Effects of Microorganisms on the Fate of Iodine in the Soil Environment

The roles of microbial activities in the accumulation of iodine in soils and its loss from soils were studied. Concentrations of stable iodine in several type of soils were determined by inductively coupled plasma-mass spectroscopy. High iodine concentrations were found in upland soils, particularly in Andosol, whereas the concentrations in lowland soils were considerably lower. Accumulation of iodine in soils was explained by the effects of microorganisms or their products (e.g., enzymes), or both. Iodine was observed to be desorbed from the flooded soils because of the reducing conditions (low Eh) created by the microbial activities. Evaporation of biogenerated methyl iodide from the soilplant system, specifically from rice plants, may also decrease the iodine concentrations in lowland soils.