Occurrence of N-nitrosamines and their precursors in Spanish drinking water treatment plants and distribution systems†
N-Nitrosamines are carcinogenic compounds that can be formed during disinfection processes as by-products in drinking and recycled water systems. Among them, N-nitrosodimethylamine (NDMA) is of particular interest, especially in systems employing chloramines, because its presence is regulated in various countries. Although there is a lot of emphasis on NDMA due to its toxicity, there may be other N-nitrosamines formed during disinfection processes that pose similar or higher toxicities and are currently scarcely studied. This work investigates the presence of NDMA and six additional N-nitrosamines in different drinking water treatment plants (DWTPs) and strategic sampling points from drinking water networks in Spain that employ monochloramines. The other N-nitrosamines investigated are N-nitrosodiethylamine (NDEA), N-nitrosomethylamine (NMEA), N-nitrosodibutylamine (NDBA), N-nitrosopiperidine (NPIP), N-nitrosodipropylamine (NDPA) and N-nitrosopyrrolidine (NPYR). Moreover, the fate of N-nitrosamine precursors was measured across different DWTPs. The actual concentration of NDMA in the final treated water and samples taken from the distribution system was never above 4.2 ± 0.2 ng L−1. NDEA and NDBA were also detected in almost all samples, however, their concentrations did not exceed 1.5 ng L−1 in any case. The maximum concentration of NDMA formation potential following chloramination was 41.5 ± 4.3 ng L−1. The concentration of other N-nitrosamines originating during NDMA formation potential tests was lower than 3 ng L−1. Among the studied DWTPs, those that included ozone followed by granular activated carbon (GAC) in the treatment train removed NDMA formation potential best, showing that this can be an efficient strategy to control NDMA formation during drinking water production when chloramines are used in the distribution systems.