Effects of humic substances on plutonium speciation in marine systems

The dominant oxidation state of plutonium in the dissolved phase of seawaters has been shown to be Pu(V). Data are presented that indicate a significant role by humic materials which cause rapid reduction of Pu(VI) to Pu(IV). The latter leaves the solution phase via hydrolysis. The humic material also seems to reduce Pu(V) but at a much slower rate and, in sunlight, this reduction may be negated by an oxidation process of unknown origin at this time. The role of humics sorbed on suspended particulate and sedimentary matter is discussed