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

(1)稻田土壤砷浓度为5.2 ~ 29.0mg/kg，大于钻孔样地表土壤砷浓度（5 ~ 15mg/kg），在深度方向上，地表点和中间点的砷含量最高。(2)水稻植株中的砷大部分集中在根部（孟加拉国为95%，日本为97%），水稻中的砷浓度很小。人们认为孟加拉国生产的大米可以安全食用。(3)土壤中砷含量一般在旱季以地下水灌溉稻田时升高。另一方面，在雨季，由于雨水造成淹没，砷含量下降到旱季的50%左右。2)除砷装置的发展(1)我们安装了两台除砷装置，并在村民正常使用的情况下，对一年的除砷效果进行了测试。演出非常好。地下水砷浓度由0.18 ~ 0.26mg/L降至0.02 ~ 0.04mg/L；gsf2为0.10 ~ 0.14mg/L ~ 0.01 ~ 0.03mg/L。(2) GSF砷污泥浸出试验砷浓度为0.21 ~ 0.27mg/L （gsf1）和0.10 ~ 0.15mg/L （gsf2）。这些数值小于日本污染土壤反测量的第二标准0.3Omg/L。(3)污泥中砷的浸出率为5 ~ 9%，说明砷污泥（铁共沉淀的砷）与铁形成较强的化学键，污泥的处理可能并不困难。

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.