Simultaneous decrease of arsenic and cadmium in rice (Oryza sativa L.) plants cultivated under submerged field conditions by the application of iron-bearing materials

Figures & data

Table 1. Soil properties.

Site	Soil type	pH	Total carbon	Total nitrogen	CEC	Available phosphorus	PAC	Fe		Available silicate	As	Cd
								Free iron oxide	Non-crystalline iron oxide
			(g kg^−1)		(cmolc kg^−1)	(mg P2O5 kg^−1)	(g P2O5 kg^−1)	(g kg^−1)		(mg kg^−1)
A	Humic Gley Lowland soil	5.62	54.4	4.03	28.7	149	12.5	33.8	16.8	13.5	8.45	3.76
B	Mottled Gley Lowland soil	5.78	16.6	1.54	12.1	189	5.56	13.5	5.60	11.0	2.45	0.791
C	Epi–gray Gley Lowland soil	5.92	20.7	1.65	13.2	131	4.59	9.03	5.52	24.6	1.83	0.144
D	Haplic Gray Lowland soil	5.96	28.5	2.62	26.5	101	12.8	22.9	11.3	31.1	6.46	0.288
E	Haplic Gray Upland soil	6.79	15.7	1.46	10.6	327	3.74	7.33	3.84	30.9	1.63	0.222
F	Wet Andosol	6.45	85.6	5.53	43.8	88.2	22.4	20.1	16.9	19.3	1.39	0.166

CEC: cation exchange capacity, PAC: phosphorus absorption capacity (Araki et al. 1986), Si: available silicate (Nonaka and Takahashi 1988), Mn: exchangeable manganese, As: 1 mol L⁻¹ HCl-extractable As, Cd: 0.1 mol L⁻¹ HCl extractable Cd. Fe: Iron, P₂O₅: diphosphorus pentoxide.

Table 2. Cultivation design.

Site	Year	Location	Plot size (m^2)	Variety	Transplanting	Rice heading	Harvest	Fertilizer* (N:P2O5:K2O g m^−2)
A	2013	Farmer’s field	14	Akitakomachi	28 May	3 August	20 September	6:9:7
B	2013	Farmer’s field	12	Koshihikari	13 May	8 August	18 September	4.2:3:3
C	2013	Experintal station	20	Koshihikari	10 May	26 July	30 August	7:3:8
D	2013	Farmer’s field	25	Koshihikari	5 May	20 July	18 August	3:4:3
E	2014	Experintal station	9.2	Hinohikari	10 June	24 August	1 October	8:8:7
F	2014	Experintal station	18	Koshihikari	13 May	30 July	2 September	6:12:9

*: Total amount including basal and additional fertilization. N: nitrogen; P₂O₅: diphosphorus pentoxide.

Table 3. Two-way analysis of variance (ANOVA) of arsenic (As), iron (Fe) and silicon (Si) concentration and pH of soil solution during cultivation period in each site and material.

Site	As (μM L^−1)	Fe (mM L^−1)	Si (mM L^−1)	pH
A	1.03a	1.88a	0.376a	6.87a
B	0.570b	1.16a	0.269b	6.57c
C	0.599b	1.94b	0.328ab	6.61bc
E	0.153c	0.344c	0.257b	6.95a
F	0.022c	0.217c	0.116c	6.70b
Material
REF	0.741a	1.18a	0.244a	6.49a
SCS	0.589a	0.718b	0.332b	7.02b
FH	0.346b	1.07a	0.234a	6.63c
ZVI	0.134c	1.33a	0.246a	6.81d
Analysis of variance
Site	**	**	**	**
Material	**	**	**	**
Site × Material	**	NS	NS	**

Data represents mean values of sampled soil solutions during the cultivation period.

Values with different letters are significantly different as judged by Tukey-Kramer multiple comparison test at p < 0.05.

**: Significant at 0.01 probability on analysis of variance.

NS: no significant difference.

REF: reference, no treatment; FH: non-crystalline iron hydroxide; SCS: steel converter furnace slag; ZVI: zero-valent iron.

Table 4. Two-way analysis of variance (ANOVA) of arsenic (As) and cadmium (Cd) concentration in rice (Oryza Sativa L.) grain and rice stem.

Site	Rice As (mg kg^−1)	Rice iAs (mg kg^−1)	Rice Cd (mg kg^−1)	Stem As (mg kg^−1)	Stem Cd (mg kg^−1)
A	0.253b	0.164b	0.013a	4.27b	0.326a
B	0.380a	0.295a	0.006b	8.07a	0.046b
C	0.389a	0.265a	0.001b	7.40a	0.013b
D	0.321a	0.303a	0.007ab	4.86b	0.019b
E	0.147c	0.117c	0.002b	1.07c	0.019b
F	0.070d	0.050d	0.008ab	0.144c	0.027b
Material
REF	0.347a	0.272a	0.009a	7.54a	0.099a
SCS	0.234b	0.178b	0.004a	3.51b	0.042b
FH	0.239b	0.184b	0.007a	4.01b	0.092a
ZVI	0.161c	0.138c	0.007a	2.01c	0.080ab
Analysis of variance
Site	**	**	**	**	**
Material	**	**	NS	**	*
Site × Material	**	**	NS	**	**

Data represent mean values of sampled soil solutions during cultivation period.

Values with different letters are significantly different as judged by Tukey-Kramer multiple comparison test at p < 0.05.

*, **: significant at 0.05 and 0.01 probabilities on analysis of variance, respectively.

NS: no significant difference.

REF: reference, no treatment; FH: non-crystalline iron hydroxide; SCS: steel converter furnace slag; ZVI: zero-valent iron.

Table 5. Two-way analysis of variance (ANOVA) of yield and whole grain ratio.

Site	Rice yield (g/m^2)	Stem yield (g/m^2)	Whole grain ratio (%)
A	516c	594b	86.1a
B	576b	602b	67.5b
C	652a	644ab	63.2c
D	528bc	697a	48.8d
E	484c	450d	76.3e
F	572b	521c	71.9f
Material
REF	563a	574ab	70.0b
SCS	571a	591a	69.9b
FH	556a	571ab	72.8ab
ZVI	542a	546b	73.2a
Analysis of variance
Site	**	**	**
Material	NS	NS	**
Site × Material	NS	NS	**

Data represent mean values of sampled soil solutions during cultivation period. Values with different letters are significantly different as judged by Tukey-Kramer multiple comparison test at p < 0.05.

** Significant at 0.01 probability on analysis of variance. NS: no significant difference.

REF: reference, no treatment; FH: non-crystalline iron hydroxide; SCS: steel converter furnace slag; ZVI: zero-valent iron.

Figure 1. (a) Relationship between iron (Fe) and arsenic (As) concentrations in soil solution in (a) Site A, (b) Site B, (c) Site C, (d) Site E and (e) Site F (soil depth: 5 cm). REF: reference, no treatment; FH: non-crystalline iron hydroxide; SCS: steel converter furnace slag; ZVI: zero-valent iron.

Figure 2. Effect of iron materials on cadmium (Cd) concentration in soil solution at site B during the cultivation period (soil depth: 5 cm). Error bars indicate standard deviation. The numbers on the x-axis indicate sampling times, which are: 1, just before midseason drainage; 2, after midseason drainage; 3, 2 weeks before heading; 4, at heading; and 5, 2–3 weeks after heading. REF: reference, no treatment; FH: non-crystalline iron hydroxide; SCS: steel converter furnace slag; ZVI: zero-valent iron.

Figure 3. Relationship between arsenic (As) in soil solution and that in brown rice (Oryza sativa L.).

Figure 4. Relationship between arsenic (As) concentration in brown rice (Oryza sativa L.) and reduction ratio of As by iron-relevant materials. FH: non-crystalline iron hydroxide; SCS: steel converter furnace slag; ZVI: zero-valent iron.

Araki S, Hirai H, Kyuma K 1986: Phosphate absorption of red and/or yellow colored soil materials in relation to the characteristics of free oxides. Soil Sci. Plant Nutr., 32, 609–616. http://www.tandfonline.com/doi/abs/10.1080/00380768.1986.10557542.

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Nonaka K, Takahashi K 1988: A method of measuring available silicates in paddy soils. JARQ, 22, 91–95.

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