DISTRIBUTION OF PU(V) AND PU(VI) IN SEAWATER

The stability of tracer concentrations of Pu(V) and Pu(VI) in surface seawater from the Gulf of Mexico was studied by adsorption to silica gel and calcium carbonate, and extraction by TTA. The methods were consistent in confirming that Pu(VI) was reduced rapidly to Pu(V) and Pu(IV). In darkness, the Pu(V) was slowly reduced to Pu(IV) with a first-order dependence on Pu(V) concentration and a half-life of ∼ 70 days for 10-10 M. In 0.7 M NaCl solution (pH 8.2), reduction of Pu(V) (in the dark) was much slower (t 1 2 ∼ 1.6 year). When exposed to normal external light, Pu(V) was ∼ 60% reduced to Pu(IV) in a few hours, then remained stable over a month's observation time. When such a sample was removed from sunlight, no further redox change was observed. These data are discussed in terms of actinide redox and complexation behavior in marine waters. © 1990.