Potentially Carcinogenic N-nitrosodimethylamine in Drinking Water: Factors Influencing NDMA Formation During Water Chlorination

N-nitrosodimethylamine (NDMA) is a potentially carcinogenic byproduct of disinfecting drinking water. NDMA has been classified as a Group B2 carcinogen by the U.S. Environmental Protection Agency (EPA). The pathway of NDMA formation during chlorination has been proposed; however, it is still necessary to identify the most influential factor in this process. The objective of this study was to compare the factors and conditions that lead to the formation of NDMA from dimethylamine (DMA) to identify the primary factors responsible for the occurrence of this compound in drinking water. The study examined the formation of NDMA in chlorinated water under seven different conditions, considering three factors (NO2-, NO3-, and NH3). All factors were maintained at their actual concentrations in tap or surface water. The highest levels of NDMA were observed at pH 6 when NO3- and NH3 were present, with concentrations of 22.7 ng/L and 9.79 ng/L, respectively. At pH 6, NDMA levels were observed to be 22 times higher than at pH 8. Chlorine alone was not sufficient to convert DMA to NDMA within a short period of time, specifically at least 5 h, in the absence of other factors. The concentration of NDMA increased to 41.6 ng/L in the presence of NH3. After 16 h, the presence of NO3- led to a gradual increase in NDMA levels to 19.0 ng/L. However, no further increase was observed at this point. The findings suggest that NO3- and NH3 are important factors of NDMA in chlorinated drinking water. Although previous mechanisms have not given much attention to these factors, they are expected to play a significant role in the formation of nitrosamines in both natural water and drinking water. Controlling the factors or pH appeared to be crucial for managing NDMA formation, and further research on reducing N-nitrosamines is necessary.