Institute of Municipal and Environmental Engineering, College of Civil Engineering, Huaqiao University, Fujian 361021, China.
Institute of Municipal and Environmental Engineering, College of Civil Engineering, Huaqiao University, Fujian 361021, China.
Sci Total Environ. 2021 Oct 20;792:148316. doi: 10.1016/j.scitotenv.2021.148316. Epub 2021 Jun 7.
Unsymmetrical dimethylhydrazine (UDMH) is found to generate substantial carcinogenic nitroso-dimethylamine (NDMA) during ozonation, moreover, its formation is promoted by ubiquitous bromide ions (Br) in water matrixes, but the mechanism is still unclear. In this study, effects of Br on NDMA formation during ozonation of UDMH were studied, meanwhile, its promotion pathways were also determined. The results demonstrated that Br promoted NDMA formation from UDMH during ozonation, the formation rate constant with Br is over 7 times of that without Br. NDMA amount raised from 142.5 to 327.5 μg/L when Br dosages increased from 0 to 100 μM. No matter with or without Br, the augment of O dosages facilitated NDMA formation; the maximum value was achieved at pH 8. NDMA decreased dramatically from 173.8 to 123.5 μg/L with HCO raising from 0 to 160 μM, while increasing remarkably to 222.5 μg/L with SO dosing. In addition, NOM inhibited NDMA formation from UDMH during ozonation. The mass spectrum of LC-MS/MS verified that the generation of Br-UDMH was main cause for promoting NDMA formation. Moreover, hypobromous acid (HBrO) was confirmed to be responsible for Br-UDMH formation. In addition, the position that oxidants and Br attacked was demonstrated based on Gaussian calculation. The results of this study could provide theoretical basis for the application of ozonation in bromine-containing water matrixes.
不对称二甲肼（UDMH）在臭氧化过程中会产生大量致癌的亚硝二甲胺（NDMA），此外，其生成受到水中普遍存在的溴离子（Br）的促进，但机制尚不清楚。本研究考察了 Br 对 UDMH 臭氧化过程中 NDMA 生成的影响，同时确定了其促进途径。结果表明，Br 促进了 UDMH 在臭氧化过程中生成 NDMA，其生成速率常数是没有 Br 时的 7 倍以上。当 Br 剂量从 0 增加到 100 μM 时，NDMA 的生成量从 142.5μg/L 增加到 327.5μg/L。无论有无 Br，增加 O 剂量都有利于 NDMA 的生成；在 pH 8 时达到最大值。随着 HCO 从 0 增加到 160 μM，NDMA 从 173.8μg/L 急剧下降到 123.5μg/L，而随着 SO 剂量的增加，NDMA 显著增加到 222.5μg/L。此外，NOM 抑制了 UDMH 在臭氧化过程中生成 NDMA。LC-MS/MS 的质谱证实了 Br-UDMH 的生成是促进 NDMA 生成的主要原因。此外，还证实了次溴酸（HBrO）是 Br-UDMH 形成的原因。此外，还基于高斯计算确定了氧化剂和 Br 攻击的位置。本研究结果可为臭氧化在含溴水基质中的应用提供理论依据。
