Nitrosamine formation from the oxidation of secondary amines

The nitrosamines are potent carcinogens which can be formed as by-products during water treatment. Much recent research activity has been focussed upon the formation, occurrence and control of N-nitrosodimethylamine (NDMA) in particular. In this study, seven secondary amines were oxidised by chlorine, ozone, and UV-irradiation, with and without post-chloramination, to quantify the effect on the formation of seven nitrosamines, including NDMA. While the yields of nitrosamines ranged from 0.01% for N-nitroso-di-n-butylamine (NDBA) to 2.01% for N-nitrosopyrrolidine (NPYR) under conditions of excess monochloramine at pH 7, yields from other oxidants were zero. Pre-oxidation with chlorine reduced nitrosamine formation by up to 83% compared with chloramination alone. This illustrates that in situations where secondary amines are key precursors, chlorine addition before ammonia during chloramination can be expected to limit nitrosamine formation. UV irradiation at 40 mJ cm⁻² had little observed impact. Ozonation enhanced NDMA and N-nitrosomethylethylamine (NMEA) formation by subsequent chloramination to 7.48% and 10.15%, respectively.