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 studies. We selected ceramic prills in varying size fractions, labeled with 10 to 15% (w/w) Dy during manufacture, as inert tracers to simulate soil aggregates because of their similar surface properties. Prills added to soil (Typic 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 detected; approximately one 300-micrometers sphere is detectable in 5 g of soil containing a background level of 3.1 micrograms 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 calculated numbers of spheres was detected (P = 0.05), indicating that the variability is insufficient to affect tracer sphere detection. Tracer integrity tests showed no leaching losses of the Dy label, and tracer sphere abrasion resulted in losses of < 1% of sphere Dy content. The tracers have proven sufficiently homogeneous and robust for practical use and are currently being used to study soil aggregate dynamics.