1 Electronic Supporting Information. 2 The transformation and fate of silver nanoparticles in a paddy soil:

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1 Electronic Supplementary Material (ESI) for Environmental Science: Nano. This journal is The Royal Society of Chemistry Electronic Supporting Information 2 The transformation and fate of silver nanoparticles in a paddy soil: 3 Effects of soil organic matter and redox conditions 4 Min Li, ab Peng Wang, c Fei Dang *a and Dong-Mei Zhou *a 5 a Key Laboratory of Soil Environment and Pollution Remediation, Institute of Soil Science, Chinese Academy of 6 Sciences, Nanjing , P.R. China; 7 b University of Chinese Academy of Sciences, Beijing , P.R. China; 8 c College of Resources and Environmental Sciences, Nanjing Agricultural University, Nanjing , P.R. China; * Corresponding Author. Tel.: ; Fax: Address: fdang@issas.ac.cn (Fei Dang); dmzhou@issas.ac.cn (Dong-Mei Zhou). 16 Summary 17 9 SI pages containing 2 figures, 3 tables, 3 detailed descriptions and 1 reference. S1

2 19 Contents 20 Soil organic matter removal...page S3 21 AgNP and soil characterization... page S3 22 Characteristics of soils... page S3 23 References page S4 24 TEM-EDS characterization of soil (Figure S1)... page S5 25 Eh and ph in liquid phase of all treatments (Figure S2)... page S6 26 Soil properties in this study (Table S1)... page S7 27 Dissolved TAg and Ag(I) levels in the liquid phase (Table S2)... page S8 28 Results of two-way analysis of variance (Table S3) page S9 S2

3 30 Soil organic matter removal 31 Subsamples of soil were reacted with sodium hypochlorite, which was less invasive for soil organic matter (OM) 32 removal than other oxidants described previously. 1 Briefly, g soil was reacted with 1 L 6% NaClO (ph 8.0) 33 for 6 h at 25 o C. The mixture was then centrifuged at 2574 g for 5 min and washed twice using 1.0 M NaNO The procedure was repeated twice. Finally, samples were washed with 18 MΩ water until conductivity was < μs cm AgNP and soil characterization 37 The particle size distribution and morphology of polyvinylpyrrolidone (PVP)-coated silver nanoparticles (AgNPs) 38 were determined by TEM (JEM-2100, JEOL, Japan). Number weighted hydrodynamic diameters were measured 39 using dynamic light scattering (DLS, BI-200SM, Brookhaven Instruments, USA). AgNPs stock suspension was 40 sonicated in a benchtop sonicator (KQ-300VDE, China) at 45 khz for 3 min prior to experiments. 41 Soils with or without OM removal were characterized for ph (0.01 mol L -1 CaCl 2 ), OM content (Waikley-Balck 42 method), water holding capacity (WHC), cation exchange capacity (CEC, ammonium acetate centrifugal exchange 43 method) particle-size (Laser particle size analyzer, Beckman LS 13320) and total S (elemental analyzer, Elementar 44 vario max cube, Germany ). 45 Characteristics of soils 46 The soil revealed characteristics typical of paddy soils in China (Table S1). Background Ag concentration was 47 below detection limit (< mg kg -1 ). Sodium hypochlorite treatment decreased soil OM contents significantly 48 from 3.8% to 1.0% (on average), and the residual refractory organic carbon was comprised of pyrogenic materials 49 and aliphatic compounds. 1 Total S concentrations decreased, on average, from mg kg -1 to mg kg Conversely, other soil properties (e.g., ph, CEC, and amorphous Fe/Mn) showed relatively little change (Table S1) 51 after OM removal. S3

4 52 References: 53 1 R. Mikutta, M. Kleber, M. S. Torn and R. Jahn, Biogeochemistry, 2006, 77, S4

5 Fig. S1. Representative TEM images of soil without organic matter removal spiked with AgNPs and incubated for days. S5

6 60 61 Fig. S2. Eh and ph in the liquid phase of all treatments (same legends for a and c, b and d). Data are presented as 62 mean ± SD (n=3). S6

7 64 Table S1. Soil properties in this study. Property Soil without OM removal (HOM) Soil with OM removal (LOM) ph a 7.1 ± ± 0.2 CEC (cmol/kg) Sand (%) Silt (%) Clay (%) Amorphous Fe (mg/kg) Amorphous Mn (mg/kg) OM (%) a 3.73 ± ±0.001 WHC (%) Total S (mg/kg) a 605.8± ±11.3 Ag concentration (mg/kg) < < a Data are given as mean ± SD (n=3). S7

8 67 Table S2. Dissolved TAg and Ag(I) levels in the liquid phase treatment AgNPs-A AgNPs-AN AgNO 3 -A AgNO 3 -AN AgNPs-HOM AgNPs-LOM AgNO 3 -HOM AgNO 3 -LOM Time (d) TAg levels in liquid phase (μg L -1 ) Ag(I) levels in liquid phase (μg L -1 ) ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± S8

9 69 Table S3. Results of Two-way Analysis of Variance (ANOVA) among treatments. Experiment Time (d) Factor TAg Ag(I) K d F Sig. F Sig. F Sig. Experiment 1 a Experiment 2 a Ag form Eh Ag form Eh Ag form Eh Ag form OM Ag form OM Ag form OM Ag form OM Ag form OM a See text for details of experiments 1 and S9