Water Sulfide Research Articles

Composition of microbial communities as an indicator of the condition of water reservoirs artificially separated from the sea basins (based on the example of the Kislogubskaya tidal power plant bay, Barents sea)

The Kislaya Bay currently refers to the water reservoirs formed as a result of the construction of the dam of the tidal power station (TPP) in the Russian Federation (1968). As a result of the reduction in the influence of tidal currents mixing the water column of the bay, the hydrological regime of the reservoir has changed. The reduction in water exchange led to the appearance of bottom stagnant waters deprived of oxygen, as well as hydrogen sulfide contamination. In the 90-s of the twentieth century, the operation of the Kislogubskaya TPP ceased and the flow regime was partially restored. In the winter season of 2024, we conducted microbiological and biogeochemical studies of the Kislaya Bay. It was shown that there was no hydrogen sulfide in the bottom water of the bay, and the processes of sulfate reduction, methane formation and methane oxidation were extremely low. At the same time, in the subsurface layer of sediment, bacteria and archaea were found that dominate the microbial communities of anoxic waters of meromictic reservoirs. We believe that with a stable exchange of water through the TPP dam, the composition of the microbial community of water and sediment will be restored. In case of negative developments, it is possible to predict the transformation of the bay into a reservoir with a community of microorganisms similar to meromictic reservoirs.

Термальные сульфидные воды Баргузинской долины (Республика Бурятия)

Abstract. Relevance. Hydrogen sulfide mineral waters are widely used in spa treatment. The therapeutic effect of exposure to hot water procedures gives positive results in chronic pathologies of the musculoskeletal system, gastroenterology, as well as in other areas of prevention and rehabilitation of human health, where hydrogen sulfide is considered an important therapeutic component. The aim of the work. Investigation of the hydrochemical and microbiological composition of thermal hydrogen sulfide waters of Umkhey, Kuchiger, Alla springs of the Barguzin Valley of the Republic of Buryatia. Materials and methods. The composition of sulfur-containing compounds in sources, which by their composition belong to the nitric thermal siliceous waters of the Baikal hydromineral region, where the accumulation of chemical components is facilitated by an alkaline environment and elevated temperature, has been studied using hydrochemical analysis, mass spectrometry and high-performance liquid chromatography. Results. The conducted studies have shown that in addition to sulfides and sulfates, sulfites, thiosulfates, mineral water contains elemental and polysulfide sulfur, cyclic polynuclear organosulfur compounds and cyclic polysulfides. These compounds can exhibit high balneological activity due to their better permeability through the skin at high temperatures. The composition of the microbial community of water and bottom sediments has been studied, which is represented by various taxonomic groups, where the chemolithotrophic bacteria Thiobacillus, Thermodesulfovibrio, Geobacter and Gallionella are the dominant group. The microbial community in thermal springs is involved in the transformation of chemicals, the formation and consumption of gases, in biogeochemical cycles of sulfur, the formation of the chemical composition and therapeutic factor of waters and sediments. Conclusions. The presence of organic sulfanes simultaneously with elemental sulfur and hydrogen sulfide suggests that they are active balneological components of thermal hydrogen sulfide mineral waters. The microbial community of water and bottom sediments in thermal springs is involved in the transformation of chemicals and the formation of the chemical composition and therapeutic factor of waters and bottom sediments.

О проблемах комплексного использования и охраны водных ресурсов Оренбуржья и сопредельных1 территорий

The water resources of the Orenburg region are formed mainly due to water of infiltration origin. Their dynamics and chemical composition change zonally, decreasing from north to south, from forest-steppes to dry steppes and further to the deserts of Kazakhstan in accordance to the laws of latitudinal and altitudinal zonation, which vary depending on the regions. Well hydrogeologically closed areas have a powerful zone of hydrohalogenesis. With a decrease in the closeness of the subsoil, the thickness of zones of hydrogenesis increases, reaching a maximum in the folded mountainous Urals, where hydrogeological zoning is consistent with landscape-geochemical heterogeneity and drainage basins. Concentrations of elements in waters increase from the aeration zone to the zone of normal base flow. A regional geochemical barrier of hydrogen sulfide waters for metals has been identified in the structures of the Cis-Ural region. The volume of chemical denudation decreases towards the dry steppe zone and increases in elevated areas composed of gypsum and karst rocks. To solve water management problems it is necessary to introduce modern technologies. These include complex devices with geochemical, hydrodynamic and complex barriers.

Groundwater dilution and flow conditions in sulfuric acid caves: the case study of Frasassi (Italy)

This study analyzes the dilution process of the sulfidic groundwater in the Frasassi caves due to the recharge of O2-rich freshwater and its influence on the sulfuric acid speleogenesis and morphogenesis. The drainage pattern and the seasonal changes of the chemo-physical characteristics of the groundwater through a year-long monitoring and the measurements of the groundwater levels are presented. The inflow of water infiltrating from the karst surface influenced the sulfidic groundwater parameters, reflecting the seasonal meteoric cycle. On the contrary, the Sentino River, which represents the local base level, directly influenced the groundwater only in the most external part of the cave. The water level measurements evidenced a low hydraulic gradient (~3‰), due to the high karstification, and also some differences in the permeability depending on the drainage direction. Most cave pools are isolated on the surface and connected to each other through a network of submerged passages. In the present conditions, a surface layer of bicarbonate water forms above the sulfidic water in a large part of the cave, where it impedes subaerial corrosion by released acidic gases. Conversely, the distribution of residual gypsum deposits and corrosional wall features in the upper old cave levels demonstrate that large interfaces between sulfidic water and cave atmosphere existed during some periods of the cave history. Here, the release of acidic gases (CO2 and H2S) and the production of H2SO4 from H2S oxidation caused the widespread subaerial corrosion which significantly contributed to the morphogenesis. The comparison between these residual morphologies and the active processes shows that morphogenesis in the cave has evolved through time, influenced by hydrodynamic conditions, in turn depending on the general morphological and hydrogeological setting of the whole karst area.

Oceanic Redox State During the Early Cambrian: Insights From Mo‐S Isotopes and Geochemistry of Himalayan Shales

AbstractThe Precambrian‐Cambrian (Pc‐C) boundary marks significant biological, atmospheric, and oceanic changes. These changes include extinction of the Ediacaran fauna, initiation of complex lifeforms, and oxygenation of the atmosphere and oceans. In this contribution, elemental and Mo‐S isotopic compositions of organic‐rich shales overlying the Pc‐C boundary from the Tal Formation, Lesser Himalaya, have been investigated. These datasets are used to reconstruct past oceanic redox state and sulfate concentrations. The principal component analysis of the elemental dataset identifies six major factors, with factors associated with organic matter and sulfide phases accounting for about half of the total variance. Iron speciation and Mo/U data suggest that the shales were deposited in anoxic and ferruginous deep water conditions. The δ98Mo data (1.5 ± 0.2‰) and their mass balance calculations indicate that the areal extent of sulfidic waters and pyrite burial rates were about 2–4 times higher during the Pc‐C transition than in the modern ocean. The pyrite‐δ34S values (3.6–8.3‰) for the Tal shales are isotopically heavier compared to modern‐day sedimentary pyrites (∼−21‰). Calculations involving earlier‐reported δ34S values for early Cambrian seawater and our measured pyrite‐δ34S data estimate the seawater sulfate concentration (8 ± 3 mM) during their deposition. This sulfate value for the Tal basin is higher than that reported for the late Neoproterozoic ocean (<5 mM), attributable to increasing oxygen availability and continental supply during this time. The observed basinal conditions and high terrestrial input may have influenced metazoan diversification.

A new cave-dwelling hadzioid amphipod (Senticaudata, Hadzioidea, Melitidae) from sulfidic groundwaters in Iran

Abstract Cave systems fed with hydrogen sulfide-rich groundwater are unique chemoautotrophy-dependent ecosystems. Although globally widespread and known to harbor unique subterranean metazoan communities, they have mostly been studied in Europe and North America, less so in Asia. Here, we report on a discovery of a new species of amphipod crustacean from sulfidic waters of Tashan-Chah Kabootari aquifer from Zagros Mountains in Iran. The new species corresponds morphologically to the melitid genus Tegano Barnard & Karaman, 1982, and Tegano tashanensis sp. nov. is the first amphipod from the superfamily Hadzioidea found exclusively in sulfidic water. Phylogenies derived from the mitochondrial coi and the nuclear 28S rRNA sequences recover T. tashanensis sp. nov. in a clade that contains representatives of the currently para- or polyphyletic genera Barnardomelita, Brachina, Josephosella, and Tegano indicating the need for a revised melitid genus level systematics. This clade comprises marine, freshwater and subterranean species globally distributed in regions that were connected by the ancient Tethys Sea. As such, these taxa may be suitable biogeographic models for studying past dispersal, vicariance and multiple colonization of inland groundwaters.

Mercury concentrations in sediments and oysters in a temperate coastal zone: a comparison of farmed and wild varieties.

Oyster aquaculture has progressively increased to meet growing demands for seafood worldwide; however, its effects on methylmercury (MeHg) production in sediment and accumulation in oysters are largely unknown. In this study, total Hg (THg) and MeHg in sediments collected from aquaculture and reference sites and in farmed and wild oysters were measured and compared to explore potential factors that regulate MeHg production and bioaccumulation at the aquaculture sites. The results showed that the mean concentrations of THg and MeHg in varying sediment depths at the aquaculture site were 34 ± 4.1 ng g-1 and 16 ± 12 pg g-1, respectively. In comparison, the mean concentrations of THg and MeHg in sediments at the reference site were 25 ± 2.5 ng g-1 and 63 ± 28 pg g-1, respectively. While the MeHg/THg in the aquaculture sediments increased with organic carbon content, the slope of MeHg/THg versus organic carbon content was suppressed by high concentrations of dissolved sulfide in the pore water. Multiple parameters (total sulfur, total nitrogen and acid volatile sulfide in sediment, and dissolved sulfide in pore water) showed significant negative relationships with MeHg/THg in the sediment, and the total sulfur content in the sediment showed the highest inverse correlation factor with MeHg/THg (r = - 0.83). The mean concentrations of THg and MeHg in farmed oysters (mean weight 3.2 ± 1.5 g) were 36 ± 10 ng g-1 and 15 ± 6.7 ng g-1, respectively, while those in wild oysters (mean weight 0.92 ± 0.32 g) were 47 ± 9.9 ng g-1 and 15 ± 6.7 ng g-1, respectively. Concerning oysters of the same size range, THg and MeHg levels were higher in farmed oysters than in wild oysters despite the faster growth rate of farmed oysters, suggesting that the Hg content of food sources is more important than growth dilution rates in the control of Hg levels. The mean hazardous quotient for MeHg in farmed oyster was calculated as 0.044 ± 0.020, suggesting no expected health risk from farmed oyster consumption.

Evolution of iron and oxygen biogeochemical cycles during the Precambrian.

Iron (Fe) is an essential element for life, and its geochemical cycle is intimately linked to the coupled history of life and Earth's environment. The accumulated geologic records indicate that ferruginous waters existed in the Precambrian oceans not only before the first major rise of atmospheric O2 levels (Great Oxidation Event; GOE) during the Paleoproterozoic, but also during the rest of the Proterozoic. However, the interactive evolution of the biogeochemical cycles of O2 and Fe during the Archean-Proterozoic remains ambiguous. Here, we develop a biogeochemical model to investigate the coupled biogeochemical evolution of Fe-O2 -P-C cycles across the GOE. Our model demonstrates that the marine Fe cycle was less sensitive to changes in the production rate of O2 before the GOE (atmospheric pO2 < 10-6 PAL; present atmospheric level). When the P supply rate to the ocean exceeds a certain threshold, the GOE occurs and atmospheric pO2 rises to ~10-3 -10-1 PAL. After the GOE, the marine Fe(II) concentration is highly sensitive to atmospheric pO2 , suggesting that the marine redox landscape during the Proterozoic may have fluctuated between ferruginous conditions and anoxic non-ferruginous conditions with sulfidic water masses around continental margins. At a certain threshold value of atmospheric pO2 of ~0.3% PAL, the primary oxidation pathway of Fe(II) shifts from the activity of Fe(II)-utilizing anoxygenic photoautotrophs in sunlit surface waters to abiotic process in the deep ocean. This is accompanied by a shift in the primary deposition site of Fe(III) hydroxides from the surface ocean to the deep sea, providing a plausible mechanistic explanation for the observed cessation of iron formations during the Proterozoic.

Solubility modeling of hydrogen sulfide in aqueous sodium salt solutions

Accurate solubility prediction of hydrogen sulfide in aqueous electrolyte solutions is critical for gas exploitation and geological storage. However, there is a lack of electrolyte Equation of State model that can accurately calculate the solubilities of hydrogen sulfide in aqueous electrolyte solutions over wide ranges of temperature, pressure, and salt molality. This work presents a modeling study on the solubilities of hydrogen sulfide in pure water and several aqueous sodium salt solutions. The thermodynamic framework used in this work is an electrolyte version of Cubic-Plus-Association Equation of State. The model’s temperature-dependent ion-gas binary interaction parameters are obtained by regressing the experimental solubilities in the aqueous electrolyte solutions. The modeling results show that the electrolyte Cubic-Plus-Association Equation of State can satisfactorily correlate the solubilities of hydrogen sulfide in aqueous electrolyte solutions over wide ranges of temperature, pressure, and salt molality. For the typical water–sodium chloride–hydrogen sulfide system, the model can satisfactorily correlate the gas solubilities with the mean relative deviation being 6.2%, with the temperature up to 593.95 K, pressure up to 32.30 MPa, and salt molality up to 6.0 mol⋅kg−1 water. Moreover, the salting-out effects and model adaptability are analyzed and discussed.

Constraining the major pathways of vanadium incorporation into sediments underlying natural sulfidic waters

Vanadium (V) is a redox-sensitive trace metal. Interconversion between different vanadium species (e.g., VIII, VIV, VV) occurs rapidly in association with changes in redox conditions in natural environments. Different vanadium species exhibit variable geochemical behavior that impacts if and how they are sequestered into sediments, which makes vanadium a useful proxy for ancient ocean redox conditions. However, we still lack constraints on how different dissolved vanadium sink pathways impact distributions of vanadium in water column, pore waters, and sediments, especially in natural sulfidic settings. In the present study, we combined field and experimental data to constrain the major scavenging processes that influence the partitioning of vanadium between aqueous and solid phases to provide an improved picture of vanadium geochemical cycling under anoxic-sulfidic conditions. We find that in the sulfidic bottom waters and sediment pore waters of the Chesapeake Bay, vanadium concentrations are correlated with manganese (Mn) concentrations in both aqueous and solid phases. Our experimental results support our interpretation that elevated concentrations of vanadium in anoxic-sulfidic waters result from the release of vanadium due to desorption from and/or dissolution of Mn oxides in anoxic/sulfidic waters. While sorption of vanadium results in strongly adsorbed complexes on both Mn oxides and pyrite surfaces, vanadium preferentially sorbs to Mn oxides rather than to pyrite. Thus, the impact of Mn oxides on vanadium geochemistry is greater than that imposed by scavenging via sorption on pyrite, although both processes should be considered. Mn oxides also have a greater impact on vanadium geochemistry than reductive formation of solid V(OH)3 by H2S. Sorption of vanadium is sensitive to pH conditions (especially in anoxic waters), moderately sensitive to ionic strength, and weakly sensitive to phosphate concentrations. In addition, our results show that as waters become more sulfidic, dissolved V/Mn molar ratios increase, whereas solid phase V/Mn molar ratios decrease, indicating that the V/Mn molar ratio can be used to trace redox changes. Finally, we investigate the V/Mn record of black shales that span the Proterozoic and Phanerozoic to show a framework of utilizing this proxy with applicability to identify changes in redox conditions associated with both oxygenation and anoxic events in ancient oceans.

Geochemistry of Cryogenian Datangpo manganese deposits in the southeastern Yangtze Platform of South China: implications for the origin of metallogenesis and depositional environment

ABSTRACT Sedimentary manganese (Mn) deposits in the southeastern Yangtze Platform of China have been newly discovered with considerable potential for resource exploration. Such deposits formed due to dynamic changes in the global environment, including the break-up of the supercontinent Rodinia, Snowball Earth glaciation, and the Neoproterozoic Oxygenation Event. The Mn-bearing sequences are hosted in the basal Datangpo Formation and are interbedded with black carbonaceous shale in a series of graben sub-basins in the Nanhua Rift Basin. We investigated the origin of these Mn deposits by analysing the major and trace elements, total organic carbon, and stable carbon and oxygen isotopes. Positive Eu anomalies were observed, indicating that the Mn was derived from a hydrothermal system. Redox-related elements, including Ce, Mo, U, V, S, and P, indicated that the depositional environment of the Mn layers was oxidative and that Mn2+ was initially oxidized to Mn oxides. However, the host rock (i.e. black carbonaceous shale) was deposited under dysoxic – anoxic and even sulfidic water conditions. The alternating distribution of Mn ore and host rock suggested alternating redox conditions in the sub-basins. A negative correlation between the Mn content and δ 13Ccarb values (−10‰–−7‰) and a deficiency of sulphide minerals indicate that the diagenetic degradation of organic matter (δ 13Corg from − 34‰ to − 31.9‰) took place through Mn oxide reduction rather than microbial sulphate reduction and can contribute to a considerable source of bicarbonates. The approximately homogeneous δ 13Ccarb depletion and their apparent discrepancy with δ 13Corg indicate that the post-depositional genesis of the Mn carbonate ore occurred in a relatively open early diagenetic pore water system with a considerable contribution from seawater-derived carbon sources.

Synthesis, characterization and application of a highly dispersed and reactive hypervalent iodine(V)/polyvinylpyrrolidone dendrimer nanocomposite: Hetero- vs. homo-intermolecular secondary O---I bonds

Polyvinylpyrrolidone (PVP) assisted aerobic oxidation of bulk iodosylbenzene or hydrolysis/oxidation of iodobenzene diacetate under mild conditions leading to the formation of nanostructured iodylbenzene is reported. AFM and FESEM-EDX analyses confirmed the formation of dendrimer iodylbenzene-polyvinylpyrrolidone nanocomposite (PhIO2-PVP) through the two top-down approaches. The formation of PhIO2 was confirmed by 1H NMR spectroscopy. Strong interactions between iodylbenzene molecules and the polymer through secondary intermolecular O---I bonds was evident from the large difference between the morphology of PVP (cubic) and PhIO2-PVP (dendrimer) nanoparticles. FESEM images showed a maximum width and length of 70 and 1000 nm for the dendrimers, respectively. The dual role played by PVP, i.e., facilitating the oxidation of I(III) to I(V) and stabilization the hypervalent I(V) compound was attributed to the formation of strong secondary hetero-intermolecular O---I bonds, between the polymer and iodine centre. The very fine aqueous and dichloromethane suspensions of PhIO2-PVP were indistinguishable to the naked eye. Efficient direct oxidation of cyclohexene and methylene blue with PhIO2-PVP at room temperature and a short reaction time provided evidence of significantly increased reactivity of PhIO2-PVP compared to that of the bulk oxidant. PhIO2-PVP was also used in the oxidation of methyl phenyl sulfide and styrene in water and dichloroethane, using water soluble and insoluble metalloporphyrins, respectively. The former led to the formation of the corresponding sulfoxide as the sole product in the two solvents. In addition to styrene oxide formed in both solvents, benzaldehyde was also formed with a selectivity of 24% in water. Almost complete oxidation of the organic substrates was observed in dichloroethane. The results of this study show that the nanostructured iodine(V) compound can be used as an efficient terminal oxidant in biomimetic oxidations.

Nozzle Electrode Point Discharge-Enhanced Oxidation and Portable Gas Phase Molecular Fluorescence Spectrometry for Sensitive Field Detection of Sulfide

It is still a challenge to accurately determine dissolved sulfide due to its susceptibility to contamination and loss during transportation, storage, and analysis in the laboratory, thus highlighting the necessity for its sensitive field analysis. Herein, a robust nozzle electrode point discharge (NEPD) enhanced oxidation coupling with chemical vapor generation (CVG) is described for the highly efficient and flameless conversion of sulfide (S2-) to SO2. Subsequently, a portable and low-power consumption gas phase molecular fluorescence spectrometry (GP-MFS) was constructed for the highly selective and sensitive determination of the generated SO2 via detecting its molecular fluorescence excited by a zinc hollow cathode lamp. Under optimal conditions, a limit of detection (LOD) of 0.1 μM was obtained for dissolved sulfide with a relative standard deviation (RSD, n = 11) of 2.6%. The accuracy and practicability of the proposed method were validated by the analyses of two certified reference materials (CRMs) and several river and lake water samples with satisfactory recoveries of 99%-107%. This work confirms that NEPD enhanced oxidation is a low energy consumption yet highly efficient method for the flameless oxidation of hydrogen sulfide and thus is suitable for the easy field detection of dissolved sulfide in environmental water by CVG-GP-MFS.

Isotopic constraints on the sulfur cycle of the Bottom Convective Layer in the Black Sea

The Black Sea is the largest euxinic seawater basin with H2S at depths of below 90 m. Previously found that the presence of H2S in water was caused by microbial sulfate reduction. Herein, we report the sulfur isotopic composition of sulfate and sulfide in seawater at stations in the central part of the Black Sea, especially from the Bottom Convective Layer (BCL) located below a water depth of 1750 m. Our study shows that the sulfur isotopic composition of sulfate (δ34S(SO4)) in the surface layer of the oxic zone is +21.1‰ ± 0.1‰ relative to the Vienna Canyon Diablo troilite (VCDT), and does not differ from sulfate in the Mediterranean Sea. In the BCL, the average δ34S(SO4) value is +23.0‰ ± 0.2‰, which does not change vertically or laterally owing to effective convective mixing. The sulfur isotopic composition of H2S varies from −40.0‰ to −41.9‰ between 200 m water depth down to the seafloor with an average δ34S(H2S) value of −40.6‰ ± 0.4‰ for the BCL.Based on the water mass balance and sulfur isotopic composition of sulfate in the relevant water masses affecting the BCL, we have formulated a model to calculate the sulfate reduction rate in the BCL. After evaluating the sulfate and sulfide sources in the BCL, we assumed that the only apparent sulfide source is a bacterial sulfate reduction in the water column, and the main sulfate source is a mixture of water from the Black Sea and the lower Bosporus current with an initial sulfate isotopic composition of +21‰. The weak water exchange in the BCL leads to the largest observed isotopic difference ΔSR = δ34S(SO4) − δ34S(H2S) of 63.6‰ between sulfate and sulfide in the sulfidic water column of the Black Sea. To achieve a steady state with respect to the sulfate isotopic composition +23‰ in the BCL, an average sulfate reduction (SR) rate of 1.1 ± 0.1 nmol L−1 day−1 is required. A steady state relative to sulfur isotopic composition of sulfate in the BCL water was established 4200 years ago. The estimated residence time of H2S was 1.5 times shorter (946 years) than that of sulfate (1390 years). The latter is close to the water renewal time of the BCL (1432 years). Different residence times of sulfide and sulfate in the BCL are explained using their different fluxes from the BCL. Sulfate is mainly removed from the BCL via vertical advection, while a considerable part of the sulfide generated in the BCL (1/3 of total annual production) is probably spent on the sulfidation (FeS → FeS2) of muddy turbidites. The estimated annual H2S production in the BCL is 0.78 ± 0.07 Tg. The developed model predicts that the sulfide concentration in the BCL remains practically unchanged (380 ± 5 μM) over the last 1800 years (after 5700 years from the onset of anoxia).

Plasma jet decontamination of sulfur mustard and its analogues in water by oxidation effect

Atmospheric pressure plasma jet (APPJ), as an emerging clean and efficient technology, has been found a great potential for chemical warfare agents (CWAs) decontamination. In this study, we first proposed APPJ for the degradation of sulfur mustard (HD) and its surrogate 2-chloroethyl ethyl sulfide (2-CEES) in water. Under optimal conditions, the degradation efficiency of 2-CEES and HD reached 100 % after 5 min or 6 min plasma treatment. The degradation products of 2-CEES and HD were mainly non-toxic alcohols or low toxic sulfones, which can be degraded and converted into some small molecules (HCl, SO2, or CO2) under further plasma treatment. We then identified two dominant short-lived reactive species (·OH and 1O2) and long-lived reactive molecule (H2O2) and distinguished the effect of these three active particles during the degradation process of 2-CEES in water. This work provides detailed evidence of a novel decontamination strategy for HD and 2-CEES.

Chitosan-thymolsulfonephthalein-cobalt nanocomposites for colorimetric detection of sulfide anions in aqueous solution

BackgroundWater pollution by sulfide ions, arising from the exploration and exploitation of sulfide mineral ore, can cause many chronic and acute health challenges. However, owing to the cost of sophisticated equipment and technical expertise required to detect anionic sulfides in water has inspired the preparation of easy-to-use naked-eye colorimetric devices. MethodsIn this study, the functionalization of chitosan solution with thymolsulfonephthalein solution (CFTS) at moderate conditions was utilized for the chemical synthesis of cobalt nanocomposites (CFTS-CoNCs) based chemosensors. ResultsThe prepared material's scanning electron micrograph shows the high Co dispersion on the surface of CFTS with a thorn-shaped morphology in uniform spheres. In contrast, the transmission electron micrograph shows good dispersibility of the tiny rod-like particles distributed on a dendrite-like surface. The interaction of the orange-colored CFTS-CoNCs chemosensor solution with the colorless S2− ions was accompanied by an instant and stable black color change. Furthermore, the selective and sensitive chemosensor could detect ≥ 15 ppm aqueous S2− ions solution at lower pH. The mechanism of detection could be due to a nucleophilic attack of S2− on the cobalt-induced hydroxylmethylpropyl benzoxathiole amine cation giving rise to the strong UV–Vis absorption at 592 nm. ConclusionThe highly selective and sensitive CFTS-CoNCs chemosensor can be applied for real-time and quick on-site analysis. In addition, the colorimetric device will serve as a lifesaver in terms of reducing both time and cost, user-friendly, and hands-on tools for the rapid/accurate detection of sulfide ions in water.

Dynamic oceanic redox conditions across the late Cambrian SPICE event constrained by molybdenum and uranium isotopes

The Steptoean Positive Carbon Isotope Excursion Event (SPICE) represents one of the largest carbon cycle perturbations in the Cambrian, which coincided with climatic changes and dramatic extinction of shallow-shelf faunas. This carbon perturbation has been linked to a global expansion of marine euxinia (SPICE-OAE), but the precise timing, duration and extent of changing redox conditions across the SPICE event, as well as its influences on the coeval biotic evolution, remain unclear. Here, we report paired δ98Mo–δ238U data across this event, constrained by a radioisotopically anchored astrochronology, based on Alum Shale samples from the Albjära-1 and Billegrav-2 drill-cores in Scandinavia. The δ98Mo profiles are largely invariant around 1.08±0.21‰ with short-term fluctuations parallelling changes in pyritization of iron, possibly as a result of locally varying [H2S]aq in the water column and/or fluctuating reactive iron delivery. The bottom water is interpreted to have been primarily anoxic, but with frequent local variations between oxic and sulfidic conditions in a moderately restricted basin. A novel analytic method based on variation of Mo concentrations at millimeter scale stratigraphic resolution was applied to distinguish between local and global redox signatures, revealing that cyclic redox changes are recorded in the Alum Shale sea with periods of ∼0.3 Myr, ∼0.9 Myr and ∼0.15 Myr before, during and after the SPICE-OAE, respectively. Stratigraphic profiles of Mo, U, Mo/TOC ratios and δ238U in the two cores show comparable trends, facilitating recognition of three chemically distinct stages across the SPICE event: 1) global expansion of marine euxinia (SPICE-OAE; 497.9–496.6 Ma), 2) global contraction of euxinia accompanied by enhanced carbonate weathering inputs (496.6–495.8 Ma) and 3) general global oxygenation (495.8–494.4 Ma). The first in situ correlation between the onset of the SPICE-OAE and the end-Miaolingian extinctions in Baltica corroborates that expansive anoxic and sulfidic water masses likely contributed to the biotic crisis. The time gap between the start of the extinction and the appearance of the new fauna in Baltoscandia is estimated to be ∼600 kyr.

A portable electrochemical microsensor for in-site measurement of dissolved oxygen and hydrogen sulfide in natural water

Dissolved oxygen (O2) and hydrogen sulfide (H2S) are two important indicators of water quality, their levels are of intimate dependence and varying over time. It is of great significance to monitoring of dissolved O2 and H2S simultaneously in natural water, yet has not been reported because of lack of effective approaches. In this work, a portable electrochemical microsensor was developed for simultaneously quantifying dissolved O2 and H2S. Here, Pd@Ni nanoparticles (NPs) were self-assembled onto the microelectrode by MXene titanium carbide (Ti3C2Tx), which were of responsibility towards O2 and H2S detection within single electrochemical reduction process. On this regard, Pd NPs facilitated catalyzing the electrochemical reduction of O2, while Ni NPs were employed as recognition element for H2S detection. With the electrochemical reduction sweep, the initial application of a positive voltage rendered the Ni to be oxidized to be Ni ions, contributing to their following capture of surrounding S2− to form nickel sulfide. Nickel sulfide with highly electrochemical activity were capable of generating detecting reduction current. In consequence, the as-designed microsensor can simultaneously determine O2 concentrations ranging from 36 to 318 μM and H2S levels ranging from 0.1 to 2.5 μM with high selectivity. Finally, the portable microsensor was successfully applied to simultaneous detection dissolved O2 and H2S in natural water in-site, the results of which were comparable to the classical methods.

Digging Deeper: Bioturbation increases the preserved sulfur isotope fractionation

Bioturbation enhances mixing between the seafloor and overlying ocean due to changes the redox state of the sediment and influences the biogeochemical cycling of redox-sensitive elements such as sulfur. Before the widespread appearance of burrowing fauna over the Proterozoic-Phanerozoic transition, marine sediments were largely undisturbed and transport of material across the sediment-water interface was diffusion-dominated. Through both a microcosm experiment and numerical model, we show that the effect of bioturbation on marine sediments is to enhance the drawdown of sulfate from the water column into the sediment and thus “open-up” the sedimentary system. The key finding is that bioturbation increases the difference between the isotopic signature of seawater sulfate and pore water sulfide, the latter of which is preserved in sedimentary sulfide minerals. Our study empirically demonstrates a long-held assumption and helps identify the isotopic impact of bioturbation in the geological record and its environmental effects in modern marine systems.

On-site and high-resolution spectrophotometric measurement of total dissolved sulfide in natural waters

Reliable high-resolution data is essential for understanding the aquatic sulfur biogeochemical processes. However, the accurate quantification of total dissolved sulfide (TDS) remains challenging due to its low concentration and vulnerability to oxidation. Furthermore, the frequency and the spatial coverage of TDS measurements are constrained by the cost of the laboratory analysis. In this study, an automated portable system was developed for on-site real-time measurement of trace TDS in natural waters. This system was based on the classic methylene blue (MB) spectrophotometric assay combined with on-line solid phase extraction (SPE) and flow injection analysis (FIA). A commercially available weak-cation-exchange cartridge was used as the SPE sorbent. Experimental parameters affecting the performance of the proposed system were optimized. Under the optimized conditions, linear calibration range of 0.02–2.50 μmol L−1 was obtained with a sample loading volume of 5.0 mL and a sample throughput of 12 h−1. The limit of detection could be lowered to 0.003 μmol L−1 by pre-concentrating 10.0 mL sample. The precision, determined as the relative standard deviation (RSD), was <2.75 % (n = 11) and the recoveries from spiked samples ranged from 54.4 % to 97.5 % with RSDs of 1.1–2.3 % (n = 3). Furthermore, the FIA-SPE-MB system was successfully deployed in the Taihu Lake for continuous 48 h monitoring of variations in TDS, demonstrating the applicability of this system for on-site TDS measurement in natural waters.