Redox speciation of plutonium in natural waters

To ascertain the range of conditions of pH, ionic strength for which plutonium(V) (the dominant oxidation state of trace concentrations of plutonium in natural waters) showed stability in natural waters, several laboratory experiments were carried out. Solutions of 0.1 and 1.0 M sodium chloride and pH 3-10 confirmed the dominance of plutonium(V) as the major species in solution. In neutral brine solutions plutonium(VI) was the more stable species. The total amount of plutonium(IV) on colloidal and suspended material, where it was strongly adsorbed, might exceed the concentration of plutonium(V) in true solution. Humic materials were a major factor in the behaviour of plutonium in natural waters, even at low (0.1 ppm) levels. Humics caused reduction of plutonium(V) to plutonium(IV).