Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UMLS:C0847097 (acidity)
 15,165 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The duration of acid mine drainage flowing out of underground mines is important in the design of watershed restoration and abandoned mine land reclamation projects. Past studies have reported that acid water flows from underground mines for hundreds of years with little change, while others state that poor drainage quality may last only 20 to 40 years. More than 150 above-drainage (those not flooded after abandonment) underground mine discharges from Pittsburgh and Upper Freeport coal seams were located and sampled during 1968 in northern West Virginia, and we revisited 44 of those sites in 1999-2000 and measured water flow, pH, acidity, Fe, sulfate, and conductivity. We found no significant difference in flows between 1968 and 1999-2000. Therefore, we felt the water quality data could be compared and the data represented real changes in pollutant concentrations. There were significant water quality differences between year and coal seam, but no effect of disturbance. While pH was not significantly improved, average total acidity declined 79% between 1968 and 1999-2000 in Pittsburgh mines (from 66.8 to 14 mmol H+ L(-1)) and 56% in Upper Freeport mines (from 23.8 to 10.4 mmol H+ L(-1)). Iron decreased an average of about 80% across all sites (from an average of 400 to 72 mg L(-1)), while sulfate decreased between 50 and 75%. Pittsburgh seam discharge water was much worse in 1968 than Upper Freeport seam water. Twenty of our 44 sites had water quality information in 1980, which served as a midpoint to assess the slope of the decline in acidity and metal concentrations. Five of 20 sites (25%) showed an apparent exponential rate of decline in acidity and iron, while 10 of 20 sites (50%) showed a more linear decline. Drainage from five Upper Freeport sites increased in acidity and iron. While it is clear that surface mines and below-drainage underground mines improve in discharge quality relatively rapidly (20-40 years), above-drainage underground mines are not as easily predicted. In total, the drainage from 34 out of 44 (77%) above-drainage underground mines showed significant improvement in acidity over time, some exponentially and some linearly. Ten discharges showed no improvement and three of these got much worse.
 ...
PMID:Longevity of acid discharges from underground mines located above the regional water table. 1507 18

Biosynthesis and uptake of siderophores in Aspergillus nidulans are regulated not only by iron availability but also by ambient pH: expression of this high-affinity iron uptake system is elevated by an increase in the ambient pH. Mediation of this regulation by the transcriptional regulator PacC has been confirmed via acidity- and alkalinity-mimicking mutants.
 ...
PMID:Biosynthesis and uptake of siderophores is controlled by the PacC-mediated ambient-pH Regulatory system in Aspergillus nidulans. 1507 86

Water samples draining a disused copper mine (Parys Mountain) in Anglesey, North Wales, were analysed for distribution of acidophilic bacteria (iron oxidising and heterotrophic) and for changes in physicochemical composition along the length of the drainage stream. Ten samples were taken at regular distance intervals along a 1 km stretch from the source of the acid mine drainage. The stream remained highly acidic (pH < 2.8) although a slight decrease (0.6 pH unit) in acidity with distance from source was observed. Concentrations of most metals measured decreased with distance along the length of the stream, although some showed a gradual increase and others peaked at c. 200 m from source. Most dissolved iron was in the ferrous form in the upper reaches of the stream, but ferric iron became increasingly dominant downstream as a result of microbial oxidation. Although concentrations of nutrients such as nitrogen and phosphorus were low in the acid mine drainage, they were not limiting rates of bacterial iron oxidation, which appeared to be limited more by temperature. The iron oxidising bacteria Thiobacillus ferrooxidans and Leptospirillum ferrooxidans were both isolated from all sampling sites, although their relative abundances varied; L. ferrooxidans accounted for 57% of all iron oxidising isolates. Numbers of iron oxidising bacteria decreased with distance from drainage source, in contrast to those of acidophilic heterotrophic bacteria which increased. The diversity of heterotrophic isolates also increased with distance. The relationship between the chemistry and microbiology of the stream is discussed.
 ...
PMID:Microbiological and chemical characteristics of an acidic stream draining a disused copper mine. 1509 99

The subsurface sorption of Suwannee River fulvic acid (SRFA) and humic acid (SRHA) onto a synthetic aquifer material (iron-oxide-coated quartz) and two natural aquifer materials (Ringold sediment and Bemidji soils) was studied in both batch and column experiments. The hypothesis that hydrophobic effects followed by ligand exchange are the dominant mechanism contributing to the chemical sorption happening between dissolved natural organic matter (NOM) and the mineral surfaces is supported by observations of several phenomena: nonlinear isotherms, faster sorption rates versus slower desorption rates, phosphate competition, a solution pH increase during NOM sorption, and functional groups and aromaticity-related sorption. In addition, high-pressure size exclusion chromatography (HPSEC) and carboxylic acidity showed that lower molecular weight NOM components of SRHA are preferentially sorbed to iron oxide, a result in contrast to that for SRFA. Phosphate increased the desorption of sorbed NOM as well as soil organic matter. All of these trends support ligand exchange as the dominant reaction between NOM and the iron oxide surfaces; however, if the soil surface has been occupied by soil organic matter, then the sorption of NOM is more due to hydrophobic effect.
 ...
PMID:Kinetic study on the sorption of dissolved natural organic matter onto different aquifer materials: the effects of hydrophobicity and functional groups. 1514 9

Iron oxide (Fe2O3) was identified and characterized by surface area, X-ray diffractometry, and FTIR analyses. Surface charge densities, point of zero charge (PZC), and surface ionization constants were determined from the potentiometric titration data in various aqueous and aqueous organic mixed solvents in the temperature range 293-313 K. The surface charge densities were observed to decrease with the increase in temperature and concentration of metal ions in both the aqueous and aqueous organic mixed solvents. The absolute values of the surface charge density were found to change in the order aqueous > aqueous/methanol > aqueous/ethanol. Further, the PZC of the iron oxide was observed to shift to the higher pH values in the order ethanol > methanol > aqueous solution, which indicated a decrease in the acidity of the surface -OH groups. The pKa1 and pKa2 values of iron oxide were also determined and then used for determination of the surface potential (psi0) of the solid in aqueous and aqueous organic mixed solvents. The surface potential-surface charge curves generally supplemented the results derived from psi0-pH curves.
 ...
PMID:Surface charge properties of Fe2O3 in aqueous and alcoholic mixed solvents. 1517 82

The oxidative dissolution of pyrite (FeS2) by pure and mixed cultures of moderately thermophilic acidophiles was studied in shake flask cultures and in pH-controlled bioreactors, incubated at 45 degrees C. Various combinations of seven eubacteria (a Leptospirillum sp. (MT6), Acidimicrobium ferrooxidans, Acidithiobacillus caldus, an Alicyclobacillus sp. (Y004), and three Sulfobacillus spp.) and one archaeon (Ferroplasma sp. MT17) were examined. Pyrite dissolution was determined by measuring changes in soluble iron and generation of acidity, and microbial populations were monitored using a combined culture-dependent (plate counts) and culture-independent (fluorescent in situ hybridization) approach. In pure cultures, the most efficient pyrite-oxidizing acidophile was Leptospirillum MT6, which was unique among the prokaryotes used in being obligately autotrophic. Mixed cultures of Leptospirillum MT6 and the sulfur-oxidizer At. caldus generated more acidity than pure cultures of the iron-oxidizer, though this did not necessarily enhance pyrite dissolution. In contrast, a mixed culture of Leptospirillum MT6 and the obligate heterotroph Alicyclobacillus Y004 oxidized pyrite more rapidly and more completely than a pure culture of Leptospirillum MT6, in synchronized bioreactors. Although the autotroph, At. caldus, and the "heterotrophically inclined" iron-oxidizer, Am. ferrooxidans, were both ineffective at leaching pyrite in pure culture, a mixed culture of the two bacteria was able to accelerate dissolution of the mineral. Concentrations of dissolved organic carbon accumulated to >100 mg/L in some mixed cultures, and the most effective bioleaching systems were found to be consortia containing both autotrophic and heterotrophic moderate thermophiles. A mixed culture comprising the autotrophs Leptospirillum MT6 and At. caldus, and the heterotroph Ferroplasma MT17, was the most efficient of all of those examined. Mutualistic interactions between physiologically distinct moderately thermophilic acidophiles, involving transfer of organic and inorganic carbon and transformations of iron and sulfur, were considered to have critical roles in optimizing pyrite dissolution.
 ...
PMID:Biooxidation of pyrite by defined mixed cultures of moderately thermophilic acidophiles in pH-controlled bioreactors: significance of microbial interactions. 1535 55

Chitosan microspheres are highly effective in neutralizing the acidity of wastewaters from coal mining. The saturation capacity for the formation of a superficial monolayer on the adsorbent was interpreted using Langmuir isotherm and considering the amino groups as the adsorption sites for hydronium ions. The saturation capacity of the surface of the static system was 0.428 mol kg(-1), higher than that of the dynamic one. This value corresponds to the neutralization of 135 liters of wastewater per kilogram of microspheres. One gram of chitosan microspheres was capable of increasing wastewater pH from 2.5 to 4.0 and removing approximately 100% of its iron (III) contents.
 ...
PMID:Use of chitosan microspheres as remedial material for acidity and iron (III) contents of coal mining wastewaters. 1536 52

A series of iron(III) complexes of the tetradentate ligand BPMEN (N,N'-dimethyl-N,N'-bis(2-pyridylmethyl)ethane-1,2-diamine) were prepared and structurally characterized. Complex [Fe(2)(mu-O)(mu-OH)(BPMEN)(2)](ClO(4))(3) (1) contains a (mu-oxo)(mu-hydroxo)diiron(III) diamond core. Complex [Fe(BPMEN)(urea)(OEt)](ClO(4))(2) (2) is a rare example of a mononuclear non-heme iron(III) alkoxide complex. Complexes [Fe(2)(mu-O)(mu-OC(NH(2))NH)(BPMEN)(2)](ClO(4))(3) (3) and [Fe(2)(mu-O)(mu-OC(NHMe)NH)(BPMEN)(2)](ClO(4))(3) (4) feature N,O-bridging deprotonated urea ligands. The kinetics and equilibrium of the reactions of 1 with ligands L (L = water, urea, 1-methylurea, 1,1-dimethylurea, 1,3-dimethylurea, 1,1,3,3-tetramethylurea, and acetamide) in acetonitrile solutions were studied by stopped-flow UV-vis spectrophotometry, NMR, and mass spectrometry. All these ligands react with 1 in a rapid equilibrium, opening the four-membered Fe(III)(mu-O)(mu-OH)Fe(III) core and forming intermediates with a (HO)Fe(III)(mu-O)Fe(III)(L) core. The entropy and enthalpy for urea binding through oxygen are DeltaH degrees = -25 kJ mol(-1) and DeltaS degrees = -53.4 J mol(-1) K(-1) with an equilibrium constant of K(1) = 37 L mol(-1) at 25 degrees C. Addition of methyl groups on one of the urea nitrogen did not affect this reaction, but the addition of methyl groups on both nitrogens considerably decreased the value of K(1). An opening of the hydroxo bridge in the diamond core complex [Fe(2)(mu-O)(mu-OH)(BPMEN)(2)] is a rapid associative process, with activation enthalpy of about 60 kJ mol(-1) and activation entropies ranging from -25 to -43 J mol(-1) K(-1). For the incoming ligands with the -CONH(2) functionality (urea, 1-methylurea, 1,1-dimethylurea, and acetamide), a second, slow step occurs, leading to the formation of stable N,O-coordinated amidate diiron(III) species such as 3 and 4. The rate of this ring-closure reaction is controlled by the steric bulk of the incoming ligand and by the acidity of the amide group.
 ...
PMID:Reactivity of a (mu-oxo)(mu-hydroxo)diiron(III) diamond core with water, urea, substituted ureas, and acetamide. 1550 Mar 59

Investigation of the water quality of the Ubu river has been carried out. The upstream course of the river is slightly acidic (pH 5.45 +/- 0.23), and the acidity decreases along the lower courses of the river. Turbidity, surfactant, and iron content parameters of the river increased during the wet season, and these changes have been attributed to inputs from flood, leachates of soil erosion, and storm water runoff discharged into the river in increased quantities during the season. Concentrations of some metals were found to increase during the dry season because of absence of dilution of the river by storm water runoff. Most water quality parameters are within World Health Organization acceptable limits set for potable water, and they include most of the cationic and anionic constituents. Although there is no hydrocarbon or metal ion pollution, potability is reduced along the mid to downstream courses of the river by unacceptable levels of turbidity, surfactant concentration, and iron content, particularly during the wet season.
 ...
PMID:Monitoring of seasonal variation in the water quality of Ubu river in Ekwusigo and Nnewi local government areas of Anambra State, Nigeria. 1551 85

This field evaluation study was conducted to assess new technology designed to measure number concentrations of strongly acidic ultrafine particles. Interest in these particles derives from their potential to cause adverse health effects. Current methods for counting and sizing airborne ultrafine particles cannot isolate those particles that are acidic. We hypothesized that the size-resolved number concentration of such particles to which people are exposed could be measured by newly developed iron nanofilm detectors on which sulfuric acid (H2SO4*) droplets produce distinctive ringed reaction sites visible by atomic force microscopy (AFM). We carried out field measurements using an array of samplers, with and without the iron nanofilm detectors, that allowed indirect comparison of particle number concentrations and size-resolved measures of acidity. The iron nanofilm detectors are silicon chips (5 mm x 5 mm x 0.6 mm) that are coated with iron by vapor deposition. The iron layer was 21.5 or 26 nm thick for the two batches used in these experiments. After exposure the detector surface was scanned topographically by AFM to view and enumerate the ringed acid reaction sites and deposited nonacidic particles. The number of reaction sites and particles per scan can be counted directly on the image displayed by AFM. Sizes can also be measured, but for this research we did not size particles collected in the field. The integrity of the surface of iron nanofilm detectors was monitored by laboratory analysis and by deploying blank detectors and detectors that had previously been exposed to H2SO4 calibration aerosols. The work established that the detectors could be used with confidence in temperate climates. Under extreme high humidity and high temperature, the surface film was liable to detach from the support, but remaining portions of the film still produced reliable data. Exposure to ambient gases in a filtered air canister during the field tests did not affect the film quality. Sampling sessions to obtain particle measurements were scheduled for two 1-week periods in each of the four seasons at a rural site in Tuxedo, New York. This schedule was selected to test outdoor performance of the iron nanofilm detectors under a variety of weather conditions. To seek possible artifacts caused by local source differences, we also sampled outdoors for two 1-week sessions during the winter in New York City. Indoor tests were conducted in the cafeteria at the Nelson Institute of Environmental Medicine (NIEM) in Tuxedo and in a residence in Newburgh, New York. For the outdoor tests we simultaneously deployed several particle samplers to obtain several measures: --the number concentration of acidic and total particles that penetrated the 100-nm cut size of a microorifice impactor (MOI) and were electrically precipitated in an electrostatic aerosol sampler (EAS) onto the iron nanofilm detectors; --the number concentrations of acidic and total particles estimated from detectors placed in a simple ultrafine diffusion monitor (UDM); --the size-fractionated mass concentration of strong acids in samples from the submicrometer collection stages of the MOI and from a polycarbonate filter, parallel to the EAS, that also collected particles penetrating the MOI's 100-nm cut size; and --the number concentration of all ambient particles with diameters of 300 nm or smaller, determined using a scanning mobility particle sizer (SMPS). In the results from these samplers, the mean number concentration of acidic particles ranged from about 100 to 1800/cm3, representing 10% to 88% of all ambient ultrafine particles for the different seasons and sites. The number concentration did not correlate with the acidic mass (hydrogen ion, or H+, content) for particles smaller than 100 nm in diameter. This was not surprising because a single 100-nm particle may contain the same acid volume as many smaller particles if they are pure acid droplets. The ambient concentrations of H+, sulfate (SO4(2-)), and ammonium (NH4+), collected on polycarbonate filters and measured as a function of particle size, were highest for particles with diameters between 280 and 530 nm, but the size distributions also suggested that a small peak of these ions existed in the particle size range below 88 nm. The H+ / SO4(2-) ratio was somewhat higher for particles below 88 nm, suggesting greater excess acidity for these small particles. Our continuous monitoring showed that airborne concentrations of ultrafine particles varied substantially with time. The iron nanofilm detectors provided a time-integrated number concentration over several days or weeks. The counts on the detectors were relatively low for some of the sampling sessions, resulting in high statistical errors in calculations. Nonetheless, agreement of the mean values was remarkably good for some of the measurements. In future tests, longer collection times and new technologies, such as improved particle-charging methods for electrical precipitation samplers, could provide more efficient collection of particles onto the detectors, higher counts, and lower count-associated uncertainties. In general, concentrations of ultrafine particles determined by AFM analysis of the detectors in the MOI-EAS and UDM appeared to underestimate the total number concentration as determined by comparison samplers. The ability to monitor airborne acidic particles provided by these iron nanofilm detectors enlarges the array of air quality variables that can be measured. This may help to resolve some of the outstanding questions related to causal relations between demonstrated health effects of ambient particles and particulate matter (PM) components.
 ...
PMID:Field evaluation of nanofilm detectors for measuring acidic particles in indoor and outdoor air. 1555 89


<< Previous 1 2 3 4 5 6 7 8 9 10