Distribution coefficient of selenium in Japanese agricultural soils

The soil/soil solution distribution coefficient (Kd) of selenium (Se) was measured by the batch technique using 58 Japanese agricultural soils in order to evaluate Se migration behavior. Soils used were air-dried and passed through a 2-mm mesh sieve. Three gram amounts of each soil were transferred into a plastic bottle and 30 mL of deionized water were added to the soil. Prior to adding 75Se, a radioactive tracer of Se, the mixture was shaken for 24 h using an end-over-end shaker. Seven days after the addition of 75Se tracer, the soil solution was separated by centrifugation and filtration. Activity was measured with a NaI (Tl) autowell scintillation counter, and Kd-Se values were calculated. For the agricultural soils, the Kd-Se values ranged from 12 to 1060. Among the soil groups, Andosols had higher Kd-Se values. All the Kd-Se values were significantly correlated with acid oxalate extractable Al (Alo) and Fe (Feo) at the 0.1% level. Alo and Feo contents refer to the amount of active-Al and active-Fe, respectively. These results indicated that the active-Al and the active-Fe were the major adsorbents of Se in Japanese agricultural soils. (author)