Mercury transformations by heterotrophic bacteria isolated from cinnabar and other metal sulfide deposits in Italy
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Abstract Several mercury‐resistant bacteria were isolated from sites in Italy that surrounded natural mercury deposits. Bacterial strains resistant to 5 mg mercuric chloride per liter reduced Hg2+ to elemental mercury by an inducible process. One bacterial strain was resistant to methylmercuric chloride and produced elemental mercury when incubated with several organomercurial compounds. No methylmercury was detected in bacterial cultures growing in the presence of 2 mg mercuric chloride per liter. Mercury reduction is the major mercury transformation in mercury‐resistant bacteria isolated from these environments. Notes NATO‐CNR Fellow, NBS Guest Worker 1984–1985.Keywords:
Mercury
Cinnabar
Methylmercury
Elemental mercury
Sulfate-Reducing Bacteria
Research in China Assesses ExposuresHuman activities such as mining, smelting, and coal combustion dis perse mercury that can be methylated by bacteria to produce methyl mercury, a potent neurotoxicant.Methylating bacteria thrive in aquatic sediments rich in organic matter, and methylmercury biomagnification eventually leads to heavy contamination of top predators, including fish consumed by humans.Although fish and seafood are the most common dietary sources of methylmercury worldwide, new research from China demonstrates that rice, a staple food for billions, can be a primary source of methylmercury in areas where there is substantial inorganic mercury pollution, with calculated exposure exceeding cur rent tolerable daily intakes [EHP 118( 9):1183-1188; Zhang et al.].The research was conducted in four regions in Guizhou province, an area of inland China with rich deposits of cinnabar (a mercury ore).Mercury mining and smelting have led to heavy pollution in Wanshan, while zinc smelting and coal combustion, which also release mercury, are the main contributors in Weining and Qingzhen, respectively.The fourth region, Leigong, is a remote nature reserve selected to represent an area with no sources of direct mercury contamination.Methylmercury and total mercury exposure through drinking water, diet, and respiration were assessed for adults in the four regions.Previous sampling provided data for air, water, fish, meat, and poultry, while agricultural products (rice, corn, and vegetables), drinking water from Wanshan and Leigong, and total gaseous mercury in Wanshan were newly evaluated in this study.These data were collectively used to calculate probable daily intakes for the general adult population.In all regions rice, vegetables, and meat (not including poultry and fish) accounted for 89-97% of total mercury exposure, whereas rice consumption accounted for 94-96% of methylmercury exposure.Fish contributed little; most of the fish consumed here are farmed species that grow rapidly and eat a diet that precludes significant methyl mercury bioaccumulation.
Methylmercury
Mercury
Cinnabar
Biomagnification
Zinc smelting
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Sulfate-Reducing Bacteria
Oligomer restriction
Desulfovibrio
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Sulfate reducing bacteria (SRB) is identified as the primary organisms responsible for the treatment of heavy metal wastewater. However, most heavy metals can inhibit the growth of SRB during heavy metal treatment processes. Sulfide is a metabolic product of SRB and it can precipitate or reduce heavy metals. This study focused on the effects of sulfide on SRB resistance to Cu(II), Hg(I) and Cr(VI) toxicity. First, we considered the existence style of various heavy metals with and without sulfide addition by sequential extraction experiments. Second, the particle size distribution was evaluated and the cell structure during the metabolism of a SRB culture, containing different heavy metals, was analyzed by particle size distribution and TEM analyses. Third, the evolution of sulfate under the influence of different concentrations of heavy metals with and without sulfide addition was investigated to evaluate SRB activity. The results indicated that sulfide played an important role in alleviating and even eliminating the toxicity of Cu(II), Hg(II) and Cr(VI). We also discuss the mechanism of sulfide on SRB resistance to Cu(II), Hg(I) and Cr(VI) toxicity.
Sulfate-Reducing Bacteria
Metal Toxicity
Sulfide Minerals
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Different from the corrosion under anaerobic conditions, oxygen (O 2 ) takes part in the cathodic reaction under aerobic conditions. Sulfate-reducing bacteria (SRB) have been regarded for many years as strictly anaerobic bacteria, but recently, they are found to be able to survive in the presence of O 2 , and how they affect the oxygen reduction reaction (ORR) has not been clear. In this study, the role of sulfide, a key inorganic metabolite of SRB, in ORR has been investigated on Q235 carbon steel electrode with cyclic voltammetry and electrochemical impedance spectroscopy. Three cathodic processes are recorded on cyclic voltammograms in O 2 -saturated 3.5% NaCl solution: ORR, iron oxides reduction and hydrogen evolution. The peak current of ORR decreases with the introduction of sulfide, and finally vanishes when the sulfide concentration is more than 0.5 mM. EIS reveals that sulfide leads to the disappearance of the feature of semi-infinite diffusion of ORR and the fitting results demonstrate that charge transfer resistance increases with increasing sulfide concentration. Therefore sulfide hinders the cathodic reduction of O 2 on Q235 carbon steel in 3.5% NaCl solution.
Sulfate-Reducing Bacteria
Sodium sulfide
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Sulfate-Reducing Bacteria
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Sulfate-Reducing Bacteria
Metal Toxicity
Sulfide Minerals
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Sulfate-reducing bacteria (SRB) can beneficially be applied to domestic wastewater treatment. In general, formed sulfide will stay in liquid phase, resulting in an elevated sulfide content, which might have inhibiting effects on the SRB. To study effects of environmental conditions on the SRB resistance against sulfide, two sequencing batch reactors fed with artificial domestic wastewater were operated at sulfate-reducing conditions. Required sulfide concentration within the reactor was achieved by adding 400 or 800 mg COD/L (acetate and propionate), the latter resulting in proportionally more sulfide production. Batch tests revealed that sulfide inhibited the rate of sulfate reduction by 50% at a concentration of 200 mg/L sulfide for biomass from the reactor fed with 400 mg COD/L. After adaptation to a feed of 800 mg COD/L, resulting in higher sulfide exposures, sulfide was less inhibitive to SRB. Complete COD removal was achieved in the reactor fed with 800 mg COD/L, and the SRB population changed from one (Desulfotalea arctica) to two (Desulfobacter postgatei and Desulfocapsa sulfexigens) dominant species. Results indicate that SRB are capable of adapting to higher sulfide exposure. Therefore, the SRB can also be applied to treat wastewater with higher COD levels, blackwater for instance.
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Sulfate-Reducing Bacteria
Electron acceptor
Electron donor
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Abstract Expense of bactericide treatment in injection water can be a major item in the operation of a waterflood or disposal system. Each operator of such a system desires to know whether such expense is necessary and which bactericidal chemical is most economical for his system. The diagnosis to be described makes use of modifications in recognized analytical methods for on-the-spot determinations of total sulfide and of populations of "sulfate-reducing bacteria". Activity of the bacteria is judged on the basis of increases in sulfide concentrations and/or in increases in bacterial populations as the water progresses through the system under study. The methods used in this diagnosis are of sufficient sensitivity that indications of bacterial activity should be apparent if down-hold bacterial sulfide formation is a significant factor in any water injection system. If the diagnosis fails to show a definite bacterial problem, more careful study of other factors is indicated. Descriptions will be made to cover typical evidence for:Uncomplicated appearance of bacterial sulfide in injection water accompanied by increasing numbers of sulfate-reducing bacteria or accompanied by high bacterial populations.Localized pockets of bacterial sulfide formation. Water passing such pockets would pick up sulfide and bacteria either continuously or in "slugs".Cases where one or more supply waters contain dissolved sulfide with or without significant numbers of sulfate-reducing bacteria. Little or no additional sulfide is formed by the bacteria but the soluble sulfide reacts with iron salts, metallic iron etc., to produce "black water". Treatment with chemicals having properties other than or in addition to bactericidal activity is required.Complications associated with imperfect mixing of widely differing supply waters. Concentrations of sulfide and bacteria passing sample points fluctuate, hence diagnosis is possible only by alterations in the operation of the system.
Sulfate-Reducing Bacteria
Bacterial growth
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