Alternative Disinfectants and N-Nitrosamines in Drinking Water: Are We Really Managing Human Health Risks?

North American drinking water utilities are increasingly incorporating alternative disinfectants, such as chloramines, in order to comply with disinfection by-product (DBP) regulations. NNitrosodimethylamine (NDMA) is an unregulated, non-halogenated DBP associated with chloramination, having a drinking water carcinogenic unit risk two to four orders of magnitude greater than currently regulated halogenated DBPs. A N-nitrosamine occurrence study of twenty Alberta municipal drinking-water distribution systems was undertaken. We detected NDMA (up to 100 ng/L) as well as N-nitrosopyrrolidine (4 ng/L) and N-nitrosomorpholine (3 ng/L). NDMA drinking water concentrations consistently over 100 ng/L are some of the highest ever recorded. Ironically, in an attempt to reduce regulated halogenated DBPs, some drinking water utilities may be making process changes that could preferentially be forming potentially more toxic unregulated DBPs. Risk trade-off issues involving alternative disinfection methods and unregulated DBPs, such as NDMA, are emerging as a major water quality and public health information gap.