Enhanced N-nitrosamine formation in pool water by UV irradiation of chlorinated secondary amines in the presence of monochloramine

• Published in: Water research (Oxford) 2013-01, Vol.47 (1), p.79-90
• Main Authors: Soltermann, Fabian, Lee, Minju, Canonica, Silvio, von Gunten, Urs
• Format: Article
• Language: English
• Subjects: Amines; Amines - chemistry; Applied sciences; Byproducts; carcinogens; Chloramines - chemistry; Chlorination; chlorine; dimethylamine; disinfection; Disinfection by-products; Drinking water and swimming-pool water. Desalination; Exact sciences and technology; Hydrocarbons, Chlorinated - chemistry; Irradiation; Monochloramine; N-nitrosamine; N-Nitrosamines; N-Nitrosodimethylamine; nitric oxide; Nitrosamines - chemistry; oxidation; Photolysis; Pollution; Pool water; Pools; Precursors; swimming; Swimming Pools; ultraviolet radiation; Ultraviolet Rays; UV irradiation; Water Purification - methods; Water treatment and pollution
• ISSN: 0043-1354; 1879-2448
• DOI: 10.1016/j.watres.2012.09.034

N-Nitrosamines, in particular N-nitrosodimethylamine (NDMA), are carcinogens, which occur as chlorine disinfection by-products (DBPs) in swimming pools and hot tubs. UV treatment is a commonly used technique in swimming pools for disinfection and DBP attenuation. UV irradiation is known to efficiently degrade N-nitrosamines. However, UV irradiation (at λ = 254 nm) of chlorinated dimethylamine (CDMA) and monochloramine, two NDMA precursors present in swimming pool water, resulted in a substantial UV-induced NDMA formation (∼1–2% molar yield based on initial CDMA concentration) simultaneously to NDMA photolysis. Maximum NDMA concentrations were found at UV doses in the range used for advanced oxidation (350–850 mJ cm−2). Very similar behaviour was found for other chlorinated secondary amines, namely diethylamine and morpholine. Effectiveness of UV irradiation for N-nitrosamine abatement depends on initial N-nitrosamine and precursor concentrations and the applied UV dose. N-Nitrosamine formation is hypothesized to occur via the reaction of nitric oxide or peroxynitrite with the secondary aminyl radical, which are products from the photolysis of monochloramine and chlorinated secondary amines, respectively. Experiments with pool water showed that similar trends were observed under pool water conditions. UV treatment (UV dose: ∼360 mJ cm−2) slightly increased NDMA concentration in pool water instead of the anticipated 50% abatement in the absence of NDMA precursors. [Display omitted] ► UV irradiation of NH2Cl and chlorinated dimethylamine induced NDMA formation. ► NDMA is likely formed via nitric oxide/peroxynitrite and dimethylaminyl radicals. ► Chlorinated morpholine and diethylamine induced a similar N-nitrosamine formation. ► Experiments with pool water revealed the relevance of this formation pathway.