Large-scale zonal rotors in soil science. [Density gradients; biological availability]

A large-scale zonal rotor was developed to band isopycnically soils and sediments in nonaqueous density gradients. The major advantage of such a rotor over conventional swinging bucket rotors is that relatively large quantities may be segregated; 15 g in large-scale zonal rotors vs. 0.25 g per centrifugal tube with swinging bucket rotors. The rotor was used to isolate and identify soil-sediment reaction sites of /sup 137/Cs, /sup 60/Co, and /sup 106/Ru. The /sup 137/Cs was found to be associated with micaceous minerals, the /sup 60/Co with Fe-sesquioxides, and the /sup 106/Ru with organic rich soil components. An edge-unloading rotor containing sucrose gradients (max. density 1.3 g/cm/sup 3/) was used in a rate-zonal mode to isolate Cd and Ni enriched fractions of sediment taken near the wastewater discharge of a Cd-Ni battery plant. In sediments enriched in carbonates Cd was found to be largely associated with the carbonates while Ni was concentrated in the organic rich soil components. Biological availability of Cd was evaluated by growing bush bean seedlings (Phaseolus vulgaris L.) in nutrient solutions containing density fractions of a soil clay. Density gradient separations using large-scale rotors were shown to be a valuable adjunct to chemical extraction techniques for characterizingmore » trace element interactions with soils and sediments.« less