Sulfide Oxidation Products Research Articles

The response of partially oxidised acid sulfate soil materials to anoxia

Four acid sulfate soil (ASS) materials were subjected to anoxia after varying periods of oxidation to determine the geochemical response of these types of soils to flooding. The response of the partially oxidised ASS materials to the exclusion of oxygen was variable. The rate of sulfide oxidation, acidification, and the production of soluble oxidation products such as sulfate, iron, and aluminium generally decreased markedly when subjected to anoxia. However, especially in the highly acidic ASS materials (i.e. pH <3.5), sulfide oxidation and acidification generally continued (albeit at much slower rates), most probably due to oxidation by Fe3+. Rapid sulfide re-formation occurred in the peat ASS material that had been oxidised for 63 days, with 0.47% reduced inorganic sulfur (SCR) formed over 60 days of anoxia. This substantial sulfide re-formation was accompanied by only a slight increase in pH. Minimal sulfide re-formation occurred in 2 of the ASS materials when placed in anoxic conditions, most likely due to a lack of readily available organic matter in these materials. The results show that the imposition of anoxic conditions on partially oxidised ASS materials is generally effective in decreasing the rates of further sulfide oxidation, acidification, and the production of soluble sulfide oxidation products. Biogeochemical sulfide formation consumes acidity; however, sulfide re-formation was ineffective in reversing acidification under the conditions of this experiment. The results indicate that the treatment of sites containing actual ASS materials by management strategies relying on oxygen exclusion need to be accompanied by other strategies that include acidty neutralisation or containment.

Spectroscopic and XRD studies of the air degradation of acid-reacted pyrrhotites

Monoclinic and hexagonal pyrrhotites leached in 1 mol/L HCl and exposed to the air at 100% and ∼10% relative humidity for up to 5 months were studied using X-ray diffraction, Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray emission spectroscopy, Mössbauer spectroscopy, and electron paramagnetic resonance (EPR). The amorphous, nonequilibrium, iron-depleted layer (NL) produced by the leaching amounted to half of the residue mass and was composed of predominantly low-spin ferrous iron and polysulfide anions. Elemental sulfur and goethite were the only crystalline products of the NL decomposition. FTIR spectroscopy and XPS also revealed several sulfoxy species and, at low humidity, a small amount of ferric oxide. Neither alterations of the underlying pyrrhotite nor new iron sulfide phases (pyrite, pyrrhotite, etc.) crystallized from the amorphous NL were found. The NL decomposition was faster in the wet environment than in the dry one, and the oxidation of the NL was much more rapid than that of starting pyrrhotites. The intensity and quadruple split of the Mössbauer signal from the product (an isomer shift of 0.36 mm/s) were found to increase over the aging, indicating that the NL structure becomes more rigid and the singlet Fe(II) gradually converts to Fe(III). X-ray Fe Lα,β emission spectra showed the formation of intermediate, high-spin Fe(II) within the NL oxidized in the humid environment, but not in the dry air. No unpaired electron spins were detected by EPR; lines of paramagnetic Fe 3+ appeared after the samples were aged in the dry air for 49 d and even later in the humid atmosphere. These phenomena are explained in terms of the formation of defects with negative correlation energy, similar to noncrystalline semiconductor chalcogenides, and of the fast electron exchange between the iron species, respectively. Mechanisms for reactions involved with the weathering of iron sulfides, which take into consideration the NL lattice elasticity, S-S and S-O bonding, oxygen incorporation, and oxidative and spin state of iron, are discussed. It is suggested in particular that the surface layer, strongly enriched in sulfur, as well as elemental sulfur and ferric oxyhydroxides, do not inhibit sulfide oxidation and acid production under weathering conditions, but the partially oxidized, disordered, nonstoichiometric layer may be passive.

Chemical composition and sources of the high Arctic aerosol relevant for cloud formation

The chemical composition, sources, and methods of production of cloud condensation nuclei (CCN) were studied over the pack ice covered Arctic Ocean in summer. After ∼2 days' travel of air over the pack ice, two local CCN sources were identified: particles derived from the bursting bubbles on open water between ice floes (film and jet drops) and particles reaching CCN size by acquisition of oxidation products of dimethyl sulfide. The bubble‐derived particle modes were found to have an exponential dependence on prevailing wind speed. The film drop generation depended less on wind speed and jet drop production depended more on wind speed than particles over open water did. However, the enhanced presence of film drop particles at wind speeds <5 m s−1 suggested a source of bubbles, other than wind, that is most active during clear sky days and ice melting. The film drop particles were mainly organic in nature, but their sea‐salt component increased at high wind speeds >12 m s−1 to dominate both mass and number. The jet drop mode was composed largely of sea salt, making a significant mass contribution already for wind speeds >5 m s−1. However, the smaller‐sized jet drops were not pure sodium chloride but contained a varied and appreciable organic component. The sulfur‐containing particles dominated the CCN population and mass for the most common wind speeds of 5–12 m s−1. Measured CCN concentrations were on average less than would have been expected from either a sulfate or a sea‐salt composition and the observed particle‐size distribution. It is concluded that other components, probably organic, depressed the nucleating ability of the particles. However, on clear sky days, there were a majority of occasions on which CCN concentrations were more than predicted from a sulfate composition and the measured size distribution.

Reactivity of Oxidized Sulfidic Mine Tailings during Lime Treatment

Lime amendment is a common method for neutralizing the accumulated acidity and sequestering metals in oxidized mine tailings. This study assessed the reactivity of sulfide oxidation products during lime treatment of tailings samples from the Kam Kotia mine site in Timmins, Ontario. The contributions of several alkalinity consumption mechanisms to the lime requirements were compared. Methods involved lime treatment tests, multiple water extractions, sequential extractions, analytical scanning electron microscopy, and X-ray diffractometry. The majority of the alkalinity consumption was due to the reaction of water-insoluble Fe-oxyhydroxysulfate minerals (including K-jarosite, Na-jarosite, H-jarosite, and schwertmannite) with lime to form Fe-oxyhydroxides (including goethite) and gypsum. The cation exchange capacity of the oxidized tailings contributed a minor proportion to the alkalinity consumption. Measurements of water-soluble acidity underestimated lime requirements by more than 50% on average.

Cloud‐active particles over the central Arctic Ocean

Concentrations of cloud condensation (CCN) and ice forming nuclei (IFN) were measured throughout an expedition by icebreaker around the central Arctic Ocean including the North Pole from July 15 to September 23, 1996. Daily median CCN concentrations at 0.25% supersaturation were typically in the range 15 to 50 cm−3, but concentrations varied by 3 orders of magnitude over the expedition and commonly by an order of magnitude within a day. They were highest near the ice edge and fell by almost an order of magnitude in the first 36 hours of transport from the open sea into the pack ice region. For longer transport times they increased again indicating a local source, suggested to be drops injected into the air by bubbles bursting on open leads. Median concentrations of IFN ranged from 18 m−3 just inside the pack ice at the beginning of the expedition to 1 m−3 at the end. The differences with transport time from the ice edge were less marked than for CCN. Comparison of CCN measurements with simultaneously measured number size distributions showed that the median concentration active at a given supersaturation was only 71% of the number expected if all the particles had been composed of pure ammonium sulfate. Transmission electron microscope observations of individual particles suggested an evolution of many CCN from nonvolatile, nonhygroscopic particles <50 nm by acquisition of the oxidation products of dimethyl sulfide. Cloud processing added further mass. The largest primary source within the pack ice region was deduced to be film drops from bursting bubbles yielding liquid particles with a high organic content and surfactant properties. A relationship between CCN number and sulfur mass is derived which extends previous results to lower CCN numbers and indicates a greater sensitivity to change in sulfate mass than at lower latitudes. Bacteria and probable submicron fragments of marine organisms were identified in the samples and suggested to be the source of IFN.

Sulfur chemistry over the central Arctic Ocean during the summer: Gas‐to‐particle transformation

Atmospheric gas‐to‐particle transformation of the oxidation products of dimethyl sulfide (DMS) was investigated over the central Arctic Ocean by using observational data and a coupled gas phase chemistry‐aerosol dynamics model. Chemical compounds investigated were sulfuric acid (H2SO4(g)), methasulfonic acid (MSA(g)), and sulfur dioxide (SO2(g)) in the gas phase, and non‐sea‐salt sulfate (nss‐SO42−) and MSA in the particulate phase. During the advection from the open ocean to over the pack ice region, the particulate phase was found to be influenced significantly by three processes: (1) rapid removal of particulate matter during the first 1–2 days of advection, (2) continual formation of particulate nss‐SO42− and MSA, and (3) local production of particles consisting mostly of matter other than nss‐SO42− and MSA over the pack ice. In the absence of clouds and fogs, the principal sink for the vapors H2SO4(g) and MSA(g) were their condensational transport to submicron particles. SO2(g) was influenced significantly by both dry deposition and gas phase oxidation. Although there is a local source of coarse sea‐salt particles within the pack ice region, the role of these particles in the budgets of nss‐SO42− and SO2(g), and probably also in the budget of MSA, is only minor, especially when compared with marine regions at lower latitudes. The performance of the DMS gas‐phase chemistry scheme was tested against field data using a measurement case influenced minimally by clouds/fogs and the free troposphere. The predicted concentration of nss‐SO42− was within the uncertainties of the analysis, whereas that of MSA was high by a factor of 3–6. This demonstrates that not only heterogeneous reactions involved in atmospheric DMS chemistry but also certain gas‐phase reactions require further investigation.

Implications of Predicted Hydrologic Changes on Lake Senftenberg as Calculated Using Water and Reactive Mass Budgets

Lake Senftenberg, Germany, is a post-mining lake that was flooded 30 years ago. It is anticipated that the levels of the surrounding post-mining lakes will rise, and that this will lead to a reversal of groundwater flow and consequently to an increase of acidifying groundwater flux into the lake. A tool to predict the future water quality of Lake Senftenberg has been developed. Present and future groundwater fluxes were calculated using a 3D hydraulic model of the surrounding aquifers. Oscillating hydraulic fluxes within the saturated and the unsaturated zones of the island within the lake, caused by continuous lake level changes, were calculated using a 2D sub-model. Mass fluxes into the lake from the aquifers, from the island, and from the River Schwarze Elster were determined by sampling or by laboratory experiments and were coupled with the hydraulic fluxes. The fluxes of acidifying components from the island sediments and sulfide oxidation products from drained zones were determined in laboratory experiments. Sediment erosion due to rill and gully formation after significant lake level change were calculated. The amount of acidifying compounds released from the eroded sediments was determined by laboratory experiments. The input of alkalinity due to the sedimentation of biomass was estimated. Gaseous partial pressures and mineral phases were used to describe the geochemical boundary conditions of the resulting lake water.

Biological Sulfide Oxidation in a Fluidized Bed Reactor

Feasibility of a laboratory scale fluidized bed process for biological sulfide oxidation to elemental sulfur and the formation of well-settleable sulfur sludge is demonstrated. Sulfide oxidation strongly depends upon oxygen concentration, sulfide loading rate and upflow velocity. At reactor dissolved oxygen concentrations (DOr) higher than 0.1 mg l−1, sulfate was the main product of sulfide oxidation. Upon increasing the sulfide loading rate, the sulfate production rate decreased as sulfide oxidation to sulfur showed marked increase. Low formation of sulfate could mean that sulfide was inhibitory to sulfate producing bacteria or that conversion of sulfide to sulfur was more favorable than sulfate production. Sulfide conversions higher than 90% were obtained at sulfide loading rates of 0.13 - 1.6 kgS mr −3d−1. At DOr less than 0.1 mg l−1, sulfur was the major end product of the sulfide oxidation. Upflow velocity in the range of 16 - 26 m h−1 and sulfide loading rate of 0.9 - 1.6 kgS mr −3d−1 were necessary for generation of biogranules containing 65 - 76% of elemental sulfur. The elemental sulfur production of 76% was obtained at upflow velocity of 17 m h−1 with sulfide loading rate up to 1.6 kgS mr −3d−1. Morphological examination of the biogranules showed elemental sulfur deposition in the sludge granule and outside the bacterial cells.

Minerals controlling arsenic and lead solubility in an abandoned gold mine tailings

Numerous areas have been contaminated by heavy metals and metalloids due to industrial and mining activities. Studies investigating the behavior of such contaminants in the environment have identified speciation as a key factor controlling their mobility, availability and toxicity. Here we characterize As- and Pb-bearing phases resulting from the oxidation of sulfide-rich tailings of a former gold mine (La Petite Faye, France) in order to assess the risk for water quality. Elements were first pre-concentrated by granulometric fractionation (sedimentation in deionized water) and then investigated using X-ray diffraction and electron microprobe analyses. Two main As–Pb-bearing minerals were clearly identified: scorodite (FeAsO 4·2H 2O) and beudantite PbFe 3(AsO 4)(SO 4)(OH) 6. Minor amounts of As and Pb were dissolved in deionized water during granulometric fractionation, indicating the possible presence of other soluble Pb-sulfates which could be some of the primary metastable products of sulfide oxidation. This dissolution also provides information about the fate of these phases in the case of intensive leaching of the tailings. Scorodite may not be considered as a relevant candidate for As on-site immobilization, because its solubility largely exceeds drinking water standards whatever the pH. Since beudantite solubility has not yet been determined, an estimation of its solubility product was obtained using the Gibbs free energy of formation of plumbojarosite [Pb 0.5Fe 3(SO 4) 2(OH) 6]. This estimation suggests that beudantite should efficiently maintain low Pb concentration in waters. However, Pb dissolution in deionized water during the granulometric fractionation led to Pb concentrations much higher than the French and US drinking water standards (2.4×10 −7 mol l −1), which may be due to dissolution of the suspected metastable Pb-sulfates. Accurate determination of beudantite solubility is now required to improve the Pb risk assessment on such polluted sites.

Isolation and characterization of strains CVO and FWKO B, two novel nitrate-reducing, sulfide-oxidizing bacteria isolated from oil field brine.

Bacterial strains CVO and FWKO B were isolated from produced brine at the Coleville oil field in Saskatchewan, Canada. Both strains are obligate chemolithotrophs, with hydrogen, formate, and sulfide serving as the only known energy sources for FWKO B, whereas sulfide and elemental sulfur are the only known electron donors for CVO. Neither strain uses thiosulfate as an energy source. Both strains are microaerophiles (1% O(2)). In addition, CVO grows by denitrification of nitrate or nitrite whereas FWKO B reduces nitrate only to nitrite. Elemental sulfur is the sole product of sulfide oxidation by FWKO B, while CVO produces either elemental sulfur or sulfate, depending on the initial concentration of sulfide. Both strains are capable of growth under strictly autotrophic conditions, but CVO uses acetate as well as CO(2) as its sole carbon source. Neither strain reduces sulfate; however, FWKO B reduces sulfur and displays chemolithoautotrophic growth in the presence of elemental sulfur, hydrogen, and CO(2). Both strains grow at temperatures between 5 and 40 degrees C. CVO is capable of growth at NaCl concentrations as high as 7%. The present 16s rRNA analysis suggests that both strains are members of the epsilon subdivision of the division Proteobacteria, with CVO most closely related to Thiomicrospira denitrifcans and FWKO B most closely related to members of the genus Arcobacter. The isolation of these two novel chemolithotrophic sulfur bacteria from oil field brine suggests the presence of a subterranean sulfur cycle driven entirely by hydrogen, carbon dioxide, and nitrate.

A Comparative Study of Spectrophotometric and Iodometric Back Titration Methods for Hydrogen Sulfide Determination in Anoxic Basins

Iodometric Back Titration (IBT) and Spectrophotometric (SPM) methods are two common methods used in the determination of hydrogen sulfide concentrations in anoxic basins, like in the upper sections of the Black Sea anoxic waters. Although the results obtained by both methods are in agreement when the concentrations of sulfide are higher than 30 μM/1, IBT analysis gives more reproducible results compared to SPM analysis. On the other hand, the reproducibility of the SPM is better than that of IBT method when the concentration of sulfides is less than 30 μM/1, but in this case SPM method provides lower results compared to IBT method. This discrepancy can be explained by the presence of the hydrogen sulfide oxidation products (i.e., thiosulfate) formed as a result of aeration of water samples. These products consume the iodine added to the sample. Therefore, they are measured as hydrogen sulfide in the IBT method, but are not detected by the SPM method since they do not react with the N,N-dimethyl-p-phenylendiamine – FeCl3 mixed reagent.

Methanesulfonic acid in a Svalbard Ice Core as an indicator of ocean climate

Methanesulfonic acid (MSA) is an atmospheric oxidation product of dimethyl sulfide, produced by marine biota. MSA preserved in a Svalbard glacier between 1920 and 1996 is compared with the sea surface temperature (SST) and sea‐ice extent of the surrounding ocean over the same period. On decadal timescales high MSA concentrations are found to be associated with warm SST and reduced sea‐ice extent. MSA appears to be influenced by climatic changes related to variations in the import of warm Atlantic Water to the Barents Sea. Atlantic Water plays an important role in the Arctic climate system, therefore MSA concentrations may indirectly reflect larger‐scale changes in the region and may be useful as a proxy for past climate.

Modelling of sulfide oxidation with reactive transport at a mine drainage site

A plume of groundwater affected by sulfide oxidation extends 160 m downgradient from the Nickel Rim Mine tailings impoundment and discharges to a small lake. The plume water has near neutral pH, but contains high concentrations of Fe and SO 4. Field observations indicate that the release of SO 4, H +, Fe 2+ and other metals and their distribution in the aquifer is controlled by the rate of sulfide oxidation in the vadose zone of the tailings and by subsequent dissolution and precipitation of carbonate and oxyhydroxide mineral phases in the tailings and aquifer. Using field-determined aqueous and solid geochemistry, a conceptual geochemical model for the site was developed. This model accounts for trends in pH and in the concentrations of Fe and SO 4. The numerical model MINTOX was used in conjunction with this conceptual model to simulate sulfide oxidation and two-dimensional reactive transport of dissolved sulfide oxidation products. Simulated sulfide oxidation and transport are compared to trends observed in the field after 35 years of oxidation. Similarity between observed and simulated concentrations demonstrates that, when used with a well-developed conceptual geochemical model, MINTOX is capable of simulating sulfide oxidation and plume evolution at mine drainage sites.

Nitrogen, carbon, and sulfur metabolism in natural thioploca samples

Filamentous sulfur bacteria of the genus Thioploca occur as dense mats on the continental shelf off the coast of Chile and Peru. Since little is known about their nitrogen, sulfur, and carbon metabolism, this study was undertaken to investigate their (eco)physiology. Thioploca is able to store internally high concentrations of sulfur globules and nitrate. It has been previously hypothesized that these large vacuolated bacteria can oxidize sulfide by reducing their internally stored nitrate. We examined this nitrate reduction by incubation experiments of washed Thioploca sheaths with trichomes in combination with 15N compounds and mass spectrometry and found that these Thioploca samples produce ammonium at a rate of 1 nmol min-1 mg of protein-1. Controls showed no significant activity. Sulfate was shown to be the end product of sulfide oxidation and was observed at a rate of 2 to 3 nmol min-1 mg of protein-1. The ammonium and sulfate production rates were not influenced by the addition of sulfide, suggesting that sulfide is first oxidized to elemental sulfur, and in a second independent step elemental sulfur is oxidized to sulfate. The average sulfide oxidation rate measured was 5 nmol min-1 mg of protein-1 and could be increased to 10.7 nmol min-1 mg of protein-1 after the trichomes were starved for 45 h. Incorporation of 14CO2 was at a rate of 0.4 to 0.8 nmol min-1 mg of protein-1, which is half the rate calculated from sulfide oxidation. [2-14C]acetate incorporation was 0.4 nmol min-1 mg of protein-1, which is equal to the CO2 fixation rate, and no 14CO2 production was detected. These results suggest that Thioploca species are facultative chemolithoautotrophs capable of mixotrophic growth. Microautoradiography confirmed that Thioploca cells assimilated the majority of the radiocarbon from [2-14C]acetate, with only a minor contribution by epibiontic bacteria present in the samples.

The function of the periplasmic Sud protein in polysulfide respiration of Wolinella succinogenes.

The periplasmic Sud protein was previously isolated as a sulfide dehydrogenase from Wolinella succinogenes. Sud modified by a C-terminal His-tag (Sud-His6) was produced in Escherichia coli by expression of the sud gene. Sud-His6 catalyzed thiocyanate formation from cyanide and polysulfide. The Vmax of this activity was more than one order of magnitude higher than that of sulfide oxidation by dimethyl-naphthoquinone and that of polysulfide reduction by BH4-. The apparent Km was less than 20 microM polysulfide. Polysulfide and not elemental sulfur was found to be the product of sulfide oxidation by dimethyl-naphthoquinone, in contrast to the earlier view [Kreis-Kleinschmidt, V., Fahrenholz, F., Kojro, E. & Kröger. A. (1995) Arch. Microbiol. 165, 65-68]. Sud-His6 did not contain metal ions or other prosthetic groups. Replacement by site-directed mutagenesis of the single cysteine residue of the Sud monomer caused complete loss of activity, while the exchange of the single histidine residue or of the lysine residue situated next to cysteine did not affect activity. In equilibrium dialysis, the Sud-His6 monomer bound up to ten polysulfide sulfur atoms with a dissociation constant of 0.2 mM. Sud-His6 loaded with polysulfide sulfur showed an absorption spectrum in the range of 350-400 nm; this spectrum differed from that of free polysulfide. Electron transport from H2 to polysulfide catalyzed by the membrane fraction of W. succinogenes was stimulated by the presence of small amounts of Sud-His6. The apparent Km for polysulfide decreased sevenfold in the presence of saturating amounts of Sud-His6 (1 microM Sud-His6 dimer). Similar results were obtained with intact W. succinogenes cells containing low and high amounts of Sud. Sud appears to function as a polysulfide binding protein and probably binds polysulfide sulfur to its cysteine residue and transfers it to the substrate site of the membraneous polysulfide reductase.

Sulfide oxidation in brown coal overburden and chemical modeling of reactions in aquifers influenced by sulfide oxidation

Surface mining of brown coal in the Rhineland brown coal mining area (Germany) causes acidification of pyritic sandy overburden sediments. Convective transport of air, indicated by an enrichment of nitrogen gas in oxidized overburden, is, in addition to diffusion of oxygen, the driving mechanism for sulfide oxidation. Products of sulfide oxidation (2SO42− + 2H+ + Fe2+) stored in acidic material in the overburden dump are leached by groundwater filling the dump and react with the carbonate phases of nonacidic material. The resulting hydrochemical composition (up to 6000 mg l−1 SO42−, 3000 mg l−1 Fe2+, pH 4.5) in groundwaters is controlled by simultaneous solubility equilibria with CaSO4·2H2O(s), Fe(OH)3(s), Fe0.9Ca0.1CO3(s) and CO2(g). Calculated equilibrium concentrations of major components and pH in groundwater, partial pressure of CO2(g) in soil gas, and coupled mass transfer match observed conditions.

Alvinellids and Sulfides at Hydrothermal Vents of the Eastern Pacific: A Review

SYNOPSIS. At Eastern Pacific hydrothermal vents, alvinellid polychaetes are among the first metazoans to colonize newly formed surfaces of sulfide chimneys. In this environment of rapid mineral precipitation, alvinellids are confronted by steep physico-chemical gradients and high temporalvariability. This paper examines the interaction of alvinellids with chimney mineralization processes and then reviews what is known of mechanisms that could enable these worms to deal with potentially toxic levels of sulfide in their environment. Studies of sulfide chimneys consistently show mineralogy to be locally modified around alvinellid tubes. This may be linked to sulfide oxidation products that accumulate in tube material or to the circulation of seawater through the tube. At high worm densities, these local effects may have a significant influence on larger scale sulfide accretion processes that determine chimney morphology. Alvinellid polychaetes may have several lines of defense against sulfide. Tubes and mucous layers could act as passive barriers to reduce inward diffusion of sulfide across posterior surfaces. Colonization of epidermal and tube surfaces by bacteria that might be sulfide oxidizing, could create an active external barrier in some species. Sulfide oxidation by tissue homogenates has been demonstrated in two Paralvinella species, where it may serve to protect oxidative respiration from sulfide entering worm tissues. Sulfide binding in blood has not been studied in any of the alvinellids.

Microbiological, chemical, and mineralogical characterization of the kidd creek mine tailings impoundment, Timmins area, Ontario

Bacterial enumeration and geochemical characterization were undertaken at three sites on the sulfide‐rich tailings impoundment at the Kidd Creek metallurgical site, Timmins, Ontario, Canada. The three sites were selected to represent varying degrees of sulfide oxidation to assess the changes in water chemistry, in the mineralogical composition of the tailings, and in bacterial populations as the sulfide oxidation process proceeds under natural field conditions. The first site was characterized as having negligible oxidation‐derived alteration, the pH of the porewater varied from 6.5 to 7.5, and the concentrations of dissolved constituents were similar to those observed in the deeper, unaltered tailings. Mineralogical examination of the tailings grains indicated that the sulfide surfaces were sharp and unreplaced. At this site, the predominant sulfur‐oxidizing bacteria were Thiobacillus thioparus and related species. The second site showed evidence of the onset of acidification, the pH of the near‐surface porewater had decreased to 5.5, and the concentrations of some sulfide oxidation products, principally SO4 and Zn, had increased beyond those observed in the unaltered tailings. At the second site, T. thioparus and related species predominated. At the third site the acidification process was well established. The pH of the shallow porewater had decreased to <4.0, and high concentrations of several sulfide oxidation products were observed. Mineralogical examination of the tailings indicated the presence of alteration rims of ferric oxyhydroxide minerals that surrounded the oxidizing sulfide grains. At this site the predominant bacterial groups were T. ferrooxidans and T. thiooxidans types. At the third site the bacterial abundance reached a maximum at 25–45 cm below the tailings surface. The occurrence of the peak abundances coincided with the interface between the zones of the unaltered tailings and the overlaying altered sulfides. This coincidence suggests that the iron oxyhydroxide coatings, which surround the partly oxidized sulfide grains, may shield the partly altered grains, thereby inhibiting bacterial growth. The data are consistent with an initial chemical oxidation of the metal sulfides to produce elemental sulfur and polysulfides, which are subsequently oxidized by neutrophilic thiobacilli to produce sulfuric acid. After the pH has decreased to the 3.5–4.0 range, the acidophilic thiobacilli, such as T. ferrooxidans, can directly oxidize the metal sulfides.

Analysis of atmospheric sulfur gases by capillary gas chromatography with atomic emission detection

AbstractThe atomic emission detector (AED) has been found to be a sensitive and selective instrument for analysis of atmospheric sulfur gases by capillary gas chromatography. It was possible to determine atmospheric dimethyl sulfide at concentrations below 0.3 nmol/m3 typical of the remote marine environment in winter. Sample analyses from the Australian Baseline Air Pollution Station, Cape Grim, are used to illustrate this.In comparison with other sulfur‐specific detectors previously used for this work, the AED has been found to exhibit the best combination of specificity and sensitivity. A configuration comprising a series of valves, gas calibration loops, and a cryogenic trap prior to the GC‐AED was used for sample analysis. Standard addition of sulfur hexafluoride was found to assist determination of carbonyl sulfide, as it could be used to take into account the magnitude of signal quenching from coeluting gases. The AED was also found to be a selective detector for the direct injection of water‐soluble dimethyl sulfide oxidation products.

Intrageneric Structure of the Genus Rhodobacter: Transfer of Rhodobacter sulfidophilus and Related Marine Species to the Genus Rhodovulum gen. nov.

Phylogenetic relationships among species of the genus Rhodobacter and related taxa were elucidated by studying 16S rRNA sequence information and genomic DNA homology data. The 16S rRNA gene was amplified by the PCR and was sequenced directly by a combined method consisting of cycle sequencing and automated fluorescence detection. Pairwise sequence comparisons and a distance matrix analysis showed that the Rhodobacter species could be divided into two major clusters; one cluster included the freshwater and terrestrial species, and the other cluster contained the marine species. The cluster containing the freshwater Rhodobacter species also included Rhodopseudomonas blastica and was linked more closely to the chemotroph Paracoccus denitrificans and the aerobic phototroph Roseobacter denitrificans than to the cluster containing the marine Rhodobacter species. Genomic DNA-DNA hybridization data supported the results of 16S ribosomal DNA sequence comparisons. With few exceptions, the marine Rhodobacter species can be differentiated phenotypically from the freshwater species on the basis of salt requirement for optimal growth, sulfide tolerance, final oxidation product of sulfide, and polar lipid composition. Thus, we propose that all marine Rhodobacter species should be transferred to the genus Rhodovulum gen. nov.; Rhodovulum sulfidophilum comb. nov. is the type species of this genus.