Iodine and bromine concentrations in agricultural soils of Japan and their controlling factors

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  • 日本の農耕地土壌のヨウ素および臭素濃度とその規定要因
  • ニホン ノ ノウコウチ ドジョウ ノ ヨウソ オヨビ シュウソ ノウド ト ソノ キテイ ヨウイン

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Abstract

To evaluate the concentrations of iodine (I) and bromine (Br) in agricultural soils of Japan and to investigate their controlling facotrs, we collected 180 soil samples from the surface layer of 96 paddy fields and 84 upland fields. Samples were extracted with tetramethylammonium hydroxide solution for determination of total I by ICP-MS, and with alkali solution for determination of total Br by the analysis of 2-bromo-3-pentanone by HPLC. The arithmetic means were 7.18 mg I and 14.7 mg Br kg^<-1>, and the geometric means were 3.12 mg I and 7.38 mg Br kg^<-1>. The total concentrations averaged 12.9 mg I and 24.0 mg Br kg^<-1> in upland soils, but only 2.17 mg I and 6.43 mg Br kg^<-1> in paddy soils. Concentrations of both had significant positive correlations with total carbon in both soils, suggesting a considerable contribution of organic fractions to their totals. Eh-pH diagrams suggested that the predominant forms of inorganic I were I_2 and IO_3^- in upland soils and I^- in paddy soils; and that Br^- was the predominant form in both soils. Because I_2 and IO_3^- can be adsorbed to soil solids and I^- and Br^- are easily leached from soil, these differences would be responsible, at least partly, for the higher concentrations of I and Br in upland soils than in paddy soils.

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