State Key Laboratory of Pollution Control and Resources Reuse, College of Environmental Science and Engineering, Tongji University, Shanghai, 200092, China; Shanghai Institute of Pollution Control and Ecological Security, Shanghai, 200092, China.
State Key Laboratory of Pollution Control and Resources Reuse, College of Environmental Science and Engineering, Tongji University, Shanghai, 200092, China; Shanghai Institute of Pollution Control and Ecological Security, Shanghai, 200092, China.
Water Res. 2018 Oct 1;142:490-500. doi: 10.1016/j.watres.2018.06.024. Epub 2018 Jun 13.
Haloacetamides (HAMs), a group of nitrogenous disinfection byproducts (N-DBPs), can decompose to form corresponding intermediate products and other DBPs. The stability of ten different HAMs, including two chlorinated, five brominated, and three iodinated species was investigated with and without the presence of chlorine, chloramines, and reactive solutes such as quenching agents. The HAM basic hydrolysis and chlorination kinetics were well described by a second-order kinetics model, including first-order in HAM and hydroxide and first-order in HAM and hypochlorite, respectively, whereas the HAM neutral hydrolysis kinetic was first-order in HAM. Furthermore, HAMs decompose instantaneously when exposed to hypochlorite, which was almost two and nine orders of magnitude faster than HAM basic and neutral hydrolysis, respectively. In general, HAM hydrolysis and chlorination rates both increased with increasing pH and the number of halogens substituted on the methyl group. Moreover, chlorinated HAMs are more unstable than their brominated analogs, followed by the iodinated ones, due to the decrease in the electron-withdrawing inductive effect from chlorine to iodine atom. During hydrolysis, HAMs mainly directly decompose into the corresponding haloacetic acids (HAAs) via a nucleophilic reaction between the carbonyl carbon and hydroxide. For HAM chlorination reactions, hypochlorite reacts with HAMs to form the N-chloro-HAMs (N-Cl-HAMs) via Cl transfer from chlorine to the amide nitrogen. N-Cl-HAMs can further degrade to form HAAs via hypochlorous acid addition. In contrast, the reactions between chloramines and HAMs were found to be insignificant. Additionally, four common quenching agents, including sodium sulfite, sodium thiosulfate, ascorbic acid, and ammonium chloride, were demonstrated to expedite HAM degradation, whereas ammonium chloride was the least influential among the four. Taft linear free energy relationships were established for both HAM hydrolysis and chlorination reactions, based on which the hydrolysis and chlorination rate constants for three monohaloacetamides were estimated. The hydrolysis and chlorination rates of 13 HAMs decreased in the following order: TCAM > BDCAM > DBCAM > TBAM > DCAM > BCAM > DBAM > CIAM > BIAM > DIAM > MCAM > MBAM > MIAM (where C = chloro, B = bromo, I = iodo, T = tri, D = di, M = mono). Lastly, using the HAM kinetic model established in this study, HAM half-lifes in drinking water distribution systems can be predicted on the basis of pH and residual chlorine concentration.
卤乙酰胺（HAMs）是一类含氮消毒副产物（N-DBPs），可分解形成相应的中间产物和其他 DBPs。本研究考察了 10 种不同 HAMs（包括 2 种氯化物、5 种溴化物和 3 种碘化物）在有和没有氯、氯胺和反应性溶质（如猝灭剂）存在时的稳定性。HAM 基本水解和氯化动力学均可用二级动力学模型很好地描述，包括 HAM 和氢氧根的一级动力学以及 HAM 和次氯酸盐的一级动力学，而 HAM 中性水解动力学则是 HAM 的一级动力学。此外，当暴露于次氯酸盐时， HAMs 会立即分解，其分解速度分别比 HAM 基本水解和中性水解快 2 个和 9 个数量级。一般来说，随着 pH 值和取代甲基上卤素数目的增加，HAM 水解和氯化速率均增加。此外，由于氯原子到碘原子的吸电子诱导效应降低，氯化 HAMs 比其溴化物类似物更不稳定，其次是碘化物类似物。在水解过程中， HAMs 主要通过羰基碳与氢氧根之间的亲核反应直接分解成相应的卤乙酸（HAAs）。对于 HAM 氯化反应，次氯酸盐通过氯从氯原子向酰胺氮的转移与 HAMs 反应形成 N-氯-HAMs（N-Cl-HAMs）。N-Cl-HAMs 可以进一步降解形成 HAAs 通过次氯酸的加成。相比之下，发现氯胺与 HAMs 的反应并不重要。此外，四种常见的猝灭剂，包括亚硫酸钠、硫代硫酸钠、抗坏血酸和氯化铵，被证明可以加速 HAMs 的降解，而氯化铵在这四种猝灭剂中影响最小。建立了 HAM 水解和氯化反应的 Taft 线性自由能关系，基于此，估计了三种单卤乙酰胺的水解和氯化速率常数。13 种 HAMs 的水解和氯化速率按以下顺序降低：TCAM＞BDCAM＞DBCAM＞TBAM＞DCAM＞BCAM＞DBAM＞CIAM＞BIAM＞DIAM＞MCAM＞MBAM＞MIAM（其中 C = 氯，B = 溴，I = 碘，T = 三，D = 二，M = 单）。最后，使用本研究建立的 HAM 动力学模型，可以根据 pH 值和余氯浓度预测饮用水分配系统中 HAM 的半衰期。
