Precursors of N-mitrosodimethylamine in natural waters

Monochloramine disinfection of drinking water can result in the formation of the potent carcinogen N-nitrosodimethylamine (NDMA). To assess NDMA precursor concentrations in natural waters, samples from lakes, reservoirs, groundwaters, and isolated natural organic matter were exposed to relatively high concentrations of monochloramine. After I week, the concentration of NDMA ranged from approximately 0.1 to 0.8 nM. Application of a sensitive new GC/MS/MS technique and amendment of a sample with the known NDMA precursor dimethylamine (DMA) prior to chloramination indicated that only a small fraction of the NDMA produced during chloramination could be attributable to DMA. Chloramination of isolated natural organic matter and application of solid-phase extraction prior to chloramination suggested that natural organic matter accounts for a significant fraction of the precursors. However, the concentrations of NDMA precursors were higher in the epilimnion than the hypolimnion of two stratified reservoirs despite similar concentrations of dissolved organic carbon throughout the water column. Experiments performed to simulate the formation of NDMA during conditions comparable to those encountered in water treatment and distribution systems that use chloramine indicated that the concentration of NDMA produced from naturally occurring precursors usually will be less than 0.1 nM. The results indicate that chloramination of natural organic matter alone is unlikely to produce NDMA levels exceeding the current regulations.