Academic literature on the topic 'CO2 induced pH decrease'

Hypercapnia and hypoxia both relax airway smooth muscle, but the mechanisms responsible are poorly understood. Because hypercapnia and hypoxia can each decrease intracellular pH (pHi) and acidosis can inhibit Ca2+ channels, we hypothesized that decreased pHi mediates relaxation of trachealis muscle by each of these respiratory gases. To examine the relationship between pHi and tone, we measured isometric tension, bath pH, and fluorescence intensity (540 nm) in porcine tracheal smooth muscle strips loaded with 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein and excited alternately with 440- and 500-nm light. Strips equilibrated in Krebs-Henseleit solution bubbled with 95% O2-5% CO2 were contracted with carbachol and then relaxed with either 95% N2-5% CO2 or 93% O2-7% CO2. The ratio of fluorescence intensity at 500 nm to 440 nm was calibrated vs. pHi with use of nigericin. Baseline pHi was 7.19 +/- 0.03 (n = 13). Hypoxia decreased active tension by approximately 60% but did not change pHi. Hypercapnia induced decreases in tension that were associated with substantial decreases in pHi. Thus, decreased pHi does not mediate hypoxic relaxation, but the relaxation during physiologically relevant increases in CO2 concentration is associated with significant cellular acidification.

High concentration carbon dioxide (CO2) is used to promote pre-slaughter anaesthesia in swine and poultry, as well as short-lasting surgical anaesthesia and euthanasia in laboratory animals. Questions related to animal welfare have been raised, as CO2 anaesthesia does not set in momentarily. Carbon dioxide promotes anaesthesia by lowering the intracellular pH in the brain cells, but the dynamics of the changes in response to a high concentration of CO2 is not known. Based on 31P NMR spectroscopy, we describe CO2-induced changes in intracellular pH in the brains of five pigs inhaling 90% CO2 in ambient air for a period of 60 s, and compare the results to changes in arterial blood pH, PCO2, O2 saturation and HCO3- concentration. The intracellular pH paralleled the arterial pH and PCO2 during inhalation of CO2; and it is suggested that the acute reaction to CO2 inhalation mainly reflects respiratory acidosis, and not metabolic regulation as for example transmembrane fluxes of H+/HCO3-. The intracellular pH decreased to approximately 6.7 within the 60 s inhalation period, and the situation was metabolically reversible after the end of CO2 inhalation. The fast decrease in intracellular pH supports the conclusion that high concentration CO2 leads to anaesthesia soon after the start of inhalation.

The contribution of Cl-/HCO3- exchange to intracellular pH (pHi) regulation in cultured chick heart cells was evaluated using ion-selective microelectrodes to monitor pHi, Na+ (aiNa), and Cl- (aiCl) activity. In (HCO3- + CO2)-buffered solution steady-state pHi was 7.12. Removing (HCO3- + CO2) buffer caused a SITS (0.1 mM)-sensitive alkalinization and countergradient increase in aiCl along with a transient DIDS-sensitive countergradient decrease in aiNa. SITS had no effect on the rate of pHi recovery from alkalinization. When (HCO3- + CO2) was reintroduced the cells rapidly acidified, aiNa increased, aiCl decreased, and pHi recovered. The decrease in aiCl and the pHi recovery were SITS sensitive. Cells exposed to 10 mM NH4Cl became transiently alkaline concomitant with an increase in aiCl and a decrease in aiNa. The intracellular acidification induced by NH4Cl removal was accompanied by a decrease in aiCl and an increase in aiNa that led to the recovery of pHi. In the presence of (HCO3- + CO2), addition of either amiloride (1 mM) or DIDS (1 mM) partially reduced pHi recovery, whereas application of amiloride plus DIDS completely inhibited the pHi recovery and the decrease in aiCl. Therefore, after an acid load pHi recovery is HCO3o- and Nao- dependent and DIDS sensitive (but not Ca2+o dependent). Furthermore, SITS inhibition of Na(+)-dependent Cl-/HCO3- exchange caused an increase in aiCl and a decrease in the 36Cl efflux rate constant and pHi. In (HCO3- + CO2)-free solution, amiloride completely blocked the pHi recovery from acidification that was induced by removal of NH4Cl. Thus, both Na+/H+ and Na(+)-dependent Cl-/HCO3- exchange are involved in pHi regulation from acidification. When the cells became alkaline upon removal of (HCO3- + CO2), a SITS-sensitive increase in pHi and aiCl was accompanied by a decrease of aiNa, suggesting that the HCO3- efflux, which can attenuate initial alkalinization, is via a Na(+)-dependent Cl-/HCO3- exchange. However, the mechanism involved in pHi regulation from alkalinization is yet to be established. In conclusion, in cultured chick heart cells the Na(+)-dependent Cl-/HCO3- exchange regulates pHi response to acidification and is involved in the steady-state maintenance of pHi.

This work presents two novel methods to investigate in situ the carbon dioxide (CO2)-induced gelation of biopolymer-based solutions. The CO2-induced gelation is performed in a viewing cell at room temperature under CO2 pressure (20 to 60 bar), whereby calcium precursors are used as cross-linkers. The novel methods allow the in situ optical observation and evaluation of the gelation process via the change in turbidity due to dissolution of dispersed calcium carbonate (CaCO3) particles and in situ pH measurements. The combination of both methods enables the determination of the gelation direction, gelation rate, and the pH value in spatial and temporal resolution. The optical gelation front and pH front both propagate equally from top to bottom through the sample solutions, indicating a direct link between a decrease in the pH value and the dissolution of the CaCO3 particles. Close-to-vertical movement of both gelation front and pH front suggests almost one dimensional diffusion of CO2 from the contact surface (gel–CO2) to the bottom of the sample. The gelation rate increases with the increase in CO2 pressure. However, the increase in solution viscosity and the formation of a gel layer result in a strong decrease in the gelation rate due to a hindrance of CO2 diffusion. Released carbonate ions from CaCO3 dissolution directly influence the reaction equilibrium between CO2 and water and therefore the change in pH value of the solution. Increasing the CaCO3 concentrations up to the solubility results in lower gelation rates.

Mixture interactions between sour and salt taste modalities were investigated in rats by direct measurement of intracellular pH (pHi) and Na+ activity ([Na+]i) in polarized fungiform taste receptor cells (TRCs) and by chorda tympani (CT) nerve recordings. Stimulating the lingual surface with NaCl solutions adjusted to pHs ranging between 2.0 and 10.3 increased the magnitude of NaCl CT responses linearly with increasing external pH (pHo). At pH 7.0, the epithelial sodium channel (ENaC) blocker, benzamil, decreased NaCl CT responses and inhibited further changes in CT responses induced by varying pHo to 2.0 or 10.3. At constant pHo, buffering NaCl solutions with potassium acetate/acetic acid (KA/AA) or HCO3−/CO2 inhibited NaCl CT responses relative to CT responses obtained with NaCl solutions buffered with HEPES. The carbonic anhydrase blockers, MK-507 and MK-417, attenuated the inhibition of NaCl CT responses in HCO3−/CO2 buffer, suggesting a regulatory role for pHi. In polarized TRCs step changes in apical pHo from 10.3 to 2.0 induced a linear decrease in pHi that remained within the physiological range (slope = 0.035; r2 = 0.98). At constant pHo, perfusing the apical membrane with Ringer's solutions buffered with KA/AA or HCO3−/CO2 decreased resting TRC pHi, and MK-507 or MK-417 attenuated the decrease in pHi in TRCs perfused with HCO3−/CO2 buffer. In parallel experiments, TRC [Na+]i decreased with (a) a decrease in apical pH, (b) exposing the apical membrane to amiloride or benzamil, (c) removal of apical Na+, and (d) acid loading the cells with NH4Cl or sodium acetate at constant pHo. Diethylpyrocarbonate and Zn2+, modification reagents for histidine residues in proteins, attenuated the CO2-induced inhibition of NaCl CT responses and the pHi-induced inhibition of apical Na+ influx in TRCs. We conclude that TRC pHi regulates Na+-influx through amiloride-sensitive apical ENaCs and hence modulates NaCl CT responses in acid/salt mixtures.

Acidification in the toad bladder occurs as a result of electrogenic H+ secretion (JH). When a pH gradient is applied in a stepwise fashion in the absence of exogenous CO2, JH decreases linearly with the mucosal (M) solution pH and is null when pHm is approximately 4.5. When pHm is returned to initial values (7.4) in a stepwise fashion, JH increases linearly with pHm. However, on this return, higher values of JH are initially obtained. To investigate this hysteresis, hemibladders mounted in chambers were used to measure the change in the H+ current before and after acid pulses were applied to the mucosal solution. In the absence of exogenous CO2, the application of graded acid pulses to mucosa for 1, 2, 4, and 8 min resulted in a graded decrease in JH. The restoration of pHm to 7.4 was followed by an immediate transient overshoot of reversed short-circuit current (Irsc), which was related to the time of exposure and the magnitude of the acid pulse. The longer the acid pulse or the larger the pulse, the greater the Irsc overshoot. The addition of protonophores, dinitrophenol, or salicylate, into the mucosal solution enhanced this overshoot. Similar Irsc overshoots could be obtained with the application of pulses of adverse electrical gradients. Introduction of exogenous CO2 into the system (3%) completely inhibited the overshoot in JH after an acid pulse. In conclusion, when pHm is decreased JH is reduced and the cell pH presumably decreases because of continued exit of alkali at the serosal side of the cell and entry of H+ from the mucosal solution. The decrease in cell pH then triggers the pump to produce a sharp overshoot in JH when pHm returns to 7.4.

The relationship between cell volume and the neural response to acidic stimuli was investigated by simultaneous measurements of intracellular pH (pHi) and cell volume in polarized fungiform taste receptor cells (TRCs) using 2',7'-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein (BCECF) in vitro and by rat chorda tympani (CT) nerve recordings in vivo. CT responses to HCl and CO2 were recorded in the presence of 1 M mannitol and specific probes for filamentous (F) actin (phalloidin) and monomeric (G) actin (cytochalasin B) under lingual voltage clamp. Acidic stimuli reversibly decrease TRC pHi and cell volume. In isolated TRCs F-actin and G-actin were labeled with rhodamine phalloidin and bovine pancreatic deoxyribonuclease-1 conjugated with Alexa Fluor 488, respectively. A decrease in pHi shifted the equilibrium from F-actin to G-actin. Treatment with phalloidin or cytochalasin B attenuated the magnitude of the pHi-induced decrease in TRC volume. The phasic part of the CT response to HCl or CO2 was significantly decreased by preshrinking TRCs with hypertonic mannitol and lingual application of 1.2 mM phalloidin or 20 μM cytochalasin B with no effect on the tonic part of the CT response. In TRCs first treated with cytochalasin B, the decrease in the magnitude of the phasic response to acidic stimuli was reversed by phalloidin treatment. The pHi-induced decrease in TRC volume induced a flufenamic acid–sensitive nonselective basolateral cation conductance. Channel activity was enhanced at positive lingual clamp voltages. Lingual application of flufenamic acid decreased the magnitude of the phasic part of the CT response to HCl and CO2. Flufenamic acid and hypertonic mannitol were additive in inhibiting the phasic response. We conclude that a decrease in pHi induces TRC shrinkage through its effect on the actin cytoskeleton and activates a flufenamic acid–sensitive basolateral cation conductance that is involved in eliciting the phasic part of the CT response to acidic stimuli.

We studied sympathetic nerve activity (SNA) responses, recorded in multifiber preparations of left third thoracic white ramus, to respiratory or isocapnic metabolic acidosis or to CO2 enhancement at constant pH in chloralose-anesthetized paralyzed artificially ventilated cats. Cardiopulmonary, baro-, and peripheral chemoreceptors were denervated by bilaterally cutting vagus and carotid sinus nerves. Acidosis was induced by either decreasing artificial ventilation or infusing HCl (0.5 M i.v.). Both respiratory and isocapnic metabolic acidosis induced a decrease in local extracellular pH, measured directly with pH-sensitive microelectrodes within medulla region containing sympathoexcitatory bulbospinal neurons. The magnitude of changes in medullary pH was independent of the way systemic acidosis was generated. Despite uniformity of changes in local medullary extracellular pH due to systemic respiratory or isocapnic metabolic acidosis, different responses were observed in preganglionic SNA. Isocapnic metabolic acidosis resulted in a slight increase in SNA, averaging 6.4% per 0.05 systemic pH unit decrease. In contrast, respiratory acidosis induced by decreasing artificial ventilation produced a more pronounced increase of SNA, reaching peak changes of approximately 70% compared with control level with normal blood gases, an average increase of 13% per 0.05 systemic pH unit decrease. We conclude that systemic CO2 and H+ concentrations represent different stimuli to sympathetic nervous system. Despite similar changes of local extracellular pH within rostral ventrolateral medulla during systemic acidosis, different responses of SNA suggest other sites or as yet unknown additional effects of CO2 as being responsible for excitation of sympathetic activity.

When muscle is elongated, there is a length dependence of twitch potentiation and an increased Ca2+ sensitivity of the myofilaments. Changes in the charge potential of myofilaments, induced by a decrease in pH, are known to abolish the length dependence of Ca2+ sensitivity. This study was aimed at testing the hypothesis that a decrease in pH, and the concomitant loss of length dependence of Ca2+sensitivity, depresses the length dependence of staircase potentiation. In vitro, isometric twitch contractions of fiber bundles dissected from the mouse extensor digitorum longus, performed before and after 10 s of 10-Hz stimulation (i.e., the staircase potentiation protocol) were analyzed at five different lengths, ranging from optimal length for maximal force production ( L o; = 12 ± 0.7 mm) to L o + 1.2 mm ( L o + 10%). These measurements were made at an extracellular pH of 6.6, 7.4, and 7.8 (pH changes induced by altering the CO2 concentration of the bath solution). At pH 7.4 and 7.8, the degree of potentiation after 10-Hz stimulation showed a linear decrease with increased fiber bundle length ( r 2 = 0.95 and r 2 = 0.99, respectively). At pH 6.6, the length dependence of potentiation was abolished, and the slope of the length-potentiation relationship was not different from zero ( r 2 = 0.05). The results of this study indicate that length dependence of potentiation in intact skeletal muscle is abolished by lowering the pH. Because decreasing the pH decreases Ca2+ sensitivity and changes the charge potential of the filaments, the mechanism of length-dependent potentiation may be closely related to the length dependence of Ca2+sensitivity, and changes in the charge potential of the myofilaments may be important in regulating this relationship.

Fish embryos may be vulnerable to seawater acidification resulting from anthropogenic carbon dioxide (CO2) emissions or from excessive biological CO2 production in aquaculture systems. This study investigated CO2 effects on embryos of the European eel (Anguilla anguilla), a catadromous fish that is considered at risk from climate change and that is targeted for hatchery production to sustain aquaculture of the species. Eel embryos were reared in three independent recirculation systems with different pH/CO2 levels representing “control” (pH 8.1, 300 μatm CO2), end-of-century climate change (“intermediate”, pH 7.6, 900 μatm CO2) and “extreme” aquaculture conditions (pH 7.1, 3000 μatm CO2). Sensitivity analyses were conducted at 4, 24, and 48 hours post-fertilization (hpf) by focusing on development, survival, and expression of genes related to acute stress response (crhr1, crfr2), stress/repair response (hsp70, hsp90), water and solute transport (aqp1, aqp3), acid-base regulation (nkcc1a, ncc, car15), and inhibitory neurotransmission (GABAAα6b, Gabra1). Results revealed that embryos developing at intermediate pH showed similar survival rates to the control, but egg swelling was impaired, resulting in a reduction in egg size with decreasing pH. Embryos exposed to extreme pH had 0.6-fold decrease in survival at 24 hpf and a 0.3-fold change at 48 compared to the control. These observed effects of acidification were not reflected by changes in expression of any of the here studied genes. On the contrary, differential expression was observed along embryonic development independent of treatment, indicating that the underlying regulating systems are under development and that embryos are limited in their ability to regulate molecular responses to acidification. In conclusion, exposure to predicted end-of-century ocean pCO2 conditions may affect normal development of this species in nature during sensitive early life history stages with limited physiological response capacities, while extreme acidification will negatively influence embryonic survival and development under hatchery conditions.

2011/2012
Molte attività antropiche sono localizzate lungo le coste e poggiano sui molteplici servizi offerti da questi particolari ecosistemi. Con l’aumentare della vulnerabilità e del sempre più accentuato stato di degrado di queste aree, diverse politiche ambientali sono state sviluppate con lo scopo di promuovere una gestione sostenibile delle risorse naturali, tra cui la Direttiva Quadro sulla Strategia per l’Ambiente Marino (2008/56/EC) in Europa. Le realtà economiche e sociali sono strettamente connesse tra loro e con i sistemi ecologici su cui poggiano. Per comprendere come l’uomo interagisce con l’ambiente, il modello concettuale DPSIR viene ampiamente adottato. Inoltre, sul piano strettamente ecologico, una solida conoscenza del funzionamento dell’ecosistema costiero costituisce un prerequisito fondamentale. Questa tematica complessa deriva dall’integrazione di parametri sia strutturali (caratterizzazione chimica e delle comunità biologiche) che funzionali (quali i principali processi di produzione primaria, respirazione e degradazione della sostanza organica), che nell’insieme descrivono come le varie forme di carbonio sono stoccate e come si realizza il fluire di carbonio ed energia attraverso il sistema. Lo studio del funzionamento dell’ecosistema bentonico costituisce uno strumento particolarmente utile nello sviluppare forme sostenibili di gestione ambientale dal momento che il dominio bentonico funge da deposito di ciò che avviene nella colonna d’acqua. I casi di studio presentati descrivono la parte PSI del modello concettuale DPSIR: come le Pressioni inducono cambiamenti nello Stato dell’ecosistema determinando di conseguenza alterazioni ambientali ed eventuali influenze negative sulle attività umane (Impatti). Lo scopo della tesi consiste nel contribuire a promuovere una gestione basata sull’ecosistema e sul suo funzionamento in aree costiere mediante una miglior conoscenza della sua funzionalità in presenza di specifici stress. I casi di studio vengono presentati secondo un ordine dettato dell’aumentare della complessità dell’approccio seguito: dal più semplice, caratterizzato solo da parametri strutturali, al più complesso, in cui sono stati indagati anche diversi parametri funzionali. La risposta della comunità microalgale bentonica (microfitobenthos - MPB) alle biodeposizioni derivanti dalle mitilicolture è stata studiata non solo paragonando una mitilicoltura con un controllo ma anche considerando le caratteristiche della comunità sotto ad un impianto più recente e in un’area dove l’attività è stata rimossa (Capitolo 2). Questo approccio innovativo permette di indagare l’evoluzione temporale dell’impatto e se è possibile un ripristino. Comparando le quattro aree, la comunità è caratterizzata da una maggiore proliferazione dei taxa tolleranti a condizioni di arricchimento organico sotto alle mitilicolture attive rispetto agli altri due siti. L’area dismessa, inoltre, presenta un popolamento microalgale simile a quello del controllo suggerendo la resilienza del sistema e, di conseguenza, una certa sostenibilità dell’attività di mitilicoltura. Tre comunità bentoniche sono state studiate sinotticamente in un’area costiera soggetta a stress multipli, come l’influenza del Po, la presenza di piattaforme per l’estrazione del gas e il prelievo/scarico di sedimenti (Capitolo3). Insieme alla caratterizzazione chimica, lo studio del MPB, della meiofauna e della macrofauna forniscono una descrizione dello stato dell’ecosistema bentonico in un esempio di monitoraggio che costituisce una base di dati a cui fare riferimento prima di qualsiasi intervento nell’area d’interesse. Lo studio di mesocosmo (Capitolo 4) è focalizzato sulla risposta della comunità microbica bentonica ad un abbassamento di pH dovuto alla fuoriuscita di CO2 da un suo sito di stoccaggio CCS (Carbon dioxide Capture and Storage). Costituisce un esempio di esperimento condotto in laboratorio con lo scopo di simulare eventuali scenari futuri derivanti da un intervento antropico in ambiente naturale prima della sua realizzazione. Relativamente a questo focus, sia i parametri strutturali (abbondanze picobentoniche, densità e composizione del MPB) che i funzionali relativi alla comunità microbica bentonica (attività enzimatiche, Produzione Procariotica di C e respirazione) sono stati studiati per la prima volta. I risultati suggeriscono che la comunità microbica è scarsamente sensibile anche ad un considerevole abbassamento di pH, probabilmente a causa di un effetto buffer esercitato dalla matrice sedimentaria. L’azione sinergica di idrocarburi e metalli pesanti sul funzionamento dell’ecosistema bentonico è stata studiata in un sistema fluviale-lagunare severamente contaminato (Capitolo 5). Numerosi parametri sono stati considerati e dalla loro integrazione deriva un’accurata descrizione del fluire di carbonio attraverso il sistema. I risultati relativi ai parametri microbici come le attività degradative, le produzioni primaria e secondaria e l’analisi del MPB, delineano una situazione inaspettata nel sito considerato più impattato. Il sedimento di tale stazione ospita infatti una comunità microbica bentonica estremamente attiva sia in termini di produttori primari che di procarioti volti al recupero della sostanza organica e conseguente conversione in nuova biomassa. Gli studi presentati in questa tesi non hanno la pretesa di costituire una descrizione esaustiva e completa del funzionamento dell’ecosistema bentonico, ma sottolineano l’importanza di questo approccio innovativo nel contribuire a sviluppare forme sostenibili di gestione delle risorse costiere.
Several human activities are settled along the coasts and rely on the ecosystem services provided by nature. The growing concern about the vulnerability of these areas promotes the development of environmental policies aimed at the sustainable management of the marine resources, such as the Marine Strategy Framework Directive (2008/56/CE) in Europe. Economic, societal and ecological systems are closely interlinked. For understanding how man interacts with the environment, the DPSIR conceptual model is largely adopted. Moreover, a robust knowledge on the coastal ecosystem functioning is needed as a prerequisite. This complex task derives by the integration of both structural (chemical and biological communities) and functional (processes as primary production, respiration and mineralisation) parameters which together describe the forms of carbon storage (organic and inorganic) and the flows of carbon and energy through the system. The study of the benthic ecosystem functioning is a tool particularly useful in developing sustainable management of coastal environments because the benthic domain acts as a repository of what happens in the overlying water. The four case-studies of my thesis focus on the PSI part of the DIPSIR conceptual model, i.e. on how Pressures translate into State changes which may, in turn, negatively affect the environment and the human activities (Impacts). The goal is to contribute in achieving an operational ecosystem-based management of coastal and shallow environments by improving the scientific knowledge on the functioning of shallow benthic ecosystems under specific pressures. The order of the papers is from the simplest to the most complex approach by adding the structural parameters first and then the functional ones. The response of the benthic microalgal community (microphytobenthos - MPB) to the mussel farm biodeposition has been investigated not only comparing the sediment beneath a mussel farm with a control site but also considering a relatively recent mussel farm and a disused one (Chapter 2). This innovative approach in the experimental design allows to study the temporal evolution of the mussel farming impact and the potential recovery of microphytobenthos. The community changes among the four areas with a more pronounced proliferation of those taxa that are tolerant to organic enrichment under the active mussel farms than in the other two sites. The disused farm is characterised by an assemblage similar to that of the control suggesting a resilience of the system and consequently the sustainability of this productive activity. Three benthic communities have been synoptically investigated in a shallow area subjected to multiple-stressor impacts such as the Po River influence, the presence of gas platforms, sediment dumping and sand extraction (Chapter 3). Together with some chemical parameters (Total Organic Carbon, Total Nitrogen, etc.), the synoptic study of different communities (MPB, meiofauna and macrofauna) gives a description of the state of the benthic ecosystem as an example of monitoring survey which represents the reference point for decision-makers prior to any kind of intervention. The mesocosm study (Chapter 4) focuses on the response of shallow benthic microbial communities to a decrease of pH due to the leakage of CO2 from a Carbon dioxide Capture and Storage (CCS) site. This is an example of a laboratory experiment aimed to simulate and predict the possible scenarios derived by an anthropogenic intervention in the natural environment before its actual execution. Benthic microbial structural (prokaryote abundance, MPB densities and composition) and functional parameters (exoenzymatic activities, Prokaryotic C Production and benthic respiration) have been investigated for the first time within this focus. Overall, the findings suggest a microbial community slightly sensitive to consistent pH decrease probably due to a buffer effect exerted by the sedimentary matrix. The synergistic impact of hydrocarbons and heavy metals on the benthic ecosystem functioning has been investigated in a severely contaminated Adriatic lagoon (Chapter 5). Several parameters have been considered in order to describe the overall flow of C through the system. The exoenzymatic activities, the Prokaryotic C Production, MPB composition and the Primary Production suggest an unexpected situation in the site that is considered the most impacted. The sediments at this station are inhabited by a microalgal community that is extremely active in fixing inorganic C through the Primary Production process. In addition, the occurrence of an efficient prokaryotic community in transforming the sedimentary organic C in new biomass, suggests a solid benthic microbial loop. These studies have not the pretence to describe exhaustively the benthic ecosystem functioning. Nevertheless they highlight the importance of this innovative approach in contributing to the development of a sustainable management of coastal resources.
XXV Ciclo
1984

This study examined the effects of temperature and chronic hypoxia (CH) on pH/CO2- sensitive fictive breathing, and central pH/CO2 chemosensitivity, in cane toads (Bufo marinus). Toads were exposed to CH (10% or 15% O2) or control conditions (21% O2) for 10 days at either room temperature (controls), 10°C or 30°C following which in vitro brainstem-spinal cord preparations were used to examine central pH/CO2-sensitive fictive breathing (i.e., motor output from respiratory nerves which is the neural correlate of breathing). A reduction in artificial cerebral spinal fluid (aCSF) pH increased fictive breathing frequency (fR) and total fictive ventilation (TFV). Cold temperature reduced and hot temperature increased fR and TFV under control conditions. CH attenuated fictive breathing independently of temperature. Additional experiments in which the aCSF temperature was varied indicate that the effects of temperature acclimation result from neural plastic changes within respiratory control centres in the brain.

Respiratory alkalosis is a condition characterized by low partial pressure of carbon dioxide and an associated elevation in arterial pH caused by an imbalance between CO2 production and removal, in favour of the latter. Conditions that cause increased alveolar ventilation, without having a reduction in pH as input stimulus, will cause hypocapnia associated with a variable degree of alkalosis. The major effect of hypocapnia is the increase in pH (alkalosis) and the consequent shift of electrolytes that occurs in relation to it. As a general law, in plasma, anions will increase, while cations will decrease. The acute reduction in ionized calcium, due to the change in extracellular pH, may cause neuromuscular symptoms ranging from paraesthesias, to tetany and seizures. The effect on urine is an increase in urinary strong ion difference/urinary anion gap and a consequent increase in urinary pH. Finally, acute hypocapnic alkalosis causes a constriction of cerebral arteries that can lead to a reduction of cerebral blood flow. The clinical approach to respiratory alkalosis is usually directed toward the diagnosis and treatment of the underlying clinical disorder.

Abstract To analyze the ripple effects of CO2 emissions from the introduction of renewable energy power plants, this study developed input–output tables for analysis of next-generation energy systems (IONGES). The results revealed that the environmental benefits obtained from investing in power plants of the same capacity vary significantly depending on the type of renewable energy. Using the IONGES, under assumptions of three carbon taxation methods (upstream, midstream, and downstream), we calculated the taxable CO2 emissions induced when producing each good or service and estimated the carbon tax burden associated with the final demand. We found that, in the upstream method, the taxation effects of one unit of carbon tax is concentrated in energy goods such as coal products and petroleum basic, while the effects are relatively dispersed in the downstream taxation method. If renewable energy is added to the government target level in 2030, taxable CO2 emissions will decrease by 12–13.3%. Compared with the upstream taxation method, in the midstream and downstream methods, the CO2 emissions induced by each final demand are distributed more evenly across various goods and services. Compared to the downstream taxation method, upstream taxation leads to higher CO2 emissions from exports, but lower CO2 emissions from household consumption. This is because energy-intensive industries such as machinery have high export ratios. We analyzed which expenditure categories contribute to the carbon tax burden associated with household consumption. In the case of upstream taxation, households mainly focus on reducing electricity consumption; in the case of downstream taxation, households reduce consumption of various energy-intensive goods and services.

Photoelectrochemical (PEC) splitting of natural water was studied using silicon nanowires decorated with silver dendrites (dendritic nanostructures) as working electrode. A metal assisted wet chemical etching method has been used for the synthesis of dendritic heteronanostructures. Measured photocurrent density 1.7 mA/cm2 under white light illumination exhibits the efficient decomposition of natural water. The decomposition of water is primarily ascribed to the enhancement in the working electrode surface and water effective interface and the decrease in the recombination of light induced (photoexcited) carriers in the existence of silver dendritic nanostructures. Enhancement in photoinduced charge carriers separation caused due to the existence of Schottky barrier between the silicon and silver dendritic nanostructures. The light induced carriers (holes) in silicon are transferred to the metal (Ag) dendritic nanostructures that work as a charge basin to effectively carry out the oxidation reaction of water during PEC measurement. The solar-to-hydrogen (STH) conversion efficiency of about 4.5% was reported, indicating the efficient PEC solar water (pH 7) splitting. A cost-effective and efficient method for the PEC solar water splitting is presented in order to enhance the STH efficiency for the production of clean and renewable fuel.

Abstract Epithermal, Carlin, and orogenic Au deposits form in diverse geologic settings and over a wide range of depths, where Au precipitates from hydrothermal fluids in response to various physical and chemical processes. The compositions of Au-bearing sulfidic hydrothermal solutions across all three deposit types, however, are broadly similar. In most cases, they comprise low-salinity waters, which are reduced, have a near-neutral pH, and CO2 concentrations that range from <4 to >10 wt %. Experimental studies show that the main factor controlling the concentration of Au in hydrothermal solutions is the concentration of reduced S, and in the absence of Fe-bearing minerals, Au solubility is insensitive to temperature. In a solution containing ~300 ppm H2S, the maximum concentration of Au is ~1 ppm, representing a reasonable upper limit for many ore-forming solutions. Where Fe-bearing minerals are being converted to pyrite, Au solubility decreases as temperature cools due to the decreasing concentration of reduced S. High Au concentrations (~500 ppb) can also be achieved in strongly oxidizing and strongly acidic chloride solutions, reflecting chemical conditions that only develop during intense hydrolytic leaching in magmatic-hydrothermal high-sulfidation epithermal environments. Gold is also soluble at low to moderate levels (10–100 ppb) over a relatively wide range of pH values and redox states. The chemical mechanisms which induce Au deposition are divided into two broad groups. One involves achieving states of Au supersaturation through perturbations in solution equilibria caused by physical and chemical processes, involving phase separation (boiling), fluid mixing, and pyrite deposition via sulfidation of Fe-bearing minerals. The second involves the sorption of ionic Au on to the surfaces of growing sulfide crystals, mainly arsenian pyrite. Both groups of mechanisms have capability to produce ore, with distinct mineralogical and geochemical characteristics. Gold transport and deposition processes in the Taupo Volcanic Zone, New Zealand, show how ore-grade concentrations of Au can accumulate by two different mechanisms of precipitation, phase separation and sorption, in three separate hydrothermal environments. Phase separation caused by flashing, induced by depressurization and associated with energetic fluid flow in geothermal wells, produces sulfide precipitates containing up to 6 wt.% Au from a hydrothermal solution containing a few ppb Au. Sorption on to As-Sb-S colloids produces precipitates containing tens to hundreds of ppm Au in the Champagne Pool hot spring. Sorption on to As-rich pyrite also leads to anomalous endowments of Au of up to 1 ppm in hydrothermally altered volcanic rocks occurring in the subsurface. In all of these environments, Au-undersaturated solutions produce anomalous concentrations of Au that match and surpass typical ore-grade concentrations, indicating that near-saturated concentrations of dissolved metal are not a prerequisite for generating economic deposits of Au. The causes of Au deposition in epithermal deposits are related to sharp temperature-pressure gradients that induce phase separation (boiling) and mixing. In Carlin deposits, Au deposition is controlled by surface chemistry and sorption processes on to rims of As-rich pyrite. In orogenic deposits, at least two Au-depositing mechanisms appear to produce ore; one involves phase separation and the other involves sulfidation reactions during water-rock interaction that produces pyrite; a third mechanism involving codeposition of Au-As in sulfides might also be important. Differences in the regimes of hydrothermal fluid flow combined with mechanisms of Au precipitation play an important role in shaping the dimensions and geometries of ore zones. There is also a strong link between Au-depositing mechanisms and metallurgical characteristics of ores.

Over the period from 1750 to 2000, the oceans have absorbed about one-third of the carbon dioxide (CO2) emitted by humans. As the CO2 dissolves in seawater, the oceans become more acidic and between 1750 and 2000, anthropogenic CO2 emissions have led to a decrease of surface-ocean total pH (pH T) by ~0.1 units from ~8.2 to ~8.1 (see Chapters 1 and 3). Surface-ocean pHT has probably not been below ~8.1 during the past 2 million years (Hönisch et al. 2009). If CO2 emissions continue unabated, surface-ocean pH T could decline by about 0.7 units by 2300 (Zeebe et al. 2008). With increasing CO2 and decreasing pH, carbonate ion (CO32–) concentrations decrease and those of bicarbonate (HCO-3) rise. With declining CO32– concentration ([CO32–]), the stability of the calcium carbonate (CaCO3) mineral structure, used extensively by marine organisms to build shells and skeletons, is reduced. Other geochemical consequences include changes in trace metal speciation (Millero et al. 2009 ) and even sound absorption ( Hester et al. 2008 ; Ilyina et al. 2010 ). Do marine organisms and ecosystems really ‘care’ about these chemical changes? We know from a large number of laboratory, shipboard, and mesocosm experiments, that many marine organisms react in some way to changes in their geochemical environment like those that might occur by the end of this century (see Chapters 6 and 7). Generally (but not always), calcifying organisms produce less CaCO3, while some may put on more biomass. Extrapolating such experiments would lead us to expect potentially significant changes in ecosystem structure and nutrient cycling. But can one really extrapolate an instantaneous environmental change to one occurring on a timescale of a century? What capability, if any, do organisms have to adapt to future ocean acidification which is occurring on a slower timescale than can be replicated in the laboratory? Simultaneous changes in ocean temperature and nutrient supply as well as in organisms’ predation environment may create further stresses or work to ameliorate the effect of changes in ocean chemistry.

Acute respiratory distress syndrome (ARDS) is a common cause of admission in the intensive care unit, with pressure- and volume-limited ventilation the cornerstone of mechanical ventilation management. Some physiological studies suggested that an additional decrease of the tidal volume and the respiratory rate could benefit reduction of ventilator-induced lung injury. However, the application of this strategy could be limited by hypercapnia. In that context, extracorporeal CO₂ removal devices could allow further decrease of the tidal volume, respiratory rate, and driving pressure by extracting CO₂ generated by this ultraprotective strategy. However, there are potential complications related to this device, such as bleeding, clotting, and hemolysis, that should be known and promptly recognized by clinicians. This review starts with a clinical case to illustrate this strategy, followed by a review of the actual literature in that field.

This chapter is about the ongoing human-induced shifts in fundamental ocean carbonate chemistry that are occurring globally and are a growing concern to scientists studying marine organisms. It reviews the current state of ocean pH and related carbonate system variables, how they have changed during the industrial era, and how they are expected to continue to change during this century and beyond. Surface-ocean pH has been relatively stable for millions of years, until recently. Over the 800 000 years prior to industrialization, average surfacewater pH oscillated between 8.3 during cold periods (e.g. during the Last Glacial Maximum, 20 000 yr ago) and 8.2 during warm periods (e.g. just prior to the Industrial Revolution), as reviewed by Zeebe and Ridgwell in Chapter 2. But human activities are upsetting this stability by adding large quantities of a weak acid to the ocean at an ever increasing rate. This anthropogenic problem is referred to as ocean acidification because ocean acidity is increasing (i.e. seawater pH is declining), even though surface-ocean waters are alkaline and will remain so. The cause of the decline in seawater pH is the atmospheric increase in the same gas that is the main driver of climate change, namely carbon dioxide (CO2). Due to increasing atmospheric CO2 concentrations, the ocean takes up large amounts of anthropogenic CO2, currently at a rate of about 106 metric tons of CO2 per hour (Brewer 2009), which is equivalent to one-fourth of the current global CO2 emissions from combustion of fossil fuels, cement production, and deforestation (Canadell et al. 2007 ; Le Quéré et al. 2009 ). If we would partition these emissions equally per capita, each person on the planet would be responsible for 4 kg per day of anthropogenic CO2 invading the ocean. To grasp the size of the problem, this invisible invasion may be compared with a recent, highly visible environmental disaster. The ocean currently absorbs anthropogenic carbon at a rate that is about a thousand times greater than from when carbon escaped from the BP Deepwater Horizon oil well that exploded on 20 April 2010, releasing 57 000 barrels of petroleum per day into the Gulf of Mexico until it was capped almost 3 months later.

By the year 2008, the ocean had taken up approximately 140 Gt carbon corresponding to about a third of the total anthropogenic CO2 emitted to the atmosphere since the onset of industrialization (Khatiwala et al. 2009 ). As the weak acid CO2 invades the ocean, it triggers changes in ocean carbonate chemistry and ocean pH (see Chapter 1). The pH of modern ocean surface waters is already 0.1 units lower than in pre-industrial times and a decrease by 0.4 units is projected by the year 2100 in response to a business-as- usual emission pathway (Caldeira and Wickett 2003). These changes in ocean carbonate chemistry are likely to affect major ocean biogeochemical cycles, either through direct pH effects or indirect impacts on the structure and functioning of marine ecosystems. This chapter addresses the potential biogeochemical consequences of ocean acidification and associated feedbacks to the earth system, with focus on the alteration of element fluxes at the scale of the global ocean. The view taken here is on how the different effects interact and ultimately alter the atmospheric concentration of radiatively active substances, i.e. primarily greenhouse gases such as CO2 and nitrous oxide (N2O). Changes in carbonate chemistry have the potential for interacting with ocean biogeochemical cycles and creating feedbacks to climate in a myriad of ways (Box 12.1). In order to provide some structure to the discussion, direct and indirect feedbacks of ocean acidification on the earth system are distinguished. Direct feedbacks are those which directly affect radiative forcing in the atmosphere by altering the air–sea flux of radiatively active substances. Indirect feedbacks are those that first alter a biogeochemical process in the ocean, and through this change then affect the air–sea flux and ultimately the radiative forcing in the atmosphere. For example, when ocean acidification alters the production and export of organic matter by the biological pump, then this is an indirect feedback. This is because a change in the biological pump alters radiative forcing in the atmosphere indirectly by first changing the nearsurface concentrations of dissolved inorganic carbon and total alkalinity.

Abstract.—To provide a synthesis of the physiological responses to otter-trawl capture in spiny dogfish <em>Squalus acanthias</em>, blood values from trawled individuals were evaluated against values from minimally stressed dogfish caught rapidly by hook and line (control). Values and analyses from published studies are considered along with those from the most expansive set of blood samples taken from dogfish captured by both methods to date. Significant impacts of trawling on dogfish blood physiology were reflected in all parameters excluding log plasma protein. Parameters for whole-blood acid–base status (pH, significant decrease; pO₂, 45% decrease; pCO₂, 82% increase), and the metabolite lactate anion (125% increase) were most perturbed relative to differences induced by the capture methods in other parameters. The concentrations of sera monovalent electrolytes (Na⁺, K⁺, Cl^-) and glucose were significantly elevated by trawling, but not to the magnitude seen in other studies related to capture stress in fish. Significant elevations in hematocrit and reductions in blood urea nitrogen (BUN) concentrations were also observed subsequent to trawling. Overall, this capture method incited marked changes in blood physiology relative to values in minimally stressed dogfish. However, previous studies demonstrating high rates of posttrawl dogfish survival indicate that such changes are resolvable in this species prior to lethal consequences.

The average surface-ocean pH is reported to have declined by more than 0.1 units from the pre-industrial level ( Orr et al. 2005 ), and is projected to decrease by another 0.14 to 0.35 units by the end of this century, due to anthropogenic CO2 emissions (Caldeira and Wickett 2005 ; see also Chapters 3 and 14). These global-scale predictions deal with average surface-ocean values, but coastal regions are not well represented because of a lack of data, complexities of nearshore circulation processes, and spatially coarse model resolution (Fabry et al. 2008 ; Chapter 3 ). The carbonate chemistry of coastal waters and of deeper water layers can be substantially different from that in surface water of offshore regions. For instance, Frankignoulle et al. ( 1998 ) reported pCO2 (note 1) levels ranging from 500 to 9400 μatm in estuarine embayments (inner estuaries) and up to 1330 μatm in river plumes at sea (outer estuaries) in Europe. Zhai et al. (2005) reported pCO2 values of > 4000 μatm in the Pearl River Estuary, which drains into the South China Sea. Similarly, oxygen minimum layers show elevated pCO2 levels, associated with the degree of hypoxia (Millero 1996). These findings suggest that some coastal and mid-water animals, both pelagic and benthic, are regularly experiencing hypercapnic hypercapnic conditions (i.e. elevated pCO2 levels), that reach beyond those projected in the offshore surface ocean. These organisms might, therefore, be preadapted to relatively high ambient pCO2 levels. The anthropogenic signal will nonetheless be superimposed on the pre-existing natural variability. These phenomena lead to the question of whether future changes in the ocean’s carbonate chemistry pose a serious problem for marine organisms. Those with calcareous skeletons or shells, such as corals and some plankton, have been at the centre of scientific interest. However, elevated CO2 levels may also have detrimental effects on the survival, growth, and physiology of marine animals more generally (Pörtner and Reipschläger 1996; Seibel and Fabry 2003; Fabry et al. 2008; Pörtner 2008; Melzner et al. 2009a).

A soil is acidic if the pH value of the soil solution is less than 7.0. This condition is met in many soils where rainfall exceeds evapotranspiration, including Alfisols, Histosols, Inceptisols, Oxisols, Spodosols, and Ultisols—almost half of the ice-free land area worldwide. Soils of the humid tropics offer examples of acidic soils (Ultisols and Oxisols), as do soils of forested regions in the temperate zones of Earth (Alfisols, Histosols, Inceptisols, and Spodosols). Soils in peat-producing wetlands and those influenced strongly by oxidation reactions, such as rice-producing uplands, can be mentioned as examples in which the biota play a direct role in acidification. The phenomena that produce a given proton concentration in the soil solution to render it acidic are complex and interrelated. Those pertaining to sources and sinks for protons are shown in Fig. 11.1, which is a special case of Fig. 1.4 with “free cation or anion” in the center of the latter figure now interpreted as H+. In addition to the biogeochemical determinants of soil acidity, the field-scale transport processes wetfall (rain, snow, throughfall), dryfall (deposited solid particles), and interflow (lateral movement of soil water beneath the land surface down hill slopes) carry protons into a soil solution from external sources. Their existence and that of proton-exporting processes, such as volatilization and erosion, underscore the fact that the soil solution is an open natural water system subject to anthropogenic inputs that may dominate the development of soil acidity. Industrial effluents, such as sulfur and nitrogen oxide gases or mining waste waters, that produce acidic deposition or infiltration, and nitrog-enous fertilizers, the transformation and transport of which produce acidic soil conditions, are examples of anthropogenic inputs. Despite all this complexity, proton cycling in acidic soils at field scales has been quantified well enough to allow some general conclusions to be drawn. Acidic deposition, production of CO2(g) and humus, plus proton biocycling, all serve to increase soil solution acidity, whereas proton adsorption and mineral weathering serve to decrease it.

Mass transfer from a bubble to the surrounding liquid plays an important role in chemical engineering processes. To improve the efficiency and safety of the processes, a deep understanding of the mass transfer mechanism from bubbles to the surrounding liquid is essential. In the present study, we examined a CO2 single bubble of 2∼3 mm in equivalent diameter that ascended zigzag in purified water and contaminated water (500ppm 1-pentanol solution). We used a high speed video camera systems with high spatial and temporal resolution, for visualization of the bubble wake and bubble-induced surrounding liquid motion. The dissolution process of CO2 from the bubble to the surrounding liquid was visualized via LIF/HPTS (Laser Induced Fluorescence) method. HPTS, which is a fluorescent substance, was excited by Ar ion laser with a wavelength of 458 nm, then emitted with a wavelength of 513 nm. A pH level of CO2 solution decreased with increase in CO2 concentration; hence the emission intensity of HPTS was reduced. As a result, dark regions observed below the bubble rear accorded with the bubble wakes; from visualization of this bubble wakes through the high speed video cameras, dynamic CO2 dissolution process was obtained. In the purified water, the bubble shape was oblate ellipsoid, and horse-shoe-like vortices were formed in the rear of the bubble. On the other hand, in the contaminated water, the bubble was nearly spherical. Furthermore, behavior of the vortices changed. These different results in two conditions were caused by the decrease in the surface tension owing to the bubble surface contamination. While the bubble was rising, the non-uniform distribution of the surfactant on the bubble surface occurred. Hence, a gradient of the surface tension was formed on the bubble surface, furthermore, it caused the Marangoni convection. Meanwhile, in order to consider the relationship between dissolution process and the surrounding liquid motion, we measured the liquid phase velocities via PIV.

Abstract Sequestration of liquid CO2 into the intermediate depth ocean has been considered as a means to reduce atmospheric concentration of this greenhouse gas and mitigate global warming. A number of CO2 droplets are released and diluted into the intermediate ocean. The behavior of CO2 dissolution is very important in order to control the concentration of CO2 and to keep the environmental impact minimum. Under conditions in the intermediate ocean, that is, high pressure and low temperature, the CO2 clathrate hydrate film was formed on the CO2 droplet surface. The hydrate film has been considered to decrease the dissolution rate and the CO2 concentration near the droplet surface. The authors applied a LIF technique with a new kind of the dye as a pH indicator. The new dye in the CO2 dissolved water emitted intense fluorescence dependent on its pH. The visualized images showed the two dimensional distribution of the pH, i.e., CO2 concentration, around the CO2 droplet with or without the hydrate film.

Cathodic protection (CP) shielding and the presence of carbon dioxide (CO2) in the soil environment are necessary for the occurrence of near-neutral pH stress corrosion cracking (NNPHSCC). Quantitative understanding of the relationship between external conditions, coating deterioration and NNPHSCC is emerging but needs further improvements in modeling and experimental tool. This paper is aimed at understanding the environments initiating the NNPHSCC. New experimental results are presented on crevice chemistry due to the degradation of the mastic of a commercial high-density polyethylene (HDPE) coating and due to CO2 penetration into a disbonded crevice through the coating. Also presented are the results obtained from a comprehensive model, TECTRAN, on the effect of CO2 penetration into a crevice through the holiday alone and through both the holiday and the coating. The experimental results show that as the coating mastic degrades in the soil solution, the solution pH decreases within a few days from about 9 to a steady-state value of about 7.5. The Co2 diffusion through a 0.3 mm commercial HDPE coating is rapid, with a decrease of the soil solution pH from 9 to 5 within a matter of days (external CO2 pressure is 1 atm). The model results show that the presence of CO2 in the soil (0.05 atm partial pressure) can reduce the crevice solution pH to near neutral due mainly to its penetration through the coating, confirming previous hypotheses regarding its role in initiating NNPHSCC.

Initiation of environment-induced cracks in pipeline steels involves interactions among microstructural features, loading conditions and environmental variables. Cyclic, or dynamic, loading has an important role in crack initiation, a competitive process in which cracks form first at the most favorable sites. Under simultaneous cyclic loading and exposure of a Grade 448 (X-65) pipeline steel to aqueous solution of near-neutral pH, NS-4 solution saturated either with CO2 or 5% CO2/ balance N2, cracks that initiated early in the process were associated with pits. A correlation between pits and non-metallic inclusions has been observed. Other locations favorable for localized corrosion attack, such as along the steel surface at the edge of a coating, were also found to be sites for crack initiation. The dense population of cracks that appeared at a later stage of exposure most likely developed from slip-dissolution along certain crystallographic planes. Cracks that formed at an early stage did not always remain as the largest cracks, as crack coalescence, dormancy and/or re-activation, as well as initiation of new cracks, all occurred simultaneously on different parts of the exposure surface.

Abstract Injection of foams can be used to optimize different gas injection processes such as CCUS (Carbon Capture Use & Storage) and possibly to boost oil recovery kinetics in heterogenous or naturally fractured reservoirs (Enick R.M. 2012). In this case, foams, which are more viscous and dense than gases, aim at limiting early gas breakthrough during field operation by improving the sweeping efficiency of reservoirs and by blocking the most permeable areas of the latters (A. Al Sumaiti 2017, Chabert M. and D'Souza D. 2016). A large part of the world oil reservoirs that have already been operated by primary and secondary recovery methods are carbonate reservoirs and are mostly located in the Middle East (Talebian S.H. 2014). In these reservoirs, which are often operated by CO2 injection, the adsorption of surfactants on positively charged carbonates may be a major hindrance to foam injection (Pownall 1989, Cui L. and Ma K. 2014). That is why, cationic surfactants have been developed for these CO2 foam applications (Chen Y. 2016). However, these cationics are often hardly soluble at pH&gt;6 (Jian G. 2019) and/or not industrially avalaible (Cui et Dubos 2018). For this study, we selected three different cationic surfactants. Using automated robotic platforms, we explored a large range of surfactant combination (combining each cationic surfactant with a whole co-surfactant portfolio) at high temperature and in a hard concentrated brine (120g/LTDS, [Ca2+]= 8100ppm). We show that adding co-surfactants to each of these cationics boosts their foaming properties in porous media as well as their solubility at high pH (pH=8) while maintaining low levels of adsorption on carbonates. While a high shear rate is required for cationic surfactants to generate foam in sandpacks, formulations combining cationics and co-surfactants form foams at much lower shear rates. Moreover, the fact that these formulations are soluble at pH=8 means that, on field, the water would no longer need to be acidified at the wellhead to solubilize the surfactant blend. Thus, pipe corrosion induced by the flow of acidified solutions in the surface facilities is prevented. Lastly, all the molecules that are tested in this study are industrially available.

A relation between the integrity of platelet GP IIb/IIIa complex and aggregability by ADP or thrombin was studied on intact platelets with EDTA-induced irreversibly dissociated GP IIb/IIIa complex. Human platelets were washed once and suspended in Ca-, Mg-free HEPES-Tyrode's solution (pH 7d). Aliquots of the suspensions were incubated with 2mM EDTA at 37°C for 2 to 60 min. Control platelets were incubated at 22°C. Then, kwM CaCl2 were added to the samples, which were incubated for another 30 min at 37°C. The platelets were washed twice with HEPES-Tyrode1s solution (pH 6.7). For the measurement of amounts of GP IIb/IIIa complex, the platelets were solubilized with 1% Triton X-100 to 1+ X 10 /yl, five yl of which were subjected to crossed immunoelectrophoresis using constant volumes of anti-platelet antibody. The areas under the immunbprecipitates of GP IIb/IIIa complexes were measured as the amounts of GP Ilb/IIIa complex. For the aggregation studies, the platelets were suspended in HEPES- Tyrode's solution (pH 7d). ADP-aggregations were measured in the presence of added 1mg/ml fibrinogen and 2mM Ca. Platelets incubated with EDTA or CaCl2 at 22°C showed the same amounts of GP IIb/IIIa complex.ADP-aggregability declined more rapidly than the decrease GP Ilb/IIIa complex. In contrast, thrombin-aggregation were much better maintained than ADP-Aggregation during the incubation with 2mM EDTA. These results suggest either that the integrity of GP Ilb/IIIa complex required for ADP-aggregation is more strict than for thrombin-aggregation, or that thrombin-aggreagtion can be caused by an alternative mechanism which does not require the integrity of GP Ilb/IIIa complex.

Stress corrosion cracking behavior of X70 pipeline steel was studied using slow strain rate tests (SSRT) and cyclic loading at high R and low frequency in a nearneutral pH soil solution saturated with 5% CO2+95% N2. The soil was from Xinjiang Uygur Autonomous Region where the Chinese West-East natural gas transmission pipeline started. Electrochemical tests including a potentiodynamic polarization technique and electrochemical impedance spectrum (EIS) were also conducted in order to analyze the effect of the concentration of bicarbonate, bubbled gas and the addition of chloride ion on the polarization behaviors. The results of SSRT showed that transgranular stress corrosion cracking (TGSCC) occurred in Xinjiang soil solution. Crack initiation was associated with pitting, inclusion and streamline of rolling. The susceptibility to SCC increased with the decrease of the applied electrochemical potential and strain rate. Cyclic loading tests with smooth specimens showed that some cracks initiated after certain cycles and cracking mode was transgranular. Under the cyclic loading of high R and low frequency, the crack propagation rate (CPR) of precracked specimens did not increase at some region of stress intensity factor range (ΔK), which showed that the crack propagation process was dominated by SCC. The results of the electrochemical tests showed that the polarization behaviors were influenced greatly by the concentration of bicarbonate, bubbled gas and the addition of chloride ion. Low concentration of chloride ion in bicarbonate could cause the elimination of passivity and SCC behavior to that in near-neutral pH soil solution.