14C Compounds Research Articles

Contrasting effects of two antimicrobial agents (triclosan and triclocarban) on biomineralisation of an organophosphate pesticide in soils

We examined the impact of triclosan (TCS) and triclocarban (TCC) antimicrobial compounds on the biomineralisation of glucose and cadusafos pesticide in three Australian soils. Mineralisations of radiolabelled (14C) compounds were measured over a period of up to 77d in sterile and non-sterile soils treated with different concentrations of TCS and TCC (0–450mgkg−1). The rates of mineralisation of cadusafos were found to decrease with increasing concentration of TCS in all soils, but varied with soil type. Soils treated with TCS at the highest concentration (270mgkg−1) reduced cadusafos mineralisation by up to 58%. However, glucose mineralisation was not significantly affected by the presence of TCS. While TCS, significantly reduced the mineralisation of cadusafos (by 17%; p<0.05) even at the lowest studied concentration (30mgkg−1), no significant effect of TCC was observed on cadusafos or glucose mineralisation even at the highest concentration used (450mgkg−1).

ADME characterization in rats revealed immediate secretion of AZD7903 into the stomach after IV dosing

1. The distribution of AZD7903 and/or its metabolites was studied in rats following a single p.o. or i.v. dose using quantitative whole-body autoradiography (QWBA). At 5 min after i.v. administration of the 14C compound, high levels of radioactivity were observed in the fundus of the stomach compared to blood and plasma and the rest of the stomach, indicating an active secretion of 14C material into the stomach.2. Also, excretion and pharmacokinetics were studied following p.o. and i.v. dosage in rats. The radioactivity was mainly excreted via feces, and even in i.v. administered bile-duct cannulated (BDC) animals a significant part of radioactivity (26% in males and 57% in females) was recovered in the feces in the form of parent compound and two minor metabolic products.3. The compound was well absorbed (F% 98 in males and 76 in females), and showed low clearance in plasma (0.14 L/h/kg in males and 0.03 L/h/kg in females) and low-intermediate Vdss (0.7 L/kg). Clear differences in metabolic pathways (qualitative) and rates (quantitative) and consequently in PK parameters between sexes were observed.4. In summary, the results indicate AZD7903 being substrate for a transporter protein and support the hypothesis that the differences in disposition between sexes are due to differences in metabolic pathways and rates.

Acetate biodegradation by anaerobic microorganisms at high pH and high calcium concentration

Acetate biodegradation at a high pH and a high calcium concentration was examined to clarify the effect of bacterial activity on the migration of organic 14C compounds in cementitious repositories. Tamagawa river sediment or Teganuma pond sediment was anaerobically cultured with 5 mM acetate and 10 mM nitrate at pH 9.5–12 at 30 °C. After 20 and 90 days, the acetate concentration of the culture medium was analyzed and found to have decreased below 5 mM at pH ≤ 11. On the other hand, it did not decrease when either sediment was incubated in the absence of nitrate. These results suggest that nitrate-reducing bacteria can biodegrade acetate under more alkaline conditions than the reported pH range in which nitrate-reducing bacteria can exhibit activity. Acetate biodegradation was also examined at a high calcium concentration. Sediments were anaerobically cultured at pH 9.5 with 5 mM acetate and 10 mM nitrate in solution, equilibrated with ordinary Portland cement hydrate, in which the Ca concentration was 14.6 mM. No decrease in acetate concentration after incubation of the sediments was observed, nor was it lower than in the absence of cementitious composition, suggesting that kinetics of acetate biodegradation by anaerobic microorganisms is lowered by a high Ca concentration.

Evaluation of 14C release characteristics in Korean standard pressurized water reactor

This paper focuses on evaluation of the characteristics of organic and inorganic 14C, which is purged to the environment via purge line of each building in Korean standard reactor. 14C has a half-life of 5730 years and emits pure beta rays. 14C is a radioactive element that is easily transferred to the environment and has considerable environmental biological effects. According to recent research, organic 14C compounds are produced in reactor coolants via deoxidizing pathways. However, in oxidizing conditions, 14C changes to an oxidized carbon form and finally to 14CO 2. The radioactivity in purge lines and the purged quantity of organic and inorganic 14C in each building at Yonggwang #5unit were measured and evaluated during the three-year period from 2006 to 2008. During normal operation the annual purge quantity is about 100 GBq/GWe-yr, lower than the annual purge quantity in European pressurized water reactors. During normal operation inorganic 14C shows a higher purge rate than organic 14C in the purge line. During the outage period, the purge of 14C shows a slightly higher rate than the purge rate in normal operation. In Korean standard reactors the portion of 14C in inorganic chemical form is higher than those in foreign nuclear power plants, and this is attributable to operation characteristics such as volume control tank purge operation during normal operation. From the evaluation of the purge quantity through the purge line, it was found that considerable 14C was purged to the environment via the fuel handling building. This evaluation study will provide useful information for establishing radiocarbon ( 14C) control policy and for purge management.

10th international symposium on the synthesis and applications of isotopes and isotopically labelled compounds—the role of isotopes in pharmacokinetics and drug metabolism Session 15, Wednesday, June 17, 2009

AbstractConducting ADME studies on new drug candidates remains one of the primary uses of isotopically labelled compounds. In this session, the synthesis of isotopically labelled (2H, 3H, and 14C) compounds for this purpose has been discussed. Coupling the use of AMS and isotopically labelled compounds for studies in neonatal research and care is also highlighted. Copyright © 2010 John Wiley &amp; Sons, Ltd.

Dispersal and transformation of organic carbon across an episodic, high sediment discharge continental margin, Waipaoa sedimentary system, New Zealand

The rivers that drain active, collisional margins deliver ∼ 35% of particulate organic carbon (POC) to the world ocean, and are a key component of the global organic carbon flux. However, knowledge of the fate of terrestrial POC in the ocean is both limited and necessary for quantifying terrestrial and coastal ocean carbon budgets. Here, the fate of terrestrial POC is determined off the high discharge, Waipaoa River (sediment yield 15 Mt y − 1 ) based on a transect of seven cores from the river floodplain to the adjacent continental shelf and slope. Total organic carbon (%TOC), δ 13C, 14C, C/N ratios and lipid biomarker compounds were used to determine biogeochemical characteristics of surface sediments from terrestrial source to marine sink, and how these characteristics vary with river discharge. Complementary to surface sediments, down-core characteristics of three multi-cores covering the shelf and slope regions were used to identify perturbations in sediment supply via major floods. The presence of flood deposits allows us to compare their OC characteristics with non-flood sediment, thereby helping address the question of how flood events in the river catchment affect the transfer and fate of terrestrial OC through the marine environment. Results from this study show that as surface sediments are physically and biologically processed across the continental margin, they gain a marine signature. Biomarker analyses of surface samples show decreases in terrigenous vascular plant sources with increasing distance offshore. Biomarkers also demonstrate that terrestrial OC is being transferred across the continental margin, with plant sterols, long chain alcohols and long chain fatty acids (biomarkers indicative of vascular plants) persisting as far offshore as the mid-continental slope. In contrast to ambient conditions represented by surface sediments, rapid delivery by floods allows for more complete transfer of terrestrial carbon to the marine environment. A 1–10 cm thick flood layer preserved from Cyclone Bola (March 1988) contains a significant amount of terrestrially-sourced OC which subsequently was rapidly buried by sediments delivered during less extreme conditions.

Dispersal and transformation of organic carbon across an episodic, high sediment discharge continental margin, Waipaoa Sedimentary System, New Zealand

The rivers that drain active, collisional margins of the southwest Pacific deliver up to 35% of particulate organic carbon (POC) to the world ocean, and are a key component of the global organic carbon flux. However, knowledge of the fate of terrestrial POC in the ocean is both limited and necessary for quantifying terrestrial and coastal ocean carbon budgets. Here, the fate of terrestrial POC is determined off the high discharge, Waipaoa River (sediment yield 15 Mt y − 1 ) based on a transect of seven cores from the river floodplain to the adjacent continental shelf and slope. Total organic carbon (%TOC), δ 13C, 14C, C/N ratios and lipid biomarker compounds were used to determine biogeochemical characteristics of surface sediments from terrestrial source to marine sink, and how these characteristics vary with river discharge. Complementary to surface sediments, down-core characteristics of three multi-cores covering the shelf and slope regions were used to identify perturbations in sediment supply via major floods. The presence of flood deposits allows us to compare their OC characteristics with non-flood sediment, thereby helping address the question of how flood events in the river catchment affect the transfer and fate of terrestrial OC through the marine environment. Results from this study show that as surface sediments are physically and biologically processed across the continental margin, they gain a marine signature. Biomarker analyses of surface samples show decreases in terrigenous vascular plant sources with increasing distance offshore. Biomarkers also demonstrate that terrestrial OC is being transferred across the continental margin, with plant sterols, long-chain alcohols and long-chain fatty acids (biomarkers indicative of vascular plants) persisting as far offshore as the mid-continental slope. In contrast to ambient conditions represented by surface sediments, rapid delivery by floods allows for more complete transfer of terrestrial carbon to the marine environment. A 1–10 cm thick flood layer preserved from Cyclone Bola (March 1988) contains a significant amount of terrestrially-sourced OC which subsequently was rapidly buried by sediments delivered during less extreme conditions.

Structure, phase transformation, and magnetic properties of R16Fe76−xCoxC8 (R≡Nd, Dy; 0⩽x⩽76) alloys prepared by a remilling process

The effect of Co substitution on structure, phase transformation, and magnetic properties of R16Fe76−xCoxC8 (R≡Nd, Dy; 0⩽x⩽76) alloys prepared by a remilling process has been studied systematically. The process of remilling and subsequent annealing is more beneficial for the formation of Nd2(Fe,Co)14C compound in Nd16Fe76−xCoxC8 alloys than in Dy16Fe76−xCoxC8 alloys. The R2(Fe,Co)14C phase is obtained for Nd16Fe76−xCoxC8 alloys with 0⩽x⩽20 and Dy16Fe76−xCoxC8 alloys with 0⩽x⩽25. Higher Co content results in the formation of Nd2(Fe,Co)17Cδ-type phase and Dy(Fe,Co)7 phase for Nd16Fe76−xCoxC8 and Dy16Fe76−xCoxC8 alloys, respectively. The high coercivity, Hci=48.5kOe, is achieved for Dy16Fe51Co25C8 alloy.

Long-Term Biokinetics and Radiation Exposure of Patients Undergoing14C-Glycocholic Acid and14C-Xylose Breath Tests

The (14)C-glycocholic acid and (14)C-xylose breath tests are clinically used for the diagnosis of intestinal diseases, such as bacterial overgrowth in the small intestine. The two tests have in earlier studies been thoroughly evaluated regarding their clinical value, but due to the long physical half-life of (14)C and the limited biokinetic and dosimetric data, which are available for humans, several hospitals have been restrictive in their use. The aim of this study was to investigate the long-term biokinetics and dosimetry of the two (14)C compounds in patients and volunteers, using the highly sensitive accelerator mass spectrometry (AMS) technique. Eighteen (18) subjects were included, 9 for each compound. The (14)C content in samples from exhaled air, urine, and, for some subjects, also feces were analyzed with both liquid scintillation counting (LSC) and AMS. The results from the glycocholic acid study showed that, up to 1 year after the administration, 67%+/-6% (mean+/-standard deviation) of the administered activity was recovered in exhaled air, 2.4%+/-0.4% was found in urine, and 7.6% (1 subject) in feces. In the xylose study, the major part was found in the urine (66%+/-2%). A significant part was exhaled (28%+/-5%), and the result from an initial 72-hour stool collection from 2 of the subjects showed that the excretion by feces was insignificant. The absorbed dose to various organs and tissues and the effective dose were calculated by using biokinetic models, based on a combination of experimental data from the present study and from earlier reports. In the glycocholic acid study, the highest absorbed dose was received by the colon (1.2 mGy/MBq). In the xylose study, the adipose tissue received 0.8 mGy/MBq. The effective dose was estimated to 0.5 (glycocholic acid) and 0.07 mSv/MBq (xylose). Thus, from a radiation protection point of view, we see no need for restrictions in using the two (14)C-labeled radiopharmaceuticals on adults with the activities normally administered (0.07-0.4 MBq).

14C in spent ion-exchange resins and process water from nuclear reactors: A method for quantitative determination of organic and inorganic fractions

A method of separately quantifying organic and inorganic 14C compounds present in spent ion-exchange resins and process water from nuclear power reactors has been developed. Extraction of carbon compounds is accomplished by means of acid stripping (inorganic 14C) and subsequent wet oxidation (organic 14C) or by N2 purging in combination with a catalytic furnace (oxidized and reduced gaseous compounds) with organic and inorganic 14C species collected separately. Recovery experiments on simulated samples spiked with 14C-labeled sodium carbonate, sodium acetate and sodium formate, showed extraction yields of 94–98%. The sample-specific procedures were also tested on authentic samples of spent resins and reactor water with good results. Validation and reliability of the procedures are presented and the method is compared to previous methods reported in the literature.

Phase formation and magnetic properties of Nd 2Fe 14B-type Nd 16Co 76B 8−xC x alloys and their hydrides

An attempt is made to synthesize Nd 2Co 14C compound by mechanical alloying Nd 16Co 76B 8− x C x (0⩽ x⩽8) alloys and subsequent annealing. Phase formation and magnetic properties of Nd 2Fe 14B-type Nd 16Co 76B 8− x C x alloys and their hydrides are investigated. The Nd 2Co 14(B,C) phase with Nd 2Fe 14B-type structure is formed for Nd 16Co 76B 8− x C x (0⩽ x⩽7) alloys, while NdCo 7C δ phase with TbCu 7-type structure is observed in Nd 16Co 76C 8 alloy. The lattice parameter c of the Nd 2Co 14(B,C) phase decreases with increasing the carbon content. A limit volume of the unit cell to form the Nd 2Fe 14B-type structure is estimated to be 0.870 nm 3. The spin-reorientation temperature T SR increases with increasing the carbon content, due to an enhancement of magnetocrystalline anisotropy caused by carbon substitution for boron. After hydrogenation, the lattice expansion is observed for Nd 16Co 76B 8− x C x (0⩽ x⩽7) alloys. The spin-reorientation temperature of Nd 16Co 76B 8− x C x H y (0⩽ x⩽7) is much lower than that of the host alloys. Some structural and magnetic properties of hypothetic Nd 2Co 14C and Nd 2Co 14CH y compounds are estimated by extrapolation.

The initial rate of C substrate utilization and longer-term soil C storage

The initial reaction of microbial transformation and turnover of soil carbon inputs may influence the magnitude of longer-term net soil C storage. The objective of this study was to test the merit of the hypothesis that the more rapid substrates are initially utilized, the longer the residual products remain in the soil. We used simple model C compounds to determine their decomposition rates and persistence over time. Pure 14C compounds of glucose, acetate, arginine, oxalate, phenylalanine, and urea were incubated in soil for 125 days at 24°C. Total respired CO2 and 14CO2 was quantitatively measured every day for 15 days and residual soil 14C after 125 days. The percent 14C remaining in the soil after 125 days of incubation was positively and significantly correlated with the percent substrate utilized in the first day of incubation. The 14C in the microbial biomass ranged from 4–15% after 15 days and declined through day 125, contributing significantly to the 14C that evolved over the longer time period. Priming of 12C soil organic matter (SOM) was negative at day 3 but became positive, reaching a maximum on day 12; the total increase in soil C from added substrates was greater than the primed C. The primed C came from 12C SOM rather than the microbial biomass. This data supports the concept that the more rapidly a substrate is initially mineralized, the more persistent it will be in the soil over time.

Transfer of 14C to prenatal and neonatal rats from their mothers exposed to 14C compounds by ingestion.

The transfer of 14C through placenta or milk was investigated and the radiation dose to fetal and newborn rats was estimated. Female rats at different gestational stages or after delivery were exposed to 14C in the form of sodium bicarbonate, thymidine and lysine by a single ingestion. Radioactivity in maternal tissues and conceptuses (placenta, fetal membrane and fetus) and in the newborn was determined at various times after ingestion. After exposure to these 14C compounds, there was no significant difference between the 14C concentration in the fetus and that in the maternal tissues, suggesting that the placenta has no effect in preventing or accelerating the placental transfer of 14C. The concentration and content of 14C in the fetus and newborn were, however, dependent on the chemical form of 14C and on the prenatal or neonatal stage at the time of ingestion. The result of the dose estimation showed that 14C-lysine gave significantly higher prenatal and neonatal doses than 14C-sodium bicarbonate or 14C-thymidine.

On-Line Liquid Chromatography-Accurate Radioisotope Counting Coupled with a Radioactivity Detector and Mass Spectrometer for Metabolite Identification in Drug Discovery and Development

A novel detection method combining on-line liquid chromatography-accurate radioisotope counting (LC-ARC, advanced stop flow controller) coupled with a radioactivity detector and mass spectrometer has been developed. One of the major benefits of this method is that this system enhances the sensitivity of radioisotope measurement for metabolite identification in drug metabolism studies. Another advantage to this system is the easy interface with the mass spectrometer, which allows acquisition of mass spectrometric data on-line. For purposes of evaluating this system, in vitro microsomal incubations with [3Hlpropranolol were conducted. On-line separation and identification of [3H]propranolol metabolites was achieved without intensive sample preparation, concentration, or fraction collection. Mass spectrometric analysis showed the presence of propranolol major metabolites formed by hydroxylation, correlating with previously published results. Further evaluations of this system also were conducted using two 14C compounds, which are herein labeled X and Y. As our results show, 14C peaks were detected down to 6 cpm, which is approximately 20 times more sensitive than commercially available flow through radioactivity detectors. The overall results suggest that the combination of LC-ARC with radioactivity detection and mass spectrometry has great potential as a powerful tool for improving the sensitivity of radioisotope measurement in metabolite identification studies during drug discovery and development.

EFFECT OF POTASSIUM NUTRITION ON CURRENT PHOTOSYNTHESIZED CARBON DISTRIBUTION TO CARBON AND NITROGEN COMPOUNDS AMONG RICE, SOYBEAN, AND SUNFLOWER

ABSTRACT Type I crops (wheat and soybean), in which the potassium concentration (Kc) decreases when the nitrogen concentration (Nc) decreases, and type II crop (sunflower), in which Kc remains constant when Nc decreases, were grown in K-sufficient and K-deficient soils in pots. The CO2 exchange rate (Pnet; photosynthetic rate, PR; photorespiratory rate, and DR; dark respiratory rate), the distribution of photosynthesized 14C to organs, and the chemical compounds and free amino acids in fully expanded leaves were investigated. The results obtained can be summarized as follows. 1) Potassium (K) deficiency affected type II crop by causing a decrease in Pnet and an increase in PR and DR, while in type I crops, K deficiency affected the CO2 exchange rate less markedly. 2) Potassium (K) deficiency affected type II crop by causing the 14C distribution ratio to TCA/amino acids to decrease at 0 hours after 14C assimilation, and the 14C distribution ratio to serine to increase at 0.5 hours after 14C assimilation. In type I crops, the 14C distribution ratio among chemical compounds and free amino acids were less affected by K deficiency. 3) When 14CO2 was assimilated for 10 min, the 14C distribution ratio to organs was less affected by K deficiency in type I crops than in type II crop. In type II crop, the 14C distribution ratio to the stem was reduced by K deficiency, an effect that was caused by a low 14C translocation from the assimilated leaf blade. When 14C-sucrose and 14C-serine were introduced directly into the phloem, the translocation rate was not reduced by K deficiency in type II crop. When 14CO2 was assimilated into the leaf at a different leaf position, 14C distribution was not affected in type I crops. In type II crop, however, when 14CO2 was assimilated into the lower leaf, 14C distribution to the roots increased under K deficiency as compared to the control. 4) In type II crop when 14C-sucrose was introduced directly to the phloem, 14C compounds were translocated quickly to the lower organs, especially the roots. When 14C-serine was introduced, a major part of the 14C compounds remained in the assimilated leaf blade. Consequently, in type II crop, it can be assumed that current photosynthate distribution to TCA/amino acids and the distribution of carbon in serine to other amino acids are restricted by K deficiency at first, then, the photosynthetic rate and the translocation of photosynthates from the leaf blade are restricted by K deficiency.

Biodegradation of RDX and HMX Mixtures: Batch Screening Experiments and Sequencing Batch Reactors

Biodegradation is a potential treatment method for the high explosives RDX and HMX. In batch biodegradation tests, a facultative microbial consortium consumed the dissolved oxygen (DO) or reduced the oxidation-reduction potential (ORP) of the culture medium and biodegraded mixtures of RDX and HMX when supplied with various carbon and nitrogen sources. In batch tests with a mixture of carbon sources (glucose, glycerol, and succinic acid), RDX was reduced from 1.1 mg/L to below detectable levels within 4 days in the presence of 0.6 mg HMX/L. With ethanol as the carbon source, the culture degraded 90% of the initial 2.5 mg RDX/L over 8 days in the presence of 0.5 mg HMX/L. In batch mineralization tests, the culture converted 8 and 30% of the initial 14C-RDX to 14CO2 when supplied with ethanol and the mixed carbon sources, respectively. In both cases, a significant fraction of the initial 14C-RDX was converted to water-soluble 14C compounds, indicating triazine ring cleavage. However, mineralization was limit...

The effect of Dy content on magnetoelastic coupling in Nd 2− xDy xFe 14C compounds

In this research the effect of partial replacement of Nd by Dy atoms on magnetoelastic properties of Nd 2Fe 14C (2-14-1) alloys is studied by magnetostriction measurement of Nd 2− x Dy x Fe 14C with x=0.1, 0.3, 0.5 samples at 77 K up to 300 K temperatures. Spin re-orientation temperature, T sr, is also determined by measuring temperature dependence of magnetic susceptibility in this range. Results show that spin re-orientation temperature increases rapidly with increasing Dy content up to x=0.3. But, T sr was not affected with higher Dy substitution, substantially. Magnetostriction results show that the partial substitution of Dy increases the anisotropic magnetostriction, which is attributed to stronger magnetocrystalline anisotropy. Dy partial substitution also changes magnetoelastic energy of the two spin phases of high and low temperatures. Increasing x causes the single particle contribution in magnetoelastic energy of low-temperature phase to increase rapidly, so that Callens theory would be sufficient for describing observed temperature dependence of magnetostriction. In addition, partial substitution of Dy with x=0.3 and 0.5 causes a rapid increase in volume magnetostriction after T sr, i.e. in the high-temperature phase. This rapid increase in volume magnetostriction indicates that the exchange interaction contribution in the magnetoelastic energy is promoted at the high-temperature phase by Dy substitution.

Review of the ICRP tritium and 14C internal dosimetry models and their implementation in the Genmod-PC code.

Biokinetic models for tritium and 14C compounds, as described by various ICRP publications, have been incorporated into the Genmod-PC internal dosimetry code. This work reviews the models for tritium and 14C labeled compounds that the ICRP has formulated over several decades. The ICRP dosimetry prescribed for hydrogen and carbon radionuclides is fundamentally different from that recommended for other elements in that it is based on retention functions for whole body activity instead of compartmental biokinetic models. The ICRP recommends dosimetric methods for tritium and 14C compounds, ten of which are coded in Genmod-PC as compartmental models, namely, five tritium compounds, e.g., tritiated water, tritium gas, and five 14C compounds, e.g., carbon dioxide, carbon-labeled methane. The values of the Genmod-PC calculated dose coefficients were compared with the ICRP's values. It is shown how the dose coefficients for intakes of tritium and 14C compounds are affected by different interpretations of the methods recommended by the ICRP for two of the three classes of vapors and gases. Some aspects of the ICRP models, such as the percent oxidized, would benefit from reconsideration so as to produce tritium and 14C biokinetics that are less dependent on the radionuclide.

Fate of 14C from glucose and the herbicide metsulfuron–methyl in a plant–soil microcosm system

The effects of weeds and soil nutrient additions on the fate of 14C-labelled glucose and metsulfuron–methyl (metsulfuron) herbicide were determined in a growth-chamber soil–plant microcosm study. Nodding thistle (Carduus nutans) was used as a test weed species to which these compounds were applied. The experiment consisted of a full factorial design of N addition, P addition, planting with C. nutans, and addition of 14C-labelled compounds (glucose and herbicide metsulfuron). The experiment ran for 131 days following addition of the 14C-labelled compounds. There was a significant positive effect of C. nutans plants on soil microbial biomass-C and basal respiration. The addition of nutrients did not consistently affect any of the parameters measured in this study. The fate of 14C-labelled compounds was determined by quantifying the relative amounts of 14C absorbed by plants, incorporated into soil, taken up into microbial biomass and respired by soil organisms. Two days after application of the 14C compounds, 7–8% of the 14C was absorbed by the C. nutans (weed) canopy. By day 131, approximately 2–3% of the applied 14C was still detected in the tissues of dead thistle plants. The amounts and pattern of decomposition differed considerably between metsulfuron and glucose. Almost all (99%) of the applied 14C glucose was either respired by the microbes or incorporated into microbial biomass by day 131 while only 38–42% of the applied metsulfuron was respired or incorporated into microbes by this time. Greater amounts of metsulfuron pesticide were degraded in microcosms containing C. nutans plants than in those without plants. By day 131, 27.4% of 14C added from metsulfuron was respired in the planted treatment and only 22.8% from the non-planted treatment. This would suggest that the presence of decomposing weed litter (dying weed plants) has the potential to enhance the decomposition of added xenobiotics such as herbicides.

Exudation-reabsorption in a mycorrhizal fungus, the dynamic interface for interaction with soil and soil microorganisms

The mycelium of Suillus bovinus slowly absorbed [U-14C]glucose and other tracers from droplets placed on the cords, translocated them to the peripheral hyphae and exuded them into fluid drops on the hyphal tips. The exudate was characterized by 1H NMR spectroscopy and by sugar and amino acid analysis. The exuded compounds were mainly carbohydrates and peptides. Acetic acid and oxalic acid were also present in the exudate along with a number of unidentified compounds. Released ions (K, Na, Cl, P, Mg and Ca) were identified by X-ray microanalysis. The mycelium was shown to reabsorb up to 65% of the exuded 14C compounds in 2 days. Glucose, mannitol, glutamic acid (pH 3.2), and Rb+ (as well as other mineral ions) were all readily absorbed by the mycelium, while oxalic acid at pH 4.2 and glutamic acid at pH 6.5 were not. Exudation of fluid droplets on the surface of the hydrophobic mycorrhizal fungus S. bovinus may represent an ecophysiologically important function of the extramatrical hyphae, which provides an interface for interaction with the immediate hyphal environment and its other microorganisms where the peripheral hyphae exchange their photosynthetically derived products for nutrients to be used later by the pine host. We hypothesize that actively absorbed carbohydrates from the root are translocated to the peripheral hyphae along a concentration gradient of sugars and polyols by means of active translocation and diffusion in cell elements and by acropetal water transport in the cord vessels.