**3.2 Selection of arsenic removing plants in the laboratory**


**133**

**Figure 3.**

*After [9].*

*Protecting Rice Grains from Arsenic Toxicity through Cultural Management...*

nitrogenase activity (**Figure 3a**–**d**) [9]. *A. pinnata* var. *pinnata* Dh 111, Dh 112, and Dh 113 strains grew well at 100 μg iAs/l. The growth of strains Dh 112 and Dh113 was identical even at 400 μg iAs/l in 3 days (**Figure 3b**). Only *A. pinnata* var. *pinnata* Dh 113 appeared to be suitable for absorption of iAs from 100 μg iAs/l [9]*.* This was due to the substantial absorption of PO4-P at 100 μg iAs/l and mild absorption in higher concentrations (**Figure 3c**)*. A. pinnata* var. *pinnata* Dh 113 absorbed about 0.0066% arsenic of d. wt. from 100 to 200 μg/l As in 3 days (**Figure 3b**) [9]*.* Only *A. pinnata* var. *pinnata* Dh 113 appeared to be suitable for absorption of As from 100 μg/l As [43]*.* The presence of higher amount of PO4-P in the iAs containing medium (**Figure 3c**) than the control (without iAs) suggests that after three days growth phosphate uptake was limited by plants and replaced by arsenate or competitively absorbed limiting ATP formation, indicated by decreased ATP-dependent nitrogenase activity, which was nil at 400 µg As/l (**Figure 3d**) [9]*. S. polyrhiza* Dh 116 and *S. punctata* Dh 116 were treated with arsenic trioxide in the laboratory to determine their ability to grow and absorb As and PO4-P (**Figure 4a**–**c**) [9]. The highest accumulation of 0.0351% iAs on dry wt. basis (**Figure 4b**) was observed in *S. polyrhiza* from 1000 μg iAs/l, and this was due to substantial absorption of PO4-P

*(a–d) Effects of arsenic trioxide in batch culture under controlled environments measured after 3 days of inoculation: (a) on growth, (b) % accumulation of As, (c) absorption of PO4-P, and (d) nitrogenase activity by Azolla species/strains—(1) A. caroliniana Dh103, (2) A. filiculoides Dh104, (3) A. pinnata var. pinnata Dh111, (4) A. pinnata var. pinnata Dh112, (5) A. pinnata var. pinnata Dh113, and (6) A. filiculoides Dh115.* 

*DOI: http://dx.doi.org/10.5772/intechopen.85909*

from medium containing 1000 μg iAs/l (**Figure 4c**).

Six strains of *Azolla* under three species were treated with arsenic trioxide in the laboratory to determine their ability to grow and absorb As, PO4-P uptake, and

### **Table 1.**

*Prevalence of arsenic in soils and waters at Sonargaon.*

### *Protecting Rice Grains from Arsenic Toxicity through Cultural Management... DOI: http://dx.doi.org/10.5772/intechopen.85909*

nitrogenase activity (**Figure 3a**–**d**) [9]. *A. pinnata* var. *pinnata* Dh 111, Dh 112, and Dh 113 strains grew well at 100 μg iAs/l. The growth of strains Dh 112 and Dh113 was identical even at 400 μg iAs/l in 3 days (**Figure 3b**). Only *A. pinnata* var. *pinnata* Dh 113 appeared to be suitable for absorption of iAs from 100 μg iAs/l [9]*.* This was due to the substantial absorption of PO4-P at 100 μg iAs/l and mild absorption in higher concentrations (**Figure 3c**)*. A. pinnata* var. *pinnata* Dh 113 absorbed about 0.0066% arsenic of d. wt. from 100 to 200 μg/l As in 3 days (**Figure 3b**) [9]*.* Only *A. pinnata* var. *pinnata* Dh 113 appeared to be suitable for absorption of As from 100 μg/l As [43]*.* The presence of higher amount of PO4-P in the iAs containing medium (**Figure 3c**) than the control (without iAs) suggests that after three days growth phosphate uptake was limited by plants and replaced by arsenate or competitively absorbed limiting ATP formation, indicated by decreased ATP-dependent nitrogenase activity, which was nil at 400 µg As/l (**Figure 3d**) [9]*.*

*S. polyrhiza* Dh 116 and *S. punctata* Dh 116 were treated with arsenic trioxide in the laboratory to determine their ability to grow and absorb As and PO4-P (**Figure 4a**–**c**) [9]. The highest accumulation of 0.0351% iAs on dry wt. basis (**Figure 4b**) was observed in *S. polyrhiza* from 1000 μg iAs/l, and this was due to substantial absorption of PO4-P from medium containing 1000 μg iAs/l (**Figure 4c**).

#### **Figure 3.**

*Protecting Rice Grains in the Post-Genomic Era*

again for the next one week [29].

**3. Results and discussion**

**3.1 Water and soil chemistry**

several hundred or more.

is shown in **Figure 2**.

3.40 ± 0.90\* 0.95\* 495 ± 10.00

alternative source(s) need to be found out.

**3.2 Selection of arsenic removing plants in the laboratory**

**DTW STW HTW Pond**

8.85

8.15

8.10

6.10\*

*\*Indicate values of two tube wells from village Kachua P.S. Kachua (moderately affected area).*

(3 years old) 313 ± 4.00 (2 years old) 92.2 ± 1.50 (1 year old) 150 ± 3.00\* (3 years old)

*Prevalence of arsenic in soils and waters at Sonargaon.*

were transplanted and irrigated once in a week with pond water as control and 500 µg As/l contaminated STW water that dries up by the end of that week and watered

Prevalence of total arsenic (As) in soil and water sources collected from areas at a gap of 0.5–1.0 km in the winter and spring seasons at Sonargaon is given in **Table 1**. Arsenic in pond water was due to seepage and water flow from the household use of As-contaminated HTW. The concentration of iron had direct correlation to the amount of arsenic present. Rice field soils in the areas had highest arsenic ranging from 5.83 to 8.01 mg/kg (due to weekly irrigation about nine times with STW water), followed by wheat (due to broadcast seeding and standing irrigation after 20, 60, and 80 days (before flowering)) and vegetable fields (due to non-standing irrigation two times during dry period). Water from the HTW was found to have 131 ± 0.1 μg As/l (10 years old) to 475.5 ± 10.6 μg As/l (25 years old). Similarly, 1-year-old STW water was found to have 92.2 ± 1.5 μg As/l, while the 3-year-old one had 495.0 ± 10 μg As/l indicating that the older the tube well, the more is the groundwater arsenic indicating tube wells having less than 100 μg As/l in the early 2000s most likely have now increased to

The water of 1-year-old DTW was with very little or no arsenic, while STW had 150 ± 3.0 μg As/l and has been found to be moderately affected [1] at village Kachua in Meghna floodplain. In Ganges floodplain, there are reports of an average 210 μg As/l in DTW water in many areas of Jessore district and in highly affected areas (**Figure 1**). The most alarming point is that each and every crop had arsenic toxicity for irrigating with GW (**Table 1**). To get a good yield, irrigation is a must and

Quality of pond and STW waters used in irrigating rice cultivation experiments

Six strains of *Azolla* under three species were treated with arsenic trioxide in the laboratory to determine their ability to grow and absorb As, PO4-P uptake, and

**As Iron As Iron As Iron As Iron Rice Wheat Vege.**

7.40

9.66 ± 1.16 9.13 ± 0.31 3.20 ± 0.20 3.11 ± 0.17

0.83 0. 70 0. 44 0.30

7.65 6.39 7.88 8.01 5.83 7.48 4.42 4.23 3.15 4.09

3.15 2.53 1.96 4.21 3.65 3.68 4.02 2.66

6.10

6.30

7.60

**Waters (μg/l for As, mg/l for iron) Soils (mg/kg)**

250.5 ± 2.08 (15 years old) 131.0 ± 0.10 (10 years old) 152.0 ± 3.5 (10 years old) 475.5 ± 10.6 (25 years old)

**132**

**Table 1.**

*(a–d) Effects of arsenic trioxide in batch culture under controlled environments measured after 3 days of inoculation: (a) on growth, (b) % accumulation of As, (c) absorption of PO4-P, and (d) nitrogenase activity by Azolla species/strains—(1) A. caroliniana Dh103, (2) A. filiculoides Dh104, (3) A. pinnata var. pinnata Dh111, (4) A. pinnata var. pinnata Dh112, (5) A. pinnata var. pinnata Dh113, and (6) A. filiculoides Dh115. After [9].*

### **Figure 4.**

*(a–c) Effects of arsenic trioxide in batch culture under controlled environments measured after 3 days of inoculation: (a) on growth, (b) % accumulation of As, and (c) absorption of PO4-P by Spirodela—(1) S. polyrhiza Dh116 and (2) S. punctata Dh117. After [9].*

Of the eight floating plants tested, *S. polyrhiza* Dh 116 showed the highest absorption capacity to be much higher than *A. pinnata* var. *pinnata* Dh 113 [9].

### **3.3 Bio-mitigation of As from contaminated STW water using** *S. polyrhiza*

### *3.3.1 Removing As in a mini-scale with the water in cemented tubs*

In the laboratory *S. polyrhiza* showed the highest accumulation (0.0351% As on dry wt. basis) among floating plants from 1000 μg/l in 3 days (**Figure 4b**) [9]. Therefore, outdoor experiments were carried out at Sonargaon growing the DW in RCC tubs in 475.5 ± 10.6 μg As/l water and 6.30 mg Fe/l (**Figure 5a**–**c**). The DW absorbed about 295 mg As/kg d. wt. after 24-hour treatment (**Figure 5a**). A substantial amount of As was coagulated with iron (synergistic reaction) from 24 hours to 6 days giving similar curve like absorption of As by DW (**Figure 5b** and **c**).

### *3.3.2 Removing As in a large-scale keeping the water in a pond*

The *S. polyrhiza* Dh 116 absorbed about 295 mg/kg d. wt. after 24 hours in tub experiment and thus could be a good candidate for mitigating As from the contaminated STW water in a large scale (**Figure 6a**–**c**). The 350 m2 pond contains 350 m3

**135**

**Figure 5.**

*cemented (RCC) tubs.*

*Protecting Rice Grains from Arsenic Toxicity through Cultural Management...*

or 350,000 l water. One liter STW water contains 500 μg As/l. Three hundred fifty thousand liters of water would contain 175 g As from which 157.5 g is to be removed to get 50 μg As/l acceptable level of irrigation water. The DW removed 325 mg As/ kg dry DW (**Figure 7a**) with similar iron absorption curve in 2 days (**Figure 7b**). Therefore, 350 kg fresh DW was equal to 20 kg dry DW (5% basis) which could remove 6500 mg or 6.5 g As, and thus to remove 157.5 g arsenic 24-hour treatment means 8.4 ton fresh DW would be needed in 48 days. In each 24 hour, arsenic loaded roots and plant debris, and As and Fe coagulates (synergistic) deposited 63.7 mg As on the pond bottom (**Figure 7d** and **e**), estimated to be about 1.529 g As after treatment. The bioremediation technique is time-consuming and expensive, requiring

*(a–c) Changes in concentration of 475.5 ± 10.6 μg As/l HTW water after treatment with S. polyrhiza dh 116 in* 

two ponds and over eight tons As-loaded DW waste.

*DOI: http://dx.doi.org/10.5772/intechopen.85909*

*Protecting Rice Grains from Arsenic Toxicity through Cultural Management... DOI: http://dx.doi.org/10.5772/intechopen.85909*

### **Figure 5.**

*Protecting Rice Grains in the Post-Genomic Era*

Of the eight floating plants tested, *S. polyrhiza* Dh 116 showed the highest absorption capacity to be much higher than *A. pinnata* var. *pinnata* Dh 113 [9].

*(a–c) Effects of arsenic trioxide in batch culture under controlled environments measured after 3 days of inoculation: (a) on growth, (b) % accumulation of As, and (c) absorption of PO4-P by Spirodela—(1) S.* 

**3.3 Bio-mitigation of As from contaminated STW water using** *S. polyrhiza*

In the laboratory *S. polyrhiza* showed the highest accumulation (0.0351% As on dry wt. basis) among floating plants from 1000 μg/l in 3 days (**Figure 4b**) [9]. Therefore, outdoor experiments were carried out at Sonargaon growing the DW in RCC tubs in 475.5 ± 10.6 μg As/l water and 6.30 mg Fe/l (**Figure 5a**–**c**). The DW absorbed about 295 mg As/kg d. wt. after 24-hour treatment (**Figure 5a**). A substantial amount of As was coagulated with iron (synergistic reaction) from 24 hours to 6 days giving similar curve like absorption of As by DW (**Figure 5b**

The *S. polyrhiza* Dh 116 absorbed about 295 mg/kg d. wt. after 24 hours in tub experiment and thus could be a good candidate for mitigating As from the contami-

pond contains 350 m3

*3.3.1 Removing As in a mini-scale with the water in cemented tubs*

*polyrhiza Dh116 and (2) S. punctata Dh117. After [9].*

*3.3.2 Removing As in a large-scale keeping the water in a pond*

nated STW water in a large scale (**Figure 6a**–**c**). The 350 m2

**134**

and **c**).

**Figure 4.**

*(a–c) Changes in concentration of 475.5 ± 10.6 μg As/l HTW water after treatment with S. polyrhiza dh 116 in cemented (RCC) tubs.*

or 350,000 l water. One liter STW water contains 500 μg As/l. Three hundred fifty thousand liters of water would contain 175 g As from which 157.5 g is to be removed to get 50 μg As/l acceptable level of irrigation water. The DW removed 325 mg As/ kg dry DW (**Figure 7a**) with similar iron absorption curve in 2 days (**Figure 7b**). Therefore, 350 kg fresh DW was equal to 20 kg dry DW (5% basis) which could remove 6500 mg or 6.5 g As, and thus to remove 157.5 g arsenic 24-hour treatment means 8.4 ton fresh DW would be needed in 48 days. In each 24 hour, arsenic loaded roots and plant debris, and As and Fe coagulates (synergistic) deposited 63.7 mg As on the pond bottom (**Figure 7d** and **e**), estimated to be about 1.529 g As after treatment. The bioremediation technique is time-consuming and expensive, requiring two ponds and over eight tons As-loaded DW waste.

### **Figure 6.**

*(a–c) Bioremediation process of arsenic contaminated GW using S. polyrhiza. (a) 50o μg/l As STW water immediately after storage in the pond appeared grayish red colored, (b) a complete cover of the DW on the water, and (c) half of the DW cover removed after 8 days of treatment showing relatively clear water. Inset in "c" shows dorsal and ventral surfaces of the plant.*
