Tracer Loss Research Articles

Geochemical influences on methanogenic groundwater from a low rank coal seam gas reservoir: Walloon Subgroup, Surat Basin

Hydrochemical data responds at a much slower rate to changes in groundwater conditions than does the propagation of hydraulic pressure, and therefore may provide more insight to groundwater flow paths. In low rank coal measures, where gas is biogenic, it is important to understand the fluid-rock and microbial interactions that affect the spatial and temporal distribution of groundwater composition. Pressure data may not reflect true groundwater conditions pre-anthropogenic influence, nor does it provide information on the main drivers of groundwater composition, actual aquifer behaviour or even prove groundwater flow.This study uses a process-based approach to interpret a combination of tracer (36Cl, 14C, 87Sr/86Sr, 18O/16O) and hydrochemical data obtained from coal seam gas production wells to identify the main geochemical processes and thus controls on the groundwater composition in different coal seam producing areas of the Walloon Subgroup, Surat Basin, Australia. This is arguably one of the largest coal seam gas producing regions in the world. Tracer data measured in this study show that the Walloon Subgroup behaves as a stagnant aquitard, as indicated by the almost total loss of cosmogenic tracers over relatively short groundwater flow distances (~15 km), suggestive of very low ground water flow velocities. The range of 36Cl is 9.0 to 23.8 (x 10−15) while the 36Cl values across the Undulla anticline in the eastern edge of the basin, are essentially the same (12.2–14.7) within analytical error. It is argued that these isotopic values represent secular equilibrium for the Walloon Subgroup. Radiometric carbon (14C) levels across all three production areas (Roma, Undulla Nose, Kogan Nose) are also too low (range = 0.12–1.95 pMC) for viable field interpretation largely owing to the long residence time of the groundwater and the local activity of methanogens. Groundwater flow velocity was estimated to be <0.1 m/y, which is significantly less than the 0.7 m/y recently reported for the underlying Hutton Sandstone.As a result of the low groundwater flow velocities, trends in geochemistry are visible only in production regions proximal to the subcrop. At flow distances greater than 10–15 km from subcrop, several low-temperature interactions (cation exchange, silicate weathering, matrix diffusion and hyperfiltration) start to influence groundwater composition. Shallow subsurface chemical and microbial reactions may initially dominate the geochemical composition of the meteoric groundwater, but this is then overprinted by the actions of sulfate reducers and methanogens, resulting in groundwater with the typical geochemical characteristics similar to other coal bed methane groundwater in basins across the world (low SO4, Ca, Mg and high HCO3, Na, Cl). As distance and depth increase further, low temperature fluid-rock interactions then begin to influence the groundwater composition.This holistic, process-based approach applied to a combination of cosmogenic and stable isotopes, and standard hydrochemical data interpreted against basin lithology has enabled a more comprehensive picture on the behaviour of the groundwater of the Walloon Subgroup and is applicable to the study of other sedimentary basins.

Temporal fate of 15N and 14C leaf-fed to red and white clover in pure stand or mixture with grass – Implications for estimation of legume derived N in soil and companion species

The supply of nitrogen (N) from legumes is a key in maintaining soil N fertility in plant production with low fertilizer N inputs. Leaf-feeding of isotope tracers is a commonly used methodology to study the flow of carbon (C) and N from legumes into soil and companion plants. Here we investigated the temporal fate of 15N and 14C fed as a single-pulse via leaves to red and white clover in pure stands and in mixtures with grass in order to investigate the suitability of leaf-labeling for estimation of rhizodeposition and N transfer. The 15N was present in all sampled plant parts of the legumes, soil and companion ryegrass already at the first day after the end of the labeling period. Thereafter, tracer levels remained surprisingly constant especially in the legume root parts. The rapid appearance of 15N in soil was most likely dominated by tracer in unrecovered root parts, whereas 15N in companion ryegrass was most likely caused by root exudation. After the rapid phase of tracer translocation, a second slower phase was best described by tracer loss from shoot tissue (phyllodeposition), rather than turnover of root and nodules with time. We conclude that labeling studies with multiple pulses need intensive labeling schemes and greater temporal sampling resolution in order to avoid bias and determine dominating sources of tracer moving from legumes to companion species for N transfer estimation. The study also underlined the importance of identifying the dominating sources of legume C and N losses to soil in order to select the correct approach to estimate rhizo- and phyllodeposition.

Fluorescent tracers to evaluate pesticide dissipation and transformation in agricultural soils

This study evaluates the mobility and dissipation of two organic fluorescent tracers (uranine, UR and sulforhodamine-B, SRB) in soil from an agricultural field. Two plot experiments were conducted for 2.5months in 2012 and 2016 to compare the behavior of reactive fluorescent tracers (UR and SRB) to the chloroacetanilide herbicide S-metolachlor (S-MET) and bromide (BR), used as a traditional conservative tracer. SRB in top soil closely mimicked the gradual recession of S-MET, while BR overrated both top soil mobility and slow leaching of S-MET in the soil column. In contrast, UR quickly receded in the soil and was entirely dissipated at the end of the study periods. Instead, a strong fluorescent signal that was stable against acidification, and non-traceable in background samples, gradually developed at an excitation wavelength of 510nm in samples from the uppermost soil layer starting 40 (2012) and 22 (2016) days after tracer application. We hypothesize that (bio-)chemical transformation of UR accelerated tracer loss with concomitant formation of the specific transformation product TP510. By LC-MS/MS analysis we propose a probable molecular structure of TP510 and sulfonation as one likely transformation process. Overall, we anticipate our results to be a starting point to use fluorescent tracers in longer term (>2months) agricultural soil studies as a proxy for S-MET and possibly also other organic pesticides, as they are non-conservative in unsaturated soil and may follow similar dissipation and transformation patterns. At the same time their analysis is less costly and they pose smaller environmental risks.

Deproteinization assessment using isotopically enriched compounds to trace the coprecipitation of low-molecular-weight selenium species with proteins

Studies have shown that information related to the presence of low-molecular-weight metabolites is frequently lost after deproteinization of complex matrices, such as blood and plasma, during sample preparation. Therefore, the effect of several deproteinization reagents on low-molecular-weight selenium species has been compared by species-specific isotope labeling. Two isotopically enriched selenium tracers were used to mimic models of small inorganic anionic (77Se-selenite) and organic zwitterionic (76Se-selenomethionine) species. The results presented here show that the use of a methanol-acetonitrile-acetone (1:1:1 v/v/v) mixture provided approximately two times less tracer loss from plasma samples in comparison with the classic procedure using acetonitrile, which may not be optimal as it leads to important losses of low-molecular-weight selenium species. In addition, the possible interactions between selenium tracers and proteins were investigated, revealing that both coprecipitation phenomena and association with proteins were potentially responsible for selenite tracer losses during protein precipitation in blood samples. However, coprecipitation phenomena were found to be fully responsible for losses of both tracers observed in plasma samples and of the selenomethionine tracer in blood samples. This successfully applied strategy is anticipated to be useful for more extensive future studies in selenometabolomics.

Modification of Rhodamine WT tracer tests procedure in activated sludge reactors

One of the tracers recommended for use in wastewater treatment plants and natural waters is Rhodamine WT, which is a fluorescent dye, allowing to work at low concentrations, but may be susceptible to sorption to activated sludge flocs and chemical quenching of fluorescence by dissolved water constituents. Additionally raw sewage may contain other natural materials or pollutants exhibiting limited fluorescent properties, which are responsible for background fluorescence interference. This paper presents the proposed modifications to the Rhodamine WT tracer tests procedure in activated sludge reactors, which allow to reduce problems with background fluorescence and tracer loss over time, developed on the basis of conducted laboratory and field experiments.

Stream tracer breakthrough curve decomposition into mass fractions: A simple framework to analyze and compare conservative solute transport processes

AbstractEcological functions are coupled to the physical transport of water and solutes in streams. Transport of conservative tracers in lotic systems is subject to the processes of advection, dispersion, transient storage, and mass loss to groundwater. Stream tracer experiments and the simulation of observed tracer breakthrough curve (BTC) data with 1‐D numerical transient storage models (TSMs) are commonly used to quantify these processes. Results from TSMs can be useful, but issues related to model appropriateness and parameter identifiability suggest a need for conceptually simpler approaches to BTC analyses. We present a new approach to analyze BTCs to quantify the amount of stream water transported by each dominant process. BTCs are analyzed to parse the total quantity of injected tracer mass into three dominant process domains: advection and dispersion, transient storage, and gross loss of tracer. This method can be used to quantify the relative influence of transport processes within, and among streams, and estimate the proportion of stream water associated with each mode of transport. As proof of concept, we apply this approach to conservative tracer injections on two streams of contrasting morphology. Application of this method indicates that transport of injected solute mass in an alluvial stream is dominated by advection and dispersion, relative to a beaded, peat‐bottomed stream, where more tracer mass transport was found to be associated with longer timescale transient storage processes. This approach provides a simple, inexpensive, and useful quantification of dominant transport processes and provides an additional tool for analyzing experimental BTC data.

Sr–Nd elements and isotopes as tracers of dust input in a tropical soil chronosequence

Although Hainan Island is located in one of the relative least dusty regions in China, Asian dust has been identified in Hainan soils. We used Sr and Nd isotopes of soils, saprolite, bedrocks and Asian dust to not only identify long-range transported dust but also quantify the dust contribution to Hainan soils. Sr and Nd isotopic compositions of the soils are clearly affected by dust deposition. The soils in near-surface horizons have 87Sr/86Sr values as high as 0.7193 that are more radiogenic than the basalts, indicating involvement of Asian dust; whereas deep horizons show a dominantly basaltic signature (87Sr/86Sr=0.7038). The εNd(0) values for Hainan soils range from −6.46 to 1.85. The higher value closely approximates the values measured for the Hainan lava, and the lower value indicates the fingerprint of the Asian dust. The 87Sr/86Sr and εNd(0) values for soils also show a progressive trend with time, which implies that dust accumulates with soil age. We calculated the dust accretion rates for Sr-based and Nd-based to quantify the dust contributions to soils. The estimate of dust accreted shows an approximate increasing trend with the ages of soils for Sr-based and Nd-based methods. The soils in the old sites are likely to have undergone long-term dust input and accumulated high dust levels. We also find excellent agreement in the amount of dust present and dust accretion rates based on the two tracers at the 300ka site and the 1120ka site, respectively. Besides lower dust deposition in the Pliocene epoch than the late Quaternary over eastern Eurasian, the loss of mineralogical and geochemical tracers over million year time scales also may lead to underestimates of time-averaged dust deposition rates in the old sites. Therefore, the young sites (180ka and 300ka) should provide more realistic estimates of average dust accretion rates. The importance of dust in the tropical Hainan soil chronosequence highlights the significance of dust accretion to soils globally.

Investigating the sensitivity of surface-level nitrate seasonality in Antarctica to primary sources using a global model

Determining the sources of total nitrate (TNIT ≡ NO3− + HNO3) reaching Antarctica is a long-standing challenge. Here we analyze the monthly sensitivity of surface-level TNIT in Antarctica to primary sources using a global 3-D chemical transport model, GEOS-Chem, and its adjoint. Modeled seasonal variation of TNIT concentrations shows good agreement with several measurement studies, given that the lack of post-depositional processing in the model leads to an expected underestimate of maximum values in November through January. Remote NOx sources have the greatest impact May–July, during when the model background concentrations are sensitive to NOx emissions from fossil fuel combustion, soil, and lightning originating from 25°S to 65°S. In this season, NOx is transported to Antarctica as TNIT, which is formed above continental source regions at an altitude of 5–11 km. In other seasons, more NOx is transported as a reservoir species (e.g., peroxyacetyl nitrate, PAN) through the free troposphere, transforming into TNIT within a cone of influence that extends to 35°S and above 4 km altitude. Photolysis of PAN over Antarctica is the main driver of modeled NOx seasonality. Stratospheric production and loss of tracers are relatively unimportant in monthly sensitivities in GEOS-Chem, driving only a few percent of surface level variability of TNIT. A small peak concentration in August is captured by the model, although some measured values in August fall outside the range of simulated concentrations. Modifications to the model to represent sedimentation of polar stratospheric clouds (PSCs) lead to increased surface level August TNIT concentrations. However, this simple representation does not explicitly account for PSC particle deposition or disappearance of the tropopause in the middle of winter, and thus the influence of stratospheric nitrate sources estimated in this study is likely a lower bound.

Pathways of Infusate Loss during Convection-Enhanced Delivery into the Putamen Nucleus

Background: New strategies aiming to treat Parkinson’s disease, such as delivery of trophic factors via protein infusion or gene transfer, depend upon localized intracerebral infusion, mainly into the putamen nucleus. Convection-enhanced delivery (CED) has been proposed as a method to improve intracerebral distribution of therapies. Yet analysis of controversial results during the clinical translation of these strategies suggests that intracerebral misdistribution of infusate may have affected the outcomes by limiting the amount of treatment into the target region. Objectives: This study aimed to identify possible pathways of infusate loss and their relative impact in the success of targeted CED into the postcommissural ventral putamen nucleus. Methods: Thirteen adult macaque monkeys received intraputaminal CED infusions of 100 µl of 2.0 m<smlcap>M</smlcap> gadoteridol and bromophenol blue (0.16 mg/ml) solution at a rate of 1.0 µl/min under intraoperative magnetic resonance imaging (MRI) guidance. Quantitative maps of infusate concentration were computed at 10-min intervals throughout the procedure in a 3-Tesla MRI scanner. The fraction of tracer lost from the putamen as well as the path of loss were evaluated and quantified for each infusion. Results: All injections (total 22) were successfully placed in the ventral postcommissural putamen nucleus. Four major paths of infusate loss from the putamen were observed: overflow across putamen boundaries, perivascular flow along large blood vessels, backflow along the inserted catheter and catheter tract leakage into the vacated catheter tract upon catheter removal. Overflow loss was observed within the first 30 µl of infusion in all cases. Measurable tracer loss following the path of an artery out of the putamen was observed in 15 cases, and in 8 of these cases, the loss was greater than 10% of infusate. Backflow that exited the putamen was observed in 4 cases and led to large loss of infusate (80% in 1 case) into the corona radiata. Loss into the vacated catheter tract amounted only to a few microliters. Conclusions: Our analysis demonstrates that after controlling for targeting, catheter type, infusion rate and infusate, the main issues during surgical planning are the identification of appropriate infusate volume that matches the target area, as well as mapping the regional vasculature as it may become a pathway for infusate loss. Most importantly, these results underscore the significance of presurgical planning for catheter placement and infusion, and the value of imaging guidance to ensure targeting accuracy.

Measuring gross N2O production in soil: a reply to Well and Butterbach‐Bahl

Measuring gross <scp><scp>N₂O</scp></scp> production in soil: a reply to <scp>W</scp>ell and <scp>B</scp>utterbach‐<scp>B</scp>ahl

Field demonstration and evaluation of the Passive Flux Meter on a CAH groundwater plume

This study comprises the first application of the Passive Flux Meter (PFM) for the measurement of chlorinated aliphatic hydrocarbon (CAH) mass fluxes and Darcy water fluxes in groundwater at a European field site. The PFM was originally developed and applied to measurements near source zones. The focus of the PFM is extended from near source to plume zones. For this purpose, 48 PFMs of 1.4 m length were constructed and installed in eight different monitoring wells in the source and plume zone of a CAH-contaminated field site located in France. The PFMs were retrieved, sampled, and analyzed after 3 to 11 weeks of exposure time, depending on the expected contaminant flux. PFM evaluation criteria include analytical, technical, and practical aspects as well as conditions and applicability. PFM flux data were compared with so-called traditional soil and groundwater concentration data obtained using active sampling methods. The PFMs deliver reasonable results for source as well as plume zones. The limiting factor in the PFM applicability is the exposure time together with the groundwater flux. Measured groundwater velocities at the field site range from 2 to 41 cm/day. Measured contaminant flux data raise up to 13 g/m(2)/day for perchloroethylene in the plume zone. Calculated PFM flux averaged concentration data and traditional concentration data were of similar magnitude for most wells. However, both datasets need to be compared with reservation because of the different sampling nature and time. Two important issues are the PFM tracer loss during installation/extraction and the deviation of the groundwater flow field when passing the monitoring well and PFM. The demonstration of the PFM at a CAH-contaminated field site in Europe confirmed the efficiency of the flux measurement technique for source as well as plume zones. The PFM can be applied without concerns in monitoring wells with European standards. The acquired flux data are of great value for the purpose of site characterization and mass discharge modeling, and can be used in combination with traditional soil and groundwater sampling methods.

(11)C-PET imaging reveals transport dynamics and sectorial plasticity of oak phloem after girdling.

Carbon transport processes in plants can be followed non-invasively by repeated application of the short-lived positron-emitting radioisotope 11C, a technique which has rarely been used with trees. Recently, positron emission tomography (PET) allowing 3D visualization has been adapted for use with plants. To investigate the effects of stem girdling on the flow of assimilates, leaves on first order branches of two-year-old oak (Quercus robur L.) trees were labeled with 11C by supplying 11CO2-gas to a leaf cuvette. Magnetic resonance imaging gave an indication of the plant structure, while PET registered the tracer flow in a stem region downstream from the labeled branches. After repeated pulse labeling, phloem translocation was shown to be sectorial in the stem: leaf orthostichy determined the position of the phloem sieve tubes containing labeled 11C. The observed pathway remained unchanged for days. Tracer time-series derived from each pulse and analysed with a mechanistic model showed for two adjacent heights in the stem a similar velocity but different loss of recent assimilates. With either complete or partial girdling of bark within the monitored region, transport immediately stopped and then resumed in a new location in the stem cross-section, demonstrating the plasticity of sectoriality. One day after partial girdling, the loss of tracer along the interrupted transport pathway increased, while the velocity was enhanced in a non-girdled sector for several days. These findings suggest that lateral sugar transport was enhanced after wounding by a change in the lateral sugar transport path and the axial transport resumed with the development of new conductive tissue.

Seedling establishment in eelgrass: seed burial effects on winter losses of developing seedlings

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 448:197-207 (2012) - DOI: https://doi.org/10.3354/meps09612 Seedling establishment in eelgrass: seed burial effects on winter losses of developing seedlings Scott R. Marion*, Robert J. Orth Virginia Institute of Marine Science, College of William and Mary, Gloucester Point, Virginia 23062, USA *Email: smarion@vims.edu ABSTRACT: Constraints on the transition of seeds to seedlings have the potential to control plant dispersal and persistence. We investigated the processes leading to low initial seedling establishment in eelgrass Zostera marina through a manipulative field experiment assessing the relative importance of germination failure and seedling loss during the winter. Seed plots were established in October at 3 unvegetated sites in the Chesapeake Bay (USA) region, with seeds either at the sediment surface or buried at 2 to 3 cm. Emerging seedlings were monitored at 6 wk intervals between December and April using a video camera, and seed germination was tracked in separate destructively-sampled plots. Sediment height change was measured, and sediment disturbance depth was estimated by deploying cores layered with tracer particles and examining tracer loss upon core retrieval. We found a low rate of seedling establishment 6 mo after seeding (1.2, 3.8, and 2.8% for surface seeds at the 3 sites) that was largely due to seed and seedling loss rather than to germination failure, with 90% of seeds retrieved after December having germinated. Seed burial significantly enhanced seedling establishment at 2 of 3 sites (40.4, 16.8, and 10.3% establishment for buried seeds). Seed loss occurred mostly within the first month of the experiment, and was most severe for seeds at the sediment surface. Indicator core results showed widespread disturbance of sediments to depths that could have dislodged early seedlings developing from surface seeds, and to a lesser degree seedlings from buried seeds. Our findings help identify the nature and timing of a substantial Z. marina seedling establishment bottleneck in our region, and show that some of the key processes pivotal to Z. marina recruitment dynamics and optimal restoration strategies involve physical sediment−seedling interactions rather than seed germination. KEY WORDS: Seagrass · Recruitment limitation · SAV restoration · Sediment disturbance · Wave energy · Germination · Seed burial Full text in pdf format PreviousNextCite this article as: Marion SR, Orth RJ (2012) Seedling establishment in eelgrass: seed burial effects on winter losses of developing seedlings. Mar Ecol Prog Ser 448:197-207. https://doi.org/10.3354/meps09612 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 448. Online publication date: February 23, 2012 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2012 Inter-Research.

13C tracer recovery in human stools after digestion of a fat‐rich meal labelled with [1,1,1‐13C3]tripalmitin and [1,1,1‐13C3]triolein

Lipid metabolism studies focus mainly on oxidation and storage but rarely on faecal elimination, which is needed to assess total lipid distribution during the postprandial period. The purpose of the present work was to set up and validate the analysis of lipid tracers in stools, with an aim of later using this methodology in studies of postprandial lipid tracer metabolism. Eight subjects received a mixture of [1,1,1-(13)C3]tripalmitin and [1,1,1-(13)C3]triolein with a fat-rich meal. The nature and amounts of (13)C lipids excreted in stools during 3 days post-dose were determined by gas chromatography/mass spectrometry (GC/MS) and gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS) analysis of fatty acid methyl esters (FAMEs) from total fatty acid (TFA), free fatty acid (FFA) and triacylglycerol (TAG) fractions. The results were expressed as the Cumulative Tracer Recovery of the administered dose (CTR%). The quantities and labelling of FAMEs were higher in FFA than in TAG, indicating that label loss was not due to a lack of digestive lipase activity. The labelling was higher for C16:0 than for C18:1. The CTRs were 7.03 ± 0.77% and 6.87 ± 0.91%, respectively, in TFA and FFA for [1-(13)C] C16:0, while they were 0.60 ± 0.15% and 0.51 ± 0.11% for [1-(13)C] C18:1 (mean ± sem). By studying the kinetics of lipid excretion from subjects, two groups emerged. The first one showed rapid excretion in stool #1, whereas the second showed slower excretion in stools #2-#3. A significant difference was found in the FFA in stool #1 for C16:0 (p < 0.01) and C18:1 (p < 0.05). Individual excretion kinetics showed marked variability. Nevertheless, the CTR over the 3-day study period was substantial and homogenous for all subjects. These results confirm that the assessment of faecal elimination is of great importance when establishing total lipid distribution during the postprandial period and validate the analysis of cumulative tracer loss during 72 h post-tracer ingestion.

Determination of Inorganic Salt Solubility at a Temperature above the Boiling Point of Water by Multiple Headspace Extraction Gas Chromatography

This paper describes a novel method for the determination of the solubility of sodium carbonate and sodium sulfate in single- and bisalt aqueous solutions at 110 °C, using multiple headspace extraction gas chromatography (MHE-GC). Both benzene alcohol and methanol were used as the tracer compounds whose vapor–liquid equilibrium (VLE) partition coefficients (CV/CL) are related to the concentration of salt in the studied solution, thereby indirectly providing solubility data. During the MHE process, small amounts of water are removed stepwise by a series of headspace vapor extractions, which simulates the evaporation process, resulting in an increase in the salt concentration in the solution and a decrease in the amount of tracer in the headspace vapor. Eventually, the salt concentration reaches saturation (the limit of solubility), a transition point that can be identified experimentally via GC, because of the different behaviors of the tracer loss before and after the salt saturation point. Knowing the salt concentration in the initial solution and gathering data on the amount of water lost in reaching the transition point, we calculated the solubilities of sodium sulfate and sodium carbonate at 110 °C as 30.6 and 31.9 wt %, respectively, which are in good agreement with data reported previously, using more-complex conventional methods. The method reported here has several advantages, including its simplicity and ease of automation.

Advantage of predictive modeling in tracer studies

Letters to the EditorAdvantage of predictive modeling in tracer studiesStewart RussellStewart RussellMarc and Ruti Bell Vascular Biology Program, Department of Medicine (Cardiology), New York University School of Medicine, New York, New YorkPublished Online:01 Jan 2011https://doi.org/10.1152/ajpendo.00537.2010MoreSectionsPDF (27 KB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations to the editor: Sorensen et al. (1) compare the production rate of triglyceride, as calculated from a bolus injection decay curve, to that obtained from a primed constant infusion curve of the specific activity of radiolabeled tracer. They note a difference in the two rates and choose the constant infusion as the more accurate method. But is it? The bi-exponential model is a predictive model and uses measurements of the disappearance of tracer from the plasma compartment, over a limited period of time, to predict the plasma concentration of tracer for all time. The integral of this function over all time is the specific activity of the injected dose, which is used to calculate the production rate. On the other hand, the steady-state infusion model relies on measurement of the appearance of tracer in the plasma and therefore is only appropriate once the bi-directional flux of tracer between compartments has reached a steady state. At equilibrium, the primed constant infusion method will give the same production rate as the bolus. That it is different suggests that the time course is long enough to fit a bi-exponential decay curve but not long enough to establish steady state. In the bolus experiment, if tracer loss from the fast compartment is very rapid, its effect is negligible by the end of the experiment, which allows a second, slower decay curve to be detected. But in constant infusion, tracer that is fast to leave but slow to return will make the specific activity of the injected dose appear artificially low until equilibrium is reached. This is the power of the exponential function when used in this context: if the decay data fit a bi-exponential model, then all future information about the transfer of tracer between compartments will be described by the shape of the predicted curves. This two-pool model was introduced in these pages by Sapirstein et al. (2) as a simplified method to avoid possible errors in estimation attendant upon constant infusion methods. The specific activity of the rapid pool, as calculated from Sørensen, et al. solution of the bi-exponential model, is 22% of the total specific activity; if this missing amount is added to the measured specific activity in the constant infusion experiment, then the calculated production rates are the same. The more accurate number is derived from the bi-exponential equation, not the steady-state experiment, and, as the authors correctly conclude, is a strong indicator of rapid recycling of VLDL-TG through the periphery.DISCLOSURESNo conflicts of interest are reported by the author.REFERENCES1. Sørensen LP, Gormsen LC, Nielsen S. VLDL-TG kinetics: a dual isotope study for quantifying VLDL-TG pool size, production rates, and fractional oxidation in humans. Am J Physiol Endocrinol Metab 297: E1324–E1330, 2009.Link | ISI | Google Scholar2. Sapirstein LA, Vidt DG, Mandel MJ, Hanusek G. Volumes of distribution and clearances of intravenously injected creatinine in the dog. Am J Physiol 181: 330–336, 1955.Link | ISI | Google ScholarAUTHOR NOTESAddress for reprint requests and other correspondence: S. Russell, Marc and Ruti Bell Vascular Biology Program, Department of Medicine (Cardiology), NYU School of Medicine, Smilow Bldg., 522 1st Ave., 8th Floor, New York, NY 10016 (e-mail: stewart.[email protected]org). Download PDF Previous Back to Top Next FiguresReferencesRelatedInformation Related ArticlesReply to Russell: VLDL-TG kinetics: how to interpret a dual-isotope study 01 Jan 2011American Journal of Physiology-Endocrinology and Metabolism More from this issue > Volume 300Issue 1January 2011Pages E252-E252 Copyright & PermissionsCopyright © 2011 the American Physiological Societyhttps://doi.org/10.1152/ajpendo.00537.2010PubMed21189361History Published online 1 January 2011 Published in print 1 January 2011 Metrics

Measurement of 18O tracer diffusion coefficients in thin yttria stabilized zirconia films

In this paper we present a method to measure oxygen tracer diffusion coefficients in thin ion conducting films without being limited by slow oxygen incorporation kinetics. The method is based on a two step process. In the first step a substantial amount of 18O tracer is locally incorporated for example into an yttria stabilized zirconia (YSZ) layer at low temperatures with the aid of an electric current, thus overcoming slow thermal oxygen exchange while still limiting lateral diffusion to a minimum. In the second step controlled diffusion takes place at elevated temperatures in ultra high vacuum (UHV) to impede loss of tracer due to oxygen exchange at the film surface. In this second step the surface of the thin film may additionally be modified compared to the oxygen incorporation step. This allows to easily investigate effects of interfaces on ion transport. The achieved in-plane concentration profiles are then measured by secondary ion mass spectrometry (SIMS). Comparison with electrical measurements on YSZ thin films proves the applicability of the method.

Heterogeneous oxidation of atmospheric aerosol particles by gas-phase radicals

Atmospheric aerosol particles play pivotal roles in climate and air quality. Just as chemically reduced gases experience oxidation in the atmosphere, it is now apparent that solid and liquid atmospheric particulates are also subject to similar oxidative processes. The most reactive atmospheric gas-phase radicals, in particular the hydroxyl radical, readily promote such chemistry through surficial interactions. This Review looks at progress made in this field, discussing the radical-initiated heterogeneous oxidation of organic and inorganic constituents of atmospheric aerosols. We focus on the kinetics and reaction mechanisms of such processes as well as how they can affect the physico-chemical properties of particles, such as their composition, size, density and hygroscopicity. Potential impacts on the atmosphere include the release of chemically reactive gases such as halogens, aldehydes and organic acids, reactive loss of particle-borne molecular tracer and toxic species, and enhanced hygroscopic properties of aerosols that may improve their ability to form cloud droplets.

Whole Body and Cardiac Metaiodobenzylguanidine Kinetics in Parkinson Disease and Multiple System Atrophy

This study investigates whether combined analysis of I-123 metaiodobenzylguanidine (MIBG) kinetics in the heart and in the whole body can improve the accuracy of differential diagnosis between idiopathic Parkinson disease (PD) and a Parkinson variant of multiple system atrophy (MSA-P). A total of 30 patients with clinical suspicion of PD (n = 16) or MSA-P (n = 14) underwent MIBG whole-body planar imaging. Final diagnosis was confirmed at follow-up. Images were collected 30 minutes and 4 hours after tracer injection. Myocardial uptake was evaluated by measuring heart/mediastinum (H/M) ratio and the percent fraction of the injected dose retained by the heart (calculated by whole-body counts). Tracer washout was measured from both the heart and the whole body. H/M ratio was lower in PD than in MSA-P at early imaging (1.32 +/- 0.21 vs. 1.81 +/- 0.46, respectively, P < 0.01), although a large overlap in individual data was observed. By contrast, % of injected dose taken up by the heart documented a large difference between PD and MSA-P (0.97% +/- 0.51% vs. 1.91% +/- 0.66% of the dose, P < 0.01), and a very small overlap in individual values. There was no difference in the heart washout between the 2 Groups (31% +/- 13% vs. 32% +/- 15%, P = 0.9), while tracer loss from the whole body was higher in PD than in MSA-P (29% +/- 12% vs. 19% +/- 10%, P < 0.01). PD and its correlated global postganglionic dysfunction alter MIBG kinetics in the heart and in the whole body. Image analysis accounting for tracer kinetics in the whole body may improve the diagnostic accuracy of this test in patients with suspected PD or MSA-P.

Single photon emission-computed tomography (SPECT) for functional investigation of the proximal tubule in conscious mice

Noninvasive analysis of renal function in conscious mice is necessary to optimize the use of mouse models. In this study, we evaluated whether single photon emission-computed tomography (SPECT) using specific radionuclear tracers can be used to analyze changes in renal proximal tubule functions. The tracers included (99m)TC- dimercaptosuccinic acid ((99m)Tc-DMSA), which is used for cortex imaging; (99m)Tc-mercaptoacetyltriglycine ((99m)Tc-MAG3), used for dynamic renography; and (123)I-beta(2)-microglobulin, which monitors receptor-mediated endocytosis. (99m)Tc-DMSA SPECT imaging was shown to delineate the functional renal cortex with a approximately 1-mm spatial resolution and accumulated in the cortex reaching a plateau 5 h after injection. The cortical uptake of (99m)Tc-DMSA was abolished in Clcn5 knockout mice, a model of proximal tubule dysfunction. Dynamic renography with (99m)Tc-MAG3 in conscious mice demonstrated rapid extraction from blood, renal accumulation, and subsequent tubular secretion. Anesthesia induced a significant delay in the (99m)Tc-MAG3 clearance. The tubular reabsorption of (123)I-beta(2)-microglobulin was strongly impaired in the Clcn5 knockout mice, with defective tubular processing and loss of the native tracer in urine, reflecting proximal tubule dysfunction. Longitudinal studies in a model of cisplatin-induced acute tubular injury revealed a correlation between tubular recovery and (123)I-beta(2)-microglobulin uptake. These data show that SPECT imaging with well-validated radiotracers allows in vivo investigations of specific proximal tubule functions in conscious mice.