Laboratory experiments were carried out to assess the role of photoche
mical reactions upon the dissolution of Pu-239+240 and Am-241 from mar
ine sediment in seawater. Supplementary information was obtained by co
mparing their behaviour with that of Mn-54 under similar experimental
conditions. Irradiation from natural sunlight resulted in more than a
ten-fold increase in the extent of Pu-239+240 desorption relative to t
hat observed in the dark. Remobilisation of Mn-54 from sediment was al
so enhanced by natural sunlight, albeit to a lesser extent than Pu-239
+240, whilst the behaviour of Am-241 was largely unaffected. Data for
concentrations of dissolved Pu-239+240(IV) and Pu-239+240(V) species s
howed that only the oxidised form was significantly affected by irradi
ation, indicating remobilisation occurs as a result of photooxidation
reactions. Further experiments were carried out using artificial light
sources to establish the influence of wavelength. Data from these inv
estigations indicated Pu-239+240 photooxidation (hence desorption) was
a function of both light intensity and wavelength. Remobilisation dec
reased concomitant with light intensity but increased as the wavelengt
h decreased. Similar trends were observed for photoreduction of Mn-54,
although differences were less pronounced than those observed for. Pu
-239+240.