Showing papers on "Sulfide published in 1985"
TL;DR: In this paper, a colloidal solution of copper sulfide was determined spectrophotometrically as a colloid solution of sulfide, and the maximum deviation error was below 5%.
683 citations
01 Jan 1985
TL;DR: In this article, the authors studied aqueous, abiotic pyrite oxidation in oxygen-saturated and anaerobic Fe(III)-saturated systems, and they concluded that Fe is the more important, direct oxidant of pyrites, which is supported by theoretical consideration regarding the low probability of a direct reaction between paramagnetic molecular oxygen and diamagnetic disulfide.
Abstract: The authors studies of aqueous, abiotic pyrite oxidation in oxygen-saturated and anaerobic Fe(III)-saturated systems span pH values from 2 to 9 and include analyses of sulfite, thiosulfate, polythionates, and sulfate. In addition, they evaluated procedures for cleaning oxidation products from pyrite surfaces. As in silicate experiments, the preparation of the pyrite surface is critical to a valid interpretation of the onset of pyrite oxidation. The rates in oxygen-saturated systems (1) were relatively independent of pH, (2) gave linear sulfoxy anion production, (3) produced thiosulfate and polythionates at pH >3.9, and (4) produced intermediate sulfoxy anions only at high stirring rates. In anaerobic Fe(III)-saturated systems no intermediates were observed. From these results, along with the generally faster rate of oxidation in Fe(III)-saturated systems, we conclude that Fe(III) is the more important, direct oxidant of pyrite. This conclusion is supported by theoretical consideration regarding the low probability of a direct reaction between paramagnetic molecular oxygen and diamagnetic disulfide. The authors findings extend earlier models for the pyrite oxidation mechanism because of the larger range of experimental conditions that they have studied. Preliminary results from studies of sphalerite oxidation, in which they have found thiosulfate, support the hypothesis that thiosulfate is a keymore » intermediate related to the reaction mechanisms, independent of the bounding structure of the sulfide mineral.« less
662 citations
TL;DR: In this paper, the results of a water column of a permanently anoxic basin, Framvaren Fjord, Norway, were determined in order to better understand the geochemical processes operating on metals in anoxic marine waters.
290 citations
TL;DR: A series of hydrothermal experiments was performed over a wide range of pressures, temperatures, oxygen fugacities, and melt FeO content, in order to examine the effects of physical changes on sulfur solubility in fractionated hydrous silicate melts as mentioned in this paper.
Abstract: A series of hydrothermal experiments was performed over a wide range of pressures, temperatures, oxygen fugacities, and melt FeO content, in order to examine the effects of physical changes on sulfur solubility in fractionated hydrous silicate melts. On the basis of the experimental results, it is concluded that upper crustal oxidation-reduction reactions and crystal fractionation processes may exert considerable influence on the amount of sulfur contained in magmas erupted at the surface. The application of the experimental results to investigations of volatile transport and volcanic degassing processes on the earth, Venus, and Mars is discussed
281 citations
TL;DR: In this article, the authors investigated vertical stratified microbial communities of phototrophic bacteria in the upper intertidal zones of the North Sea island of Mellum and concluded that the initial colonization of the sandy sediments was by the cyanobacterium Oscillatoria.
Abstract: Vertically stratified microbial communities of phototrophic bacteria in the upper intertidal zones of the North Sea island of Mellum were investigated. Growth and population dynamics of the cyanobacterial mat were followed over three successive years. It was concluded that the initial colonization of the sandy sediments was by the cyanobacterium Oscillatoria. In well-established mats, however, the dominant organism was Microcoleus chthonoplastes. The observed succession of cyanobacteria during mat development is correlated with nitrogen fixation. Nitrogen fixation is necessary in this low-nutrient environment to ensure colonization by mat-constructing cyanobacteria. Under certain conditions, a red layer of purple sulfur bacteria developed underneath the cyanobacterial mat in which Chromatium and Thiocapsa spp. dominated, but Thiopedia and Ectothiorhodospira spp. have also been observed. Measurements of light penetrating the cyanobacterial mat indicated that sufficient light is available for the photosynthetic growth of purple sulfur bacteria. Profiles of oxygen, sulfide and redox potential within the microbial mat were measured using microelectrodes. Maximum oxygen concentrations, measured at a depth of 0.7 mm, reached levels more than twice the normal air saturation. Dissolved sulfide was not detected by the microelectrodes. Determination of acid-distilled sulfide, however, revealed appreciable amounts of bound sulfide in the mat. Redox profiles measured in the mat led to the conclusion that the upper 10 mm of the sedimentary sequence is in a relatively oxidized state.
267 citations
TL;DR: Germanium is enriched in the following geologic environments: 1) iron meteorites and terrestrial iron-nickel; 2) sulfide ore deposits, particularly those hosted by sedimentary rocks; 3. iron oxide deposits; 4. oxidized zones of Ge-bearing sulfide deposits; 5. pegmatites, greisens, and skarns; and 6. coal and lignitized wood.
253 citations
TL;DR: The survival after oxygen stress was studied with eight species of sulfate-reducing bacteria and reducing agents did not protect the vegetative cells of this strain against oxygen toxicity, and sulfhydryl group-containing agents increased the oxygen sensitivity considerably.
Abstract: Summary The survival after oxygen stress was studied with eight species of sulfate-reducing bacteria. In the absence of sulfide all species tolerated 6 min of aeration without loss of viability. Even after 3 h of aeration the viability of four species ( Desulfovibrio vulgaris, D. desulfuricans, D. salexigens and Desulfobacter postgatei ) was not impaired. Four other species were sensitive to 3 h of aeration: the surviving fractions of Desulfotomaculum ruminis, D. nigrificans and Desulfococcus multivorans were about 1%, that of Desulfotomaculum orientis about 0.01%. Formation of spores resulted in oxygen resistance of D. orientis . Reducing agents did not protect the vegetative cells of this strain against oxygen toxicity. In contrast, sulfhydryl group-containing agents increased the oxygen sensitivity considerably. Growth of sulfate- and sulfur-reducing bacteria in oxygen-sulfide gradients in agar tubes was studied. In the gradients these strictly anaerobic bacteria revealed oxygen-dependent growth in sulfate- and sulfur-free medium. Three sulfate-reducing bacteria that could not use thiosulfate or sulfur as electron acceptor failed to grow in oxygen-sulfide gradients. Obviously, not directly molecular oxygen, but oxidation products of sulfide, such as thiosulfate or sulfur, were used as electron acceptors and were continuously regenerated in a cycling process from sulfide by autoxidation. The conceivable ecological significance of a short sulfur cycle driven by autoxidation of sulfide is discussed.
208 citations
TL;DR: The flux of iron is found to exceed both the oxygen and the sulfide fluxes, which implies that dissolved iron was fairly abundant and that oxygen and sulfide were rare in the atmosphere and ocean.
177 citations
TL;DR: Tributylstannyl alkyl or aryl sulfide and bis(tributyl stannyl) sulfide were found to be useful to prepare arylsides in good yields under the usual conditions of the palladium-catalyzed reaction with aryln bromides as discussed by the authors.
Abstract: Tributylstannyl alkyl or aryl sulfide and bis(tributylstannyl) sulfide were found to be useful to prepare aryl sulfides in good yields under the usual conditions of the palladium-catalyzed reaction with aryl bromides.
170 citations
AT&T1
TL;DR: In this article, a general mechanism for atmospheric sulfidation in which the absorption of the gas into the surface water layer is followed directly by dissociative coordination with metal atoms is proposed.
167 citations
TL;DR: In this article, the depth profiles observed suggest that the more labile ester sulfate is diagenetically converted to the carbon-bonded form, and the isotopic data suggest that sulfate concentrations over 5 mg/1 accompanied by an enrichment of surficial sediments with isotopically different S may signal significant inputs of pollutant S into the lake and its basin.
TL;DR: In this paper, the sulfidation kinetics and mechanism of metals and alloys are compared with oxidation processes, showing the differences from and similarities with oxide systems, and defect and transport properties of metal sulfides are discussed.
Abstract: Defect and transport properties of metal sulfides are discussed, showing the differences from and similarities with oxide systems. The sulfidation kinetics and mechanism of metals and alloys are compared with oxidation processes.
TL;DR: The absence of elemental sulfur in the animal cytoplasm suggests that its formation from sulfide is not a detoxification scheme to protect animal tissue from sulfides toxicity, and probably represents inorganic energy reserves that permit the symbiotic bacteria to function even during the temporary absence of external sulfide.
Abstract: Sulfur content and fine structure were studied for tissues of three species of clams, Lucinoma annulata, Calyptogena elongata and Lucina floridana, which inhabit sulfide-rich environments and whose gills harbor symbiotic sulfur bacteria. Lucinoma annulata and C. elongata were dredged from the Santa Barbara basin, California, USA, at a depth of 480 to 490 m, and Lucina floridana were dug from below the roots of seagrasses in Saint Joseph Bay, Florida, at a depth of 0.25 to 2m. Foot tissue of Lucinoma annulata, without symbionts, had a total sulfur content of 1.4±0.1 (SD) mg 100 mg-1 dry weight of tissue (%DW). The symbiont-containing gill tissue of different individuals of L. annulata varied in color from dark red to pale yellow, and the total sulfur content was 2.5±0.4% DW in red gills and was 5.6±3.3 % DW in the yellowest gills. Maintenance of L. annulata in the laboratory for 21 d in the absence of sulfide resulted in the loss from the gill of yellow deposits which were elemental sulfur in the form of liquid-crystalline sulfur globules rather than solid orthorhombic sulfur crystals. The foot tissue did not contain elemental sulfur. When examined by freeze-etch microscopy, sulfur globules were found only within bacteria and not in the animal host cytoplasm. Sulfur globules were confined to the periplasmic space of the bacteria. C. elongata and Lucina floridana resembled Lucinoma annulata in the physical form and distribution of elemental sulfur. The absence of elemental sulfur in the animal cytoplasm suggests that its formation from sulfide is not a detoxification scheme to protect animal tissue from sulfide toxicity. The sulfur deposits probably represent inorganic energy reserves that permit the symbiotic bacteria to function even during the temporary absence of external sulfide.
TL;DR: The results suggest that past attempts to explain mangrove distribution in terms of monotonic soil gradients, the dispersal characteristics of propagules, and interspecific competition are incomplete, and that it will be necessary to examine the link between soil sulfur chemistry and mangroves distribution more fully.
Abstract: At Humingbird Cay, Exuma, Bahamas, distributions of bothRhizophora mangle (red mangrove) andAvicennia germinans (black mangrove) are closely correlated with amounts of hydrogen sulfide (H2S) in the soil.R. mangle is primarily distributed within large areas of low to moderate H2S concentrations (mean= 40 mg/l). H2S levels underA. germinans are lower (mean = 22 mg/l), but the area immediately beyond their root zone often has extremely high sulfide concentrations (mean= 120 mg/l). These results suggest that past attempts to explain mangrove distribution in terms of monotonic soil gradients, the dispersal characteristics of propagules, and interspecific competition are incomplete, and that it will be necessary to examine the link between soil sulfur chemistry and mangrove distribution more fully.
TL;DR: In this paper, a 15m-high hydrothermal mound atop the flat turbidite pond in the Southern Trough of Guaymas Basin was dredged from a 15 m-high basin.
Abstract: Samples dredged from a 15-m-high hydrothermal mound atop the flat turbidite pond in the Southern Trough of Guaymas Basin consist of pyrrhotite-rich massive sulfide, barite, barite + calcite, talc, and opaline silica as well as substrate material composed of fossiliferous, clay-rich ooze. An 11-m-long sediment core taken near the dredge site shows increasing hydrothermal alteration with depth; anhydrite-filled fractures near the base of the core appear to be channels for hydrothermal discharge. Oxidation of the sulfide-rich samples to an assemblage of geothite, lepidocrocite, and amorphous Fe oxyhydroxide is ubiquitous. Compared to other massive sulfide deposits on sediment-starved oceanic ridges, the hydrothermal deposit dredged in Guaymas Basin has a high pyrrhotite/pyrite ratio, a low Zn sulfide and combined ore metal (Cu + Zn + Pb + Ag + Cd) content, and a greater abundance of sulfate, carbonate, and silicate phases. Venting hydrothermal solutions are alkaline with moderately high pH; high Ca, Ba, and SiO2 content; low ƒS2 and ƒo2; and very low transition metal content. Disequilibrium assemblages of pyrrhotite and sulfate minerals form during rapid mixing of this evolved vent fluid with ambient bottom waters at the discharge site. Talc is formed at a temperature near 270°C by mixing or entrainment of Mg-rich bottom water or pore fluid with upwelling hydrothermal fluid that is saturated with silica. Calcite may precipitate from the alkaline, Ca-rich fluid during degassing of CO2. The minimum temperature range for sulfide and nonsulfide deposition is approximately 190°–326°C. The composition of hydrothermal deposits, vent solutions, and altered sediment requires that circulating fluids evolve during deep penetration into the basaltic basement complex, further interaction with the organic-and carbonate-rich sediment pile, and near-surface mixing with ambient seawater. Although the stable assemblage albite-epidote-clinochlore present at depth in the sediment pile requires very low dissolved Mg and Fe in the altering fluid, the addition of Mg to deeply buried sediment indicates significant recharge of the system by Guaymas Basin bottom water.
TL;DR: In this paper, the authors investigated the crystallization kinetics of polyphenylene sulfide by using differential scanning calorimetry and found that glass fibers have an accelerating influence on crystallization resulting in a 15-25% reduction in crystallization time.
Abstract: The crystallization kinetics of unfilled and glass-reinforced grades of polyphenylene sulfide has been investigated by using differential scanning calorimetry. The maximum rate of crystallization is observed at about 170°C. From the crystallization data, it is recommended that the molding parameters should be so specified that the polymer spends 10–15 s over the temperature range of 155–190°C during cooling, before demolding, in order to ensure stable morphology of the molded part. The glass fibers have an accelerating influence on crystallization resulting in a 15–25% reduction in crystallization time. The kinetic data have been interpreted by using Avrami analysis followed by a discussion of the possible crystallization mechanisms.
TL;DR: In this article, a plume model of the Stillwater complex is proposed, where a pulse of replenishing magma enters the stillwater chamber as a buoyant plume and subsequently spreads to form a layer of hybrid melt.
Abstract: Platinum mineralization in the Stillwater Complex occurs within a complex sequence of olivine-bearing, plagioclase-rich cumulates about 400 m above the base of the Banded zone. The reef consists of a 2-m-thick layer of disseminated sulfides extending over the entire strike length of the complex. In the area of this study the host rock to the reef sulfides shows a lateral transition over a strike length of 700 m from a heterogeneous olivine-plagioclase cumulate ("mixed rock") to a plagioclase-olivine cumulate containing a high proportion of postcumulus bronzite, with olivine preserved only as rare resorbed cores on bronzite grains.Platinum-group elements within the reef correlate strongly with abundances of sulfides, which show convincing textural evidence for having originated as immiscible sulfide liquid. Strong correlations are also observed between all six platinum-group elements, Ni, and Cu. Despite the gradation in host-rock mineralogy, the sulfide fraction of the reef displays a constant bulk composition over 700 m of strike length, containing 9.3 percent Ni, 6.9 percent Cu, and approximately 0.7 percent total platinum-group elements (principally Pd). These platinum-group element concentrations are two to three orders of magnitude higher than those found in typical magmatic sulfide deposits and are attributed to equilibration of sulfide liquid with a very large volume of silicate melt.Olivines from the reef show a range of compositions from Fo 71 to Fo 85 , and from 2,400 to 4,500 ppm Ni. A positive correlation is observed between NiO and FeO in olivines from sulfide-bearing samples, indicating Ni-Fe exchange between olivine and sulfides on a local scale, such that Ni contents of olivines were buffered by that of the sulfide phase. A value of 9.70 + or - 1.49 is obtained for the Ni-Fe distribution coefficient between sulfide and olivine, in agreement with values obtained at magmatic temperatures by Boctor (1982).These observations may be interpreted in the framework of the plume model of Campbell et al. (1983). A pulse of replenishing magma enters the Stillwater chamber as a buoyant plume and subsequently spreads to form a layer of hybrid melt. Sulfide liquation and olivine crystallization occur within the plume and the hybrid layer in response to mixing and subsequent cooling. Sulfide liquid attains high platinum-group element concentrations during turbulent ascent and spreading of the plume. Crystallization of olivine from the hybrid layer gives rise to olivine-sulfide "boulders," which settle to the floor of the chamber. Reaction between the boulders and the evolved liquid at the bottom of the chamber causes olivine to become more iron rich. Subsequent reequilibration between olivine and sulfide grains gives rise to the observed Ni-Fe distribution.
TL;DR: In gills of S. reidi, the sulfide-oxidizing activity was detected not in the symbiotic bacteria, but within organelles of the gill cells the authors have named sulfide oxidizing bodies, which provide a major energy source for the symbiosis.
Abstract: A gutless clam, Solemya reidi, from sulfide-rich habitats has gills containing symbiotic, chemoautolithotrophic bacteria that are presumed to oxidize sulfide to provide a major energy source for the symbiosis. Sulfide oxidation was studied for S. reidi; activity of gill and foot extracts displayed Michaelis-Menten kinetics and was presumably due to sulfide oxidase enzymes. The activity of S. reidi gill extracts was protease sensitive and heat sensitive and was 10 to 20 times higher than in tissues from bivalves not living in sulfide-rich environments. The site of sulfide oxidation was studied by cytochemistry, 35S-sulfide autoradiography, cell fractionation methods, and by X-ray microanalysis. In gills of S. reidi, the sulfide-oxidizing activity was detected not in the symbiotic bacteria, but within organelles of the gill cells we have named sulfide oxidizing bodies. In foot tissue of S. reidi, sulfide oxidation activity was distributed diffusely throughout the superficial cell layers of the foot. The dis...
TL;DR: In this article, a twin roller apparatus has been designed to be used in a controlled environment, so that even hydroscopic and oxidizable glasses may be prepared by rapid quenching.
TL;DR: In this paper, the authors focused on the influence of sulfate-reducing bacteria Desulfovibrio desulfuricans (ATCC 7757) on the uranium removal process.
Abstract: The formation of many important sediment‐hosted uranium ore deposits is thought to have resulted from the reduction of relatively soluble uranyl ion—U(VI)—to insoluble uranium (IV) oxides and silicates by aqueous sulfide species. This study focused on the influence that the sulfate‐reducing bacteria Desulfovibrio desulfuricans (ATCC 7757) has on this process. Preliminary studies showed that bacterial growth was not inhibited by concentrations of uranyl ion up to 100 mg U per liter. More detailed studies showed that sulfate‐reducing bacteria have an influence on uranyl ion removal beyond the simple production of the aqueous sulfide reductant. Comparative studies of bacterial cultures containing high densities of the sulfate reducers with bacterial cell‐free but otherwise identical media showed that the bacteria themselves enhance uranium removal from solution. At pH 8.0, no reaction was observed in H2S‐bearing cell‐free media, whereas at the same H2S concentration, the uranyl ion decreased markedl...
Journal Article•
TL;DR: In this paper, the equilibrium concentrations of the toxic trace metals copper and cadmium were calculated for the physico-chemical conditions characterizing pore waters of anaerobic estuarine sediments using available thermodynamic data and assuming simple sulfide minerals control solubilities.
TL;DR: In this article, the relationship between depth of erosion since time of placement and spontaneous polarization observed on the surface, together with the effects of weathering, is presented from field surveys over known porphyry sulfide deposits.
Abstract: In the years 1978 through 1981, many spontaneous polarization (SP) surveys of porphyry sulfide deposits and prospects were done in the western United States. Effective depth of exploration using SP was found to exceed 1 km for large porphyry sulfide orebodies. The relationship between depth of erosion since time of em placement and the spontaneous polarization observed on the surface, together with the effects of weathering, are presented from field surveys over known deposits. Successful use of the spontaneous polarization tech nique in porphyry sulfide exploration led to an investi gation of the causative mechanism. The field data do not support the electrochemical model first proposed in Sato and Mooney (1960). The measured potential ap pears to be simply the oxidation potential !1E between a reference electrode outside the mineralization and a roving electrode within the mineralization. The !1E mea sured in the field is dominated by the difference in Eh (!1Eh) potential between the two electrodes, but it is not equivalent due to the unavoidable inclusion of other potentials in the field measurement. Without a wire con necting the electrodes, current between the sulfide min eralization and the surrounding country rock is sensibly zero, as evidenced by the persistence of the sulfides through geologic time.
TL;DR: In this article, different glass compositions which exhibit ionic transport properties in the oxide, sulfide and fluoride systems are presented and the main data concerning the conductivities and activation energies for conduction are given and compared to those of the best superionic conductors.
Abstract: The different glass compositions which exhibit ionic transport properties in the oxide, sulfide and fluoride systems, are presented. The main data concerning the conductivities and activation energies for conduction are given and compared to those of the best superionic conductors. The available models on ion transport in glasses are briefly discussed and the applicability of the weak electrolyte theory emphasized. Future development concerns protonic conduction in glasses and “soft” methods for synthesis of new glass compositions.
TL;DR: The role of organic matter in mechanisms of base metal transport during Mississippi Valley-type mineralization is not well understood as mentioned in this paper, however, specific ligands capable of concentrating significant quantities of lead and zinc in these ore solutions have not been identified.
Abstract: The role of organic matter in mechanisms of base metal transport during Mississippi Valley-type mineralization is not well understood. Evidence from field, experimental, and theoretical studies suggests that ore metals may be transported as organic complexes in Mississippi Valley-type ore fluids. However, specific ligands capable of concentrating significant quantities of lead and zinc in these ore solutions have not been identified. As a preliminary evaluation of metal transport by metal-organic complexing, activities of lead and zinc complexes involving nine carboxylate ligands (acetate, propionate, n-butyrate, phthalate, oxalate, tartronate, malate, D-tartrate, and salicylate) have been calculated for PbS- and ZnS-saturated, average ore solutions (those proposed by Giordano and Barnes, 1981) at 100 degrees and 200 degrees C. Calculated concentrations of lead and zinc in all of the complexes considered are well below the 10 ppm (10 (super -4) ) molal) minimum required to form an ore deposit.To ascertain the nature of other organic ligands which may have contributed significantly to base metal transport during Mississippi Valley-type mineralization, speciations of acetate, phthalate, and salicylate were calculated for three different average ore fluids at, or near, 100 degrees C. Results suggest that for weakly alkaline, sulfide-rich ore solutions, organic ligands should have stability constants for 1:1 and 1:2 base metal complexes of at least 10 10 and 10 20 , respectively. Such high stabilities would not be required if actual ore fluids were more acid or more oxidized, contained lower amounts of inorganic sulfide, or contained specific organic ligands at concentrations greater than 10 (super -4) molal. In addition to carboxylate, or similar complexes, metal-organic sulfide complexes may have provided a mechanism to transport significant quantities of lead, zinc, and reduced sulfur in Mississippi Valley-type ore solutions.
TL;DR: In this article, the process for forming native sulfide films on p-type Hg1−xCdxTe with x≂0.2-0.3 by anodic sulfidization is described and the analytical, optical and electrical properties of the resulting interface are reported.
Abstract: The process for forming native sulfide films on p‐type Hg1−xCdxTe with x≂0.2–0.3 by anodic sulfidization is described and studied. The analytical, optical, and electrical properties of the resulting interface are reported. The results of Auger electron spectroscopy analysis indicate that homogeneous CdS films with an abrupt interfacial transition are formed on Hg1−xCdxTe with x=0.215–0.290. The measured dispersion of the index of refraction and the dielectric constant of the native sulfide films are consistent with the reported data for bulk CdS. The interface between Hg1−xCdxTe and its native sulfide in combination with deposited ZnS has excellent electrical properties. A low fixed surface state density of the order of Nss ≂5×1010 cm−2, a low concentration of fast surface state density of the order of 5×109 cm−2 eV−1, and a small amount of trapping effects in the sulfide are observed. The MIS capacitors exhibit thermal stability up to 95 °C anneal in vacuum. The main features of the interface of p‐HgCdTe...
TL;DR: In this article, an unsupported tungsten sulfide catalysts of high surface area (60 m2/g) were prepared by in situ decomposition of ammonium tetrathiotungstate (ATT) in flowing helium at 450 °C.
TL;DR: It is shown that hydrogen sulfide is formed from L-Cysteine and that sodium sulfide could substitute for L-cysteine in the potentiation of hydrogen peroxide-induced killing of E. coli K-12.
Abstract: L-Cysteine potentiates 100-fold the hydrogen peroxide-induced killing of a growing culture of Escherichia coli K-12 (Berglin et al., J. Bacteriol. 152:81-88). In the present study it is shown that hydrogen sulfide is formed from L-cysteine and that sodium sulfide could substitute for L-cysteine in the potentiation of hydrogen peroxide-induced killing of E. coli K-12. Addition of an amino acid, L-leucine, L-valine, or L-alanine, to an L-cysteine-containing medium with a growing culture of E. coli K-12 inhibited hydrogen sulfide formation and the potentiation of hydrogen peroxide-induced killing. These amino acids did not inhibit hydrogen sulfide formation from L-cysteine by a cell extract, and they did not inhibit the potentiation by sulfide of hydrogen peroxide-induced killing. This indicated that the amino acids protected the culture from L-cysteine-potentiated, hydrogen peroxide-induced killing by inhibiting the transport of L-cysteine into the cell. The potentiation by sodium sulfide of hydrogen peroxide-induced killing was abolished by the metal ion chelator 2,2'-bipyridyl. This indicated that metal ions, in addition to sulfide, were involved in the killing. Toxic effects of hydrogen peroxide are often presumed to be mediated by hydroxyl radicals formed in iron-catalyzed reactions. It was demonstrated that iron sulfide was more efficient than ferrous iron in catalyzing the formation of hydroxyl radicals from hydrogen peroxide. It was suggested that hydrogen sulfide formed in polymicrobial infections may play an important role in the host defense by potentiating the antimicrobial effect of hydrogen peroxide produced by phagocytic cells.