Sulfate Amendment Research Articles

Bottom-up Approach for Designing Cobalt Tungstate Nanospheres through Sulfur Amendment for High-Performance Hybrid Supercapacitors.

Nanofabrication of heteroatom-doped metal oxides into a well-defined architecture via a "bottom-up" approach is crucial to overcome the boundaries of the metal oxides for energy storage systems. In the present work, this issue was addressed by developing sulfur-doped bimetallic cobalt tungstate (CoWO4 ) porous nanospheres for efficient hybrid supercapacitors via a single-step, ascendable bottom-up approach. The combined experimental and kinetics studies revealed enhanced electrical conductivity, porosity, and openness for ion migration after amendments of the CoWO4 via sulfur doping. As a result, the sulfur-doped CoWO4 nanospheres exhibited a specific capacity of 248.5 mA h g-1 with outstanding rate capability and cycling stability. The assembled hybrid supercapacitor cell with sulfur-doped CoWO4 nanospheres and activated carbon electrodes could be driven reversibly in a voltage of 1.6 V and exhibited a specific capacitance of 177.25 F g-1 calculated at 1.33 A g-1 with a specific energy of 63.41 Wh kg-1 at 1000 W kg-1 specific power. In addition, the hybrid supercapacitor delivered 94.85 % initial capacitance over 10000 charge-discharge cycles. The excellent supercapacitive performance of sulfur-doped CoWO4 nanospheres may be credited to the sulfur doping and bottom-up fabrication of the electrode materials.

Kinetics and mechanism of arsenic removal using sulfide-modified nanoscale zerovalent iron

Sulphur modified nano zerovalent iron (S–nZVI) has shown considerable promise for removal of various aqueous contaminants. However studies utilizing S–nZVI for removal of aqueous inorganic arsenic (As) is relatively rare, which was studied in this work. Characterization of the synthesized S–nZVI showed typical core-shelled structure with distorted outer shell consisting of iron oxide and FeS. The removal rate of both As(III) and As(V) by S–nZVI was considerably enhanced compared to nZVI and highest As removal was observed at S/Fe ratio of 0.1 under acidic condition. Results showed slight decrease in As removal efficiencies for S–nZVI aged upto 48 h, with obvious drop in As removal efficiencies for longer aging time which although still exhibited higher reactivity than bare nZVI. Spectroscopic investigation showed sulphur amendment of nZVI completely altered the As sequestration mechanism compared to nZVI. While reduction of the adsorbed As(III) and As(V) was observed for bare nZVI, in contrast, uptake of As(III) and As(V) by S–nZVI involves adsorption as As(III) and As(V) oxyanion respectively with additional precipitation of As2S3. Overall, the study shows that incorporation of FeS on the surface of nZVI can be an effective modification strategy for efficient sequestration of As from contaminated water.

Enhancing Roxarsone Degradation and In Situ Arsenic Immobilization Using a Sulfate-Mediated Bioelectrochemical System.

Roxarsone (ROX) is widely used in animal farms, thereby producing organoarsenic-bearing manure/wastewater. ROX cannot be completely degraded and nor can its arsenical metabolites be effectively immobilized during anaerobic digestion, potentially causing arsenic contamination upon discharge to the environment. Herein, we designed and tested a sulfate-mediated bioelectrochemical system (BES) to enhance ROX degradation and in situ immobilization of the released inorganic arsenic. Using our BES (0.5 V voltage and 350 μM sulfate), ROX and its metabolite, 4-hydroxy-3-amino-phenylarsonic acid (HAPA), were completely degraded within 13-22 days. In contrast, the degradation efficiency of ROX and HAPA was <85% during 32-day anaerobic digestion. In a sulfate-mediated BES, 75.0-83.2% of the total arsenic was immobilized in the sludge, significantly more compared to the anaerobic digestion (34.1-57.3%). Our results demonstrate that the combination of sulfate amendment and voltage application exerted a synergetic effect on enhancing HAPA degradation and sulfide-driven arsenic precipitation. This finding was further verified using real swine wastewater. A double-cell BES experiment indicated that As(V) and sulfate were transported from the anode to the cathode chamber and coprecipitated as crystalline alacranite in the cathode chamber. These findings suggest that the sulfate-mediated BES is a promising technique for enhanced arsenic decontamination of organoarsenic-bearing manure/wastewater.

EFFECT OF ORGANIC FERTILIZER RATES AND SULFUR ON GROWTH AND PRODUCTIVITY OF BROAD BEAN UNDER SOUTH SINAI CONDITIONS

The field work was carried out at a private farm at Tour city, South Sinai Governorate, during the two consecutive winter seasons of 2018/2019 and 2019/2020.The experiments were conducted to study the effect of organic manure, soil amendment i.e., 0; 25; 30 and 35 m³/feddan, and four rates of sulfur application i.e., 0; 100; 150 and 200 kg/feddan, where added during soil preparation for planting, on growth, yield and chemical composition of broad bean, Aspany F1 cv., grown in sandy soil conditions. Results revealed that all organic manure treatments showed increase in all growth and yield characters when compared with control treatment in both growing seasons. Organic manure at the rate of 35 m³/feddan has given significant increase in plant height and weight; number of branches/plant;pods length, pod fresh weight and N; P and K (%), while organic manure at the rate of30 m³/feddanhad superior significantly effect on number of pods/plant; number of seeds/pod; plant yield and total yield (ton/feddan), followed by organic manure at the rate of 35 m³/feddan. No significant differences occurred between these two organic treatments in both seasons. Sulfur amendment at the rate of 200 kg/feddan, followed by the rate of 150 kg/feddan had got the highest values and significantly increased plant height and weight; number of branches/plant; number of pods/plant, pods length, average pod fresh weight, number of seeds/pod; plant yield; total yield (ton/feddan), as well asK and P (%). There were no significant differences between both treatments in both growing seasons.

Diverse Communities of hgcAB+ Microorganisms Methylate Mercury in Freshwater Sediments Subjected to Experimental Sulfate Loading.

Methylmercury (MeHg) is a bioaccumulative neurotoxin produced by certain sulfate-reducing bacteria and other anaerobic microorganisms. Because microorganisms differ in their capacity to methylate mercury, the abundance and distribution of methylating populations may determine MeHg production in the environment. We compared rates of MeHg production and the distribution of hgcAB genes in epilimnetic sediments from a freshwater lake that were experimentally amended with sulfate levels from 7 to 300 mg L-1. The most abundant hgcAB sequences were associated with clades of Methanomicrobia, sulfate-reducing Deltaproteobacteria, Spirochaetes, and unknown environmental sequences. The hgcAB+ communities from higher sulfate amendments were less diverse and had relatively more Deltaproteobacteria, whereas the communities from lower amendments were more diverse with a larger proportion of hgcAB sequences affiliated with other clades. Potential methylation rate constants varied 52-fold across the experiment. Both potential methylation rate constants and % MeHg were the highest in sediments from the lowest sulfate amendments, which had the most diverse hgcAB+ communities and relatively fewer hgcAB genes from clades associated with sulfate reduction. Although pore water sulfide concentration covaried with hgcAB diversity across our experimental sulfate gradient, major changes in the community of hgcAB+ organisms occurred prior to a significant buildup of sulfide in pore waters. Our results indicate that methylating communities dominated by diverse anaerobic microorganisms that do not reduce sulfate can produce MeHg as effectively as communities dominated by sulfate-reducing populations.

Cable bacteria reduce methane emissions from rice-vegetated soils

Methane is the second most important greenhouse gas after carbon dioxide and approximately 11% of the global anthropogenic methane emissions originate from rice fields. Sulfate amendment is a mitigation strategy to reduce methane emissions from rice fields because sulfate reducers and methanogens compete for the same substrates. Cable bacteria are filamentous bacteria known to increase sulfate levels via electrogenic sulfide oxidation. Here we show that one-time inoculation of rice-vegetated soil pots with cable bacteria increases the sulfate inventory 5-fold, which leads to the reduction of methane emissions by 93%, compared to control pots lacking cable bacteria. Promoting cable bacteria in rice fields by enrichment or sensible management may thus become a strategy to reduce anthropogenic methane emissions.

Anaerobic 1,4-dioxane biodegradation and microbial community analysis in microcosms inoculated with soils or sediments and different electron acceptors.

1,4-Dioxane, a probable human carcinogen, is a co-contaminant at many chlorinated solvent-contaminated sites. Although numerous 1,4-dioxane-degrading aerobic bacteria have been isolated, almost no information exists on the microorganisms able to degrade this chemical under anaerobic conditions. Here, the potential for 1,4-dioxane biodegradation was examined using multiple inocula and electron acceptor amendments. The inocula included uncontaminated agricultural soils and river sediments as well as sediments from two 1,4-dioxane contaminated sites. Five separate experiments involved the examination of triplicate live microcosms and abiotic controls for approximately 1year. Compound-specific isotope analysis (CSIA) was used to further investigate biodegradation in a subset of the microcosms. Also, DNA was extracted from microcosms exhibiting 1,4-dioxane biodegradation for microbial community analysis using 16S rRNA gene amplicon high-throughput sequencing. Given the long incubation periods, it is likely that electron acceptor depletion occurred and methanogenic conditions eventually dominated. The iron/EDTA/humic acid or sulfate amendments did not result in 1,4-dioxane biodegradation in the majority of cases. 1,4-dioxane biodegradation was most commonly observed in the nitrate amended and no electron acceptor treatments. Notably, both contaminated site sediments illustrated removal in the samples compared to the abiotic controls in the no electron acceptor treatment. However, it is important to note that the degradation was slow (with concentration reductions occurring over approximately 1year). In two of the three cases examined, CSIA provided additional evidence for 1,4-dioxane biodegradation. In one case, the reduction in 1,4-dioxane in the samples comparing the controls was likely too low for the method to detect a significant 13C/12C enrichment. Further research is required to determine the value of measuring 2H/1H for generating evidence for the biodegradation of this chemical. The microbial community analysis indicated that the phylotypes unclassified Comamonadaceae and 3 genus incertae sedis were more abundant in 1,4-dioxane-degrading microcosms compared to the live controls (no 1,4-dioxane) in microcosms inoculated with contaminated and uncontaminated sediment, respectively. The relative abundance of known 1,4-dioxane degraders was also investigated at the genus level. The soil microcosms were dominated primarily by Rhodanobacter with lower relative abundance values for Pseudomonas, Mycobacterium, and Acinetobacter. The sediment communities were dominated by Pseudomonas and Rhodanobacter. Overall, the current study indicates 1,4-dioxane biodegradation under anaerobic and, likely methanogenic conditions, is feasible. Therefore, natural attenuation may be an appropriate cleanup technology at sites where time is not a limitation.

Sulfur Amendment of Soil Improves Establishment and Growth of Firs in a Field Naturally Infested with Phytophthora1

Abstract Acidification of soil from pH 6 to 4 by incorporating elemental sulfur reduced mortality and improved color and initial growth of Fraser fir, Abies fraseri (Pursh) Poir., and Canaan fir, Abies balsamea (L.) Mill. var. phanerolepis Fernald, planted into a field that had previously experienced significant losses consistent with phytophthora root rot. Acidifying the soil improved tree color starting the year of planting and persisting through five years. During their second year after planting, extension of terminal growth was 12.5 vs. 5.6 cm (4.9 vs. 2.2 in) for plots with soil pH of 4 and 6, respectively, averaged across tree species. In subsequent years, the growth rate of trees was unaffected by having acidified the soil. Over the course of five years, the average annual mortality rate for the trees was 1.4, 4.0, 9.7, and 12.2% for Canaan fir (pH 4), Canaan fir (pH 6), Fraser fir (pH 4), and Fraser fir (pH 6), respectively. However, all tree mortality for Canaan fir planted into acidified soil occurred during the first two years. A root dip with potassium phosphite at the time of planting only benefitted Fraser fir. Minimizing losses of trees in this field would require planting species less susceptible or resistant to phytophthora root rot infection and soil acidification. Index words: soil acidification, phytophthora root rot, potassium phosphite, root dip Species used in this study: Fraser fir; Abies fraseri (Pursh) Poir.; Canaan fir; Abies balsamea (L.) Mill. var. phanerolepis Fernald Chemicals used in this study: acibenzolar-S-methyl (Actigard 50WDG); clothianidin (Arena 50WDG); imidacloprid (Xytect 2F); potassium phosphite (Helena Prophyt); sulfur

Impacts of redox conditions on dissolved organic matter (DOM) quality in marine sediments off the River Rhône, Western Mediterranean Sea

Sedimentary dissolved organic matter (DOM) is an important pool of intermediates produced and consumed during early diagenesis of organic matter in the anoxic subseafloor. Rapid degradation of organic matter in the coastal sediment results in stratification of redox zones. However, to date little is known about the selectivity with respect to organic matter of the initial microbially mediated anaerobic degradation processes under contrasting redox conditions and how these affect the composition of DOM. In order to study the effect of sulfate reducing vs. methanogenic conditions on DOM quality and degradation, sediments (0–18 cm) from the Rhône River Delta were incubated, with redox conditions being controlled by sulfate amendment. The progress of incubation was monitored by H2, CH4, sulfate, DIC, DOC and acetate production. DOM composition was determined by 3D Fluorescence Spectroscopy, i.e., Excitation Emission Matrix Spectroscopy (EEMs), and ultra-high-resolution Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR-MS). Parallel factor analysis (PARAFAC) of EEMs was used to distinguish different groups of DOM (humic-like and protein-like compounds) to evaluate composition, conjugation and size of DOM. Prior to incubation, humic-like sedimentary DOM predominated; nearly half of the molecular formulae (>5000) identified by FT-ICR-MS were CHO and one third were CHNO compounds. During incubation, protein-like DOM and CHNO formulae with 3 and 4 N atoms formulae were rare under both sulfate reducing and methanogenic conditions. Incubation under sulfate reducing conditions resulted in rapid release and net accumulation of dissolved organic carbon (DOC). Protein-like DOM was rapidly cycled and humic-like DOM accumulated. Consistently, CHNO formulae with 3 and 4 N atoms decreased faster, whereas formulae with one N and oxygen-rich unsaturated compounds became more concentrated. In contrast, during incubation under methanogenic conditions, there was no net accumulation of DOC; blue-shift of humic-like peaks suggest the transformation possibly associated with loss of oxygen-bearing functional groups in conjugated structures of humic substances. This interpretation is consistent with the relative decrease of oxygenation and carbon number in the pool of aromatic and highly unsaturated compounds observed by FT-ICR-MS analysis. Approximately 90% of molecular formulae that were lost under methanogenic conditions were accumulated under sulfate reducing conditions. Our results suggest that under sulfate reducing conditions degradation of organic matter results in the accumulation of highly oxidized DOM, while protein-like compounds are selectively consumed. When the redox regime changes to methanogenic conditions, microbes apparently utilize the humic-like and oxygen-rich compounds of the oxidized DOM pool that accumulated under sulfate reducing conditions. Consequently, redox regimes and the associated biogeochemical processes influence rate and fractions of DOM released by and consumed in the deep biosphere, which could ultimately shape the composition of the preserved sedimentary organic matter and the DOM released to the ocean.

Reactions of chlorinated ethenes with surface-sulfidated iron materials: reactivity enhancement and inhibition effects.

Recent studies on the use of controlled sulfur amendment to improve the reactivity and selectivity of zerovalent iron (ZVI) in reductive dechlorination reactions have generated renewed interest in ZVI-based remediation materials. However, existing studies have focused on the reactions between trichloroethene (TCE) and lab-synthesized ZVI, and the applicability of sulfidation to ZVIs with different material characteristics for reductive dechlorination of chloroethenes such as tetrachloroethene (PCE) and cis-dichloroethene (cis-DCE) has not been systematically examined. In this study, four ZVI materials from commercial sources having different sizes and morphological and compositional characteristics were subjected to various sulfidation treatments and were assessed in batch reactions with PCE, TCE, or cis-DCE. Sulfur amendment induces modest increases in PCE degradation rates and steers reactions towards a cleaner pathway that has minimum accumulation of partially dechlorinated intermediates. In the case of cis-DCE, bifurcating outcomes were observed that include enhancement effects for two high-purity ZVIs and inhibitory effects for two ZVIs possessing low levels of metal impurities. Further investigations based on controlled metal dosing reveal that the trace metals commonly present in cast iron or recycled metal scraps, such as Cu and Ni, can act as adventitious catalysts for cis-DCE reduction. Sulfidation results in poisoning of these catalytic ingredients and accounts for the adverse effect observed with a subset of ZVIs. Collectively, this study confirms enhanced degradation of highly chlorinated ethenes (PCE and TCE) by sulfidation of ZVIs from diverse origins; nonetheless, the effects of sulfidation can be highly variable for the less chlorinated ethenes due to differences in the material characteristics of ZVI and the predominant dechlorination pathways.

Effects of sulfate on cadmium uptake in wheat grown in paddy soil - pot experiment

Rice-wheat rotation is common in China. Cadmium (Cd) and sulfur (S) are added to rice fields through various activities. The sulfur amendment has been recommended to control the uptake of Cd in rice. However, the effect of S on Cd uptake in winter wheat cultivated in paddy soil is rarely reported. A greenhouse pot experiment including two Cd levels (0, 10 mg Cd/kg, as CdCl&lt;sub&gt;2&lt;/sub&gt;) combined with three S rates (0, 30, 60 mg S/kg, as Na&lt;sub&gt;2&lt;/sub&gt;SO&lt;sub&gt;4&lt;/sub&gt;) was performed to investigate the effect of S application on uptake and allocation of Cd in wheat cultivated in paddy soil. Cadmium concentrations in wheat grain significantly (P &amp;lt; 0.05) increased by 37% at 30 mg S/kg, and the percentage of Cd allocation to grain significantly (P &amp;lt; 0.05) increased by 7% at 60 mg S/kg compared with non-S addition treatment when wheat was grown in Cd-added soil. For the low Cd soil, a similar trend was seen, but Cd increases were insignificant for grain while significant (P &amp;lt; 0.05) for root at 60 mg S/kg. In conclusion, S fertiliser may promote Cd accumulation in wheat grain and should be considered when it is used for wheat in paddy soils.

Effect of the Soil Amendments on the Mechanical Harvest of Potato Crop Grown under Centre Pivot Irrigation System

A field trial was conducted at TADCO to evaluate the mechanical harvest of autumn potato crop under different soil amendments: sand, gypsum, cow manure, and granular sulfur. The application of the sand amendment to the soil of the pivot showed easier mechanical and semi-mechanical harvest. The potato yield under the mechanical harvest was less than semi-mechanical harvest by 15.48% at the different soil amendments. More bruises were observed on the potato tubers harvested by mechanical harvest which ranged 9.34-16.33%, while bruises at semi-mechanical harvest ranged 4.28-4.75%. The final yield of stored potato was less than harvested yield by 10.68, 7.78%, 14.85, 11.08 for the sand, gypsum, cow manure, and sulfur amendments respectively. The stored yield of the different treatments was significantly less than the yield of the test harvest by around 24.03-32.24% at J34 and by 29.64 -56.27% at F18 and this was due to harvest method, cleaning out the damaged potato and moisture loss. The results of this trial highlighted the importance of selecting pivots for growing potato to be with less clay and more sand; also, it highlighted the importance of leaving the wheat straw to decompose in the soil instead of burning to improve the soil structure to be suitable for mechanical harvest. The sand amendment was not suitable for TADCO crop production as it is difficult to apply, need more time to execute besides less productivity. Due to one-month delay in planting potato, the average yield of stored potato from the trial pivots reached 20.2 M.T. /Ha which is significantly less than the yield of stored potato from the other pivots at TADCO of the same season with a range of 27-43 M.T. /Ha.

Dactylis glomerata L. cultivation on mercury contaminated soil and its physiological response to granular sulphur aided phytostabilization

Most mercury (Hg) deposition in the environment results from anthropogenic inputs, Chlor-Alkali Plants (CAPs) particularly had a significant Hg impact on the environment at a regional scale. Exposure to mercury compounds resulting in various toxic effects for living organisms. The aim of this study was to investigate the capacity of granular sulphur (S) soil amendment and cultivation of Dactylis glomerata to decrease gaseous mercury emission to the atmosphere and mercury mobility in soils affected by CAP activity in the past. The effect of this approach on D. glomerata physiological status was also assessed (Hg concentration in biomass, chlorophyll a fluorescence, pigment contents and oxidative stress). Stabilization of mercury in soil and reduction of root and shoot concentration did not influence biomass production. Despite similar yields, photosynthetic efficiency was higher for plants grown in sulphur amended soil compared to unamended soil, particularly observed in phenomenological energy fluxes. Relative chlorophyll content was 30% lower for amended soil plants, however based on chlorophyll fluorescence data those were in high portion ineffective. Oxidative stress products and catalase activity did not differ significantly between experimental treatments. Sulphur amendment was a key factor for reduction of Hg mobility in soil (reduced by about 30%) while plant cover was significant for the reduction of Hg atmospheric emission (emissions were 2-times higher in sulphur amended soil without plant cover). Due to the very high concentration of Hg in soil (798.2 ± 7.3 mg kg−1), growth inhibition was consistent regardless of treatment, demonstrated in the overload Reactive Oxygen Species scavenging mechanism and similar biomass yields. This leads to the conclusion that Hg may have greater impact on Calvin-Benson cycle associated enzymes than on the light-dependent photosynthesis phase. Despite these limitations this approach may still decrease environmental risks by reducing Hg emission to the atmosphere and reducing groundwater contamination.

Community succession in an anaerobic long-chain paraffin-degrading consortium and impact on chemical and electrical microbially influenced iron corrosion.

Community compositional changes and the corrosion of carbon steel in the presence of different electron donor and acceptor combinations were examined with a methanogenic consortium enriched for its ability to mineralize paraffins. Despite cultivation in the absence of sulfate, metagenomic analysis revealed the persistence of several sulfate-reducing bacterial taxa. Upon sulfate amendment, the consortium was able to couple C28H58 biodegradation with sulfate reduction. Comparative analysis suggested that Desulforhabdus and/or Desulfovibrio likely supplanted methanogens as syntrophic partners needed for C28H58 mineralization. Further enrichment in the absence of a paraffin revealed that the consortium could also utilize carbon steel as a source of electrons. The severity of both general and localized corrosion increased in the presence of sulfate, regardless of the electron donor utilized. With carbon steel as an electron donor, Desulfobulbus dominated in the consortium and electrons from iron accounted for ∼92% of that required for sulfate reduction. An isolated Desulfovibrio spp. was able to extract electrons from iron and accelerate corrosion. Thus, hydrogenotrophic partner microorganisms required for syntrophic paraffin metabolism can be readily substituted depending on the availability of an external electron acceptor and a single paraffin-degrading consortium harbored microbes capable of both chemical and electrical microbially influenced iron corrosion.

Elemental sulfur amendment enhance methylmercury accumulation in rice (Oryza sativa L.) grown in Hg mining polluted soil.

The influence of elemental sulfur (S(0)) amendment on methylmercury (MeHg) accumulation in rice and the chemical form of Hg in the rhizosphere were investigated under waterlogged conditions in Hg-contaminated soil (the majority of the Hg (˜70%) in forms similar to HgS). Different levels of S(0) addition increased the MeHg accumulation in rice. After a sequential extraction analysis of the chemical forms of Hg in the rhizosphere, the results showed that S(0) addition increased the organic bound Hg and decreased the residual Hg in the soils. An Hg LIII XANES further showed that S(0) addition increased the proportion of Hg in the form of RS-Hg-SR and decreased the proportion of Hg in the form of HgS, indicating that S(0) input may reactivate the non-bioavailable Hg in the rhizosphere and improve the net Hg methylation. These findings suggest that the application of S fertilizers to Hg-contaminated paddy soils may increase the MeHg concentration in the edible parts of crops, which may lead to more potential health problems in humans depending on the crop type. However, our study also suggests that S(0) addition could be an effective measure for mobilizing the insoluble Hg and accelerating the phytoremediation process in Hg-contaminated paddy soils.

Sulfur application combined with water management enhances phytoextraction rate and decreases rice cadmium uptake in a Sedum plumbizincicola - Oryza sativa rotation

Soil cadmium (Cd) contamination threatens food safety and human health. Increasing Cd phytoextraction efficiency by hyperaccumulators and growing safe products during remediation remain challenges. A pot experiment was conducted to explore the effects of different rates of sulfur (S) associated with alternating drying and wetting on a Sedum plumbizincicola-Oryza sativa rotation in Cd-contaminated neutral and calcareous soils. The oxidation of added S under aerobic conditions significantly decreased soil solution pH and increased soluble sulfate (SO42−), Cd and iron (Fe) concentrations in both soils. During the rice growing season the soil solution redox (Eh) decreased to < −200 mV and the solution pH increased to neutral during the first few days of flooding. Soluble SO42− and Cd in the S treatments decreased significantly with increasing duration of flooding. Sulfur addition promoted shoot Cd concentrations of S. plumbizincicola by 1.7–5.5 times on calcareous soil and 1.7–2.3 times on neutral soil compared to the controls. Rice yields increased but Cd concentrations decreased at suitable S addition rates. Appropriate sulfur amendment combined with water management can be a feasible strategy to enhance the Cd remediation efficiency of the hyperaccumulator and reduce the accumulation of Cd in the rice grains in this rotation.

Assessment of potential dietary toxicity and arsenic accumulation in two contrasting rice genotypes: Effect of soil amendments

High concentration of arsenic (As) in rice is a serious problem worldwide. Pot experiments were conducted to assess the potential dietary toxicity of arsenic and effect of various soil amendments on arsenic accumulation in rice grains. Two basmati rice genotypes were used to conduct pot experiments using various levels of arsenic (10, 25, 50 and 100 mg kg−1 soil). In addition, plants were exposed to soil collected from a well documented arsenic contaminated site. Contrasting results for growth, yield and grain arsenic concentration were obtained for basmati-385 (Bas-385), exhibiting tolerance (56% yield improvement at 10 mg As kg−1), while genotype BR-1 showed 18% yield decline under same conditions. Furthermore, application of soil amendments such as iron (Fe), phosphate (PO4) and farmyard manure (FYM) at 50 mg kg−1, 80 kg ha−1 and 10 t ha−1, respectively improved the plant height and biomass in both genotypes. Accumulation of arsenic in rice grain followed a linear trend in BR-1 whereas a parabolic relationship was observed in Bas-385. Both genotypes exhibited a positive response to iron sulfate amendment with significant reduction in grain arsenic concentrations. Regression analysis gave soil arsenic threshold values of 12 mg kg−1 in Bas-385 and 10 mg kg−1 in BR-1 for potential dietary toxicity. This study suggests that genotype Bas-385 can be used for safe rice production in areas with soil arsenic contamination up to 12 mg kg−1 and that appropriate dose of iron sulfate for soil amendment can be used effectively to reduce translocation of arsenic to rice grain.

Understanding Enhanced Microbial MeHg Production in Mining-Contaminated Paddy Soils under Sulfate Amendment: Changes in Hg Mobility or Microbial Methylators?

Elevated methylmercury (MeHg) production in mining-contaminated paddy soils, despite the high fraction of refractory HgS(s), has been frequently reported, while the underlying mechanisms are not fully understood. Here, we hypothesized that sulfate input, via fertilization, rainfall, and irrigation, is critical in mobilizing refractory HgS(s) and thus enhancing Hg methylation in mining-contaminated paddy soils. To test this hypothesis, the effects of sulfate amendment on Hg methylation and MeHg bioaccumulation in mining-contaminated soil-rice systems were examined. The results indicated 28-61% higher net MeHg production in soils under sulfate amendment (50-1000 mg kg-1), which in turn increased grain MeHg levels by 22-55%. The enhancement of Hg methylation by Hg mobilization in sulfate-amended soils was supported by two observations: (1) the increased Hg(aq) release from HgS(s), the dominant Hg species in the paddy soils, in the presence of sulfide produced following sulfate reduction and (2) the decreases of refractory HgS(s) in soils under sulfate amendment. By contrast, changes in the abundances/activities of potential microbial Hg methylators in different Hg-contaminated soils were not significant following sulfate amendment. Our results highlight the importance to consider enhanced Hg mobility and thus methylation in soils under sulfate amendment.

Comparative Genomics and Proteomic Analysis of Assimilatory Sulfate Reduction Pathways in Anaerobic Methanotrophic Archaea.

Sulfate is the predominant electron acceptor for anaerobic oxidation of methane (AOM) in marine sediments. This process is carried out by a syntrophic consortium of anaerobic methanotrophic archaea (ANME) and sulfate reducing bacteria (SRB) through an energy conservation mechanism that is still poorly understood. It was previously hypothesized that ANME alone could couple methane oxidation to dissimilatory sulfate reduction, but a genetic and biochemical basis for this proposal has not been identified. Using comparative genomic and phylogenetic analyses, we found the genetic capacity in ANME and related methanogenic archaea for sulfate reduction, including sulfate adenylyltransferase, APS kinase, APS/PAPS reductase and two different sulfite reductases. Based on characterized homologs and the lack of associated energy conserving complexes, the sulfate reduction pathways in ANME are likely used for assimilation but not dissimilation of sulfate. Environmental metaproteomic analysis confirmed the expression of 6 proteins in the sulfate assimilation pathway of ANME. The highest expressed proteins related to sulfate assimilation were two sulfite reductases, namely assimilatory-type low-molecular-weight sulfite reductase (alSir) and a divergent group of coenzyme F420-dependent sulfite reductase (Group II Fsr). In methane seep sediment microcosm experiments, however, sulfite and zero-valent sulfur amendments were inhibitory to ANME-2a/2c while growth in their syntrophic SRB partner was not observed. Combined with our genomic and metaproteomic results, the passage of sulfur species by ANME as metabolic intermediates for their SRB partners is unlikely. Instead, our findings point to a possible niche for ANME to assimilate inorganic sulfur compounds more oxidized than sulfide in anoxic marine environments.

Role of sulfate on the potential biodegradation of pentabromodiphenyl ether (BDE-99) in soil columns with reclaimed water and microbial community

During groundwater recharge with reclaimed water, pentabromodiphenyl ether (BDE-99) might contaminate the underground aquifers. In order to understand the effects of elevated sulfate concentrations on the biodegradation of BDE-99, lab-scale column experiments were performed to study the changes in bacterial and archaeal communities. The results confirmed that the biodegradation rate of BDE-99 improved significantly with the addition of sulfate. Oxygen was replaced by sulfate as the predominant electron acceptor, and the major biodebromination metabolites of BDE-99 were BDE-28 and BDE-47, respectively, The results from 454 pyrosequencing of 16s rRNA genes showed that the microbial community structure shifted toward communities with BDE-99 co-metabolism ability. At the bacterial genus level, Geothrix, Thiobacillus, Sphingomonas, Paenibacillus and Desulforhabdus were the five most abundant genera, wherein, Thiobacillus was able to treat the toxic products generated during polybrominated diphenyl ethers (PBDE) biodegradation. In the case of archaea at the genus level, Methanobrevibacter, Methanomethylovorans, DHVEG-6, Candidatus Nitrososphaera and Methanosphaera were the predominant groups, of which Methanobrevibacter and Methanosphaera showed good ability to metabolize BDE-99 with sulfate amendment.