Distribution coefficient of selenium in Japanese agricultural soils

Abstract

In order to evaluate the selenium (Se) sorption level in Japanese soils, soil/soil solution distribution coefficients ( K ds) were obtained for 58 agricultural soil samples (seven soil classification groups) using 75Se as a tracer. Although several chemical forms of Se are present in agricultural fields, selenite was used, because it is the major inorganic Se form in acid soils such as found in Japan. The K d values obtained covered a wide range, from 12 to 1060 l/kg, and their arithmetic mean was 315 l/kg. Among the soil groups, Andosols had higher K d values. The K d values for all samples were highly correlated with soil active-aluminum (Al) and active-iron (Fe) contents. Thus, active-Al and active-Fe were considered to be the major adsorbents of Se. Then, a new sequential extraction procedure was applied to 12 soil samples in order to quantify the effect of soil components on Se adsorption. The sequential extraction results showed that 80–100% of the adsorbed Se was recovered as Al-bound Se and Fe-bound Se. The amount of Al-bound Se was the highest in the soils that showed high K d values, though the relative contribution of Fe-bound Se tended to increase with decreasing K d values. The high values of K d seemed to be caused mainly by the adsorption of Se onto active-Al in Japanese soils.