**3.4 Effects of As-contaminated irrigation water on rice cultivation**

"Boro" rice BR28 was grown in 500 μg As/l STW water (Section 2.6).

### *3.4.1 Arsenic in rice-cultivated soil*

Arsenic concentration in soils of the experimental plots during rice cultivation is shown in **Figure 8**. Initial soil As was 3.21 mg/kg, increased to 7.51 mg/kg due to low uptake of As during seedling adaptation stage for 7 days irrigation with 500 μg As/l and 8.85 mg Fe/l STW water. During March rapid vegetative growth results in rapid uptake of As, reducing it to 5.50 mg As/kg soil. Further absorption

**137**

**Figure 7.**

*pond and natural coagulation.*

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

during panicle initiation, grain formation, and maturation in April reduced As to 4.90 mg/kg soil. Irrigation was stopped after a week creating non-flooded condition when As solubility decreased [15] simultaneously with low or no nutrient uptake by mature plants, increasing As concentration to 8.27 ± 1.35 mg/kg soil during harvest (**Figure 8**). There are reports on the increased soil As for using contaminated GW in rice fields year after year to 1.0 and 1.1 mg/kg soil in

*(a–e) Changes in As (500 μg As/l) and Fe (8.85 mg/l iron) after treating with S. polyrhiza in the treatment* 

In irrigated pond water (**Figure 8**), As concentration insignificantly decreases till the day of harvesting, ranging from 1.91 ± 0.26 to 2.6 ± 0.80 mg/kg soil from initial 3.21 mg/ kg. Only roots absorbed 0.075–0.156 mg As/kg in the presence of a good amount of As for the growing period (**Figures 8** and **9**). It appears that As absorption in pond water

Bangladesh [16] and West Bengal [44], respectively.

*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 7.**

*Protecting Rice Grains in the Post-Genomic Era*

**136**

**Figure 6.**

*3.4.1 Arsenic in rice-cultivated soil*

*"c" shows dorsal and ventral surfaces of the plant.*

**3.4 Effects of As-contaminated irrigation water on rice cultivation**

"Boro" rice BR28 was grown in 500 μg As/l STW water (Section 2.6).

*(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* 

Arsenic concentration in soils of the experimental plots during rice cultivation is shown in **Figure 8**. Initial soil As was 3.21 mg/kg, increased to 7.51 mg/kg due to low uptake of As during seedling adaptation stage for 7 days irrigation with 500 μg As/l and 8.85 mg Fe/l STW water. During March rapid vegetative growth results in rapid uptake of As, reducing it to 5.50 mg As/kg soil. Further absorption

*(a–e) Changes in As (500 μg As/l) and Fe (8.85 mg/l iron) after treating with S. polyrhiza in the treatment pond and natural coagulation.*

during panicle initiation, grain formation, and maturation in April reduced As to 4.90 mg/kg soil. Irrigation was stopped after a week creating non-flooded condition when As solubility decreased [15] simultaneously with low or no nutrient uptake by mature plants, increasing As concentration to 8.27 ± 1.35 mg/kg soil during harvest (**Figure 8**). There are reports on the increased soil As for using contaminated GW in rice fields year after year to 1.0 and 1.1 mg/kg soil in Bangladesh [16] and West Bengal [44], respectively.

In irrigated pond water (**Figure 8**), As concentration insignificantly decreases till the day of harvesting, ranging from 1.91 ± 0.26 to 2.6 ± 0.80 mg/kg soil from initial 3.21 mg/ kg. Only roots absorbed 0.075–0.156 mg As/kg in the presence of a good amount of As for the growing period (**Figures 8** and **9**). It appears that As absorption in pond water

### **Figure 8.**

*Arsenic concentration in soils of the experimental plots during rice cultivation transplanted on 15 Feb 2004, irrigated with pond and shallow tube well waters. Initial soil arsenic was 3.21 mg/kg; contaminated pond water had only 9.50 ± 0.50 μg/l, while STW water had 500 μg As/l. Rice crop harvested on 10 may. After [43]. n = 5; vertical bars, standard deviation.*

#### **Figure 9.**

*Arsenic concentration in roots, straw, and brown rice grains of BR 28 at the time of harvest. Initial soil arsenic was 3.21 mg/kg, while pond and shallow tube well waters contained 9.50 ± 0.50 and 476 ± 3 μg/l arsenic, respectively. After [43]. n = 5; ± and vertical bars are standard deviation.*

irrigated plots is limited at 2.6 ± 0.80 mg/kg soil. Therefore, 2.5 mg/kg soil could be considered as a safe level for arsenic-free rice cultivation in Bangladesh. The permissible limit for the USA is 5 mg As/kg soil for agricultural use [45].

**139**

of arsenic in nails and hairs.

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

needed for producing 1 kg rice, considering production of 4.0 ton/ha.

It has been estimated that Bangladesh clayey soil needs about 1000 l irrigation

Arsenic accumulation in the "Boro" rice plant parts was mostly in roots followed by shoots, brown-rice grains (**Figure 9**), and husks. The rice grain contained 2.552 ± 0.507 mg/kg As, similar to adjacent rice field (2.56 ± 0.20 mg/kg) which was determined by neutron activation analysis. The presence of 1.7–1.8 mg/kg rice grains was recorded in areas having 15–27 mg As/kg soil [13]. The high As content in straws found in the present study might affect cattle due to bioaccumulation when consumed, while roots would contribute about 5.7 mg/kg for the next crop. Using pond water as a control in the same field, only roots absorbed o.113 ± 0.054 mg As/kg

The concentration of absorbed As in rice grains was much above the permissible limit of 1.00 mg/kg [14] for human consumption. It was estimated that elevated inorganic arsenic in rice significantly contributes to dietary arsenic intake in USA [17], which was estimated to be double (80%) in Bangladesh and India, and the rest was dimethyl-arsenate (DMA). Bioavailability of iAs from rice was reported to be high [15]. It was estimated that As concentration in rice would have to be as low as 0.050 mg/kg if consumed at 200 g/d to equate to similar exposure from drinking water at 10 μg/l [18]. Sonargaon rice contain 2.552 ± 0.507 mg As/kg which would have 0.85–1.276 mg iAs per kg rice assuming about 33–50% of As according to [46], while there are reports of 22–42% iAs, and the rest was DMA [15]. This in quantity ranged from 0.561 to 1.072 mg iAs/kg for Bangladesh rice. If the lowest amount 0.561 mg iAs/kg rice grain is considered and equates to permissible limit of 0.050 mg/l water (which would be about 0.250 mg iAs/kg consumed at 200 g/day by a 60 kg adult person), then a person in the study area is consuming double the amount of permissible iAs compared to China's food standard limit of 0.15 mg iAs/ kg [38]. Thus estimated high iAs present in the rice grain at Sonargaon can lead to

The presence of arsenic affects PO4-P absorption from the liquid medium by plants where phosphate is replaced by arsenates and prevents ATP synthesis [6, 9, 23]. Therefore, if the phosphorus, for example, is 50% less than the required amount in a cell, it could be assumed that the required amount of ATP synthesis would not take place affecting physiology, cell division to new cell formation, etc. in any affected organism. The high total arsenic in the soil would affect all the biotic communities including biological N2-fixing soil bacteria, as is found in *A. pinnata* var. *pinnata* where ATP-dependent nitrogenase activity was severely affected [9]. A Rickshaw (a three-wheeler, non-mechanized) puller in the present study area had melanosis (hyper-pigmentation) or reddish spots, hairs having 3.99 ± 0.21, and nails having 8.90 ± 0.29 mg As/kg identified as "first stage group" [14] drinking 250 μg/l As for 2 years which was 8.42 mg/kg body wt. The lower value (4–8 mg As/kg samples) was due to the release of arsenic by deamination, and the accumulation may be higher in other parts of a body. Piped water from DTW was supplied for 2 years by the NGO Forum in the village of Nilkanda, Sonargaon; still farmers, day laborers, and Rickshaw pullers of many villages show symptoms of arsenicosis. The reason could be retention of arsenic in their body and most likely also eating high arsenic-containing rice, wheat, and vegetables (**Table 1**). The manifestation of the symptom (melanosis) appears to take place after some years of drinking and eating arsenic-contaminated water, rice, vegetables, etc. [17] as indicated by high amount

/year (in conservative use) [11]; in other words 2500 l/kg surface water is

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

leaving mean As 2.60 mg/kg soil.

*3.4.2 Arsenic distributions/accumulations in rice crops*

greatly increased exposure to chronic carcinogen.

water/m2

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

It has been estimated that Bangladesh clayey soil needs about 1000 l irrigation water/m2 /year (in conservative use) [11]; in other words 2500 l/kg surface water is needed for producing 1 kg rice, considering production of 4.0 ton/ha.

### *3.4.2 Arsenic distributions/accumulations in rice crops*

*Protecting Rice Grains in the Post-Genomic Era*

*Arsenic concentration in soils of the experimental plots during rice cultivation transplanted on 15 Feb 2004, irrigated with pond and shallow tube well waters. Initial soil arsenic was 3.21 mg/kg; contaminated pond water had only 9.50 ± 0.50 μg/l, while STW water had 500 μg As/l. Rice crop harvested on 10 may. After [43].* 

*Arsenic concentration in roots, straw, and brown rice grains of BR 28 at the time of harvest. Initial soil arsenic was 3.21 mg/kg, while pond and shallow tube well waters contained 9.50 ± 0.50 and 476 ± 3 μg/l arsenic,* 

irrigated plots is limited at 2.6 ± 0.80 mg/kg soil. Therefore, 2.5 mg/kg soil could be considered as a safe level for arsenic-free rice cultivation in Bangladesh. The permissible

*respectively. After [43]. n = 5; ± and vertical bars are standard deviation.*

limit for the USA is 5 mg As/kg soil for agricultural use [45].

**138**

**Figure 9.**

**Figure 8.**

*n = 5; vertical bars, standard deviation.*

Arsenic accumulation in the "Boro" rice plant parts was mostly in roots followed by shoots, brown-rice grains (**Figure 9**), and husks. The rice grain contained 2.552 ± 0.507 mg/kg As, similar to adjacent rice field (2.56 ± 0.20 mg/kg) which was determined by neutron activation analysis. The presence of 1.7–1.8 mg/kg rice grains was recorded in areas having 15–27 mg As/kg soil [13]. The high As content in straws found in the present study might affect cattle due to bioaccumulation when consumed, while roots would contribute about 5.7 mg/kg for the next crop. Using pond water as a control in the same field, only roots absorbed o.113 ± 0.054 mg As/kg leaving mean As 2.60 mg/kg soil.

The concentration of absorbed As in rice grains was much above the permissible limit of 1.00 mg/kg [14] for human consumption. It was estimated that elevated inorganic arsenic in rice significantly contributes to dietary arsenic intake in USA [17], which was estimated to be double (80%) in Bangladesh and India, and the rest was dimethyl-arsenate (DMA). Bioavailability of iAs from rice was reported to be high [15]. It was estimated that As concentration in rice would have to be as low as 0.050 mg/kg if consumed at 200 g/d to equate to similar exposure from drinking water at 10 μg/l [18]. Sonargaon rice contain 2.552 ± 0.507 mg As/kg which would have 0.85–1.276 mg iAs per kg rice assuming about 33–50% of As according to [46], while there are reports of 22–42% iAs, and the rest was DMA [15]. This in quantity ranged from 0.561 to 1.072 mg iAs/kg for Bangladesh rice. If the lowest amount 0.561 mg iAs/kg rice grain is considered and equates to permissible limit of 0.050 mg/l water (which would be about 0.250 mg iAs/kg consumed at 200 g/day by a 60 kg adult person), then a person in the study area is consuming double the amount of permissible iAs compared to China's food standard limit of 0.15 mg iAs/ kg [38]. Thus estimated high iAs present in the rice grain at Sonargaon can lead to greatly increased exposure to chronic carcinogen.

The presence of arsenic affects PO4-P absorption from the liquid medium by plants where phosphate is replaced by arsenates and prevents ATP synthesis [6, 9, 23]. Therefore, if the phosphorus, for example, is 50% less than the required amount in a cell, it could be assumed that the required amount of ATP synthesis would not take place affecting physiology, cell division to new cell formation, etc. in any affected organism. The high total arsenic in the soil would affect all the biotic communities including biological N2-fixing soil bacteria, as is found in *A. pinnata* var. *pinnata* where ATP-dependent nitrogenase activity was severely affected [9].

A Rickshaw (a three-wheeler, non-mechanized) puller in the present study area had melanosis (hyper-pigmentation) or reddish spots, hairs having 3.99 ± 0.21, and nails having 8.90 ± 0.29 mg As/kg identified as "first stage group" [14] drinking 250 μg/l As for 2 years which was 8.42 mg/kg body wt. The lower value (4–8 mg As/kg samples) was due to the release of arsenic by deamination, and the accumulation may be higher in other parts of a body. Piped water from DTW was supplied for 2 years by the NGO Forum in the village of Nilkanda, Sonargaon; still farmers, day laborers, and Rickshaw pullers of many villages show symptoms of arsenicosis. The reason could be retention of arsenic in their body and most likely also eating high arsenic-containing rice, wheat, and vegetables (**Table 1**). The manifestation of the symptom (melanosis) appears to take place after some years of drinking and eating arsenic-contaminated water, rice, vegetables, etc. [17] as indicated by high amount of arsenic in nails and hairs.
