Formation Of Hydrogen Sulfide Research Articles

Molten carbonate fuel cells fed with biogas: Combating H 2S

The use of biomass and waste to produce alternative fuels, due to environmental and energy security reasons, is a high-quality solution especially when integrated with high efficiency fuel cell applications. In this article we look into the coupling of an anaerobic digestion process of organic residues to electrochemical conversion to electricity and heat through a molten carbonate fuel cell (MCFC). In particular the pathway of the exceedingly harmful compound hydrogen sulphide (H 2S) in these phases is analysed. Hydrogen sulphide production in the biogas is strongly interrelated with methane and/or hydrogen yield, as well as with operating conditions like temperature and pH. When present in the produced biogas, this compound has multiple negative effects on the performance and durability of an MCFC. Therefore, there are important issues of integration to be solved. Three general approaches to solve the sulphur problem in the MCFC are possible. The first is to prevent the formation of hydrogen sulphide at the source: favouring conditions that inhibit its production during fermentation. Secondly, to identify the sulphur tolerance levels of the fuel cell components currently in use and develop sulphur-tolerant components that show long-term electrochemical performance and corrosion stability. The third approach is to remove the generated sulphur species to very low levels before the gas enters the fuel cell.

Hydrogen sulfide promotes transient receptor potential vanilloid 1-mediated neurogenic inflammation in polymicrobial sepsis*

To investigate the interaction and involvement of hydrogen sulfide and transient receptor potential vanilloid type 1 in the pathogenesis of sepsis. Hydrogen sulfide has been demonstrated to be involved in many inflammatory states including sepsis. Its contribution in neurogenic inflammation has been suggested in normal airways and urinary bladder. However, whether endogenous hydrogen sulfide would induce transient receptor potential vanilloid type 1-mediated neurogenic inflammation in sepsis remains unknown. Prospective, experimental study. Research laboratory. Male Swiss mice. Mice were subjected to cecal ligation and puncture-induced sepsis and treated with transient receptor potential vanilloid type 1 antagonist capsazepine (15 mg/kg subcutaneous) 30 mins before cecal ligation and puncture. To investigate hydrogen sulfide-mediated neurogenic inflammation in sepsis, DL-propargylglycine (50 mg/kg intraperitoneal), an inhibitor of hydrogen sulfide formation was administrated 1 hr before or 1 hr after the induction of sepsis, whereas sodium hydrosulfide (10 mg/kg intraperitoneal), a hydrogen sulfide donor, was given at the same time as cecal ligation and puncture. Lung and liver myeloperoxidase activities, liver cystathionine-gamma-lyase activity, plasma hydrogen sulfide level, histopathological examination, and survival studies were determined after induction of sepsis. Capsazepine treatment attenuates significantly systemic inflammation and multiple organ damage caused by sepsis, and protects against sepsis-induced mortality. Similarly, administration of sodium hydrosulfide exacerbates but capsazepine reverses these deleterious effects. In the presence of DL-propargylglycine, capsazepine causes no significant changes to the attenuation of sepsis-associated systemic inflammation, multiple organ damage, and mortality. In addition, capsazepine has no effect on endogenous generation of hydrogen sulfide, suggesting that hydrogen sulfide is located upstream of transient receptor potential vanilloid type 1 activation, and may play a critical role in regulating the production and release of sensory neuropeptides in sepsis. The present study shows that hydrogen sulfide induces systemic inflammation and multiple organ damage characteristic of sepsis via transient receptor potential vanilloid type 1-mediated neurogenic inflammation.

Analysis of Hypoxia Dynamics Using Pelagic and Benthic Biogeochemical Model: Focus on the Formation and Release of Hydrogen Sulfide

A field survey and laboratory analyses of sediment quality in the eastern part of Osaka Bay are carried out to clarify their characteristics and influence on the dynamics of hypoxia. Nitrogen, phosphorus and sulfur cycling in the coastal water and sediment are modeled with a focus on the formation of hydrogen sulfide in hypertrophic sediment and its release to the bottom water. In the calculated results the oxygen consumption in the bottom water by the release of sulfide is much larger than the direct oxygen consumption by the sediment in the northern port of the bay. Without the release of sulfide, the hypoxic water area would be estimated to be limited in and near the port area of the head of the bay. The wide spreading of hypoxia in the eastern part of the bay would be contributed largely by the sulfide release.

Possible role of hydrogen sulphide gas in self-heating of pyrrhotite-rich materials

Self-heating of sulphides poses safety, environmental and economic concerns to the mining and metallurgical industries, especially when sulphide ores or concentrates have to be stored or transported. The first target of this investigation is the self-heating of pyrrhotite (Po), the most commonly suspected mineral to trigger the phenomenon because of its fast oxidation in moist air. Following a standard experimental protocol, self-heating was assessed on samples of Po mixed with sand as an inert material. With increasing Po content, self-heating rates progressively increased but the samples visually appeared less and less oxidized. A high Po content, it was hypothesized, may give a more reducing environment favouring formation of hydrogen sulphide (H 2S). The presence of this gas could be significant for self-heating for several reasons which are discussed. The hypothesis was tested by including copper pieces to detect the gas by forming copper sulphide, and adding copper sulphate in excess which suppressed self-heating, apparently by reacting with and removing the gas.

Hydrogen Sulfide Production From Cysteine and Homocysteine by Periodontal and Oral Bacteria

Hydrogen sulfide is one of the predominant volatile sulfur compounds (VSCs) produced by oral bacteria. This study developed and evaluated a system for detecting hydrogen sulfide production by oral bacteria. L-methionine-alpha-deamino-gamma-mercaptomethane-lyase (METase) and beta carbon-sulfur (beta C-S) lyase were used to degrade homocysteine and cysteine, respectively, to produce hydrogen sulfide. Enzymatic reactions resulting in hydrogen sulfide production were assayed by reaction with bismuth trichloride, which forms a black precipitate when mixed with hydrogen sulfide. The enzymatic activities of various oral bacteria that result in hydrogen sulfide production and the capacity of bacteria from periodontal sites to form hydrogen sulfide in reaction mixtures containing L-cysteine or DL-homocysteine were assayed. With L-cysteine as the substrate, Streptococcus anginosus FW73 produced the most hydrogen sulfide, whereas Porphyromonas gingivalis American Type Culture Collection (ATCC) 33277 and W83 and Fusobacterium nucleatum ATCC 10953 produced approximately 35% of the amount produced by the P. gingivalis strains. Finally, the hydrogen sulfide found in subgingival plaque was analyzed. Using bismuth trichloride, the hydrogen sulfide produced by oral bacteria was visually detectable as a black precipitate. Hydrogen sulfide production by oral bacteria was easily analyzed using bismuth trichloride. However, further innovation is required for practical use.

Making and working with hydrogen sulfide: The chemistry and generation of hydrogen sulfide in vitro and its measurement in vivo: A review

Hydrogen sulfide is rapidly emerging as an important vasoactive mediator formed in health and disease. Its biological action is centered on its reactivity with heme-proteins and its ability to activate K ATP channels. Hydrogen sulfide is a signalling molecule of the inflammatory and nervous systems, and in particular the cardiovascular system where it regulates vascular tone, cardiac work, and exerts cardioprotection. This has led to an explosion of papers in which the role of hydrogen sulfide generated in vitro has been used to stimulate biological responses, and where a variety of methods have been used to measure the concentration of this compound in biological fluids. Understanding the chemistry and the inherent problems in the analytical techniques used to measure hydrogen sulfide concentrations is critical to our expanding knowledge on the biology of hydrogen sulfide. In this brief review we will cover the chemistry of hydrogen sulfide, including sources of hydrogen sulfide, its speciation at physiological pH, the susceptibility of sulfide to aerobic oxidation, and the methods used to measure hydrogen sulfide concentrations in solution, including biological fluids. We also give a brief overview of knockout animals and inhibition of the enzymes involved in the formation of hydrogen sulfide in vivo.

Controlling Bacterial Biofilms

Methods of controlling bacteria cells are disclosed. These methods comprise upregulating expression of a DVU2956 sigma 54-dependent enhancer-binding protein (EBP) in bacteria cells, resulting in (i) dispersing a biofilm of the cells or reducing biofilm formation by the cells, and/or (ii) reducing hydrogen sulfide formation by the cells. Further disclosed are methods of identifying compounds for controlling bacteria cells as in (i) and/or (ii) above. Polynucleotides and cells are disclosed that can optionally be used to practice compound identification methods.

Lactate has the potential to promote hydrogen sulphide formation in the human colon

High concentrations of sulphide are toxic for the gut epithelium and may contribute to bowel disease. Lactate is a favoured cosubstrate for the sulphate-reducing colonic bacterium Desulfovibrio piger, as shown here by the stimulation of sulphide formation by D. piger DSM749 by lactate in the presence of sulphate. Sulphide formation by D. piger was also stimulated in cocultures with the lactate-producing bacterium Bifidobacterium adolescentis L2-32. Other lactate-utilizing bacteria such as the butyrate-producing species Eubacterium hallii and Anaerostipes caccae are, however, expected to be in competition with the sulphate-reducing bacteria (SRB) for the lactate formed in the human colon. Strains of E. hallii and A. caccae produced 65% and 96% less butyrate from lactate, respectively, in a coculture with D. piger DSM749 than in a pure culture. In triculture experiments involving B. adolescentis L2-32, up to 50% inhibition of butyrate formation by E. hallii and A. caccae was observed in the presence of D. piger DSM749. On the other hand, sulphide formation by D. piger was unaffected by E. hallii or A. caccae in these cocultures and tricultures. These experiments strongly suggest that lactate can stimulate sulphide formation by SRB present in the colon, with possible consequences for conditions such as colitis.

Characterization of microbial trophic structures of two anaerobic bioreactors processing sulfate-rich waste streams

A multi-compartment anaerobic bioreactor, designated the anaerobic migrating blanket reactor (AMBR), did not perform well in terms of chemical oxygen demand (COD) removal after an increase in sulfate load, compared to a conventional upflow anaerobic sludge blanket (UASB) reactor. The trophic structures of the bioreactors were characterized by analyzing the electron flows, formation and consumption of fermentation intermediates and terminal product (methane and hydrogen sulfide) formation. Critical performance parameters were linked to operational perturbations such as increase in sulfate load and changes in flow reversal schemes in the AMBR. Both of these manipulations affected the microbial communities, which were monitored by terminal restriction fragment length polymorphism (T-RFLP) analysis targeting the bacterial and archaeal domains. The less stable AMBR did not produce granular biomass, and in response to increased sulfate concentrations, experienced a reversal in the distribution of hydrogenotrophic methanogens that correlated with a shift in electron flow from butyrate to propionate. As this shift occurred, bacterial populations such as butyrate-producing clostridia, became predominant, thus leading to reactor imbalance. The stable UASB reactor developed and retained granules and maintained a relatively stable archaeal community. Sulfate perturbation led to the selection of a novel bacterial group ( Thermotogaceae), which was most likely well adapted to the increasingly sulfidogenic conditions in the bioreactor.

Leaching of a low-grade, copper–nickel sulfide ore. 1. Key parameters impacting on Cu recovery during column bioleaching

This study was prompted by the disparate recoveries of nickel (> 70%) and copper (< 20%) from a test heap of copper–nickel sulfide ore after about 200 days of leaching. Variables tested in bioleaching columns charged with a pyrrhotite-rich, chalcopyrite and pentlandite ore were acid pre-conditioning, inoculation and aeration. The results indicated that the rapid reaction of pyrrhotite with acid created conditions that impacted directly and/or indirectly on copper recovery. Important reactions were hydrogen sulfide formation, high soluble iron concentrations and the formation of large amounts of elemental sulfur. It was hypothesized that copper loss, evidenced by copper re-distribution during passage through the ore, was mainly the result of reaction with hydrogen sulfide to form covellite, although this could not be confirmed by XRD analysis of leached residues. A layer of iron-oxy-hydroxy-sulfate “scale” on particle surfaces encapsulated sulfide grains as well as elemental sulfur formed by the oxidation of pyrrhotite and was of sufficient depth and integrity to have hindered but not prevented leaching and bioleaching. Lack of aeration (oxygen, carbon dioxide) impacted on ferrous ion biooxidation and probably sulfur biooxidation. More extensive sulfur biooxidation to form acid might have lowered the solution pH and reduced the amount of scale formation, resulting in higher ferric ion concentrations and better chalcopyrite oxidation.

Case Study: Pretreatment of Challenging Pork Rinds Manufacturing Wastewater

Problem: Gaytan Foods facilities in City of Industry (Los Angeles, CA) manufacture pickled pork rinds, pickled pig feet and “cheese” puffs. The resulting wastewater is loaded with FOG’s, proteins and salts. Wastewater varies hourly and daily. Drastic changes in amount and type of contaminants occur (two orders of magnitude). During some hours wastewater is loaded with proteins, and as it cools down, highly viscous gel is produced. Protein degradation produces hydrogen sulfide (odor problem). Goals and Objectives: Local municipality complained about amount of FOG in wastewater and formation of gel in pipes. Reduction of BOD was also suggested. Odor problems (hydrogen sulfide) also had to be dealt with. The goal was to design and build wastewater treatment plant that will reduce amount of FOG, TSS and BOD and prevent formation of gel and hydrogen sulfide. Solution: Wastewater treatment plant was designed and installed to deal with those problems. Rotating drum screen was installed to remove large particles and objects. Large equalization tank collecting 24 hours of produced wastewater with intense mixing was installed to prevent gelation. Equalization also helped reduce the salinity of the stream (dilution with low salinity streams). Following equalization, flocculation – flotation system was used for primary treatment. Individual samples were very difficult to coagulate and flocculate. Large amounts of flocculants were needed to achieve the flocculation. This made the process too expensive. However, equalization solved these problems. Equalized stream was easy to flocculate. Hybrid centrifugal – dissolved air flotation system reduces TSS to less than 50 mg/l and FOG to less than 5 mg/l. Dissolved BOD’s are also removed, probably due to flocculation of some large protein molecules. Total BOD’s reductions average around 75%. Aeration of the equalization tank prevents formation of hydrogen sulfide. This significantly reduces odor problems. Since the installation of the system, gel formation in pipes never occurred, either. Flotation produces sludge with over 25% of solids that is reused (pet food manufacturing). Municipal wastewater treatment plant has no problem with treatment of dissolved BOD’s that remain in wastewater after the pretreatment. Fees and fines that Gaytan Foods faced in the past are significantly reduced or eliminated (fines). In the future, even more robust odor control will be attempted (deodorizing solutions).

Structural Basis for the Inhibition Mechanism of Human Cystathionine γ-Lyase, an Enzyme Responsible for the Production of H2S

Impairment of the formation or action of hydrogen sulfide (H(2)S), an endogenous gasotransmitter, is associated with various diseases, such as hypertension, diabetes mellitus, septic and hemorrhagic shock, and pancreatitis. Cystathionine beta-synthase and cystathionine gamma-lyase (CSE) are two pyridoxal-5'-phosphate (PLP)-dependent enzymes largely responsible for the production of H(2)S in mammals. Inhibition of CSE by DL-propargylglycine (PAG) has been shown to alleviate disease symptoms. Here we report crystal structures of human CSE (hCSE), in apo form, and in complex with PLP and PLP.PAG. Structural characterization, combined with biophysical and biochemical studies, provides new insights into the inhibition mechanism of hCSE-mediated production of H(2)S. Transition from the open form of apo-hCSE to the closed PLP-bound form reveals large conformational changes hitherto not reported. In addition, PAG binds hCSE via a unique binding mode, not observed in PAG-enzyme complexes previously. The interaction of PAG-hCSE was not predicted based on existing information from known PAG complexes. The structure of hCSE.PLP.PAG complex highlights the particular importance of Tyr(114) in hCSE and the mechanism of PAG-dependent inhibition of hCSE. These results provide significant insights, which will facilitate the structure-based design of novel inhibitors of hCSE to aid in the development of therapies for diseases involving disorders of sulfur metabolism.

Application of bacteria involved in the biological sulfur cycle for paper mill effluent purification

In anaerobic wastewater treatment, the occurrence of biological sulfate reduction results in the formation of unwanted hydrogen sulfide, which is odorous, corrosive and toxic. In this paper, the role and application of bacteria in anaerobic and aerobic sulfur transformations are described and exemplified for the treatment of a paper mill wastewater. The sulfate containing wastewater first passes an anaerobic UASB reactor for bulk COD removal which is accompanied by the formation of biogas and hydrogen sulfide. In an aeration pond, the residual COD organic and the formed dissolved hydrogen sulfide are removed. The biogas, consisting of CH 4 (80–90 vol.%), CO 2 (10–20 vol.%) and H 2S (0.8–1.2 vol.%), is desulfurised prior to its combustion in a power generator thereby using a new biological process for H 2S removal. This process will be described in more detail in this paper. Biomass from the anaerobic bioreactor has a compact granular structure and contains a diverse microbial community. Therefore, other anaerobic bioreactors throughout the world are inoculated with biomass from this UASB reactor. The sludge was also successfully used in investigation on sulfate reduction with carbon monoxide as the electron donor and the conversion of methanethiol. This shows the biotechnological potential of this complex reactor biomass.

Perspective on Recent Developments on Sulfur-Containing Agents and Hydrogen Sulfide Signaling

The last couple of years have witnessed the coming together of several initially unconnected lines of investigation which now link natural sulfur products to hydrogen sulfide release and wide ranging cardiovascular protection. It has become apparent that sulfur compounds contained within garlic, onions, mushrooms and various edible beans and fruits may be transformed chemically or enzymatically in the human body with subsequent formation of hydrogen sulfide. The latter has emerged during the last decade from a shadowy existence as toxic gas to be recognized as the third gaseous transmitter besides nitric oxide ( (.)NO) and carbon monoxide (CO). Hydrogen sulfide is formed endogenously in the human body by enzymes such as cystathionine beta-synthase (CBS) in the brain and cystathionine gamma-lyase (CSE) in liver, vascular and non-vascular smooth muscle. Although its exact chemical and biochemical modes of action are still not fully understood, levels of hydrogen sulfide in the brain and vasculature have unambiguously been associated with human health and disease. Not surprisingly, agents releasing hydrogen sulfide, as well as inhibitors of hydrogen sulfide synthesis (CBS and CSE inhibitors) have been investigated. Apart from linking our daily diet to a healthy brain and cardiovasculature, these findings may also provide new leads for drug design. Future studies will therefore need to focus on how such compounds are formed and transformed in the relevant plants, how food processing affects their chemical constitution, and how they release hydrogen sulfide (or control its levels) in the human body. Such multidisciplinary research should ultimately answer the all-important question if a hearty diet is also good for the heart.

Kinetic Properties of Polymorphic Variants and Pathogenic Mutants in Human Cystathionine γ-Lyase

Human cystathionine-gamma-lyase (CGL) is a pyridoxal-5'-phosphate (PLP)-dependent enzyme, which functions in the transsulfuration pathway that converts homocysteine to cysteine. In addition, CGL is one of two major enzymes that can catalyze the formation of hydrogen sulfide, an important gaseous signaling molecule. Recently, several mutations in CGL have been described in patients with cystathioninuria, a rare but poorly understood genetic disease. Moreover, a common single nucleotide polymorphism in CGL, c.1364G>T that converts serine at position 403 to isoleucine, has been linked to elevated plasma homocysteine levels. In this study, we have characterized the pathogenic T67I and Q240E missense mutations and the polymorphic variants at amino acid residues 403 using kinetic and spectrophotometric methods. We report that the polymorphism does not influence the cofactor content of the enzyme or its steady-state kinetic properties. In contrast, the T67I mutant exhibits a 3.5-fold decrease in V max compared to that of wild-type CGL, while the Q240E mutant exhibits a 70-fold decrease in V max. The K Ms for cystathionine for both pathogenic mutants are comparable to that of wild type CGL. The PLP content of the T67I and Q240E mutants were about 4-fold and 80-fold lower than that of wild-type enzyme, respectively. Preincubation of the T67I mutant with PLP restored activity to wild-type levels while the same treatment resulted in only partial restoration of activity of the Q240E mutant. These results reveal that both mutations weaken the affinity for PLP and suggest that cystathionuric patients with these mutations should be responsive to pyridoxine therapy.

Geochemistry of iron in the Salton Sea, California

The Salton Sea is a large, saline, closed-basin lake in southern California. The Sea receives agricultural runoff and, to a lesser extent, municipal wastewater that is high in nutrients, salt, and suspended solids. High sulfate concentrations (4× higher than that of the ocean), coupled with warm temperatures and low-redox potentials present during much of the year, result in extensive sulfate reduction and hydrogen sulfide production. Hydrogen sulfide formation may have a dramatic effect on the iron (Fe) geochemistry in the Sea. We hypothesized that the Fe(II)-sulfide minerals should dominate the iron mineralogy of the sediments, and plans to increase hypolimnetic aeration would increase the amount of Fe(III)-oxides, which are strong adsorbers of phosphate. Sequential chemical extractions were used to differentiate iron mineralogy in the lake sediments and suspended solids from the tributary rivers. Iron in the river-borne suspended solids was mainly associated with structural iron within silicate clays (70%) and ferric oxides (30%). The iron in the bottom sediments of the lake was associated with silicate minerals (71% of the total iron in the sediments), framboidal pyrite (10%), greigite (11%), and amorphous FeS (5%). The ferric oxide fraction was <4% of the total iron in these anaerobic sediments. The morphological characteristics of the framboidal pyrite as determined using SEM suggest that it formed within the water column and experiences some changes in local redox conditions, probably associated with alternating summer anoxia and the well-mixed and generally well-aerated conditions found during the winter. The prevalence of Fe(II)-sulfide minerals in the sediments and the lack of Fe(III)-oxide minerals suggest that the classic model of P-retention by Fe(III)-oxides would not be operating in this lake, at least during anoxic summer conditions. Aeration of the hypolimnion could affect the internal loading of P by changing the relative amounts of Fe(II)-sulfides and Fe(III)-oxides at the sediment/water interface.

Activity of cobalt sulfide catalysts in the hydrogenolysis of dimethyl disulfide to methanethiol: Effects of the nature of a support and the procedure of supporting a cobalt precursor

The conversion of dimethyl disulfide to methanethiol on various catalysts containing supported cobalt sulfide in an atmosphere of hydrogen was studied at atmospheric pressure and T = 190°C. On CoS introduced into the channels of zeolite HSZM-5, the process occurred at a high rate but with a low selectivity for methanethiol because the proton centers of the support participated in a side reaction with the formation of dimethyl sulfide and hydrogen sulfide. Under the action of sulfide catalysts supported onto a carbon support, aluminum oxide, silicon dioxide, and an amorphous aluminosilicate, the decomposition of dimethyl disulfide to methanethiol occurred with 95–100% selectivity. The CoS/Al2O3 catalysts were found to be most efficient. The specific activity of alumina-cobalt sulfide catalysts only slightly depended on the phase composition and specific surface area of Al2O3. The conditions of the thermal treatment and sulfurization of catalysts and, particularly, the procedure of supporting a cobalt precursor onto the support were of key importance. Catalysts prepared through the stage of supporting nanodispersed cobalt hydroxide were much more active than the catalysts based on supported cobalt salts.

Methane formation in sewer systems

Methane formation and emission in sewer systems has not received as much attention as hydrogen sulphide formation. Through field measurements from two rising mains, with an average sewage temperature of 28.4 and 26.6 °C, respectively, at the time of sampling, this study shows that a significant amount of methane can be produced in sewer systems, and that this production is positively correlated with the hydraulic retention time of wastewater in these systems. The experimental results from a laboratory-scale sewer system fed with real sewage with a temperature of approximately 21 °C confirmed these field observations and further revealed that methanogenesis and sulphate reduction occur simultaneously in sewers, with methane production contributing considerably more to the loss of soluble COD in sewers than sulphate reduction. The production of methane in sewers at levels revealed by this study is a serious environmental concern as it potentially results in greenhouse emissions that is comparable to that caused by the energy consumption for the treatment of the same wastewater. Further, methane production in sewers influences sulphide production and its management due to the competition between methanogens and sulphate-reducing bacteria for potentially the same electron donors. The potential interactions between sulphate-reducing and methanogenic bacteria in sewer networks are discussed.

Antioxidant Impacts on Volatile Formation in High-Pressure-Processed Milk

The effect of antioxidants on volatile formation in milk under high pressure was investigated. Raw milk samples with addition of either butylated hydroxyanisole (BHA), epicatechin, ascorbic acid, beta-carotene, or L-cystine were pressurized under 655 MPa at 75 degrees C for 3, 5, and 10 min. Formation of selected volatile compounds including aldehydes, ketones, and sulfur compounds was studied using headspace solid-phase microextraction and gas chromatography. BHA and epicatechin effectively inhibited the aldehyde formation. Ascorbic acid and beta-carotene also inhibited aldehyde formation but to a much lower extent. L-cystine was capable of inhibiting aldehyde and hydrogen sulfide formation. In general, the inhibition of volatile formation was proportional to the concentration of the added antioxidants. Reducing oxygen contents in milk also decreased aldehyde formation. Results suggested that the inhibition of volatile formation under high pressure could be similar to that under normal-pressure condition.

The contents of labile sulfides in the bottom sediments of the central part of the Sea of Azov: Impact on benthic communities

At 17 stations in the central part of the Sea of Azov, the contents of labile (acid-soluble) sulfides were determined in the upper layer (0–3 cm) of the bottom sediments. At 14 of these stations, the contents of sulfides in the oozy silts were over 300 mg S/dm3 of wet sediment; at seven of the stations, the contents of sulfide were as high as 420–720 mg S/dm3 of wet ooze, or 0.1–0.2% of dry weight. At the other three stations, where neutral matter such as shells and sand prevailed in the samples, the contents of sulfides varied from 80 to 110 mg S/dm3. At these stations, a high density and species diversity of the benthic fauna was retained. At other stations with labile sulfide contents over 200–300 mg S/dm3, the benthos biomass decreased by one or two orders of magnitude. At most of them, it was below 3 g/m2 and the small gastropod Hydrobia tolerant to sulfides dominated. The data obtained show that, in the central part of the Sea of Azov, reduced sediments with high contents of labile sulfides migrate towards the bottom surface, which conforms to the high intensity of the hydrogen sulfide formation process caused by the bacterial sulfate reduction. The study considers the environmental effects of the sulfide contamination of the upper layer of the bottom sediments in the Sea of Azov as a key factor causing the recurrent hypoxy in the near-bottom layers of the water, the suffocation occurrence, and the progressive depletion of the benthic and pelagic fauna.