Determination of bioavailable rhenium fraction in agricultural soils

Rhenium (Re) mobility in agricultural soils was studied in order to obtain information relevant to 99Tc mobility in soil-to-plant systems. Since water soluble Tc and Re are highly bioavailable, extraction of Re with water was carried out in addition to a total Re determination in the soils. The geometric means of total Re for paddy field, upland field and other soils were 0.34, 0.23, and 0.28 ng g−1, respectively, while those of water soluble Re (<0.45 μm membrane filterable) were 0.053, 0.015 and 0.008 ng g−1, respectively. There were no differences for total Re among soil uses; however, the water soluble Re/total Re ratio was significantly higher in paddy field soils (16%) than in other soil uses (6% for upland fields and 3% for other uses). Rhenium mobility and plant availability were higher in paddy fields than in other agricultural fields, and similar phenomena would be expected for 99Tc.