Iodine-129 is one of three key risk drivers at several US Department of Energy waste management sites. Natural organic matter (NOM) is thought to play important roles in the immobilization of aqueous iodide (I^–) and iodate (IO₃^–) in the environment, but molecular interactions between NOM and iodine species are poorly understood. In this work, we investigated iodine and carbon speciation in three humic acid (HA)-I systems using I K-edge XANES and EXAFS and C K-edge XANES spectroscopy: (1) I^– in the presence of laccase (an oxidase enzyme) and a mediator, 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) in a pH 4 buffer, (2) I^– in the presence of lactoperoxidase (LPO) and H₂O₂ in a pH 7 buffer, and (3) IO₃^– in a pH 3 groundwater. Both oxidase and peroxidase systems could oxidize I^– to I₂ or hypoiodide (HOI) leading to organo-I formation. However, the laccase-ABTS mediator was the most effective and enhanced I^– uptake by HA up to 13.5 mg/g, compared to 1.9 mg/g for the LPO–H₂O₂. IO₃^– was abiotically reduced to I₂ or HOI leading to an organo-I formation. Pathways for HA iodination include covalent modification of aromatic-type rings by I₂ / HOI or iodine incorporation into newly formed benzoquinone species arising from the oxidation of phenolic C species. This study improves our molecular-level understanding of NOM–iodine interactions and stresses the important role that mediators may play in the enzymatic reactions between iodine and NOM.

中文翻译：

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I和C K边X射线吸收光谱研究碘水溶液与腐殖酸的分子相互作用

Iodine-129是美国能源部多个废物管理站点的三个主要风险驱动因素之一。天然有机物质（NOM）被认为在水性碘化物的固定中发挥重要作用（I ^- ）和碘酸盐（IO ₃ ^- ）的环境中，但之间的分子相互作用NOM和碘物质知之甚少。在这项工作中，我们使用I K-edge XANES和EXAFS和C K-edge XANES光谱学研究了三种腐殖酸（HA）-I系统中的碘和碳形态：（1）I ^–存在漆酶（氧化酶）和介体，在pH 4缓冲液中的2,2'-叠氮基双（3-乙基苯并噻唑啉-6-磺酸）（ABTS），（2）I ^–在乳过氧化物酶（LPO）和H ₂ O存在下₂在pH 7的缓冲液中，（3）IO ₃ ^–在pH 3的地下水中。氧化酶和过氧化物酶系统都可以将I ^–氧化为I ₂或低碘化物（HOI），从而形成有机I。然而，漆酶-ABTS介体是最有效和增强的I ^– HA吸收量高达13.5 mg / g，而LPO–H ₂ O ₂为1.9 mg / g 。IO ₃ ^–非生物还原为I ₂或HOI，导致形成有机I。HA碘化的途径包括通过I ₂共价修饰芳族环/ HOI或碘结合到由于酚C物种的氧化而形成的新形成的苯醌物种中。这项研究提高了我们对NOM-碘相互作用的分子水平的理解，并强调了介体可能在碘与NOM之间的酶促反应中发挥重要作用。