*3.4.3 Effects of high arsenic on weeds in rice fields*

Effects of high arsenic on the occurrence of weeds in the rice field soil were studied. Out of 14 species recorded, six could not grow in the experimental rice field [47]. The Importance Value Index (IVI) indicated that *Alternanthera sessilis*, *Cynodon dactylon*, *Echinochloa colonum*, *Enhydra fluctuans*, *Hedyotis corymbosa*, and *Lippia nodiflora* are very sensitive to arsenic; *Lindernia antipoda* and *Eriocaulon setaceum* were not affected at all, while the growth of *Cyperus rotundus*, *Eclipta alba*, and *Fimbristylis* sp. was enhanced in the presence of arsenic (**Table 2**). The sensitiveness appears to be due to enhanced arsenic absorption by seeds, reduced germination percentage, radical length, and biomass accumulation leading to their death, as seen in seed germination of *Glycine max* at 25 and 100 μM sodium arsenate


*Abbreviations: Den., density; Freq., frequency; Abun., abundance; Rel. den., relative density; Rel. Freq., relative frequency; Rel. Abun., relative abundance. After [47].*

*Average and standard errors cannot be determined through the abovementioned indices.*

### **Table 2.**

*Phytosociological analysis, Shannon index (H), Simson's index (D) of diversity of the weeds in plots irrigated with pond water and arsenic-contaminated STW waters.*

**141**

hazardous [29].

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

before enhanced food chain accumulation occurred [49].

and sodium arsenite [48]. It was suggested that because of the so-called soil/plant barrier effect, elevated arsenic in soil may well reduce crop production substantially

Of the 4 million ha irrigated crop fields, 75% of fields use 100% GW [10]. A significant amount of arsenic withdrawn from underground remains as soil arsenic. Monsoon rain and flood waters are washing away As which is carried to the estuaries at the end and is being accumulating there year after year. This would affect the marine flora and fauna in the near future [47]. A significant amount of As (0.86 (SE 0.057; CV 34.66) mg As/kg) was absorbed by the leaves of *Sonneratia apetala*, a mangrove plant in three coastal islands of Bangladesh, indicating that groundwater As is being accumulated in the biotic and abiotic components along the coast as

In 1997 the presence of arsenic in all coastal districts, in different level of toxicities—highly contaminated (Bagerhat and Noakhali), moderately contaminated (Sundarbans and Lakshmipur), and low contaminated (Pirojpur, Patuakhali, Bhola, and Feni)—was reported [1] (**Figure 1**). Various studies showed increased arsenic in all types of tube wells as they become older (**Table 1**), indicating that the toxicity levels seen in the mid-1990s might have increased from low to moderate, moderate to high, or even absence of arsenic in the rest of the districts to low or moderate presence of arsenic in over the last 20 years. However, status of arsenic throughout

Bangladesh including sites mentioned in [1] should be thoroughly checked.

There are two methods to manage arsenic toxicity in arsenic-loaded DW: first

The arsenic-loaded DW can be predigested for 4–5 days in summer months covering in polythene. The predigested 60–70 kg DW and similar amount of cow dung can be charged into a doom-shaped biogas digester buried into the soil. The retention time can be 50 days. Everyday 25 kg *S. polyrhiza* and 10 kg cow dung can be mixed and then added into the digester. The gas contains 63–65% methane compared to 60%

cooking twice by a family with eight members. The slurry containing concentrated arsenic can also best be disposed by making bricks binding/trapping the arsenic for over 100 years [28]. This approach requires additional huge structural investment.

*S. polyrhiza* could be used to feed fish, poultry, and cattle [29]. The fresh duckweed is used directly as fish feed keeping at corners within floating fences of a pond. The fish production was 20% higher than the normal feed (long-term effect of toxicity was not studied). The duckweed powder at 4% mixed with the normal feed of broilers per day caused accumulation of 1.28 µg/l arsenic in the blood that reduced to 0.912 ± 0.386 µg/l after 3 months, while in the same period, 4.67 µg/kg stool gradually decreased to 0.61 µg/kg. Feeding arsenic-loaded duckweed to goat resulted in increased accumulation of As (0.567–1.060 μg/kg) in the blood causing death of kids [28]. Milk had also high As (0.86 μg/l). Thus the use of arsenic-loaded DW produced in the bio-mitigation process as poultry and cattle feeds was highly

volume of biogas can be produced daily, sufficient for

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

**3.5 Arsenic toxicity management**

*3.5.1 Use in biogas production*

by cow dung only. Three m3

*3.5.2 Use as animal feed*

producing biogas and second using as animal feed.

well [49, 50].

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

and sodium arsenite [48]. It was suggested that because of the so-called soil/plant barrier effect, elevated arsenic in soil may well reduce crop production substantially before enhanced food chain accumulation occurred [49].

Of the 4 million ha irrigated crop fields, 75% of fields use 100% GW [10]. A significant amount of arsenic withdrawn from underground remains as soil arsenic. Monsoon rain and flood waters are washing away As which is carried to the estuaries at the end and is being accumulating there year after year. This would affect the marine flora and fauna in the near future [47]. A significant amount of As (0.86 (SE 0.057; CV 34.66) mg As/kg) was absorbed by the leaves of *Sonneratia apetala*, a mangrove plant in three coastal islands of Bangladesh, indicating that groundwater As is being accumulated in the biotic and abiotic components along the coast as well [49, 50].

In 1997 the presence of arsenic in all coastal districts, in different level of toxicities—highly contaminated (Bagerhat and Noakhali), moderately contaminated (Sundarbans and Lakshmipur), and low contaminated (Pirojpur, Patuakhali, Bhola, and Feni)—was reported [1] (**Figure 1**). Various studies showed increased arsenic in all types of tube wells as they become older (**Table 1**), indicating that the toxicity levels seen in the mid-1990s might have increased from low to moderate, moderate to high, or even absence of arsenic in the rest of the districts to low or moderate presence of arsenic in over the last 20 years. However, status of arsenic throughout Bangladesh including sites mentioned in [1] should be thoroughly checked.

### **3.5 Arsenic toxicity management**

There are two methods to manage arsenic toxicity in arsenic-loaded DW: first producing biogas and second using as animal feed.

### *3.5.1 Use in biogas production*

*Protecting Rice Grains in the Post-Genomic Era*

*3.4.3 Effects of high arsenic on weeds in rice fields*

**Name of weeds Den. Freq. Abun. Rel. den. Rel. freq. Rel.** 

1.0 (−)

3.0 (−)

1.0 (2.0)

— (1.0)

— (1.0)

> 2.5 (−)

> 1.5 (−)

2.75 (2.0)

— (1.5)

> 2.0 (−)

1.0 (1.0)

> 2.75 (3.5

1.5 (−)

2.0 (1.5)

*Average and standard errors cannot be determined through the abovementioned indices.*

1.96 (−)

5.88 (−)

5.88 (8.33)

— (4.16)

— (8.33)

> 9.8 (−)

5.88 (−)

21.57 (16.66)

— (12.5)

> 3.92 (−)

5.88 (8.3)

21.57 (29.16)

> 5.8 (−)

11.76 (12.5)

*Abbreviations: Den., density; Freq., frequency; Abun., abundance; Rel. den., relative density; Rel. Freq., relative* 

*Phytosociological analysis, Shannon index (H), Simson's index (D) of diversity of the weeds in plots irrigated* 

3.85 (−)

3.85 (−)

11.54 (7.69)

— (7.69)

— (7.69)

> 7.69 (−)

> 7.69 (−)

15.38 (15.38)

— (15.38)

> 3.85 (−)

11.54 (15.38

15.38 (15.38)

> 7.69 (−)

11.54 (15.38)

02 (−)

0.2 (−)

0.6 (0.2)

— (0.2)

> — (0.2

0.4 (−)

0.4 (−)

0.8 (0.4)

— (0.4)

> 0.2 (−)

0.6 (0.4)

0.8 (0.4

0.4 (−)

0.6 (0.4)

0.2 (−)

(−)

(0.4)

(0.2)

(0.4)

1.0 (−)

(−)

(0.8)

(0.6)

(−)

0.6 (0.4)

(1.4)

(−)

(0.6)

*frequency; Rel. Abun., relative abundance. After [47].*

*with pond water and arsenic-contaminated STW waters.*

*Alternanthera sessilis*

*Cynodon dactylon* 0.6

*Cyperus exaltatus* 0.6

*C. rotundus* —

*Eclipta alba* —

*Enhydra fluctuans* 0.6

*Eriocaulon* sp. 2.2

*Fimbristylis* sp. —

*Hedyotis corymbosa* 0.4

*Lindernia antipoda* 2.2

*Lippia nodiflora* 0.6

*Panicum* sp. 1.2

*Echinochloa colonum*

*Hydrocotyle rotundifolia*

Effects of high arsenic on the occurrence of weeds in the rice field soil were studied. Out of 14 species recorded, six could not grow in the experimental rice field [47]. The Importance Value Index (IVI) indicated that *Alternanthera sessilis*, *Cynodon dactylon*, *Echinochloa colonum*, *Enhydra fluctuans*, *Hedyotis corymbosa*, and *Lippia nodiflora* are very sensitive to arsenic; *Lindernia antipoda* and *Eriocaulon setaceum* were not affected at all, while the growth of *Cyperus rotundus*, *Eclipta alba*, and *Fimbristylis* sp. was enhanced in the presence of arsenic (**Table 2**). The sensitiveness appears to be due to enhanced arsenic absorption by seeds, reduced germination percentage, radical length, and biomass accumulation leading to their death, as seen in seed germination of *Glycine max* at 25 and 100 μM sodium arsenate

**abun.**

4.76 (−)

14.28 (−)

4.76 (14.81)

> — (7.41)

> — (7.41)

> > 11.9 (−)

7.14 (−)

13.09 (14.81)

— (11.11)

> 9.52 (−)

4.76 (7.41)

13.09 (25.92)

> 7.17 (−)

9.54 (11.11) 10.57 (−)

24.01 (−)

22.18 (30.83)

— (19.26)

— (23.43)

> 29.39 (−)

> 22.71 (−)

50.04 (46.85)

— (38.99)

> 17.29 (−)

22.18 (31.12)

50.04 (70.46)

> 20.71 (−)

32.82 (38.99)

**IVI H D**

3.135 (2.751)

0.865 (0.836)

**140**

**Table 2.**

The arsenic-loaded DW can be predigested for 4–5 days in summer months covering in polythene. The predigested 60–70 kg DW and similar amount of cow dung can be charged into a doom-shaped biogas digester buried into the soil. The retention time can be 50 days. Everyday 25 kg *S. polyrhiza* and 10 kg cow dung can be mixed and then added into the digester. The gas contains 63–65% methane compared to 60% by cow dung only. Three m3 volume of biogas can be produced daily, sufficient for cooking twice by a family with eight members. The slurry containing concentrated arsenic can also best be disposed by making bricks binding/trapping the arsenic for over 100 years [28]. This approach requires additional huge structural investment.

### *3.5.2 Use as animal feed*

*S. polyrhiza* could be used to feed fish, poultry, and cattle [29]. The fresh duckweed is used directly as fish feed keeping at corners within floating fences of a pond. The fish production was 20% higher than the normal feed (long-term effect of toxicity was not studied). The duckweed powder at 4% mixed with the normal feed of broilers per day caused accumulation of 1.28 µg/l arsenic in the blood that reduced to 0.912 ± 0.386 µg/l after 3 months, while in the same period, 4.67 µg/kg stool gradually decreased to 0.61 µg/kg. Feeding arsenic-loaded duckweed to goat resulted in increased accumulation of As (0.567–1.060 μg/kg) in the blood causing death of kids [28]. Milk had also high As (0.86 μg/l). Thus the use of arsenic-loaded DW produced in the bio-mitigation process as poultry and cattle feeds was highly hazardous [29].

### *3.5.3 Status of As toxicity management*

Bioremediation process for getting As-free GW for irrigation that was tested needs additional huge investment (two ponds, DW production cost, cost of labor, etc.). Moreover, an estimated 1.539 g As will remain in the bottom of the pond after treatment. Disposal of the arsenic-loaded DW to nontoxic level through various uses was hazardous (Section 3.5.2). STW and DTW waters were found to become arsenic contaminated in 2–5 years. Withdrawal of the GW contaminates biosphere permanently, i.e., circulating the element in the nature in a matter of weeks or months affecting biotic components (**Figure 3a**–**d**). Therefore, alternative arsenicfree freshwater sources (about 1000 l/m2 /year equivalent to 2500 l or 2500 kg water/kg arsenic-free rice cultivation in clayey soil) have to be managed for feeding millions of people of Bangladesh on the one hand and saving our biosphere on the other hand. It is possible only by using surface water (Section 3.6.3).

### **3.6 Current status of arsenic management in Bangladesh**

### *3.6.1 Occurrence and level of arsenic toxicity in Bangladesh*

There are 64 districts, out of which 26 were arsenicosis affected in various degrees surveyed between 1993 and 1997 [1] (**Figure 1**): (a) highly affected (>100 patients identified) in 7 districts, (b) moderately affected (>50 patients identified) in 11 districts, (c) less affected (<50 patients identified) in 8 districts, and (d) arsenic contamination present (no patient was identified) in 18 districts. Out of 64 districts, 42 were distributed in four floodplains: (a) Ganges had 26 districts (7 highly affected), (b) Meghna 10 districts (1 highly affected) and (c) Surma-Kushiara 5 districts with arsenic presence but no patients were found, (d) Jamuna 2 districts without any patient, and (e) 2 districts in Madhupur tract (less affected) all due to drinking and consuming arsenic-contaminated GW and food grains/vegetables. Two-thirds of the districts/country was affected with arsenic by the year 1997 [1]. Highly affected Bagerhat and moderately affected major part of Sundarbans south of the Ganges floodplain along the coast are alarming, indicating coastal water pollution. Data on arsenic in irrigation water and paddy soil profiles in Bangladesh [16] and West Bengal [51] indicated a yearly input of 1.0 and 1.1 mg As/kg soil, respectively, in the topsoil (soil density of 1 kg/l). Therefore, distribution of arsenicosis reported in 1997 [1] would be much higher over the last two decades through arsenic toxicity of rice, wheat grains/vegetable, etc. if not by arsenic-contaminated drinking water [17].

Why the Ganges and Meghna floodplains are so much affected with GW arsenic, when Jamuna floodplain with one of the largest and longest river is not? Is it that the GW of the two highly affected floodplains has some link with arsenic mines/ industries or there are anthropogenic reasons (dumping the contaminant, deep into the aquifer) in upstream?

### *3.6.2 Intensity of irrigation*

The total area under irrigation in Bangladesh is 4 million ha, and 75% is covered by GW resources: 2.5 m ha via 924,000 STWs (main source of GW As) and 0.6 m ha via 23,000 DTWs [11]. DTW for irrigation is installed at about 100 m depth, and in Jessore alone 74 among 85 DTW used for irrigation had >50 μg As/l arsenic [51]. The rest 25% land is irrigated using surface water of rivers, "Beels," "Haors," etc. In dry season, 3.5 m ha is used for Boro rice, 0.23 m ha for wheat, and 2.7 m ha for other crops. Rajshahi Division has the highest percentage under

**143**

Dhaka, Bangladesh].

indicates dumping sediments on to the river banks!

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

irrigation which is 39%, followed by Dhaka 27%, Chittagong 13%, Khulna 12%, Sylhet 7%, and Barisal 2% [11]. We must step up the use of surface water from

It has been clearly indicated that As concentrations in rice are increasing over time because of prolonged input of As-contaminated irrigation water, and three options are proposed to free rice grains from toxicity: reduce As-contaminated irrigation water use in rice cultivation, promote cropping patterns, and select/ breed rice cultivars that are tolerant to As and have limited uptake of As [11]. As per the first option of limited As-contaminated irrigation water use, there must be alternative sources of huge surface water, e. g., initially forming reservoirs and constructing rubber dams in rivers, and execution of long-term "Delta Plan 2100". Regarding the second option, cropping pattern throughout the country has been established over the decades of testing, while selection/breeding of rice varieties tolerant to As and limited uptake are questionable. It is known that As and P elements are in the same position in the periodic table (chemically similar), and thus the rice cultivar that will not absorb As will not absorb P as well. In the present study, arsenic bio-mitigation of irrigation water tested was not effective, and disposal of wastes was hazardous. As arsenic-contaminated GW produces toxic rice grains and accumulates arsenic in the soil year after year, avoiding the use of GW is the only solution for protecting rice grains from arsenic toxicity, including other organisms. Man might alter the quantities of arsenic in any component of an ecosystem in a localized area but cannot change or stop the natural biological processes that occur [52]. Therefore, an alternative immediate attention is needed to provide enormous volume of As-free irrigation water, and that is through the use of surface waters using river network of Bangladesh (**Figure 10**). Bangladesh is a country of rivers having almost one river in each village. The rivers have to be dredged to get continuous flow of waters from the upstreams, converting the rivers as reservoirs simultaneous with the construction of rubber dams. Several rubber dams have so far been installed in Bangladesh, one of which is at Sonargaon (**Figure 11**). Bangladesh government has the plan to establish **"Ganges Barrage"** to supply freshwater to Ganges floodplain and surroundings including Sundarbans [53]. Huge deposit of sediments in the Ganges River bed has been identified as a major problem (what to do with the sediments) for using the Ganges as a reservoir [personal communication, Rawshan Ali Khan, Project Director of Ganges Barrage Project,

The National Economic Council (NEC) of Bangladesh has recently approved **"Delta Plan 2100"** the key objective of which is to provide food and water security and fight natural disasters [54]. The theme is "let the rivers flow, let the rivers live." In the first phase, the government will be implementing about 80 projects at an estimated cost of US \$ 37 billion by 2030. Out of six goals, Delta goal 3 is "Ensuring sustainable and integrated river systems and estuaries." In a seminar, it has been mentioned that "rivers would be channelized and sediments would be removed." Details are not available regarding what is meant by the "removal." It immediately

The landmass of Bangladesh has been formed throughout the Pleistocene and up to the present by sediments washed down from the Himalaya Mountains through the Ganges, Jamuna (Brahmaputra), and Meghna Rivers and their numerous tributaries and distributaries [55]. In terms of relative age of the landmass, the region may be divided into four parts: hilly lands of the Tertiary (and older) in the southeast Chittagong and CHT districts, terrace lands of

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

25% to 100% (Section 3.6.3).

*3.6.3 Methods for arsenic's reduction*

irrigation which is 39%, followed by Dhaka 27%, Chittagong 13%, Khulna 12%, Sylhet 7%, and Barisal 2% [11]. We must step up the use of surface water from 25% to 100% (Section 3.6.3).
