Supplement 1

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Synthesis of standard and reference materials (p. S1-S2). Supplemental ... Sorption standards were prepared by reacting Zn with ferrihydrite (2-line, 264 m2g-1).
Supplemental Material for: Micro-scale investigations of soil heterogeneity: Impacts on Zn retention and uptake in Zn contaminated soils

Carla E. Rosenfeld, Rufus L. Chaney, Ryan V. Tappero, Carmen E. Martínez

Contents (8 pages, 1 table, 4 figures): Synthesis of standard and reference materials (p. S1-S2) Supplemental Table S1 (p. S3) Supplemental Fig S1 (p. S5) Supplemental Fig S2 (p. S6) Supplemental Fig S3 (p. S7) Supplemental Fig S4 (p. S8)

Synthesis of standard and reference materials. Spectra of several Zn standards were used during PCA-ITFA and LCF analysis to reconstruct the original XANES spectra including (99.9% purity reagent grade powders purchased from Sigma or Alfa Aesar): ZnS, Zn(OH)2, Zn3(PO4)2. Organic complexes (Zn-oxalate, Zn-citrate, Zn-histidine, Zn-arginine, and Zn-cysteine) were prepared as aqueous complexes by combining the ligand and Zn(NO3)2 at a molar ratio of 10:1 (Zn = 0.01 M) and adjusting the pH to 6.5. Following complex formation, aqueous solutions were frozen and lyophilized at -50°C prior to analysis. Zn-arginine, Zn-cysteine and Zn-histidine were all prepared under a N2 atmosphere in a glove box using deoxygenated double deionized water (ddH2O: 18 MΩ•cm-1) to inhibit ligand oxidation. Zinc complexes with pectin, cellulose, and cell wall extracted from N. caerulescens leaves were prepared as solids. Zinc-pectin complexes were prepared by introducing pectin extracted from citrus (TCI) in 0.4 mM Zn(NO3)2 in a M:L ratio of 1:650. Zinc-cellulose complexes were prepared with the same M:L ratio and with 0.1 mM Zn(NO3)2. Both complexes were prepared according to Isaure et. al (2006), by adjusting the suspension pH to 5.0 and stirring for 3 hours. The Zn-pectin complex formed a gel that could not be separated by centrifugation, and was therefore directly lyophilized at -50°C. The Zn-cellulose suspension was centrifuged, and the pellets frozen and lyophilized at -50°C. Ghost cell walls were obtained from leaves of N. caerulescens (Lasat, et al., 1996), and immersed in 10 mM Zn(NO3)2 solution for 24 hours. After immersion, ghosts were rinsed with dd-H2O, frozen in liquid N2, and ground to a fine powder for XANES analysis. Exchanged, adsorbed, and coprecipitated Zn minerals were also prepared in the laboratory. For all Zn exchanged/adsorbed minerals a solution:solid ratio of 10 mL:0.01 g was used. Sorption standards were prepared by reacting Zn with ferrihydrite (2-line, 264 m2g-1) (Martínez-Villegas and Martínez, 2008), gibbsite, birnessite, Wyoming montmorillonite (University of Missouri Source Clays Repository, SWy2, cleaned, 13 m2 g-1), and goethite (synthesized, 36 m2g-1) (Schwertmann and Cornell, 1991). To montmorillonite, Zn(NO3)2 in 0.1

S1

M KNO3 was added at a concentration equal to 50% of the effective cation exchange capacity (ECEC; 70 cmol(+) kg-1) (Martínez-Villegas and Martínez, 2008). To goethite, gibbsite, and ferrihydrite, 1 mM Zn(NO3)2 was added in 0.1 M KNO3. To birnessite, we added 158 µM Zn(NO3)2 in 0.1 M KNO3. These concentrations were chosen to ensure that the majority of Zn would be specifically adsorbed to the minerals and detectable by µ-XANES, while remaining low enough to prevent the formation of alternative phase Zn surface precipitates (Roberts, et al., 2002, Scheinost, et al., 2002). All mineral suspensions were adjusted to pH 6 and shaken in an end-toend shaker for 24 hours, after which the suspensions were centrifuged and air-dried prior to analysis. Two additional standards, Zn coprecipitated goethite and Zn coprecipitated ferrihydrite were formed by combining 0.5 mL of 0.5 M Zn(NO3)2, 5 mL of 1 M Fe(NO3)3 and 10 mL of 5M KOH to a 250 mL flask and adding 84.5 mL water (Schwertmann and Cornell, 1991). The Zn coprecipitated goethite was aged at 70°C for 7 days prior to washing with dd-H2O and freezedrying while the Zn coprecipitated ferrihydrite was immediately washed and freeze-dried with no aging. Goethite and ferrihydrite mineral formation were confirmed using µ-XRD.

S2

Supplemental Table S1: Principal component analysis of whole soil, fraction-averaged, and ROI Zn µ-XANES spectra (46 spectra total). PC #a

Eigenvalue

1 2 3 4 5 6 7 8 9 10

193 9.11 2.78 1.85 1.1 8.92 0.49 0.40 0.31 0.23

INDb (x10-4) 7.67 3.08 2.18 1.54 1.23 0.92 0.81 0.72 0.66 0.64

NSS (total)c (x10-3) 2.59 0.373 0.165 0.074 0.042 0.020 0.014 0.010 0.007 0.006

% Δ NSSd (total) 99.741 85.60 55.76 55.21 43.57 51.08 31.86 30.58 27.05 19.60

Included? x x

Notes: a

PC # = principal component number.

b

IND = Malinowski indicator value

NSS (total) = normalized sum-square = Σ((y − yfit)2)/ Σ(y2), total refers to the sum of all points in all spectra.

c

d

% Δ NSS (total) = ([(NSS(tot))i − (NSS(tot.))ii ]/(NSS(tot))i ) × 100. 


S3

Supplemental Table S2: Zinc µ-XANES linear combination fit results for all spots in all fractions from all three soils, categorized according to the density of the standard (i.e. LF < 1.6 g/cm3, 1.6