The neutralization of acidic coal mine lakes by additions of natural organic matter: a mesocosm test

Cylindrical polyethylene enclosures 3 m in length and 1 m in diameter reaching from the surface to the bottom were constructed in an acid (pH=3.1) lake on a coal surface mine in southern Illinois. Wheat straw was added to the enclosures to test the effects of dissimilatory sulfate reduction on water chemistry. Added straw increased sulfide concentrations, raised pH to 6.5, reduced O₂ and increased acid neutralizing capacity of the enclosed water columns when compared with a control enclosure and with the open lake. Generation of acid neutralizing capacity exceeded the standing stock of sulfide indicating that sulfide was removed either by precipitation of FeS or outgassing of H₂S. The pH and acid neutralizing capacity within the enclosures eventually returned to the level of the surrounding lake because of water exchange around the enclosure walls. Our results show that additions of organic matter to acid surface mine lakes result in the generation of acid neutralizing capacity.     

Combination of dual-energy computed tomography and iterative metal artefact reduction to increase general quality of imaging for radiotherapy patients with high dense materials. Phantom study

PurposeTo evaluate the use of pseudo-monoenergetic reconstructions (PMR) from dual-energy computed tomography, combined with the iterative metal artefact reduction (iMAR) method.MethodsPseudo-monoenergetic CT images were obtained using the dual-energy mode on the Siemens Somatom Definition AS scanner. A range of PMR combinations (70–130 keV) were used with and without iMAR. A Virtual Water™ phantom was used for quantitative assessment of error in the presence of high density materials: titanium, alloys 330 and 600. The absolute values of CT number differences (AD) and normalised standard deviations (NSD) were calculated for different phantom positions. Image quality was assessed using an anthropomorphic pelvic phantom with an embedded hip prosthesis. Image quality was scored blindly by five observers.ResultsAD and NSD values revealed differences in CT number errors between tested sets. AD and NSD were reduced in the vicinity of metal for images with iMAR (p < 0.001 for AD/NSD). For ROIs away from metal, with and without iMAR, 70 keV PMR and pCT AD values were lower than for the other reconstructions (p = 0.039). Similarly, iMAR NSD values measured away from metal were lower for 130 keV and 70 keV PMR (p = 0.002). Image quality scores were higher for 70 keV and 130 keV PMR with iMAR (p = 0.034).ConclusionThe use of 70 keV PMR with iMAR allows for significant metal artefact reduction and low CT number errors observed in the vicinity of dense materials. It is therefore an attractive alternative to high keV imaging when imaging patients with metallic implants, especially in the context of radiotherapy planning.     

EPR properties of mixed-valent μ-oxo and μ-hydroxo dinuclear iron complexes produced by radiolytic reduction at 77 K

 Radiolytic reduction at 77 K of oxo-/hydroxo-bridged dinuclear iron(III) complexes in frozen solutions forms kinetically stabilized, mixed-valent species in high yields that model the mixed-valent sites of non-heme, diiron proteins. The mixed-valent species trapped at 77 K retain ligation geometry similar to the initial diferric clusters. The shapes of the mixed-valent EPR signals depend strongly on the bridging ligands. Spectra of the Fe(II)OFe(III) species reveal an S=1/2 ground state with small g-anisotropy as characterized by the uniaxial component (g _z –g _av /2<0.03) observable at temperatures as high as ∼100 K. In contrast, hydroxo-bridged mixed-valent species are characterized by large g-anisotropy (g _z –g _av /2>0.03) and are observable only below 30 K. Annealing at higher temperatures causes structural relaxation and changes in the EPR characteristics. EPR spectral properties allow the oxo- and hydroxo-bridged, mixed-valent diiron centers to be distinguished from each other and can help characterize the structure of mixed-valent centers in proteins. Received: 27 June 1998 / Accepted: 25 February 1999     

Sodium dependence of growth and methane formation in Methanobacterium thermoautotrophicum

Methanobacterium thermoautotrophicum was found to require sodium for growth and for CO₂ reduction to methane. The dependence of the rate of growth and methane formation on the sodium concentration was hyperbolic with an apparent K _s for sodium of approximately 1 mM. The findings indicate that sodium has a specific function in the energy metabolism of this bacterium.     

Flavonoid diversity and endemism in Arnica subgenus Austromontana

Eighty-seven populations, representing eight species of Amica subgenus Austromontana, were examined for flavonoids. A total of 22 compounds, including simple and methylated flavone and flavonol glycosides as well as methylated aglycones, were isolated and identified. The two widespread species, A. cordifolia and its presumed early derivative A. latifolia, are ancestral species of the subgenus. From these two species, major evolutionary diversification within the subgenus has taken place largely in the Klamath region of Oregon and California, resulting in the formation of several rare, endemic species. These endemics are generally characterized by reduced flavonoid profiles and/or an increase in the number of methylated aglycones while, in contrast, the wider ranging species have few methylated aglycones and more glycosides. However, one species, A. viscosa, a rare volcanic endemic, exhibits the most elaborate and specialized flavonoid profile within the subgenus.     

Screening method for the detection of uptake hydrogenase activity of Rhizobium leguminosarum bacteroids

Abstract A method has been developed for screening Rhizobium leguminosarum wild-type strains and mutants for uptake hydrogenase (Hup) activity, using H₂-dependent methylene blue reduction. For this purpose, a simple device has been constructed which allows the simultaneous screening of 6 strains and 6 controls. Bacteroids of R. leguminosarum isolated from pea root nodules were suspended in buffer containing methylene blue and inhibitors of dehydrogenases. The suspensions were first sparged with argon (to remove oxygen) and then with hydrogen.     

Modification of the in vitro Cytotoxicity of Hydrogen Peroxide by Iron Complexes

The effect of a range of iron chelates on the cytotoxicity of H₂O₂ was studied on a mammalian epithelial cell line. Iron complexes which were internalised enhanced the cytotoxicity of H₂O₂ measured by delayed thymidine incorporation. Iron complexed to 8-hydroxyquinoline (Fe/8-HQ) potentiated the cytotoxicity of 50 µM by 38% and Fe/dextran by 23%. Pre-exposure of cells to Fe/dextran at 4°C did not result in any potentiation of H₂O₂-induced cytotoxicity which we ascribe to failure of the Fe/dextran to be endocytosed at low temperature. Iron complexes which are slowly taken up or remain extracellular protected the cells from H₂O₂-induced cytotoxicity. Thus, Fe/EDTA inhibited the cytotoxicity of 50 µM H₂O₂ by 33%; Fe/ADP by 80% and Fe/ATP by 88%, suggesting mutual extracellular detoxification.