oil-mature, as evident from a vitrinite reflectance (VRr) of around 0.8%. The lower section of the USPF, characterized by notably higher total sulfur (TS) concentrations, displays total organic carbon (TOC) and TS contents spanning from 2.69 to 7.83 (avg. 4.28) wt% and 0.42–1.55 (avg. 1.09) wt%, respectively. In contrast, the upper section of the USPF (average TOC of 2.59 wt%), TLF (average TOC of 2.66 wt%), and VF (average TOC of 3.17 wt%) exhibit considerably lower TS contents of 0.26 wt%, 0.22 wt%, and 0.17 wt%, respectively. The lower section of the USPF, characterized by the lowest pristane/phytane (Pr/Ph) ratio and the highest TS/TOC ratios and chemical index of alteration (CIA) values, was deposited in oxygen-depleted and saline lacustrine environments. These conditions prevailed under more humid climatic conditions and were probably related to marine incursions. In contrast, the upper section of the USPF, the TLF, and the VF display elevated Pr/Ph ratios but reduced TS/TOC and CIA values, signifying deposition within oxic-dysoxic and freshwater-brackish bottom water conditions with a significant change towards arid conditions. All samples are characterized by low vitrinite and inertinite contents together with consistently similar average values of Al2O3 and TiO2. The biomarker analysis suggests that the organic matter (OM) in most samples mainly originates from planktonic/algal biomass with additional microbial OM. Only the lower section of the USPF displays a slightly enhanced contribution of terrestrial OM input and also more detrital elements. It is concluded that the structural evolution of the basin from narrow deep towards wider and shallower settings as well as the postulated marine transgressive events during early stages played a crucial role in shaping the deposition environments of the two distinct sets of lacustrine shales, thereby influencing the OM accumulation mechanisms. In contrast, the substantial climatic aridification seems to have a relatively minor impact on the sources of OM and the conditions prevailing within the water column.

Evaluation of lipid extraction methods for fatty acid quantification and compound-specific δ13C and δ2Hn analyses

Lipids, with fatty acids (FA) as a crucial subset, have become a focal point for diverse medical, physiological, and ecological studies. However, a comprehensive assessment of the various pre-analytical FA extraction methods published in the scientific literature remains lacking. In this study, we examined the efficacy of seven well-established sample preparation methods, specifically focusing on their effectiveness in total lipid and fatty acid extraction and their impact on compound-specific stable hydrogen (δ2H) and carbon (δ13C) isotope values. We also considered the repercussions of FA removal efficacy on residual bulk tissue δ2Hn analysis, because lipids typically have low δ2H values.Our findings showed that in most cases chloroform-based extraction methods outperformed those without chloroform. While discrepancies were not as evident for smaller organisms, such as plankton, marked variations were discernible in the extraction efficiencies for muscle and liver samples, which was also manifested in the residual bulk tissue δ2Hn results. Notably, most extraction methods had little effect on specific δ13C or δ2H isotope values of FA; instead, an emphasis should be on using an extraction method that achieves optimal baseline peak separation of the chromatograms for C and H isotope measurements.

Isotope forensics of polycyclic aromatic compounds (PACs) in a contaminated shallow aquifer

Diesel was accidently released into the shallow subsurface at an industrial site in the province of Québec, Canada, in the late 1980s. Subsequent remediation efforts removed much of the contamination; however, traces of petroleum hydrocarbons continue to impact the local aquifer. In addition to the historical diesel spill, more recent yet unconfirmed accidental releases from ongoing on-site and neighbouring industrial activities may have potentially contributed to elevated levels of polycyclic aromatic compounds (PACs) in groundwater. To identify the main source(s) of contamination, compound-specific stable carbon isotope ratios (δ13C) of PACs in groundwater monitoring wells were compared to those in asphalt produced from a nearby plant and in fuel oil #6 oil being used by local industry. The δ13C values of five individual compounds (biphenyl, C2-naphthalene, C1-fluorene, dibenzothiophene and phenanthrene) and two groups of combined C1-phenanthrenes/anthracenes in all groundwater samples were within analytical uncertainty (±0.5‰). Moreover, the δ13CPAC values in groundwater samples were distinct from those in asphalt and fuel oil #6, indicating negligible contributions from these sources. The similarity in δ13CPAC values across monitoring wells, including one situated in the former source zone containing a floating hydrocarbon phase, pointed to a common source of subsurface contamination that was attributed to the historical diesel spill. These results thus demonstrate that δ13CPAC values can be used for source apportionment in shallow aquifers decades after the original spill event.

Transformation of Iminodi(methylene phosphonate) on Manganese Dioxides - Passivation of the Mineral Surface by (Formed) Mn2.

Aminopolyphosphonates (APPs) are strong chelating agents with growing use in industrial and household applications. In this study, we investigated the oxidation of the bisphosphonate iminodi(methylene phosphonate) (IDMP) - a major transformation product (TP) of numerous commercially used APPs and a potential precursor for aminomethylphosphonate (AMPA) - on manganese dioxide (MnO2). Transformation batch experiments at pH 6 revealed AMPA and phosphate as main TPs, with a phosphorus mass balance of 80 to 92% throughout all experiments. Our results suggest initial cleavage of the C-P bond and formation of the stable intermediate N-formyl-AMPA. Next, C-N bond cleavage leads to the formation of AMPA, which exhibits lower reactivity than IDMP. Reaction rates together with IDMP and Mn2+ sorption data indicate formation of IDMP-Mn2+ surface bridging complexes with progressing MnO2 reduction, leading to the passivation of the mineral surface regarding IDMP oxidation. Compound-specific stable carbon isotope analysis of IDMP in both sorbed and aqueous fractions further supported this hypothesis. Depending on the extent of Mn2+ surface concentration, the isotope data indicated either sorption of IDMP to the mineral surface or electron transfer from IDMP to MnIV to be the rate-limiting step of the overall reaction. Our study sheds further light on the complex surface processes during MnO2 redox reactions and reveals abiotic oxidative transformation of APPs by MnO2 as a potential process contributing to widespread elevated AMPA concentrations in the environment.

Botanical characterization and authentication of lavender essential oil using its volatile organic compounds and compound-specific carbon and hydrogen isotope ratio analysis

The determination of authenticity and provenance is one of the main issues in high-value natural products such as lavender (L. angustifolia) essential oil. Due to their high value, natural products are often totally or partially substituted with cheaper alternatives. Therefore, it is necessary to accurately characterize the composition of lavender essential oil and its related species, particularly lavandin (L. intermedia) essential oil, which is frequently used as an adulterant. In this study, we analyzed the most distinctive volatile organic compounds (VOCs) and their relative compound-specific stable carbon and hydrogen (δ13C and δ2H) isotope ratios in lavender, lavandin, and commercial lavender essential oil samples using fast GC-MS/MS and GC-IRMS methods and sparse Partial Least Square Discriminant Analysis (sPLS-DA) to classify and verify their botanical origin. For the first time, concentration ranges for 79 VOCs and the δ13C and δ2H values in 32 VOCs were used to characterize lavender essential oils. sPLS-DA models with either VOCs, δ13C and δ2H, or in combination successfully classify lavender and lavandin with 100% accuracy. VOCs such as camphor, borneol, eucalyptol, α-bisabolol, and α-pinene were found to be the most important variables for differentiating lavender oil from lavandin. Similarly, δ13C in camphor, eucalyptol, trans-β-ocimene and 3-octanone, and δ2H in α-terpineol and trans-β-ocimene and 3-octanone also differentiated lavender and lavandin oil. In addition, we demonstrated that compound-specific δ13C and δ2H detected the adulteration of natural lavender or lavandin oil if more than 15% of linalool, linalyl acetate, eucalyptol, and α-terpineol were of synthetic origin. These preliminary results with sPLS-DA models suggest that VOCs and compound-specific δ13C and δ2H can be a promising tool for the botanical classification of lavender essential oil and the detection of possible adulteration with synthetic compounds.

Molecular compositions and stable carbon isotopes (δ13C) of PAHs in wintertime PM2.5 in urban Xi'an, China: Implications for source distribution and atmospheric oxidation

Atmospheric polycyclic aromatic hydrocarbons (PAHs) are potentially carcinogenic and mutagenic to human beings, and thus have attracted significant attention in recent decades. Compound-specific stable carbon isotopes (δ13C) of PAHs are indicative for source identification, but have not been extensively applied in tracing atmospheric oxidation processes. In this study, we examined the molecular compositions and δ13C values of PAHs in wintertime PM2.5 in a highly polluted urban region in Norwest China. The average concentrations of total parent-PAHs (pPAHs) and oxygenated-PAHs (OPAHs) were measured as 70 ± 29 and 36 ± 17 ng m−3, respectively. The results obtained from the incremental lifetime cancer risk (ILCR) model suggested a high potential cancer risk of PAHs in the urban region. The temperoal variations of PAHs and carbonaceous fractions implied that the contribution of secondary organic compounds was limited during the severe pollution period (PM2.5 > 115 μg m−3). Both molecular diagnostic ratios and δ13C values indicated that the major emission sources of the pPAHs were coal and/or biomass burning. The δ13C value of fluorene became heavier as the OPAHs concentration increased, while the concentrations of fluorene was negatively correlated with OPAHs, indicating the secondary formation of OPAHs from fluorene oxidation in the cold season. Our results also confirmed that δ13C values of pPAHs are indeed indicative of atmospheric oxidation processes.

An Overview of Lipid Biomarkers in Terrestrial Extreme Environments with Relevance for Mars Exploration.

Lipid molecules are organic compounds, insoluble in water, and based on carbon-carbon chains that form an integral part of biological cell membranes. As such, lipids are ubiquitous in life on Earth, which is why they are considered useful biomarkers for life detection in terrestrial environments. These molecules display effective membrane-forming properties even under geochemically hostile conditions that challenge most of microbial life, which grants lipids a universal biomarker character suitable for life detection beyond Earth, where a putative biological membrane would also be required. What discriminates lipids from nucleic acids or proteins is their capacity to retain diagnostic information about their biological source in their recalcitrant hydrocarbon skeletons for thousands of millions of years, which is indispensable in the field of astrobiology given the time span that the geological ages of planetary bodies encompass. This work gathers studies that have employed lipid biomarker approaches for paleoenvironmental surveys and life detection purposes in terrestrial environments with extreme conditions: hydrothermal, hyperarid, hypersaline, and highly acidic, among others; all of which are analogous to current or past conditions on Mars. Although some of the compounds discussed in this review may be abiotically synthesized, we focus on those with a biological origin, namely lipid biomarkers. Therefore, along with appropriate complementary techniques such as bulk and compound-specific stable carbon isotope analysis, this work recapitulates and reevaluates the potential of lipid biomarkers as an additional, powerful tool to interrogate whether there is life on Mars, or if there ever was.

Mechanistic investigation of phosphonate photolysis in aqueous solution by simultaneous LC-IRMS and HRMS analysis

The mechanism of photolytic degradation of aminotrimethylphosphonic acid (ATMP) in an aqueous solution is not completely elucidated with respect to the transformation products formed during technical photodegradation. For the first time, the degradation of ATMP was investigated with simultaneous analysis by isotope ratio and high-resolution mass spectrometry (LC-IRMS+HRMS). This instrumental coupling combines quantitative data on degradation with compound-specific stable carbon isotope analysis (CSIA) in terms of kinetic isotope effects while identifying transformation products. Additionally, in combination with wet chemical analysis of ortho-phosphate (o-PO4), phosphorus balances were established to elucidate and interpret the degradation mechanism of ATMP under photolysis. Various experimental conditions during photolysis (temperature, dissolved oxygen concentration, and wavelength range) were investigated.ATMP was transformed to iminodimethylphosphonic acid (IDMP), aminomethylphosphonic acid (AMPA), and o-PO4 as main products during photolysis with a medium pressure mercury lamp. UV radiation < 310 nm was found to be required for ATMP degradation. The degradation of ATMP and its transformation products is slightly affected by temperature and dissolved oxygen concentration. Considering possible reactive oxygen species, such as hydroxyl radicals, it is assumed that the degradation of ATMP occurs to a small extent via a parallel degradation pathway in addition to photolysis. Complementary CSIA revealed an inverse carbon isotopic effect of ATMP due to direct photolysis, unaffected by the experimental conditions considered, while no isotopic effect was associated with the hydroxyl radical (H2O2) oxidation of ATMP. In UV/H2O2 oxidation of ATMP, four of five additional unknown transformation products, which have not yet been described in literature, could be assigned to postulated structures based on HRMS data. The findings achieved in this study demonstrate the advantages of simultaneous analysis by LC-IRMS+HRMS as a tool to elucidate reaction mechanisms for the first time.

Late Paleocene CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; drawdown, climatic cooling and terrestrial denudation in the southwest Pacific

Abstract. ​​​​​​​Late Paleocene deposition of an organic-rich sedimentary facies on the continental shelf and slope of New Zealand and eastern Australia has been linked to short-lived climatic cooling and terrestrial denudation following sea level fall. Recent studies confirm that the organic matter in this facies, termed “Waipawa organofacies”, is primarily of terrestrial origin, with a minor marine component. It is also unusually enriched in 13C. In this study we address the cause of this enrichment. For Waipawa organofacies and its bounding facies in the Taylor White section, Hawke's Bay, paired palynofacies and carbon isotope analysis of heavy liquid-separated density fractions indicate that the heaviest δ13C values are associated with degraded phytoclasts (woody plant matter) and that the 13C enrichment may be partly due to lignin degradation. Compound-specific stable carbon isotope analyses of samples from the Taylor White and mid-Waipara (Canterbury) sections display similar trends and further reveal a residual 13C enrichment of ∼ 2.5 ‰ in higher plant biomarkers (long chain n-alkanes and fatty acids) and a ∼ 2 ‰–5 ‰ change in subordinate marine biomarkers. Using the relationship between atmospheric CO2 and C3 plant tissue δ13C values, we determine that the 3 ‰ increase in terrestrial δ13C may represent a ∼ 35 % decrease in atmospheric CO2. Refined age control for Waipawa organofacies indicates that deposition occurred between 59.2 and 58.5 Ma, which coincides with an interval of carbonate dissolution in the deep sea that is associated with a Paleocene oxygen isotope maximum (POIM, 59.7–58.1 Ma) and the onset of the Paleocene carbon isotope maximum (PCIM, 59.3–57.4 Ma). This association suggests that Waipawa deposition occurred during a time of cool climatic conditions and increased carbon burial. This relationship is further supported by published TEX86-based sea surface temperatures that indicate a pronounced regional cooling during deposition. We suggest that reduced greenhouse gas emissions from volcanism and accelerated carbon burial, due to tectonic factors, resulted in short-lived global cooling, growth of ephemeral ice sheets and a global fall in sea level. Accompanying erosion and carbonate dissolution in deep-sea sediment archives may have hidden the evidence of this “hypothermal” event until now.

Two Pathways Compete in the Mn(II)-Catalyzed Oxidation of Aminotrismethylene Phosphonate (ATMP).

Mn(II)-catalyzed oxidation by molecular oxygen is considered a relevant process for the environmental fate of aminopolyphosphonate chelating agents such as aminotrismethylene phosphonate (ATMP). However, the potential roles of Mn(III)ATMP-species in the underlying transformation mechanisms are not fully understood. We combined kinetic studies, compound-specific stable carbon isotope analysis, and equilibrium speciation modeling to shed light on the significance of such Mn-ATMP species for the overall ATMP oxidation by molecular oxygen. The fraction of ATMP complexed with Mn(II) inversely correlated with both (i) the Mn(II)-normalized transformation rate constants of ATMP and (ii) the observed carbon isotope enrichment factors (εc-values). These findings provide evidence for two parallel ATMP transformation pathways exhibiting distinctly different reaction kinetics and carbon isotope fractionation: (i) oxidation of ATMP present in Mn(III)ATMP complexes (εc ≈ -10 ‰) and (ii) oxidation of free ATMP by such Mn(III)ATMP species (εc ≈ -1 ‰) in a catalytic cycle. The higher reaction rate of the latter pathway implies that aminopolyphosphonates can be trapped in catalytic Mn-complexes before being transformed and suggests that Mn(III)ATMP might be a potent oxidant also for other reducible solutes in aqueous environments.

Compound specific stable carbon isotope analysis of aromatic organic contaminants in water using gas chromatography coupled to mid-infrared laser spectroscopy

A mid-infrared laser based analytical approach is newly developed in this study for gas chromatography (GC) separation and carbon compound specific isotope analysis (CSIA) of aromatic organic pollutants in water.

Compound-specific stable carbon and hydrogen isotope analyses of late-Holocene vegetation and precipitation change at Laguna Los Mangos, Costa Rica

New compound-specific isotope analyses of a sediment core from Laguna Los Mangos in southern Pacific Costa Rica improves understanding of late-Holocene precipitation change in a region with limited paleoprecipitation records that is vulnerable to future climate change. We established paleoprecipitation and paleovegetation records from compound-specific stable hydrogen and carbon isotopic compositions of terrestrially-derived n-alkanes (δ2Halkane and δ13Calkane) to assess paleohydrologic variability and potential linkages to paleoecological change and human activity as revealed by prior analyses of the Los Mangos core. The δ2Halkane values were corrected for isotopic fractionation using pollen counts from the same core. The Los Mangos record extends to 4200 cal yr BP and small increases in δ13C values of C29, +0.6‰, and C31 alkanes, +0.3‰, (δ13CC29, 31) indicate a slight increase in C4 vegetation after initial introduction of maize agriculture to the watershed at ca. 3360 cal yr BP. This slight increase in C4 vegetation is followed by the largest positive carbon isotope excursions in the record, as compared to record averages (δ13CC29 = +3.2‰, δ13CC31 = +5.0‰). Paleohydrologic variability likely influenced vegetation and human activity at Los Mangos. Lake desiccation during the late-Terminal Classic Drought (TCD) resulted in a sedimentary hiatus in the Los Mangos record from ca. 950 to 450 cal yr BP. Positive excursions in comparison to record averages occur for both δ2HC29 and δ2HC31 proxies (δ2HC29 = +25.3 to +13.4‰ and δ2HC31 = +6.5‰) during the middle Little Ice Age (LIA) and indicate drier than average conditions, but there is no evidence of desiccation during this period. Thus, drought conditions during the LIA were apparently not as severe at Los Mangos as during the TCD, possibly because of differing forcing mechanisms for LIA climate that originated, or were more clearly expressed, in the Atlantic basin.

Evaluation of a quick one-step sample preparation method for the determination of the isotopic fingerprint of rapeseed (Brassica napus): Investigation of the influence of the use of 2,2-dimethoxypropane on compound-specific stable carbon and hydrogen isotope analyses by gas chromatography combustion/pyrolysis isotope ratio mass spectrometry.

Gas chromatographic analyses for vegetable oils require transesterification, which generally involves multiple steps, mainly to generate fatty acid methyl esters (FAMEs). A quick method based on acid-catalyzed transesterification using 2,2-dimethoxypropane (DMP) enables the conversion in one step, in a single reactor. For compound-specific stable carbon and hydrogen isotope analyses (C- and H-CSIA) of individual fatty acids (FAs) in oil, the verification of this one-step method has not yet been reported. In this study, we evaluated the feasibility of the one-step method for C- and H-CSIA of individual FAMEs in rapeseed samples. The focus was on the investigation of the influence of methanol, which was produced from the reactions of DMP with glycerol and water during transesterification, on the accuracy of isotope composition of FAMEs, consequently of the FAs. The reproducibility of the one-step method was assessed by the measurement of the FAMEs from rapeseed and rapeseed oil. For the C- and H-CSIA of individual FAMEs, a gas chromatography combustion/pyrolysis isotope ratio mass spectrometry system was used. Our results showed that no significant differences arise in the carbon and hydrogen isotope compositions of the selected main FAMEs produced with and without DMP except for the H-CSIA value of C18:3. The reproducibility of the one-step method for rapeseed was in the range of ±0.1 mUr to ± 0.3 mUr for C-CSIA and ±1 mUr to ±3 mUr for H-CSIA of the main FAMEs. DMP improves the transesterification efficiency without influencing the accuracy of the C- and H-CSIA of FAMEs. The performance of the one-step method for rapeseed samples for the determination of C- and H-CSIA values of FAMEs is satisfactory. Thus, the applicability of the one-step method for isotopic fingerprint analyses of FAs in oilseeds is reported for the first time.

Synthesis and release of fatty acids under the interaction of Ulva pertusa and Heterosigma akashiwo by stable isotope analysis

Symbiosis of marine algae is inevitable in the marine environment, and species may occur interaction on the growth. In this study, the macroalgae Ulva pertusa and marine microalgae Heterosigma akashiwo were selected as target species to study the interaction mechanism between them. After the 8 days of co-cultivation, the inhibition on growth was observed for both of U. pertusa and H. akashiwo. Eight fatty acids in U. pertusa was detected, with the significant decrease in contents of polyunsaturated fatty acids (PUFAs) especially for C18:2, C18:3n-3 and C18:3n-6. Twelve fatty acids in H. akashiwo was detected, with the significant change for PUFAs. PUFA concentrations in the co-culture group were less than those in the mono-culture. Meanwhile the principal component analysis was conducted to insight into the interaction between U. pertusa and H. akashiwo by fatty acids content and carbon stable isotope ratio of fatty acids (δ13CFAs). Fatty acid content could not distinguish mono and co-culture. However, δ13CFAs could distinguish not only the culture time of algae, but also the living environment of algae. In addition, this study combined fatty acids content and δ13CFAs to explore the release of fatty acids by algae into the seawater. The C18:3n-3 was identified as the allelochemical released by U. pertusa to inhibit the growth of H. akashiwo. The ratio of δ13CFAs in seawater decreased. This study provides a theoretical basis for the symbiosis of marine algae, and a new method of compound-specific stable carbon isotopes was used to better explore the metabolism of fatty acids in algae.

Patterns and compound specific stable carbon isotope analysis (δ13 C) of capsaicinoids in Cayenne chilli fruits of different ripening stages.

Capsaicinoids are alkaloids of high pungency which are exclusively formed by fruits of the genus Capsicum. Capsaicinoid content and composition of Capsicum fruits are influenced by ripening. Determination of changes in content and pattern of individual capsaicinoids in chilli pods with fruit ripening. Compound specific stable carbon isotope analysis (δ13 C values (‰), CSIA) was used for a better understanding of capsaicinoid development during fruit ripening. Cayenne chillies (Capsicum annuum) were grown in a glasshouse and harvested from different plants at four ripening stages (unripe, semi-ripe, ripe, overripe). Nine capsaicinoids (one verified by synthesis) were quantified by gas chromatography with mass spectrometry (GC-MS). For CSIA, an acetylation method for derivatising capsaicinoids was developed. Variations in the patterns of the nine capsaicinoids were not relatable to a distinct ripening stage and also total contents varied extensively from plant to plant. However, changes in total capsaicinoid concentrations were systematic. In almost all plants, maximum values were reached in unripe fruits, then decreased to semi-ripe samples and increased again in the following ripening process. Likewise, δ13 C values of individual capsaicinoids were always by ~2‰ heavier in unripe than in semi-ripe or ripe fruits. However, direction of changes in sum-δ13 C values (‰) (taking contributions of all capsaicinoids together) could not be explained by corresponding variations in capsaicinoid concentrations. Both quantification and δ13 C values (‰) verified the presence of ripening-related changes in the capsaicinoid content which may be caused by simultaneously proceeding reactions like synthesis, storage and degradation of capsaicinoids.

Variable ethanol concentrations and stable carbon isotopes reveal anthropogenic ethanol contributions to rainwater

Abstract The recent rapid increase in ethanol use as a biofuel and emission to the atmosphere may impact air quality and oxidizing capacity in the atmosphere. However, the global models show large uncertainties on sources of atmospheric ethanol. Concentrations and compound-specific stable carbon isotope ratios of ethanol (δ13Cethanol) in rainwater were measured in samples collected in six countries and 16 different locations over a two-year period (n = 270 for concentration; n = 111 for δ13Cethanol). Ethanol concentrations ranged from below the limit of detection ( 0.15), indicating that biofuel ethanol in rainwater is locally supplied during rain droplet formation. The results of this study are significant because they shed new insight into the role of anthropogenic emission of ethanol to the atmosphere. This study is particularly relevant as ethanol production and usage as a biofuel continues to increase globally.

Molecular Distributions and Compound-Specific Stable Carbon Isotopic Compositions of Plant Wax n-Alkanes in Marine Aerosols along a North–South Transect in the Arctic–Northwest Pacific Region

A geographical source of n-alkanes in marine aerosols was assessed along a North–South transect in the Arctic–Northwest Pacific region. Marine aerosol samples were collected during the ARA08 cruise with the R/V Araon between 28 August and 28 September 2017. We investigated molecular distributions of n-alkanes (homologous series of C16 to C34) and compound-specific stable carbon isotopes (δ13C) of n-C27, n-C29, and n-C31. Unresolved complex mixtures (UCM) showed a latitudinal trend from the Arctic Ocean to the northwest Pacific Ocean, highlighting an increasing influence of the plume of polluted air exported from East Asian countries. The anthropogenic input was further evidenced by high U/R ratios (&gt;5) and low CPI17–23 (0.6–1.4). The occurrence of high molecular weight (HMW) n-alkanes with high CPI27–31 (&gt;3) indicated the biogenic input of terrestrial higher plant leaf waxes in all studied samples. The δ13C of HMW n-alkanes was influenced by both the relative contributions from the C3/C4 plant sources and from fossil fuel combustions. The back-trajectory analyses provided evidence that changes in molecular distributions and δ13C of n-alkanes were due to the long-range atmospheric transport of anthropogenic and biogenic organic materials from North American and East Asian countries to the Arctic Ocean and the remote northwest Pacific Ocean, respectively.

Isotopic composition of oceanic dissolved black carbon reveals non-riverine source

A portion of the charcoal and soot produced during combustion processes on land (e.g., wildfire, burning of fossil fuels) enters aquatic systems as dissolved black carbon (DBC). In terms of mass flux, rivers are the main identified source of DBC to the oceans. Since DBC is believed to be representative of the refractory carbon pool, constraining sources of marine DBC is key to understanding the long-term persistence of carbon in our global oceans. Here, we use compound-specific stable carbon isotopes (δ13C) to reveal that DBC in the oceans is ~6‰ enriched in 13C compared to DBC exported by major rivers. This isotopic discrepancy indicates most riverine DBC is sequestered and/or rapidly degraded before it reaches the open ocean. Thus, we suggest that oceanic DBC does not predominantly originate from rivers and instead may be derived from another source with an isotopic signature similar to that of marine phytoplankton.

Multiple environmental and ecological controls on archaeal ether lipid distributions in saline ponds

The distribution of archaeal ether lipids is thought to be governed by salinity in hypersaline and marine environments due to differences in their biological sources. However, little is known about their source and relationship with salinity in lacustrine environments. To explore this, we analyzed the distribution of specific archaeal lipids (isoprenoid GDGTs and diethers) of 11 ponds along a salinity gradient (0.8‰ to 279‰) in Inner Mongolia, NE China. Functional gene mcrA and compound-specific stable carbon isotope data were used to explore the biological source(s) of archaeal diether and tetraether lipids. Both lipid- and DNA-based methods showed methanogens to be abundant in ponds, which is consistent with the dominance of GDGT-0 relative to other isoprenoid GDGTs as well as the occurrence of archaeol (C20/C20 DGD), hydroxyarchaeol and the mcrA gene. However, the occurrence of the extended archaeol (C20/C25 DGD) also suggests the presence of Halobacteriales, non-halophilic methanogens and halophilic methanogens. This means that the biological sources of archaeal diethers and tetraethers are complicated. We subsequently evaluated the applicability of TEX86 temperature and ACE salinity proxies in these settings; however, due to the mixed sources of archaeal diethers and tetraethers, these proxies are not applicable in these ponds and it appears that salinity is not the dominant control on archaeal ether lipid distributions in these saline ponds.