MULTIPARAMETRIC INVESTIGATION OF THE REACTIONS OF PLUTONIUM UNDER ESTUARINE CONDITIONS

Several sampling campaigns were carried out in the Seine estuary in or der to study the behaviour of plutonium isotopes Versus salinity (Pu-2 38 and Pu-239,Pu-240), in 0.45 mu m filtered waters. During estuarine mixing, the plutonium has a non-conservative behaviour: plots of Pu ac tivities versus salinity display an excess of dissolved Pu-238 (RI = P u-238/Pu-239,Pu-240 > 1) in low salinity waters (0.5 and 1.5 g l(-1)) and a depletion (RI < 1) in the zone of intermediate salinities (8 to 15 g l(-1)), with respect to conservative dilution. Laboratory experim ents showed that Pu(V) present in seawater is reduced to the III, IV s tates and sorbed onto particles with a maximum in low salinity waters which could explain the depletion observed at intermediate salinity in the Seine estuary. Reduction occurs prior to sorption and is connecte d with the Seine river colloidal and dissolved species (humic acids). The Pu associated with estuarine sediments desorbs from the ''oxide-hy droxide'' fraction in contact with river water, thus partly explains t he plutonium excess measured in low salinity filtered waters of the Se ine.