2.Arsenic Exposure through Food Chain and Water in Arsenic Contaminated Areas of Bangladesh
Integrated Research System for Sustainability Science (IR3S), The University of Tokyo
The contamination of groundwater by sediment-derived arsenic threatens the health of tens of millions of people worldwide and has taken a serious turn in Bangladesh. Around 38% of the area of Bangladesh is irrigated with groundwater to grow dry season crops, most importantly boro rice. Due to high arsenic concentrations in groundwater, over 1000 tons of arsenic is transferred to arable soils each year, creating a potential risk for future food production. In the long term, this may lead to the accumulation of arsenic in paddy soils and potentially have adverse effects on rice yield and quality. There is significant literature on arsenic accumulation in rice grain (and other parts of rice plant) under both laboratory and field conditions . Since rice is the staple food for the people of Bangladesh and other Asian countries, it appears that intake of arsenic from rice could constitute an important part of overall arsenic intake for people living in the arsenic affected areas. Though groundwater irrigation is primarily used for growing dry season rice and wheat, some vegetables also receive groundwater irrigation during the dry season in Bangladesh. Thus, depending on the arsenic concentration in irrigation water and quantity of vegetable consumption, the intake of arsenic from vegetables could also constitute an important part of the overall arsenic intake for population living in the arsenic affected areas of Bangladesh. A number of options have been suggested for reducing arsenic concentration in the food chain, including alternative cultivation methods (e.g., raised bed rice culture, cultivation under aerobic condition, use of Si fertilizer), alternative water sources (e.g., arsenic free deep tubewell), and alternative crops. However, treatment of arsenic contaminated groundwater for use in irrigation is yet to be tested. Treatment of arsenic contaminated irrigation water could be a viable option for reducing arsenic exposure of people through food chain in many arsenic affected areas of Bangladesh.
For the removal of arsenic from groundwater, diverse technologies including membrane technology, advanced oxidation process, adsorptive filtration, ion exchange, coagulation/co-precipitation followed by filtration, and phyto-remediation (e.g., using water hyacinth) have been described in literature. However, a low-cost option yielding large quantity of treated water along with simple operation and maintenance would be best suited for rural Bangladesh. In the context of groundwater irrigation, a pond-based system adopting the removal of arsenic by adsorption and co-precipitation with iron naturally prevalent in groundwater of Bangladesh could be a very effective technique. It should be noted that ponds are quite prevalent in Bangladesh, which could potentially be used for development of pond-based arsenic removal-irrigation system. According to Bangladesh Bureau of Statistics (BBS), there are about 1,288,222 ponds in Bangladesh. However, major modifications are needed for the effectiveness of this system to achieve the desired level of treatment, considering the level of arsenic and iron present in water, pond configuration, irrigation water requirement, etc. Proper disposal of arsenic contaminated sludge (which would accumulate at the bottom of the pond) is also an important issue that needs to be addressed to ensure a sustainable environment in the long run. Other treatment options, including phyto-remediation also holds promise for treatment of arsenic contaminated groundwater.