Publications by authors named "Yohey Hashimoto"

37 Publications

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

J Hazard Mater 2021 08 19;415:125464. Epub 2021 Feb 19.

Korea Biochar Research Center, APRU Sustainable Waste Management Program & Division of Environmental Science and Ecological Engineering, Korea University, Seoul 02841, Republic of Korea. Electronic address:

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 N (BC-N) and CO (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 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.
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http://dx.doi.org/10.1016/j.jhazmat.2021.125464DOI Listing
August 2021

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

Sci Total Environ 2021 May 7;768:144521. Epub 2021 Jan 7.

Department of Chemical Engineering, Tokyo University of Agriculture and Technology, Koganei, Tokyo 184-8588, Japan.

The potential of using zero-valent iron (ZVI) or a FeO-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 (NH)SO and NHHPO 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.
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http://dx.doi.org/10.1016/j.scitotenv.2020.144521DOI Listing
May 2021

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

Sci Total Environ 2020 Jul 24;724:138203. Epub 2020 Mar 24.

Department of Chemical Engineering, Tokyo University of Agriculture and Technology, 2-24-16 Naka, Koganei, Tokyo 184-8588, Japan.

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 HSO), ZVI addition, water content reduction (adding water adsorbent CaSO·0.5HO), 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 HSO addition decreased pH to a circumneutral range and thereby suppress As release. The CaSO·0.5HO addition also contributed to the pH decrease and reduced As leachability. Besides, CaSO·0.5HO-dissolution released Ca 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.
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http://dx.doi.org/10.1016/j.scitotenv.2020.138203DOI Listing
July 2020

Assessment of indium toxicity to the model plant Arabidopsis.

J Hazard Mater 2020 04 26;387:121983. Epub 2019 Dec 26.

Agricultural Biotechnology Research Center, Academia Sinica, Taipei 11529, Taiwan, ROC. Electronic address:

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.
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http://dx.doi.org/10.1016/j.jhazmat.2019.121983DOI Listing
April 2020

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

Environ Pollut 2020 Mar 2;258:113699. Epub 2019 Dec 2.

Department of Agricultural Chemistry, National Taiwan University, Taipei 10617, Taiwan. Electronic address:

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., CaCl, HCl, ethylenediaminetetraacetic acid (EDTA), and NaHCO 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 NaHCO extracted more V than CaCl and HCl, and both, particularly NaHCO were positively and significantly correlated with the total soil content and plant shoot concentrations of V; therefore NaHCO might be recommended as a bioavailability index for soil V. We hypothesize that the NaHCO may extract vanadate from soil surfaces and also vanadate transformed from vanadyl at alkaline pH during the extraction. The NaHCO-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.
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http://dx.doi.org/10.1016/j.envpol.2019.113699DOI Listing
March 2020

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

Environ Int 2020 01 12;134:105046. Epub 2019 Nov 12.

Korea Biochar Research Center, O-Jeong Eco-Resilience Institute (OJERI), Division of Environmental Science and Ecological Engineering, Korea University, Seoul, Republic of Korea. Electronic address:

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.
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http://dx.doi.org/10.1016/j.envint.2019.105046DOI Listing
January 2020

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

Environ Sci Technol 2019 12 2;53(24):14186-14193. Epub 2019 Dec 2.

Research Institute for Geo-Resources and Environment , National Institute of Advanced Industrial Science and Technology , Tsukuba , Ibaraki 305-8567 , Japan.

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 AsS-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.
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http://dx.doi.org/10.1021/acs.est.9b03864DOI Listing
December 2019

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

J Environ Manage 2020 Jan 4;254:109768. Epub 2019 Nov 4.

Department of Agricultural Chemistry, National Taiwan University, Taipei, 10617, Taiwan. Electronic address:

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, 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.
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http://dx.doi.org/10.1016/j.jenvman.2019.109768DOI Listing
January 2020

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

J Hazard Mater 2020 02 8;383:121183. Epub 2019 Sep 8.

Department of Agricultural Chemistry, National Taiwan University, No. 1, Section 4, Roosevelt Rd, Da'an District, Taipei 10617, Taiwan.

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 (B) concentrations in the pH range from 8 to 12. The B removal by PCC reached maximum (∼200 mmol kg) at pH 10 with B concentrations between 30 and 50 mM. The transformation of vaterite to calcite was promoted with increasing B 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 (B, 55-70%) over trigonal (B, 30-45%) at B <75 mM. In contrast, the preferential incorporation of B 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 B concentrations.
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http://dx.doi.org/10.1016/j.jhazmat.2019.121183DOI Listing
February 2020

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

Chemosphere 2020 Feb 24;241:124956. Epub 2019 Sep 24.

Department of Agricultural Chemistry, National Taiwan University, Taipei, 10617, Taiwan. Electronic address:

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, 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.
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http://dx.doi.org/10.1016/j.chemosphere.2019.124956DOI Listing
February 2020

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

Sci Total Environ 2019 Nov 29;689:958-962. Epub 2019 Jun 29.

Faculty of Agriculture, Tokyo University of Agriculture and Technology, 3-5-8 Saiwaicho, Fuchu, Tokyo 1838509, Japan.

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 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 (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.
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http://dx.doi.org/10.1016/j.scitotenv.2019.06.486DOI Listing
November 2019

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

Environ Sci Technol 2018 11 29;52(22):13270-13278. Epub 2018 Oct 29.

Bioapplications and Systems Engineering , Tokyo University of Agriculture and Technology , 2-24-16 Koganei , Tokyo 184-8588 , Japan.

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, Zn from 109 to 224 mg kg, and Cu from 87 to 95 mg kg for 23 years. The continual SM compost application also enhanced the formation of soil WDC in which Zn (215 mg kg) and Cu (62 mg kg) were highly accumulated and P (25 g kg) 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.
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http://dx.doi.org/10.1021/acs.est.8b02823DOI Listing
November 2018

Functional Expression and Characterization of Tetrachloroethene Dehalogenase From sp.

Front Microbiol 2018 10;9:1774. Epub 2018 Aug 10.

Department of Biotechnology and Life Science, Tokyo University of Agriculture and Technology, Tokyo, Japan.

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 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 sp. PceA was expressed as a fusion protein with a trigger factor tag in . PceA was purified and denatured in aerobic condition. Subsequently, this protein was refolded in the presence of FeCl, NaS 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.
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http://dx.doi.org/10.3389/fmicb.2018.01774DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6095959PMC
August 2018

Investigations of water-extractability of As in excavated urban soils using sequential leaching tests: Effect of testing parameters.

J Environ Manage 2018 Jul 5;217:297-304. Epub 2018 Apr 5.

Department of Chemical Engineering, Tokyo University of Agriculture and Technology, 2-24-16 Naka, Koganei, Tokyo 184-8588, Japan. Electronic address:

Excavated soils with low-level As contamination obtained from construction projects during city development have been of great concern in Japan. Water-extractable As represents the most easily mobilized and ecotoxicologically relevant fraction in the soil environment. In the present study, the water-extractability of As in excavated alkaline urban soils was assessed using sequential leaching tests (SLTs) with a focus on the effects of test parameters. In addition, the potentially water-leachable As over an extremely long period was assessed using the pollution potential leaching index (PPLI), from which one can estimate the number of extractions required to reduce the As in the cumulative leachates to below the Japanese environmental standard (10 μg L). Total As concentrations varied from 6.75 to 79.4 mg kg, and As was continuously detectable among replicate SLT experiments. The water-extractable As obtained in the first step of the SLT accounted for 0.41%-7.60% of total As (average: 2.36%), while the cumulative released As in the SLTs corresponded to 1.30%-21.6% of the total (average: 10.6%). The variability of the water-soluble fractions was sensitive to the test conditions. The shaking time at each SLT step had the largest effect on the As water-extractability; followed by sample storage, shaking speed and shaking interruption. A longer shaking time in the standard leaching test of excavated soils is suggested for regulatory purposes in Japan. The use of the PPLI concept for quick estimation of the potential As leachability from excavated soils was supported by the good reproducibility of PPLI results obtained from SLTs under different test parameters.
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http://dx.doi.org/10.1016/j.jenvman.2018.03.105DOI Listing
July 2018

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

Environ Pollut 2018 Jul 31;238:617-623. Epub 2018 Mar 31.

Tokyo University of Agriculture and Technology, Japan.

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% AsS-like species, regardless of initial S treatments. In the following soil reoxidation, AsS-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 AsS-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 SO in paddy soils can help mitigate the dissolution of As in reduction and reoxidation periods.
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http://dx.doi.org/10.1016/j.envpol.2018.03.039DOI Listing
July 2018

Stabilization of arsenic and lead by magnesium oxide (MgO) in different seawater concentrations.

Environ Pollut 2018 Feb 6;233:952-959. Epub 2017 Nov 6.

Korea Biochar Research Center, O-Jeong Eco-Resilience Institute (OJERI) & Division of Environmental Science and Ecological Engineering, Korea University, Republic of Korea.

Ongoing sea level rise will have a major impact on mobility and migration of contaminants by changing a number of natural phenomena that alter geochemistry and hydrology of subsurface environment. In-situ immobilization techniques may be a promising remediation strategy for mitigating contaminant mobility induced by sea level rise. This study investigated the reaction mechanisms of magnesium oxide (MgO) with aqueous Pb and As under freshwater and seawater using XAFS spectroscopy. Initial concentrations of Pb and As in freshwater strongly controlled the characteristics of the reaction product of MgO. Our study revealed that i) the removal of aqueous Pb and As by MgO was increased by the elevation of seawater concentration, and ii) the removal of As was attributed primarily to (inner-sphere) surface adsorption on MgO, independent on seawater concentrations, and iii) the retention mechanism of Pb was dependent on seawater concentrations where formations of Pb oxides and adsorption on the MgO surface were predominant in solutions with low and high salinity, respectively. The release of As fixed with MgO significantly increased in seawater compared to freshwater, although the amount of As desorbed accounted for <0.2% of total As.
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http://dx.doi.org/10.1016/j.envpol.2017.09.067DOI Listing
February 2018

Pollution potential leaching index as a tool to assess water leaching risk of arsenic in excavated urban soils.

Ecotoxicol Environ Saf 2018 Jan 14;147:72-79. Epub 2017 Sep 14.

Department of Chemical Engineering, Tokyo University of Agriculture and Technology, 2-24-16 Naka, Koganei, Tokyo 184-8588, Japan. Electronic address:

Leaching of hazardous trace elements from excavated urban soils during construction of cities has received considerable attention in recent years in Japan. A new concept, the pollution potential leaching index (PPLI), was applied to assess the risk of arsenic (As) leaching from excavated soils. Sequential leaching tests (SLT) with two liquid-to-solid (L/S) ratios (10 and 20Lkg) were conducted to determine the PPLI values, which represent the critical cumulative L/S ratios at which the average As concentrations in the cumulative leachates are reduced to critical values (10 or 5µgL). Two models (a logarithmic function model and an empirical two-site first-order leaching model) were compared to estimate the PPLI values. The fractionations of As before and after SLT were extracted according to a five-step sequential extraction procedure. Ten alkaline excavated soils were obtained from different construction projects in Japan. Although their total As contents were low (from 6.75 to 79.4mgkg), the As leaching was not negligible. Different L/S ratios at each step of the SLT had little influence on the cumulative As release or PPLI values. Experimentally determined PPLI values were in agreement with those from model estimations. A five-step SLT with an L/S of 10Lkg at each step, combined with a logarithmic function fitting was suggested for the easy estimation of PPLI. Results of the sequential extraction procedure showed that large portions of more labile As fractions (non-specifically and specifically sorbed fractions) were removed during long-term leaching and so were small, but non-negligible, portions of strongly bound As fractions.
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http://dx.doi.org/10.1016/j.ecoenv.2017.08.002DOI Listing
January 2018

Chemical Species of Phosphorus and Zinc in Water-Dispersible Colloids from Swine Manure Compost.

J Environ Qual 2017 Mar;46(2):461-465

The release of phosphorus (P) and zinc (Zn) from swine manure compost and from soils applied with swine manure compost can be accelerated by colloidal particles. This study investigated the concentrations and chemical species of P and Zn in water-dispersible colloids (WDCs) collected from swine manure compost by using X-ray absorption fine structure (XAFS) spectroscopy. A filtration and ultracentrifugation process was used to separate and collect WDCs (20-1000 nm) from the bulk swine manure compost (<2 mm). The swine manure compost contained 2.7 g kg WDC, in which P (140 g kg) was highly concentrated and Zn concentrations were greater than in the bulk compost (1.45 g kg). Phosphorus K-edge X-ray absorption near-edge structure (XANES) spectroscopy determined the presence of struvite (NHMgPO·6HO) as a major P species (74%), followed by tricalcium phosphate as a secondary component (26%). In the WDC fraction, struvite was not found, but tricalcium phosphate (56%) occurred as a primary component. Zinc K-edge XAFS spectroscopy determined hopeite [Zn(PO)·4HO, 59%] and to a lesser extent smithsonite (ZnCO, 24%) and Zn adsorbed on ferrihydrite (17%). In the WDC fraction, hopeite (44%) and organically bound Zn (35%) were predominant. Our results demonstrate the notable difference in the concentration and chemical species of P and Zn between the WDC and bulk fractions of swine manure compost.
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http://dx.doi.org/10.2134/jeq2016.11.0433DOI Listing
March 2017

Slow pyrolyzed biochars from crop residues for soil metal(loid) immobilization and microbial community abundance in contaminated agricultural soils.

Chemosphere 2017 Jun 6;177:157-166. Epub 2017 Mar 6.

Korea Biochar Research Center & School of Natural Resources and Environmental Science, Kangwon National University, Chuncheon 24341, Republic of Korea. Electronic address:

This study evaluated the feasibility of using biochars produced from three types of crop residues for immobilizing Pb and As and their effects on the abundance of microbial community in contaminated lowland paddy (P-soil) and upland (U-soil) agricultural soils. Biochars were produced from umbrella tree [Maesopsis eminii] wood bark [WB], cocopeat [CP], and palm kernel shell [PKS] at 500 °C by slow pyrolysis at a heating rate of 10 °C min. Soils were incubated with 5% (w w) biochars at 25 °C and 70% water holding capacity for 45 d. The biochar effects on metal immobilization were evaluated by sequential extraction of the treated soil, and the microbial community was determined by microbial fatty acid profiles and dehydrogenase activity. The addition of WB caused the largest decrease in Pb in the exchangeable fraction (P-soil: 77.7%, U-soil: 91.5%), followed by CP (P-soil: 67.1%, U-soil: 81.1%) and PKS (P-soil: 9.1%, U-soil: 20.0%) compared to that by the control. In contrast, the additions of WB and CP increased the exchangeable As in U-soil by 84.6% and 14.8%, respectively. Alkalinity and high phosphorous content of biochars might be attributed to the Pb immobilization and As mobilization, respectively. The silicon content in biochars is also an influencing factor in increasing the As mobility. However, no considerable effects of biochars on the microbial community abundance and dehydrogenase activity were found in both soils.
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http://dx.doi.org/10.1016/j.chemosphere.2017.02.112DOI Listing
June 2017

Simultaneous and continuous stabilization of As and Pb in contaminated solution and soil by a ferrihydrite-gypsum sorbent.

J Hazard Mater 2017 Apr 22;327:171-179. Epub 2016 Dec 22.

Ishihara Sangyo Kaisha, Ltd, Japan.

For the increasing need of stabilization both cationic and anionic metal(loid)s simultaneously, we newly developed a metal sorbent (FIXALL), consisting mainly of ferrihydrite and gypsum. The objectives of this study were to determine the molecular mechanisms of Pb and As stabilization in an aqueous system and to examine a simultaneous and long-term (up to 754days) effect on Pb and As stabilization in an anthropogenically contaminated soil using the FIXALL sorbent. When the solution contained a low concentration of Pb (5mgL), the mechanisms of Pb removal by FIXALL were based chiefly on the formation of inner-sphere surface complex with ferrihydrite. In the highly concentrated Pb solution (1200mgL), contrarily, the removal of Pb by FIXALL was the direct consequence of the dissolution of gypsum and subsequent precipitation of PbSO, which strengthens the drawback of low capability of ferrihydrite for Pb removal. Regardless of initial concentrations, the primary mechanism of FIXALL for As stabilization is attributed to the formation of inner-sphere surface complex with ferrihydrite. A contaminated soil study demonstrated that FIXALL could decrease the concentration of water soluble As and Pb simultaneously and continuously for 754days without notable changes in their chemical species and soil pH.
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http://dx.doi.org/10.1016/j.jhazmat.2016.12.039DOI Listing
April 2017

Impact of natural and calcined starfish (Asterina pectinifera) on the stabilization of Pb, Zn and As in contaminated agricultural soil.

Environ Geochem Health 2017 Apr 31;39(2):431-441. Epub 2016 Aug 31.

Korea Biochar Research Center, Kangwon National University, Chuncheon, 24341, Korea.

Metal stabilization using soil amendments is an extensively applied, economically viable and environmentally friendly remediation technique. The stabilization of Pb, Zn and As in contaminated soils was evaluated using natural starfish (NSF) and calcined starfish (CSF) wastes at different application rates (0, 2.5, 5.0 and 10.0 wt%). An incubation study was conducted over 14 months, and the efficiency of stabilization for Pb, Zn and As in soil was evaluated by the toxicity characteristic leaching procedure (TCLP) test. The TCLP-extractable Pb was reduced by 76.3-100 and 91.2-100 % in soil treated with NSF and CSF, respectively. The TCLP-extractable Zn was also reduced by 89.8-100 and 93.2-100 % in soil treated with NSF and CSF, respectively. These reductions could be associated with the increased metal adsorption and the formation of insoluble metal precipitates due to increased soil pH following application of the amendments. However, the TCLP-extractable As was increased in the soil treated with NSF, possibly due to the competitive adsorption of phosphorous. In contrast, the TCLP-extractable As in the 10 % CSF treatment was not detectable because insoluble Ca-As compounds might be formed at high pH values. Thermodynamic modeling by visual MINTEQ predicted the formation of ettringite (CaAl(SO)(OH)·26HO) and portlandite (Ca(OH)) in the 10 % CSF-treated soil, while SEM-EDS analysis confirmed the needle-like structure of ettringite in which Pb was incorporated and stabilized in the 10 % CSF treatment.
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http://dx.doi.org/10.1007/s10653-016-9867-4DOI Listing
April 2017

Chemical speciation and enzymatic impact of silver in antimicrobial fabric buried in soil.

J Hazard Mater 2016 Nov 14;317:602-607. Epub 2016 Jun 14.

Tokyo University of Agriculture and Technology, Japan.

This study investigated the impact of Ag in antibacterial fabric on soil enzymes in relation to solubility and speciation of Ag. Sections of Ag-containing sock fabric (1.0-1.5cm(2)) were incubated in soils with aerobic and anaerobic conditions and periodically determined activity of arylsulfatase, dehydrogenase and urease. Microscale distribution and speciation of Ag at the interface between socks and soil particles were investigated using micro-focused X-ray fluorescence (μ-XRF), and Ag speciation was determined using micro-focused X-ray absorption near edge structure (μ-XANES) spectroscopy. Results showed that the sock fabric consisted of elemental Ag and Ag2S. After 60-day exposure to soil, majority (50-90%) of Ag in sock did not undergo phase transformation and present as elemental Ag and Ag2S in aerobic and anaerobic conditions. A part of Ag in sock fabric was bound with soil colloids (<15%), depending on the distance from the edge of sock fabric. Soil enzyme activities were overall unaffected by Ag in sock textile after 60days of incubation, although a significant decrease in arylsulfatase activity was found only in the initial stage of soil incubation. Silver in the sock fabric is relatively stable and has little detrimental impacts on enzyme activity in ordinary soil conditions.
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http://dx.doi.org/10.1016/j.jhazmat.2016.06.027DOI Listing
November 2016

Potential for leaching of arsenic from excavated rock after different drying treatments.

Chemosphere 2016 Jul 6;154:276-282. Epub 2016 Apr 6.

Department of Chemical Engineering, Tokyo University of Agriculture and Technology, 2-24-16 Naka, Koganei, Tokyo 184-8588, Japan. Electronic address:

Leaching of arsenic (As) from excavated rock subjected to different drying methods is compared using sequential leaching tests and rapid small-scale column tests combined with a sequential extraction procedure. Although the total As content in the rock was low (8.81 mg kg(-1)), its resulting concentration in the leachate when leached at a liquid-to-solid ratio of 10 L kg(-1) exceeded the environmental standard (10 μg L(-1)). As existed mainly in dissolved forms in the leachates. All of the drying procedures applied in this study increased the leaching of As, with freeze-drying leading to the largest increase. Water extraction of As using the two tests showed different leaching behaviors as a function of the liquid-to-solid ratio, and achieved average extractions of up to 35.7% and 25.8% total As, respectively. Dissolution of As from the mineral surfaces and subsequent re-adsorption controlled the short-term release of As; dissolution of Fe, Al, and dissolved organic carbon played important roles in long-term As leaching. Results of the sequential extraction procedure showed that use of 0.05 M (NH4)2SO4 underestimates the readily soluble As. Long-term water extraction removed almost all of the non-specifically sorbed As and most of the specifically sorbed As. The concept of pollution potential indices, which are easily determined by the sequential leaching test, is proposed in this study and is considered for possible use in assessing efficacy of treatment of excavated rocks.
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http://dx.doi.org/10.1016/j.chemosphere.2016.03.129DOI Listing
July 2016

Chemical speciation of silver (Ag) in soils under aerobic and anaerobic conditions: Ag nanoparticles vs. ionic Ag.

J Hazard Mater 2017 Jan 3;322(Pt A):318-324. Epub 2015 Sep 3.

Korea Biochar Research Center & Department of Biological Environment, Kangwon National University, Chuncheon 200-701, South Korea.

This study investigated how silver nanoparticles (AgNP) and ionic silver (AgNO) undergo phase-transformations in soils under aerobic and anaerobic conditions using extended X-ray absorption fine structure (EXAFS) spectroscopy. After 30 days of aerobic incubation, 88% of AgNP added to the soil remained persistent, whereas AgNO was completely transformed into Ag associated with humus and clay minerals. In the anaerobic soil, 83% of the spiked AgNP was transformed into AgS, accompanied by significant decrease in water- and acid-extractable Ag fractions. About 50% of AgNO spiked to the anaerobic soil underwent transformations into metallic Ag and associations with clay minerals. Oxide (AgO) and carbonate (AgCO) forms of Ag were not predominant in aerobic and anaerobic soils. The redox potential of soil had a profound effect on determination of the phase-transformation pathways for AgNP and ionic Ag.
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http://dx.doi.org/10.1016/j.jhazmat.2015.09.001DOI Listing
January 2017

Formations of hydroxyapatite and inositol hexakisphosphate in poultry litter during the composting period: sequential fractionation, P K-edge XANES and solution (31)P NMR investigations.

Environ Sci Technol 2014 May 29;48(10):5486-92. Epub 2014 Apr 29.

Department of Bioapplications and Systems Engineering, Tokyo University of Agriculture and Technology 2-24-16 Nakamachi, Koganei, Tokyo, 184-8588 Japan.

Little is known about how the solubility and chemical speciation of phosphorus (P) in poultry litters are altered during the composting period. This study investigated the quantitative and qualitative changes in organic P (Po) and inorganic P (Pi) compositions in poultry litters during the seven-day composting period using sequential extraction in combination with P K-edge X-ray absorption near-edge structure (XANES) and solution (31)P nuclear magnetic resonance (NMR) spectroscopy. The result of sequential extraction illustrated that the significant decrease of H2O-P by 55% in poultry litters occurred concomitantly with the increase of HCl-Pi and HCl-Po during the composting period (p < 0.05). X-ray diffraction results for poultry litter samples showed three distinct peaks indicative of hydroxyapatite. Phosphorus K-edge XANES confirmed the increase of hydroxyapatite during the composting period, corresponding to the increase of HCl-Pi determined by the sequential extraction. The NaOH-EDTA extraction for solution (31)P NMR revealed that myo-inositol hexakisphosphate (IHP) constituted about 80% of phosphate monoesters and was increased from 16 to 28% in the poultry litter during the composting period. The combined applications of chemical extraction and molecular-spectroscopic techniques determined that water-soluble P in poultry litter was transformed into less soluble phases, primarily hydroxyapatite and IHP, during the composting period.
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http://dx.doi.org/10.1021/es404875jDOI Listing
May 2014

Speciation and phytoavailability of lead and antimony in a small arms range soil amended with mussel shell, cow bone and biochar: EXAFS spectroscopy and chemical extractions.

Chemosphere 2014 Jan 30;95:433-41. Epub 2013 Oct 30.

Korea Biochar Research Center & Department of Biological Environment, Kangwon National University, Chuncheon 200-701, Republic of Korea; University Institute of Biochemistry and Biotechnology, PMAS Arid Agriculture University, Rawalpindi, Pakistan.

Mussel shell (MS), cow bone (CB) and biochar (BC) were selected to immobilize metals in an army firing range soil. Amendments were applied at 5% (wt) and their efficacies were determined after 175 d. For metal phytoavailability test, maize (Zea mays L.) plants were cultivated for 3weeks. Results showed that all amendments decreased the exchangeable Pb by up to 99% in planted/unplanted soils. Contrarily, exchangeable Sb were increased in the MS- and CB-amended soils. The rise in soil pH (~1 unit) by the amendments affected Pb and Sb mobility in soils. Bioavailability of Pb to maize was reduced by up to 71% in the amended soils. The Sb uptake to maize was decreased by up to 53.44% in the BC-amended soil. Sequential chemical extractions showed the transformation of easily available Pb to stable residual form with the amendment treatments. Scanning electron microscopic elemental dot mapping revealed the Pb association with Al and Si in the MS-amended soil and that with P in the CB- and BC-amended soils. Additionally, the extended X-ray absorption fine structure spectroscopic analysis indicated the transformation of organic bound Pb in unamended control soil to relatively more stable Pb-hydroxide (Ksp=10(-17.1)), chloropyromorphite (Ksp=10(-84.4)) and Pb-phosphate (Ksp=10(-23.8)) in soils amended with MS, CB and BC, respectively. Application of BC was the best in decreasing the phytoavailability of Pb and Sb in the studied army firing range soil.
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http://dx.doi.org/10.1016/j.chemosphere.2013.09.077DOI Listing
January 2014

Field and laboratory assessments on dissolution and fractionation of Pb from spent and unspent shots in the rhizosphere soil.

Authors:
Yohey Hashimoto

Chemosphere 2013 Nov 1;93(11):2894-900. Epub 2013 Oct 1.

Department of Bioapplications and Systems Engineering, Tokyo University of Agriculture and Technology, 2-24-16 Koganei, Tokyo 184-8588, Japan. Electronic address:

The objective of this study was to determine the effect of plant root growth on Pb dissolution from shot under laboratory and field-scale conditions. For a laboratory study, a 100-d incubation experiment was conducted to assess Pb dissolution from unspent shot (new) and spent shot (>10yr in fields) in rhizosphere and non-rhizosphere (bulk) soils using the Toxicity Characteristic Leaching Procedure (TCLP) and sequential extraction methods. This study found that increasing the soil pH value to 7.5 by liming significantly reduced Pb dissolution from unspent and spent shot (<5mgL(-1)). Dissolution of Pb from shot was induced more in rhizosphere than bulk soils. Regardless of shot types, the averaged TCLP-Pb concentration in acidic and limed soils was 12.9- and 8.1-fold greater in rhizosphere than in bulk soils, respectively. For a field-scale investigation, a total of 31 individual plant samples of 6 different species and their rhizosphere soils were collected from a clay-target shooting range (<35000mgPbkg(-1)). The Pb concentration in plant aboveground tissues depended on species with a mean value of 72mgkg(-1) (15-254mgkg(-1)), which was far smaller than that reported in previous studies. Regardless of high soil Pb levels, aboveground tissue Pb concentrations of Solidago altissima (i.e., Canada goldenrod, 15mgkg(-1)) and Andropogon virginicus (i.e., broomsedge, 18mgkg(-1)) were below the toxicity threshold, suggesting that these indigenous species could have phytostabilization potentials. The limited Pb accumulation by vegetation was attributed to the abundance of soil calcite derived from spent clay-target fragments.
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http://dx.doi.org/10.1016/j.chemosphere.2013.08.095DOI Listing
November 2013

Immobilization of lead in a Korean military shooting range soil using eggshell waste: an integrated mechanistic approach.

J Hazard Mater 2012 Mar 23;209-210:392-401. Epub 2012 Jan 23.

Department of Biological Environment, Kangwon National University, Chuncheon 200-701, Republic of Korea.

This study evaluated the effectiveness of eggshell and calcined eggshell on lead (Pb) immobilization in a shooting range soil. Destructive and non-destructive analytical techniques were employed to determine the mechanism of Pb immobilization. The 5% additions of eggshell and calcined eggshell significantly decreased the TCLP-Pb concentration by 68.8% due mainly to increasing soil pH. Eggshell and calcined-eggshell amendments decreased the exchangeable Pb fraction to ≈ 1% of the total Pb in the soil, while the carbonate-associated Pb fraction was increased to 40.0-47.1% at >15% application rates. The thermodynamic modeling on Pb speciation in the soil solution predicted the precipitation of Pb-hydroxide [Pb(OH)(2)] in soils amended with eggshell and calcined eggshell. The SEM-EDS, XAFS and elemental dot mapping revealed that Pb in soil amended with calcined eggshell was associated with Si and Ca, and may be immobilized by entrapping into calcium-silicate-hydrate. Comparatively, in the soil amended with eggshell, Pb was immobilized via formation of Pb-hydroxide or lanarkite [Pb(2)O(SO(4))]. Applications of amendments increased activities of alkaline phosphatase up to 3.7 times greater than in the control soil. The use of eggshell amendments may have potential as an integrated remediation strategy that enables Pb immobilization and soil biological restoration in shooting range soils.
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http://dx.doi.org/10.1016/j.jhazmat.2012.01.047DOI Listing
March 2012

Effects of rapeseed residue on lead and cadmium availability and uptake by rice plants in heavy metal contaminated paddy soil.

Chemosphere 2011 Oct 20;85(4):677-82. Epub 2011 Jul 20.

Department of Biological Environment, Kangwon National University, Chuncheon 200-701, Republic of Korea.

Rapeseed (Brassica napus L.) has been cultivated for biodiesel production worldwide. Winter rapeseed is commonly grown in the southern part of Korea under a rice-rapeseed double cropping system. In this study, a greenhouse pot experiment was conducted to assess the effects of rapeseed residue applied as a green manure alone or in combinations with mineral N fertilizer on Cd and Pb speciation in the contaminated paddy soil and their availability to rice plant (Oryza sativa L.). The changes in soil chemical and biological properties in response to the addition of rapeseed residue were also evaluated. Specifically, the following four treatments were evaluated: 100% mineral N fertilizer (N100) as a control, 70% mineral N fertilizer+rapeseed residue (N70+R), 30% mineral N fertilizer+rapeseed residue (N30+R) and rapeseed residue alone (R). The electrical conductivity and exchangeable cations of the rice paddy soil subjected to the R treatment or in combinations with mineral N fertilizer treatment, N70+R and N30+R, were higher than those in soils subjected to the N100 treatment. However, the soil pH value with the R treatment (pH 6.3) was lower than that with N100 treatment (pH 6.9). Use of rapeseed residue as a green manure led to an increase in soil organic matter (SOM) and enhanced the microbial populations in the soil. Sequential extraction also revealed that the addition of rapeseed residue decreased the easily accessible fraction of Cd by 5-14% and Pb by 30-39% through the transformation into less accessible fractions, thereby reducing metal availability to the rice plant. Overall, the incorporation of rapeseed residue into the metal contaminated rice paddy soils may sustain SOM, improve the soil chemical and biological properties, and decrease the heavy metal phytoavailability.
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http://dx.doi.org/10.1016/j.chemosphere.2011.06.073DOI Listing
October 2011

Enhanced transformation of lead speciation in rhizosphere soils using phosphorus amendments and phytostabilization: an x-ray absorption fine structure spectroscopy investigation.

J Environ Qual 2011 May-Jun;40(3):696-703

Department of Bioresource Science, Mie University, Japan.

To formulate successful phytostabilization strategies in a shooting range soil, understanding how heavy metals are immobilized at the molecular level in the rhizosphere soil is critical. Lead (Pb) speciation and solubility in rhizosphere soils of five different plant species were investigated using extended X-ray absorption fine structure (EXAFS) spectroscopy and chemical extraction. The EXAFS analysis indicated that Pb occurred as PbCO (37%), Pb sorbed to organic matter (Pb-org: 15%), and Pb sorbed to pedogenic birnessite and/or ferrihydrite (Pb-ox: 36%) in the bulk soil. Comparison of the EXAFS spectra between bulk and rhizosphere soils demonstrated notable differences in fine structure, indicating that Pb species had been modified by rhizosphere processes. The estimated proportion of PbCO (25%) in the buckwheat soil was smaller than the other rhizosphere soils (35-39%). The addition of P significantly reduced Pb solubility in the bulk and rhizosphere soil except in the rhizosphere of buckwheat, for which the Pb solubility was 10-fold greater than in the other P-amended soils. This larger solubility in the buckwheat rhizosphere could not be explained by the total Pb speciation in the soil but was presumably related to the acidifying effect of buckwheat, resulting in a decrease of the soil pH by 0.4 units. The reduced Pb solubility by P amendment resulted from the transformation of preexisting PbCO (37%) into Pb(PO)Cl (26-32%) in the bulk and rhizosphere soils. In the P-amended rhizosphere soils, Pb-org species were no longer detected, and the Pb-ox pool increased (51-57%). The present study demonstrated that rhizosphere processes modify Pb solubility and speciation in P-amended soils and that some plant species, like buckwheat, may impair the efficiency of Pb immobilization by P amendments.
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http://dx.doi.org/10.2134/jeq2010.0057DOI Listing
June 2011