Is the akagare phenomenon important to iodine uptake by wild rice ( Zizania aquatica)?

Abstract

Akagare reclamation disease of plants, reported in Japan, is the situation where naturally occurring stable iodine (I) is released from the soil to the extent that it is chemically toxic to rice plants. It occurs after a soil is reflooded for rice production. Any process such as this, where a change in the environment results in a release of I, is important for the safe management of 129I. Iodine-129 is the most critical radionuclide in the safe disposal of Canada's nuclear fuel waste. The present concept for disposal anticipates a boreal setting, where wild rice ( Zizania aquatica) grows naturally and is cultivated. This study investigated the effect of flooding on I uptake by wild rice, using 125I. We grew wild rice on flooded and drained soils, and observed that I in flooded soil was an order of magnitude more soluble than in drained soil. The soil solid/liquid partition coefficient K d , in flooded soil was about 0.6 l kg −1 and in drained soil was about 6 l kg −1. This effect did result in higher concentrations of I in the plants grown on the flooded soil. The plant/soil concentration ratio on a dry weight basis, CR, for the edible seed, prior to processing, was 0.25 for wild rice grown on flooded soil and 0.17 for wild rice grown on drained soil. This difference is small and the values are not higher than many other crops. Very high mean CR values, up to 69, were observed for the lower submerged and emergent leaves of flooded wild rice. These may indicate a need to investigate I entry into littoral food chains.