Soluble soil Pb minimized by thermal transformation to Pb-bearing feldspar.

Thermal transformation is an effective remediation measure to stabilize soil Pb and other heavy metals via transformation into less soluble compounds. This study aimed to determine the solubility of Pb in soils subjected to heating at a range of temperatures (100-900 °C) in relation to the changes in Pb speciation using XAFS spectroscopy. Lead solubility in the contaminated soils after thermal treatment corresponded well to the chemical species of Pb present. As the temperature was increased to 300 °C, cerussite and Pb associated with humus started to decompose in the soils. As the temperature was further increased to 900 °C, the amount of water and HCl extractable Pb decreased significantly from the soils, whereas Pb-bearing feldspar started to occur, accounting for nearly 70% of the soil Pb. During thermal treatment, Pb species in the soils were little affected by Fe oxides that showed a significant phase transformation into hematite. Our study proposes the following underlying mechanisms for Pb immobilization in thermally treated soils: i) thermally labile Pb species such as PbCO3 and Pb associated with humus start to decompose at temperatures around 300 °C, ii) aluminosilicates with crystalline and poorly ordered structures undergo thermal decomposition at temperatures around 400 °C, iii) liberating Pb in the soil is then associated with a Si and Al rich liquid derived from thermally decomposed aluminosilicates at higher temperatures, and iv) the formation of Pb-feldspar like minerals is enhanced at 900 °C.

Temporal transformation of indium speciation in rice paddy soils and spatial distribution of indium in rice rhizosphere.

Indium is a potentially toxic element that could enter human food chains, including soil-rice systems. The submerged environment in rice paddy soil results in temporal and spatial variations in the chemical properties of the rice rhizosphere and bulk soils, expected to cause changes in indium's chemical speciation and consequently affect its bioavailability. Therefore, this study aimed to investigate indium speciation and fractionation in soils at different periods of rice growth under continuous submergence using X-ray absorption spectroscopy and a sequential extraction method. The predominant indium species were identified as indium-associated Fe hydroxide, and indium hydroxide and phosphate precipitates. The reductive dissolution of indium-associated Fe hydroxides led to the release of indium into the soil solution under continuous submergence of soils, and the released indium concentration decreased with time due to re-sorption and re-precipitation. Meanwhile, indium hydroxide was found to be the predominant species in rice rhizosphere using µ-X-ray absorption spectroscopy. The relative depletion of indium-associated Fe hydroxides in the rice rhizosphere was attributed to the low mobility of indium from bulk soil to rice rhizosphere and the root uptake of indium associated with Fe hydroxide around rice roots. Consequently, indium uptake by rice roots was lower during the reproductive and grain-ripening stage of rice growth. Understanding the behavior of indium will help develop a strategy to minimize uptake into crops in indium-contaminated paddy soils.

Characterization of trace elements in coal fly ash by extraction, micro-PIXE, TOF-SIMS, and XAFS.

Coal fly ash (CFA) contains considerable amounts of potentially hazardous trace elements. Characterization of trace elements in CFA is essential for the safe disposal and recycle of CFA. The objectives of this study were i) to determine and predict the solubility of trace elements in CFA in relation to their chemical and mineralogical properties, and ii) to characterize trace elements using the surface chemical analysis including time-of-flight secondary ion mass spectrometry (TOF-SIMS) and accelerator-based micro particle induced X-ray emission (PIXE) analysis, in combination with X-ray absorption fine structure (XAFS) spectroscopy with a primary focus on As and Cr. The CFA samples from 12 thermal power plants contained B (ave. 203 mg kg-1), F (90 mg kg-1), Cr (63 mg kg-1), As (21 mg kg-1), and Se (3.2 mg kg-1), in which the water soluble fraction relative to the total concentration decreased in the order B (24 %) > Se (23 %) > F (20 %) > As (1.7 %) > Cr(IV) (0.71 %). A regression model indicated that water extractable As and Cr(VI) from CFA increased linearly with increasing SiO2 and CaO in CFA, respectively. The SIMS images showed that B was finely and heterogeneously distributed on CFA, whereas F was distributed homogeneously on CFA. The combined results from micro-PIXE and XAFS revealed that i) As was distributed on about 50-µm particles in the form of As(V) associated with Al and Ca, and ii) Cr was co-located with Fe and Ca on about 50-µm particles and was present as Cr(III). This study demonstrated that the combined results from TOF-SIMS, micro-PIXE, and XAFS techniques enable trace elements in CFA to be better characterized in terms of spatial distribution and chemical speciation.

Zero valent iron or Fe3O4-loaded biochar for remediation of Pb contaminated sandy soil: Sequential extraction, magnetic separation, XAFS and ryegrass growth.

In this study, the feasibility of using zero-valent iron (ZVI) and Fe3O4-loaded biochar for Pb immobilization in contaminated sandy soil was investigated. A 180-day incubation study, combined with dry magnetic separation, chemical extraction, mineralogical characterization, and model plant (ryegrass, namely the Lilium perenne L.) growth experiment was conducted to verify the performance of these two materials. The results showed that both amendments significantly transferred the available Pb (the exchangeable and carbonates fraction) into more stable fractions (mainly Fe/Mn oxides-bound Pb), and ZVI alone showed a better performance than the magnetic biochar alone. The magnetic separation and extended X-ray absorption fine structure (EXAFS) analysis proved that Fe (oxyhydr)oxides on aged ZVI particles were the major scavengers of Pb in ZVI-amended soils. In comparison, the reduced Pb availability in magnetic biochar-amended soil could be explained by the association of Pb with Fe/Mn (oxyhydr)oxides in aged magnetic biochar, also the possible precipitation of soil Pb with soluble anions (e.g. OH-, PO43-, and SO42-) released from magnetic biochar. ZVI increased ryegrass production while Fe3O4-loaded biochar had a negative effect on the ryegrass growth. Moreover, both markedly decreased the Pb accumulation in aboveground and root tissues. The simple dry magnetic separation presents opportunities for the removal of Pb from soils, even though the efficiencies were not high (17.5% and 12.9% of total Pb from ZVI and biochar-treated soils, respectively). However, it should be noted that the ageing process easily result in the loss of magnetism of ZVI while the magnetic biochar tends to be more stable and has high retrievability during the dry magnetic separation application.

Ruptured Hepatic Hemangioma in the Third Trimester of Pregnancy: A Rare Case Report.

Hepatic hemangiomas are considered the most common benign mesenchymal hepatic tumors. Most cases are asymptomatic. However, giant hemangiomas can present with a variety of clinical presentations, with a rupture being the most catastrophic outcome. Only a few cases of ruptured perinatal hepatic hemangiomas have been reported. Accelerated growth of hepatic hemangiomas caused by increased estrogen in pregnancy, increased intra-abdominal pressure, and direct contact with a gravid uterus are possible mechanisms for increased risk of rupture during pregnancy. The safety of either non-operative or surgical treatment of symptomatic giant hemangioma during pregnancy has not been adequately investigated. We present a rare case of a 28-year-old G1P0 female at 33 weeks gestation that presented with a ruptured hepatic hemangioma treated with damage control surgery followed by nonanatomic surgical resection.

A remediation approach to chromium-contaminated water and soil using engineered biochar derived from peanut shell.

Hexavalent chromium (Cr[VI]) is one of the major environmental concerns due to its excessive discharge through effluents from the leather tanning industry. Peanut production leads to the generation of residual shells as waste calling for sustainable disposal. In this study, we employed an innovative approach of applying peanut-shell-derived pristine and engineered biochar for the remediation of Cr-contaminated wastewater and soil. The peanut shell waste was converted to biochar, which was further engineered with cetyltrimethylammonium bromide (CTAB, a commonly used cationic surfactant). The biochars were then used for the adsorption and immobilization of Cr(VI) in water and soil, respectively. The adsorption experiments demonstrated high Cr(VI) removal efficiency for the engineered biochar (79.35%) compared with the pristine biochar (37.47%). The Langmuir model best described the Cr(VI) adsorption onto the biochars (R2 > 0.97), indicating monolayer adsorption. Meanwhile, the adsorption kinetics indicated that chemisorption was the dominant mechanism of interaction between the Cr(VI) and the biochars, as indicated by the best fitting to the pseudo-second-order model (R2 > 0.98). Adsorption through the fixed-bed column also presented higher Cr(VI) adsorption onto the engineered biochar (qeq = 22.93 mg g-1) than onto the pristine biochar (qeq = 18.54 mg g-1). In addition, the desorption rate was higher for the pristine biochar column (13.83 mg g-1) than the engineered biochar column (10.45 mg g-1), indicating that Cr(VI) was more strongly adsorbed onto the engineered biochar. A higher immobilization of Cr(VI) was observed in the soil with the engineered biochar than with the pristine biochar, as was confirmed by the significant decreases in the Cr(VI) bioavailability (92%), leachability (100%), and bioaccessibility (97%) compared with the control (soil without biochar). The CTAB-engineered biochar could thus potentially be used as an efficient adsorbent for the removal and the immobilization of Cr(VI) in water and soil, respectively.

Fe(III) loaded chitosan-biochar composite fibers for the removal of phosphate from water.

Excess phosphorous (P) in aquatic systems causes adverse environmental impacts including eutrophication. This study fabricated Fe(III) loaded chitosan-biochar composite fibers (FBC-N and FBC-C) from paper mill sludge biochar produced under N2 (BC-N) and CO2 (BC-C) conditions at 600 °C for adsorptive removal of phosphate from water. Investigations using SEM/EDX, XPS, Raman spectroscopy, and specific surface area measurement revealed the morphological and physico-chemical characteristics of the adsorbent. The Freundlich isotherm model well described the phosphate adsorption on BC-N, while the Redlich-Peterson model best fitted the data of three other adsorbents. The maximum adsorption capacities were 9.63, 8.56, 16.43, and 19.24 mg P g-1 for BC-N, BC-C, FBC-N, and FBC-C, respectively, indicating better adsorption by Fe(III) loaded chitosan-biochar composite fibers (FBCs) than pristine biochars. The pseudo-first-order kinetic model suitably explained the phosphate adsorption on BC-C and BC-N, while data of FBC-N and FBC-C followed the pseudo-second-order and Elovich model, respectively. Molecular level observations of the P K-edge XANES spectra confirmed that phosphate associated with iron (Fe) minerals (Fe-P) were the primary species in all the adsorbents. This study suggests that FBCs hold high potential as inexpensive and green adsorbents for remediating phosphate in contaminated water, and encourage resource recovery via bio-based management of hazardous waste.

Arsenic immobilization and removal in contaminated soil using zero-valent iron or magnetic biochar amendment followed by dry magnetic separation.

The potential of using zero-valent iron (ZVI) or a Fe3O4-loaded magnetic biochar to stabilize arsenic (As) in contaminated soil was investigated in the processes of incubation trial, chemical extraction, pot experiments with ryegrass growth. Additionally, a dry magnetic separation technique was applied to verify the possible permanent removal of As from the bulk soil. Results showed the ZVI amendment greatly reduced the As leaching, and the leached concentration became much lower than the Japanese environment standard (10 µg/L) after 180 days of incubation. Contrarily, the magnetic biochar amendment readily increased the As leachability due to the changes in pH, dissolved organic carbon, and soluble P and Si. The ZVI had a greater effect over the magnetic biochar, supported by the significantly reduced As leachability in the combined amendments. Furthermore, results from sequential extraction analysis indicate that both amendments significantly decreased the available As in (NH4)2SO4 and NH4H2PO4 extraction and increased the As bound to amorphous Fe oxides. But ZVI amendment alone performed better than magnetic biochar amendment alone. Plant growth experiment showed that the ZVI amendment enhanced ryegrass growth and significantly increased the ryegrass biomass. However, the magnetic biochar amendment resulted in an adverse effect on the ryegrass root growth, probably due to a marked enhancement of salinity. Meanwhile, the As uptake by ryegrass was significantly reduced in both ZVI and magnetic biochar-amended soils. Results of dry magnetic separation showed that averaged 20% and 25% of total As could be retrieved from ZVI and magnetic biochar amended soil, respectively; and the As bound to amorphous Fe oxides was the main retrieved fraction. This study indicated that ZVI or magnetic biochar could be applied as a promising amendment for reducing (phyto)availability of As in soil, and dry magnetic separation could be served as an alternative option for permanently removing As.

Reducing geogenic arsenic leaching from excavated sedimentary soil using zero-valent iron amendment followed by dry magnetic separation: A case study.

Although the deep-layer sedimentary soils excavated from construction sites contain low level of geogenic arsenic (As), remediation is necessary when the As leachability exceeds the environmental standard (10 µg/L) in Japan. In this study, the zero-valent iron (ZVI) amendment followed by dry magnetic separation (ZVI-DMS) was implemented for the treatment of a geogenic As-contaminated alkaline sedimentary soil (pH 8.9; 7.5 mg/kg of total As; 0.33 mg/kg of water-extractable As). This technology involves pH adjustment (adding H2SO4), ZVI addition, water content reduction (adding water adsorbent CaSO4·0.5H2O), and dry magnetic separation. The short-term and long-term As leachability before and after treatment was compared using sequential water leaching tests (SWLT). The results illustrated that As could be removed from the bulk soil through the magnetic separation of As-ZVI complexes, although the amount was limited (about 2% of total As). Moreover, immobilization played a dominant role in suppressing As leaching. The H2SO4 addition decreased pH to a circumneutral range and thereby suppress As release. The CaSO4·0.5H2O addition also contributed to the pH decrease and reduced As leachability. Besides, CaSO4·0.5H2O-dissolution released Ca2+ that favored As adsorption, and enhanced dissolved organic carbon (DOC) coagulation that decelerated As dissolution. SWLT results indicated that As leachability from remediated soil satisfied the environmental standard (10 µg/L) in both short-term and long-term perspective. However, the secular stability of treated soil deserves more attention due to the easy re-release of As caused by As-bearing framboidal pyrite oxidation. Additionally, during ZVI-DMS process, there is a need to scientifically decide the dosage of ZVI to avoid excessive addition. Our results demonstrated that ZVI-DMS technology could be a promising remediation strategy for geogenic As contaminated sedimentary soils/rocks.

Evaluating vanadium bioavailability to cabbage in rural soils using geochemical and micro-spectroscopic techniques.

Assessing the vanadium (V) fractionation and speciation to predict its bioavailability using a combined approach of geochemical extractions and micro-spectroscopic techniques is still not well studied. Therefore, we aimed to determine the bioavailability of V in rural soils using single extractants, sequential extraction procedure, and the X-ray absorption near edge structure (XANES) spectroscopy. We collected and characterized ninety four samples originated from horizons of seventeen soil profiles in Taiwan. We determined the total content of V and its geochemical fractions using the BCR sequential extraction procedure to predict its potential mobility. We also assessed the bioavailability of V in the soils using four availability indices i.e., CaCl2, HCl, ethylenediaminetetraacetic acid (EDTA), and NaHCO3 and related them to its uptake by Chinese cabbage (Brassica chinensis L.). Additionally, we determined the V speciation by vanadium K-edge XANES spectra. Moreover, we studied the elemental compositions of the soils using Electron Probe Micro Analysis (EPMA). Vanadium was mainly distributed in the residual fraction (81-98% of total V). Among the potential mobile fractions, V was mainly associated with Fe oxides, as identified by the BCR sequential extraction and EMPA. The XANES analysis indicated that V mainly existed in the soils as V(IV) and V(V). The EDTA and NaHCO3 extracted more V than CaCl2 and HCl, and both, particularly NaHCO3 were positively and significantly correlated with the total soil content and plant shoot concentrations of V; therefore NaHCO3 might be recommended as a bioavailability index for soil V. We hypothesize that the NaHCO3 may extract vanadate from soil surfaces and also vanadate transformed from vanadyl at alkaline pH during the extraction. The NaHCO3-extracted V can be predicted by a function of soil total V, CEC, and pH. Our results should be verified using different soils and plants in the future.

Assessment of indium toxicity to the model plant Arabidopsis.

The use of indium in semiconductor products has increased markedly in recent years. The release of indium into the ecosystem is inevitable. Under such circumstances, effective and accurate assessment of indium risk is important. An indispensable aspect of indium risk assessment is to understand the interactions of indium with plants, which are fundamental components of all ecosystems. Physiological responses of Arabidopsis thaliana exposed to indium were investigated by monitoring toxic effects, accumulation and speciation of indium in the plant. Indium can be taken up by plants and is accumulated mainly in roots. Limited indium root-to-shoot translocation occurs because of immobilization of indium in the root intercellular space and blockage of indium by the Casparian band in the endodermis. Indium caused stunted growth, oxidative stress, anthocyanization and unbalanced phosphorus nutrition. Indium jeopardizes phosphate uptake and translocation by inhibiting the accumulation of phosphate transporters PHOSPHATE TRANSPORTER1 (PHT1;1/4), responsible for phosphate uptake, and PHOSPHATE1 (PHO1), responsible for phosphate xylem loading. Organic acid secretion is stimulated by indium exposure. Secreted citrate could function as a potential detoxifier to lower indium uptake. Our findings provide insights into the potential fate and effects of indium in plants and will aid the evaluation of risks with indium contamination.

Boron incorporation into precipitated calcium carbonates affected by aqueous pH and boron concentration.

The objectives of this study were to investigate the amount of B incorporation into precipitated calcium carbonate (PCC) in the coprecipitation process, and to determine specific mineral phases (calcite or vaterite) and the mode of B coordination (trigonal or tetrahedral) in PCC under different pH and B concentrations. The amount of B incorporation into PCC increased in general with increasing aqueous B (Baq) concentrations in the pH range from 8 to 12. The B removal by PCC reached maximum (∼200 mmol kg-1) at pH 10 with Baq concentrations between 30 and 50 mM. The transformation of vaterite to calcite was promoted with increasing Baq at pH 8 and 10, whereas an excess concentration of aqueous (poly)borate anions (100 mM) inhibited crystal growth of calcite. As determined by B K-edge X-ray absorption fine structure spectroscopy, the coordination of B incorporated in PCC was preferentially tetrahedral (IVB, 55-70%) over trigonal (IIIB, 30-45%) at Baq <75 mM. In contrast, the preferential incorporation of IVB into PCC was not observed in the solution with a high B concentration (i.e., 100 mM). The amount of B incorporation, the morphology of PCC and B coordination in PCC were remarkably changed in high Baq concentrations.

Evolution of As speciation with depth in a soil profile with a geothermal As origin.

High contents of arsenic were detected in soils in Guandu plain, northwest Taiwan. To determine the sources and speciation of As in the soils, the depth profiles of soil properties, elemental composition and As speciation were investigated. The As concentrations in the soil profile ranged from 152 to 1222 mg kg-1, with the highest concentration at the depth of 70-80 cm. The As distribution was found to be positively correlated to Fe, Pb, and Ba. The As(V)-adsorbed ferrihydrite and scorodite were the predominant phases in the top layers (<50 cm), while beudantite was the predominant phase below 50 cm along with As(III)- and As(V)-adsorbed ferrihydrite as the minor components. The results of sequential extraction showed that As-associated with noncrystalline and crystalline Fe/Al hydrous oxides and residual phases were predominant at the depths of 0-60, 60-100 and 100-140 cm, respectively, indicating an increasing As recalcitrance with soil depth. Based on the soil properties, and elemental and mineral compositions at different soil depths, the origin of beudantite in the soils was likely allogenic rather than authigenic or anthropogenic. The formation of scorodite in the surface soils was suggested to be transformed from beudantite. As-associated Fe hydrous oxides may be contributed by the progressive dissolution of beudantite and scorodite, and the continuous influxes of As and Fe. While Fe hydrous oxides were able to immobilize As during the dissolution of As-bearing minerals, the increase of As mobility in soils may imply an increase in the environmental risk of As over time.

Soil amendments for immobilization of potentially toxic elements in contaminated soils: A critical review.

Soil contamination by potentially toxic elements (PTEs) has led to adverse environmental impacts. In this review, we discussed remediation of PTEs contaminated soils through immobilization techniques using different soil amendments with respect to type of element, soil, and amendment, immobilization efficiency, underlying mechanisms, and field applicability. Soil amendments such as manure, compost, biochar, clay minerals, phosphate compounds, coal fly ash, and liming materials are widely used as immobilizing agents for PTEs. Among these soil amendments, biochar has attracted increased interest over the past few years because of its promising surface properties. Integrated application of appropriate amendments is also recommended to maximize their use efficiency. These amendments can reduce PTE bioavailability in soils through diverse mechanisms such as precipitation, complexation, redox reactions, ion exchange, and electrostatic interaction. However, soil properties such as soil pH, and clay, sesquioxides and organic matter content, and processes, such as sorption/desorption and redox processes, are the key factors governing the amendments' efficacy for PTEs immobilization in soils. Selecting proper immobilizing agents can yield cost-effective remediation techniques and fulfill green and sustainable remediation principles. Furthermore, long-term stability of immobilized PTE compounds and the environmental impacts and cost effectiveness of the amendments should be considered before application.

Effects of long-term paddy rice cultivation on soil arsenic speciation.

Geochemical behavior of arsenic (As) in rice paddy soils determines the availability and mobility of As in the soils, but little is known about the long-term effects of paddy rice cultivation on As speciation in the soils. In this study, surface soil samples were collected from a rice paddy land and its adjacent dry land with similar soil properties and known cultivation histories. The soils of the paddy land and dry land contained 378 and 423 mg As kg-1, respectively. The predominant As species in the soils were investigated using As K-edge X-ray absorption spectroscopy (XAS) in combination with two sequential chemical fractionation methods. The XAS results showed that the predominant As species in the soils were As(III)- and As(V)-ferrihydrite, As(V)-goethite and scorodite. In comparison to the dry land soil, the paddy land soil contained a higher proportion of As(V)-ferrihydrite and a lower proportion of scorodite. The results of chemical fractionation revealed that As in the paddy land soil was more labile than that in the dry land soil. It is therefore suggested that long-term rice cultivation enhances the mobility and availability of As in paddy soils.

Speciation and Fractionation of Soil Arsenic from Natural and Anthropogenic Sources: Chemical Extraction, Scanning Electron Microscopy, and Micro-XRF/XAFS Investigation.

A large amount of excavated soils with low-level As contamination caused by civil construction projects is of great concern in Japan. This study investigated the chemical speciation and extractability of As in 24 soil samples from the sites affected and unaffected (naturally contaminated) by anthropogenic pollution. The results of As K-edge XANES demonstrated that naturally contaminated soils were grouped into two types: (i) soils containing FeAsS-like and As2S3-like species (ave. 53%, hereafter As-S species) and (ii) soils with no or minor As-S species (ave. 3%). Clear differences were found in As, Fe, and S fractionations by sequential extraction. From naturally contaminated soils enriched with As-S species, more than 50% of As was extracted in the oxidizable fraction. Arsenic was mainly recovered in the reducible fraction for naturally contaminated soils with no or minor As-S species and anthropogenically contaminated soils. The µ-XRF and µ-XAFS revealed that the naturally contaminated soils containing As-S species were abundant in pyrite framboids (∼20 µm in diameter) in which As occurred as multiple oxidation states. The results suggest that framboidal pyrite becomes a source of As in naturally contaminated soils after being excavated and exposed to the surface environment.

Copper and zinc in vineyard and orchard soils at millimeter vertical resolution.

Intensive uses of agrochemicals and soil amendments often cause the elevation of Cu and Zn concentrations in vineyard (VY) and orchard soils. The concentration and speciation of Cu and Zn in the soils at millimeter resolution is critical to understanding the risk of transport of these metals via surface runoff and infiltration. The objective of this study was to investigate the concentration and chemical species of Zn and Cu in VY and persimmon (PS) soils at millimeter vertical resolution. The soils were collected with 5 mm increments down to 5 cm depth and with 5 cm increments down to 25 cm depth. The total concentration and chemical species of Zn and Cu were determined by total digestion and X-ray absorption fine structure (XAFS) spectroscopy, respectively. The Zn concentration of VY soil reached a maximum of 290 mg kg-1 at the uppermost layer of the profile (0.5-1.0 cm). The Cu concentration of VY soil reached a maximum of 201 mg kg-1 (10-15 cm). These Zn and Cu concentrations were greater than background levels. Zinc K-edge XAFS spectroscopy determined that the uppermost layer of VY soil (0-0.5 cm) contained 42% Zn associated with humus and lesser extent of Zn associated with gibbsite (37%) and kaolinite (21%). Zinc associated with humus was not observed in the VY soil profiles below 0.5 cm, whereas Zn associated with gibbsite and kaolinite contributed >83% of total Zn species. Copper K-edge XAFS spectroscopy determined the presence of Cu bonded with humus (40-67%) and Cu adsorbed on kaolinite (26-45%) in the entire soil profile. Our study found the remarkable variation of Cu and Zn concentration and speciation within several centimeters from the soil surface in vineyard and orchard landscapes.

Speciation of Phosphorus Zinc and Copper in Soil and Water-Dispersible Colloid Affected by a Long-Term Application of Swine Manure Compost.

The objective of this study was to investigate the concentration and chemical species of Zn, Cu, and P in the bulk soil and water-dispersible colloid (WDC) fraction collected from a field where swine manure (SM) compost has been continually applied for 23 years. A filtration and ultracentrifugation process was used to separate and collect WDC (20-1000 nm) from the soil. The continual application of SM increased soil P from 1.6 to 4.5 g kg-1, Zn from 109 to 224 mg kg-1, and Cu from 87 to 95 mg kg-1 for 23 years. The continual SM compost application also enhanced the formation of soil WDC in which Zn (215 mg kg-1) and Cu (62 mg kg-1) were highly accumulated and P (25 g kg-1) was greater than in the bulk soil. According to the result of X-ray absorption spectroscopy (XAS), the continual application of SM compost increased P associated with Fe hydroxides in the soil and WDC fraction. Iron K-edge XAS revealed the dominance of goethite and ferrihydrite in the WDC fraction, suggesting that P was bound to these (oxy)hydroxides. Copper K-edge XAS determined the dominance of Cu(II) associated with humus in the soil and WDC fraction. For Zn species in the SM-compost-applied soil, hopeite and Zn associated with humus were accumulated in the bulk soil, whereas Zn associated with humus was the primary species in the WDC fraction. Our study suggests that the formation of organic complexes in the WDC fraction could enhance the mobility of Zn and Cu as the repeated application of SM compost continues.

Functional Expression and Characterization of Tetrachloroethene Dehalogenase From Geobacter sp.

Reductive dehalogenase (RDase) consists of two parts, RdhA and RdhB. RdhA is the catalytic subunit, harboring a cobalamin cofactor and two Fe-S clusters. RdhA is anchored to the cytoplasmic membrane via the membrane anchoring subunit, RdhB. There are many genes encoding RDases in the genome of organohalide-respiring bacteria, including Dehalococcoides spp. However, most genes have not been functionally characterized. Biochemical studies on RDases have been hampered by difficulties encountered in their expression and purification. In this study, we have expressed, purified and characterized RdhA of RDase for tetrachloroethene (PceA) from Geobacter sp. PceA was expressed as a fusion protein with a trigger factor tag in Escherichia coli. PceA was purified and denatured in aerobic condition. Subsequently, this protein was refolded in the presence of FeCl3, Na2S and cobalamin in anaerobic condition. The reconstituted PceA exhibited dechlorination ability for tetrachloroethene. UV-Vis spectroscopy has shown that it contains cobalamin and Fe-S clusters. Since this method requires anaerobic manipulation only in the reconstituting process and has a relatively high yield, it will enable further biochemical studies of RDases.

Redox changes in speciation and solubility of arsenic in paddy soils as affected by sulfur concentrations.

A substantial amount of sulfate is often supplied in paddy fields with concomitant applications of chemical fertilizers and manure for rice growth. It is unclear how solubility and speciation of arsenic (As) are affected by the levels of soil sulfate and their relationship to soil redox status and sulfur (S) and iron (Fe) speciation in a short cycle of soil reducing (flooding) and oxidizing (drying) periods. The objective of this study was to investigate the solubility of As in relation to chemical speciation of As and S in different levels of soil sulfate through a time series of measurements during a 40-day reduction period (Eh < -130 mV) followed by a 32-day reoxidation period (Eh > 400 mV) using X-ray absorption fine structure (XAFS) spectroscopy. An excess of sulfate decreased extractable and dissolved As in the soil reducing period due to retardation of soil reduction process that decreased soluble As(III) in the soil solid phase. The As species at the end of soil reducing period were 38-41% As(V), 46-51% As(III), and 11-13% As2S3-like species, regardless of initial S treatments. In the following soil reoxidation, As2S3-like species were sensitive to oxidation and disappeared completely in the first 2 days when the Eh value increased rapidly above 160 mV. The addition of extra sulfate to the soil did not result in the formation of neither reduced S species nor As2S3-like species. About 50% of As(III) to the total As persisted over 32 days of soil reoxidation period (Eh > 400 mV), suggesting some mechanisms against oxidation of As(III) such as physical sequestration in soil microsites. This study demonstrates that the extra SO4 in paddy soils can help mitigate the dissolution of As in reduction and reoxidation periods.