Volatilization of methyl iodide from the soil-plant system

Iodine volatilization from the soil-plant system has been studied by radiotracer experiments and gas chromatography. Iodine emission was highly stimulated by the presence of plants. A marked emission of gaseous iodine from rice plants grown on flooded soil was observed, whereas oat plants showed considerably lower emission. Seasonal patterns in the iodine emission were observed for both plants. The emission rate increased with time from planting and the maximum value was observed in the late tillering stages (shortly before heading) of the plants. The chemical species of volatilized iodine was identified as methyl iodide (CH3I) from gas chromatography. It was presumed that iodine in the flooded soil was methylated by the action of roots or microorganisms. The methyl iodide produced was mainly emitted, not from the soil surface, but from the plant shoot into the atmosphere.