A tracer sphere detectable by neutron activation for soil aggregation and translocation studies

Current radiological and particle tracer methods used in soil translocation studies have several limitations, Studies of soil aggregate dynamics also require an improved particle tracer approach. Our objective was to develop an inert tracer sphere applicable in soil aggregation and translocation stu dies, We selected ceramic prills in varying size fractions, labeled with 10 to 15% (w/w) Dy during manufacture, as inert tracers to simulate soil aggr egates because of their similar surface properties. Frills added to soil (T ypic Cryoboroll) were detected and quantified via the Dy content of a mixed tracer-soil sample using instrumental neutron activation analysis (INAA), Detection limit measurements demonstrated that the tracers were easily dete cted; approximately one 300-mu m sphere is detectable in 5 g of soil contai ning a background level of 3.1 mu g g(-1) Dy Coefficients of variation for tracer sphere properties within size fractions were determined: 5.3 to 16.6 % for mass in composite samples,12.2 to 22.6% for diameter, and 6.5 to 10.8 % for Dy concentration. However, no difference between actual and calculate d numbers of spheres was detected (P = 0.05), indicating that the variabili ty is insufficient to affect tracer sphere detection. Tracer integrity test s showed no leaching losses of the Dy label, and tracer sphere abrasion res ulted in losses of <1% of sphere Dy content. The tracers have proven suffic iently homogeneous and robust for practical use and are currently being use d to study soil aggregate dynamics.