Improved cyanolysis protocol for detection of zero-valent sulfur in natural aquatic systems

We propose a novel protocol for detection of reactive zero‐valent sulfur (ZVS) in natural aquatic samples including seawater. Reaction with hot potassium cyanide at slightly acidic conditions recovers ZVS from colloidal fraction of particulate elemental sulfur, polysulfides (Sn2−), and their protonated forms. Preconcentration by partial evaporation of the sample and separation of thiocyanate anions by high‐performance liquid chromatography on the C30 reverse phase column modified with poly(ethylene glycol) followed by spectrophotometric detection at 220 nm wavelength allows us to detect reactive ZVS with detection limit of 3 nmol L−1 for fresh water samples and 6 nmol L−1 for seawater samples. Storage at 4°C for 6 weeks does not change the concentration of thiocyanate in the sample by more than 10%

Quantification of free and metal-complexed cyanide by tetrathionate derivatization

A sensitive and robust method for detection of free and metal-complexed cyanide in solutions is described. The method does not require a distillation step and is applicable for both low ionic strength and sea-water samples. The method is based on the reaction of cyanide with potassium tetrathionate followed by high-performance liquid chromatography (HPLC) separation and UV detection of formed thiocyanate. The detection limit of the method is 250 nmol L−1 cyanide (6.5 µg L−1 CN−) without a pre-concentration step. Storage for three days does not significantly change the results. The sum of free and weak metal-complexed cyanide can be measured by tetrathionate derivatization at a pH of 10. The sum of free, weak metal-complexed cyanide, iron(II) and iron(III)-complexed cyanides may be measured by tetrathionate derivatization at pH 4.4. Derivatization requires heating to 90°C for 20 min at pH = 10 and for 12 h at pH = 4.4. Weighted mean recoveries for free, iron(II), iron(III), nickel(II), silver(I), Cd(II) and Zn(II) complexed cyanide were in the range of 87 to 112% and weighted standard deviations were in the range of 1.7 to 10.0%. The method is not applicable for cyanide complexes of gold and cobalt. We illustrate an application of cyanide quantification using pore-waters from the Delaware Great Marsh

Multiple sulfur isotopes fractionations associated with abiotic sulfur transformations in Yellowstone National Park geothermal springs

Background: The paper presents a quantification of main (hydrogen sulfide and sulfate), as well as of intermediate sulfur species (zero-valent sulfur (ZVS), thiosulfate, sulfite, thiocyanate) in the Yellowstone National Park (YNP) hydrothermal springs and pools. We combined these measurements with the measurements of quadruple sulfur isotope composition of sulfate, hydrogen sulfide and zero-valent sulfur. The main goal of this research is to understand multiple sulfur isotope fractionation in the system, which is dominated by complex, mostly abiotic, sulfur cycling. Results: Water samples from six springs and pools in the Yellowstone National Park were characterized by pH, chloride to sulfate ratios, sulfide and intermediate sulfur species concentrations. Concentrations of sulfate in pools indicate either oxidation of sulfide by mixing of deep parent water with shallow oxic water, or surface oxidation of sulfide with atmospheric oxygen. Thiosulfate concentrations are low (<6 mu mol L-1) in the pools with low pH due to fast disproportionation of thiosulfate. In the pools with higher pH, the concentration of thiosulfate varies, depending on different geochemical pathways of thiosulfate formation. The delta S-34 values of sulfate in four systems were close to those calculated using a mixing line of the model based on dilution and boiling of a deep hot parent water body. In two pools delta S-34 values of sulfate varied significantly from the values calculated from this model. Sulfur isotope fractionation between ZVS and hydrogen sulfide was close to zero at pH < 4. At higher pH zero-valent sulfur is slightly heavier than hydrogen sulfide due to equilibration in the rhombic sulfur-polysulfide - hydrogen sulfide system. Triple sulfur isotope (S-32, S-33, S-34) fractionation patterns in waters of hydrothermal pools are more consistent with redox processes involving intermediate sulfur species than with bacterial sulfate reduction. Small but resolved differences in Delta S-33 among species and between pools are observed. Conclusions: The variation of sulfate isotopic composition, the origin of differences in isotopic composition of sulfide and zero-valent sulfur, as well as differences in Delta S-33 of sulfide and sulfate are likely due to a complex network of abiotic redox reactions, including disproportionation pathways

Hydrogen Cyanide Accumulation and Transformations in Non-polluted Salt Marsh Sediments

While cyanide is known to be produced by many organisms, including plants, bacteria, algae, fungi and some animals, it is generally thought that high levels of cyanide in aquatic systems require anthropogenic sources. Here, we report accumulation of relatively high levels of cyanide in non-polluted salt marsh sediments (up to 230 μmol kg[superscript −1]). Concentrations of free cyanide up to 1.92 μmol L[superscript −1], which are toxic to aquatic life, were detected in the pore-waters. Concentration of total (free and complexed) cyanide in the pore-waters was up to 6.94 μmol L[superscript −1]. Free cyanide, which is released to the marsh sediments, is attributed to processes associated with decomposition of cord grass, Spartina alterniflora, roots and possibly from other sources. This cyanide is rapidly complexed with iron and adsorbed on sedimentary organic matter. The ultimate cyanide sink is, however, associated with formation of thiocyanate by reaction with products of sulfide oxidation by Fe(III) minerals, especially polysulfides. The formation of thiocyanate by this pathway detoxifies two poisonous compounds, polysulfides and hydrogen cyanide, preventing release of free hydrogen cyanide from salt marsh sediments into overlying water or air

Annual sulfur cycle in a warm monomictic lake with sub-millimolar sulfate concentrations.

We studied the annual variability of the concentration and isotopic composition of main sulfur species and sulfide oxidation intermediates in the water column of monomictic fresh-water Lake Kinneret. Sulfate concentrations in the lake are <1 mM and similar to concentrations that are proposed to have existed in the Paleoproterozoic ocean. The main goal of this research was to explore biogeochemical constrains of sulfur cycling in the modern low-sulfate fresh-water lake and to identify which processes may be responsible for the isotopic composition of sulfur species in the Precambrian sedimentary rocks. RESULTS: At the deepest point of the lake, the sulfate inventory decreases by more than 20% between March and December due to microbial sulfate reduction leading to the buildup of hydrogen sulfide. During the initial stages of stratification, sulfur isotope fractionation between sulfate and hydrogen sulfide is low (11.6 ‰) and sulfur oxyanions (e.g. thiosulfate and sulfite) are the main products of the incomplete oxidation of hydrogen sulfide. During the stratification and at the beginning of the lake mixing (July-December), the inventory of hydrogen sulfide as well as of sulfide oxidation intermediates in the water column increases and is accompanied by an increase in sulfur isotope fractionation to 30 ± 4 ‰ in October. During the period of erosion of the chemocline, zero-valent sulfur prevails over sulfur oxyanions. In the terminal period of the mixing of the water column (January), the concentration of hydrogen sulfide decreases, the inventory of sulfide oxidation intermediates increases, and sulfur isotope fractionation decreases to 20 ± 2 ‰. CONCLUSIONS: Sulfide oxidation intermediates are present in the water column of Lake Kinneret at all stages of stratification with significant increase during the mixing of the water column. Hydrogen sulfide inventory in the water column increases from March to December, and sharply decreases during the lake mixis in January. Sulfur isotope fractionation between sulfate and hydrogen sulfide as well as concentrations of sulfide oxidation intermediates can be explained either by microbial sulfate reduction alone or by microbial sulfate reduction combined with microbial disproportionation of sulfide oxidation intermediates. Our study of sulfur cycle in Lake Kinneret may be useful for understanding the range of biogeochemical processes in low sulfate oceans over Earth history

The bacterial sulfur cycle in expanding dysoxic and euxinic marine waters

Dysoxic marine waters (DMW, <1 M oxygen) are currently expanding in volume in the oceans, which has biogeochemical, ecological, and societal consequences on a global scale. In these environments, distinct bacteria drive an active sulfur cycle, which has only recently been recognized for openocean DMW. This review summarizes the current knowledge on these sulfurcycling bacteria. Critical bottlenecks and questions for future research are specifically addressed. Sulfatereducing bacteria (SRB) are core members of DMW. However, their roles are not entirely clear, and they remain largely uncultured. We found support for their remarkable diversity and taxonomic novelty by mining metagenomeassembled genomes from the Black Sea as model ecosystem. We highlight recent insights into the metabolism of key sulfuroxidizing SUP05 and Sulfurimonas bacteria, and discuss the probable involvement of uncultivated SAR324 and BSGSO2 bacteria in sulfur oxidation. Uncultivated Marinimicrobia bacteria with a presumed organoheterotrophic metabolism are abundant in DMW. Like SRB, they may use specific molybdoenzymes to conserve energy from the oxidation, reduction or disproportionation of sulfur cycle intermediates such as S0 and thiosulfate, produced from the oxidation of sulfide. However, this complex network of reactions is yet to be constrained quantitatively. This article is protected by copyright. All rights reserved.SIAM Gravitation grant 024.002.002 to AJMS and JSSD of the Netherlands Ministry of Education, Culture and Science and the Netherlands Organisation for Scientific Research (NWO). BED and FABvM were supported by the NWO Vidi grant 864.14.004. BED was supported by the European Research Council (ERC) Consolidator grant 865694: DiversiPHIinfo:eu-repo/semantics/publishedVersio

Optimisation of substrate angles for multi-material and multi-functional inkjet printing

Three dimensional inkjet printing of multiple materials for electronics applications are challenging due to the limited material availability, inconsistencies in layer thickness between dissimilar materials and the need to expose the printed tracks of metal nanoparticles to temperature above 100 °C for sintering. It is envisaged that instead of printing a dielectric and a conductive material on the same plane, by printing conductive tracks on an angled dielectric surface, the required number of silver layers and consequently, the exposure of the polymer to high temperature and the build time of the component can be significantly reduced. Conductive tracks printed with a fixed print height (FH) showed significantly better resolution for all angles than the fixed slope (FS) sample where the print height varied to maintain the slope length. The electrical resistance of the tracks remained under 10Ω up to 60° for FH; whereas for the FS samples, the resistance remained under 10Ω for samples up to 45°. Thus by fixing the print height to 4 mm, precise tracks with low resistance can be printed at substrate angles up to 60°. By adopting this approach, the build height “Z” can be quickly attained with less exposure of the polymer to high temperature

A novel enzymatically-mediated drug delivery carrier for bone tissue engineering applications: combining biodegradable starch-based microparticles and differentiation agents

In many biomedical applications, the performance of biomaterials depends largely on their degradation behavior. For instance, in drug delivery applications, the polymeric carrier should degrade under physiological conditions slowly releasing the encapsulated drug. The aim of this work was, therefore, to develop an enzymaticmediated degradation carrier system for the delivery of differentiation agents to be used in bone tissue engineering applications. For that, a polymeric blend of starch with polycaprolactone (SPCL) was used to produce a microparticle carrier for the controlled release of dexamethasone (DEX). In order to investigate the effect of enzymes on the degradation behavior of the developed system and release profile of the encapsulated osteogenic agent (DEX), the microparticles were incubated in phosphate buffer solution in the presence of a-amylase and/or lipase enzymes (at physiological concentrations), at 37 C for different periods of time. The degradation was followed by gravimetric measurements, scanning electron microscopy (SEM) and Fourier transformed infrared (FTIR) spectroscopy and the release of DEX was monitored by high performance liquid chromatography (HPLC). The developed microparticles were shown to be susceptible to enzymatic degradation, as observed by an increase in weight loss and porosity with degradation time when compared with control samples (incubation in buffer only). For longer degradation times, the diameter of the microparticles decreased significantly and a highly porous matrix was obtained. The in vitro release studies showed a sustained release pattern with 48% of the encapsulated drug being released for a period of 30 days. As the degradation proceeds, it is expected that the remaining encapsulated drug will be completely released as a consequence of an increasingly permeable matrix and faster diffusion of the drug. Cytocompatibility results indicated the possibility of the developed microparticles to be used as biomaterial due to their reduced cytotoxic effects

Impacts of chemical gradients on microbial community structure

Succession of redox processes is sometimes assumed to define a basic microbial community structure for ecosystems with oxygen gradients. In this paradigm, aerobic respiration, denitrification, fermentation and sulfate reduction proceed in a thermodynamically determined order, known as the ‘redox tower’. Here, we investigated whether redox sorting of microbial processes explains microbial community structure at low-oxygen concentrations. We subjected a diverse microbial community sampled from a coastal marine sediment to 100 days of tidal cycling in a laboratory chemostat. Oxygen gradients (both in space and time) led to the assembly of a microbial community dominated by populations that each performed aerobic and anaerobic metabolism in parallel. This was shown by metagenomics, transcriptomics, proteomics and stable isotope incubations. Effective oxygen consumption combined with the formation of microaggregates sustained the activity of oxygen-sensitive anaerobic enzymes, leading to braiding of unsorted redox processes, within and between populations. Analyses of available metagenomic data sets indicated that the same ecological strategies might also be successful in some natural ecosystems