Sulfidic Sediments Research Articles

Mobilization of phosphorus in sediments of eutrophic lakes induced by elevated sulfate levels

Elevated sulfate levels in eutrophic lakes have been observed to induce the release of endogenous phosphorus. While previous studies have predominantly examined its impact on iron-bound phosphorus (FeP), the influence on organic phosphorus (OP), a crucial active phosphorus component in sediments, remains poorly understood. In this study, mesocosms were established with lactate supplementation and varying sulfate concentrations to explore sulfate reduction and its impacts on phosphorus mobilization in freshwater sediments. Lactate addition induced hypoxia and provided substrates, thereby stimulating sulfate reduction with a decline of sulfate levels, an increase of sulfide concentrations, and fluctuations of sulfate-reducing bacteria. Meanwhile, concentrations of total dissolved phosphorus and phosphate were dramatically promoted during lactate decomposition, with a higher sulfate concentration associated with greater phosphorus elevation, correlating with the decrease of total phosphorus in sediment. The increase in phosphorus of the overlying water was partly attributed to FeP release from the sediment, confirmed by a decrease in its sediment content. FeP release was ascribed to dissimilatory reduction of iron oxides or chemical reduction mediated by sulfides in anoxic sediments, leading to the desorption and subsequent release of phosphorus. Evidences included the proliferation of iron-reducing bacteria, a decrease in Fe(II) concentrations in sediment pore- water, and the continuous accumulation of solid iron sulfides in surface sediments. Furthermore, OP mineralization in sediment also contributed to the increase in phosphorus in water columns, confirmed by a reduction in its content and the abundance of fermentation bacteria in surface sediment. Notably, the decrease in OP content accounted for >80 % of the total phosphorus reduction in surface sediment in the end. Thus, sulfur cycling plays a critical role in iron and phosphorus cycling, significantly stimulating not only the mobilization of FeP but also OP in sediments, with OP mineralization potentially being the primary contributor to endogenous phosphorus release.

Seasonal Sulfur Redox Cycling in Two Constructed Wetlands with Insight on How They Age.

Long-term metal remediation in wetland treatment systems (WTSs) involves facilitating dissimilatory sulfate reduction to produce sulfide and mineralize metals in deep sediments. We evaluated seasonal sulfur cycling in two constructed wetlands (Maintained WTS constructed in 2007, and the Unmaintained WTS constructed in 2000) on the Savannah River Site in Aiken, South Carolina, USA. Significant interactions in sulfide concentration were observed between sediment depth, season, and wetland (F = 4.64, df = 11, P = 3.28 × 10 - 5). In the Maintained WTS, dissimilatory sulfate reduction dominated the surface sediments during the warm season (0-2cm depth, t=-2.66, P = 9.70 × 10 - 3), unlike the Unmaintained system. Sulfate concentrations in pore waters increased in the warm season (F = 7.84, df = 1, P = 6.50 × 10 - 3), contrary to expectations. Sulfur limitation in the Unmaintained WTS during the warm season correlated with increased sulfur assimilation in giant bulrush. Lower sulfide concentrations in surface sediments of the Unmaintained WTS illustrated aging effects. The Maintained WTS shows potential for managing erosion, pH reduction, and sulfur limitation observed in the older Unmaintained WTS.

Long-distance electron transport in multicellular freshwater cable bacteria.

Filamentous multicellular cable bacteria perform centimeter-scale electron transport in a process that couples oxidation of an electron donor (sulfide) in deeper sediment to the reduction of an electron acceptor (oxygen or nitrate) near the surface. While this electric metabolism is prevalent in both marine and freshwater sediments, detailed electronic measurements of the conductivity previously focused on the marine cable bacteria (Candidatus Electrothrix), rather than freshwater cable bacteria, which form a separate genus (Candidatus Electronema) and contribute essential geochemical roles in freshwater sediments. Here, we characterize the electron transport characteristics of Ca. Electronema cable bacteria from Southern California freshwater sediments. Current-voltage measurements of intact cable filaments bridging interdigitated electrodes confirmed their persistent conductivity under a controlled atmosphere and the variable sensitivity of this conduction to air exposure. Electrostatic and conductive atomic force microscopies mapped out the characteristics of the cell envelope's nanofiber network, implicating it as the conductive pathway in a manner consistent with previous findings in marine cable bacteria. Four-probe measurements of microelectrodes addressing intact cables demonstrated nanoampere currents up to 200 μm lengths at modest driving voltages, allowing us to quantify the nanofiber conductivity at 0.1 S/cm for freshwater cable bacteria filaments under our measurement conditions. Such a high conductivity can support the remarkable sulfide-to-oxygen electrical currents mediated by cable bacteria in sediments. These measurements expand the knowledgebase of long-distance electron transport to the freshwater niche while shedding light on the underlying conductive network of cable bacteria.

Characteristics of pipestems from acid sulfate soils of Finland and Australia

AbstractThis study describes iron (Fe) pipestems formed around and within root channels during the development of a homogeneous unripe sulfidic sediment into a ripe soil where redox‐ or pH‐active elements segregate. Pipestems and adjacent soil material samples were characterised by chemical and mineralogical analyses and scanning electron microscopy (SEM) associated with energy dispersive spectroscopy (EDS). Pipestems occurred at 60–190 cm and at 30–130 cm in a young Finnish soil and a more mature Australian soil, respectively, while sulfidic materials were found below 170–180 cm. The pipestems consisted of mineral grains cemented together by Fe precipitate. There was an up to 24‐fold enrichment of Fe and an up to 13‐fold enrichment of sulfur (S) in the Finnish pipestems compared to the adjacent soil material, whereas the corresponding enrichment in the Australian soil was up to 27‐fold for Fe and up to 8‐fold for S. In the Australian pipestem matrices, the Fe concentration was as high as 40% compared to 14% in the Finnish ones. It was estimated that about 70 ton ha−1 S had been mobilised from the sulfidic material in the Finnish soil at the depth of 50–150 cm. Part of S has leached out but a substantial amount remained in the soil constituting the stock of retained acidity. Almost all pipestems contained a new solid phase precipitated within the former cortex cells of the plant roots. In the Finnish samples, this precipitate consisted of jarosite and schwertmannite. After oxidative exhaustion of sulfidic material in the surrounding soil, these metastable minerals are gradually hydrolysed, associated with leaching of S. In the mature Australian soil, most of these minerals had already been transformed to goethite. Pipestems formed after roots in unripe soil are sites for synthesis and hydrolysis of minerals and serve as routes for atmospheric oxygen into the reduced subsoil and for soluble reaction products to exit the soil. Pipestems have an important role in the ripening of the soil profile.

Characterizing the Stoichiometry of Individual Metal Sulfide and Phosphate Colloids in Soils, Sediments, and Industrial Processes by Inductively Coupled Plasma Time-of-Flight Mass Spectrometry.

Size and purity of metal phosphate and metal sulfide colloids can control the solubility, persistence, and bioavailability of metals in environmental systems. Despite their importance, methods for detecting and characterizing the diversity in the elemental composition of these colloids in complex matrices are missing. Here, we develop a single-particle inductively coupled plasma time-of-flight mass spectrometry (sp-icpTOF-MS) approach to characterize the elemental compositions of individual metal phosphate and sulfide colloids extracted from complex matrices. The stoichiometry was accurately determined for particles of known composition with an equivalent spherical diameter of ≥∼200 nm. Assisted by machine learning (ML), the new method could distinguish particles of the copper sulfides covellite (CuS), chalcocite (Cu2S), and chalcopyrite particles (CuFeS2) with 75% (for Cu2S) to 99% (for CuFeS2) accuracy. Application of the sp-icpTOF-MS method to particles recovered from natural samples revealed that iron sulfide (FeS) particles in lake sediment contained ∼4% copper and zinc impurities, whereas pure pyrite (FeS2) was identified in hydraulic fracturing wastewater and confirmed by selected area electron diffraction. Colloidal mercury in an offshore marine sediment was present as pure mercury sulfide (HgS), whereas geogenic HgS recovered from an industrial process contained ∼0.08 wt % silver per Hg, enabling source apportionment of these colloids using ML. X-ray absorption spectroscopy confirmed that Hg was predominantly present as metacinnabar (β-HgS) in the industrial process sample. The determination of impurities in individual colloids, such as zinc and copper in FeS, and silver in HgS may enable improved assessment of their origin, reactivity, and bioavailability potential.

Extreme iron cycling in a coastal lake-lagoon system driven by interactions between climate and entrance management

Intermittently closed and open coastal lakes and lagoons (ICOLLs) are ecologically important and hydrologically sensitive estuarine systems. We explore how extreme drought and ICOLL entrance management intersect to influence the geochemical cycling of iron. Opening the ICOLL entrance just prior to an extreme drought in 2019 led to prolonged extremely low water levels, thereby exposing intertidal/subtidal sulfidic sediments and causing oxidation of sedimentary pyrite. Subsequent reflooding of exposed sediments for ∼4 months led to extremely elevated Fe2+(aq) (>10 mM) in intertidal hyporheic porewaters, consistent with Fe2+(aq) release via pyrite oxidation and via reductive dissolution of newly-formed Fe(III) phases. Re-opening the ICOLL entrance caused a rapid fall in water levels (∼1.5 m over 7 d), driving the development of effluent groundwater gradients in the intertidal zone, thereby transporting Fe2+-rich porewater into surface sediments and surface waters. This was accompanied by co-mobilisation of some trace metals and nutrients. On contact with oxic, circumneutral-pH estuarine water, the abundant Fe2+(aq) oxidised, forming a spatially extensive accumulation of poorly crystalline Fe(III) oxyhydroxide floc (up to 25 % Fe dry weight) in shallow intertidal zone benthic sediments throughout the ICOLL. Modelling estimates ∼4050 × 103 kg of poorly-crystalline Fe was translocated into surficial sediments. The newly formed Fe(III)-oxyhydroxides serve as a metastable sink encouraging enrichment of both phosphate and various trace metal(loid)s in near-surface sediments, which may have consequences for future cycling of nutrients, metals and ICOLL ecological function. The additional Fe also may enhance ICOLL sensitivity to similar future drought events by encouraging pyrite formation in shallow (<5 cm) benthic sediments. This system-wide translocation of Fe from deeper sediments into surficial benthic sediments represents a form of geochemical hysteresis with an uncertain recovery trajectory. This study demonstrates how climate extremes can interact with anthropogenic management to amplify ICOLL hydrological oscillations and influence biogeochemistry in complex ways.

Storage and Distribution of Organic Carbon and Nutrients in Acidic Soils Developed on Sulfidic Sediments: The Roles of Reactive Iron and Macropores.

In a boreal acidic sulfate-rich subsoil (pH 3-4) developing on sulfidic and organic-rich sediments over the past 70 years, extensive brownish-to-yellowish layers have formed on macropores. Our data reveal that these layers ("macropore surfaces") are strongly enriched in 1 M HCl-extractable reactive iron (2-7% dry weight), largely bound to schwertmannite and 2-line ferrihydrite. These reactive iron phases trap large pools of labile organic matter (OM) and HCl-extractable phosphorus, possibly derived from the cultivated layer. Within soil aggregates, the OM is of a different nature from that on the macropore surfaces but similar to that in the underlying sulfidic sediments (C-horizon). This provides evidence that the sedimentary OM in the bulk subsoil has been largely preserved without significant decomposition and/or fractionation, likely due to physiochemical stabilization by the reactive iron phases that also existed abundantly within the aggregates. These findings not only highlight the important yet underappreciated roles of iron oxyhydroxysulfates in OM/nutrient storage and distribution in acidic sulfate-rich and other similar environments but also suggest that boreal acidic sulfate-rich subsoils and other similar soil systems (existing widely on coastal plains worldwide and being increasingly formed in thawing permafrost) may act as global sinks for OM and nutrients in the short run.

Effect of organic matter on the environmental behavior of sulfur and heavy metals in mariculture sediments during the aging process

Organic matter (OM) significantly impacts the environmental behavior of sulfur and heavy metals. In this study, the effects of OM on the migration and transformation of sulfur and heavy metals in mariculture sediments were investigated. The results indicated that baiting had a strong impact on the accumulation of acid volatile sulfur (AVS) (P < 0.05) and increased the environmental risk of sulfide in sediments. The addition of bait promoted the generation of chromium (II)-reducible sulfur (CRS); however, the resistance of AVS to CRS conversion increased with increasing bait addition. The addition of bait considerably influenced Cd accumulation. The acid-soluble fractions of Cr and Cu and the oxidizable fraction of Cd were primarily affected by the bait addition (coefficient of variation>15 %). An increase in the reducible fraction promoted the conversion of AVS to CRS, which reduced the degree of sediment aging. Higher OM levels reduced the diversity and abundance of the bacterial communities. The sulfate respiration functional microbiota was particularly affected by OM.

A simple and rapid method for measuring total free sulfides in marine sediments

AbstractThe quantitatively most important process by which organic matter in marine sediments is mineralized is performed by sulfate‐reducing bacteria, resulting in the accumulation of total dissolved (free) sulfide (S2− = H2S + HS− + S2−) in porewater. S2− is toxic to benthic animals and vascular plants and measurements serve as a proxy for the deleterious effects of organic enrichment on benthic habitat, biodiversity, and ecosystem function. Methodologies for measuring S2− in water have been pursued for at least a century, and standard approaches employ colorimetry (methylene blue and iodometric titration) and potentiometry. These standard methods require between 1 and 200 mL of porewater, which can be laborious to obtain. The ion‐selective electrode method is widely employed as a practical approach for sediment S2− analysis but lacks analytical robustness and is highly prone to measurement biases that misinform research and environmental management decisions. A technically simple method is described, based on direct UV spectrophotometry, for the near real‐time field analysis of small porewater samples. The procedure prevents known measurement biases associated with particulate sulfide interference, S2− volatilization and oxidation, and represents a practical approach for monitoring organic enrichment and classifying benthic ecological quality status. Porewater concentrations between 200 and 15,000 μmol L−1 can be measured and instrument calibration is highly stable. The method has the capacity to rapidly process and analyze sediment samples at low cost, which helps resolve the problem of chronic under‐sampling associated with the use of traditional S2− methods.

Trends in estuarine pyrite formation point to an alternative model for Paleozoic pyrite burial

The early Paleozoic Era (∼540–420 Ma) was an interval of profound biogeochemical changes including increasing oxygen (O2) and the onset of bioturbation (sediment mixing by animals). It is hypothesized that incipient bioturbation caused a monotonic decrease in sedimentary burial of pyrite (FeS2), which would have slowed atmospheric O2 accumulation. However, pyrite accumulation can exhibit complex responses to dynamic, low-O2 environmental conditions. To assess pyrite burial in a potential modern analogue to early Paleozoic environments, we collected sediment cores from the Chesapeake Bay, an estuary with multiple gradients in sulfate concentration, hypoxia intensity, organic carbon flux and lability, and bioturbation. Results indicate that pyrite accumulation is maximized not under strong sulfate depletion in highly reducing sediments, but rather in sediments that occupy the mid-range of sulfate–chloride ratios. This probably occurs through efficient replenishment of pore water sulfate and/or through the generation of sulfur redox intermediates, which promote pyrite formation via the polysulfide reaction pathway. In light of these results and in contrast to earlier models, we hypothesize that mild early Paleozoic bioturbation temporarily increased pyrite burial efficiency by stimulating higher sulfate reduction rates and increasing sedimentary sulfide retention. Compiled sulfur and carbon data from a geochemical database indicate that median sulfur-carbon ratios of fine-grained marine siliciclastic rocks increased from the Ediacaran through the Ordovician, then decreased and became much less variable from the Silurian onward. Thus, the Cambrian and Ordovician Periods may constitute a distinct interval of the Proterozoic-Phanerozoic transition in which bioturbation temporarily accelerated O2 buildup. This transition probably ended in the Silurian, when pO2 rose to sufficient levels to homogenize sedimentary carbon–sulfur cycling.

Metagenomic sequencing of a Patescibacteria-containing enrichment from Zodletone spring in Oklahoma, USA.

An enrichment of sulfidic sediments from Zodletone spring was sequenced as a metagenome. Draft genomes representing Cloacimonadota, Deltabacterota, Firmicutes, and Patescibacteria were binned and annotated and will aid functional genomics and cultivation efforts.

Sulfur isotopes in Archaean crustal reservoirs constrain the transport and deposition mechanisms of nickel-sulfides in komatiites

Assimilation and prolonged suspension of crust-derived sulfide liquid in komatiites are essential to form Ni-rich mineralisation. Evaluating the spatial relationship between komatiite-hosted Ni mineralisation and crustal S sources may thus provide insights into mechanisms of transport, metal enrichment and deposition of assimilated sulfide liquid. This study applied facies analysis and S isotopes to sulfides in Ni-mineralised komatiites and stratigraphically underlying bimodal volcanic-volcaniclastic and sedimentary rocks, which formed during rifting in the Agnew-Wiluna Greenstone Belt, Western Australia. The results revealed a lateral variation from rift-distal sedimentary sulfides, through sulfidic BIF, to rift-proximal VMS-style sulfides, the latter of which was predominantly assimilated by komatiites. Both crustal and komatiite-hosted sulfides were overprinted by granite-related skarn alteration during later basin inversion. Spatial S isotopes correlation revealed that Ni mineralisation in komatiites predominantly formed < 5 km from their crustal S sources, excluding long lateral transport as the main metal enrichment mechanism. Rather, metal enrichment likely happened through multiple cycles of sulfide entrapment and entrainment in lava flow vortices that formed in the wake of topographic steps represented by syn-rift faults. These faults were the main loci for pre-existing crustal weaknesses, hydrothermal fluid circulation, and VMS-style sulfide deposition, which were subsequently utilised by komatiites for enhanced thermo-mechanical erosion and crustal sulfide assimilation. This study shows that proximity to the syn-rift faults was the dominant control on the formation of komatiite-hosted Ni–sulfide mineralisation, regardless of substrate lithology. The S isotope signatures of crustal sulfides may be used as a proxy to identify syn-rift faults in highly deformed terranes.

Coupled carbon‑iron‑phosphorus cycling in the Rainbow hydrothermal vent field

Hydrothermal venting has been shown to play a role in the global biogeochemical cycles of three bio-essential elements: iron (Fe), carbon (C) and phosphorus (P). However, our insight into the coupled cycling of Fe and associated C and P in hydrothermal plumes as well as their long-term fate in the underlying sediments remains limited. We present a detailed study, tracing the biogeochemical pathways of hydrothermally sourced Fe and the associated C and P from a buoyant to a neutrally buoyant plume and to the underlying sediments. Combining chemical and micro(spectro)scopic methods, we characterize particulate and dissolved phases recovered from the water column and sediment at two sites: one located directly in the active Rainbow hydrothermal vent field at 36°N on the mid-Atlantic ridge (MAR) and one located 3 km NE of the active vents. Our results show that the precipitates in one of the largest hydrothermal plumes on the MAR consist of aggregates of Fe nanoparticles, comprising poorly-ordered Fe oxyhydroxides and polycrystalline Fe sulfides, coated with carbon that is likely of organic origin. The sediments underlying the hydrothermal plume show enrichments in organic C, Fe, P and vent-derived trace metals such as Cu that decrease with distance from active vents. The enrichment in organic C and persistence of apparently highly-reactive Fe phases after sediment burial may reflect enhanced preservation potential of both phases as a result of the formation of organic-mineral complexes. We further demonstrate that the scavenging of dissolved seawater phosphate (PO43−) by Fe nanoparticles is constrained to early stages of particle formation and sorption reactions in the buoyant hydrothermal plume and that P burial close to the vent field is driven by the deposition of the Fe nanoparticles. In the sediment, P is then efficiently retained through sink-switching from Fe-bound to more stable, authigenic apatite phases. As such, the sediments underlying the Rainbow vent seem to faithfully record coupled emission, scavenging and burial of essential elements and therefore offer potential for reconstruction of past venting activity. The deposition and burial of partly reduced plume material (e.g., Fe sulfides) in an oxic deep-sea sediment results in sediment chemistry and diagenesis that is very specific to the hydrothermal environment, while the redox signature of the plume is gradually lost. Beyond its role as a potential source of bioavailable Fe, we highlight how hydrothermal venting represents an efficient sink for organic C and bioavailable P. The findings contribute to understanding the profound impact of geological episodes of increased hydrothermal activity on ocean biogeochemistry and the coupled ocean-climate system.

Discharge of potentially toxic elements from acid sulfate soils in western Finland: Conflict between water protection and land use?

Acid sulfate soils (ASS) are commonly found in many coastal areas worldwide and typically develop from artificial draining of sulfidic sediments, which release acidity and metals, causing unfavuorable effects on recipient watercourses. This study estimates the actual amounts of metals and elements carried to the Gulf of Bothnia and the Baltic Sea by stream water yearly. The combined load from the many small streams and ditches was found to be proportionally high related to the size of their catchment, emphasizing the importance of including numerous small streams in the understanding of pollution in fresh water and marine environments. This study shows that Cd concentrations in the majority of the studied rivers exceed the Environmental Quality Standard set by the European Union (EU). This causes lowered ecological and chemical status according to the European classification system. Many potentially toxic elements discharge yearly to the Baltic Sea in large quantities from the study area: Thousands of tons of Al and Mn, tens of tons of Co, Cu and Ni, and hundreds of kg of Cd. A challenge for the estimation was irregular, or even missing, data for many rivers, which highlights careful planning of monitoring programs. While the current land use on ASS requires efficient drainage, the national and European strategies and legislation aim towards improved status in water bodies and forbid pollution of the environment. Therefore, the land use and water protection policy conflict.

Mapping, impacts, characterization and extent of acid sulfate soils in Finland

Acid sulfate soils (ASS) cause big problems worldwide due to their potential to form sulfuric acid during oxidation of sulfidic materials, resulting in very acid soil (pH &lt;4.0). Impacts include acidification of soil and water, leaching of metals, decreased nutrient supply, deterioration of water fauna and flora, and corrosion of infrastructure. These soils also exhibit poor geotechnical properties. Finland has the largest occurrences of ASS in Europe, mainly along the coast of the Baltic Sea. The EU Water Framework Directive brought about wide co-operation to reduce the harmful impacts of ASS in Finland. One urgent step was to localize and characterize the occurrences of ASS. The more than 10 year-long programme, led by the Geological Survey of Finland (GTK), started in 2009 and field work was completed in 2021. During the programme observations, measurements, sampling and analyses were made at 23 000 sites in an area of 5 010 000 ha. Traditionally ASS in Finland have been considered to comprise fine-grained sulfidic sediments and/or their oxidized layers, occurring on agricultural land along the coast below the highest shoreline of the Littorina Sea transgression. This study recognized and classified significant occurrences of other types of potentially harmful ASS materials: (1) coarse-grained ASS (sand), (2) organic ASS (peat) and (3) unsorted ASS (till material). The methods, definition and classification of Finnish ASS have been revised. We calculated the extent of ASS along the coast to be about 1 000 000 ha corresponding to 21% of the area covered in the past by the Littorina Sea, and three to six times more than earlier estimates. In addition, some occurrences of ASS were recognized inland, mainly related to black shales and sulfidic ores. The mapping data can be accessed via the GTK map service (www.gtk.fi) providing information about the distribution and properties of ASS.

Seaward alteration of arsenic mobilization mechanisms based on fine-scale measurements in Pearl River estuarine sediments

Identification of key As mobilization processes in estuarine sediments is challenging due to the transitional hydrodynamic condition and the technical restriction of obtaining fine-scale results. Herein, high-resolution (μm to mm) and in situ profiling of As with associated elements (Fe, Mn, and S) by the diffusive gradients in thin-film (DGT) technique were applied and coupled with pore water and solid phase analysis as well as microbial high-throughput sequencing, to ascertain the driving mechanisms of As mobilization in the sediments of Pearl River Estuary (PRE). Significant diffusion fluxes of As from sediment to water were observed, particularly in the upper estuary. With the seaward increase of salinity, the driving mechanism of As mobilization gradually shifted from microbial-induced dissimilatory Fe reduction to saltwater-induced ion exchange. Correspondingly, the dominant Fe-reducing bacteria (FeRB) in sediments changed from the genera Clostridium_sensu_stricto_1 and Bacillus to Ferrimonas and Deferribacter. The presence of dissolved sulfide in deeper sediments contributes to As removal through the formation of As-S precipitates as supported by theoretical calculations. Fine-scale findings revealed seaward changes of As mobilization mechanism in the sediments of a human-impacted estuary and may benefit the understanding of As biogeochemical behavior in estuaries worldwide.

A Yokenella regensburgei strain effectively removes Cu(II), Pb(II), and Cd(II) through a combination of absorption and mineralization modes

Microbial-based heavy metal removal from wastewater is a widely embraced and environmentally friendly method. Nevertheless, its sustainability and efficacy necessitate further improvement. In this study, the strain Yokenella regensburgei GXAS49-I was isolated and characterized for its bioremediation potential. The strain exhibited remarkable resistance to heavy metals, demonstrating a high removal efficiency of 85 % and 90 % for Cu(II) and Pb(II), respectively. The extracellular polymeric substance of GXAS49-I, rich in CO and CO groups, facilitated heavy metal adsorption and played a role in the removal of heavy metal ions. Additionally, GXAS49-I produced hydrogen sulfide, transforming heavy metals into sulfide sediments. Immobilizing GXAS49-I on aerobic granular sludge ensured consistently high removal efficiency for Cu(II) and Pb(II) over four consecutive cycles. The unique dual modes of absorption and mineralization of heavy metals by GXAS49-I, in conjunction with aerobic granular sludge immobilization, position it as an excellent candidate for the sustainable and effective removal of hazardous metals.

Iron sulfides in sediments of glacial lakes of the upper Kolyma region

Iron sulfides are common in the sediments of glacier lakes of the Magadan region -Gryazevoe (61°08’21” N, 152°19’57” E), Nalimnoe (61°07’41” N, 152°20’8” E), Sosednee (62°03’29” N, 149°3122” E), Sapog (63°29’9” N, 147°50’41” E), Vodorazdel’noe (63°44’8” N, 148°13’4” E), Ui (63°49’31” N, 147°53’21” E) and others. Most of the lakes were formed at the end of the Late Pleistocene or at the beginning of the Early Holocene. Sulfides occur in the spheroid forms with a framboidal structure, dusty clusters, and individual crystals. Sometimes sulfides fill up the diatom valves. The size of framboids does not exceed 100 µm. Sulfides have pyrite, greigite and pyrrhotite compositions. They are distributed unevenly in sections. Greigite and pyrrhotite are distinguished by their magnetic characteristics.

Distribution characteristic and risk assessment of acid volatile sulfide and heavy metals in sulfate-rich reservoir sediment

Distribution characteristic and risk assessment of acid volatile sulfide and heavy metals in sulfate-rich reservoir sediment

The Chemical Nature of Mercury and Copper Sulfides and Its Implication for Bioavailability Assessments in Sediments

Sulfur chemistry plays an important role in regulating the bioavailability of heavy metals (HMs) because HM sulfides are extremely insoluble in sediments. However, quantifying HM sulfides in sediments has been difficult because they are considered acid-extractable (AE). Previous studies also found that Hg and Cu behaved differently from other HMs in sediments. This study investigated the chemical nature of Hg and Cu sulfides and the causes of Hg and Cu anomalies in sediments. The results indicated that Hg and Cu sulfides are not mono-sulfides (HS− or S=) but bi-sulfides (S2=), which are non-acid-extractable (NAE) under nitrogen. These results explain the Hg and Cu anomalies compared to other HMs and facilitate a procedure to quantify Hg and Cu sulfides in sediments. We analyzed the AE and NAE fractions of Hg, Cu, and Zn under nitrogen in the sediments of Apalachicola Bay, North Florida. Zn was included for comparison because Zn sulfide is mono-sulfide. The NAE Hg and Cu were, on average, 97.9 ± 2.7% and 84.6%, respectively, of the total, much higher than that of Zn (24.3% of the total) in the sediments, as expected. The NAE fractions of Hg and Cu were sulfides and thus could be excluded from the bioavailability assessments.