Concentration of particulate plutonium in surface and deep-water samples collected during the IAEA’97 expedition

Concentrations of particulate plutonium together with dissolved plutonium and the biogenic unique organic ligand (SOL) in particulate matter (PM) in surface and deep waters were determined in samples collected during the IAEA’97 cruise to the Pacific Ocean. Concentrations of particulate 239,240Pu in the water column ranged from 0.04 to 0.28 mBq m−3. The percentage of particulate 239,240Pu to total 239,240Pu in seawater was less than 10% in surface waters and less than 2% in deep waters. In order to characterize particulate 239,240Pu in seawater, the relationship between particulate 239,240Pu, dissolved 239,240Pu and SOL concentrations in surface PM was examined. The results reveal that particulate 239,240Pu in surface waters was linearly related to SOL concentration and independent of dissolved 239,240Pu concentrations. On the other hand, particulate 239,240Pu in deep waters does not seem to be related to the SOL concentration alone. pH values are discussed as another factor controlling particulate 239,240Pu in deep waters. The results suggest that the dominant chemical form of 239,240Pu in surface and deep PM, which may exist as Pu(IV), is a complex of SOL onto PM.