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At least 19 recordsLinked to original sources
PubMed2003

Capacity for biodegradation of CFCs and HCFCs in a methane oxidative counter-gradient laboratory system simulating landfill soil covers.

The attenuation of methane and four chlorofluorocarbons was investigated in a dynamic methane and oxygen counter-gradient system simulating a landfill soil cover. Soil was sampled at Skellingsted Landfill, Denmark. The soil columns showed a high capacity of methane oxidation with oxidation rates of 210 g m(-2) d(-1) corresponding to a removal efficiency of 81%. CFC-11 and to a lesser extent also CFC-12 were degraded in the active soil columns. The average removal efficiency was 90% and 30% for CFC-11 and CFC-12, respectively. Soil gas concentration profiles indicated that the removal was due to anaerobic degradation, which was verified in anaerobic batch experiments where CFC-11 was rapidly degraded. HCFC-21 and HCFC-22 were also degraded in active soil columns (61% and 41%, respectively), but compared to the CFCs, the degradation was located in the upper oxic part of the column with overlapping gradients of methane and oxygen. High oxidation rates of methane and HCFCs were obtained in soil microcosms incubated with methane. When increasing the column inlet flow, the oxidation zone was moved upward in the column, and the removal efficiency of methane and HCFCs decreased. The removal of CFCs was, however, less affected since the anaerobic zone expanded with increasing inlet flow rates. This study demonstrates the complexity of landfill soil cover systems and shows that both anaerobic and aerobic bacteria may play a very important role in reducing the emission of not only methane but also trace components into the atmosphere.

Bacteria, Aerobic↗
PubMed2003

Gas-phase reaction of CCl2F2 (CFC-12) with methane.

Gas-phase reaction of CFC-12 (CCl2F2) with methane was carried out in a plug flow reactor over the temperature range of 873-1123 K. The major organic halocarbons formed during the reaction were C2F4, C2H2F2, CHClF2, CH3Cl, C3H2F6 and CCl3F. The formation of all products except C2H2F2 decreased with temperature, while the selectivity to C2H2F2 (difluoroethylene) increased with temperature and reached approximately 80% at 1123 K. Under these reaction conditions, methane acts as hydrogen and carbon source, resulting in the formation of an unsaturated C2 hydrofluorocarbon from two C1 precursors.

Chlorofluorocarbons, Methane↗
PubMedDate not supplied

Topical vapocoolant quickly and effectively reduces vaccine-associated pain: results of a randomized, single-blinded, placebo-controlled study.

BACKGROUND: Comprehensive international travel preparation often requires several vaccines. Up to 90% of adults have some fear of injections, mostly due to injection-related pain. Pediatric studies with routine vaccines have shown topical anesthetic EMLA cream (lidocaine and prilocaine, Astra Pharmaceuticals, Inc.) and the topical vapocoolant Fluori-Methane (dichlorodifluoromethane and trichlorodifluoromethane, Gebauer Co.) to be equally effective in reducing pain from vaccinations. EMLA cream is expensive and requires a 60-min application, while Fluori-Methane (FM) is immediate in onset of action and inexpensive. Skin anesthesia begins at 10 degrees C. Fluori-Methane can briefly cool the skin to 0 degrees C. METHODS: We studied the effectiveness of topical vapocoolant on adult clients at our international travel clinic in a randomized, controlled trial of topical FM vs. cold (4 degrees C) saline placebo. Using a preset randomization table, participants served as their own controls, receiving placebo/control or active agent (participant blinded) in one arm (left or right), and a similar number of vaccines in the untreated arm. Vaccines were administered according to a set protocol per arm to minimize the risk of bias. Pain was measured using a modified McGill present pain intensity (PPI) pain index. Subjects rated their pain immediately and at 5 min on a six-level scale, noting treated and untreated arms separately. A questionnaire was completed on intervention preferences. Sample size was predetermined to achieve 90% statistical power estimating 25% efficacy (minimum n=172). RESULTS: One hundred and eighty-five participants were enrolled; 93 FM and 92 cold saline placebo. FM-treated arms had a significant reduction in immediate pain compared to untreated arms (pain scale mean 2.2 vs. 3.1; p<.0001), and compared to placebo (mean 2.2 vs. 2.8; p<.01). Delayed pain at 5 min was not affected by FM or control (mean 1.9 vs. 2.0) compared to no intervention (pain scale 1.9). The intervention preference questionnaire indicated that participants did not find FM therapy uncomfortable. They would choose FM therapy in the future, over a cream, especially if a wait was involved. CONCLUSION: The topical vapocoolant Fluori-Methane is an effective, quick, preferred, inexpensive agent for reducing vaccine-associated injection pain for international travel clients.

Administration, Topical↗
PubMed2001

Detection of chlorinated methanes by tin oxide gas sensors.

Tin oxide thin films prepared by thermal oxidation of Sn films were used for the detection of chlorinated methanes (CH2Cl2, CHCl3 and CCl4). This resulted in better chemical selectivity, sensitivity, response speed and detection limit than seen with previous detectors. The temperature dependence of the sensing of 1% CCl4 gas was studied and the best sensing behavior was observed at 300 degrees C. The films showed different chemical selectivity in both speed and direction of sensing response to each gas and were stable for more than 3 weeks under operating conditions. The films showed rapid gas sensing (<40 s to reach 90% of full response) and low detection limits (< 4 ppm CCl4). The role of oxygen in the detection of chlorinated methanes and in resistance changes without chlorinated methanes was also studied. The changes at the surface of the film after gas sensing were examined using scanning electron microscopy with energy-dispersive X-ray spectrometry.

Chlorofluorocarbons, Methane↗
PubMed1981

Effect of Fluori-Methane spray on passive hip flexion.

The purpose of the study was to evaluate the influence of Fluori-Methane spray as a method of affecting passive range of motion measured at the right hip joint. Subjects were 30 normal volunteers randomly divided into an experimental group and a control group. A special table was constructed to position and stabilize each subject for monitoring the right lower extremity's resistance to side-lying straight leg raising. Specific right hip flexion goniometric measurements were compared and analyzed before and after application of Fluori-Methane spray to the soft tissue overlying the posterior part of the right thigh. The results of the study showed that the experimental group, which received application of Fluori-Methane spray and static passive stretch, did significantly (p less than .02) increase the range of passive hip flexion over that of the control group, which received only static passive stretch.

Adult↗
PubMed1992

Strengthening the Montreal protocol: does it cool down the greenhouse?

Strengthening of the Montreal Protocol is recently being negotiated in London in 1990 in order to achieve further reductions of the regulated CFCs and to include possibly more substances. In this article the implications of different policies with respect to control of ozone depleting substances for climate change are analysed, including the proposed substitution by HCFCs and HFCs, carbon tetrachloride and methylchloroform. A special halocarbon module was developed within the framework of RIVM's Integrated Model to Assess the Greenhouse Effect (IMAGE). IMAGE is a parameterized science based policy model and has been developed to give policy agencies a concise overview of the quantitative aspects of the greenhouse problem, to evaluate various policy options concerning climate change and to serve as a means of communication. It is concluded, from simulations with the halocarbon module, that it is of primary importance to achieve a further reduction of the regulated CFCs compared to the Montreal Protocol with compliance by as many countries as possible. From the perspective of the greenhouse effect the inclusion of longer lived halocarbons, such as carbon tetrachloride and HCFC-22 in the protocol comes second. The application of methylchloroform, halons and HCFCs and HFCs with lower global warming potentials (GWPs) than HCFC-22 contributes only marginally to the greenhouse effect in comparison with the much more important greenhouse gases carbon dioxide, methane, ozone and nitrous oxide. Especially if further growth of the total production of HCFCs after complete replacement of the present CFCs can be avoided by using these alternatives with a lower GWP, these substances could therefore be tolerated in a transition period, from the perspective of global warming.

Carbon Dioxide↗
PubMed2003

Decomposition of halogenated methanes in oxygen-free gas mixtures by the use of a silent electric discharge.

A silent electric discharge was applied to decompose halogenated methanes including CCl4, CHCl3, CFCl3, CF2Cl2 and CF3Cl, in argon-containing gas mixtures. The decompositions of the target compounds were studied in static reactors at a fixed electric field and room temperature. The reaction products were analyzed by FT-IR spectroscopy, gas chromatography and UV spectrophotometry. The results demonstrated, that the radical-type decomposition of chlorofluoromethanes led to products formed by realignment of the halogen atoms. The decomposition of CCl4 was faster than that of the cholorofluoromethanes, and produced perchloroethane and chlorine. CHCl3 exhibited the highest decomposition rate and produced a large variety of products.

Argon↗
PubMed1985

Effects of vapocoolants on passive hip flexion in healthy subjects.

Vapocoolants have been documented clinically to increase range of motion limited by pain, but only one research study has been undertaken to investigate these observations. The purposes of this study were twofold: to replicate one existing quantitative study on Fluori-Methane Spray and to examine the effects of other brief, cold stimuli (ethyl chloride and isopropyl alcohol) to increase passive hip flexion in healthy adults. Three experimental groups and a control group were used; each subject served as his own control. Pretest and posttest measurements of passive hip flexion were measured in a gravity-minimized position. A specially designed table to ensure trunk stabilization was used. Brief, cold stimuli applied to the posterior region of the thigh were found ineffective in increasing passive hip flexion in healthy adults. The rationale for the findings is described in terms of the effects of brief, cold stimuli on a quiescent CNS as opposed to a CNS demonstrating heightened excitability in the pain-spasm-pain cycle.

1-Propanol↗
PubMed2005

Modified direct relining method produces an accurate adaptation of denture.

The purpose of this study was to examine if a modified direct relining method could result in excellent denture adaptation compared to a conventional method. Direct relining was done using heat-polymerized acrylic resin base on a maxillary cast with two times of three seconds of cooling using dichloro-difluoro-methane coolant. Discrepancy between cast and intaglio surface at residual ridge and center of palate was measured at 12 minutes after mixing of resin (Time 0) and at 24 hours or seven days after water immersion (36 degrees C). At Time 0 (with three seconds of cooling), the discrepancy at ridge (0.39 +/- 0.27) and palate (0.66 +/- 0.31) was significantly lower compared to that of control (ridge = 0.93 +/- 0.51; palate = 1.14 +/- 0.13, P < 0.05); and the same observations occurred at 24 hours and seven days too. On intaglio side (with three seconds of cooling), the peak temperature was 5 degrees C lower than that of control and it occurred at a delay of about 60 seconds. Based on the results of this study, we therefore suggested that this delayed and lowered temperature served to improve the adaptability of denture base.

Acrylic Resins↗
PubMed2004

Standards development of global warming gas species: methane, nitrous oxide, trichlorofluoromethane, and dichlorodifluoromethane.

Environmental scientists from federal agencies, such as the National Oceanic and Atmospheric Administration (NOAA), and academia have long suspected that increasing anthropogenic inputs of various trace gases into the atmosphere can cause changes in the earth's climate and protective ozone layer. Nitrous oxide and methane, cited in the Kyoto Protocol, as well astrichlorofluoromethane (CFC-11) and dichlorodifluoromethane (CFC-12), cited in the Montreal Protocol, are all greenhouse gases and are implicated in the destruction of the stratospheric ozone layer. The lack of national standards prompted research to determine the feasibility of preparing accurate and stable standards containing these four compounds. Development of these standards would support the measurement of these species by those in the atmospheric research community not having their own source of standards. A suite of eight primary gas standards containing methane, nitrous oxide, CFC-11, and CFC-12 in a balance of air were prepared gravimetrically to bracket the ambient atmospheric concentrations. The combined uncertainties (uc) were calculated from error propagation analysis that included the weighing data from the gravimetric preparation and other sources of error such as the purity analysis of the compounds and air matrix. The expanded uncertainties (U) for the gravimetric standards were < 0.5% as calculated from the equation U = kuc, where the coverage factor k is equal to 2 for a 95% confidence interval. Analyses of the suite of standards by gas chromatography with flame-ionization and electron capture detection resulted in average absolute residuals of < 0.25% from regression models. The NIST suite of eight gravimetric standards was used to determine the concentrations in two standardsfrom NOAA. Those analyses resulted in bias across the two laboratories of < or = 2.1%.

Air Pollutants↗
PubMed1993

Reductive dehalogenation by cytochrome P450CAM: substrate binding and catalysis.

Biological reductive dehalogenation reactions are important in environmental detoxification of organohalides. Only scarce information is available on the enzymology underlying these reactions. Cytochrome P450CAM with a known X-ray structure and well-studied oxygenase reaction cycle, has been studied for its ability to reduce carbon-halogen bonds under anaerobic conditions. The reductive reactions functioned with NADH and the physiological electron-transfer proteins or by using artificial electron donors to reduce cytochrome P450CAM. Halogenated methane and ethane substrates were transformed by a two-electron reduction and subsequent protonation, beta-elimination, or alpha-elimination to yield alkanes, alkene, or carbene-derived products, respectively. Halogenated substrates bound to the camphor binding site as indicated by saturable changes in the Fe(III)-heme spin state upon substrate addition. Hexachloromethane was bound with a dissociation constant (KD) of 0.7 microM and caused > 95% shift from low- to high-spin iron. Ethanes bearing fewer chlorine substituents were bound with increasing dissociation constants and gave lesser degrees of iron spin-state change. Camphor competitively inhibited hexachloroethane reduction with an inhibitor constant (KI) similar to the dissociation constant for camphor (KI = KD = 0.9 microM). Rate determinations with pentachloroethane indicated a 100-fold higher enzyme V/K compared to the second-order rate constant for hematin free in solution. These studies on substrate binding and catalysis will help reveal how biological systems enzymatically reduce carbon-halogen bonds in the environment.

Camphor 5-Monooxygenase↗
PubMed2002

The influence of redox potential on the degradation of halogenated methanes.

To determine the influence of redox potential on the reaction mechanism and to quantify kinetics of the dechlorination by digester sludge, the test compounds trichlorofluoromethane (CFCl3), carbon tetrachloride (CCl4), and chloroform (CHCl3) were incubated in the presence of sludge and variable concentrations of reducing agent. Different sources of dehalogenation were examined, including live sludge and heat-killed sludge, and abiotic mechanisms were quantified in the absence of sludge. Batch incubations were done under redox conditions ranging from +/-534 to -348 mV. The highest rates for the dehalogenation of the three compounds were observed at -348 mV. The dechlorination rate of all the compounds by the heat-resistant catalysts was approximately twofold higher than the live treatments. It was proposed that the higher degradation rates by heat-killed sludge were due to the absence of physical barriers such as cell wall and cell membranes. There was no abiotic dechlorination of CFCl3, whereas CCl4 and CHCl3 were both reduced in the absence of sludge catalyst by Ti (III) citrate at > or =2.5 mM. The degradation pathways of CFCl3 and CHCl3 appeared to be only partially reductive since the production of reduced metabolites was low in comparison with the total amount of original halogenated compounds degraded. For CFCl3, the partial reductive degradation implied that different intra- and extracellular pathways were concurrent. The Gibbs free energy and the redox potential for the dehalogenation reactions utilizing Ti (III) citrate and acetate as electron donors are reported here for the first time.

Carbon Tetrachloride↗
PubMed2006

An experimental and kinetic modeling study of the reaction of CHF3 with methane.

The gas-phase reaction of CHF3 with CH4 has been studied experimentally and computationally. The motivation behind the study is that reaction of CHF3 with CH4 provides a possible route for synthesis of CH2=CF2 (C2H2F2). Experiments are carried out in a plug flow, isothermal alpha-alumina reactor at atmospheric pressure over the temperature range of 973-1173 K. To assist in understanding the reaction mechanism and the role of the reactor material involved in the reaction of CHF3 with CH4, the reaction of CHF3 with CH4, pyrolysis of CH4, and pyrolysis of CHCIF2 have been studied in the presence of alpha-alumina or alpha-AIF3 particles under various conditions. Under all conditions studied for the reaction of CHF3 and CH4, the major products are C2F4, C2H2F2, and HF. Minor products include C2H2, C2H4, C2H3F, C2HF3, C3F6, CO2, and H2. C2H6, CH2F2, and CHF2CHF2 are detected in trace amounts. The initial step is the gas-phase unimolecular decomposition of CHF3, producing CF2 and HF. It is proposed that CF2 decomposes on the surface of alpha-alumina, producing F radicals that are responsible for the activation of CH4. A reaction scheme developed on the basis of the existing NIST HFC and GRI-Mech 3.0 mechanisms is used to model the reaction of CHF3 with CH4. Generally satisfactory agreement between experimental and modeling results is obtained on the conversion levels of CHF3 and CH4 and rates of formation of major products. Using the software package AURORA, the reaction pathways leading to the formation of major products are elucidated.

Chlorofluorocarbons, Methane↗
PubMed1997

Vapocoolant spray is equally effective as EMLA cream in reducing immunization pain in school-aged children.

BACKGROUND: Untreated immunization pain causes undue distress and contributes to underimmunization through physician, and possibly parental, resistance to multiple simultaneous injections. OBJECTIVE: To compare the efficacies of two pain management methods in reducing immediate immunization injection pain and distress in school-aged children. DESIGN: A randomized, controlled clinical trial of eutectic mixture of local anesthetics (EMLA) cream and vapocoolant spray. PATIENTS: Children aged 4 to 6 years and scheduled to receive diphtheria and tetanus toxoids and acellular pertussis vaccine (DTaP) during health supervision visits. INTERVENTIONS: Enrolled children were randomized to one of three treatment groups: 1) EMLA cream + distraction; 2) vapocoolant spray + distraction; or 3) distraction alone (control). The specific pharmacologic pain control interventions consisted of EMLA cream (2.5% lidocaine, 2.5% prilocaine [Astra Pharmaceutical Products, Inc, Westborough, MA] $15. 00/patient; applied 60 minutes before injection) and vapocoolant spray (Fluori-Methane [Gebauer Company, Cleveland, OH] $0. 50/patient; applied via spray-saturated cotton ball for 15 seconds immediately before injection). MAIN OUTCOME MEASURES: The blinded investigator (BI) measured (by edited videotape) cry duration and the number of pain behaviors using the Observational Scale of Behavioral Distress. Pain visual analog scales (linear and faces scales) were completed by the child, parent, nurse, and the BI. RESULTS: Sixty-two children, aged 4.5 +/- 0.4 years (mean +/- SD) were randomized. The three treatment groups had similar subject characteristics. All pain measures and cry duration were similar for EMLA and vapocoolant spray. Both EMLA and spray were significantly better than control. Results for spray vs control: cry duration (seconds): 8.5 +/- 21.0 vs 38.6 +/- 50.5; number of pain behaviors: 1.2 +/- 1.9 vs. 3.1 +/- 2.1; child-scored faces scale: 2.0 +/- 2.4 vs. 4.1 +/- 2.3; parent-scored faces scale: 1.6 +/- 1.6 vs. 3.0 +/- 1.7; nurse-scored faces scale: 1.6 +/- 1.2 vs. 3.1 +/- 1.4; and BI-scored faces scale: 1.0 +/- 1.5 vs. 2.4 +/- 1.4. CONCLUSIONS: When combined with distraction, vapocoolant spray significantly reduces immediate injection pain compared with distraction alone, and is equally effective as, less expensive, and faster-acting than EMLA cream. As an effective, inexpensive, and convenient pain control method, vapocoolant spray may help overcome physician and parent resistance to multiple injections that leads to missed opportunities to immunize.

Age Factors↗
PubMed1985

Longitudinal dispersion of gases measured in a model of the bronchial airways.

We investigated the longitudinal dispersion of helium (He), methane, acetylene, butane, sulfur hexafluoride, and octafluorocyclobutane (C4F8) in a clear plastic model of the human bronchial airways. The dimensions of the seven airway generations (0-6) of the model were chosen to be equal to those given by Weibel's model A (Morphometry of the Human Lung; New York: Academic, 1963). Total volume of the model amounts to 52 ml. A small bolus of each of the tracer gases was injected within 1 ms into a constant airflow at the inlet of the model, and the bolus dispersion curve was measured at the outlet by means of a mass spectrometer. Both inspirations and expirations were simulated; the four selected values of the flow rate (V) for each simulation were 0.25, 0.5, 1, and 2 1/s, respectively. The measured bolus dispersion curves were corrected for the response characteristics of the mass spectrometer. In this way, the basal shape of the dispersion curve could be shown to be Gaussian. No significant changes in the standard deviation (sigma v) (Ultman et al., J. Appl. Physiol. 44: 297-303, 1978) of each tracer gas are found for the V values applied. sigma v increases significantly (approximately 50%), however, between the lightest (He) and the heaviest (C4F8) tracer gas used. The mean sigma v values of the 24 results (4 V values and 6 tracer gases) obtained for inspirations and expirations are 15.3 and 13.6 ml, respectively.

Acetylene↗