Levels Of 14CO2 Research Articles

Vertical measurements of atmospheric CO2 and 14CO2 at the northern foot of the Qinling Mountains in China

The CO2 and 14CO2 levels in air samples from the northern foot of the Qinling Mountains (Xi'an, China) were determined. In 2021, a hexacopter unmanned aerial vehicle sampled air at different heights, from near-ground to 2000 m. The objectives of this study were to determine vertical characteristics of CO2 and 14CO2, the sources of different-height CO2, and the influence of air mass transport. The CO2 concentrations mainly exhibited a slight decreasing trend with increasing height during summer observations, which was in contrast to the increasing trend that was followed by a subsequent gradual decreasing trend during early winter observations, with peak CO2 levels (443.4 ± 0.4–475.7 ± 0.5 ppm) at 100–500 m. The variation in vertical concentrations from 20 to 1000 m in early winter observations (21.6 ± 19.3 ppm) was greater than that in summer observations (14.6 ± 14.3 ppm), and the maximum vertical variation from 20 to ∼2000 m reached 61.1 ppm. Combining Δ14C and δ13C vertical measurements, the results showed that fossil fuel CO2 (CO2ff, 56.1 ± 15.2 %), which mainly come from coal combustion (81.2 ± 3.4 %), was the main contributor to CO2 levels in excess of the background level (CO2ex) during early winter observations. In contrast, biological CO2 (CO2bio) dominated CO2ex in summer observations. The vertical distributions of CO2ff in early winter observations and CO2bio in summer observations were consistent with those of CO2 during early winter and summer observations, respectively. The strong correlation between winter CO2bio and ΔCO (r = 0.81, p < 0.01) indicated that biomass burning was the main contributor to CO2bio during early winter observations. Approximately half of the air masses originated from the Guanzhong Basin during observations. The results provide insights into the vertical distribution of different-sources of atmospheric CO2 in scientific support of formulating carbon emission-reduction strategies.

Heterologous Expression of Key C and N Metabolic Enzymes Improves Re-assimilation of Photorespired CO2 and NH3, and Growth.

We investigated the effect of the heterologous expression of phosphoenolpyruvate carboxylase (ZmPepcase), aspartate aminotransferase (GmAspAT), and glutamine synthetase (NtGS) on carbon (C) and nitrogen (N) metabolism in Arabidopsis (Arabidopsis thaliana). These transgenes were expressed either separately or in different combinations. The highest gains in shoot dry weight were observed in transgenic lines coexpressing all three genes. Tracer experiments using NaH14CO3 suggested that the coexpression of ZmPepcase, GmAspAT, and NtGS resulted in a higher flux of assimilated CO2 toward sugars and amino acids. Upon feeding the leaf discs with glycine-1-14C, transgenic lines evolved significantly lower 14CO2 levels than the wild type, suggesting that a higher reassimilation of CO2 evolved during photorespiration. Leaves of transgenic plants accumulated significantly lower ammonium without any significant difference in the levels of photorespiratory ammonium relative to the wild type, suggesting a higher reassimilation of photorespired NH3 Transgenic lines also showed improved photosynthetic rates, higher shoot biomass accumulation, and improved seed yield in comparison with wild-type plants under both optimum and limiting N conditions. This work demonstrates that the heterologous coexpression of ZmPepcase, GmAspAT, and NtGS reduced the photorespiratory loss of C and N with concomitant enhancements in shoot biomass and seed yield.

Evolution of Radiocarbon in a Sandy Aquifer Across Large Temporal and Spatial Scales: Case Study from Southern Poland

We present the results of a comprehensive study aimed at tracing the evolution of carbon isotopic composition of the TDIC (total dissolved inorganic carbon) reservoir from the unsaturated zone down to the discharge area, in a sandy aquifer near Kraków, southern Poland. A multilevel well penetrating the unsaturated zone in the study area was equipped with horizontally mounted lysimeters with ceramic suction cups to collect samples of pore water and metal probes to collect soil air. Strong seasonal fluctuations were observed of soil pCO2 extending down to the water table, coupled with distinct, well-defined depth profiles of δ13CTDIC reaching approximately −10′ at 8 m depth and almost constant radiocarbon content in the TDIC pool, comparable to 14CO2 levels in the local atmosphere. Simple models (closed/open system) do not account for the observed depth variations of carbon isotopic composition of the TDIC pool. This suggests that the TDIC reservoir of pore waters is evolving under conditions gradually changing from an open towards a closed system. In order to explain 13C and 14C content of dissolved carbonates in groundwater in the recharge area of the studied aquifer, additional sources of carbon in the system are considered, such as organic matter decomposition accompanied by reduction of dissolved nitrates and sulfates. The piston-flow l4C ages of groundwater in the confined part of the studied system were calculated using 2 approaches: 1) the correction model proposed by Fontes and Garnier (1979) was used to calculate groundwater ages, utilizing the chemical and carbon isotopic data available for the sampled wells; and 2) inverse geochemical modeling was performed for selected pairs of wells using NETHPATH code. The calculated 14C ages of groundwater range from approximately 0.6 to 37.5 ka BP. Although both methods appeared to be in a broad agreement, NETHPATH calculations revealed that isotopic exchange processes between TDIC pool and solid carbonates present in relatively small amounts in the aquifer matrix play an important role in controlling the 13C and 14C signatures of the dissolved carbonate species in groundwater and should be taken into account when 14C ages are calculated.

Remedial options for chlorinated volatile organics in a partially anaerobic aquifer

AbstractA laboratory study was conducted for the selection of appropriate remedial technologies for a partially anaerobic aquifer contaminated with chlorinated volatile organics (VOCs). Evaluation of in situ bioremediation demonstrated that the addition of electron donors to anaerobic microcosms enhanced biological reductive dechlorination of tetrachloroethene (PCE), trichloroethene (TCE), and 1,1,1‐trichloroethane (1,1,1‐TCA) with half‐lives of 20, 22, and 41 days, respectively. Nearly complete reductions of PCE, TCE, 1,1,1‐TCA, and the derivative cis‐dichloroethene were accompanied by a corresponding increase in chloride concentrations. Accumulation of vinyl chloride, ethene, and ethane was not observed; however, elevated levels of 14CO2 (from 14C‐TCE spiked) were recovered, indicating the occurrence of anaerobic oxidation. In contrast, very little degradation of 1,2‐dichloropropane (1,2‐DCP) and 1,1‐dichlorethane (1,1‐DCA) was observed in the anaerobic microcosms, but nutrient addition enhanced their degradation in the aerobic biotic microcosms. The aerobic degradation half‐lives for 1,2‐DCP and 1,1‐DCA were 63 and 56 days, respectively. Evaluation of in situ chemical oxidation (ISCO) demonstrated that chelate‐modified Fenton's reagent was effective in degrading aqueous‐phase PCE, TCE, 1,1,1‐TCA, 1,2‐DCP, etc.; however, this approach had minimal effects on solid‐phase contaminants. The observed oxidant demand was 16 g‐H2O2/L‐groundwater. The oxidation reaction rates were not highly sensitive to the molar ratio of H2O2:Fe2+:citrate. A ratio of 60:1:1 resulted in slightly faster removal of chemicals of concern (COCs) than those of 12:1:1 and 300:1:1. This treatment resulted in increases in dissolved metals (Ca, Cr, Mg, K, and Mn) and a minor increase of vinyl chloride. Treatment with zero‐valent iron (ZVI) resulted in complete dechlorination of PCE, and TCE to ethene and ethane. ZVI treatment reduced 1,1,1‐TCA only to 1,1‐DCA and chloroethane (CA) but had little effect on reducing the levels of 1,2‐DCP, 1,1‐DCA, and CA. The longevity test showed that one gram of 325‐mesh iron powder was exhausted in reaction with &gt; 22 mL of groundwater. The short life of ZVI may be a barrier to implementation. The ZVI surface reaction rates (ksa) were 1.2 × 10−2 Lm−2h−1, 2 × 10−3 Lm−2h−1, and 1.2 × 10−3 Lm−2h−1 for 1,1,1‐TCA, TCE, and PCE, respectively. Based upon the results of this study, in situ bioremediation appeared to be more suitable than ISCO and ZVI for effectively treating the groundwater contamination at the site. © 2004 Wiley Periodicals, Inc.

Analysis and processing of samples for a carbon-14 monitoring program at a radioactive waste storage site.

A monitoring program was undertaken to determine the levels of airborne radioactive 14CO2 in an operating waste management area, and it its vicinity. As a part of this program, alkaline microporous pellets, recently developed, were used to sample the 14CO2 in air near waste storage structures and near the waste management area. These pellets were never fully characterized for their ability to capture high levels of 14CO2, and the processing and analysis needed to be improved to provide data on recoveries and consistencies, for an eventual method validation, with independent calibrations and standards. The sample analysis scheme also had to accommodate 14CO2 levels varying from near the natural background (250 Bq kg-1 C), to potentially three to four orders of magnitude above this value, near the wastes. The porous alkaline solid pellets were used for the passive capture of airborne 14CO2 over a period of weeks, to a few months. The pellets were processed to release the captured CO2 (14CO2 and 12CO2) into a NaOH solution, which was subsequently analyzed by liquid scintillation. Processing of the pellets yielded a 14C recovery of 96.0 +/- 4.2% and a lower, but consistent total carbon recovery, i.e., 85.9 +/- 2.7 and 86.9 +/- 2.6%, for procedural blanks and standards, respectively. The detection limits for the pellet sampling and processing was sufficient to reach environmental levels. For the higher levels of 14CO2 and for 'spot' sampling, we also used air samples, pumped into a NaOH solution to trap the 14CO2. These NaOH solutions were counted directly for 14C, also by liquid scintillation. The method limits of this latter technique, although much higher than for pellet samples, also achieved the performance objective for detecting airborne 14CO2. Both sampling and processing techniques, when used together, provided sufficient flexibility to be used for low (environmental) levels and high levels, near the wastes.

Effects of Morphine and Naloxone on Glucose Metabolism in Uterine Strips from Ovariectomized and Non-Ovariectomized Restricted Diet Rats

The effect of underfeeding over glucose metabolism in uteri isolated from ovariectomized and non-ovariectomized rats subjected to a restricted diet for 25 days (50% of the normal food intake), was studied. Underfeeding decreases 14CO2 formation from U14 C-glucose in intact animal uteri. While in ovariectomized rats (25 days), the effect is the opposite. The addition of morphine 10−6 M to the medium does not affect rats fed ad libitum. However, 14CO2 levels increase significantly in intact animals receiving a restricted diet. In ovariectomized rats morphine does not show any activity, regardless of the type of diet rats were subjected to. None of the rat groups seems to be sensitive to naloxone 10−6 M. The s.c. injection of morphine (4 mg.kg−1) increases glucose metabolism only in intact rats provided with a restricted diet, while naloxone (2.5 mg.kg−1) produces a decrease of 14CO2 in ovariectomized underfed animals. To conclude, morphine either ‘in vivo’ or ‘in vitro’ is active only in uteri from intact rats subjected to underfeeding. Naloxone produces a decrease in 14CO2 production, particularly when it is s.c. injected to ovariectomized rats undergoing a dietary restriction. Since the uterus does not react to naloxone, the effect of the opiod blocker may be the result of endogenous opioids originated in other tissues.

Atmospheric 14CO2 Variations in the Equatorial Region

We present here first results of 14CO2 monitoring at two sampling sites in the equatorial region of the South American continent (station Aychapicho, Ecuador and station Llano del Hato, Venezuela). We also include the data for two other stations representing undisturbed marine atmosphere at mid-latitudes of both hemispheres, far from large continental sources and sinks of CO2 (station Izaña, Tenerife, Spain and station Cape Grim, Tasmania). Between 1991 and 1993, 14CO2 levels in the tropical troposphere were generally higher by 2–5‰ when compared to mid-latitudes of both hemispheres. This apparent maximum of 14C in the tropics can be explained by two major factors: 1) emissions of 14C-free fossil fuel CO2, restricted mainly to mid-latitudes of the northern hemisphere; and 2) 14C depletion due to gas exchange with circumpolar Antarctic upwelling water, influencing mainly mid- and high southern latitudes. The δ14C record so far available for the Aychapicho station provides direct evidence for a regional reduction of atmospheric 14CO2 levels due to gas exchange with 14C-depleted equatorial surface ocean in the upwelling regions and dilution with the 14C-depleted CO2 released in these areas. Recurrent ENSO events, turning on and off the 14C-depleted CO2 source in the tropical Pacific, lead to relatively large temporal variations of the atmospheric 14C level in this region.

Development of a 14C-urea breath test in ferrets colonised with Helicobacter mustelae: effects of treatment with bismuth, antibiotics, and urease inhibitors.

A 14C-urea breath test analogous to its clinical counterpart is described for use in ferrets naturally or experimentally infected with Helicobacter mustelae. The test is performed within a sealed glass metabolism chamber through which air is drawn at a constant rate and expired breath collected into sodium hydroxide. Peak 14CO2 production occurred approximately 1 hour after substrate administration. Both inter- and intra-animal responses were highly reproducible, with mean coefficients of variation less than 10%. Other than enhancing peak 14CO2 levels very slightly, fasting had little influence on the response. In infant animals challenged with H mustelae, breath test activity increased linearly with the total count of culturable bacteria isolated from the antrum. Treatment of established infections with colloidal bismuth subcitrate (DeNol) for 4 weeks resulted in clearance of all detectable bacteria but retention of some breath test activity. Subsequent regrowth of bacteria was parallelled by an increase in the breath test response. Inclusion of amoxycillin and metronidazole in the treatment regimen, however, eradicated all the bacteria and almost totally eliminated 14CO2 production. This response parallels the clinically observed suppressive effect on H pylori achieved with bismuth alone relative to the total eradication seen with triple therapy. A single oral dose of the urease inhibitor, flurofamide, inhibited over 90% of the response for at least 24 hours. Acetohydroxamic acid was less effective. These findings suggest that in the ferret H mustelae model, breath test analysis can be a useful, non-invasive alternative to endoscopy for evaluation of agents affecting either growth of the organism or urease activity.

Studies on the Dormancy-Awakening and -Breaking in the Two-Rowed Barley Seed. III. The dormancy-awakening of seeds obtained from plants affected by flooding and lodging during the ripening period.

登熟期に湛水処理, 倒伏した二条オオムギ「アサヒ19号」,「成城17号」,「さつき二条」の種子を用い休眠覚醒を検討した. 湛水処理は, 登熟期に4回行い, 成熟期に刈取った. 倒伏の有無について, 対照区のなかで倒伏程度4以上のところから, 対照区の成熟期と同じ日に刈取った. 湛水処理, 倒伏した植物よりの休眠覚醒は, 種子の粒厚が (2.8mm以上)>(2.5≦～<2.6mm)>(2.2≦～2.4mm) の順に早かった. また, 一穂の着粒位置ごとの種子では, 休眠覚醒程度における発芽率は, 1000粒重と高い相関を示した. また, 湛水処理が芒の光合成におよぼす影響を,「さつき二条」と「四系8473」を用いオートラジオグラフィーによって調査した結果, 一穂の上部において光合成能力の低下を示していた. したがって, 湛水処理, 倒伏によって休眠覚醒の早い大粒種子が減少することにより, 間接的に休眠覚醒が遅れるものと思われる.

Comparison of the 1-gram [14C]xylose, 10-gram lactulose-H2, and 80-gram glucose-H2 breath tests in patients with small intestine bacterial overgrowth

The sensitivity of three breath tests (1-g [14C]xylose, 10-g lactulose-H2, and 80-g g!ucose-H2) was studied in 20 subjects with culture-documented small intestine bacterial overgrowth. Elevated breath 14CO2 levels were seen within 30 min of [14C]xylose administration in 19 of 20 subjects with bacterial overgrowth and 0 of 10 controls. In contrast, H2 breath tests demonstrated (a) uninterpretable tests [absence of H2-generating bacteria]in 2 of 20 subjects with bacteria]overgrowth and 1 of 10 controls and (b) nondiagnostic increases in H2 production in 3 of 18 glucose-H2 and 7 of 18 lactulose-H2 breath tests in subjects with bacterial overgrowth. These findings (a) demonstrate continued excellent reliability of the 1-g [14C]xylose breath test as a diagnostic test for bacterial overgrowth, (b) indicate inadequate sensitivity of H2 breath tests in detecting bacterial overgrowth, and (c) suggest the need for evaluation of a 13CO2 breath test having the same characteristics as the [14C]xylose test (avidly absorbed substrate having minimal contact with the colonic flora]for nonradioactive breath detection of bacterial overgrowth in children and reproductive-age women.

14CO2 Fixation, Translocation, and Carbon Metabolism in Rapidly Expanding Leaves ofPopulus deltoides

To examine 14CO2 fixation, potential translocation, and carbon flow among leaf chemical fractions of young developing leaves, the shoot tip of 24-leaf cottonwood (Populus deltoides Bartr. ex. Marsh) plants were cut off under water, placed in artificial xylem sap, and treated with 14CO2 in continuous and pulse-chase experiments. Additional leaves on whole plants were spot treated on the lamina tip to follow export from the tip only. The analysed leaves ranged in age from leaf plastochron index(LPI) −5 to 3, the spot treated leaves from LPI 2 to 5. After 30 min fixation, the specific activity in the lamina tip increased linearly with leaf age from LPI −5 to 1 (0.5 to 4.5 kBq mg−1). Specific activity in the lower lamina increased slowly with leaf age and did not reach 500 kBq mg−1 until LPI −1. Total 14CO2 fixed in the lower lamina exceeded that fixed in the tip by LPI −2 because of the large amount of tissue present in the lower lamina. Although the lamina tip fixed high levels of 14CO2, pulse-chase studies coupled with autoradiography indicated no vein loading or translocation from the tip until about LPI 4 or 5. The 14C fixed in both tip and lower lamina was incorporated at the site of fixation and was not distributed to younger tissue or translocated from the lamina. Although the percentage distribution (14C in each chemical fraction compared with the total in all fractions) of 14C among certain chemical fractions, e.g. sugars, amino acids and proteins, indicated that the mesophyll of the tip was more mature than the lower lamina, physiologically both leaf sectors were immature based on the expected 14C distribution in mature tissue. Information from this and other studies indicates that the extreme tip of a developing cottonwood leaf first begins to export photosynthate about LPI 4 or 5 on a 24-leaf plant. The first photosynthate translocated may be incorporated into the vascular tissues and mesophyll directly below the tip. However, as the tip continues to mature photosynthate is translocated past the immature lower lamina into the petiole and out of the leaf.

Anaerobic metabolism of hexadecane in sediments

Reducing sediments of Lake Mendota were challenged to demonstrate evidence of anaerobic conversion of l‐14C‐hexadecane to 14CO2. Low levels of 14CO2 were detected above formaldehyde controls in anoxic sediment and bottom waters and in surface water sparged with nitrogen. Aerobic incubation of the same sediment and water demonstrated extensive conversion of l‐14C‐hexade‐cane to 14CO2. The low levels of 14CO2 detected in anaerobic incubation were not increased by addition of nitrate or in a pre‐reduced medium containing nitrate and sulfate. An isotope‐recovery experiment demonstrated that 13.7% of added l‐14C‐hexadecane was converted to 14C‐cell carbon and 14CO2 after 375 h incubation.

Effects of diet on catabolism and excretion of (26-14C)cholesterol in rats.

The catabolism and excretion of [26-14C]cholesterol was studied in rats on semisynthetic and commercial diets low in fat or containing 15% butter or corn oil. Rats on the low fat commercial diet oxidized the labeled cholesterol to 14CO2 at more than twice the rate of those on the semisynthetic diet. Fecal excretion of labeled lipid was also somewhat higher with the commercial diet. The added fats had little effect on rate of oxidation of cholesterol but dietary corn oil stimulated fecal excretion of labeled lipid. The rate of loss of labeled cholesterol through oxidation and excretion showed a positive correlation with cholesterol biosynthesis, as measured previously by acetate incorporation into cholesterol in rats on the same kinds of diet. A simple method for efficient trapping and counting of 14CO2 was developed, which facilitated measurement of low levels of 14CO2 in expired air. Estimation of bile acid production from the rate of oxidation of [26-14C]cholesterol to expired 14CO2 and the specific activity of plasma cholesterol gave somewhat higher values than those obtained by other methods. Possible reasons for this difference are discussed.

Rapid detection of bacteremia by a radiometric system. A clinical evaluation.

Bactec, a radiometric method for the detection of bacterial growth in blood cultures, was used in comparison with conventional technics in 1,261 aerobic blood cultures. Bactec monitors levels of 14CO2 produced during bacterial metabolism from 14C-glucose and other 14C substrates, including carbohydrates and amino acids present in the media. A 3–5-ml. sample of blood was drawn via a closed system into the Bactec vials, each of which contained 30 ml. of medium. A 5-ml. sample in 50 ml. of Columbia broth was used for conventional technics. All cultures were read daily for 10 days. A total of 311 blood cultures from 55 patients was positive by one or both methods. Bactec detected 91% of all positive cultures, compared with 88% detected by routine methods. Both methods detected 88% of all positive patients. Of the 311 positive blood cultures, 59% were detected first by Bactec, 11% were detected first by the routine method, and 30% required the same time for detection by both methods. These results show that Bactec is equal to our conventional technic in terms of number of positive cultures detected. Bactec also frequently detected positive cultures on the average 1 to 2 days sooner than the routine system.

Effect of Vanadium on Metabolism of Glucose in the Rat

A radiorespirometry experiment was conducted to determine the effects of the trace element vanadium on the metabolism of glucose-14C in adult male rats by the collection of 14CO2Ammonium metavanadate solution was injected intraperitoneally, and labeled glucose was given per os. At the 0.05 significance level, an effect on metabolism was indicated by reduced levels of 14CO2 after 1 and 3 hr. of collection but not at later times.

The Effects of Benzylaminopurine on Growth and 14Carbon Translocation in Excised Mustard Cotyledons

AbstractWhen localized areas of blades of recently excised mustard cotyledons were fed with 14CO2 it was found that the fixation products passed rapidly into the veins and then were translocated to the petiole. Since other cotyledons similarly treated subsequently rooted at the petiole base, this suggested that it acted as a sink for assimilates. Treatment of excised cotyledons with benzylaminopurine (BAP) resulted in the enhancement of blade growth and the suppression of root initiation and development. Quantitative determinations of labelled assimilate in both the cotyledon blade and the terminal 2 mm portion of the petiole were made. It was found that cotyledons treated with BAP at a concentration high enough to suppress completely root initiation had a higher level of radioactivity in the petiole base than the terminal segments in untreated petioles, whether expressed as specific activity or as a percentage of the total radiocarbon fixed. BAP‐treated cotyledons also fixed consistently higher levels of 14CO2, probably due to an increase in photosynthetic area. The results suggest that BAP alters the pattern of differentiation at the base of the petiole rather than the polarity of movement of assimilates to the petiole base.

Vitamin B6 Deficiency in Rats: Utilization of 14C-labeled glutamic acid and sodium 2-ketoglutarate

The effect of a vitamin B6 deficiency on the utilization of 14C-labeled glutamic acid and 2-ketoglutarate in brain and liver tissue was investigated. When glutamate-2-14C was injected the activity in the expired carbon dioxide from vitamin B6-depleted rats was less than that from the control rats. Three fractions were isolated from the brain and liver hydrolysates: 1) all amino acids minus glutamic and aspartic acid, 2) glutamic acid, and 3) aspartic acid. There was no difference in the proportion of 14C found in the 3 fractions isolated from the brains of the deficient group as compared with the control group except in the 14C activity of aspartic acid. In this instance the least 14C activity was noted in the pyridoxine-supplemented group. Liver amino acid fractions from the vitamin B6-deficient rats showed lower levels of 14C activity. Variable levels of 14CO2 were obtained upon injection of 2-ketoglutarate-3,5-14C. In the brain fractions 1 and 3 were significantly lower in the vitamin B6-deprived group than in the vitamin-supplemented group. The 3 fractions from vitamin B6-deficient livers showed lower levels of 14C activity than from the control rats, but the difference was only significant with fraction 3.