Limitations of the radon tracer method (RTM) to estimate regional greenhouse gas (GHG) emissions – a case study for methane in Heidelberg

Correlations of nighttime atmospheric methane (CH4) and 222radon (222Rn) observations in Heidelberg, Germany, were evaluated with the radon tracer method (RTM) to estimate the trend of annual nocturnal CH4 emissions from 1996–2020 in the footprint of the station. After an initial 30 % decrease in emissions from 1996 to 2004, there was no further systematic trend but small inter-annual variations were observed thereafter. This is in accordance with the trend of total emissions until 2010 reported by the EDGARv6.0 inventory for the surroundings of Heidelberg and provides a fully independent top-down verification of the bottom-up inventory changes. We show that the reliability of total nocturnal CH4 emission estimates with the RTM critically depends on the accuracy and representativeness of the 222Rn exhalation rates estimated from soils in the footprint of the site. Simply using 222Rn fluxes as estimated by Karstens et al. (2015) could lead to biases in the estimated greenhouse gas (GHG) fluxes as large as a factor of 2. RTM-based GHG flux estimates also depend on the parameters chosen for the nighttime correlations of CH4 and 222Rn, such as the nighttime period for regressions and the R2 cut-off value for the goodness of the fit. Quantitative comparison of total RTM-based top-down flux estimates with bottom-up emission inventories requires representative high-resolution footprint modelling, particularly in polluted areas where CH4 emissions show large heterogeneity. Even then, RTM-based estimates are likely biased low if point sources play a significant role in the station footprint as their emissions may not be fully captured by the RTM method, for example, if stack emissions are injected above the top of the nocturnal inversion layer or if point-source emissions from the surface are not well mixed into the footprint of the measurement site. Long-term representative 222Rn flux observations in the footprint of a station are indispensable in order to apply the RTM method for reliable quantitative flux estimations of GHG emissions from atmospheric observations.

The application of the tracer method with peer observation and formative feedback for professional development in clinical practice: a scoping review

Introduction The tracer method, commonly used for quality assessment, can also be used as a tool for peer observation and formative feedback on professional development. This scoping review describes how, by whom, and with what effect the tracer method is applied as a formative professional development instrument between healthcare professionals of equal status and aims to identify the types of scientific evidence for this use of the tracer method. Methods The authors searched four electronic databases for eligible articles, which were screened and assessed for eligibility by two independent researchers. From eligible studies, data were extracted to summarize, collate, and make a narrative account of the findings. Results The electronic search yielded 1757 unique studies, eight of which were included as valid and relevant to our aim: five qualitative, two mixed methods, and one quantitative study. Seven studies took place in hospitals and one in general practice. The tracer method was used mainly as a form of peer observation and formative feedback. Most studies evaluated the tracer method’s feasibility and its impact on professional development. All but one study reported positive effects: participants described the tracer method generally as being valuable and worth continuing. Discussion Although the body of evidence is small and largely limited to the hospital setting, using the tracer method for peer observation and formative feedback between healthcare professionals of equal status appears sufficiently useful to merit further rigorous evaluation and implementation in continuous professional development in healthcare.

Limitations of the Radon Tracer Method (RTM) to estimate regional Greenhouse Gases (GHG) emissions – a case study for methane in Heidelberg

Correlations of night-time atmospheric methane (CH4) and 222Radon (222Rn) observations in Heidelberg, Germany, were evaluated with the Radon Tracer Method (RTM) to estimate the trend of annual CH4 emissions from 1996–2020 in the catchment area of the station. After an initial 30 % decrease of emissions from 1996 to 2004, no further systematic trend but small inter-annual variations were observed thereafter. This is in accordance with the trend of emissions until 2010 reported by the EDGARv6.0 inventory for the surroundings of Heidelberg. We show that the reliability of total CH4 emission estimates with the RTM critically depends on the accuracy and representativeness of the 222Rn exhalation rate from soils in the catchment area of the site. Simply using 222Rn fluxes as estimated by Karstens et al. (2015) could lead to biases in the estimated greenhouse gases (GHG) fluxes as large as a factor of two. RTM-based GHG flux estimates also depend on the parameters chosen for the night-time correlations of CH4 and 222Rn, such as the night-time period for regressions as well as the R2 cut-off value for the goodness of the fit. Quantitative comparison of total RTM-based top-down with bottom-up emission inventories requires representative high-resolution footprint modelling, particularly in polluted areas where CH4 emissions show large heterogeneity. Even then, RTM-based estimates are likely biased low if point sources play a significant role in the station/observation footprint as their emissions are not captured by the RTM method. Long-term representative 222Rn flux observations in the catchment area of a station are indispensable in order to apply the RTM method for reliable quantitative flux estimations of GHG emissions from atmospheric observations.

Comparison of Dual Isotope and Ileal Sampling Methods for the Determination of the Amino Acid Digestibility of Pea Protein and Casein in Adult Humans

Objectives The measurement of amino acid (AA) digestibility of protein through direct ileal sampling is highly invasive and inappropriate for vulnerable populations, such as children or elderly. The new dual tracer method relies on comparing meal and plasma isotopic ratios of 1/a test protein 2/a reference protein (or AA mix) of known digestibility, each one being labelled with a different isotope. The aim of this study was to compare this new indirect dual tracer method to standard ileal method, for the determination of AA digestibility of pea protein and milk casein. Methods Fifteen healthy adult volunteers completed the study and were equipped with a naso-ileal tube. They were given 9 portions of mashed potatoes containing either pea protein or casein isolates that were intrinsically labelled with 15N and 2H. A 13C algal free AA mix was added in the meals as the reference for dual tracer method. Plasma samples were collected regularly from before the first ingestion to 8-h later, while ileal digesta were collected continuously. For ileal sampling method, the AA digestibility (RIDAA) was determined using the recovery a non-absorbable marker (PEG-4000) perfused in the ileum, and the measurement of 15N enrichment of the digesta. For the dual tracer method, the amount of AA absorbed (AbAA) was calculated by the ratio of 2H/13C enrichments in plasma and in meals. The isotopic enrichments were evaluated in digesta, plasma samples and meals by GC-C-IRMS. The AA content was measured in digesta and meals by U-HPLC. Results Mean AbAA and RIDAA of pea protein were 102.2 ± 3.1% and 94.3 ± 1.5%, respectively. Mean AbAA and RIDAA of casein were 91.9 ± 2.0% and 97.1 ± 0.8%, respectively. The dual tracer method overestimated by 10% and 5% the AA digestibility of pea protein and casein, respectively, and the variability was high. The mean ileal AA digestibility of the 13C free AA mix was high (98.1 ± 1.1%), which validated our choice to use it as the reference ‘protein’ in the dual tracer method. Conclusions Several AA digestibilities obtained with dual tracer method were in the same range as the digestibilities from ileal sampling method. The variability was high and the effect of the protein source was inconsistent. After further research and validation, the dual tracer method could lead to notable advances in the determination of protein quality in humans. Funding Sources Roquette.

Confrontation of the “Dual Tracer” Indirect Method With Direct Ileal Sampling for Indispensable Amino Acid Digestibility of Sunflower Isolate in Humans

Objectives The direct assessment of ileal samples of amino acid (AA) digestibility is invasive in humans. A less invasive but indirect method, namely « dual tracer » was recently developed. It relies on the plasma isotopic enrichment ratio of two labeled protein, a reference protein or alternately AAs labeled with 13C and the test protein labeled with 15N. This recent method has not yet been challenged against direct measurement of ileal digestibility. Methods Seven healthy volunteers were intubated with naso-ileal tube. Every 30min for 4h, they ingested sunflower biscuits containing a total of 25g of 15N intrinsically labeled sunflower protein isolate. They also ingested 60g chocolate containing a total of 400mg of a mix of 13C algal individual AAs. Ileal contents were collected continuously for 8h following the first meal and plasma was sampled every 30min for 4h and hourly between 4 and 8h. 15N and 13C indispensable amino acid (IAA) ileal digestibility were determined by measuring 15N and 13C enrichment in AAs by GC-C-IRMS and AA content by UHPLC in ileal effluent. Plasma and meal 15N and 13C IAA enrichment were measured by GC-C-IRMS. Isotopic 15N/13C ratio were determined using area under the curve value for each isotope. Results Using direct ileal sampling, average IAA ileal digestibility was: (i) 88.5 ± 5.0% for sunflower isolate (15N) with values ranged from 85.8 ± 5.1% for threonine to 91.1 ± 5.8% for methionine, and (ii) 97.6 ± 1.7% for free AAs (13C) with values ranged from 95.9 ± 2.3% for lysine to 98.8 ± 0.8% for phenylalanine. With the “dual tracer” method, digestibility of isoleucine, leucine, threonine and valine was significantly lower than with ileal determination (from 7.9% for threonine to 24.3% for leucine), Methionine and phenylalanine values were aberrant (over 100%) For lysine, the difference between the two methods was not statistically different (4.7%, p = 0.49). Conclusions With our methodological conditions, the “dual tracer” method provides physiological values for most IAA except methionine and phenylalanine. However, values were low compared to ileal digestibility (about 10%) and interindividual variability was high. This less invasive method is promising but requires methodological improvements. Funding Sources French Research National Agency (ANR), financial support of SOFIPROTEOL under the FASO Project PRODIAL.