Eawag, Swiss Federal Institute of Aquatic Science and Technology, Ueberlandstrasse 133, 8600, Dubendorf, Switzerland.
Environ Sci Technol. 2010 Aug 1;44(15):5762-8. doi: 10.1021/es1011862.
N,N-Dimethylsulfamide (DMS), a newly identified, ubiquitous degradation product of the fungicide tolylfluanide, has been shown to be a N-nitrosodimethylamine (NDMA) precursor during ozonation. In this study, batch ozonation experiments in ultrapure buffered water, surface water, and tap water were performed to determine the kinetics and elucidate the mechanism of NDMA formation from DMS. It was found that at circumneutral pH, DMS reacts slowly with ozone (k approximately 20 M(-1) s(-1)) and moderately with hydroxyl radicals (k=1.5x10(9) M(-1)s(-1)). The reaction of DMS with these oxidants does not lead to NDMA. NDMA was only formed if bromide was present during ozonation of DMS-containing waters. Bromide is oxidized to hypobromous acid (HOBr) by ozone which then reacts with the primary amine of DMS to form a Br-DMS species. The rate limiting step of the formation of Br-DMS is the formation of HOBr. The reaction to form Br-DMS has an apparent second order rate constant at pH 8 of >3x10(4) M(-1)s(-1). The Br-DMS is transformed by ozone to NDMA and nitrate (k>or=5000 M(-1) s(-1)), with yields of 54% and 39%, respectively, based on the primary amine nitrogen of DMS. These reactions release bromide, making bromide a catalyst. NDMA is also formed during ozonation of DMS in the presence of hypochlorous acid (20-30% yield). The last step of NDMA formation is an intramolecular rearrangement with sulfur dioxide extrusion. On the basis of the mechanistic and kinetic information, it was possible to model NDMA formation in DMS-containing Lake Zurich water.
N,N-二甲基甲酰胺（DMS）是一种新发现的、普遍存在的杀真菌剂甲苯氟磺胺的降解产物，已被证明在臭氧化过程中是亚硝二甲胺（NDMA）的前体。在这项研究中，进行了超纯缓冲水、地表水和自来水的分批臭氧化实验，以确定动力学并阐明 DMS 形成 NDMA 的机制。结果表明，在近中性 pH 值下，DMS 与臭氧缓慢反应（k 约为 20 M(-1) s(-1)），与羟基自由基适度反应（k=1.5x10(9) M(-1)s(-1)）。DMS 与这些氧化剂的反应不会导致 NDMA 的形成。只有在臭氧化含 DMS 的水时存在溴化物，才会形成 NDMA。臭氧将溴化物氧化为次溴酸（HOBr），然后次溴酸与 DMS 的伯胺反应形成 Br-DMS 物种。Br-DMS 形成的速率限制步骤是 HOBr 的形成。在 pH 值为 8 时，形成 Br-DMS 的反应的表观二级速率常数大于 3x10(4) M(-1) s(-1)。Br-DMS 被臭氧转化为 NDMA 和硝酸盐（k>or=5000 M(-1) s(-1)），基于 DMS 的伯胺氮，分别得到 54%和 39%的产率。这些反应释放溴化物，使溴化物成为催化剂。在次氯酸（20-30%产率）存在下，DMS 的臭氧化也会形成 NDMA。NDMA 形成的最后一步是分子内重排，伴随着二氧化硫的排出。根据机理和动力学信息，可以对含 DMS 的苏黎世湖水进行 NDMA 形成的建模。
