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Query: UMLS:C0847097 (acidity)
 15,165 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Observations of high acidity (pH as low as 1.7) in fogwater collected in polluted areas have provoked concern for public health. Effects of exposure to acidic pollutants have not been studied under foggy conditions; thus there is no directly relevant information from which to estimate the health risk. Indirectly relevant information is available from numerous studies of volunteers exposed to "acid fog precursors" under controlled conditions at less than 100% relative humidity. The effect of fog in modifying responses to inhaled acidic pollutants is difficult to predict: depending on circumstances, fog droplets might either increase or decrease the effective dose of pollutants to the lower respiratory tract. Fog inhalation per se may have unfavorable effects in some individuals. Sulfur dioxide is known to exacerbate airway constriction in exercising asthmatics, at exposure concentrations attainable in ambient air. Nitrogen dioxide has shown little untoward respiratory effect at ambient concentrations in most studies, although it has been suggested to increase bronchial reactivity. Sulfuric acid aerosol has shown no clear effects at concentrations within the ambient range. At somewhat higher levels, increased bronchial reactivity and change in mucociliary clearance have been suggested. Almost no information is available concerning nitric acid.
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PMID:Potential risks to human respiratory health from "acid fog": evidence from experimental studies of volunteers. 300 Jul 61

The endogenous synthesis of cancerogenic N-nitroso compounds: Bacterial flora and nitrite formation in the human stomach. In the discussion of the endogenous nitrosamine synthesis, nitrites play a decisive role. Since in a healthy stomach the acidity important for the nitrosamine formation is present, but since this acid environment is hostile to the bacterial growth and thus counteracts bacterial endogenous nitrite formation, the oral cavity has so far been regarded as the main site of endogenous nitrite formation. An analysis of 130 gastric secretions taken from empty stomachs has demonstrated that also in a healthy stomach considerable germ counts may be obtained in part when acidity is lowered physiologically (e.g. at night). Nitrite concentrations, which are six times as high as the quantities supplied with the saliva at the same time, are also produced in the acid pH range from 4 to 6. Consequently, in a healthy stomach as well the quantity of nitrite available for an endogenous nitrosamine synthesis is by far higher than has been assumed previously. This physiological risk should be allowed for in evaluating the pathophysiological or therapeutic changes in the gastric environment.
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PMID:[Endogenous synthesis of carcinogenic N-nitroso compounds: bacterial flora and nitrite formation in the healthy human stomach]. 667 Apr 12

The toxic action of nitrates and nitrites has often been summarized by methemoglobinemia and nitrosation of amines inducing carcinogenic effects; these two impacts are spectacular, but they hide varying more or less insidious actions recently studied and perceived. In the NO3/NO2 couple, it is accepted that especially nitrite ion lays down a toxicological problem, probably because of its particular chemical reactivity: nitrite ion, which is the base of nitrous acid HNO2 (pKa = 3.36) can react with many functional groups from dietary or endogenous origin; it is also a reducing agent, only oxidable by chemical oxidants or adequate enzyme systems; at the same time it is an oxidant for many reduced substrates. These different possibilities explain the chemical complexity of these compounds and almost their reactivity in biological various media with toxicological implications (modification of the redox state). In man, the presence of nitrates in the digestive tract may result in nitrite formation, because nitrate-reductase from bacterial or enterocyte origin; more particularly in stomach, nitrites are characterized by a great instability imputable to the low pH of gastric juice and to secreted factors which accelerate phenomena; at the same time, nitrates and nutrites exercise opposite effects on gastric secretion (volume, acidity, pepsin) and on gastric mucosal irrigation: while nitrates increase these different parameters, nitrites reduce secretory activity but correlations between secretion and irrigation show that nitrates induce a deep modification of hydric compartment whereas nitrites rather react through cellular anoxy. In intestine, nitrates and chiefly nitrites are very quickly absorbed by a passive mechanism and they are characterized by an extrahepatic cycle; nitrates and nitrites are also eliminated in large quantities by kidneys, and nitrates have a very high diuretic effect: these NO3- ions move Cl- ions, inducing a Na+ waste, a decrease in extracellular space and an alkalosis; this diuretic action of ionic origin is moreover increased by a rise in glomerular blood flow facilitating filtration; these compounds therefore present vasomotor effects, probably by an action on catecholamines whose metabolism is modified. Last, nitrates are suspected to be responsible for reproduction troubles, thyroid dysfunction, perturbances of vitamins availability and nutritional effects. Most of the impacts of nitrates and nitrites are now well known, but their cellular of molecular action is not clear, and as a result there is a suspicion in regard to these products very widely present in food.
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PMID:[Toxicologic and nutritional aspects of nitrates and nitrites]. 702 May 46

The effect of temperature, pH, sodium chloride concentration and a preservative (sodium benzoate, sodium nitrite or potassium sorbate) on the growth of three foodborne bacterial pathogens (Bacillus cereus, Vero cytotoxigenic Escherichia coli and Staphylococcus aureus) was studied using gradient gel plates. Growth, expressed in optical density units, was recorded using image analysis techniques, and was expressed as three-dimensional grids. These gave a visual indication of the effects of any three of the environmental factors on bacterial proliferation. Sorbate was completely effective against E. coli at all temperature/pH/NaCl combinations, and was the most effective preservative tested against B. cereus. Increase in the acidity and/or the NaCl concentration improved the effect of all the preservatives, except nitrite when used against St. aureus. Nitrite was the least effective preservative, particularly against St. aureus. At < 25 degrees C, sorbate was more effective than benzoate against St. aureus when used with higher concentrations of NaCl. At 35 degrees C benzoate was the most effective preservative against St. aureus, especially when used at pH < 6.
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PMID:Effect of three preservatives on the growth of Bacillus cereus, Vero cytotoxigenic Escherichia coli and Staphylococcus aureus, on plates with gradients of pH and sodium chloride concentration. 846 2

Nitrobacter agilis was entrapped in calcium alginate beads and used as a floating bed supplied with a continuous flow of nitrite medium. Complete nitrite oxidation was achieved within 30 h, and the system could be maintained for at least 210 h. The immobilized Nitrobacter system was subjected to sulfur oxyanions, acidity, and metal ions. Thiosulfate and tetrathionate (up to 20 mM each) did not inhibit the nitrite oxidation activity. A low pH of 4.2 resulted in the complete cessation of nitrite oxidation, and the activity was not restored upon increasing the pH to 7. Nitrite oxidation by N. agilis was sensitive to 10 mM each Ni and Al but insensitive to 10 mM MoO(4).
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PMID:Inhibitor Evaluation with Immobilized Nitrobacter agilis Cells. 1634 30

Mucoid, mucA mutant Pseudomonas aeruginosa cause chronic lung infections in cystic fibrosis (CF) patients and are refractory to phagocytosis and antibiotics. Here we show that mucoid bacteria perish during anaerobic exposure to 15 mM nitrite (NO2) at pH 6.5, which mimics CF airway mucus. Killing required a pH lower than 7, implicating formation of nitrous acid (HNO2) and NO, that adds NO equivalents to cellular molecules. Eighty-seven percent of CF isolates possessed mucA mutations and were killed by HNO2 (3-log reduction in 4 days). Furthermore, antibiotic-resistant strains determined were also equally sensitive to HNO2. More importantly, HNO2 killed mucoid bacteria (a) in anaerobic biofilms; (b) in vitro in ultrasupernatants of airway secretions derived from explanted CF patient lungs; and (c) in mouse lungs in vivo in a pH-dependent fashion, with no organisms remaining after daily exposure to HNO2 for 16 days. HNO2 at these levels of acidity and NO2 also had no adverse effects on cultured human airway epithelia in vitro. In summary, selective killing by HNO2 may provide novel insights into the important clinical goal of eradicating mucoid P. aeruginosa from the CF airways.
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PMID:Anaerobic killing of mucoid Pseudomonas aeruginosa by acidified nitrite derivatives under cystic fibrosis airway conditions. 1644 61

We present an ab initio procedure for accurately calculating aqueous-phase pKa values and apply it to study the acidity of nitrous acid (HNO2, or HONO). The aqueous-phase pK(a) of nitrous acid was obtained from calculated gas-phase acidities and solvation free energies via a thermodynamic cycle and the solvation model chemistry of Barone et al. (J. Chem. Phys. 1997, 107, 3210). Solvation free energies were calculated at the HF/6-31G(d) level using the dielectric-polarizable continuum and the integral equation formalism-polarizable continuum solvent models (D-PCM and IEF-PCM, respectively), with the D-PCM model yielding the most accurate pKa values. For HF free energies of solvation, significant improvements in accuracy could be made by moving to the larger 6-311++G(3df,3pd) and aug-cc-pVQZ basis sets. Solvation free energies were also calculated using the density functional theory (DFT) methods B3LYP, TPSS, PBE0, B1B95, VSXC, B98 and O3LYP, with the most accurate methods being TPSS and VSXC, which provided average errors of less than 0.11 pKa units. Solvation free energies calculated with the different DFT methods were relatively insensitive to the basis set used. Our theoretical calculations are compared with experimental results obtained using stopped flow spectrophotometry. The pKa of nitrous acid was measured as 3.16 at 25 degrees C, and the enthalpy and entropy of nitrous acid dissociation were calculated from measurements as 6.7 kJ mol(-1) and -38.4 J mol(-1) K(-1), respectively, between 25 and 45 degrees C. The UV/visible absorption spectra of the nitrite ion and nitrous acid were also examined, and molar extinction coefficients were obtained for each.
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PMID:Ab initio procedure for aqueous-phase pKa calculation: the acidity of nitrous acid. 1700 48

An automatic direct spectrophotometric method for the simultaneous determination of nitrite and nitrate by flow-injection analysis has been developed. Nitrite reacts with 3-nitroaniline in the presence of hydrochloric acid (0.96-1.8 M HCl or pH 0.5-0.7) to form a diazonium cation, which is subsequently coupled with N-(1-naphthyl)-ethylenediamine dihydrochloride to form a stable purple azo dye, the absorbance of which is measured at 535 nm. Nitrate is reduced on-line to nitrite in a copper-coated cadmium column which is then treated with azo dye reagent and the absorbance due to the sum of nitrite and nitrate is measured; nitrate is determined from the difference in absorbance values. A copper column incorporated into the reaction manifold before the copperised cadmium column not only improves the long-term accuracy, but also extends the life time of the copperised cadmium column. Various analytical parameters, such as effect of acidity (pH), flow rate, sample size, dispersion coefficient, time, temperature, reagent concentration and interfering species, were studied. The calibration graphs were rectilinear for 0.1-3.5 mug ml(-1) of NO(3) and 10 ng ml(-1)-2.2mug ml(-1) of NO(2). The method is successfully applied to some food samples (meat, flour and cheese), environmental waters (inland and surface), beer and soil samples. Up to 30 samples can be analysed per hour with a relative precision of approximately 0.1-2%.
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PMID:Simultaneous spectrophotometric determination of nitrite and nitrate by flow-injection analysis. 1896 74

Water sample were collected from six different point of the Mouri River Khulna, Bangladesh with a regular intervals in the months of January-March 2002 for the analyzing different physicochemical parameters of the water. Total 22 different physicochemical parameters were investigated. Correlation and the t value among the parameters were also determined. In the present investigation the minimum and maximum value of water temperature, Transparency, Turbidity, TSS, TDS, Electric Conductivity, water pH, dissolve oxygen, free Carbon dioxide, Alkalinity, Acidity, Hardness, BOD, COD, Sulphate, Phosphate, Nitrite, Sodium, Calcium, Potassium, Manganese and Iron were noted as 21.6 and 32.2 degrees C; 15 and 66 cm; 16 and 22 NTU; 74 and 125 mg L(-1); 255 and 305 mg L(-1); 159 and 275 microS cm(-1); 1.10 mg L(-1) 8.18 mg L(-1); 7.5 and 8.3; 1.1 and 8.3 mg L(-1); 27.5 and 35.5 mg L(-1); 350 and 610 mg L(-1); 32.4 and 171 mg L(-1); 310 and 529 mg L(-1); 13 and 31 mg L(-1); 290 and 365 mg L(-1); 42046 and 57.35 mg L(-1); 4.89 and 11.46 mg L(-1); 0.54 and 1.82 mg L(-1); 16.8 and 33.9 mg L(-1); 1.5 and 6.9 mg L(-1); 49 and 94 mg L(-1); 31 and 59 mg L(-1); 2.6 and 3.8 mg L(-1), respectively. River water did not show any significant pollution during the present study. During the study period dissolved oxygen show direct relation with water temperature but inverse with BOD and COD.
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PMID:Study on the physico chemical properties of water of Mouri River, Khulna, Bangladesh. 1906 52

Nitrite has been implicated in carcinogenesis, especially under acidic conditions such as in the stomach or in urine, where it forms nitrosating species that can react with secondary amines to form nitrosamines. Recent studies have shown that nitrite and acid form a variety of other nitrogen oxides in vivo including nitric oxide-a compound with documented antitumor activity. Here we tested the effects of nitrite on bladder tumor cells incubated in mildly acidified urine. Nitrite (50 microM) inhibited thymidine incorporation in human T24 bladder cancer cells. This inhibition required slight acidification (pH 5.5-6), and no effect of nitrite could be observed at pH 7. Nitrite effects were further augmented in the presence of ascorbic acid, whereas ascorbic acid alone had no effect. The effects were paralleled by formation of nitric oxide gas. We here demonstrate an inhibitory effect of nitrite on cancer cell replication at concentrations and acidity commonly found in urine and gastric juice. The inhibitory effect is likely caused by nitric oxide and possibly other reactive nitrogen oxides formed from acidified nitrite.
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PMID:Inhibition of cancer cell replication by inorganic nitrite. 2043 71


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