Redox reaction of iodine in paddy soil investigated by field observation and the IK-edge XANES fingerprinting method

In order to elucidate the cause for the leaching of iodine in a flooded paddy field, we investigated the transformation of an iodine species affected by the water management of the paddy field. The increased concentration of iodide (I-) in soil solution of a flooded paddy field suggested that I- was leached from the soil under anaerobic conditions. The post-edge feature of X-ray absorption near-edge structure (XANES) for iodate (IO3-) spiked to soil totally disappeared after anaerobic incubation of the soils, and I- was dissolved in the solution. On the other hand, I- in contact with the soil was not likely to be oxidized to IO3- under aerobic incubation. Iodine was leached out in soil solution as I- under anaerobic conditions, whereas part of the iodine species was retained by soil as I-2 or organoiodine both under anaerobic and aerobic conditions. (c) 2005 Elsevier Ltd. All rights reserved.