Use of water-treatment residue containing polysilicate-iron to stabilize arsenic in flooded soils and attenuate arsenic uptake by rice (Oryza sativa L.) plants

Figures & data

Table 1. Time course of the concentrations of dissolved arsenic (As), iron (Fe) and silicon (Si) in soil solution during the cultivation period.

WTR application rate (t ha^‒1)	Sampling day
	Day 46	Day 61	Day 69	Day 79	Day 90	Day 107
Dissolved As (μg L^‒1)
0	93.3 ± 7.9	220 ± 24	251 ± 8	265 ± 6	299 ± 18	247 ± 20
5	71.3 ± 11.4	201 ± 33	203 ± 27	234 ± 41	255 ± 49	216 ± 33
10	70.9 ± 17.3	159 ± 18	185 ± 10	181 ± 33	212 ± 15	177 ± 29
20	60.5 ± 9.5	138 ± 15	127 ± 32	138 ± 41	167 ± 36	138 ± 41
Dissolved Fe (mg L^‒1)
0	174 ± 37	272 ± 0.0	266 ± 18	230 ± 16	213 ± 12	214 ± 12
5	161 ± 7.0	252 ± 55	252 ± 39	214 ± 29	207 ± 25	214 ± 14
10	168 ± 40	260 ± 23	261 ± 41	214 ± 39	200 ± 29	210 ± 27
20	179 ± 26	266 ± 35	243 ± 72	209 ± 52	199 ± 53	206 ± 53
Dissolved Si (mg L^‒1)
0	1.88 ± 0.33	3.20 ± 0.94	3.24 ± 1.03	5.73 ± 1.24	9.05 ± 1.08	10.1 ± 0.8
5	2.07 ± 0.18	3.31 ± 1.03	3.35 ± 1.01	5.39 ± 2.02	8.39 ± 2.88	9.6 ± 2.1
10	3.01 ± 0.47	4.53 ± 0.22	4.14 ± 0.13	6.15 ± 0.60	9.24 ± 1.17	10.1 ± 0.8
20	3.39 ± 0.28	5.49 ± 0.94	4.34 ± 1.62	6.44 ± 1.34	8.67 ± 2.25	9.3 ± 3.6
			(mean ± standard deviation, n = 3)

WTR: water-treatment residue.

Table 2. Simple linear regression analyses for dissolved arsenic (As), iron (Fe) and silicon (Si) (Y) against water-treatment residue (WTR) application rate (X).

X: WTR application rate (t ha^‒1)	Sampling day
	Day 46	Day 61	Day 69	Day 79	Day 90	Day 107
Y: Dissolved As (μg L^‒1)
Slope	−1.44	−4.29	−5.93	−6.50	−6.54	−5.52
Intercept	87	217	243	261	291	243
R^2	0.471	0.689	0.842	0.736	0.748	0.702
r	−0.686	−0.830	−0.918	−0.858	−0.865	−0.838
Significance^†	P < 0.01	P < 0.001	P < 0.001	P < 0.001	P < 0.001	P < 0.001
Y: Dissolved Fe (mg L^‒1)
Slope	0.482	−0.048	−0.956	−0.849	−0.669	−0.414
Intercept	166	263	264	224	211	215
R^2	0.019	0.000	0.033	0.042	0.032	0.014
r	0.138	−0.012	−0.181	−0.205	−0.180	−0.120
Significance^†	NS	NS	NS	NS	NS	NS
Y: Dissolved Si (mg L^‒1)
Slope	0.081	0.123	0.060	0.045	−0.007	−0.032
Intercept	1.88	3.05	3.25	5.54	8.90	10.04
R^2	0.760	0.609	0.193	0.075	0.001	0.017
r	0.872	0.781	0.439	0.273	−0.033	−0.130
Significance^†	P < 0.001	P < 0.01	NS	NS	NS	NS
						(n = 12)

^†Left tail for As, right tail for Fe and Si.

NS: not significant.

Table 3. Time course of the decrease percentage of dissolved arsenic (As) concentration by water-treatment residue (WTR) application and two-way repeated measures analysis of variance (ANOVA)

WTR application rate (t ha^‒1)	Sampling day						Average
	Day 46	Day 61	Day 69	Day 79	Day 90	Day 107
5	23.5 ± 12.2	8.6 ± 15.1	19.0 ± 10.7	11.5 ± 15.3	14.6 ± 16.4	12.5 ± 13.4	15.0 ± 5.5
10	24.0 ± 18.6	27.9 ± 8.2	26.1 ± 3.9	31.7 ± 12.6	29.1 ± 5.0	28.5 ± 11.7	27.9 ± 2.6
20	35.2 ± 10.2	37.6 ± 6.9	49.5 ± 12.8	48.0 ± 15.5	44.2 ± 12.2	44.4 ± 16.6	43.1 ± 5.7
				(mean ± standard deviation, n = 3)
Two-way ANOVA
Application rate (A)		P < 0.05
Sampling day (S)		NS
A × S		NS

NS: not significant.

Figure 1. Simple linear regressions for rice grain, husk, straw and total shoot biomass against water-treatment residue (WTR) application rate.

Table 4. Concentrations and contents of arsenic (As) and silicon (Si) in rice (Oryza sativa L.) tissues and simple linear regression analyses for As and Si in rice (Oryza sativa L.) tissues (Y) against water-treatment residue (WTR) application rate (X).

	Y: Concentration (mg kg^‒1)			Y: Content (mg pot^‒1 for As, g pot^‒1 for Si)
X: WTR application rate (t ha^‒1)	As in grain	As in husk	As in straw	As in shoot	Si in shoot
0	0.941 ± 0.064	5.78 ± 0.19	26.2 ± 1.2	1.09 ± 0.01	1.56 ± 0.05
5	0.766 ± 0.010	4.64 ± 0.18	20.9 ± 0.7	0.91 ± 0.02	1.77 ± 0.08
10	0.753 ± 0.120	4.46 ± 0.67	19.4 ± 3.7	0.86 ± 0.12	2.05 ± 0.25
20	0.743 ± 0.104	3.95 ± 0.68	15.3 ± 3.0	0.74 ± 0.09	2.42 ± 0.05
			(mean ± standard deviation, n = 3)
Slope	−0.008	−0.082	−0.508	−0.016	0.043
Intercept	0.9	5.4	24.9	1.0	1.6
R^2	0.322	0.602	0.735	0.718	0.890
r	−0.567	−0.776	−0.858	−0.847	0.943
Significance^†	P < 0.05	P < 0.01	P < 0.001	P < 0.001	P < 0.001
					(n = 12)

^†Left tail for As, right tail for Fe and Si.

Figure 2. Effects of water-treatment residue (WTR) application on arsenic (As) speciation in rice (Oryza sativa L.) grain. DMA denotes dimethylarsinic acid. The sum of As(III), As(V) and DMA was set as 100%. Monomethylarsonic acid was not detected (< 0.0006 mg As kg^‒1).