Distribution coefficients K
ds of several radionuclides on suspended particulate matter (SPM) have been determined with laboratory batch experiments using samples collected in the Kinki district, Japan. Most SPM in coastal water was retained on the initial filter of four sequential filtering stages (20, 5, 1 and 0.45μm pore size), maximum K
d also being found for the SPM retained in this first stage. When the filtrations were not performed in series, however, but were conducted from the same tracer solution in parallel, the K
d values were identical for the smaller filter sizes (5, 1 and 0.45 am) and were greater, by ca. 150% than those derived from the 20μm filter. The degree of association of the radionuclides with SPM was
85Sr<
137Cs<
65Zn <
54Mn<
60Co. The particulate radioactivity fraction of the SPM in coastal water was estimated at most 0.1 for radionuclides with K
d of ca. 5×10
4 ml/g, i.e. which are highly associated with the SPM (2 mg/l). The scavenging effect by SPM seemed to be, however, considerable, the settling velocity being estimated at ca. 25 cm/day for particles of the Stoke's diameter of 30μm.
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