129I/127I Ratios and Iodine Speciation in Surface and Groundwaters: Link Between Speciation and Retardation

0538074碘是一种亲生物元素，具有几种短寿命同位素（例如，131 I，t1/2 = 8天）、一种长寿命同位素129 I（t1/2= 1560万年）和一种稳定同位素127 I。在过去的50年里，地表环境中的129 I库存已被人为释放所淹没。在所有地表环境中，碘与有机物的循环密切相关。海藻和溶解的大分子有机物中碘的相对富集证明了其亲生物性。129 I在许多储层中的平衡时间足够长，使得129 I可用作地表和地下沃茨之间相互作用的示踪剂。在对比鲜明的环境和设置（例如，1）碘在含水层中的阻滞与其形态有关，低分子量（LMW）有机碘物种的阻滞因子最低（R~1.2至1.5），碘化物的阻滞因子中等（R~6）; 2）难降解的LMW有机碘物种的129 I/127 I比率（例如，富里酸的芳族部分）可以适合作为新的地球化学示踪剂和/或地质年代计; 3）虽然在河水中，高分子量（HMW）溶解的有机碘（DOI）物质起主导作用，但在地下水中，仅碘化物和LMW DOI物质可以存在; 3）在来自干旱地区的河流中，例如，圣安娜河（加州），DOI中的129 I浓度[129 I-DOI]受蒸发蒸腾效应的调节，这可以反映在橙子县站点新渗入地下水中DOI的同位素信号中; 4）格拉特河中的[129 I-DOI]（瑞士）受到土壤吸附过程的调节，缓冲其浓度并降低其在河水中的变异性，提供相对恒定的129 I来源，碘同位素是一种放射性核素，可能以碘化物的形式进入地下水，而大多数有机碘物种在河流/含水层边界处被过滤掉。智力价值和更广泛的影响：拟议研究的智力价值有三个方面：1）核释放和沉降的短期和长期剂量的很大一部分来自碘同位素; 2）129 I是贮存放射性废物中仅有的两种高迁移率长寿命核素之一，可以为核设施和核事故释放的放射性核素的长期归宿提供示踪剂; 3）129 I可以为科学界提供一种新型的水文和地球化学示踪剂。拟议的跨学科研究不仅将为碘和有机碳循环的耦合提供新的见解，而且还将提高我们对水生系统中调节碘化反应过程的潜在分子机制的理解。拟议的研究不仅将对环境科学和海洋学教育产生广泛影响，而且这一项目产生的新成果将影响到若干环境学科。有机质与碘的结合可能改变碘同位素的迁移、生物利用和向人体的转移，更好地了解碘及其同位素在环境中的地球化学特征对碘缺乏病和勘查地球化学中的成矿作用具有重要意义。

0538074SantschiIodine is a biophilic element with several short-lived isotopes (e.g., 131I, t1/2 = 8 days), one long-lived isotope, 129I (t1/2= 15.6 million years), and one stable isotope, 127I. The inventory of 129I in surface environments has been overwhelmed by anthropogenic releases over the past 50 years. Iodine is significantly involved in the cycle of organic matter in all surface environments. Its biophilic nature is demonstrated by a relative enrichment of iodine in seaweed and dissolved macromolecular organic matter. Equilibration times for 129I in many reservoirs are long enough that 129I can be used as a tracer for interactions between surface and subsurface waters. A combination of controlled laboratory experiments and field observations (aquifers and rivers) in contrasting environments and settings (e.g., North America and Europe) will be used to test the following hypotheses: 1) The retardation of iodine in aquifers is linked to its speciation, with lowest retardation factors (R~1.2 to 1.5) for low molecular weight (LMW) organo-iodine species, and medium retardation factors for iodide (R~6); 2) The 129I/127I ratio of refractory LMW organo-iodine species (e.g., aromatic moieties of fulvic acids) can be suitable as a novel biogeochemical tracer and/or geochronometer; 3) While in river water, high molecular weight (HMW) dissolved organo-iodine (DOI) species play a dominant role, in groundwater, only iodide and LMW DOI species can exist; 3) In rivers from arid regions, e.g., the Santa Ana River (California), concentrations of 129I in DOI, [129I-DOI], are modulated by evapotranspiration effects, which could be reflected in the isotopic signal of DOI in freshly infiltrated groundwater at the Orange County site; 4) The [129I-DOI] in the Glatt River (Switzerland) is modulated by soil sorption processes that buffer its concentrations and lower its variability in river water, providing a relatively constant source of 129I, likely as iodide, to the groundwater, while most organo-iodine species are filtered out at the river/aquifer boundary.Intellectual Merit and Broader Impacts: The intellectual merit of the proposed research is threefold: 1) A significant fraction of the short-term and long-term dose from nuclear releases and fallout is from iodine isotopes; 2) 129I is one of only two long-lived nuclides with high mobility in stored radioactive waste, and can provide a tracer for the long-term fate of radionuclides released from nuclear facilities and accidents; 3) 129I could provide the scientific community with a novel hydrological and biogeochemical tracer. The proposed interdisciplinary research will not only provide new insights into the coupling of iodine and organic carbon cycles, but will also improve our understanding of the underlying molecular mechanisms of the processes regulating iodination reactions in aquatic systems. The proposed research will not only have a broad impact to education in environmental science and oceanography, but the new results generated from such a project will impact a number of environmental disciplines. The binding of iodine by organic matter has the potential to modify the transport, bioavailability and transfer of iodine isotopes to man. A better understanding of the biogeochemistry of iodine and its isotopes in the environment is also important for assessing iodine deficiency disorders and mineralization in exploration geochemistry.