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ARSENIC CONTAMINATION AND PHYTOREMEDIATION IN BANGLADESH

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					ARSENIC CONTAMINATION AND PHYTOREMEDIATION IN BANGLADESH M. Z. Hossain* In Bangladesh, the development of irrigated winter (Boro) season rice since the 1970s now accounts for 61% of the total rice production (BBS, 2009) and has enabled the country to shift from chronic food shortages to self sufficiency by the mid-1990’s (Baffes and Gautam, 1996). About 70% of the total arable land area is currently irrigated from shallow tubewells (STW). Build up of As in soil associated with the use of As contaminated irrigation water has been shown to lead to elevated levels of As in paddy soil and soil solution (Van Geen et al., 2006; Dittmar et al., 2007). Arsenic concentration in Bangladeshi soils is in the range of 4-8 mg kg-1. However, in areas where irrigation is performed with arsenic contaminated groundwater, soil arsenic level can reach up to 83 mg kg-1 (Ullah, 1998). Arsenic uptake and accumulation is greatly affected by arsenic contamination in soil and increased greatly with increasing arsenic levels (Meharg and Rahman, 2003). Arsenic accumulating in irrigated soils poses a serious threat to sustainable agriculture in affected areas (Heikens, 2006). It is also reported by FAO (2006) that the ‘As’ concentration in soil is increasing over time. This soil is being transported to plant system and ultimately contaminating the food chain. The National Screening Programme indicates that 29% of about 5 million tube-wells tested in 270 upazilas have arsenic concentration exceeding Bangladesh standard of 0.05 mg L-1(Ahmed, 2005). A global normal range of 0.08 to 0.2 mg As kg−1 has been suggested for rice (Zavala and Duxbury, 2008), but values as high as 1.8 mg As kg−1 have been found in Bangladesh rice (Meharg and Rahman 2003). Mean values for brown rice grain from three large studies in Bangladesh ranged between 0.18– 0.29 mg As kg−1 (Williams et al., 2006; Zavala and Duxbury, 2008). The average daily intake of As from rice for a Bangladeshi adult is approximately 100 μg As (400 g dry wt×0.25 mg As kg−1), which is 5 times the 20 μg As intake from consumption of 2 L of water at the WHO limit of 10 μg L−1. Arsenic has recently drawn attention due to its chronic and epidemic toxic effects to humans through widespread contamination of water and food crops through natural release of the element from aquifer rocks in Bangladesh (Smith et al., 2000; Fazal et al., 2001; Hopenhayn, 2006; Rahman et al., 2007). Hossain (2006) reported that many organizations have implemented different As programs and revealed the extent and severity of the problem. To date, different issues such as population exposed to contaminations, assessment and modeling of As transport, As mobility and groundwater extraction, cause of contamination and number of people suffering from arsenosis have been addressed. Patients with skin disease caused by arsenic have also been observed in Bangladesh (Karim, 2000). Ahmed et al., (2004) estimated that more than 80% of the populations depend on groundwater as their source of drinking water; high As concentrations has resulted in the exposure of nearly 35 million people to arsenic toxicity, while Hossain (2006) estimated that 85 million were at risk in Bangladesh. The World Bank is currently taking the lead in coordinating an integrated response to the arsenic crisis and through the GOB is supporting the Bangladesh Arsenic-Mitigation Water Supply Project (BAMWSP). A key component of the BAMWSP is community-based, demand driven projects, in which community members play an active role in choosing and implementing solutions to the site specific problems of arsenic contamination. However, no one has devised practical methods of groundwater remediation, most studies and actions have focused on testing tube well water for arsenic.
*Agrotechnology Discipline, Khulna University, Khulna-9208, Bangladesh 1

Recently, in the coastal areas (17% of Bangladesh surface), the DPHE-Danida water supply and sanitation project has started to provide safe water outlets for the poorest of the poor and management of the project (Hossain, 2006). Atkins et al., (2007) reported that pollution by one of the trace elements in the groundwater has caused a major environmental health emergency. This started in a low-key fashion. “About six or seven years ago blisters developed on my whole body and there was a lot of itching. A few months later, these blisters turned into black spots on my hands and legs. They itched and there was some pain. A few years later, these black spots became hard and rough. Now they have turned into sores” (In-depth interview, Basiapara village, 2001).

Figure 1. Activity spaces for arsenic mitigation. Abbreviations: BAMWSP – Bangladesh Arsenic Mitigation Water Supply Project; UNICEF – United Nations Children’s Fund; DANIDA – Danish International Development Agency; WVI – World Vision; WPP – Watsan Partnership Project; AAN –Asia Arsenic Network. Source: BAMWSP, 2005. 2

The experience of this patient is now a common one across Bangladesh, due to chronic arsenic poisoning. So far, 38,380 people have been diagnosed as having arsenicosis (BAMWSP, 2004) but the expectation is that the figure will rise to two million as patients present with a complex variety of symptoms, including internal cancers (Yu et al., 2003). Some conventional methods have been applied for removing As from contaminated water, but found to be high-cost or low efficiency (Mondal et al., 2006). Some unavoidable limitations of the traditional chemical and physical methods have made phytoremediation, a plant-based green technology, a viable alternative to remediate environmental pollution (Lasat, 2002; Cherian and Oliveira, 2005; Dickinson et al., 2009). Its relative inexpensiveness and eco-friendliness have made it an attractive method for water and soil remediation (Raskin et al., 1994).Phytoremediation is defined as the use of green plants to remove pollutants from the environment or to render them harmless. It has recently become a subject of intense public and scientific interest and a topic of many recent reviews. Phytoremediation takes advantage of the fact that a living plant can be considered a solar-driven pump, which can extract and concentrate particular elements from the environment (Raskin et al., 1997). Some plants have the ability to accumulate toxic metals at high concentrations (McGrath et al., 1998). Arsenic, accumulated into plants primarily through their root system, is not readily translocated to the shoots (Raskin et al., 1994; Kumar et al., 1995). Brooks et al. (1977) first used the term ‘‘hyperaccumulators’’ to describe those plants that uptake and accumulate metals more than 1000 µg metal g-1 dry mass (Visoottiviseth et al., 2002) which is still in common use (Reeves and Baker, 2000). Some terrestrial plant species such as Bentgrass (Agrostis castellana); Agrostis delicatula (De Koe, 1994), West Indian beggarticks (Bidens cynapiifolia) (Bech et al., 1997), Chinese brake fern (Pteris vittata L.) (Ma et al., 2001) and Silver fern (Pityrogramma calomelanos L.) (Gulz et al., 2005) have been reported to be arsenic hyperaccumulators. In particular, Chinese brake ferns remove a formidable quantity of arsenic from soil (Komar et al., 1998; Gulz et al., 2005), and store it in the fronds (Tu et al., 2002; Gulz et al., 2005). The arsenic hyperaccumulating terrestrial plants are considered for soil remediation. However, restoration of contaminated waters of ponds, lacks and ditches as well as irrigation water remains unresolved. Aquatic macrophytes could be a good tool for the environmentally sound and effective remediation of arsenic contaminated waters (Mkandawire and Dudel, 2005; Robinson et al., 2003). (16) Arsenic accumulation in aquatic plants, such as Duckweed (Spirodela polyrhiza L.) (Chakraborti and Das, 1997; Rahman et. al., 2008), Lemna gibba L. (duckweed) (Mkandawire et al., 2004; Mkandawire and Dudel, 2005), Waterthyme (Hydrilla verticullata) (Lee et al., 1991), New Zealand watercress (Lepidium sativum) (Robinson et al., 2003), Water fern (Salvinia natans L.) (Rahman et al., 2008) and Azolla (Zhang et al., 2008) has also been reported in literatures. Arsenate As(V) and arsenite As(III) are the inorganic forms in the oxic aquatic systems. Arsenate predominates and arsenite is oxidized to arsenate in the oxic aquatic systems (Sizova et al., 2002). The use of aquatic macrophytes or other floating plants in phytoremediation technology is commonly known as phytoextraction. This clean up process involves biosorption and accumulation of pollutants. Recently, aquatic macrophytes and some other small floating plants have been investigated for the remediation of wastewater contaminated with Cu, Cd(II) and Hg(II) (Selvapathy and Sreedhar , 1991; Alam et al., 1995; Sen and Mondal, 1987).

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Phytostabilization methods using plants can also be applied for long-term remediation of As. This method limits uptake and excludes mobilization of As. One of the major benefits of phytostabilization is that the above-ground vegetative biomass is not contaminated with As, thus reducing the risk of arsenic transfer through food chains (Madejon et al., 2002). Woody species have also been investigated with respect to photostabilization (French et al., 2006; Vazquez et al., 2006). More recently, four Eucalyptus species were used for photostabilization of As in gold mine tailings (King et al., 2008). Additionally, natural attenuation processes including many biological applications may transform arsenic to less toxic species and this topic has been recently reviewed (Wang and Mulligan, 2006). This acute problem of arsenic in Bangladesh is not resolved yet. Till to date various remediation technologies or mitigation techniques have been tested (such as deep tubewells, water treatment, selection of aquifers, rainwater harvest, use of surface water etc.) for the well being of our country, but no technologies has not been sustained in our country. Now the problem is not only for drinking and irrigation water but also the soil is polluted and ultimately the human beings are suffering through food chain. For these reasons, I think Phytoremediation technologies can be sustained for removal of arsenic from the soil as well as from water, because the various effective terrestrial (such as Pteris vittata L.) and aquatic (such as Spirodela polyrhiza L., Salvinia natans L. and Azolla) plants as arsenic extraction or accumulation or stabilization are well known and available in our environment as well as in the rice field. In Bangladesh, a limited research work has been done in the field of phytoremediation for arsenic or heavy metal. So, now it is necessary to this problem oriented research should be done as soon as possible for the sustainable agriculture in Bangladesh.

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