Arsenic accumulation in the ground & foods and development of arsenic removal unit in Bangladesh

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1)Arsenic flow in the ground & foods(1)The arsenic concentration of soil in the rice fields were 5.2-29.0mg/kg and larger than those of surface soil (5-15mg/kg) from boring samples, showing the highest value at the surface points or at the middle points in the depth direction.(2)Most of arsenic in the rice plant was contained in the root (Bangladesh : 95%, Japanese : 97%), and the arsenic concentration in the rice was very small. It was considered the rice produced in Bangladesh was safe for eating.(3)The arsenic content in the soil, generally, became higher in the dry season, when rice fields had been irrigated with ground water. On the other hand, in rainy season, when submergence was caused by rainwater, the arsenic contents decreased to about 50% of that in dry season.2)Development of arsenic removal unit (GSF)(1)We installed two GSFs and checked the arsenic removal performance for a year under the usual usage by the villagers. The performance was very good. The arsenic concentration of groundwater, 0.18-0.26mg/L decreased to 0.02-0.04mg/L for GSFNo. 1, and 0.10-0.14mg/L to 0.01-0.03mg/L for GSFNo.2.(2)The arsenic concentration of the leaching tests for the arsenic sludge from GSF was 0.21-0.27mg/L (GSFNo.1) and 0.10-0.15mg/L (GSFNo.2). These values are smaller than Japanese second standard, 0.3Omg/L, for the counter measurement of contaminated soil.(3)The leaching ratio of arsenic from sludge was 5〜9 %, illustrating that arsenic sludge (arsenic co-precipitated by iron) forms strong chemical bond with the iron and the treatment of sludge may not be difficult.