[en] Plutonium in geologic matrices undergoes a variety of complex reactions which complicate its environmental behavior. These complexities in plutonium chemistry whereby a large variety of precipitation, dissolution, adsorption/desorption, and redox reactions control plutonium speciation and concentrations, result in the need for a rather large amount of reliable, fundamental data to predict Pu behavior in geologic media. These data are also needed for evaluation of remediation strategies that involve removing most of the contaminants by selective methods, followed by in situ immobilization of residual contaminants. Two areas were studied during this project: (1) thermodynamic data for Th(IV) and Pu(IV) complexes of EDTA and for Pu(V) interactions with chloride; (2) kinetic data for redox reactions of Pu in the presence of common redox agents (e.g., H₂O₂, MnO₂, and NaOCl) encountered under waste disposal conditions. These studies are relevant to understanding Pu behavior in wastes disposed of in diverse geologic conditions (e.g., at the WIPP and YUCCA Mountain repositories and in contaminated sediments at many different DOE sites) and also for developing effective remediation strategies (e.g., processing of high level waste tanks). These studies have yielded data to address redox reactions of plutonium in the presence of environmentally important agents (e.g. organic and inorganic oxidants/reductants)