[en] A study is being conducted of the effect of organic complexing agents on the behavior of low-level waste radionuclides in soil/groundwater systems. This report contains the results of recent work with Ni and Co, two elements that have radioactive isotopes that are important to low-level waste disposal. The complexants studied were EDTA, DTPA, oxalate, and citrate. Data were obtained from experiments using soils from both an arid site (Hanford, Washington) and a humid site (Savannah River, South Carolina). Some work with cobalt was done in the absence of air to allow the behavior of the lower oxidation state to be studied. Important variations were observed in both the rates at which equilibrium was approached (from both the precomplexed and the presorbed directions) and the equilibrium positions themselves. The oxalate and citrate complexes are weaker and dissociate more rapidly than the EDTA and DTPA complexes. Dissociation of the EDTA and DTPA complexes occurred much more rapidly in solutions contacting Savannah River soil than in solutions contacting Hanford soil. 20 figures, 6 tables