School of Environmental Science and Engineering, Guangdong Provincial Key Laboratory of Environmental Pollution Control and Remediation Technology, Sun Yat-sen University, Guangzhou 510275, China.
School of Sustainable Engineering and the Built Environment, Arizona State University, Tempe, Arizona 85287-3005, United States.
Environ Sci Technol. 2022 Apr 19;56(8):5189-5199. doi: 10.1021/acs.est.2c00549. Epub 2022 Mar 29.
Dissolved organic matter (DOM) is a major scavenger of bromine radicals (e.g., Br and Br) in sunlit surface waters and during oxidative processes used in water treatment. However, the literature lacks quantitative measurements of reaction rate constants between bromine radicals and DOM and lacks information on the extent to which these reactions form brominated organic byproducts. Based on transient kinetic analysis with different fractions and sources of DOM, we determined reaction rate constants for DOM with Br ranging from <5.0 × 10 to (4.2 ± 1.3) × 10 M s, which are comparable with those of HO but higher than those with Br ( = (9.0 ± 2.0) × 10 to (12.4 ± 2.1) × 10 M s). Br and Br attack the aromatic and antioxidant moieties of DOM via the electron transfer mechanism, resulting in Br release with minimal substitution of bromine into DOM. For example, the total organic bromine was less than 0.25 μM (as Br) at environmentally relevant bromine radicals' exposures of ∼10 M·s. The results give robust evidence that the scavenging of bromine radicals by DOM is a crucial step to prevent inorganic bromine radical chemistry from producing free bromine (HOBr/OBr) and subsequent brominated byproducts.
溶解有机物（DOM）是阳光照表层水中溴自由基（例如 Br 和 Br）的主要清除剂，也是水处理中氧化过程的主要清除剂。然而，文献中缺乏溴自由基与 DOM 之间反应速率常数的定量测量，也缺乏有关这些反应形成溴代有机副产物的程度的信息。基于对不同 DOM 分数和来源的瞬态动力学分析，我们确定了 Br 与 DOM 的反应速率常数范围为 <5.0×10 至 (4.2±1.3)×10 M s，与 HO 的反应速率常数相当，但高于 Br 的反应速率常数（= (9.0±2.0)×10 至 (12.4±2.1)×10 M s）。Br 和 Br 通过电子转移机制攻击 DOM 的芳香族和抗氧化部分，导致 Br 释放，而 DOM 中溴的取代程度最小。例如，在环境相关的溴自由基暴露约 10 M·s 时，总有机溴的含量（以 Br 计）小于 0.25 μM。结果有力地证明了 DOM 对溴自由基的清除是防止无机溴自由基化学产生游离溴（HOBr/OBr）和随后的溴代副产物的关键步骤。
