Sulfate Flux Research Articles

Temperature sensitivity of the mineral permafrost feedback at the continental scale.

Oxidative weathering of sulfide minerals in sedimentary rocks releases carbon dioxide (CO2) into the atmosphere. In permafrost zones, this could be a positive feedback on climate change if it increases with warming, yet sulfide oxidation rates and their temperature response remain unknown over large spatial and temporal scales. We analyze a 60-year sulfate concentration dataset from catchments across the Mackenzie River Basin. Sulfate fluxes increased by 45% in the mainstem with 2.3°C of warming, and the temperature sensitivity suggests that continental-scale CO2 fluxes could double by 2100. The largest increases occur in catchments with geomorphic settings which act to rapidly expose rocks through physical weathering and thermokarst processes. Comparisons with a weathering model suggest that warming can increase reaction rates, and changes in the exposure of minerals with warming are also required. Future warming across vast Arctic landscapes could further increase sulfide oxidation rates and affect regional carbon cycle budgets.

A cascade of sulfur transferases delivers sulfur to the sulfur-oxidizing heterodisulfide reductase-like complex.

A heterodisulfide reductase-like complex (sHdr) and novel lipoate-binding proteins (LbpAs) are central players of a wide-spread pathway of dissimilatory sulfur oxidation. Bioinformatic analysis demonstrate that the cytoplasmic sHdr-LbpA systems are always accompanied by sets of sulfur transferases (DsrE proteins, TusA, and rhodaneses). The exact composition of these sets may vary depending on the organism and sHdr system type. To enable generalizations, we studied model sulfur oxidizers from distant bacterial phyla, that is, Aquificota and Pseudomonadota. DsrE3C of the chemoorganotrophic Alphaproteobacterium Hyphomicrobium denitrificans and DsrE3B from the Gammaproteobacteria Thioalkalivibrio sp. K90mix, an obligate chemolithotroph, and Thiorhodospira sibirica, an obligate photolithotroph, are homotrimers that donate sulfur to TusA. Additionally, the hyphomicrobial rhodanese-like protein Rhd442 exchanges sulfur with both TusA and DsrE3C. The latter is essential for sulfur oxidation in Hm. denitrificans. TusA from Aquifex aeolicus (AqTusA) interacts physiologically with AqDsrE, AqLbpA, and AqsHdr proteins. This is particularly significant as it establishes a direct link between sulfur transferases and the sHdr-LbpA complex that oxidizes sulfane sulfur to sulfite. In vivo, it is unlikely that there is a strict unidirectional transfer between the sulfur-binding enzymes studied. Rather, the sulfur transferases form a network, each with a pool of bound sulfur. Sulfur flux can then be shifted in one direction or the other depending on metabolic requirements. A single pair of sulfur-binding proteins with a preferred transfer direction, such as a DsrE3-type protein towards TusA, may be sufficient to push sulfur into the sink where it is further metabolized or needed.

Contamination of depressional wetlands in the Mpumalanga Lake District of South Africa near a global emission hotspot

The Mpumalanga Lake District (MLD) of South Africa hosts a regionally unique cluster of water bodies of great importance for wetland biodiversity. It is also located close to a global hotspot for coal-fired power station emissions but the local impacts from these sources of pollution are poorly understood. Sediment cores from three contrasting wetlands were 210Pb dated and analysed for a range of contaminants linked to fossil fuel combustion, including trace elements, Hg, sulphur and spheroidal carbonaceous fly-ash particles (SCPs). At the two sites with pre-industrial (1900) baseline sediments, Pb, Zn and especially Cr concentrations and fluxes showed significant increases in the impact period (post-1975). Mercury showed the greatest proportional increase in flux (>4-fold) of all trace metals. Mercury and sulphur concentrations and fluxes showed highly significant correlations with emissions over the corresponding periods, while SCPs in sediments also closely tracked emissions. In a global context, levels of sediment contamination are relatively minor compared with other heavily industrialised regions, with only Cr exceeding the sediment Probable Effects Concentration for biological impact post-1975. Despite the relatively large increases in Hg, concentrations do not reach the Threshold Effects Concentration. The unexpectedly low levels of contamination may be due to i) low levels of many trace contaminants in South African coals compared to global averages, ii) prevailing recirculation patterns which transport pollution away from the study area during the wet season, minimising wet deposition, and iii) pollutant remobilisation through desiccation of wetlands or volatilization. The effects of hydrology and sediment accumulation rates lead to differential transport and preservation of organic-associated and more volatile contaminants (e.g. Hg, S) relative to non-volatile trace elements in wetlands of the MLD. The greatest fluxes of Hg and S are recorded in the site with the highest catchment: lake area ratio, lowest salinity and greatest sediment organic matter content.

A volatile sulfur sink aids in reconciling the sulfur isotope mass balance of closed basin lakes

Sedimentary rocks from the early Eocene Green River Formation comprise the largest known lacustrine oil shale deposits, contain remarkably well-preserved fossils, and provide a unique record of climate evolution across the Early Eocene Climate Optimum, a period of high atmospheric CO2. The depositional environment of these intermountain lakes spanned from relatively fresh and fluvially influenced to expanded and stratified saline closed basin lakes under the influence of the Laramide orogeny and alternating humid and arid climatic conditions. As the surface area of the lakes expanded, alkalinity and salinity increased, with depositional cycles that linked to evaporative cycles and marked by an increasing abundance of organic matter-rich shales (TOC > 10 wt%). Simultaneously, an intriguing 20 ‰ positive shift in the sulfur isotope composition of sulfide minerals and organic sulfur is observed. Given that this trend cannot be simply explained by a change in the source of sulfate delivered to the basin, the evolution of biogeochemical sulfur cycling and the balance of fluxes in response to basin evolution remain unresolved. Here, we combine the sulfur isotope compositions of pyrite, organic sulfur, and carbonate-associated sulfate and molecular proxies of euxinia in samples from the Uinta basin's depocenter. We find that organic matter-rich sediments reflect deposition in a stratified water column with enhanced burial of pyrite and sulfurized organic matter, while organic-lean facies present evidence of, at least transiently, euxinic conditions reaching the photic zone during arid conditions presumably because of evaporation. As the lake became both saline-stratified and euxinic, we observe that δ34S values of all measured sulfur-bearing sedimentary proxies increase and evolve along a 1:1 line, a trend independent of facies that we interpret as reflecting a sulfate-limited system despite saline conditions. The isotopic mass balance of sulfur fluxes implies the existence of a sink of sulfur depleted in 34S that is spatially decoupled from burial in the depocenter. Modeling sulfur biogeochemical processes in a saline stratified lake system allows us to estimate that at least 50 % of the sulfur entering the lake could have been lost from the upper part of the euxinic water column where the fractionation factor imparted by microbial sulfate reduction is expressed. We propose that the overall isotopic enrichment of the system was caused by H2S degassing during arid climate intervals, presumably enhanced by transient water column mixing events. Further, episodic intrusion of euxinic bottom waters into the upper part of the water column might have triggered mass fish and plankton mortality, consequently facilitating the formation of these exceptionally fossiliferous and organic matter-rich rocks. Our study finds that volatile outgassing may be an underappreciated mechanism for the sulfur mass balance of stratified lacustrine systems.

Prominent Role of Sulfate Reduction in Considerable Sulfur Retention in a Subtropical Soil

AbstractThe sulfur biogeochemical cycle controls the sulfur dynamics in the soil. In contrast to almost all deposited sulfur leaching out in temperate catchments, approximately 80% of the deposited S is retained in the catchments in subtropical regions. However, the mechanisms for sulfur retention were unclear, hindering the understanding of potential threats of legacy sulfur with environmental changes. Here, we demonstrated that sulfate reduction (as sulfide fixed in soil) was a prominent yet overlooked mechanism for sulfur retention in addition to the widely recognized sulfate adsorption in soil, based on a study on soil sulfur storage and stable isotope signatures within entire soil profiles in a typical subtropical catchment in China. Using a dual‐isotopic model, the sulfate reduction flux was further determined to be 30% of the S deposition. Due to a lot of deposited sulfur fixed via sulfate reduction, the release of soil legacy sulfur would be less in response to decreasing sulfur deposition compared to the projections only considering adsorption. However, the remobilization of large amounts of reduced S should be regarded as a threat to the environment under climate change in the future.

DMSOP-cleaving enzymes are diverse and widely distributed in marine microorganisms

Dimethylsulfoxonium propionate (DMSOP) is a recently identified and abundant marine organosulfur compound with roles in oxidative stress protection, global carbon and sulfur cycling and, as shown here, potentially in osmotolerance. Microbial DMSOP cleavage yields dimethyl sulfoxide, a ubiquitous marine metabolite, and acrylate, but the enzymes responsible, and their environmental importance, were unknown. Here we report DMSOP cleavage mechanisms in diverse heterotrophic bacteria, fungi and phototrophic algae not previously known to have this activity, and highlight the unappreciated importance of this process in marine sediment environments. These diverse organisms, including Roseobacter, SAR11 bacteria and Emiliania huxleyi, utilized their dimethylsulfoniopropionate lyase ‘Ddd’ or ‘Alma’ enzymes to cleave DMSOP via similar catalytic mechanisms to those for dimethylsulfoniopropionate. Given the annual teragram predictions for DMSOP production and its prevalence in marine sediments, our results highlight that DMSOP cleavage is likely a globally significant process influencing carbon and sulfur fluxes and ecological interactions.

Sulfate distribution and sulfate reduction in global marine sediments

The quantification of anaerobic oxidation of organic matter in the global seabed is to a large extent based on transport-reaction modeling of pore water ions involved in the mineralization processes. As the predominant of these processes, sulfate reduction can be modeled from the depth distribution of sulfate and other relevant solutes. An active organoclastic sulfate reduction is typically characterized by sulfate profiles with a concave-down shape. We use here a comprehensive database to show that half of all competent sulfate profiles have an opposite, concave-up shape, which may appear inconsistent with this concept. We also show that there is a strong discrepancy between sulfate profiles obtained by gravity coring and by IODP coring, with generally much higher sulfate flux and shallower sulfate penetration depth in the gravity cores (the term IODP here covers the international ocean drilling programs, DSDP, ODP and IODP). The discrepancy is correlated with a selectivity for coring sites in the published studies, by which gravity coring is focused towards the ocean margins and continental shelf and towards high surface water productivity and high sedimentation rate. In contrast, IODP coring is more frequently done in low sedimentation regions and is largely absent from the continental shelf. As a result, estimates of sulfate reduction in the global seabed may be biased by a selection of only IODP core data for the modeling. Furthermore, the modeling of pore water profiles shows net rates of sulfate reduction, while 35S-radiotracer experiments show the higher gross rates of the process. Estimates from 35S-radiotracer measurements suggest that dissimilatory sulfate reduction oxidizes 77 Tmol yr−1 of organic carbon globally, which is 3- to 4-fold higher than recent data based on modeling of IODP data. The potential biases by global estimates of sulfate reduction in marine sediments are discussed.

Wet deposition of sulfur and nitrogen in the Jiuzhaigou World Heritage Site, China: Spatial variations, 2010–2022 trends, and implications for karst ecosystem conservation

Excessive sulfur and nitrogen deposition is a threat to natural ecosystems. This study investigated the spatio-temporal changes of wet sulfur and nitrogen deposition in Jiuzhaigou to understand the responses of wet deposition chemistry to local and national air pollutant emission changes and to assess relevant ecological risks. The results show that local emission sources (e.g., tourism, post-earthquake reconstruction, and vegetation damages) largely elevated the concentrations of SO42−, NO3−, NH4+, and Ca2+ at the non-background sites during 2021–2022; However, the gaps of annual sulfur and nitrogen wet deposition fluxes among the background, semi-background, and non-background sites were reduced by annual precipitation. The pH was also higher at the non-background sites due to stronger acid neutralization capacities from crustal dust there, and acid precipitation (pH < 5.6) was not detected at all the sites. During the 2010 to 2022 period, the wet deposition of SO42− and TIN (i.e. total inorganic nitrogen) and the equivalent ratio of SO42−: NO3− generally presented a declining trend at the background and semi-background sites, as a result of regional and national emission reductions. The TIN reduction from 2015 to 2016 to 2021–2022 at the background site was more from wet NH4+ deposition and the site's NO3− concentrations and fluxes were relatively stable. Compared to the critical loads (CLs) of sulfur and nitrogen for acidification and eutrophication, the annual wet and wet+dry deposition fluxes of sulfur and nitrogen were lower in almost the entire watershed, except for the CLmin of nitrogen for acidification in considerable areas. However, all the wet deposition samples were calcite-unsaturated and had annual TIN concentrations higher than the national environmental standard of total nitrogen for surface water. More field investigations are needed to better assess the ecological risks.

Seafloor spreading and the delivery of sulfur and metals to Earth’s oceans

Abstract Circulating fluids within Earth’s mid-ocean ridge system cool and alter the oceanic crust, contribute distinct chemistry to the ocean, and generate economically and geologically important metal-sulfide deposits at the seafloor. Yet, we have few constraints on the characteristics of these fluids at peak subseafloor pressure and temperature conditions or how the primary variable, seafloor spreading, affects these fluids’ delivery of metals and sulfur to seawater. Here, we develop a new, robust technique for estimating the peak endowment of heat and dissolved sulfur, iron, and copper in subseafloor hydrothermal fluids and determining their fate as these superheated fluids rise to the seafloor. Calculations using this technique indicate that &amp;gt;20%–70% of sulfur, iron, and copper dissolved at peak subseafloor conditions are lost during upflow due to cooling and concomitant decreases in sulfide mineral solubility. The interpretation of these estimates within the geologic context of vent fields allows us to demonstrate a strong inverse relationship between seafloor spreading rate and peak pressure-temperature conditions, subseafloor heat loss, and the magnitude of subseafloor sulfide mineralization. Our results demonstrate the extent to which the secular variation of Earth’s mid-ocean ridge system over geologic time has impacted sulfide deposition rates and hydrothermal fluxes of sulfur and metals to the ocean.

Quantifying the Extent of Authigenic Carbonate Formation in Shallow Marine Sediments Through a Correlation Between Carbonate Precipitation Rate and Sulfate Flux

AbstractThe accumulation of authigenic carbonate in marine sediments has been regarded as a significant contributor to the carbon cycle over Earth's history. However, accurate quantification of the extent of authigenic carbonate formation in both modern and ancient oceans has been challenging due to limited approaches. Here, we analyzed calcium, magnesium, dissolved inorganic carbon, and alkalinity pore‐water profiles of 153 sites influenced by methane diffusion from the northern South China Sea. By combining these data with published data of diffusive sulfate flux, we found a significant positive correlation between carbonate precipitation rate and sulfate flux in the subseafloor. This correlation can be used to quantify the regional extent of authigenic carbonate formation, representing an advantage over a spatial interpolation approach. We therefore propose that the observed correlation can serve as a new approach for quantifying authigenic carbonate formation in shallow sediments along continental margins for both modern and ancient oceans.

Significant influence of water diversion and anthropogenic input on riverine sulfate based on sulfur and oxygen isotopes

The transportation of dissolved sulfate (SO42-) to the ocean via river systems plays a critical role in the global sulfur cycle. However, the increasing anthropogenic input has made it challenging to quantify the various pristine contributions accurately. The riverine sulfur and oxygen isotopes of sulfates (δ34SSO4 and δ18OSO4) and the advantages of the Markov-Chain Monte Carlo model were used to distinguish the anthropogenic input in Fenhe River, a tributary of the Yellow River. The SO42- concentrations and δ34SSO4 and δ18OSO4 values of the mainstream river were normally distributed with minor seasonal variations (P > 0.05). However, the upstream riverine SO42- concentrations were significantly altered by the water diversion from the Yellow River. The midstream and downstream sections exhibited a continuous increase in the riverine SO42- concentration and δ34SSO4 and δ18OSO4 values during both seasons. The coal mining drainage significantly impacted the tributaries near coal mining activities, and chemical fertilizers and sewage contributed more sulfate in the midstream and downstream sections. The yearly sulfate flux of the Fenhe River accounted for 4.2% of that of Yellow River, among which over 60% was from anthropogenic sources. The average δ34SSO4 and δ18OSO4 values had elevated to 11.0‰ and 6.0‰, respectively, due to the extensive input of anthropogenic sulfate. Our findings confirm the utility of δ34SSO4 and δ18OSO4 for tracing anthropogenic input and underscore its impacts on river systems and the global sulfur cycle.

Triple oxygen isotope composition of combustion sulfate

The estimated contribution of “primary” combustion sulfate to the total atmospheric sulfate flux is inconsistent, hindering our interpretation of the atmospheric “missing sulfate”. We expect combustion sulfate to inherit the characteristic triple oxygen isotope composition of air O2 to variable degrees. To test the hypothesis, we extracted sulfate from soot samples collected from 48 residential chimneys throughout China. The mean sulfate's Δ′17O0.5305 and δ18O values are −0.27 ± 0.06‰ and 12.8 ± 3.6‰, respectively, and the Δ′17O0.5305 and δ18O values correlate negatively and extend to air O2's triple oxygen isotope composition as an endmember, suggesting that combustion sulfate is generated dominantly by S(IV) multiphase oxidation via O2 in the plume, with possible additional pathways through •OH in aqueous films or droplets and NO2 at soot surface. Oxygen sources (i.e., air O2, fuel, ambient moisture) and oxidation kinetics determine the triple oxygen isotope composition of combustion sulfate. The characterization of combustion sulfate's triple isotope composition helps to improve global and regional atmospheric sulfur chemistry models.

Sulfur origin and flux variations in fumarolic fluids of Vulcano Island, Italy

A sharp increase in volatiles, especially SO2 fluxes from the solfataric plume and diffuse CO2 from the soils of the La Fossa crater area, started in June 2021, and subsequently from the Levante Bay area, suggests renewed unrest at Vulcano Island, Italy. This event has encouraged monitoring activities and stimulated new research activities aimed at understanding the recent evolution of the volcanic system. In this study, the chemical and isotopic composition of fumaroles, thermal waters, and soil gases from the main degassing areas of Vulcano Island with a special focus on sulfur isotopes, are used to investigate the fluid transfer mechanism inside the volcano. Sulfur is one of the most abundant volatile elements present in magmas and volcanic fluids from the La Fossa crater, where it mostly occurs as SO2 and H2S at variable relative concentrations depending on oxygen fugacity and temperature. The isotope composition and the chemical ratio of sulfur species depict a complex hydrothermal-magmatic system. In addition, we utilize the installed SO2 monitoring network that measures the total outgassing of SO2 with the UV-scanning DOAS technique. The SO2 fluxes from the La Fossa crater fumaroles, coupled with the SO2/CO2 and SO2/H2O ratios, were measured to evaluate the total mass of fluids emitted by the shallow plumbing system and its relationship with the status of volcanic activity. Combining the whole chemical composition of fumaroles analyzed with a discrete, direct sampling of high-temperature fumaroles located on the crater summit, the output of discharged water vapor has been estimated (5,768 t·d−1). On the basis of the water output, we estimated the total thermal energy dissipated by the crater during the last enhanced degassing activity (167 MW). This strong and sharp increase in energy observed during the current crisis confirms the long-growing trend in terms of mass and energy recorded in recent decades, which has brought the surface system of Vulcano Island to a critical level that has never been recorded since the last eruptive event of 1888–91.

FEASIBILITY OF ZEBRAFISH LARVA MODEL AS A VIABLE SUBSTITUTE TO RAT NON-EVERTED SAC MODEL FOR PERMEATION EVALUATION OF BCS III DRUGS

The oral route is the most convenient route of drug administration. Many drugs exhibit poor oral bioavailability. BCS III drugs exhibit high solubility and present a massive challenge due to poor permeability. Different permeation enhancers viz., nonionic Cremophor® RH 40, Tween® 80 and Lutrol® F68, anionic docusate sodium with sodium cholate, and anionic polymer sodium carboxymethyl cellulose were evaluated using rat non-everted sac method and zebrafish larva model. Maximum permeation enhancement was seen with docusate sodium for both drugs. The permeation enhancement ratio for netilmicin sulphate was 4.07±0.657, while for deferoxamine mesylate it was 1.482±0.378. Cremophor® RH 40 enabled augmented flux of netilmicin sulphate, and Tween® 80 showed enhanced permeation of deferoxamine mesylate. An excellent correlation was observed between apparent permeability and flux with drug absorbed per zebrafish larva (µg) (R2 = 0.938) for netilmicin sulphate and for deferoxamine mesylate (R2 = 0.9397). An important outcome of the study is the demonstration of the feasibility of the zebrafish larvae model as a viable substitute to the non-everted sac method, which could also enable screening of potential permeation enhancers for the development of orally bioavailable formulations of BCS III.

Optical and Morphological Properties of Cu2FeSnS4 Chalcogenide Films

P-type Cu2FeSnS4 (CFTS) and Cu2ZnSnS4 (CZTS) quaternary chalcogenide films have been grown by the method of spin coating on glass substrates relate to 30 and 40 sccm sulfur flux. Physical properties of obtained samples were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM) and ultraviolet visible spectroscopy (UV-Vis) to see the effect of deposition parameters on the thin film. The crystal parameters including crystal size, dislocation density and strain value of the samples were changed related to the deposition parameters. XRD results indicated an improvement of the crystalline quality of quaternary chalcogenide CFTS with a maximum crystal size of about 50 nm for (112) peak orientation. SEM images illustrated that the particle size was changed with an increase in the flux of sulfur, which was confirmed with both XRD and AFM images. It was seen that the absorption and energy band gap value of the samples changed the effect of sulfur flux and CZTS film for 40 sccm exhibited more strong absorption all samples in the UV-Vis region. The band gap values of the samples were calculated 1.51, 1.53, 1.82 and 1.91 eV for CZTS (30 sccm), CZTS (40 sccm), CFTS (30 sccm) and CFTS (40 sccm) films annealed H2S gas, respectively.

Estimating source-sink distributions and fluxes of reactive nitrogen and sulfur within a mixed forest canopy

Estimating source-sink distributions and fluxes of reactive nitrogen and sulfur within a mixed forest canopy

Long-term warming modulates diversity, vertical structuring of microbial communities, and sulfate reduction in coastal Baltic Sea sediments.

Coastal waters such as those found in the Baltic Sea already suffer from anthropogenic related problems including increased algal blooming and hypoxia while ongoing and future climate change will likely worsen these effects. Microbial communities in sediments play a crucial role in the marine energy- and nutrient cycling, and how they are affected by climate change and shape the environment in the future is of great interest. The aims of this study were to investigate potential effects of prolonged warming on microbial community composition and nutrient cycling including sulfate reduction in surface (∼0.5 cm) to deeper sediments (∼ 24 cm). To investigate this, 16S rRNA gene amplicon sequencing was performed, and sulfate concentrations were measured and compared between sediments in a heated bay (which has been used as a cooling water outlet from a nearby nuclear power plant for approximately 50 years) and a nearby but unaffected control bay. The results showed variation in overall microbial diversity according to sediment depth and higher sulfate flux in the heated bay compared to the control bay. A difference in vertical community structure reflected increased relative abundances of sulfur oxidizing- and sulfate reducing bacteria along with a higher proportion of archaea, such as Bathyarchaeota, in the heated compared to the control bay. This was particularly evident closer to the sediment surface, indicating a compression of geochemical zones in the heated bay. These results corroborate findings in previous studies and additionally point to an amplified effect of prolonged warming deeper in the sediment, which could result in elevated concentrations of toxic compounds and greenhouse gases closer to the sediment surface.

Melt inclusion evidence for limestone assimilation, calc-silicate melts, and “magmatic skarn”

Abstract Chemical exchange between silicate magmas and carbonate rocks has major implications for igneous fractionation, atmospheric CO2 flux, and formation of mineral deposits. However, this process is only partly understood, and long-standing questions of whether, where, and how carbonate rocks can be digested by silicate melts remain controversial. We describe evidence for pervasive chemical exchange between silicate melt and carbonate rock in a shallow porphyry setting driven by limestone assimilation. Melt inclusions in endoskarn from the Chating Cu-Au deposit in eastern China reveal that the calc-silicate assemblage (diopside + andradite ± wollastonite ± epidote) was molten at the time of skarn formation and coexisted with CO2 vapor as well as sulfate- and chloride-salt melts. Hence, we argue that endoskarn at Chating formed by crystallization of an immiscible calc-silicate melt produced by assimilation of carbonate rock, aided by the presence of sulfate and other fluxes, which in turn promoted desilication of the intruding magma and drove vigorous CO2 release.

The effects of organic matter and anaerobic oxidation of methane on the microbial sulfate reduction in cold seeps

Cold seep sediments are dominated by intensive microbial sulfate reduction coupled to anaerobic oxidation of methane. However, the contribution proportion between this process and the role of organic matter has remained enigmatic. Here, pore water data combined with PROFILE model, fluxes of sulfate and methane concentration calculated from Fick's first law, and δ34SSO4 and δ18OSO4 of pore water sulfate were studied to reconstruct co-occurring microbial organoclastic sulfate reduction and anaerobic oxidation of methane coupled with sulfate reduction in methane seep sediments collected from South China Sea. The sulfate concentration profiles of C9 and C14 in Qiongdongnan Basin generally show quasilinear depletion with depth. Reaction-transport modeling provided close fits to concentration data. δ18OSO4 and δ34SSO4 increase fastest with sediment depth above 400 cmbsf and slowest below that depth. The values of methane flux are always lower than those of total sulfate reduction of sulfate diffusive flux at GC-10, GC-9, GC-11 and HD319 sites in Taixinan Basin. Besides, positions of sulfate methane transition zone in all study sites are approximately ~400 to 800 centimeters below seafloor. These results showed that microbial sulfate reduction in sediments is mainly controlled by intense anaerobic oxidation of methane, but there is a certain relationship with organic matter metabolism process. This emphasizes that traditional redox order of bacterial respiration is highly simplified, where, in sediments such as these seeps, all of these microbial sulfate reduction processes can occur together with complex couplings between them.

Black ginger extract and its active compound, 5,7-dimethoxyflavone, increase intestinal drug absorption via efflux drug transporter inhibitions

Black ginger is used as an herbal medicine for self-care and health promotion. Black ginger extract has been shown to alter the function of transporters in several cell types. This study demonstrates the interaction between the extract and 5,7-dimethoxyflavone (DMF) on drug efflux mediated by breast cancer resistance proteins (BCRP) and P-glycoprotein (P-gp) in Caco-2 cells and heterologous cell systems [Madin-Darby canine kidney type II (MDCKII) stably transfected with human BCRP (MDCKII/BCRP) or human P-gp (MDCKII/P-gp)]. The transepithelial flux of 3H-Digoxin and 3H-Estrone sulfate, prototypic substrates of P-gp, and BCRP, respectively, across Caco-2 cell monolayers, MDCKII/BCRP, and MDCKII/P-gp cells were determined. The results demonstrate that black ginger extract (10 μg/ml) significantly increases 3H-Digoxin and 3H-Estrone sulfate transport from the apical to basolateral side while decreasing transport from the basolateral to apical side of Caco-2 cells and MDCKII cell overexpression of BCRP or P-gp. The effect of the extract on 3H-Digoxin and 3H-Estrone sulfate transport was related to a decrease in efflux ratio. Likewise, DMF (5 μM) significantly increased 3H-Digoxin and 3H-Estrone sulfate absorption with a decreased efflux ratio compared to the control. Interestingly, the extract also significantly increased absorption of paclitaxel, an anti-cancer drug, which has poor oral absorption. Taken together, co-administration of drugs as substrates of BCRP and P-gp, with the black ginger extract containing DMF, might alter the pharmacokinetic profiles of the medicine.