Journal articles: 'Stable isotope tracers'

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Rosenblatt, J., and R. R. Wolfe. "Calculation of substrate flux using stable isotopes." American Journal of Physiology-Endocrinology and Metabolism 254, no. 4 (April 1, 1988): E526—E531. http://dx.doi.org/10.1152/ajpendo.1988.254.4.e526.

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The use of stable isotope tracers to calculate substrate kinetics in humans is favored over the use of radioactive isotopes because of their greater safety and versatility. However, potential complications not met when dealing with radioactive tracers are caused by 1) the natural occurrence of the stable isotope used as a tracer and 2) the necessity to administer the tracer in an amount that cannot be treated as "massless." We therefore found it desirable to derive a theoretically valid equation for calculating the rate of appearance, Ra, of a substrate under steady-state conditions using a stable isotope tracer. This theoretically valid equation yields results that differ from those of the equations conventionally used to calculate (endogenous) Ra in steady state. Quantitative determination of the error in one of these equations revealed that for tracers commonly used in metabolic studies the error is negligible, whereas the error made in the other equation is likely to be quite high in commonly encountered situations. Finally, to allow for proper use of different definitions of isotopic enrichment that have arisen from practical considerations, we use the results derived above to determine valid equations for Ra appropriate to the two prevalent definitions.

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Patterson, Kristine Y., and Claude Veillon. "Stable Isotopes of Minerals as Metabolic Tracers in Human Nutrition Research." Experimental Biology and Medicine 226, no. 4 (April 2001): 271–82. http://dx.doi.org/10.1177/153537020122600403.

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Enriched stable isotopes used as tracers have proven to be valuable in studies of the absorption and metabolism of minerals. Unlike radioisotopes, they can be used in high-risk population groups such as infants, children, and pregnant or lactating women. Estimates of mineral absorption can be made from the oral administration of a single tracer or from two tracers, one given orally and the other intravenously (IV). It is possible to determine the metabolism of the mineral with modeling based on the amount of the tracer or tracers in different biological samples. One of the key decisions in studies of this type is determining which enriched isotope and what amount to use. An example is given of calculations to estimate and compare the amounts of tracers needed for an absorption study. Methods for calculating the amounts of tracer in oral and IV doses are presented, and limits of detection and quantitation are discussed in terms of percent of enrichment and related to isotope ratio measurement precision. A general review of the use of mass spectrometric instruments for quantifying various stable isotopes is given.

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Cobelli, C., G. Toffolo, D. M. Bier, and R. Nosadini. "Models to interpret kinetic data in stable isotope tracer studies." American Journal of Physiology-Endocrinology and Metabolism 253, no. 5 (November 1, 1987): E551—E564. http://dx.doi.org/10.1152/ajpendo.1987.253.5.e551.

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In contrast to "weightless" radioactive tracers, stable isotope tracers have nonnegligible mass and are naturally present in the system, and the measured variable is a ratio of two isotopic species. These features do not allow stable isotopic tracer data analysis using straightforward analogy with radioactive tracer approaches, even though this practice is common. In this study, we present kinetic variables, models, and measurements for the analysis and interpretation of stable isotope tracer data. Assumptions and mathematical techniques for modeling the data when perturbation is both nonnegligible and negligible are discussed. Emphasis is placed on the rich information content of the dynamic portion of a stable isotope tracer curve and on the role of compartmental and noncompartmental modeling approaches for its interpretation. A presumed and commonly used analogy between the radioactive specific activity and stable isotopic enrichment is shown to be incorrect. We show that the proper analogue of specific activity is the tracer-to-tracee molar ratio. This variable is not a directly measurable one, but a formula is derived that allows its computation from the data. A method for reconstructing the time course in blood of the concentration component due to endogenous synthesis is presented. This allows measurement of the extent of the perturbation in the case where a nonweightless tracer is used. Special attention is given to data analysis originating from a multiple tracer experiment, a configuration necessary for studying more complex systems, e.g., the kinetics of interacting substrates.

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Kelleher, J. K., and T. M. Masterson. "Model equations for condensation biosynthesis using stable isotopes and radioisotopes." American Journal of Physiology-Endocrinology and Metabolism 262, no. 1 (January 1, 1992): E118—E125. http://dx.doi.org/10.1152/ajpendo.1992.262.1.e118.

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Important syntheses in living systems occur by condensation reactions of the type nA----1B (where n is the number of A molecules needed to synthesize 1 molecule of B). Quantitative relationships for estimating the rate of synthesis of B from radioactive and stable isotope tracers are compared. With radioisotope tracers, only a single quantity is detected, the amount of radioactivity in B. In contrast, isotopes of varying mass produce multiple mass isotopomers B that are detected using mass spectrometry. The analysis demonstrates that the rate of synthesis of B is identifiable from stable isotope data but not from radioisotope data. This results because the isotopomer distribution of B at any time after tracer addition is a function of only the multinomial distribution representing the synthesis of B from n molecules of A and two parameters representing the fractional fluxes of isotopically enriched molecules to the sampled compartment of B. The model considers the possibility that the sampled compartment of B may not reach isotopic steady state during the experiment. A graphical method for obtaining initial estimates of the two parameters is presented.

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Hungate, Bruce A., Rebecca L. Mau, Egbert Schwartz, J. Gregory Caporaso, Paul Dijkstra, Natasja van Gestel, Benjamin J. Koch, et al. "Quantitative Microbial Ecology through Stable Isotope Probing." Applied and Environmental Microbiology 81, no. 21 (August 21, 2015): 7570–81. http://dx.doi.org/10.1128/aem.02280-15.

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ABSTRACTBacteria grow and transform elements at different rates, and as yet, quantifying this variation in the environment is difficult. Determining isotope enrichment with fine taxonomic resolution after exposure to isotope tracers could help, but there are few suitable techniques. We propose a modification tostableisotopeprobing (SIP) that enables the isotopic composition of DNA from individual bacterial taxa after exposure to isotope tracers to be determined. In our modification, after isopycnic centrifugation, DNA is collected in multiple density fractions, and each fraction is sequenced separately. Taxon-specific density curves are produced for labeled and nonlabeled treatments, from which the shift in density for each individual taxon in response to isotope labeling is calculated. Expressing each taxon's density shift relative to that taxon's density measured without isotope enrichment accounts for the influence of nucleic acid composition on density and isolates the influence of isotope tracer assimilation. The shift in density translates quantitatively to isotopic enrichment. Because this revision to SIP allows quantitative measurements of isotope enrichment, we propose to call it quantitative stable isotope probing (qSIP). We demonstrated qSIP using soil incubations, in which soil bacteria exhibited strong taxonomic variations in18O and13C composition after exposure to [18O]water or [13C]glucose. The addition of glucose increased the assimilation of18O into DNA from [18O]water. However, the increase in18O assimilation was greater than expected based on utilization of glucose-derived carbon alone, because the addition of glucose indirectly stimulated bacteria to utilize other substrates for growth. This example illustrates the benefit of a quantitative approach to stable isotope probing.

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Jensen, Alexandria, William Ford, James Fox, and Admin Husic. "Improving In-Stream Nutrient Routines in Water Quality Models Using Stable Isotope Tracers: A Review and Synthesis." Transactions of the ASABE 61, no. 1 (2018): 139–57. http://dx.doi.org/10.13031/trans.12545.

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Abstract. Water quality models serve as an economically feasible alternative to quantify fluxes of nutrient pollution and to simulate effective mitigation strategies; however, their applicability is often questioned due to broad uncertainties in model structure and parameterization, leading to uncertain outputs. We argue that reduction of uncertainty is partially achieved by integrating stable isotope data streams within the water quality model architecture. This article outlines the use of stable isotopes as a response variable within water quality models to improve the model boundary conditions associated with nutrient source provenance, constrain model parameterization, and elucidate shortcomings in the model structure. To assist researchers in future modeling efforts, we provide an overview of stable isotope theory; review isotopic signatures and applications for relevant carbon, nitrogen, and phosphorus pools; identify biotic and abiotic processes that impact isotope transfer between pools; review existing models that have incorporated stable isotope signatures; and highlight recommendations based on synthesis of existing knowledge. Broadly, we find existing applications that use isotopes have high efficacy for reducing water quality model uncertainty. We make recommendations toward the future use of sediment stable isotope signatures, given their integrative capacity and practical analytical process. We also detail a method to incorporate stable isotopes into multi-objective modeling frameworks. Finally, we encourage watershed modelers to work closely with isotope geochemists to ensure proper integration of stable isotopes into in-stream nutrient fate and transport routines in water quality models. Keywords: Isotopes, Nutrients, Uncertainty analysis, Water quality modeling, Watershed.

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Ludvigson, Greg A., Aaron F. Diefendorf, Marina B. Suarez, Luis A. González, Megan C. Corcoran, Kristen Schlanser, Peter P. Flaig, et al. "Stable Isotope Tracers of Cretaceous Arctic Paleoprecipitation." Geosciences 12, no. 4 (March 23, 2022): 143. http://dx.doi.org/10.3390/geosciences12040143.

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We report estimated stable isotope compositions of depositional waters and paleoprecipitation from the Cretaceous Arctic to further elucidate the role of the global hydrologic cycle in sustaining polar warmth during that period. Estimates are based on new hydrogen isotopic analyses of n-alkane biomarkers extracted from Late Cretaceous and mid-Cretaceous terrestrial deposits in northern Alaska and the Canadian High Arctic. We integrate these new results with earlier published work on oxygen isotopic analyses of pedogenic siderites, dinosaurian tooth enamel phosphates, and pedogenic clay minerals from the same field areas. Average Late Cretaceous δD values of −143‰ VSMOW corresponded with average δ18O values of −24.1‰ VSMOW, and average mid-Cretaceous δD values of −106‰ VSMOW corresponded with average δ18O values of −22.1‰ VSMOW. The distributions of water isotope δD and δ18O values from Cretaceous Arctic deposits do not intersect with the Global Meteoric Water Line, suggesting an apparent deuterium excess ranging from about 40 to 60 per mil. We considered several possible explanations for these Cretaceous results including (1) mass-balance changes in zonal patterns of evaporation and precipitation at lower latitudes, (2) concentration of 2H in leaf tissue waters from continuous transpiration by coniferous paleofloras during the Arctic growing season, and (3) concentration of 2H in the groundwaters of methane-emitting Arctic soils.

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Coggan, Andrew R. "Use of stable isotopes to study carbohydrate and fat metabolism at the whole-body level." Proceedings of the Nutrition Society 58, no. 4 (November 1999): 953–61. http://dx.doi.org/10.1017/s0029665199001263.

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The present review discusses the advantages and limitations of using stable-isotope tracers to assess carbohydrate and fat metabolism at the whole-body level. One advantage of stable-(v. radioactive-) isotope tracers is the relative ease with which the location of a label within a molecule can be determined using selected-ion-monitoring GC-mass spectrometry (SIM-GC- MS). This technique minimizes potential problems due to label recycling, allows the use of multiple-labelled compounds simultaneously (e.g. to quantify glucose cycling), and perhaps most importantly, has led to the development of unique stable-isotope methods for, for example, quantifying gluconeogenesis. However, the limited sensitivity of SIM-GC-MS sometimes requires that relatively large amounts of a stable-isotope tracer be used, thus increasing cost and potentially altering metabolism. At least theoretically, stable- (or radioactive-) isotope tracers can also be used in conjunction with indirect calorimetry to estimate utilization of muscle glycogen or triacylglycerol stores, thus potentially circumventing the need to obtain muscle biopsies. These calculations, however, require certain critical assumptions, which if incorrect could lead to major errors in the values obtained. Despite such limitations, stable-isotope tracers provide a powerful and sometimes unique tool for investigating carbohydrate and fat metabolism at the whole-body level. With continuing advances in availability, instrumentation and methods, it is likely that stable-isotope tracers will become increasingly important in the immediate future.

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Argoud, G. M., D. S. Schade, and R. P. Eaton. "Underestimation of hepatic glucose production by radioactive and stable tracers." American Journal of Physiology-Endocrinology and Metabolism 252, no. 5 (May 1, 1987): E606—E615. http://dx.doi.org/10.1152/ajpendo.1987.252.5.e606.

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Although negative hepatic glucose production rates are physiologically impossible, they have been observed when hepatic glucose production is measured with the tracer-dilution technique during the hyperinsulinemic, euglycemic glucose clamp. Because hepatic glucose production is determined from the difference between tracer-derived glucose disposal and the known exogenous glucose infusion rate, the negative values for hepatic glucose production must result from an underestimation of glucose disposal by the tracer technique. In the current investigation, tracer-derived glucose disposal was measured in 25 subjects undergoing hyperinsulinemic, euglycemic clamps. Glucose disposal was measured with both radioactive and stable isotopes that utilize different methodologies, to determine whether discriminant metabolism of the isotopes versus methodological error leads to underestimation of tracer-derived glucose disposal. Both the radioactive and stable methodologies underestimated the exogenous glucose infusion rate during the hyperinsulinemic euglycemic clamp by 27 and 17%, respectively. Mean hepatic glucose production was -2.1 +/- 0.2 and -1.3 +/- 0.2 mg X kg-1 X min-1 as determined by the radioactive and stable isotope methodologies, respectively. Methodological error was an unlikely cause of this underestimation because it occurred with two different methodologies. The most likely explanation for underestimated rates of glucose disposal determined by the two types of isotope methodologies is discrepant metabolism of glucose tracers in comparison with unlabeled glucose.

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Jackisch, Dominik, Bi Xuan Yeo, Adam D. Switzer, Shaoneng He, Danica Linda M. Cantarero, Fernando P. Siringan, and Nathalie F. Goodkin. "Precipitation stable isotopic signatures of tropical cyclones in Metropolitan Manila, Philippines, show significant negative isotopic excursions." Natural Hazards and Earth System Sciences 22, no. 1 (January 28, 2022): 213–26. http://dx.doi.org/10.5194/nhess-22-213-2022.

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Abstract. Tropical cyclones have devastating impacts on the environment, economies, and societies and may intensify in the coming decades due to climate change. Stable water isotopes serve as tracers of the hydrological cycle, as isotope fractionation processes leave distinct precipitation isotopic signatures. Here we present a record of daily precipitation isotope measurements from March 2014 to October 2015 for Metropolitan Manila, a first-of-a-kind dataset for the Philippines and Southeast Asia. We show that precipitation isotopic variation at our study site is closely related to tropical cyclones. The most negative shift in δ18O values (−13.84 ‰) leading to a clear isotopic signal was caused by Typhoon Rammasun, which directly hit Metropolitan Manila. The average δ18O value of precipitation associated with tropical cyclones is −10.24 ‰, whereas the mean isotopic value for rainfall associated with non-cyclone events is −5.29 ‰. Further, the closer the storm track is to the sampling site, the more negative the isotopic values are, indicating that in situ isotope measurements can provide a direct linkage between isotopes and typhoon activities in the Philippines.

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Umpleby, A. Margot. "HORMONE MEASUREMENT GUIDELINES: Tracing lipid metabolism: the value of stable isotopes." Journal of Endocrinology 226, no. 3 (June 4, 2015): G1—G10. http://dx.doi.org/10.1530/joe-14-0610.

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Labelling molecules with stable isotopes to create tracers has become a gold-standard method to study the metabolism of lipids and lipoproteins in humans. There are a range of techniques which use stable isotopes to measure fatty acid flux and oxidation, hepatic fatty synthesis, cholesterol absorption and synthesis and lipoprotein metabolism in humans. Stable isotope tracers are safe to use, enabling repeated studies to be undertaken and allowing studies to be undertaken in children and pregnant women. This review provides details of the most appropriate tracers to use, the techniques which have been developed and validated for measuring different aspects of lipid metabolism and some of the limitations of the methodology.

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Corfield, Richard M., and Richard D. Norris. "Isotope Paleobiology and Paleoecology: So Why Should Paleontologists Care About Geochemistry?" Paleontological Society Papers 4 (October 1998): 1–6. http://dx.doi.org/10.1017/s1089332600000371.

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Stable isotopic techniques in geology illuminate not only variations in past climates and oceans, but also the life-histories of extinct animals, plants and protistans. This volume focuses on the ways that stable isotopes can be used as tracers of the fossil biology and ecology of long-dead organisms and ecosystems. Here, we introduce relevant aspects of stable isotope systematics and provide a summary of the papers collected in this volume. The nine contributions collected here, from some of the most eminent workers in their respective fields, explore aspects of the ecology, evolution and biology of organisms from planktonic foraminifera to dinosaurs.

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Atherton, Philip, Matthew Brook, and Daniel Wilkinson. "Stable isotope tracers in muscle physiology research." Physiology News, Winter 2016 (January 1, 2017): 25–29. http://dx.doi.org/10.36866/pn.105.25.

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Bramlet, Roland. "Radioactive and Stable Isotope Tracers in Biomedicine." Clinical Nuclear Medicine 18, no. 5 (May 1993): 455–56. http://dx.doi.org/10.1097/00003072-199305000-00027.

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Knapp, Julia L. A., Colin Neal, Alessandro Schlumpf, Margaret Neal, and James W. Kirchner. "New water fractions and transit time distributions at Plynlimon, Wales, estimated from stable water isotopes in precipitation and streamflow." Hydrology and Earth System Sciences 23, no. 10 (October 28, 2019): 4367–88. http://dx.doi.org/10.5194/hess-23-4367-2019.

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Abstract. Long-term, high-frequency time series of passive tracers in precipitation and streamflow are essential for quantifying catchment transport and storage processes, but few such data sets are publicly available. Here we describe, present, and make available to the public two extensive data sets of stable water isotopes in streamflow and precipitation at the Plynlimon experimental catchments in central Wales. Stable isotope data are available at 7-hourly intervals for 17 months, and at weekly intervals for 4.25 years. Precipitation isotope values were highly variable in both data sets, and the high temporal resolution of the 7-hourly streamwater samples revealed rich isotopic dynamics that were not captured by the weekly sampling. We used ensemble hydrograph separation to calculate new water fractions and transit time distributions from both data sets. Transit time distributions estimated by ensemble hydrograph separation were broadly consistent with those estimated by spectral fitting methods, suggesting that they can reliably quantify the contributions of recent precipitation to streamflow. We found that on average, roughly 3 % of streamwater was made up of precipitation that fell within the previous 7 h, and 13 %–15 % of streamwater was made up of precipitation that fell within the previous week. The contributions of recent precipitation to streamflow were highest during large events, as illustrated by comparing new water fractions for different discharges and precipitation rates. This dependence of new water fractions on water fluxes was also reflected in their seasonal variations, with lower new water fractions and more damped catchment transit time distributions in spring and summer compared to fall and winter. We also compared new water fractions obtained from stable water isotopes against those obtained from concentrations of chloride, a solute frequently used as a passive tracer of catchment transport processes. After filtering the chloride data for dry deposition effects, we found broadly similar new water fractions using chloride and stable water isotopes, indicating that these different tracers may yield similar inferences about catchment storage and transport, if potentially confounding factors are eliminated. These stable isotope time series comprise some of the longest and most detailed publicly available catchment isotope data sets. They complement extensive solute data sets that are already publicly available for Plynlimon, enabling a wide range of future analyses of catchment behavior.

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Yergey, Alfred L., Steven A. Abrams, Nancy E. Vieira, Richard Eastell, Laura S. Hillman, and David G. Covell. "Recent studies of human calcium metabolism using stable isotopic tracers." Canadian Journal of Physiology and Pharmacology 68, no. 7 (July 1, 1990): 973–76. http://dx.doi.org/10.1139/y90-147.

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Stable isotopes of calcium are used safely as tracers for calcium in human populations ranging in age from infants to postmenopausal women. Thermal ionization mass spectrometry is used to measure calcium isotope ratios with relative accuracies of about 1% for natural abundance ratios at precisions of about 1% relative to the mean. Perturbations of natural abundance ratios are determined for the calcium in blood, urine, and feces with a limit of detection of about 2 Δ% excess. The mathematical rationale for clinical studies of fractional absorption of dietary calcium and the kinetics of calcium's internal distribution are presented.Key words: calcium, tracers, stable isotopes, mass spectrometry.

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Preston, Tom. "Existing and Emerging Technologies for Measuring Stable Isotope Labelled Retinol in Biological Samples: Isotope Dilution Analysis of Body Retinol Stores." International Journal for Vitamin and Nutrition Research 84, Supplement 1 (December 1, 2014): 30–39. http://dx.doi.org/10.1024/0300-9831/a000186.

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This paper discusses some of the recent improvements in instrumentation used for stable isotope tracer measurements in the context of measuring retinol stores, in vivo. Tracer costs, together with concerns that larger tracer doses may perturb the parameter under study, demand that ever more sensitive mass spectrometric techniques are developed. GCMS is the most widely used technique. It has high sensitivity in terms of sample amount and uses high resolution GC, yet its ability to detect low isotope ratios is limited by background noise. LCMSMS may become more accessible for tracer studies. Its ability to measure low level stable isotope tracers may prove superior to GCMS, but it is isotope ratio MS (IRMS) that has been designed specifically for low level stable isotope analysis through accurate analysis of tracer:tracee ratios (the tracee being the unlabelled species). Compound-specific isotope analysis, where GC is interfaced to IRMS, is gaining popularity. Here, individual 13C-labelled compounds are separated by GC, combusted to CO2 and transferred on-line for ratiometric analysis by IRMS at the ppm level. However, commercially-available 13C-labelled retinol tracers are 2 - 4 times more expensive than deuterated tracers. For 2H-labelled compounds, GC-pyrolysis-IRMS has now become more generally available as an operating mode on the same IRMS instrument. Here, individual compounds are separated by GC and pyrolysed to H2 at high temperature for analysis by IRMS. It is predicted that GC-pyrolysis-IRMS will facilitate low level tracer procedures to measure body retinol stores, as has been accomplished in the case of fatty acids and amino acids. Sample size requirements for GC-P-IRMS may exceed those of GCMS, but this paper discusses sample preparation procedures and predicts improvements, particularly in the efficiency of sample introduction.

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Chandra, Subhash. "Imaging transported and endogenous calcium independently at a subcellular resolution: ion microscopy imaging of calcium stable isotopes." Proceedings, annual meeting, Electron Microscopy Society of America 50, no. 2 (August 1992): 1604–5. http://dx.doi.org/10.1017/s0424820100132650.

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Ion microscopy, based on secondary ion mass spectrometry (SIMS), is a unique isotopic imaging technique. The use of stable isotopes as tracers and their SIMS localization at a subcellular resolution has introduced a significant new approach for molecular localization and ion transport studies. A molecule of interest may be tagged with stable 2H, 13C, 15N, etc. and imaged with SIMS for its intracellular location. Stable isotopes of physiologically important elements such as calcium and magnesium provide excellent tracers for ion transport imaging studies with SIMS. in a recent study with 44Ca, the brush border region in the small intestine was observed to be the main barrier for calcium transport from the intestinal lumen to the lamina propria region in chickens suffering from Rickets, a vitamin D-deficiency condition.An example of the use of 44Ca stable isotope for imaging calcium-calcium exchange between the intracellular and extracellular calcium with SIMS is shown in figure 1. 3T3 cells were grown on high purity germanium chips to about 80% confluency.

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Brkić, Željka, Mladen Kuhta, Tamara Hunjak, and Ozren Larva. "Regional Isotopic Signatures of Groundwater in Croatia." Water 12, no. 7 (July 13, 2020): 1983. http://dx.doi.org/10.3390/w12071983.

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Tracer methods are useful for investigating groundwater travel times and recharge rates and analysing impacts on groundwater quality. The most frequently used tracers are stable isotopes and tritium. Stable isotopes of oxygen (δ18O) and hydrogen (δ2H) are mainly used as indicators of the recharge condition. Tritium (3H) is used to estimate an approximate mean groundwater age. This paper presents the results of an analysis of stable isotope data and tritium activity in Croatian groundwater samples that were collected between 1997 and 2014 at approximately 100 sites. The composition of the stable isotopes of groundwater in Croatia originates from recent precipitation and is described using two regional groundwater lines. One of them is applied to groundwater accumulated in the aquifers in the Pannonian part of Croatia and the other is for groundwater accumulated in the Dinaric karst of Croatia. The isotope content shows that the studied groundwater is mainly modern water. A mix of sub-modern and modern water is mostly accumulated in semi-confined porous aquifers in northern Croatia, deep carbonate aquifers, and (sub)thermal springs.

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Jahn, A., K. Lindsay, X. Giraud, N. Gruber, B. L. Otto-Bliesner, Z. Liu, and E. C. Brady. "Carbon isotopes in the ocean model of the Community Earth System Model (CESM1)." Geoscientific Model Development 8, no. 8 (August 5, 2015): 2419–34. http://dx.doi.org/10.5194/gmd-8-2419-2015.

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Abstract. Carbon isotopes in the ocean are frequently used as paleoclimate proxies and as present-day geochemical ocean tracers. In order to allow a more direct comparison of climate model results with this large and currently underutilized data set, we added a carbon isotope module to the ocean model of the Community Earth System Model (CESM), containing the cycling of the stable isotope 13C and the radioactive isotope 14C. We implemented the 14C tracer in two ways: in the "abiotic" case, the 14C tracer is only subject to air–sea gas exchange, physical transport, and radioactive decay, while in the "biotic" version, the 14C additionally follows the 13C tracer through all biogeochemical and ecological processes. Thus, the abiotic 14C tracer can be run without the ecosystem module, requiring significantly fewer computational resources. The carbon isotope module calculates the carbon isotopic fractionation during gas exchange, photosynthesis, and calcium carbonate formation, while any subsequent biological process such as remineralization as well as any external inputs are assumed to occur without fractionation. Given the uncertainty associated with the biological fractionation during photosynthesis, we implemented and tested three parameterizations of different complexity. Compared to present-day observations, the model is able to simulate the oceanic 14C bomb uptake and the 13C Suess effect reasonably well compared to observations and other model studies. At the same time, the carbon isotopes reveal biases in the physical model, for example, too sluggish ventilation of the deep Pacific Ocean.

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Jahn, A., K. Lindsay, X. Giraud, N. Gruber, B. L. Otto-Bliesner, Z. Liu, and E. C. Brady. "Carbon isotopes in the ocean model of the Community Earth System Model (CESM1)." Geoscientific Model Development Discussions 7, no. 6 (November 6, 2014): 7461–503. http://dx.doi.org/10.5194/gmdd-7-7461-2014.

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Abstract. Carbon isotopes in the ocean are frequently used as paleo climate proxies and as present-day geochemical ocean tracers. In order to allow a more direct comparison of climate model results with this large and currently underutilized dataset, we added a carbon isotope module to the ocean model of the Community Earth System Model (CESM), containing the cycling of the stable isotope 13C and the radioactive isotope 14C. We implemented the 14C tracer in two ways: in the "abiotic" case, the 14C tracer is only subject to air–sea gas exchange, physical transport, and radioactive decay, while in the "biotic" version, the 14C additionally follows the 13C tracer through all biogeochemical and ecological processes. Thus, the abiotic 14C tracer can be run without the ecosystem module, requiring significantly less computational resources. The carbon isotope module calculates the carbon isotopic fractionation during gas exchange, photosynthesis, and calcium carbonate formation, while any subsequent biological process such as remineralization as well as any external inputs are assumed to occur without fractionation. Given the uncertainty associated with the biological fractionation during photosynthesis, we implemented and tested three parameterizations of different complexity. Compared to present-day observations, the model is able to simulate the oceanic 14C bomb uptake and the 13C Suess effect reasonably well compared to observations and other model studies. At the same time, the carbon isotopes reveal biases in the physical model, for example a too sluggish ventilation of the deep Pacific Ocean.

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Middelburg, J. J. "Stable isotopes dissect food webs from top to the bottom." Biogeosciences Discussions 10, no. 9 (September 10, 2013): 14923–52. http://dx.doi.org/10.5194/bgd-10-14923-2013.

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Abstract. Stable isotopes have been used extensively to study food web functioning, i.e. the flow of energy and matter among organisms. Traditional food-web studies are based on the natural variability of carbon and nitrogen isotopes and are limited to larger organisms that can be physically separated from their environment. Recent developments allow isotope ratio measurements of microbes and this in turn allows then measurement of entire food webs, i.e. from small producers at the bottom to large consumers at the top. Here, I provide a concise review on the use and potential of stable isotope to reconstruct end-to-end food webs. I will first discuss food web reconstruction based on natural abundances isotope data and will then show that the use of stable isotopes as deliberately added tracers provides complementary information. Finally, challenges and opportunities for end-to-end food web reconstructions in a changing world are discussed.

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Vogt, J. "Availability of stable isotope tracers for human use." European Journal of Pediatrics 156, S1 (July 25, 1997): S9—S11. http://dx.doi.org/10.1007/pl00014281.

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Ala-aho, Pertti, Doerthe Tetzlaff, James P. McNamara, Hjalmar Laudon, and Chris Soulsby. "Using isotopes to constrain water flux and age estimates in snow-influenced catchments using the STARR (Spatially distributed Tracer-Aided Rainfall–Runoff) model." Hydrology and Earth System Sciences 21, no. 10 (October 9, 2017): 5089–110. http://dx.doi.org/10.5194/hess-21-5089-2017.

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Abstract. Tracer-aided hydrological models are increasingly used to reveal fundamentals of runoff generation processes and water travel times in catchments. Modelling studies integrating stable water isotopes as tracers are mostly based in temperate and warm climates, leaving catchments with strong snow influences underrepresented in the literature. Such catchments are challenging, as the isotopic tracer signals in water entering the catchments as snowmelt are typically distorted from incoming precipitation due to fractionation processes in seasonal snowpack. We used the Spatially distributed Tracer-Aided Rainfall–Runoff (STARR) model to simulate fluxes, storage, and mixing of water and tracers, as well as estimating water ages in three long-term experimental catchments with varying degrees of snow influence and contrasting landscape characteristics. In the context of northern catchments the sites have exceptionally long and rich data sets of hydrometric data and – most importantly – stable water isotopes for both rain and snow conditions. To adapt the STARR model for sites with strong snow influence, we used a novel parsimonious calculation scheme that takes into account the isotopic fractionation through snow sublimation and snowmelt. The modified STARR setup simulated the streamflows, isotope ratios, and snow pack dynamics quite well in all three catchments. From this, our simulations indicated contrasting median water ages and water age distributions between catchments brought about mainly by differences in topography and soil characteristics. However, the variable degree of snow influence in catchments also had a major influence on the stream hydrograph, storage dynamics, and water age distributions, which was captured by the model. Our study suggested that snow sublimation fractionation processes can be important to include in tracer-aided modelling for catchments with seasonal snowpack, while the influence of fractionation during snowmelt could not be unequivocally shown. Our work showed the utility of isotopes to provide a proof of concept for our modelling framework in snow-influenced catchments.

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Leketa, Khahliso, and Tamiru Abiye. "Using Environmental Tracers to Characterize Groundwater Flow Mechanisms in the Fractured Crystalline and Karst Aquifers in Upper Crocodile River Basin, Johannesburg, South Africa." Hydrology 8, no. 1 (March 19, 2021): 50. http://dx.doi.org/10.3390/hydrology8010050.

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Environmental isotope tracers were applied in the Upper Crocodile River Basin, Johannesburg, South Africa, to understand the groundwater recharge conditions, flow mechanisms and interactions between surface and subsurface water. Stable isotope analysis indicated that recharge into the fractured quartzite aquifer occurs through direct mechanisms. The high variability in the stable isotope signature of temporal samples from Albert Farm spring indicated the importance of multiple samples for groundwater characterization, and that using a single sample may be yielding biased conclusions. The observed inverse relationship between spring discharge and isotope signature indicated the traces of rainfall amount effect during recharge, thereby suggesting piston groundwater flow. It is deduced that a measured discharge value can be used in this relationship to calculate the isotopic signature, which resembles effective rainfall. In the shallow alluvial deposits that overlie the granitic bed-rock, piezometer levels and stable isotopes revealed an interaction between Montgomery stream and interflow, which regulates streamflow throughout the year. This suggests that caution should be taken where hydrograph separation is applied for baseflow estimates, because the stream flow that overlies such geology may include significant interflow. The hydrochemistry evolution was observed in a stream fed by karst springs. As pH rises due to CO2 degassing, CaCO3 precipitates, thereby forming travertine moulds. The values of saturation indices that were greater than zero in all samples indicated supersaturation by calcite and dolomite and hence precipitation. Through 14C analysis, groundwater flow rate in the karst aquifer was estimated as 11 km/year, suggesting deep circulation in karst structures.

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Doucet, Luc S., Oscar Laurent, Dmitri A. Ionov, Nadine Mattielli, Vinciane Debaille, and Wendy Debouge. "Archean lithospheric differentiation: Insights from Fe and Zn isotopes." Geology 48, no. 10 (June 19, 2020): 1028–32. http://dx.doi.org/10.1130/g47647.1.

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Abstract The Archean continental lithosphere consists of a dominantly felsic continental crust, made of tonalite-trondhjemite-granodiorite (TTG) and subordinate granitoids, and a cratonic lithospheric mantle, made of highly refractory peridotites. Whether they stemmed from the same process of differentiation from the primitive mantle, or were two distinct components that were physically juxtaposed, remains debated. Metal stable isotope ratios are sensitive to magmatic and metamorphic processes and do not evolve with time. Therefore, stable isotope ratios are complementary to radiogenic isotope ratios, and they allow direct comparisons to be made between different terrestrial components without age corrections. Isotopes of iron and zinc, metals ubiquitous in Earth’s lithosphere, can be tracers of lithospheric formation and evolution because they are affected by partial melting (Fe, Zn), redox state (Fe), and the presence of sulfides (Fe, Zn). Here, using stable Fe and Zn isotopic data from Archean samples of the lithospheric mantle and the continental crust, we show that Fe and Zn isotopes define a linear array, best explained by their coupled fractionation behavior during magmatic processes. Our data show that high degrees of partial melting (>30%) during the formation of the cratonic mantle and mafic protocrust, and reworking of the early crust significantly fractionate Fe and Zn isotopes. Conversely, Fe and Zn isotope ratios in the TTG are similar to those in Archean mafic rocks, suggesting an origin by fractional crystallization of basalt, and implying limited Fe and Zn isotopic fractionation, instead of partial melting of mafic crust. Moreover, the absence of Fe and Zn isotope decoupling due to redox effects, melt (fluid)–rock or sediment-rock interaction, and decarbonation indicates that subduction, at least as we understand it now, is not required to explain the Fe and Zn isotope composition of the Archean lithosphere.

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Rosenblatt, J., D. Chinkes, M. Wolfe, and R. R. Wolfe. "Stable isotope tracer analysis by GC-MS, including quantification of isotopomer effects." American Journal of Physiology-Endocrinology and Metabolism 263, no. 3 (September 1, 1992): E584—E596. http://dx.doi.org/10.1152/ajpendo.1992.263.3.e584.

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In metabolic tracer studies it is frequently useful to infuse tracers that are differently labeled variants of the same molecule. These tracers are known as isotopomers. Analysis of the enrichment of each isotopic analogue can be accomplished by gas chromatography-mass spectrometry (GC-MS). However, the raw GC-MS data must be corrected to give the information required. This paper addresses how to transform the raw GC-MS data, consisting of relative abundance ratios at specific ion masses, into relative molar ratios of tracer and tracee molecules. Several correction factors are necessary. First, the background must be measured and corrected for, since it is always present in the sample. Second, the abundances in the spectrum of the labeled molecule are different from those in the unlabeled molecule, and this proportionality "skew" is corrected. A third correction factor accounts for the overlapping spectra of two or more isotopomers that cannot be measured independently. The final correction removes the "double vision" effect that may appear in some spectra due to the presence of (M - H)+ species.

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Miljević, Nada, and Dušan Golobočanin. "Potential Use of Environmental Isotopes in Pollutant Migration Studies." Archives of Industrial Hygiene and Toxicology 58, no. 2 (June 1, 2007): 251–62. http://dx.doi.org/10.2478/v10004-007-0015-5.

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Potential Use of Environmental Isotopes in Pollutant Migration StudiesThis article presents the use of natural abundance stable isotope (hydrogen, carbon, nitrogen, oxygen, chlorine) analysis data as a tool for providing important information about the origin of contaminants, the contribution of different sources to a multi-source plume, characterisation of their complex transport (rate and mechanisms) and for evaluating the success of contaminated site remediation. Isotopic signatures of contaminants are useful tracers of their sources, while isotopic fractionation can be used to quantitatively assess the progress of an environmental process such as biodegradation. This new isotopic approach is reliable and can offer more information than traditional techniques in pollutant migration studies, particularly after waste disposal. During biological degradation of any organic compound, molecules containing lighter isotopes are degraded, and the portion of heavier isotopes in the substrate is increased, identifying specific microbial roles in biogeochemical cycling. Since isotopic fractionation is proportional to degradation, depending on the type of contamination, a microbial degradation of 50% to 99% of the initial concentration can be quantified using isotope ratio measurements.

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Middelburg, J. J. "Stable isotopes dissect aquatic food webs from the top to the bottom." Biogeosciences 11, no. 8 (April 28, 2014): 2357–71. http://dx.doi.org/10.5194/bg-11-2357-2014.

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Abstract. Stable isotopes have been used extensively to study food-web functioning, that is, the flow of energy and matter among organisms. Traditional food-web studies are based on the natural variability of isotopes and are limited to larger organisms that can be physically separated from their environment. Recent developments allow isotope ratio measurements of microbes and this in turn allows the measurement of entire food webs, in other words, from small producers at the bottom to large consumers at the top. Here, I provide a concise review on the use and potential of stable isotopes to reconstruct end-to-end food webs. I will first discuss food web reconstruction based on natural abundances isotope data and will then show that the use of stable isotopes as deliberately added tracers provides complementary information. Finally, challenges and opportunities for end-to-end food web reconstructions in a changing world are discussed.

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Wang, Pei, Yujing Deng, and Zhongwang Wei. "Modeling Investigation of Diurnal Variations in Water Flux and Its Components with Stable Isotopic Tracers." Atmosphere 10, no. 7 (July 16, 2019): 403. http://dx.doi.org/10.3390/atmos10070403.

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The isotopic compositions of water fluxes provide valuable insights into the hydrological cycle and are widely used to quantify biosphere–atmosphere exchange processes. However, the combination of water isotope approaches with water flux components remains challenging. The Iso-SPAC (coupled heat, water with isotopic tracer in soil–plant–atmosphere-continuum) model is a useful framework for simulating the dynamics of water flux and its components, and for coupling with isotopic fractionation and mixing processes. Here, we traced the isotopic fractionation processes with separate soil evaporation (Ev) and transpiration (Tr), as well as their mixing in evapotranspiration (E) for simulating diurnal variations of isotope compositions in E flux (δE). Three sub modules, namely isotopic steady state (ISS), non-steady-state (NSS), and NSS Péclet, were tested to determine the true value for the isotope compositions of plant transpiration (δTr) and δE. In situ measurements of isotopic water vapor with the Keeling-plot approach for δE and robust eddy covariance data for E agreed with the model output (R2 = 0.52 and 0.98, RMSD = 2.72‰, and 39 W m−2), illustrating the robustness of the Iso-SPAC model. The results illustrate that NSS is a better approximation for estimating diurnal variations in δTr and δE, specifically during the alternating periods of day and night. Leaf stomata conductance regulated by solar radiation controlled the diurnal variations in transpiration fraction (Tr/E). The study emphasized that transpiration and evaporation, respectively, acted to increase and decrease the δ18O of water vapor that was affected by the diurnal trade-off between them.

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Young, Vernon R., and Alfred Ajami. "Isotopes in nutrition research." Proceedings of the Nutrition Society 58, no. 1 (February 1999): 15–32. http://dx.doi.org/10.1079/pns19990004.

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The present lecture begins with a brief overview of the professional and scientific journey taken by Rudolf Schoenheimer, before turning to a discussion of the power of isotopic tracers in nutrition research. Schoenheimer's remarkable contributions to the study of intermediary metabolism and the turnover of body constituents, based initially on compounds tagged with2H and later with15N, spanned a mere decade. It is difficult, however, to overestimate the enormous impact of Schoenheimer's research on the evolution of biological science. After a relative hiatus, following Schoenheimer's death in 1941, in the use of stable nuclides as tracers in metabolism and nutrition, especially in human subjects, there is now an expanded and exciting range of techniques, experimental protocols and stable-isotope tracer compounds that are helping to probe the dynamic aspects of the metabolism of the major energy-yielding substrates, amino acids and other N-containing compounds, vitamins and mineral elements in human subjects. Various aspects of the contemporary applications of these tracers in nutrition research are covered in the present lecture.

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von Freyberg, Jana, Bjørn Studer, and James W. Kirchner. "A lab in the field: high-frequency analysis of water quality and stable isotopes in stream water and precipitation." Hydrology and Earth System Sciences 21, no. 3 (March 23, 2017): 1721–39. http://dx.doi.org/10.5194/hess-21-1721-2017.

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Abstract. High-frequency measurements of solutes and isotopes (18O and 2H) in rainfall and streamflow can shed important light on catchment flow pathways and travel times, but the workload and sample storage artifacts involved in collecting, transporting, and analyzing thousands of bottled samples severely constrain catchment studies in which conventional sampling methods are employed. However, recent developments towards more compact and robust analyzers have now made it possible to measure chemistry and water isotopes in the field at sub-hourly frequencies over extended periods. Here, we present laboratory and field tests of a membrane-vaporization continuous water sampler coupled to a cavity ring-down spectrometer for real-time measurements of δ18O and δ2H combined with a dual-channel ion chromatograph (IC) for the synchronous analysis of major cations and anions. The precision of the isotope analyzer was typically better than 0.03 ‰ for δ18O and 0.17 ‰ for δ2H in 10 min average readings taken at intervals of 30 min. Carryover effects were less than 1.2 % between isotopically contrasting water samples for 30 min sampling intervals, and instrument drift could be corrected through periodic analysis of secondary reference standards. The precision of the ion chromatograph was typically ∼ 0.1–1 ppm or better, with relative standard deviations of ∼ 1 % or better for most major ions in stream water, which is sufficient to detect subtle biogeochemical signals in catchment runoff. We installed the coupled isotope analyzer/IC system in an uninsulated hut next to a stream of a small catchment and analyzed stream water and precipitation samples every 30 min over 28 days. These high-frequency measurements facilitated a detailed comparison of event-water fractions via endmember mixing analysis with both chemical and isotope tracers. For two events with relatively dry antecedent moisture conditions, the event-water fractions were < 21 % based on isotope tracers but were significantly overestimated (40 to 82 %) by the chemical tracers. These observations, coupled with the storm-to-storm patterns in precipitation isotope inputs and the associated stream water isotope response, led to a conceptual hypothesis for runoff generation in the catchment. Under this hypothesis, the pre-event water that is mobilized by precipitation events may, depending on antecedent moisture conditions, be significantly shallower, younger, and less mineralized than the deeper, older water that feeds baseflow and thus defines the pre-event endmember used in hydrograph separation. This proof-of-concept study illustrates the potential advantages of capturing isotopic and hydrochemical behavior at a high frequency over extended periods that span multiple hydrologic events.

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Li, Jing, Fan Song, Zhicheng Bao, Hongxiang Fan, and Huawu Wu. "Insights into Shallow Freshwater Lakes Hydrology in the Yangtze Floodplain from Stable Water Isotope Tracers." Water 14, no. 3 (February 8, 2022): 506. http://dx.doi.org/10.3390/w14030506.

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Stable isotopes of lake waters are widely used to identify the relative importance of hydrological processes on the lake water balance across the ungauged landscape via the coupled-isotope tracer model. The isotopic compositions of twenty shallow freshwater lakes across the mid-lower reaches of Yangtze floodplain (MLY) were investigated in January and May of 2018. The lake-specific input water (δI) and evaporation-to-inflow (E/I) ratios were estimated to explore the specific lake hydrology across the MLY. Results showed that distinct isotopic enrichment trends in May compared with those in January, which was indicative of stronger evaporation in May. The δ18OI values of specific lakes exhibited large variability across the MLY, which may be related to the watershed properties, such as watershed area and elevation, and rainfall. The estimated E/I ratios of lakes across the MLY were below 1, which suggested that these lakes (code 1–15) are flood-dominated in the middle reaches of Yangtze River where lakes are susceptible to Three Gorges Dams regulations. By contrast, the relatively lower variability of lake E/I ratios were observed from the Yangtze River Delta (code 17–20) because these lakes with developed river network systems are highly exchanged by artificial regulation. Our investigation of lake types and corresponding isotopic evolution patterns are likely typical of other floodplain landscapes and their identification could be used to better predict hydrological responses to ongoing climate change and artificial regulations by dams.

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Lane, Andrew N., Teresa W. M. Fan, Richard M. Higashi, Jinlian Tan, Michael Bousamra, and Donald M. Miller. "Prospects for clinical cancer metabolomics using stable isotope tracers." Experimental and Molecular Pathology 86, no. 3 (June 2009): 165–73. http://dx.doi.org/10.1016/j.yexmp.2009.01.005.

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Wiederhold, Jan G. "Metal Stable Isotope Signatures as Tracers in Environmental Geochemistry." Environmental Science & Technology 49, no. 5 (February 17, 2015): 2606–24. http://dx.doi.org/10.1021/es504683e.

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Abart, R. "Geometry of stable isotope fronts: Multiple monitors and tracers." Chinese Science Bulletin 43, S1 (August 1998): 1. http://dx.doi.org/10.1007/bf02891349.

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Ganot, Yonatan, Ran Holtzman, Noam Weisbrod, Anat Bernstein, Hagar Siebner, Yoram Katz, and Daniel Kurtzman. "Managed aquifer recharge with reverse-osmosis desalinated seawater: modeling the spreading in groundwater using stable water isotopes." Hydrology and Earth System Sciences 22, no. 12 (December 6, 2018): 6323–33. http://dx.doi.org/10.5194/hess-22-6323-2018.

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Abstract. The spreading of reverse-osmosis desalinated seawater (DSW) in the Israeli coastal aquifer was studied using groundwater modeling and stable water isotopes as tracers. The DSW produced at the Hadera seawater reverse-osmosis (SWRO) desalination plant is recharged into the aquifer through an infiltration pond at the managed aquifer recharge (MAR) site of Menashe, Israel. The distinct difference in isotope composition between DSW (δ18O = 1.41 ‰; δ2H = 11.34 ‰) and the natural groundwater (δ18O = −4.48 ‰ to −5.43 ‰; δ2H = −18.41 ‰ to −22.68 ‰) makes the water isotopes preferable for use as a tracer compared to widely used chemical tracers, such as chloride. Moreover, this distinct difference can be used to simplify the system to a binary mixture of two end-members: desalinated seawater and groundwater. This approach is validated through a sensitivity analysis, and it is especially robust when spatial data of stable water isotopes in the aquifer are scarce. A calibrated groundwater flow and transport model was used to predict the DSW plume distribution in the aquifer after 50 years of MAR with DSW. The results suggest that after 50 years, 94 % of the recharged DSW was recovered by the production wells at the Menashe MAR site. The presented methodology is useful for predicting the distribution of reverse-osmosis desalinated seawater in various downstream groundwater systems.

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Wastney, M. E., I. G. Gokmen, R. L. Aamodt, W. F. Rumble, G. E. Gordon, and R. I. Henkin. "Kinetic analysis of zinc metabolism in humans after simultaneous administration of 65Zn and 70Zn." American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 260, no. 1 (January 1, 1991): R134—R141. http://dx.doi.org/10.1152/ajpregu.1991.260.1.r134.

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Zinc kinetics were studied and compared after oral simultaneous administration of two tracers, radioactive (65Zn) and stable (70Zn) isotope, to four normal human volunteers. Both tracers and zinc concentration were measured in plasma, red blood cells (RBC), urine, and feces for up to 78 days. Radioactive zinc was also measured by external counting over whole body, liver, and thigh. Data from each individual were analyzed using a compartmental model for zinc metabolism. Values calculated for absorption, fractional zinc excretion in urine, exchange with RBC, and secretion into gut using 70Zn data did not differ from values calculated using 65Zn data. Results show that human zinc metabolism can be investigated using stable isotopes as tracers to determine parameters of whole body zinc metabolism, including zinc absorption, excretion, and secretion.

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Lin, Penghui, Li Dai, Daniel R. Crooks, Leonard M. Neckers, Richard M. Higashi, Teresa W.-M. Fan, and Andrew N. Lane. "NMR Methods for Determining Lipid Turnover via Stable Isotope Resolved Metabolomics." Metabolites 11, no. 4 (March 29, 2021): 202. http://dx.doi.org/10.3390/metabo11040202.

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Lipids comprise diverse classes of compounds that are important for the structure and properties of membranes, as high-energy fuel sources and as signaling molecules. Therefore, the turnover rates of these varied classes of lipids are fundamental to cellular function. However, their enormous chemical diversity and dynamic range in cells makes detailed analysis very complex. Furthermore, although stable isotope tracers enable the determination of synthesis and degradation of complex lipids, the numbers of distinguishable molecules increase enormously, which exacerbates the problem. Although LC-MS-MS (Liquid Chromatography-Tandem Mass Spectrometry) is the standard for lipidomics, NMR can add value in global lipid analysis and isotopomer distributions of intact lipids. Here, we describe new developments in NMR analysis for assessing global lipid content and isotopic enrichment of mixtures of complex lipids for two cell lines (PC3 and UMUC3) using both 13C6 glucose and 13C5 glutamine tracers.

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Guo, Zengkui, and Michael D. Jensen. "Intramuscular fatty acid metabolism evaluated with stable isotopic tracers." Journal of Applied Physiology 84, no. 5 (May 1, 1998): 1674–79. http://dx.doi.org/10.1152/jappl.1998.84.5.1674.

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We evaluated the applicability of stable isotopic tracers to the study of intramuscular fatty acid metabolism by infusing both [U-13C]palmitate and [1-13C]oleate intravenously for 4 h into fasted conscious rats. Skeletal muscles were sequentially biopsied, and the concentration and13C enrichment of fatty acids were measured by gas chromatography/combustion/isotope ratio mass spectrometry. Throughout the study, the13C enrichment of plasma palmitate and oleate remained substantially greater than intramuscular nonesterified palmitate and oleate enrichment, which in turn was greater than intramuscular triglyceride palmitate and oleate enrichment. Fractional synthesis rates of intramuscular triglycerides in gastrocnemius and soleus were 0.267 ± 0.075 and 0.100 ± 0.030/h ( P = 0.04), respectively, as determined by using [U-13C]palmitate, and were 0.278 ± 0.049 and 0.075 ± 0.013/h ( P = 0.02), respectively, by using [1-13C]oleate. We conclude that plasma free fatty acids are a source for intramuscular triglycerides and nonesterified fatty acids; the latter are likely the synthetic precursors of the former. Uniformly and singly labeled [13C]fatty acid tracers will provide an important tool to study intramuscular fatty acid and triglyceride metabolism.

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Andrei, Francesca, Maurizio Barbieri, and Giuseppe Sappa. "Application of 2H and 18O Isotopes for Tracing Municipal Solid Waste Landfill Contamination of Groundwater: Two Italian Case Histories." Water 13, no. 8 (April 13, 2021): 1065. http://dx.doi.org/10.3390/w13081065.

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Groundwater contamination due to municipal solid waste landfills leachate is a serious environmental threat. During recent years, the use of stable isotopes as environmental tracers to identify groundwater contamination phenomena has found application to environmental engineering. Deuterium (2H) and oxygen (18O) isotopes have successfully used to identify groundwater contamination phenomena if submitted to interactions with municipal solid waste landfills leachate, with a significant organic amount. The paper shows two case studies, in central and southern Italy, where potential contamination phenomenon of groundwater under municipal solid waste landfills occurred. In both cases, isotope compositions referred to 2H and 18O highlight a δ2H enrichment for some groundwater samples taken in wells, located near leachate storage wells. The δ2H enrichment is probably caused by methanogenesis phenomena, during which the bacteria use preferentially the hydrogen “lighter” isotope (1H), and the remaining enriched the “heavier” isotope (2H). The study of the isotope composition variation, combined with the spatial trend of some analytes (Fe, Mn, Ni) concentrations, allowed to identify interaction phenomena between the municipal solid waste landfills leachate and groundwater in both case histories. Therefore, these results confirm the effectiveness of 2H isotopes application as environmental tracer of groundwater contamination phenomena due to mixing with municipal solid waste landfills leachate.

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Chen, Jie-Hua, Nadia Singh, Huimin Tay, and Thomas Walczyk. "Imbalance of iron influx and efflux causes brain iron accumulation over time in the healthy adult rat." Metallomics 6, no. 8 (2014): 1417–26. http://dx.doi.org/10.1039/c4mt00054d.

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Tuvdendorj, Demidmaa, David L. Chinkes, David N. Herndon, Xiao-Jun Zhang, and Robert R. Wolfe. "A novel stable isotope tracer method to measure muscle protein fractional breakdown rate during a physiological non-steady-state condition." American Journal of Physiology-Endocrinology and Metabolism 304, no. 6 (March 15, 2013): E623—E630. http://dx.doi.org/10.1152/ajpendo.00552.2012.

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The measurement of the fractional breakdown rate (FBR) of muscle proteins during physiological non-steady state of amino acids (AAs) presents some challenges. Therefore, the goal of the present experiment was to modify the bolus stable isotope tracer injection approach to determine both fractional synthesis rate (FSR) and FBR of leg muscle protein during a physiological non-steady state of AAs. The approach uses the traditional precursor-product principle but is modified with the assumption that inward transport of AAs is proportional to their plasma concentrations. The FBR value calculated from the threonine tracer served as a reference to evaluate the validity of the FBR measurement from the phenylalanine tracer, which was under a non-steady-state condition due to the concomitant injection of unlabeled phenylalanine. Plasma phenylalanine concentration increased more than fourfold after the bolus injection, and thereafter it decreased exponentially, whereas the threonine concentration remained stable. FBR values were similar with the two tracers [0.133 ± 0.003 and 0.148 ± 0.003%/h (means ± SE) for the phenylalanine and threonine tracers, respectively, P > 0.05]. In addition, FSR values for the two tracers were similar (0.069 ± 0.002 and 0.067 ± 0.001%/h for the phenylalanine and threonine tracers, respectively, P > 0.05), indicating that the traditional FSR approach can also be used in the non-steady state. Accordingly, net balance (NB) values were similar (−0.065 ± 0.002 and −0.081 ± 0.002%/h for the phenylalanine and threonine tracers, respectively, P > 0.05). This new method of measuring muscle protein FBR during physiological non-steady state gives reliable results and allows simultaneous measurement of muscle protein FSR and thus a calculation of NB.

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Wilkinson, Daniel J., Matthew S. Brook, Kenneth Smith, and Philip J. Atherton. "Stable isotope tracers and exercise physiology: past, present and future." Journal of Physiology 595, no. 9 (October 9, 2016): 2873–82. http://dx.doi.org/10.1113/jp272277.

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O'Brien, Kimberly O., and Steven A. Abrams. "Using stable isotope tracers to study bone metabolism in children." Journal of Physiology 597, no. 5 (July 17, 2018): 1311–19. http://dx.doi.org/10.1113/jp275452.

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Preston, Tom, and Christine Slater. "Mass spectrometric analysis of stable-isotope-labelled amino acid tracers." Proceedings of the Nutrition Society 53, no. 2 (July 1994): 363–72. http://dx.doi.org/10.1079/pns19940042.

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Williams, Alan E. "Stable isotope tracers: natural and anthropogenic recharge, Orange County, California." Journal of Hydrology 201, no. 1-4 (December 1997): 230–48. http://dx.doi.org/10.1016/s0022-1694(97)00042-5.

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Nijenhuis, Ivonne, Nicole Stelzer, Matthias Kästner, and Hans-H. Richnow. "Sensitive Detection of Anaerobic Monochlorobenzene Degradation Using Stable Isotope Tracers." Environmental Science & Technology 41, no. 11 (June 2007): 3836–42. http://dx.doi.org/10.1021/es0621896.

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Kim, Il-Young, Sanghee Park, Jiwoong Jang, Yeongmin Kim, and Hee-Joo Kim. "Exploring Human Muscle Dynamics In Vivo Using Stable Isotope Tracers." Annals of Clinical Nutrition and Metabolism 14, no. 2 (December 1, 2022): 40–49. http://dx.doi.org/10.15747/acnm.2022.14.2.40.

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Watson, Elizabeth Burke, Alejandro Hinojosa-Corona, Johannes R. Krause, Juan Carlos Herguera, Julianna McDonnell, Karen Raquel Villegas Villegas Manríquez, Michelle E. Gannon, and Andrew B. Gray. "Lagoon Biogeochemical Processing is Reflected in Spatial Patterns of Sediment Stable Isotopic Ratios." Journal of Marine Science and Engineering 8, no. 11 (November 3, 2020): 874. http://dx.doi.org/10.3390/jmse8110874.

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The spatial analysis of biota, particulate organic matter, and sediments for stable isotopes of carbon (δ13C), nitrogen (δ15N), and sulfur (δ34S) have proved useful for identifying patterns in productivity, nutrient pollution, and relationships between biological and physiochemical variables at the local and global scales. Yet such approaches are rarely applied to studies of lagoon or estuarine metabolism. Focusing on Bahía San Quintín, a heterotrophic seagrass-dominated lagoon on the Pacific coast of Baja California, México, we report on spatial patterns in surficial sediment CNS stable isotopic ratios as tracers of lagoon biogeochemical function. Stable nitrogen isotopes highlighted potential spatial variability in the balance between denitrification and nitrogen-fixation within the lagoon and identified an association between elevated δ15N levels and oyster culture, suggesting that oyster presence may be enhancing N2 production. Spatial patterns in δ34S covaried with sediment particle size, underlining the importance of sediment texture in determining the depth of sub-oxic-anoxic redox zones. Sediment carbon stable isotope ratios highlighted the lack of incorporation of seagrass carbon into seagrass meadow sediments, thus emphasizing the importance of phytoplankton or microphytobenthos for carbon accumulation in seagrass meadows. This report highlights the value of sediment isotopic values in corroborating spatial patterns in estuarine metabolism or macronutrient processing identified from chamber or flux-based studies. Stable isotope mapping can provide a useful addition to assessment of estuarine metabolism, or act as a stand-alone tool for generating hypotheses, identifying the influence of spatial gradients, and/or suggesting prime locations for investigation of microbial abundance or function.

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Journal articles on the topic 'Stable isotope tracers'

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