**1. Introduction**

In Bangladesh, As was discovered in 1993, while doctors and health personnel were dealing with health effects of its contamination in drinking water. Since then, As-contaminated groundwater was found in 44 districts out of which arsenicosis patients were detected in 26 districts, 7 of which were highly affected, and out of 64 districts [1] (**Figure 1**), some districts as a catastrophe affecting human health [1, 2]. Southern districts in particular contained >300 μg As/l in GW, and more than 20% tube wells contain more than 100 μg As/l that are used for irrigation and drinking [3]. The metalloid at low concentration (10–50 μg As/l) in a sandy soil may be more phytotoxic (i.e., available) than much higher levels (200–500 μg As/l) in a heavier clay soil [4]. Arsenic is found everywhere in traces, i.e., in the air, in the ocean and freshwaters (some drinking water supplies), in soil, etc., polluting the environment and causing arsenicosis (melanosis, keratosis, gangrene, chronic ulcer, skin cancer, etc.) in human [1, 5]. Studies also confirmed that a substantial amount of this heavy metal is absorbed by plants [6–9]. The question is how as appeared heavily in soils, drinking, and irrigation waters of Bangladesh? In the 1960s, 4 million hand tube wells (HTW)

### **Figure 1.**

*Arsenic-affected areas in Bangladesh based on studies from 1993 to 1996 [1]. Round white spot (within blue) east of mid-region is the study site at Sonargaon.*

**129**

**2. Materials and methods**

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

ment was 2.6–2.9 fold higher than the non-flooded treatment [15].

were installed at a depth of 10–15 m for drinking water without checking arsenic in the aquifers [10]. In the 1970s high-yielding rice variety known as the International Rice Research Institute (IRRI) paddy var. IR8 was introduced in Bangladesh that required huge irrigation, necessitating the installation of STW at a depth of 25–30 m [personal communication Director General, Dr. Md. Shahjahan Kabir of Bangladesh Rice Research Institute, Gazipur, Bangladesh]. For decades DTW have been installed at 100– 200 m depth which are also contaminated with arsenic [11]. In Jessore alone, 74 out of 85 DTW tested had an average 210 μg As/l. Of the 4 million ha irrigated fields, 25% used surface water, 60% STW, and 15% DTW waters in Bangladesh [11]. The organic As (oAs) is not but inorganic arsenic (iAs) is toxic to human [12]. Concentration of absorbed arsenic in rice grains of Bangladesh was in toxic level for human consumption [13–15]. It was reported that 1.7–2.55 mg/kg rice grains were found in areas having 15–27 mg As/kg soil [16]. It was also reported that As concentrations in rice grains from flooded soils were 10–15 times higher than aerobically grown (non-flooded) rice, and similarly the concentration of inorganic As (iAs) in the grains from the flooded treat-

Rice is by far the largest food dietary source of iAs for populations not drinking water with elevated As [17]. Arsenic in rice, cowpeas, vegetable crops, peas, snap beans, and sweet corn plants antagonize the uptake of nutrients like N, P, K, S, Ca, Mn, and Z [18–20] and reduced height of rice plants, straw and grain yield, grain per panicle, and the number of field grains per panicle applying 10 mg As/kg soil or above [19–22]. Phosphate replacement by arsenate preventing ATP generation was observed by [4, 7, 23] reducing ATP-dependent N2 fixation [9]. Human activities like smelting, mining, the use of pesticides, making glasses and ceramics, etc. are responsible for contaminating earth surface [24], which is now a global health issue [25]. However, it has been estimated that about 30 metric ton of arsenic is borne by the biomass of the earth and is assumed to be the 12th most abundant element in the biosphere [26]. Arsenic removal efficiency varies with many conditions, like site-specific chemicals and geographic and economic conditions [27]. There have not been any significant and innovative improvements in the methods for removing arsenic from HTW water in a decade of research for drinking [28]. However, no attempt has so far been taken to remove arsenic from large volume of the contaminated STW waters for using in irrigation. In the present study, an attempt was made to use efficient arsenic-absorbing floating plant *S. polyrhiza* to remove toxic arsenic from

STW water in situ for protecting rice grains through cultural management.

under P.S. Kachua, district Chandpur, about 100 km southeast of Sonargaon.

Six strains under three species of *Azolla* (*A. caroliniana* Dh 103; *A. filiculoides* Dh 104; *A. pinnata* var. *pinnata* Dh 111; *A. pinnata* var. *pinnata* Dh 112; *A. pinnata* var. pinnata Dh 113; and *A. filiculoides* Dh 115) and two species of *Spirodela* (*S. polyrhiza* Dh

**2.1 Selection of plants and cultivation for bioremediation of arsenic**

Field studies were carried out at Nilkanda Union under P. S. Sonargaon, District Narayanganj, lying between 23°30′ and 23°46′ N and 90°31′ and 90°41′ E (**Figure 1**) [29]. A good number of submerged and exposed soil (rice, wheat, and vegetable fields) and water (STW, HTW, and pond) samples were collected in four replications at a gap of 0.5–1.0 km in the winter and spring seasons and analyzed to determine the amount of As absorbed by different crops and its presence in soils and water sources. Water samples were collected from DTW and STW one from each at village Kachua,

*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*

*Protecting Rice Grains in the Post-Genomic Era*

soil [4]. Arsenic is found everywhere in traces, i.e., in the air, in the ocean and freshwaters (some drinking water supplies), in soil, etc., polluting the environment and causing arsenicosis (melanosis, keratosis, gangrene, chronic ulcer, skin cancer, etc.) in human [1, 5]. Studies also confirmed that a substantial amount of this heavy metal is absorbed by plants [6–9]. The question is how as appeared heavily in soils, drinking, and irrigation waters of Bangladesh? In the 1960s, 4 million hand tube wells (HTW)

*Arsenic-affected areas in Bangladesh based on studies from 1993 to 1996 [1]. Round white spot (within blue)* 

**128**

**Figure 1.**

*east of mid-region is the study site at Sonargaon.*

were installed at a depth of 10–15 m for drinking water without checking arsenic in the aquifers [10]. In the 1970s high-yielding rice variety known as the International Rice Research Institute (IRRI) paddy var. IR8 was introduced in Bangladesh that required huge irrigation, necessitating the installation of STW at a depth of 25–30 m [personal communication Director General, Dr. Md. Shahjahan Kabir of Bangladesh Rice Research Institute, Gazipur, Bangladesh]. For decades DTW have been installed at 100– 200 m depth which are also contaminated with arsenic [11]. In Jessore alone, 74 out of 85 DTW tested had an average 210 μg As/l. Of the 4 million ha irrigated fields, 25% used surface water, 60% STW, and 15% DTW waters in Bangladesh [11]. The organic As (oAs) is not but inorganic arsenic (iAs) is toxic to human [12]. Concentration of absorbed arsenic in rice grains of Bangladesh was in toxic level for human consumption [13–15]. It was reported that 1.7–2.55 mg/kg rice grains were found in areas having 15–27 mg As/kg soil [16]. It was also reported that As concentrations in rice grains from flooded soils were 10–15 times higher than aerobically grown (non-flooded) rice, and similarly the concentration of inorganic As (iAs) in the grains from the flooded treatment was 2.6–2.9 fold higher than the non-flooded treatment [15].

Rice is by far the largest food dietary source of iAs for populations not drinking water with elevated As [17]. Arsenic in rice, cowpeas, vegetable crops, peas, snap beans, and sweet corn plants antagonize the uptake of nutrients like N, P, K, S, Ca, Mn, and Z [18–20] and reduced height of rice plants, straw and grain yield, grain per panicle, and the number of field grains per panicle applying 10 mg As/kg soil or above [19–22]. Phosphate replacement by arsenate preventing ATP generation was observed by [4, 7, 23] reducing ATP-dependent N2 fixation [9]. Human activities like smelting, mining, the use of pesticides, making glasses and ceramics, etc. are responsible for contaminating earth surface [24], which is now a global health issue [25]. However, it has been estimated that about 30 metric ton of arsenic is borne by the biomass of the earth and is assumed to be the 12th most abundant element in the biosphere [26].

Arsenic removal efficiency varies with many conditions, like site-specific chemicals and geographic and economic conditions [27]. There have not been any significant and innovative improvements in the methods for removing arsenic from HTW water in a decade of research for drinking [28]. However, no attempt has so far been taken to remove arsenic from large volume of the contaminated STW waters for using in irrigation. In the present study, an attempt was made to use efficient arsenic-absorbing floating plant *S. polyrhiza* to remove toxic arsenic from STW water in situ for protecting rice grains through cultural management.
