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Chemistry and Isotope Fractionation of Divalent Mercury during Aqueous Reduction Mediated by Selected Oxygenated Organic Ligands
Environmental Science & Technology ( IF 11.4 ) Pub Date : 2021-09-14 , DOI: 10.1021/acs.est.1c03171
Huifang Zhao 1, 2 , Bo Meng 1 , Guangyi Sun 1 , Che-Jen Lin 3 , Xinbin Feng 1, 4 , Jonas Sommar 1
Affiliation  

We have investigated the chemistry and Hg isotope fractionation during the aqueous reduction of HgII by oxalic acid, p-quinone, quinol, and anthraquinone-2,6-disulfonate (AQDS), a derivate of anthraquinone (AQ) that is found in secondary organic aerosols (SOA) and building blocks of natural organic matter (NOM). Each reaction was examined for the effects of light, pH, and dissolved O2. Using an excess of ligand, UVB photolysis of HgII was seen to follow pseudo-first-order kinetics, with the highest rate of ∼10–3 s–1 observed for AQDS and oxalic acid. Mass-dependent fractionation (MDF) occurs by the normal kinetic isotope effect (KIE). Only the oxalate ion, rather than oxalic acid, is photoreactive when present in HgC2O4, which decomposes via two separate pathways distinguishable by isotope anomalies. Upon UVB photolysis, only the reduction mediated by AQDS results in a large odd number mass-independent fractionation (odd-MIF) signified by enrichment of odd isotopes in the reactant. Consistent with the rate, MDF, and odd-MIF reported for fulvic acid, our AQDS result confirms previous assumptions that quinones control HgII reduction in NOM-rich waters. Given the magnitude of odd-MIF triggered via a radical pair mechanism and the significant rate in the presence of air, reduction of HgII by photoproducts of AQDS may help explain the positive odd-MIF observed in ambient aerosols depleted of HgII.

中文翻译:

选择性含氧有机配体介导的水还原过程中二价汞的化学和同位素分馏

我们研究了草酸、对-醌、醌醇和蒽醌-2,6-二磺酸盐 (AQDS)对 Hg II进行水溶液还原过程中的化学和 Hg 同位素分馏过程有机气溶胶 (SOA) 和天然有机物质的组成部分 (NOM)。检查每个反应的光、pH 值和溶解的 O 2 的影响。使用过量的配体,Hg II 的UVB 光解遵循伪一级动力学,最高速率约为 10 –3 s –1观察到 AQDS 和草酸。质量相关分馏 (MDF) 通过正常动力学同位素效应 (KIE) 发生。当存在于 HgC 2 O 4 中时,只有草酸离子而不是草酸具有光反应性,HgC 2 O 4通过两条独立的途径分解,可通过同位素异常区分。在 UVB 光解时,只有由 AQDS 介导的还原会导致大量奇数与质量无关的分馏 (odd-MIF),表现为反应物中奇数同位素的富集。与黄腐酸的比率、MDF 和奇数 MIF 一致,我们的 AQDS 结果证实了之前的假设,即醌类控制 Hg II减少富含 NOM 的水域。鉴于通过自由基对机制触发的奇数 MIF 的大小和空气存在下的显着速率,AQDS 光产物对 Hg II的还原可能有助于解释在耗尽 Hg II 的环境气溶胶中观察到的正奇数 MIF 。
更新日期:2021-10-06
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