Department of Chemistry, University of Minnesota, 207 Pleasant Street SE, Minneapolis, Minnesota 55455, United States.
Environ Sci Technol. 2011 Apr 1;45(7):2818-25. doi: 10.1021/es2000694. Epub 2011 Mar 4.
Photochemical formation of reactive oxygen species from dissolved organic matter (DOM) is incompletely understood, especially in the case of hydroxyl radical (•OH) production. Many studies have used various probes to detect photochemically produced •OH from DOM, but the fundamental reactions of these probes are not necessarily specific for free •OH and may also detect lower-energy hydroxylation agents. In this study, two tests were applied that have previously been used as a diagnostic for the presence of free •OH: methane quenching of •OH and hydroxybenzoic acid (hBZA) product yields. Upon application of these two tests to a set of five DOM isolates, it was found that methane quenching and the hBZA ratio results were not necessarily consistent. Overall, the results provide compelling evidence that all isolates studied photochemically produce free •OH. The hydroxylating acitivity of Elliot Soil Humic Acid and Pony Lake Fulvic Acid, however, also had a significant contribution from a photochemically generated hydroxylating agent that is lower in energy than free •OH. Catalase quenching experiments were conducted to assess whether hydrogen peroxide was the immediate precursor to hydroxyl in these systems. In all cases, catalase addition slowed photohydroxylation of terephthalate, but the contribution of hydrogen peroxide photolysis was determined to be less than 50%.
光化学条件下溶解态有机质（DOM）生成活性氧的过程还不完全清楚，特别是羟基自由基（•OH）的生成过程。许多研究都使用了各种探针来检测 DOM 中光化学产生的•OH，但这些探针的基本反应不一定对游离•OH具有特异性，也可能检测到能量较低的羟化试剂。在这项研究中，应用了两项先前被用于检测游离•OH存在的诊断测试：甲烷猝灭•OH 和羟基苯甲酸（hBZA）产物产率。将这两项测试应用于五组 DOM 分离物，发现甲烷猝灭和 hBZA 比值的结果并不一定一致。总的来说，结果有力地证明了所有研究的分离物都能光化学产生游离•OH。然而，Elliot 土壤腐殖酸和 Pony Lake 富里酸的羟化活性也来自于一种能量比游离•OH 低的光化学生成的羟化剂。进行了过氧化氢酶猝灭实验以评估在这些体系中，过氧化氢是否是羟基的直接前体。在所有情况下，过氧化氢酶的添加都减缓了对苯二甲酸的光羟化，但确定过氧化氢光解的贡献小于 50%。
