Supporting Information

I Detailed procedures of the plant and soil digestion and analysis

Soil pH

Soil pH was measured using a pH meter (PHS-3C, Shanghai REX, China) with a water–soil

ratio of 2.5:1.

Soil OM

Soil organic matter content was determined using the colorimetric method involving

oxidation with potassium dichromate (Nelson and Sommers, 1996).

Soil CEC

Soil cation exchange capacity was determined using the ammonium acetate method after

washing with alcohol (Kahr and Madsen, 1995).

Soil N, P, and K

The available N, P and K in the soil samples were digested by H2SO4, H2SO4-HClO4 and HF- HClO4,

respectively, and determined using a Smartchem Discrete AutoAnalyzer (Smartchem 200,

AMS/Westco, Italy).

Total Cd in the soil

The total amounts of metals (Cd, Pb, Fe, Mn, etc.) in the soil samples were determined by mixing the

samples with aqua regia and perchloric acid (Hseu, 2004) and then holding the mixture on an electric

heating plate until the soil and the solution became a clear light yellow color and had a volume less

than 1 mL. The digestion solutions were then transferred to 50 mL volumetric flasks. The

concentrations of Cd in the soil were determined with ICP-AES (ICP6300, Thermo).

Total As in the soil

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The total As in the soil samples was determined by mixing the samples with aqua regia diluted

with the same amount of deionized water, heating the mixture in a 100°C water bath for 2 hours,

and analyzing the mixtures using AFS (8220, Beijing Titan Instruments).

Specific surface area of hydroxyapatite, zeolite, and biochar

The specific surface area of each of the tested materials was determined using a Micromeritics

ASAP 2020 V4.02 Surface Area and Porosity Analyzer.

Total Cd in the rice plants

The concentration of Cd in the rice plants was determined using the dry ash method (500°C, 6

hours). The ash was then analyzed in a 0.5 mol·L-1 HNO3 digestion after dilution using ICP-AES

(ICP6300, Thermo) for roots\straw\husk samples and FAAS (iCE-3500, Thermo) for brown rice

samples.

Total As in the rice plants

The concentration of total As in the rice plants was determined using the dry ash method. Step 1,

samples of 1.00 g were weighed in a 50 mL crucible, 10 mL of 150 g·L -1 Mg(NO3)2 was added,

and the samples were dried at 200°C in a muffle furnace. Step 2, the samples were taken out and

covered with 1 g MgO, then returned to the muffle furnace and ashed at 550°C for 4 hours. Step 3,

the ash was digested with 6 mol·L-1 HCl and analyzed using AFS (8220, Beijing Titan

Instruments).

Inorganic As in the brown rice

Brown rice was digested with 6 mol·L-1 HCl, heated in a 60°C water bath for 18 hours, and

analyzed using AFS (8220, Beijing Titan Instruments).

Iron plaque

Iron plaques were extracted from the surfaces of fresh roots using a dithionite–citrate–bicarbonate

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(DCB) solution containing 0.03 mol·L-1 sodium citrate (Na3C6H5O7·2H2O), 0.125 mol·L-1 sodium

bicarbonate (NaHCO3), and 1.0 g sodium dithionite (Na2S2O4) (Liu et al., 2006). The roots were

immersed in 30 mL of DCB reagent at room temperature (20-25°C) for 60 min until the roots

changed color from brown or reddish-brown to white.

II Aqueous solution adsorption experiment and characterization analysis

Materials

Hydroxyapatite, zeolite and biochar were the same as those used in the field experiment. A 50

mg·L-1 Cd solution (CdCl2·2H2O) and a 10 mg·L-1 As solution (As standard liquid, As(V)) were

applied in all treatments except the control.

Aqueous solution adsorption experiment

Samples of 1.00 g of hydroxyapatite, zeolite and biochar were added to the Cd solution (20 mL)

and As solution (20 mL), which were then oscillated for 2 hours at 25°C and filtered with a 0.45

µm nitrocellulose filter membrane. Each material was collected and dried for characterization.

There were three replicates for each treatment.

Characterization analysis

BET, SEM and FTIR analysis were performed on the samples before and after the adsorption test.

BET surface area analysis was carried out by a surface area analyzer (ASAP 2020, Micromeritics)

using the low-temperature nitrogen adsorption method. SEM of the samples was performed with

an SEM analyzer (Quanta 450, FEI); the scanning voltage and accelerating voltage were 15 kV

and 12.5 kV, respectively. FTIR spectroscopy was performed with an FTIR spectrometer

(IRAffinity-1, Shimadzu) using a single point of reflection, KBr tableting of prepared samples, a

scanning range of 4000-500 cm-1, and a resolution of 0.35 cm-1.

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III Soil incubation experiments for 43 different treatments

A total of 50.0 g of tested soil was put into a 100 mL beaker, and the combined amendment (0.4%,

W/W) was added using the methods described in S 6. The samples were well mixed, ultra-pure

water was added, and the samples were placed in a dry and ventilated location where they were

incubated for 20 days. During the process, the soil moisture content was kept at 70% by using the

weight method. At the end of the process, the soil was taken out, air dried, and prepared for

digestion and analysis. The results of pH, exchangeable concentrations of Cd and As, and the

TCLP concentrations of Cd and As revealed that the combined amendment hydroxyapatite, zeolite

and biochar (HZB) was the best choice for the field experiment to remediate the soil polluted with

the Cd and As complex.

III Supporting data

(1) Dry weight of rice tissues with the application of HZB at 0, 2, 4 and 8 kg per plot

S. 1 Effects of combined amendment HZB on dry weight of rice tissues with the application of HZB at 0,2,4 and 8 kg per plot (9 m2)

Rice plants /Dry weight ( g·plant-1)

Tillering Filling Maturing

Roots Straw Roots StrawHusk Brown

riceRoots Straw

Husk Brown

rice

C

K

2.2

3±0.02a

9.1

0±0.13a

2.82±0.2

2b

13.7

2±2.60b

3.2

3±1.07b

4.1

5±0.20b

4.32±0.1

4b

27.63±1.3

9b

7.50±0.8

5b

26.27±2.

07a

22.2

7±0.05a

9.8

0±0.39a

3.2

4±0.26b

14.2

3±1.03b

5.5

3±1.17a

9.0

3±0.98a

4.66±0.2

0a

28.70±0.9

4ab

8.19±0.7

5b

27.79±4.

13a

42.2

4±0.03a

9.6

3±0.38a

4.0

9±0.69ab

16.6

6±1.94ab

5.0

0±1.24ab

7.1

6±1.69a

4.86±0.1

5a

29.34±1.3

2ab

8.03±1.6

6b

29.28±3.

06a

82.2

8±0.04a

9.8

4±0.99a

4.8

8±0.60a

18.0

1±1.52a

5.8

4±0.48a

8.1

8±0.17a

4.94±0.1

6a

30.70±1.9

0a

10.93±1.

38a

28.81±3.

13a

Note: Values with the same letters were not significantly different between different treatments ( p > 0.05)

(2) SEM images of hydroxyapatite, zeolite and biochar before and after adsorption

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(a) SEM images of hydroxyapatite

Before adsorption（×1000） Before adsorption（×6000）

After adsorption of Cd (×6000) After adsorption of As(V) (×6000)

(b) SEM images of zeolite

Before adsorption（×1000） Before adsorption（×6000）

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After adsorption of Cd (×6000) After adsorption of As(V) (×6000)

(c) SEM images of biochar

Original biochar(×6000) Biochar modified by HCl(×6000)

After adsorption of Cd (×6000) After adsorption of As(V) (×6000)

Scanning voltage 15 kV, and accelerating voltage 12.5 kV

S. 2 SEM images of hydroxyapatite, zeolite and biochar before and after adsorption

(3) Correlation coefficients of total Cd and As accumulation amounts in plant and

exchangeable concentration of Cd and As in the soils

S. 3 Correlation coefficients of amounts of accumulated Cd and As in the plants and bioavailable Cd and As concentration in soil

amounts of accumulated Cd amounts of accumulated As

Tillering Filling Maturing Tillering Filling Maturing

Exchangable Cd 0.869** 0.750** 0.788**

TCLP-Cd 0.824** 0.873** 0.716**

Exchangable As -0.737** 0.634* 0.854**

TCLP-As -0.641** 0.310 0.800**

* Significant at p < 0.05, ** significant at p < 0.01

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(4) Details of substances of the combined amendments for the Soil incubation

S. 4 Basic information of the amendments

Amendments Main ingredients Particle size(mm)

CaCO3 CaCO3 (AR) ≤ 0.149

Diatomite SiO2n·H2O (AR) ≤ 0.149

Zeolite A(x/q) [ (AlO2)x (SiO2)y ] n(H2O) (AR) 0.45~2.00

LaCl3 LaCl3(AR) /

Irion powder Fe(AR) ≤ 0.149

FeCl2 FeCl2(AR) /

Fe2(SO4)3 Fe2(SO4)3(AR) /

Sepiolite Mg8(H2O)4[Si6O15]2(OH)4·8H2O ≤ 0.149

Hydroxyapatite Ca10(PO4)6OH2 ≤ 0.149

Blast furnace slags* CaO、SiO2、Al2O3 ≤ 0.149

Flyash* SiO2、Al2O3 ≤ 0.149

Biochar C, SiO2, CaO ≤ 0.149

Notes: * supplied by local steel works.

S. 5 Basic properties of the tested paddy soil and part of the amendments

pHOM

（g·kg-1）CEC

（cmol·kg-1）BET

（m2·g-1）Total of heavy metal（mg·kg-1）

Pb Cd Cu Zn As

soil 5.54 36.91 12.67 - 256.61 4.60 45.28 430.97 134.89

Blast furnace slags 10.88 0 - 0.24 5.76 4.79 4.35 6.94 4.54

Flyash 11.76 0 - 0.25 4.34 6.36 5.78 6.97 7.75

Biochar 6.13 57.63 28.93 49.57 4.33 0.19 6.79 7.56 2.42

CaCO3 9.75 0 - 9.60 1.06 - - 7.76 6.66

Diatomite 5.46 0 - 46.20 2.85 - - 6.88 9.50

Sepiolite 5.48 0 - 22.80 2.75 - - 48.19 6.68

Zeolite 12.17 0 85.00 44.50 3.19 - - 135.10 7.62

Hydroxyapatite 8.21 0 28.93 20.49 1.18 - - 10.46 7.10

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S. 6 Different treatments in the experiment

Item Component and its abbreviation

one component material

0.4%(W/W)

CK:contraol group，C: CaCO3，D: Diatomite，S: Sepiolite，H:hydroxyapatite，Z: Zeolite，L: LaCl3

I: Irion powder，R: FeCl2，A: Fe2(SO4)3，E: Blast furnace slags，F: Flyash，B: Biochar

a combined amendment with two

substancesa

0.4%(W/W)

CD: CaCO3 (2)b+ Diatomite (1)，CS: CaCO3 (2)+ Sepiolite (1)，HZ: hydroxyapatite (2)+ Zeolite (1)

a combined amendment with three

substances

0.4%(W/W)

CDL: CaCO3 (2)+ Diatomite (1)+ LaCl3 (2) CDI: CaCO3 (2)+ Diatomite (1)+ Irion powder (2)

CDR: CaCO3 (2)+ Diatomite (1)+ FeCl2 (2) CDA: CaCO3 (2)+ Diatomite (1)+ Fe2(SO4)3 (2)

CDE: CaCO3 (2)+ Diatomite (1)+ Blast furnace slags (2) CDF: CaCO3 (2)+ Diatomite (1)+ Flyash (2)

CDB: CaCO3 (2)+ Diatomite (1)+ Biochar (2)

CSL: CaCO3 (2)+ Sepiolite (1) + LaCl3 (2) CSI: CaCO3 (2)+ Sepiolite (1)+ Irion powder (2)

CSR: CaCO3 (2)+ Sepiolite (1)+FeCl2 (2) CSA: CaCO3 (2)+ Sepiolite (1) + Fe2(SO4)3 (2)

CSE: CaCO3 (2)+ Sepiolite (1)+ Blast furnace slags (2) CSF: CaCO3 (2)+ Sepiolite (1)+ Flyash (2)

CSB: CaCO3 (2)+ Sepiolite (1)+ Biochar (2)

HZL: hydroxyapatite (2)+ Zeolite (1)+ LaCl3 (2) HZI: hydroxyapatite (2)+ Zeolite (1)+ Irion powder (2)

HZR: hydroxyapatite (2)+ Zeolite (1)+ FeCl2 (2) HZA: hydroxyapatite (2)+ Zeolite (1)+ Fe2(SO4)3 (2)

HZE: hydroxyapatite (2)+ Zeolite (1)+ Blast furnace slags (2) HZF: hydroxyapatite (2)+ Zeolite (1)+ Flyash (2)

HZB: hydroxyapatite (2)+ Zeolite (1)+ Biochar (2)

Others1E: 1%(W/W) Blast furnace slags，5E: 5% (W/W)Blast furnace slags，1F: 1% (W/W) Flyash

5F: 5% (W/W)Flyash，1B: 1%( W/W) Biochar，5B: 5% (W/W) Biochar

Notes：a. The combination of two substances at a mass ratio of 2:1 is referred to the preliminary test of the research group (Zhou et al., 2014; Wu et al., 2016).

b. The figure in brackets indicates the substance in the combination amendments at a mass ratio of 2:1 or 2:1:2.

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S. 7 Effects of various treatments on soil pH. The data were expressed as the means ± standard deviations (n = 3)

Abbreviation pH Abbreviation pH Abbreviation pH

one component material

CK 5.54±0.11 I 6.19±0.02 F 5.95±0.30

C 5.96±0.25 R 4.90±0.04 1F 6.37±0.10

D 5.87±0.30 A 4.85±0.07 5F 6.74±0.20

S 6.57±0.05 E 6.65±0.24 B 5.99±0.03

H 5.82±0.44 1E 6.49±0.06 1B 5.90±0.10

Z 6.11±0.12 5E 7.44±0.10 5B 5.89±0.13

L 5.47±0.15

a combined

amendment with

two substances

CD 6.40±0.06 CS 6.24±0.14 HZ 6.45±0.09

a combined

amendment with

three substances

CDL 6.20±0.10 CSL 5.94±0.04 HZL 6.14±0.10

CDI 7.02±0.13 CSI 6.26±0.07 HZI 6.70±0.16

CDR 5.93±0.06 CSR 5.86±0.09 HZR 5.71±0.23

CDA 6.10±0.02 CSA 5.60±0.12 HZA 5.65±0.07

CDE 5.93±0.11 CSE 6.25±0.08 HZE 6.11±0.18

CDF 6.34±0.18 CSF 6.18±0.11 HZF 6.07±0.08

CDB 6.23±0.04 CSB 6.10±0.07 HZB 6.00±0.06

S. 8 Effects of application of different amendments on the exchangeable of Cd and As concentrations in the tested soils. The data were expressed as the means ± standard deviations (n = 3)

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S. 9 Effects of application of different amendments on TCLP extracted concentrations of Cd and As in the tested soils. The data were expressed as the means ± standard deviations (n = 3)

References

Hseu, Z.Y., 2004. Evaluating heavy metal contents in nine composts using four digestion methods.

Bioresource Technol. 95, 53–59.

Liu, W.J., Zhu, Y.G., Hu, Y., Williams, P.N., Gault, A.G., Meharg, A.A., Charnock, J.M., Smith,

F.A., 2006. Arsenic sequestration in iron plaque, its accumulation and speciation in mature

rice plants (Oryza sativa L.). Environ. Sci. Technol. 40, 5730-5736.

Kahr, G., Madsen, F.T., 1995. Determination of the cation exchange capacity and the surface area

of bentonite, illite and kaolinite by methylene blue adsorption. Appl. Clay. Sci. 9, 327–336.

Nelson, D.W., Sommers, L.E., 1996. Total carbon, organic carbon, and organic matter. Methods of

Soil Analysis Part 3-Chemical Methods, Soil Science Society of America Inc, pp 961–1010.

Wu, Y.J., Zhou, H., Zou, Z.J., Zhu, W., Yang, W.T., Peng, P.Q., Zeng, M., Liao, B.H., 2016. A

three-year in-situ study on the persostence of a combined amendment (limestone+sepiolite)

for remedying paddy soil polluted with heavy metals. Ecotox. Environ. Safe. 130,163-173.

Zhou, H., Zhou, X., Zeng, M., Liu, L., Yang, W.T., Wang, Y.J., Liao, B.H., 2014. Effects of two

combined amendments on heavy metal bioaccumulation in paddy soil. Chin. Environ. Sci.

34, 437-444 (in Chinese).

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