Sorption of Co(II), Ni(II), and Zn(II) on biogenic manganese oxides produced by a Mn-oxidizing fungus, strain KR21-2.

The characteristics of Co(II), Ni(II), and Zn(II) sorption on freshly produced biogenic Mn oxides by a Mn-oxidizing fungus, strain KR21-2, were investigated. The biogenic Mn oxides showed about 10-fold higher efficiencies for sorbing the metal ions than a synthetic Mn oxide (gamma-MnO2) on the basis of unit weight and unit surface area. The order of sorption efficiency on the biogenic Mn oxides was Co(II) > Zn(II) > Ni(II), while that on the synthetic Mn oxide was Zn(II) > Co(II) > Ni(II). These sorption selectivities were confirmed by both sorption isotherms and competitive sorption experiments. Two-step extraction, using 10mM CuSO4 solution for exchangeable sorbed ions and 10-20mM hydroxylamine hydrochloride for ions bound to reducible Mn oxide phase, showed higher irreversibility of Co(II) and Ni(II) sorption on the biogenic Mn oxides while Zn(II) sorption was mostly reversible (Cu(II)-exchangeable). Sorptions of Co(II), Ni(II), and Zn(II) on the synthetic Mn oxide were, however, found to be mostly reversible. Higher irreversibility of Co(II) and Ni(II) sorption on the biogenic Mn oxides may partly explain higher accumulation of these metal ions in Mn oxide phases in natural environments. The results obtained in this study raise the possibility to applying the biogenic Mn oxide formation to treatment of water contaminated with toxic metal ions.

Interaction of inorganic arsenic with biogenic manganese oxide produced by a Mn-oxidizing fungus, strain KR21-2.

In batch culture experiments we examined oxidation of As(III) and adsorption of As(III/V) by biogenic manganese oxide formed by a manganese oxide-depositing fungus, strain KR21-2. We expected to gain insight into the applicability of Mn-depositing microorganisms for biological treatment of As-contaminated waters. In cultures containing Mn2+ and As(V), the solid Mn phase was rich in bound Mn2+ (molar ratio, approximately 30%) and showed a transiently high accumulation of As(V) during the early stage of manganese oxide formation. As manganese oxide formation progressed, a large proportion of adsorbed As(V) was subsequently released. The high proportion of bound Mn2+ may suppress a charge repulsion between As(V) and the manganese oxide surface, which has structural negative charges, promoting complex formation. In cultures containing Mn2+ and As(III), As(III) started to be oxidized to As(V) after manganese oxide formation was mostly completed. In suspensions of the biogenic manganese oxides with dissolved Mn2+, As(III) oxidation rates decreased with increasing dissolved Mn2+. These results indicate that biogenic manganese oxide with a high proportion of bound Mn2+ oxidizes As(III) less effectively than with a low proportion of bound Mn2+. Coexisting Zn2+, Ni2+, and Co2+ also showed similar effects to different extents. The present study demonstrates characteristic features of oxidation and adsorption of As by biogenic manganese oxides and suggests possibilities of developing a microbial treatment system for water contaminated with As that is suited to the actual situation of contamination.

Enzymatic formation of manganese oxides by an Acremonium-like hyphomycete fungus, strain KR21-2.

A Mn-depositing fungus, Acremonium-like hyphomycete strain KR21-2, was isolated from a Mn deposit occurring on the wall of a storage bottle containing Mn(III, IV) oxide-coated streambed pebbles and stream water. 18S rRNA gene sequence analysis revealed that strain KR21-2 was phylogenetically related to members of the order Hypocreales within the class Ascomycetes. The spent culture medium at the stationary phase of fungal growth contained a 54-kDa protein capable of depositing Mn oxides. The enzymatic activity was inhibited by azide and o-phenanthroline. The Mn(II)-oxidizing protein possessed a laccase activity, as indicated by direct oxidation of p-phenylenediamine and 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid). These results are consistent with the role assumed for laccase-like multicopper oxidase, which is proposed to be involved in the Mn(II)-oxidizing factors from some bacteria. Unlike laccases of basidiomycete fungi, however, the protein of strain KR21-2 did not produce soluble Mn(III) species in the presence of either of the Mn chelators pyrophosphate and malonate. This is the first report on the possible involvement of laccase and/or multicopper oxidase in Mn oxide deposition by ascomycetes (including their anamorphs) ubiquitous in natural environments.

Surface-analytical studies on environmental and geochemical surface processes.

The surface chemical compositions of solid samples from environmental and geological sources can differ from the bulk or average compositions, because of changes caused by adsorption, dissolution, oxidation, etc. Accordingly, analytical information on surface layers is important for a better understanding of the environmental chemistry involving solid surfaces. The rapid development of surface-analytical techniques has enabled us to probe the surface chemistry of environmental and geological solid samples of complex composition. This article demonstrates some examples of important items of information that can be obtained by applying surface-analytical techniques, such as X-ray photoelectron spectroscopy and secondary ion mass spectrometry, to environmental and geological samples. The surface analysis of fly ashes, soils, sediments and weathered silicate minerals is reviewed.

Application of a pentafluorobenzyl bromide derivatization method in gas chromatography/mass spectrometry of trace levels of halogenated phenols in air, water and sediment samples.

An analytical method using pentafluorobenzyl bromide (PFBB) derivatization and gas chromatography/mass spectrometry (GC/MS) has been applied to identify and quantify chloro-, bromo- and dichlorophenols in air, water and sediment samples. Phenols in air sample were collected with a PS-2 Sep-PAK cartridge, and eluted with 2-propanol. For water and sediment samples, liquid-liquid extraction with dichloromethane was carried out, and the solvent was exchanged to 2-propanol. The phenols in the solution reacted with PFBB to form the corresponding pentafluorobenzyl esters. After extracting the derivatives into hexane, the determination was carried out by GC/MS with selected-ion monitoring. The detection limits of phenols in air, water and sediment were 0.0033 - 0.0073 microg/m3, 0.0066 - 0.0147 microg/L and 0.33 - 0.73 microg/kg, respectively. More than 90% recoveries of the halogenated phenols were obtained from real environmental samples spiked by the halogenated phenols. The three isomers of mono-chlorophenols were detected in sediment samples in the range of 5.2 - 9.2 microg/kg in wet weight basis.

LC/MS studies on characterization and determination of N,N'-ethylenebisdithiocarbamate fungicides in environmental water samples.

Liquid chromatography/mass spectrometry (LC/MS) has been applied to analyze N,N'-ethylenebisdithiocarbamate fungicides (EBDCs: manzeb, maneb and zineb) in environmental water samples. The EBDCs that are zinc and/or manganese salts are transformed into readily water-soluble sodium salts by adding an alkaline EDTA solution. The N,N'-ethylenebisdithiocarbamate anion is extracted into chloroform-hexane (3:1) as an ion pair with tetrabutylammonium, and then S-alkylated with methyl iodide. The extraction and derivatization are carried out at room temperature. The derivatized ethylenebisdithiocarbamic acid dimethyl ester is introduced into an LC/MS equipped with a negative ion electrospray ionization interface. Identification of the compound is performed with the specific quasi-molecular ion, and the quantitative analyses are carried out using the peak areas. The average recoveries and coefficients of variation of EBDCs at sub-ppb level are 79.1% and 29.3% (n = 6), respectively. The limit of detection based on standard deviation of 0.043 microg/L for manzeb is achieved.

Quantitative analysis of triphenylboron in environmental water samples by liquid chromatography/mass spectrometry.

Liquid chromatography/mass spectrometry (LC/MS) has been applied to the analysis of triphenylboron, which has been produced as a substitute for organotin compounds, in water. Although commercial triphenylboron compounds are produced as pyridinyl complexes, the chemical form in water is supposed to be mainly triphenylboron after liberating pyridine. The triphenylborons were extracted from water with an Empore C18 extraction disk under acidic condition, and the extracts were introduced directly into a liquid chromatograph-mass spectrometer equipped with a negative ion electrospray ionization interface. Identification of the compounds was performed with specific ions produced from the triphenylboron, and a quantitative analysis was carried out using the peak areas. The average recoveries from distilled water, seawater and river water at 0.30 ng/ml were 92.3, 100 and 85.3%, respectively. A detection limit of 0.023 ng/ml for triphenylboron was achieved.