Dataset: Partition coefficient of 234Th, 233Pa, 210Pb, 210Po, and 7Be

Laboratory studies were conducted to examine the sorption of selected radionuclides (234Th, 233Pa, 210Po,
210Pb, and 7Be) onto inorganic (pure silica and acid-cleaned diatom frustules) and organic (diatom cells with or
without silica frustules) particles in natural seawater and the role of templating biomolecules and exopolymeric
substances (EPS) extracted from the same species of diatom, Phaeodactylum tricornutum, in the sorption process.
The range of partition coefficients (Kd, reported as logKd) of radionuclides between water and the different
particle types was 4.78–6.69 for 234Th, 5.23–6.71 for 233Pa, 4.44–5.86 for 210Pb, 4.47–4.92 for 210Po, and 4.93–7.23 for 7Be, similar to values reported for lab and field determinations. The sorption of all radionuclides was
significantly enhanced in the presence of organic matter associated with particles, resulting in Kd one to two
orders of magnitude higher than for inorganic particles only, with highest values for 7Be (logKd of 7.2). Results
further indicate that EPS and frustule-embedded biomolecules in diatom cells are responsible for the sorption
enhancement rather than the silica shell itself. By separating radiolabeled EPS via isoelectric focusing, we found
that isoelectric points are radionuclide specific, suggesting that each radionuclide binds to specific biopolymeric
functional groups, with the most efficient binding sites likely occurring in acid polysaccharides, iron hydroxides,
and proteins. Further progress in evaluating the effects of diatom frustule–related biopolymers on binding,
scavenging, and fractionation of radionuclides would require the application of molecular-level characterization
techniques.