Percent amount of organic fractions from diatoms that bind with radionuclides

<p>In order to investigate the importance of biogenic silica associated biopolymers on the scavenging of radionuclides, the diatom Phaeodactylum tricornutum was incubated together with the radionuclides 234Th, 233Pa, 210Pb, and 7Be during their growth phase. Normalized affinity coefficients were determined for the radionuclides bound with different organic compound classes (i.e., proteins, total carbohydrates, uronic acids) in extracellular (nonattached and attached exopolymeric substances), intracellular (ethylene diamine tetraacetic acid and sodium dodecyl sulfate extractable), and frustule embedded biopolymeric fractions (BF). Results indicated that radionuclides were mostly concentrated in frustule BF. Among three measured organic components, Uronic acids showed the strongest affinities to all tested radionuclides. Confirmed by spectrophotometry and two-dimensional heteronuclear single quantum coherence-nuclear magnetic resonance analyses, the frustule BF were mainly composed of carboxyl-rich, aliphatic-phosphoproteins, which were likely responsible for the strong binding of many of the radionuclides. Results from this study provide evidence for selective absorption of radionuclides with different kinds of diatom-associated biopolymers acting in concert rather than as a single compound. This clearly indicates the importance of these diatom-related biopolymers, especially frustule biopolymers, in the scavenging and fractionation of radionuclides used as particle tracers in the ocean.</p> <p>&nbsp;</p>为探究与生物成因二氧化硅（biogenic silica）结合的生物聚合物在放射性核素清除过程中的重要性，本研究将三角褐指藻（Phaeodactylum tricornutum）与放射性核素234钍（234Th）、233镤（233Pa）、210铅（210Pb）及7铍（7Be）在其生长阶段共培养。针对胞外（非附着型与附着型胞外聚合物）、胞内[乙二胺四乙酸（ethylene diamine tetraacetic acid，EDTA）与十二烷基硫酸钠（sodium dodecyl sulfate，SDS）可提取组分]以及硅质壳包埋生物聚合物组分（BF）中不同有机化合物类别（即蛋白质、总碳水化合物、糖醛酸）结合的放射性核素，测定了其标准化亲和系数。结果显示，放射性核素主要富集于硅质壳包埋生物聚合物组分中。在测定的三类有机组分中，糖醛酸对所有受试放射性核素均表现出最强的亲和性。经分光光度法与二维异核单量子相干-核磁共振（two-dimensional heteronuclear single quantum coherence-nuclear magnetic resonance，2D HSQC-NMR）分析证实，硅质壳包埋生物聚合物组分主要由富羧基脂肪族磷蛋白构成，这类物质可能是多数放射性核素高效结合的关键原因。本研究结果证实，不同种类的硅藻相关生物聚合物可协同作用而非单一化合物单独发挥功能，实现对放射性核素的选择性吸附。这明确表明，此类硅藻相关生物聚合物（尤其是硅质壳生物聚合物）在海洋中用作颗粒示踪剂的放射性核素的清除与分馏过程中具有重要意义。