Affordable event and monthly rain samplers: Improving isotopic datasets to understand meteorological processes.

RATIONALE: Water-stable isotopes in rainfall are powerful tracers of atmospheric processes at different spatial and temporal scales. However, commercially available rain samplers for isotopic analysis are prohibitively expensive, especially for high spatial resolution networks and studies conducted in developing countries. A low-cost, simple, and robust sampler was designed for event and monthly rainfall samplings. METHODS: Rainfall collectors were built based on existing designs provided in the literature and using easily accessible materials. Event samplers were filled with different volumes of reference water and left for 72 h in laboratory conditions to determine the minimum amount of rainfall to be collected to minimize isotopic fractionation, from both postsampling evaporation and equilibration. Samples were analyzed using dual-inlet isotope ratio mass spectrometry and cavity ring-down spectroscopy. RESULTS: For samples larger than 4% of the bottle's capacity, the evaporative enrichment due to Rayleigh distillation is negligible compared to the overall analytical uncertainty. Using a tube connecting the funnel to the water sample has proved to reduce postsampling evaporation by at least five times. To limit water self-diffusion, we recommend collecting the largest rainfall amount possible. Under these conditions, these collectors are suitable for rainfall sampling for isotopic analysis. CONCLUSIONS: This low-cost methodology will enable isotopic sampling of precipitation at high spatial resolutions and democratize the use of isotopes for hydrological studies in developing countries. All instructions for building and using these samplers are made openly accessible to the scientific community so they can be repeated and adapted to the needs of each project.

Characterization of vanillin carbon isotope delta reference materials.

Stable carbon isotope ratio measurements are used to investigate the provenance of vanillin. In this study, a variety of commercial vanillin samples and vanilla products were analyzed to provide a frame of reference for the variability of carbon isotope delta values in various vanillin samples, with the results ranging from -20.6 to -36.7‰ relative to the Vienna Peedee Belemnite (VPDB). We present information on the development of two synthetic vanillin reference materials, VANA-1 and VANB-1, prepared in 0.75 g units in glass vials, to be used for the calibration of carbon isotope delta measurements of vanillin and other easily combustible organic materials. Characterization of 40 vials each of VANA-1 and VANB-1 was performed by three laboratories over several measurement sequences. The certified carbon isotope delta values are -31.30 ± 0.06‰ (VANA-1) and -25.85 ± 0.05‰ (VANB-1). These uncertainties, for the 95% confidence level, include considerations for measurement uncertainty, coherence of the reference materials used for calibration, batch homogeneity, and stability during storage and transportation. The results are traceable to the VPDB through a set of nine reference materials (IAEA-CH-6, USGS65, IAEA-600, NBS22, USGS61, IAEA-603, IAEA-610, IAEA-611, and IAEA-612). For up to date certified values, users should refer to doi.org/10.4224/crm.2022.vana-1 and doi.org/10.4224/crm.2022.vanb-1.

Investigating individual migration life histories: An isotopic case study from 17th to 18th century Nouvelle France.

OBJECTIVES: This isotopic study explores the mobility patterns of a growing urban population from Notre Dame's Catholic cemetery (1691-1796), located in Montreal (Canada). The site offers a unique opportunity to investigate early colonial settlement in Nouvelle France through individual life patterns. MATERIALS AND METHODS: Stable oxygen isotopic compositions (δ18O) were measured on the enamel of 32 individuals from the Notre Dame collection. Premolars and third molars were selected, as they reflected the δ18O of the drinking water during childhood (2.5-5.5 years) and pre-adulthood (9.5-15.5 years). Firstly, premolars from three children (4-8 years of age) allowed us to provide a mean δ18O for the water consumed locally (22.7 ± 1.0 ‰ vs. VSMOW). Then, our δ18O were compared with published data from various geographical regions in North America (Eastern Canada and the United States) and Europe (France and the British Isles) to highlight mobility patterns of each individual. RESULTS: Forty-eight percent of our sample (14 out of 29 individuals) did not reflect any long-distance mobility, as all their δ18O reflected Montreal's variation during their lifetime. The remaining (15 out of 29 individuals) experienced mobility within (n = 8) and outside (n = 7) North America and at different phases of their life (five at pre-adulthood, six at adulthood and four during both phases). Their migration patterns were analyzed according to age, sex, diet and possible ancestry in order to propose some "biographies." DISCUSSION: This study highlights high population diversity in early colonial Montreal. Historians wrote that the city was growing, not only with the arrival of Europeans (e.g., young male workers, sailors), but also other groups (e.g., Indigenous people, slaves from North America). Additional analyses (e.g., ancient DNA) will be needed to explore further this phenomenon.

Discontinuity in the Realization of the Vienna Peedee Belemnite Carbon Isotope Ratio Scale.

By convention, carbon isotope ratios are expressed relative to VPDB defined by the calcite standard NBS19 in the 1980s. [See T. Coplen, Pure Appl. Chem. 1994, 66, 273-276.] To improve the realization of the VPDB scale, a second fixed point (lithium carbonate, LSVEC) was introduced in 2006 [T. Coplen et al. Anal. Chem. 2006, 78, 2439-2441], which is now known to be isotopically unstable. [Assonov, S. Rapid Commun. Mass Spectrom., 2018, 32, 827-830.] With the high-quality reference materials made available in 2020, it is now possible to realize the VPDB scale with high confidence. [Assonov, S. et al. Rapid Commun. Mass Spectrom., 2020, 34, e8867; Assonov, S. Rapid Commun. Mass Spectrom. 2021, 35, e9014; Qi, H. et al. Rapid Commun. Mass Spectrosc. 2021, 35, e9006.] Here, we report the analysis of 25 reference materials using isotope ratio combustion mass spectrometry, show the discontinuity between the values measured against the new IAEA reference materials and the values currently assigned to these reference materials on the VPDB2006, and provide a link bringing these materials onto the new VPDB2020.

Designing working standards for stable H, C, and O isotope measurements in CO2 and H2 O.

RATIONALE: We address here the selection, preparation, calibration, storage, and use of carbonate and water working standards (WSs) for stable H, C, and O isotope measurements requiring the best possible precision and accuracy vs international reference materials (iRMs). This may be of interest for laboratories working intensively in the domains of the carbon and water cycles and of paleoclimate. METHODS: Defining a WS for stable C and O isotope studies requires combining mineralogical, physical, chemical (low Mg- and trace-carbonate), and isotopic measurements to select a carbonate fit for purpose; for water, two distinct deionized or distilled waters, with high and low δ2 H and δ18 O values, respectively, are normally used. In both cases, a strict protocol must be followed to properly qualify the WS vs the current international isotopic scales, and much attention must be paid to calculating rigorous estimates of final uncertainties on these scales. RESULTS: Two specific protocols for the selection of carbonate and water WSs are detailed. Equations for a proper estimate of uncertainties are proposed. CONCLUSIONS: The selection of WSs involves a preselection of potentially suitable materials based on initial estimates of their mineralogical, chemical, and isotopic properties and long-term stability, based on literature or previous measurements. Their precise characterization vs international isotopic scales requires a thorough analytical work in a correct sequence. When properly carried out, the proposed protocols should permit WSs to be obtained, defined vs the VSMOW and VPDB scales, with uncertainties comparable with those achieved for the characterization of iRMs.

Characterisation of new reference materials IAEA-610, IAEA-611 and IAEA-612 aimed at the VPDB δ13 C scale realisation with small uncertainty.

RATIONALE: LSVEC, the second anchor Reference Material (RM) for the VPDB δ13 C scale realisation, was introduced in 2006. In 2015, its δ13 C value was found to be drifting and, in 2017, its use as an RM for δ13 C was officially discontinued by IUPAC. New RMs of low uncertainty are needed. This paper describes the preparation and characterisation of IAEA-610, IAEA-611 and IAEA-612 (calcium carbonate, of chemical origin) which shall serve as a set of RMs aimed at anchoring the VPDB scale at negative δ13 C values. METHODS: The preparation and characterisation of IAEA-610, IAEA-611 and IAEA-612 were performed by addressing the contemporary technical requirements for RM production and characterisation (ISO Guide 35:2017). The three RMs were produced in large quantities, and the first batch was sealed into ampoules (0.5 g) to ensure the integrity of the RM during storage; additional batches were sealed for long-term storage. The most accurate method of CO2 preparation and stable isotope measurements was used, namely carbonate-H3 PO4 reaction under well-controlled conditions combined with well-tested stable isotope ratio mass spectrometry. RESULTS: The assigned values of δ13 C and associated uncertainties are based on a large number of analyses (~10 mg aliquots) performed at IAEA and address all the known uncertainty components. For aliquots down to ~100 µg, the δ13 C uncertainty is increased. The uncertainty components considered are as follows: (i) material homogeneity, (ii) value assignment against IAEA-603, (iii) potential storage effects, (iv) effect of the 17 O correction, and (v) mass spectrometer linearity and cross-contamination memory in the ion source. CONCLUSIONS: The new RMs IAEA-610, IAEA-611 and IAEA-612 have been characterised on the VPDB δ13 C scale in a mutually consistent way. The use of three RMs will allow a consistent realisation of the VPDB δ13 C scale with small uncertainty to be established, and to reach metrological compatibility of measurement results over several decades.

USGS44, a new high-purity calcium carbonate reference material for δ13 C measurements.

RATIONALE: The stable carbon isotopic (δ13 C) reference material (RM) LSVEC Li2 CO3 has been found to be unsuitable for δ13 C standardization work because its δ13 C value increases with exposure to atmospheric CO2 . A new CaCO3 RM, USGS44, has been prepared to alleviate this situation. METHODS: USGS44 was prepared from 8 kg of Merck high-purity CaCO3 . Two sets of δ13 C values of USGS44 were determined. The first set of values was determined by online combustion, continuous-flow (CF) isotope-ratio mass spectrometry (IRMS) of NBS 19 CaCO3 (δ13 CVPDB = +1.95 milliurey (mUr) exactly, where mUr = 0.001 = 1‰), and LSVEC Li2 CO3 (δ13 CVPDB = -46.6 mUr exactly), and normalized to the two-anchor δ13 CVPDB-LSVEC isotope-delta scale. The second set of values was obtained by dual-inlet (DI)-IRMS of CO2 evolved by reaction of H3 PO4 with carbonates, corrected for cross contamination, and normalized to the single-anchor δ13 CVPDB scale. RESULTS: USGS44 is stable and isotopically homogeneous to within 0.02 mUr in 100-µg amounts. It has a δ13 CVPDB-LSVEC value of -42.21 ± 0.05 mUr. Single-anchor δ13 CVPDB values of -42.08 ± 0.01 and -41.99 ± 0.02 mUr were determined by DI-IRMS with corrections for cross contamination. CONCLUSIONS: The new high-purity, well-homogenized calcium carbonate isotopic reference material USGS44 is stable and has a δ13 CVPDB-LSVEC value of -42.21 ± 0.05 mUr for both EA/IRMS and DI-IRMS measurements. As a carbonate relatively depleted in 13 C, it is intended for daily use as a secondary isotopic reference material to normalize stable carbon isotope delta measurements to the δ13 CVPDB-LSVEC scale. It is useful in quantifying drift with time, determining mass-dependent isotopic fractionation (linearity correction), and adjusting isotope-ratio-scale contraction. Due to its fine grain size (smaller than 63 µm), it is not suitable as a δ18 O reference material. A δ13 CVPDB-LSVEC value of -29.99 ± 0.05 mUr was determined for NBS 22 oil.

Preparation and characterisation of IAEA-603, a new primary reference material aimed at the VPDB scale realisation for δ13 C and δ18 O determination.

RATIONALE: NBS19 carbonate, a primary reference material (RM) for the Vienna Pee Dee Belemnite (VPDB) scale realisation introduced in 1987, was exhausted in 2009, and no primary RM was available for several years. This study describes the preparation and characterisation of a new RM, IAEA-603 (Ca-carbonate, calcite of marble origin), which shall serve as a new primary RM (replacement for NBS19) or primary calibrator aimed at the highest realisation of the VPDB scale for δ13 C and δ18 O values, including the VPDB-CO2 δ18 O scale. METHODS: IAEA-603 preparation and characterisation (value transfer) against NBS19 were performed by addressing the major modern technical requirements for the production and characterisation of RMs (ISO Guide 35). IAEA-603 was produced in a large quantity, and the first batch was sealed into ampoules (0.5 g) to ensure RM integrity during storage; four other batches were sealed for long-term storage. The most accurate method of CO2 preparation for isotope mass spectrometry was used, namely carbonate-H3 PO4 reaction under controlled conditions. RESULTS: The assigned values of δ13 C = +2.460 ± 0.010‰ and δ18 O = -2.370 ± 0.040‰ (k = 1) are based on a large number of analyses (~10 mg aliquots) performed at IAEA and address all the known uncertainty components. For aliquots down to 120 µg, the δ18 O uncertainty remains unchanged but shall be doubled for δ13 C. The uncertainty components considered are as follows: (a) material homogeneity (within and between the 5200 ampoules produced), (b) value assignment against NBS19, (c) storage effects and (d) effect of the 17 O correction. CONCLUSIONS: The new primary RM IAEA-603 replaces NBS19 in its use as the highest calibrator for the VPDB δ13 C and δ18 O scale, including the VPDB-CO2 δ18 O scale. The use of IAEA-603 will allow laboratories worldwide to establish consistent realisation of the scales for δ13 C and δ18 O values and metrological comparability of measurement results for decades. The VPDB scale definition based on NBS19 stays valid.

A New Technique to Determine the Phosphate Oxygen Isotope Composition of Freshwater Samples at Low Ambient Phosphate Concentration.

The oxygen isotope composition of dissolved inorganic phosphate (δ18Op) offers new opportunities to understand the sources and the fate of phosphorus (P) in freshwater ecosystems. However, current analytical protocols for determining δ18Op are unable to generate reliable data for samples in which ambient P concentrations are extremely low, precisely the systems in which δ18Op may provide new and important insights into the biogeochemistry of P. In this Article, we report the development, testing and initial application of a new technique that enables δ18Op analysis to be extended into such ecosystems. The twist spinning mode (TSM) protocol described here enables >1000 L of sample with a P concentration <0.016 mg P L-1 to be initially processed within the field in approximately 24 h. Combined with a new freeze-drying method to maximize the yield and minimize the contamination of silver phosphate generated for isotope ratio mass spectrometry, the TSM protocol is able to generate accurate and precise δ18Op data. We evaluated the TSM protocol using synthetic test solutions and subsequently applied the protocol to samples from locations around the Saint Lawrence River in Montreal, Canada. We believe that the novel technique reported here offers the methodological basis for researchers to extend the application of δ18Op into a much wider range of freshwater ecosystems than has been possible to date.

Improved accuracy and precision of water stable isotope measurements using the direct vapour equilibration method.

RATIONALE: A method to measure the δ2 H and δ18 O composition of pore water in soil samples using direct vapour equilibration and laser spectrometry was first described in 2008, and was rapidly adopted. Here, we describe an improved setup to measure pore water δ2 H and δ18 O values through direct vapour equilibration with a laser spectrometer, combining a liquid and a vapour mode for water isotope analyses, and resulting in improved accuracy. METHODS: We first tested new gas sampling bags as part of the equilibration protocol. Then, to assess measurement accuracy, vapour samples from equilibrated liquid waters of known isotope composition were measured in the liquid mode of the analyser using the new setup as well as the manufacturer's vapour mode. Various modes of preparing liquid water standards, namely equilibration, nebulisation, and vapourisation, were tested to determine the best calibration in terms of accuracy. Finally, the proposed modified liquid setup was validated by analysing water vapour equilibrated from soil pore water of a known composition. RESULTS: The δ2 H and δ18 O measurements were found to be more accurate by the modified liquid mode than by the factory-setup vapour mode. The strong and non-linear dependence of measured δ2 H and δ18 O values on H2 O concentration in vapour mode, especially at concentrations equal to the vapour pressure saturation typically found in laboratories, is problematic for corrections. Regarding calibration and standards, the use of two equilibrated liquid water standards was found to best calibrate measurements in the modified liquid setup. Finally, the modified liquid mode setup and its calibration, as described here, were shown to be appropriate for soil pore water analysis. CONCLUSIONS: The proposed modified setup results in more precise δ2 H and δ18 O soil pore water values than the usual protocols. An average standard deviation of 0.04‰ for δ18 O values and 0.3‰ for δ2 H values, based on 228 soil sample analyses, was obtained.

Geochemical study of carbonate concretions from the aqueduct of Nîmes (southern France): a climatic record for the first centuries AD?

The first centuries AD in the Mediterranean region have generally been associated with a warm, stable climate. High-resolution sedimentary archives sensitive to local environmental change are needed to switch from this general frame to the regional scale. Similarly to cave speleothems, laminated carbonate deposits can grow in the channels of aqueducts which transported water from karstic springs during the Roman period. The deposits of the aqueduct of Nîmes (SE France) are exceptional since they may represent several centuries of paleoenvironmental record with a seasonal resolution. δ18O, δ13C and trace elements were measured in three samples from this aqueduct. The comparison of the geochemical signals with the fine texture of the deposits evidenced the seasonal nature of the lamination observed. This allowed us to document the evolution of environment as recorded through the deposit for the period 50-275 AD. The concretions of the aqueduct of Nîmes document rather stable climatic conditions for the first three centuries AD, as well as a local vegetation change possibly linked to an increased in land use.

North America's oldest boreal trees are more efficient water users due to increased [CO2], but do not grow faster.

Due to anthropogenic emissions and changes in land use, trees are now exposed to atmospheric levels of [[Formula: see text]] that are unprecedented for 650,000 y [Lüthi et al. (2008) Nature 453:379-382] (thousands of tree generations). Trees are expected to acclimate by modulating leaf-gas exchanges and alter water use efficiency which may result in forest productivity changes. Here, we present evidence of one of the strongest, nonlinear, and unequivocal postindustrial increases in intrinsic water use efficiency ([Formula: see text]) ever documented (+59%). A dual-isotope tree-ring analysis ([Formula: see text] and [Formula: see text]) covering 715 y of growth of North America's oldest boreal trees (Thuja occidentalis L.) revealed an unprecedented increase in [Formula: see text] that was directly linked to elevated assimilation rates of [Formula: see text] (A). However, limited nutrient availability, changes in carbon allocation strategies, and changes in stomatal density may have offset stem growth benefits awarded by the increased [Formula: see text] Our results demonstrate that even in scenarios where a positive [Formula: see text] fertilization effect is observed, other mechanisms may prevent trees from assimilating and storing supplementary anthropogenic emissions as above-ground biomass. In such cases, the sink capacity of forests in response to changing atmospheric conditions might be overestimated.

Strontium isotope characterization of wines from Quebec, Canada.

The (87)Sr/(86)Sr isotope ratios were measured on grape, wine and soil samples collected in 13 commercial vineyards located in three major wine producing areas of Quebec (Canada). The soils yield Sr isotope ratios that are intimately related to the local geology and unambiguously discriminate the different producing areas. A strong relationship exists between the (87)Sr/(86)Sr isotope ratios of the wine and the grapes. This suggests that the vinification process does not alter the overall Sr budget. Although the Sr isotope ratios of the grapes do not show a strong correlation with the bulk Sr isotope composition of the soil, they do correlate strongly with the Sr isotope composition contained in the labile fraction of the soil. This indicates that the labile fraction of the soil represents the Sr reservoir available to the plant during its growth. This study demonstrates that the Sr isotope approach can be used as a viable tool in forensic science for investigating the provenance of commercial wines.

Processes governing the stable isotope composition of water in the St. Lawrence river system, Canada.

Linkages between δ(18)O-δ(2)H and hydrological processes have been investigated from isotopic time series recorded in the St. Lawrence River basin. Three stations were monitored from 1997 to 2008. They include the Ottawa River, the St. Lawrence River main channel at Montreal and the fluvial estuary. All sites depict seasonal isotopic cycles characterized by heavy isotope depletions during the snowmelt period and heavy isotope enrichments throughout the ice-free period. The data define δ(2)H-δ(18)O regression lines falling below the meteoric water line. In the Ottawa River, calculations suggest that approximately 8 % of the total inflow to the basin is lost through evaporation. In the St. Lawrence River main channel, seasonal isotopic fluctuations most likely reflect hydrological processes occurring within the Great Lakes and mixing with tributaries located downstream. In the St. Lawrence River fluvial estuary, isotopic data allow partitioning streamflow components and suggest that the recorded seasonal variations mainly respond to mixing processes.

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.

Field Metabolic Rate Is Dependent on Time-Activity Budget in Ring-Billed Gulls (Larus delawarensis) Breeding in an Anthropogenic Environment.

Environmental and behavioral factors have long been assumed to affect variation in avian field metabolic rate (FMR). However, due to the difficulties in measuring continuous behavior of birds over prolonged periods of time, complete time-activity budgets have rarely been examined in relation to FMR. Our objective was to determine the effect of activity (measured by detailed time-activity budgets) and a series of extrinsic and intrinsic factors on FMR of the omnivorous ring-billed gull (Larus delawarensis). The experiment was conducted during the incubation period when both members of the pair alternate between attending the nest-site and leaving the colony to forage in aquatic and anthropogenic environments (city, agricultural). FMR was determined using the doubly labeled water method. Time-activity budgets were extrapolated from spatio-temporal data (2-5 days) obtained from bird-borne GPS data loggers. Gulls had low FMRs compared to those predicted by allometric equations based on recorded FMRs from several seabird species. Gulls proportioned their time mainly to nest-site attendance (71% of total tracking time), which reduced FMR/g body mass, and was the best variable explaining energy expenditure. The next best variable was the duration of foraging trips, which increased FMR/g; FMR/g was also elevated by the proportion of time spent foraging or flying (17% and 8% of tracking time respectively). Most environmental variables measured did not impact FMR/g, however, the percent of time birds were subjected to temperatures below their lower critical temperature increased FMR. Time-activity budgets varied between the sexes, and with temperature and capture date suggesting that these variables indirectly affected FMR/g. The gulls foraged preferentially in anthropogenic-related habitats, which may have contributed to their low FMR/g due to the high availability of protein- and lipid-rich foods. This study demonstrates that activities were the best predictors of FMR/g in ring-billed gulls, thus providing strong support for this long-standing theory in bioenergetics.

Methane baseline concentrations and sources in shallow aquifers from the shale gas-prone region of the St. Lawrence lowlands (Quebec, Canada).

Hydraulic fracturing is becoming an important technique worldwide to recover hydrocarbons from unconventional sources such as shale gas. In Quebec (Canada), the Utica Shale has been identified as having unconventional gas production potential. However, there has been a moratorium on shale gas exploration since 2010. The work reported here was aimed at defining baseline concentrations of methane in shallow aquifers of the St. Lawrence Lowlands and its sources using δ(13)C methane signatures. Since this study was performed prior to large-scale fracturing activities, it provides background data prior to the eventual exploitation of shale gas through hydraulic fracturing. Groundwater was sampled from private (n = 81), municipal (n = 34), and observation (n = 15) wells between August 2012 and May 2013. Methane was detected in 80% of the wells with an average concentration of 3.8 ± 8.8 mg/L, and a range of <0.0006 to 45.9 mg/L. Methane concentrations were linked to groundwater chemistry and distance to the major faults in the studied area. The methane δ(1)(3)C signature of 19 samples was > -50‰, indicating a potential thermogenic source. Localized areas of high methane concentrations from predominantly biogenic sources were found throughout the study area. In several samples, mixing, migration, and oxidation processes likely affected the chemical and isotopic composition of the gases, making it difficult to pinpoint their origin. Energy companies should respect a safe distance from major natural faults in the bedrock when planning the localization of hydraulic fracturation activities to minimize the risk of contaminating the surrounding groundwater since natural faults are likely to be a preferential migration pathway for methane.

(222)Rn activity in groundwater of the St. Lawrence Lowlands, Quebec, eastern Canada: relation with local geology and health hazard.

One hundred ninety-eight groundwater wells were sampled to measure the (222)Rn activity in the region between Montreal and Quebec City, eastern Canada. The aim of this study was to relate the spatial distribution of (222)Rn activity to the geology and the hydrogeology of the study area and to estimate the potential health risks associated with (222)Rn in the most populated area of the Province of Quebec. Most of the groundwater samples show low (222)Rn activities with a median value of 8.6 Bq/L. Ninety percent of samples show (222)Rn activity lower than 100 Bq/L, the exposure limit in groundwater recommended by the World Health Organization. A few higher (222)Rn activities (up to 310 Bq/L) have been measured in wells from the Appalachian Mountains and from the magmatic intrusion of Mont-Saint-Hilaire, known for its high level of indoor radon. The spatial distribution of (222)Rn activity seems to be related mainly to lithology differences between U-richer metasediments of the Appalachian Mountains and magmatic intrusions and the carbonaceous silty shales of the St. Lawrence Platform. Radon is slightly enriched in sodium-chlorine waters that evolved at contact with clay-rich formations. (226)Ra, the parent element of (222)Rn could be easily adsorbed on clays, creating a favorable environment for the production and release of (222)Rn into groundwater. The contribution of groundwater radon to indoor radon or by ingestion is minimal except for specific areas near Mont-Saint-Hilaire or in the Appalachian Mountains where this contribution could reach 45% of the total radioactive annual dose.