Supporting Information

Transcription

1 Supporting Information Chemical speciation of cadmium and sulfur K-edge XANES spectroscopy in flooded paddy soils amended with zero-valent ion Yohey Hashimoto 1), and Noriko Yamaguchi 2) 1) Corresponding author Department of Bio-applications and Systems Engineering Tokyo University of Agriculture and Technology Koganei, Tokyo, ) National Institute for Agro-Environmental Sciences Soil Environment Division Kan-nondai, Tsukuba, Ibaraki, Number of pages: 11 Number of tables: 4 (Tables S1-S4) Number of figures: 4 (Figures S1-S4) 1

2 Microcosm setup Eh reference Cd spiked soil Homogenized and puddled paddy soils from Kahi (Low-S) and Sogo (High-S) plots. 26 cm 2 cm 11 cm 7 cm Eh probe Eh probe A column is submerged in DI water to maintain the water levels at 12 cm from the top A 2 cm sand layer was prepared at the bottom of column. Fig. S1. Microcosm setting for Cd speciation in paddy soils with and without ZVI additions. 2

3 Measured ph in the soil solution during incubation Low-S soil Waterlogged Drained ph High-S soil Surface Subsurface Surface +ZVI Subsurface +ZVI Time (Day) Fig. S2. ph values of surface (2 cm) and subsurface (9 cm) layers for Low-S and High-S soil columns 3

4 Eh-pH diagram for Cd speciation in the soil solution The equilibrium reactions and equilibrium constants (log K) of Cd species were based on Lindsay (1979): Soil-Cd Cd 2+ (-7.00) Cd 2+ + S 2- CdS (27.07) SO e - + 8H + S H 2 O (20.74) Cd 2+ + CO 2 + H 2 O CdCO 3 o + 2H + (-14.06) 200 SO 4 = 10-3, CO 2 = atm 25 o C 0 Cd 2+ CdCO 3 Eh (mv) -200 H 2 O Low-S Low-S +ZVI High-S High-S +ZVI -400 H 2 CdS ph Fig. S3. Redox speciation of Cd in Low-S and High-S soils with and without ZVI. Data points correspond to subsoil Eh and ph values when Cd was detected in the soil solution (see Fig. 3). For High-S +ZVI soil (filled red circle), for example, soil solution Cd was detected at the first and second sampling periods, and therefore two data were plotted. Red and blue arrows indicate time sequence of Cd speciation in High-S and Low-S soils, respectively. This diagram does not take into account changes in stability based on variable ion concentrations. 4

5 Summary of S speciation determined by the peak-fitting procedure Fig. S4. Proportions of different S species in the Low-S (left) and High-S (right) soils determined by the peak fitting analysis on S K-edge XANES spectra. These data corresponded to Table 3 that grouped S species into reduced (<2475 ev), intermediate ( ev) and oxidized (>2480 ev) forms. 5

6 Detailed method and procedure for sequential Cd extraction Table S1. A summary of Cd fractionation methods. Fraction # Extractant Associated phases Time and temperature Solution volume (ml) M Ca(NO 3 ) 2 Exchangeable 20 h, 20 o C M CH 3 COOH Inorganically bound 20 h, 20 o C ) OM decomposition with 12% H 2 O 2 2) 0.42 M CH 3 COOH Organically bound 1) 90 o C 2) 20 h, 20 o C M H 2 C 2 O 4 and M (NH 2 ) 2 C 2 O 4 with 1 g ascorbic acid 5 HNO 3 and HF in g of dried soil from fraction 4 Oxide occluded Residual 1 h, 90 o C with occasional agitation 2 h, 200 o C 30 The methods are according to the work by Sadamoto and co-workers (Sadamoto et al., 1994). 6

7 Summary of linear combination fit (LCF) on Cd K-edge XANES spectroscopy Table S2. The best and second-best (in parentheses) results of binary LCF on Cd K-edge XANES spectra for soil samples Soil Cd sorbed with soil colloids ferrihydrite Kaolinite humus CdS R % (x10-3 ) Surface Low-S (68) (31) (1.53) Low-S +ZVI (39) (61) (2.62) High-S (92) (8) (2.79) High-S +ZVI (57) (43) (5.96) Subsurface Low-S (77) (24) (5.87) Low-S +ZVI High-S (67) (33) (4.28) High-S +ZVI (43) (57) (6.69) R: residual value for fitting; R = Σ(μ exp μ model ) 2 / Σ(μ exp ) 2 The result of second-best fit of Low-S +ZVI (Subsurface) was not shown due to poor fit (R value) with one order different from that of the best fit. 7

8 Reference characterization of S K-edge XANES spectroscopy Table S3. White-line peak energies of normalized S K-edge XANES spectra of reference compounds (compilation data) S form S oxidation state S reference White-line peak energy (ev) (citation #) Example (1) (2) (3) Inorganic sulfide I S Troilite Inorganic sulfide II S Pyrite Elemental S S o Thiols R-SH +0.5 Cysteine Sulfoxide R-S=O +2 Methionine sulfoxide Sulfite 2- SO Sodium sulfite Sulfone R-S(=O) 2 +4 Phenyl sulfone Sulfonate R-O-S-(O) 2 +5 Cysteinic acid Ester sulfate R-O-SO 3 +6 Sodium dodecyl sulfate , Prietzel et al.(2011); 2, Prietzel et al.(2003); 3, this study 8

9 Supporting information for soil properties Table S4. Available cation concentrations of Low-S and High-S soils determined by Mehlich III extraction Soil K Na Fe Mn Cu Zn cmol c kg mg kg Low-S (Kahi) High-S (Sogo)

10 Preparation of Cd reference compounds for XANES spectroscopy We included the reference standards representative of Cd phases in the soil: CdCO 3, Cd(NO 3 ) 2, CdCl 2, CdSO 4, Cd(OH) 2, Cd(CH 3 COO) 2, CdS (purchased from Wako Ltd., Japan), and Cd sorbed on ferrihydrite, gibbsite, birnessite, humus and kaolinite. Ferrihydrite, gibbsite, birnessite were synthesized by referring to the method described in Schwertmann and Cornell (2000). Humus was extracted from allopanic Andisol and then purified (Yonebayashi and Hattori, 1988). The standard reference samples of kaolinite (JCSS-1101b) was purchased from The Clay Science Society of Japan. Humus dissolved in water was mixed with Cd(NO 3 ) 2 solution at ph 4.0 and equilibrated for 5 days. Aggregated humus-cd complex was collected by centrifugation at 6000 g. The synthesis of Cd sorbed to gibbsite, ferrihydrite, birnessite, and kaolinite were conducted at ph 5.0, with Cd(NO 3 ) 2 (ionic strength 0.01 mm NaNO 3 ) for 72 hours of equilibration (5 days for gibbsite and ferrihydrite). After each sorption experiment, the suspension was centrifuged and washed three times with deionized water. We did not do any corrections for self absorption since our samples (adsorbed Cd references and Cd in soils) have variable density, particle size and elemental compositions. If self absorption significantly affected our XANES spectra, we would expect to see a decrease in the white-line peak intensity with increasing absorbed Cd. However, the white-line peak intensities for Cd associated with soil colloids (e.g., feriihydrite) remained virtually the same with those of diluted Cd references [e.g., Cd(OH) 2 ] measured by transmission mode, indicating that self-absorption did not measurably impact our result. Self absorption should be negligible for the soil samples because of its lower Cd concentration (Tröger et al., 1992). Previous studies have also face the same issues regarding the XAFS analysis on soil and adsorbed references by fluorescent mode (Khare et al., 2004; Strawn et al., 2002). References Khare, N., D. Hesterberg, S. Beauchemin, and S.-L. Wang XANES determination of adsorbed phosphate distribution between ferrihydrite and boehmite in mixtures. Soil Sci. Soc. Am. J. 68: Lindsay, W.L Chemical equilibria in soils John Wiley, New York, NY. Prietzel, J., J. Thieme, U. Neuhäusler, J. Susini, and I. Kögel-Knabner Speciation of sulphur in soils and soil particles by X-ray spectromicroscopy. Euro. J. Soil Sci. 54: Prietzel, J.r., A. Botzaki, N. Tyufekchieva, M. Brettholle, J.r. Thieme, and W. Klysubun Sulfur speciation in soil by S K-Edge XANES spectroscopy: comparison of spectral deconvolution and linear combination fitting. Environ. Sci. Technol. 45:

11 Sadamoto, H., K. Iimura, T. Honna, and S. Yamamoto Examination of fractionation of heavy metals in soils. Jpn. J. Soil Sci. Plant Nutr 65: (In Japanese, with English abstract). Schwertmann, U., and R.M. Cornell Iron Oxides in the Laboratory: Preparation and Characterization WILEY-VCH. Strawn, D., H. Doner, M. Zavarin, and S. McHugo Microscale investigation into the geochemistry of arsenic, selenium, and iron in soil developed in pyritic shale materials. Geoderma 108: Tröger, L., D. Arvanitis, K. Baberschke, H. Michaelis, U. Grimm, and E. Zschech Full correction of the self-absorption in soft-fluorescence extended x-ray-absorption fine structure. Phys. Rev. B 46: Yonebayashi, K., and T. Hattori Chemical and biological studies on environmental humic acids: I. Composition of elemental and functional groups of humic acids. Soil Sci. Plant Nutr. 34: