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，旨在探究选定放射性核素（234Th、233Pa、210Po、210Pb及7Be）在天然海水中于无机颗粒（纯二氧化硅及经酸清洗的硅藻硅质壳）与有机颗粒（带有或不带硅质壳的硅藻细胞）表面的吸附行为，以及从同一硅藻物种三角褐指藻（Phaeodactylum tricornutum）中提取的模板化生物分子与胞外聚合物（exopolymeric substances, EPS）在该吸附过程中的作用。各放射性核素在水相与不同颗粒相之间的分配系数（Kd，以logKd形式报告）范围如下：234Th为4.78~6.69，233Pa为5.23~6.71，210Pb为4.44~5.86，210Po为4.47~4.92，7Be为4.93~7.23，该范围与已有实验室及现场测定的结果相近。所有放射性核素的吸附过程均因颗粒结合的有机质存在而显著增强，其Kd较仅含无机颗粒的体系高出1~2个数量级，其中7Be的吸附增强效果最为显著（logKd达7.2）。研究结果进一步表明，硅藻细胞内的EPS与嵌合于硅质壳的生物分子是吸附增强的关键因素，而非二氧化硅外壳本身。通过等电聚焦（isoelectric focusing）分离放射性标记的EPS后发现，等电点具有放射性核素特异性，提示每种放射性核素均会结合特定的生物聚合物官能团，其中结合效率最高的位点大概率存在于酸性多糖、氢氧化铁及蛋白质中。若要进一步评估硅藻硅质壳相关生物聚合物对放射性核素结合、清除及分馏的影响，需应用分子水平的表征技术。