Forms and transformations of selenium in soil.

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1)A method for quantitative speciation of selenium (Se) in soil was developed and Se in soil was classified into five fractions : organic Se contained in humic acid, organic Se with high molecular weight in fulvic acid, inorganic Se(IV), inorganic Se(VI), and organic Se with low molecular weight such as selenoamino acids. Several soils were examined using this method, it was found that more than 50% of the total Se in the soils was in the forms of organic Se.2)Transformations of Se contained in soil by incubation and heating were studied. No remarkable temporal changes in the forms of soil Se were found by incubating soils under flooded condition for about 6 weeks. On heating soils, organic Se in the soil decreased and inorganic Se(IV) formed with increasing the heating temperature. The inorganic Se(IV) formed gradually sublimated with heating at temperature above 300 C.3)A method was developed for the selective determination of elemental Se in soil. Formation of elemental Se in the soil incubated in waterlogged condition for about 3 weeks was confirmed by the method. The elemental Se formed was estimated to be transformed from inorganic Se(IV) contained in the soil.4)Total and soluble Se contents in the soils collected at Ishigaki, Kume, and Miyako Islands of Okinawa prefecture were determined.