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TECHNICAL REPORTS

Plant and Environment Interactions

Uptake and Distribution of Iodine in Rice Plants

^a Inst. for Environmental Sciences, 1-7 Ienomae, Obuchi, Rokkasho-mura, Kamikita-gun, Aomori 039-3212, Japan
^b National Inst. of Radiological Sciences, Anagawa 4-9-1, Inage-ku, Chiba 263-8555, Japan

^* Corresponding author (hirot{at}ies.or.jp).

Received for publication January 4, 2008. Rice (Oryza sativa L.) plants were cultivated in an experimental field and separated at harvest into different components, including polished rice, rice bran, hull, straw, and root. The contents of iodine in these components and the soil were determined by inductively coupled plasma–mass spectrometry and radiochemical neutron activation analysis, respectively. Iodine content varied by more than three orders of magnitude among the plant components. Mean concentration of iodine in the entire plants was 20 mg kg^–1 dry weight, and the concentration of iodine in the surface soil (0–20 cm depth) was 48 mg kg^–1. The highest concentration of iodine (53 mg kg^–1 dry weight) was measured in root and the lowest concentration (0.034 mg kg^–1 dry weight) in polished rice. While the edible component (polished rice) accounted for 32% of the total dry weight, it contained only 0.055% of iodine found in the entire rice plants. Atmospheric gaseous iodine (5.9 ng m^–3) was estimated to contribute <0.2% of the total iodine content in the biomass of rice plants; therefore nearly all of the iodine in the rice plants was a result of the uptake of iodine from the soil. The content of iodine in the aboveground part of rice plants was 16 mg kg^–1 dry weight and the percentage of iodine transferred per cropping from the soil into the aboveground biomass corresponded to 0.27% (20 mg m^–2) of the upper soil layer content.

Abbreviations: ICP–MS, inductively coupled plasma–mass spectrometry • RNAA, radiochemical neutron activation analysis • R.S.D., relative standard deviations • TMAH, tetramethyl ammonium hydroxide • XANES, X-ray absorption near-edge structure