Absorbance from Fourier transform infrared spectroscopy sample characterization experiments.

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

本研究通过实验室实验，对所选放射性同位素（234Th、233Pa、210Po、210Pb 和 7Be）在天然海水中对无机（纯二氧化硅和酸洗硅藻壳）及有机（含或不含二氧化硅壳的硅藻细胞）颗粒的吸附进行了研究，并探讨了模板生物分子和从同种硅藻（Phaeodactylum tricornutum）中提取的异多糖类物质（EPS）在吸附过程中的作用。研究结果显示，放射性同位素在水与不同颗粒类型之间的分配系数（Kd，以 logKd 报告）范围为 234Th 的 4.78–6.69，233Pa 的 5.23–6.71，210Pb 的 4.44–5.86，210Po 的 4.47–4.92，以及 7Be 的 4.93–7.23，与实验室和现场测定值相似。在颗粒相关的有机物存在下，所有放射性同位素的吸附均显著增强，导致 Kd 值比仅无机颗粒高出一个至两个数量级，其中 7Be 的值最高（logKd 为 7.2）。进一步的研究结果还表明，硅藻细胞中嵌入的 EPS 和生物分子是吸附增强的负责因素，而非二氧化硅壳本身。通过等电聚焦分离放射性标记的 EPS，我们发现等电点具有放射性同位素特异性，表明每个放射性同位素与特定的生物大分子功能团结合，其中最有效的结合位点可能出现在酸性多糖、氢氧化铁和蛋白质中。为了进一步评估硅藻壳相关生物聚合物对放射性同位素结合、清除和分离的影响，需要应用分子水平的表征技术。