title: Formation of organic iodine supplied as iodide in a soil-water system in Chiba, Japan.
abstract: Speciation of iodine in a soil-water system was investigated to understand the mechanism of iodine mobility in surface environments. Iodine speciation in soil and pore water was determined by K-edge XANES and HPLC-ICP-MS, respectively, for samples collected at a depth of 0-12 cm in the Yoro area, Chiba, Japan. Pore water collected at a 0-6 cm depth contained 50%-60% of organic iodine bound to dissolved organic matter, with the other portion being I(-). At a 9-12 cm depth, 98% of iodine was in the form of dissolved I(-). In contrast, XANES analysis revealed that iodine in soil exists as organic iodine at all depths. Iodine mapping of soil grains was obtained using micro-XRF analysis, which also indicated that iodine is bound to organic matter. The activity of laccase, which has the ability to oxidize I(-) to I(2), was high at the surface of the soil-water layer, suggesting that iodide oxidizing enzymes can promote iodine organification. The distribution coefficient of organic iodine in the soil-water system was more than 10-fold greater than that of iodide. Transformation of inorganic iodine to organic iodine plays an important role in iodine immobilization, especially in a surface soil-water system.
authors.affiliation: Department of Earth and Planetary Systems Science, Faculty of Science, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8526, Japan. shima-yoko@hiroshima-u.ac.jp
authors.forename: Yoko S
authors.initials: YS
authors.lastname: Shimamoto
authors.forename: Yoshio
authors.initials: Y
authors.lastname: Takahashi
authors.forename: Yasuko
authors.initials: Y
authors.lastname: Terada
mesh_terms: D005618:Fresh Water / Q000737:chemistry*; D006207:Half-Life; D006847:Hydrocarbons, Iodinated / Q000032:analysis / Q000737:chemistry*; D007454:Iodides / Q000032:analysis / Q000737:chemistry*; D007564:Japan; D012987:Soil / Q000737:chemistry; D012989:Soil Pollutants / Q000032:analysis / Q000737:chemistry*; D014874:Water Pollutants, Chemical / Q000032:analysis / Q000737:chemistry*; D056928:X-Ray Absorption Spectroscopy
chemical_list: D006847:Hydrocarbons, Iodinated; D007454:Iodides; D012987:Soil; D012989:Soil Pollutants; D014874:Water Pollutants, Chemical