Abstract
Chemical countermeasures against hazardous metal contamination in paddy fields were introduced, which include the use of soil washing methods for cadmium and the use of iron materials for reducing arsenic in brown rice by combining with waterflooding cultivation. Iron (III) chloride was selected as the most suitable detergent from various chemicals. The extraction mechanism of soil cadmium by iron (III) chloride is a function of iron ion hydrolysis reaction, which causes pH decrease. The formation of complexes between chlorine ions and cadmium also contribute to the cadmium extraction. After the washing, a wastewater treatment system installed on site was used to treat the wastewater. Soil cadmium and brown rice cadmium were reduced by 60∼80 % and 70∼90 %, respectively. For arsenic, steel slag, iron hydroxide and zero-valent iron were applied to the paddy field to reduce arsenic in brown rice. The results showed application of zero-valent iron reduced arsenic in soil solution and brown rice. This may be due to the formation of hardly soluble arsenic sulfides on the strongly reducing iron zero-valent surface.
