State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Nanjing, 210023, China.
State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Nanjing, 210023, China.
Chemosphere. 2022 Dec;308(Pt 2):136326. doi: 10.1016/j.chemosphere.2022.136326. Epub 2022 Sep 6.
Organoarsenical antibiotics pose a severe threat to the environment and human health. In aquatic environment, dissolved organic matter (DOM)-mediated photochemical transformation is one of the main processes in the fate of organoarsenics. Dicarbonyl is a typical redox-active moiety in DOM. However, the knowledge on the photoconversion of organoarsenics by DOM, especially the contributions of dicarbonyl moieties is still limited. Here, we systematically investigated the photochemical transformation of three organoarsenics with the simplest β-diketone, acetylacetone (AcAc), as a model dicarbonyl moiety of DOM. The presence of AcAc significantly enhanced the photochemical conversion of roxarsone (ROX), whereas only minor effects were observed for 3-amino-4-hydroxyphenylarsonic acid (HAPA) and arsanilic acid (ASA), because the latter two (with an amino (-NH) group) are more photoactive than ROX (with a nitro (-NO) group). The results demonstrate that AcAc was a potent photo-activator and the reduction of -NO to -NH might be a rate-limiting step in the phototransformation of ROX. At a 1:1 M ratio of AcAc to ROX, the photochemical transformation rate of ROX was increased by 7 folds. In O-rich environment, singlet oxygen, peroxide radicals, and ·OH were the main reactive species that led to the breakage of the C-As bond in ROX and the oxidation of the released arsono group to arsenate, whereas the triplet-excited state of AcAc (AcAc*) and carbon-centered radicals from the photolysis of AcAc dominated in the reductive transformation of ROX. In anoxic environment, 3-amino-4-hydroxyphenylarsonic acid was one of the main reductive transformation intermediates of ROX, whose photolysis rate was about 35 times that of ROX. The knowledge obtained here is of great significance to better understand the fate of organoarsenics in natural environment.
有机胂抗生素对环境和人类健康构成严重威胁。在水生环境中，溶解有机质（DOM）介导的光化学反应是有机胂命运的主要过程之一。二羰基是 DOM 中典型的氧化还原活性部分。然而，关于 DOM 介导的有机胂光转化的知识，特别是二羰基部分的贡献仍然有限。在这里，我们系统地研究了三种有机胂的光化学转化，以最简单的β-二酮乙酰丙酮（AcAc）作为 DOM 的模型二羰基部分。AcAc 的存在显著增强了罗沙胂（ROX）的光化学转化，而 3-氨基-4-羟基苯胂酸（HAPA）和对氨基苯胂酸（ASA）的光化学转化则只有很小的影响，因为后两者（带有氨基（-NH）基团）比 ROX（带有硝基（-NO）基团）更具光活性。结果表明，AcAc 是一种有效的光激活剂，-NO 还原为-NH 可能是 ROX 光转化的限速步骤。在 AcAc 与 ROX 的摩尔比为 1:1 时，ROX 的光化学转化速率提高了 7 倍。在富氧环境中，单线态氧、过氧自由基和·OH 是导致 ROX 中 C-As 键断裂和释放的胂基团氧化为砷酸盐的主要反应性物质，而 AcAc 的三重激发态（AcAc*）和光解产生的碳中心自由基在 ROX 的还原转化中占主导地位。在缺氧环境中，3-氨基-4-羟基苯胂酸是 ROX 的主要还原转化中间体之一，其光解速率约为 ROX 的 35 倍。这里获得的知识对于更好地了解有机胂在自然环境中的命运具有重要意义。
